I realize that I have not made a blog post in a very long time. My apologies to any followers I still have left. Today marks the opening day of the 42nd Annual Benthic Ecology Meeting, and I figured it was as good a time as any to make a new blog post. Afterall, I have made multiple BEM-related posts in the past, and I am currently waiting for my ride to leave for the meeting.
A lot has changed for me since the last benthic meeting. I completed my dissertation and relocated to UNCW to start my post-doctoral career. It has been pretty hectic. When I first came down, I was trying to finish up some manuscripts from my dissertation, like the chapter on the impacts of Codium fragile on scallop demographics such as growth rate and tissue condition. My conclusions were that the invasive alga might be beneficial for scallop populations, especially in the absence of their native habitat, seagrass. I have made this argument before, and this chapter was recently published in Marine Biology. Other chapters haven’t gone through so smoothly and are still being reviewed, but that is par for the course in this field.
I was balancing those with editing other manuscripts from collaborative efforts with my former lab and one of my committee members. I also made two failed attempts at doing a laboratory study with oyster spat and an ectoparasitic snail. The results were promising, but I kept having high mortality across all treatments, and I need to come up with a better way of maintaining and feeding the oysters in a lab setting. I also have now written 4 proposals to various funding agencies, and am currently working up some old data sets for my current lab. Within all this, I crammed a 2.5 week trip to Jamaica to attempt to do some sponge work, but the weather didn’t cooperate (well, not with me anyway, my stomach is not the biggest fan of the ocean). Suffice it to say, I have been extremely busy, but that isn’t really an excuse to have stopped making regular updates. However, I have only been in “the field” once since I relocated, and it’s not very much fun writing blog posts about writing Sea Grant proposals.
However, this will be a nice little break, and I am excited to be headed down to the meeting. There are a lot of talks this year that promise to be very good and informative, plus there is also the Beneath the Waves Film Festival which is always excellent. And, in general, I like to see former colleagues, friends, potential future collaborators and have a generally good time drinking beer and talking all things marine science.
My talk this year will involve some work from my former lab on multiple predators. Natural communities have multiple predators foraging on shared prey resources, and until the last decade or so, these interactions were largely ignored in lab studies. They are interesting, because the consumption of prey is rarely additive – that is, two predators do not typically consume the same amount of prey you would expect based on how much they can eat when they are alone. More often, the prey either experiences reduced or enhanced risk relative to expected consumption. For crabs interactions, which utilize prey and habitats similarly, we expect that antagonistic interactions increase, resulting in reduced risk on the prey. Check out this video:
What you can see is the smaller crab is like your annoying little sibling who just won’t leave you alone and constantly antagonizes you. It kind of makes you stop what you are doing. In crabs, this means they might stop foraging to deal with each other. This usually means that the prey survive better than would be expected. However, this isn’t always the case when you run the trials and do the statistical analysis:
Proportion of ribbed mussels consumed by Hemigrapsus alone (pink bar), by Carcinus alone (green bar) and the two crabs together (gray bar). The circle denotes the expected consumption.
In this case, our observed consumption was not different than we expected, based on individual consumption rates. We anticipated to see a risk reduction, and based on the video, we know the crabs were interacting. So what gives? Upon further inspection, when we looked at the sizes of mussels consumed, we saw a dramatic shift:
Pink bars are mussels consumed by Hemigrapsus, Green bays by Carcinus and gray bars by both
What we saw was that when foraging along, the green crabs consumed all the size ranges that were offered, but when foraging together, they shifted to selecting smaller prey, possibly because they had less time to forage. So while the overall proportion being consumed stayed the same, they were foraging on a smaller portion of the population. We thought that was pretty cool!
Stay tuned for more posts, I promise to do better!
I have been doing some field work the past few weeks, one of the reasons for infrequent postings, so I apologize. This week, I saw some cool things. Well the things I saw were not so cool – they were spider crabs, and I see them ALL THE TIME. (In fact, I’d be more surprised to not see any spider crabs.) But it was what I saw the spider crabs DOING this week that was so cool.
While snorkling at a site in Heady Creek, Shinnecock Bay, NY, I came across this creepy (and dead) bluefish. It was pretty big, and it was being picked at by a spider crab. I know that spider crabs are typically considered scavengers, and this particular crab is no different. But its one thing to watch spider crabs picking on a dying whelk. Its something different, or rather, interesting to see them doing on this bluefish. Maybe its just funny, as I typically wish there were more large fish to consume all the spider crabs, as they eat bivalves, including my precious scallops.
And then I saw this amazing site – a spider crab, while clinging to one of my spat bags, was also clinging to a sea nettle, my assumption is to eat it. And after reading about ctenophores found in dogfish stomachs, and a recent article in Science about bearded gobies consuming jellies, it makes me think “Ecological dead-end my ass!” Well, lets not get too ahead of ourselves, but still interesting to see this today (and according to the Smithsonian Marine Station, spider crabs do eat jellies):
Plus they were just crawling all over things, including my recruitment tiles and into the eelgrass canopy (hey I thought only mud crabs did that)!
Spider crab crawling up eelgrass
Spider Crab on my recruitment tile
These little guys do some pretty interesting things. From typically scavenging, consuming vegetation, carrion and detritus, to possibly actively hunting – including on shellfish and probably jellies, maybe we need to reconsider the role of spider crabs in our coastal ecosystems. Maybe…
I have seen many interesting things in the field around the East End of Long Island, but it never ceases to amaze me that when I think I have seen it all, I see something new and totally unexpected.
Don’t get me wrong, I have seen many lobsters around Long Island – mostly in the Peconics, and in Orient Harbor in particular. Sometimes, we inadvertently catch lobsters in our cinder blocks we use to mark field sites. I have also come face to face with lobsters in the Peconics at three different spots – one in Orient Harbor just off the causeway, peeking out of a cinder block (see this photo I took in OH), one in Peter’s Neck, Orient Harbor, just walking out on the sand, and one outside of Three Mile Harbor in an old tire. So I know they are out there.
But in Shinnecock Bay? This was new. Well, not entirely new since, by chance, a few weeks back, I caught a lobster in Old Fort Pond. I was shocked that the lobster was in the pond, as it is both shallow and muddy. Everything I know about lobsters (and again, I am no expert) says that they prefer cobble habitat – the types of habitat where there are many crevices, caves, holes, etc that they can use as shelter. Because I was so surprised, I blogged about it here.
But then, today happened. We were out along the south shore of Shinnecock Bay east of Shinnecock Inlet where we have been doing some seagrass monitoring as part of a lab project. While doing our work, one of the students helping with the project grabbed this little baby lobster that was just swimming along the surface. Over the course of a few hours we spent at the site, we easily counted at least a dozen of the little baby lobsters. That may not sound like that many, but keep in mind we weren’t out there to actively monitor baby lobsters, it was more a pleasant surprise.
So what were these little guys (or gals) doing in Shinnecock Bay? While cobble is likely the best habitat, other things like eelgrass and marsh peat also serve as potential habitats for very small juveniles. and there is plenty of marsh and also eelgrass east of the inlet. In addition, there was a very large, episodic set of blue mussles this year in Shinnecock, and mussels are a food source of juvenile and adult lobsters. I wonder if there is any relationship between the two. It is possible that conditions this past winter/spring were favorable for good spawns and recruitment of some of these species, but I don’t want to speculate too much.
I apologize for the poor picture quality (I took them with a cellphone), but it was exciting to see these little buggers out there, and I wanted to share. Hopefully, this is a sign of good things for Shinnecock Bay, and that lobsters don’t become as rare here as this one (aka, 1 in 50 million).
One of my favorite Megadeth albums and songs, although that’s for another time. The title also fits for a handful of species from a group particularly close to my heart – seagrasses. Seagrasses made the news recently, as a recent report suggest as many as 10 of the 72 known seagrass species are at risk of extinction. And since this blog is named in honor of seagrass, I thought I might delve in, as I have made many seagrass related posts in the past.
Global Seagrass Distribution - from FLMNH
I probably don’t have to tell those of you who follow my blog how important seagrasses are for coastal ecosystems. Seagrasses can be found in all oceans around the globe – from the tropics and temperate zones into the Arctic (see Dr Fred Short’s website for more info and a number of useful powerpoint slides). Everywhere they occur, they provide a variety of ecosystem services – from oxygenation of the water and sediments, stabilization of the sediments, dampening of flow, help to maintain water quality, provide nursery and spawning grounds for numerous species, and are a direct food resource for a number of species. Most of my attention has been on the habitat value of seagrasses – important for a number of commercially important finfish, such as cod, and shellfish, such as my study organism the bay scallop. And much of the literature has focused on these aspects as well.
Causes for Seagrass Decline - From Orth et al 2006
However, despite the overall importance of seagrasses, they are continuing to decline on a global scale, mainly due to anthropogenic causes. Worldwide, seagrasses have declined by at least 30%, a rather alarming figure. Seagrasses typically grow close to shore – so these areas are dynamic to begin with. However, these near coastal zones are typically sites of development and use. While there are natural threats to seagrasses – overgrazing, storm events, disease – the majority of seagrass loss comes at the hands of humans either directly or indirectly. Some direct sources of loss include reckless boating, destructive fishing practices (such as trawling, dredging, raking and tonging), shoreline hardening, docks, and channel dredging. However, perhaps more important are indirect – nutrient overloading and eutrophication shifts ecosystems to water column production, increasing phytoplankton which in turn shades out seagrass. Likewise, overharvesting of filter feeding bivalves has reduced filtration capacity of basins, leading similarly to high phytoplankton and low light. Additionally, climate change, and the resultant increase in water temperature, can cause severe stress in many seagrass species.
Consequences of eutrophication on seagrass
Because seagrasses are so important, it has been the focus of our lab’s research. While I have focused much of my research on the impact of changing eelgrass landscape, as well as alternative habitats, on bay scallops, my first ever research project was investigating the ability of hard clams to facilitate eelgrass growth in a light-stressed environment. In a series of experiments, we tested the degree in which light and nutrients limit eelgrass productivity along an estuarine gradient and investigated the ability of hard clams to facilitate eelgrass growth in ambient and light limiting conditions. Not surprisingly, the farther away from the ocean inlet we went, the higher the phytoplankton and the lower the light reaching the bottom. This lead to a decrease in eelgrass productivity along this estuarine gradient. However, using an in situ shading and nutrient addition experiment, we were able to show hard clam facilitation of seagrass growth, even under light stress. However, since the grass was artificially shaded, the mechanism for increasing seagrass productivity in the shade treatments was via the clams ability to increase the sediment nutrient pool, which was reflected in the seagrass tissues. We published this work in MEPS.
However, many other lab members have also done seagrass research. In fact, we like to call ourselves the Peterson Seagrass Rangers. Current student Amber Stubler, who you may remember did a guest blog post on Chronicles, conducted numerous field and lab experiments investigating multiple stressors on eelgrass growth – light, temperature and sediment sulfide concentration – before she started in her current sponge work. Another current student, Brad Furman, is investigating landscape properties of eelgrass meadows and patch persistence over time. Former student Brooke Rodgers investigated harmful herbicides in groundwater on eelgrass growth and survival. Finally, former student Jamie Brisbin conducted a thorough investigation of eelgrass population genetics of Long Island waters (don’t ask me to give more detail, because I don’t understand genetics all that well). So our collective lab is essentially investigating many reasons for and consequences of decline of seagrasses around Long Island, NY.
That’s why this latest manuscript was so interesting. The Biological Conservation manuscript by Fred Short and others, published online, includes a veritable who’s – who of world seagrass experts. Because seagrasses are so important, numerous studies have investigated their decline worldwide. This new article looks at these studies and determines the probability of extinction using guidelines from the International Union for the Conservation of Nature (IUCN) Using criteria from the Red List of Threatened Species, the authors determined that 10 of 72 seagrass species – 14% – are at risk of extinction.
Method for determining risk from Short et al
Taking a database of existing seagrass literature, the authors used 2 main criteria for determining extinction risk and vulnerability. Criteria A examines population decline over time and Criteria B is based on geographic range. Out of the 72 species investigated, 3 could be listed as endangered already. Seven more species were listed as vulnerable due to increased declines in populations. An additional 5 species were listed as Near Threatened by the two criteria. On the other hand, 48 species were listed as Least Concern, meaning that currently, they are not likely to go extinct. That doesn’t tell the whole story, however, as most of the Least Concern species are wide-ranging. So despite being of Least Concern, many of these species are locally threatened, as declines of many of these species are occurring at a local scale.
There also appears to be global patterns in threatened and declining seagrass species. 22% of the seagrass species found in the temperate North Pacific are threatened, with an additional 17% near threatened – with up to 100% of seagrass species in some areas of this region experiencing decline. The tropical Indo-Pacific has 11% of its species threatened. In contrast, none of the 5 species of seagrass found in the temperate North Atlantic have received a threatened status – but again, this may be misleading. Despite no species listed as threatened, on the local level, many of these species are disappearing.
Distribution and decline of seagrasses - Short et al
The manuscript goes on to name some of the threats to seagrass species – many of which I have already listed. But in order to create more awareness, I will name more here. They found that the most common threat to seagrass is humans – 67 species are affected by some anthropogenic impacts. Again, and I can’t make this point more clear, the MOST COMMON THREAT TO SEAGRASS IS HUMANS. Among them, decreases in water clarity and quality due to nutrient overloading – leading to phytoplankton and nuisance algal blooms – and sediment loading – increasing suspended sediments and siltation. Beds are also destroyed by coastal construction, shoreline hardening, and dredging, destructive fishing practices, and mechanical damage due to boats. Invasive species also pose threats to seagrasses. Oh yeah, and climate change, whose potential impact is just starting to be understood.
So what are the recommendations? After all, seagrasses are vital components of coastal ecosystems, and need to be saved, if possible. Poor water quality/clarity is the major threat. Ameliorating this water quality issue is the best way to decrease stress on seagrass and hopefully reverse the trend. Unfortunately, it is likely easier said than done. Efforts to reduce run-off, nutrient and sediment loading need to be undertaken to help increase water quality. In developed countries, we can combat this by stricter rules on fertilizer use and coastal development, as well as increasing the use of tertiary treatment at sewage treatment plants and restoring filter feeding species. In developing nations, this can be done via education and encouragement of eco-tourism as a revenue source, let them know keeping their environments pristine is a great way to generate money for the economy. Additional conservation and restoration efforts are necessary, like those on Long Island and Virginia.
Carroll, J, Gobler, CJ, & Peterson,BJ (2008). Resource-restricted growth of eelgrass in New York estuaries: light limitation, and alleviation of nutrient stress by hard clams Marine Ecology Progress Series DOI: 10.3354/meps07593
ORTH, R., CARRUTHERS, T., DENNISON, W., DUARTE, C., FOURQUREAN, J., HECK, K., HUGHES, A., KENDRICK, G., KENWORTHY, W., OLYARNIK, S., SHORT, F., WAYCOTT, M., & WILLIAMS, S. (2006). A Global Crisis for Seagrass Ecosystems BioScience, 56 (12) DOI: 10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2
After a long hiatus, I am back at blogging. I know I said that two weeks ago, but I have been fairly busy writing and prepping for the upcoming field season. As a side note, out lab added yet ANOTHER project this summer – working on test oyster reefs in the Hudson River – and is likely to add another project as part of interest in restoration of the South Shore Estuaries on Long Island. So there has been a lot of reading and writing for those two, in addition to writing manuscripts and working on my dissertation, so it’s safe to say I have been sufficiently distracted from my blog. But I digress.
One of the more exciting things I have been working on is edge effects in seagrass meadows (more details below). One facet of my dissertation is looking at how changing habitat impacts bay scallop populations in New York. This is important, because as followers of my blog are aware, scallop populations crashed in the mid 1980s, and have not recovered naturally. This has led to intense restoration efforts over the past 5 years in order to boost the population and return this vibrant fishery. Many restoration efforts fail to recognize that in addition to the target species being depleted, the estuarine sites for restoration are also likely to be VERY different from the time when the species was formerly abundant. As such, much of my research and involvement with scallop restoration in New York is answering some of these questions.
Here, estuarine ecosystems have changed as well. New York supported vibrant fisheries for decades. One reason for this high productivity can be attributed to luxurious eelgrass meadows, as this biogenic habitat is important for many estuarine species. However, eelgrass has dwindled and disappeared, meadows have become patchy. Why does this matter? Many commercially important species depend on seagrasses for at least some portion of their life cycle (you can see many of my previous posts about seagrass):
Juvenile flounder in seagrass
In fact, seagrasses perform a variety of ecosystem services. High seagrass biomass traps nutrients and sediments, and, along with associated epiphytes, have high productivity. This productivity creates structurally complex habitats which serve as feeding and nursery grounds for a variety of species, provide food for megaherbivores, and encourage trophic transfer and cross-habitat utilization.
From Orth et al 2006
From Orth et al 2006
Despite their importance, seagrasses have faced a series of ecological insults. From nutrient loading, harmful algal blooms, wasting disease, shoreline hardening, propeller scarring, destructive fishing, and climate change, seagrasses worldwide have declined 30%. These factors have lead to vast meadows to be divided into a mosaic of patches that vary in size, shape, and degree of isolation. This can have dramatic impacts on seagrass associated species, including the bay scallop. This is the reason that I have concentrated a large portion of my research understanding how changing seagrass habitats will affect scallop populations moving forward. I have blogged briefly about my results with this regard here and here, although I haven’t gone into too much detail, as I am waiting to publish this portion of my research.
Example of loss of eelgrass from Waquoit Bay, Massachusetts, due to eutrophication
One of my artificial seagrass mats
One of the focuses of my research have been edge effects of seagrass meadows. So what are edge effects? Edge effects are a facet of landscape ecology. Simply, landscape ecology is a multidisciplinary approach to understand the ecological consequences of habitat spatial patterns. This has been widely studies in the terrestrial realm for the past 50 plus years, however only since the mid 1990s have these terrestrial concepts been applied to the marine world. A number of marine habitats lend themselves to these types of studies, including seagrasses, which have received much of the attention in the scientific literature (see the following figures from Bostrom et al 2011).
Figure from Bostrom et al 2011
From Bostrom et al 2011
Some of the specific landscape features investigated are patch size and shape, orientation, fragmentation and edge effects. Habitat edges, or ecotones, are transitions between two different habitats. Typically, these transitions are between a structurally complex habitat (such as seagrasses) and an adjoining less complex habitat (such as bare sand). Because these two habitat types offer different resources, complex interactions can occur at these edges. These are known as edge effects. Typically, edge effects are expected to be positive, where the response variable is enhanced at the edge and decreases with distance; negative, where the response variable is lowest at the edge and increases with distance; and neutral, where no effect is observed. Edge responses vary according to the organisms being studied. Macreadie and others demonstrated species specific responses to seagrass edges (see below). Using artificial seagrass (!), the group found 3 different edge responses, depending on the species of zooplankton: increased abundance at the seagrass/sand boundary, high densities within seagrass with decreasing abundances with distance into the sand, and high abundance in sand with decreasing abundance into the seagrass patch.
From Macreadie et al 2010
Species interactions are often enhanced along seagrass edges, as previously mentioned, these are transitional habitats. Both seagrass residents and sand residents may come to seagrass edges in search of food resources. In these situations, these species interact. Often times, larger predatory species cannot forage deep in seagrass meadows due to their structural complexity, however, they do typically forage along seagrass edges, as seagrasses typically have higher prey abundances. Therefore, seagrass edge habitats are extremely important sites of predator-prey interactions. This has been demonstrated by Paul Bologna and Ken Heck for scallops. In their study, scallop survival was lower at seagrass edges than in seagrass interiors and bare sand habitats. They decided this was due in part because scallops at seagrass edges were twice as likely to be encountered by predators (see below). More recently, a study by Timothy Smith and others out of Australia have investigated the impacts of seagrass edges on fish predation. They used some pretty cool methods – video analysis of time spent at varying locations with respect to the seagrass edges, as well as tethering of small juvenile fish at different spots along a gradient from within seagrass to bare sand (I am jealous about videos, I just don’t think we have the water clarity in New York to get anything useful from video, and I love tethering things!). Their findings corroborated earlier studies that edges are sites of enhanced predation, and this can structure the fish community around seagrasses.
From Bologna and Heck 1999
Despite these studies, reviews by Bostrom and others have frequently demonstrated no response of fauna to seagrass edges. So what gives? Well, the reality is that edge effects are fairly complex processes, and should not be simply described as ‘positive,’ ‘negative,’ or ‘neutral.’ Many factors contribute to the observed effect, and the metric used (abundance, diversity, survival, etc) to investigate the magnitude of the edge effect is just as likely to play a role in whether or not an effect is found as the habitat edge itself. It highlights the need for better understanding of the processes structuring species abundances along seagrass edges. That is where I am hoping some of my research comes in. Using scallops as my model organism, I was able to break down recruitment into seagrass meadows into its two component processes – settlement and post-settlement mortality – and investigate the impacts of seagrass edges on these processes. Scallops showed positive, negative, and neutral responses, depending on the process investigated, illustrating the complexity of edge effects. More to come once this paper is submitted!
So, in summary, why should we care about edge effects? Well, typically, habitat edges have negative consequences for seagrass associated fauna – they tend to experience higher mortality at these ecotones. And, as anthropogenic factors continue to impact seagrasses, large meadows are dwindling into smaller and smaller patches. With increasing patchiness comes increasing amounts of edge habitats. And with smaller patches, there is more edge relative to interior habitat. This could have potentially devastating consequences for seagrass associated species, including the bay scallop.
Boström, C., Pittman, S., Simenstad, C., & Kneib, R. (2011). Seascape ecology of coastal biogenic habitats in a changing world: advances, gaps and future challenges Marine Ecology Progress Series DOI: 10.3354/meps09051 Smith, T., Hindell, J., Jenkins, G., Connolly, R., & Keough, M. (2011). Edge effects in patchy seagrass landscapes: The role of predation in determining fish distribution Journal of Experimental Marine Biology and Ecology, 399 (1), 8-16 DOI: 10.1016/j.jembe.2011.01.010 Macreadie, P., Connolly, R., Jenkins, G., Hindell, J., & Keough, M. (2010). Edge patterns in aquatic invertebrates explained by predictive models Marine and Freshwater Research, 61 (2) DOI: 10.1071/MF09072 ORTH, R., CARRUTHERS, T., DENNISON, W., DUARTE, C., FOURQUREAN, J., HECK, K., HUGHES, A., KENDRICK, G., KENWORTHY, W., OLYARNIK, S., SHORT, F., WAYCOTT, M., & WILLIAMS, S. (2006). A Global Crisis for Seagrass Ecosystems BioScience, 56 (12) DOI: 10.1641/0006-3568(2006)56[987:AGCFSE]2.0.CO;2 Bologna, P. (1999). Differential predation and growth rates of bay scallops within a seagrass habitat Journal of Experimental Marine Biology and Ecology, 239 (2), 299-314 DOI: 10.1016/S0022-0981(99)00039-8
Or – What do I do when field observations don’t match lab results. This is a philosophical debate that has plagued ecologists for decades and it brings up all sorts of issues – relevant scale, extrapolation, replication and pseudoreplication, variable control, realism, and the list can go on and on. How did I arrive at the crux of this debate?Cochlodinium polykrikoides. It is a harmful algal species, now a common annual occurrence in Long Island, NY, whose blooms are known to be ichtyotoxic, and more recently, to be potentially devastating to shellfish as well. Now I am not a harmful algae person by any stretch of the imagination, but many of my colleagues are, and I often find myself engaged in healthy debates with them over the utility of lab vs field experiments.
Image from Chris Gobler
Why? Well there is a body of literature that suggests C. polykrikoides is harmful to a number of shellfish species. In fact, chronic exposure in the lab has led to high mortality and depressed growth rates of juvenile bivalves. Other studies demonstrate rapid mortality of bivalve larvae in lab exposures over periods as short as 24 hours. Lab experiments have proved especially useful in determining the mechanism of toxicity, and determining how dense blooms should be to have particularly devastating impacts. The Gobler lab at the School of Marine and Atmospheric Sciences at Stony Brook University is at the forefront of many of these studies.
Again, I am not a harmful algae person, so why do I care about this? Well, my study organism, the bay scallop, can be affected by these blooms. That, and the fact that millions of dollars have been invested to restore bay scallop populations in NY waters. The earliest research of these blooms out of New York (where they first appeared in 2002 and have recurred annually since 2004) indicated harm for bay scallops. Using 5-l plastic buckets and bloom water collected from the field, Gobler and others (2008) demonstrated up to 75% mortality of juvenile scallops (~11mm shell height) after 9 days of exposure. Additionally, this stud demonstrated a significant impact on scallop growth rates, being half in the bloom water as in controls – so even those scallops that survived were not doing well.
Other studies out of the lab have showed something even worse – up to 100% mortality of scallop larvae over relatively short time scales during the lab study. In well plates, Gobler and Tang utilized 10 ml of varying bloom densities of C. polykrikoides or a control consisting of T-Iso (Tahitian isochrysis) . In this study, with 20 larvae in each 10-ml well, the highest CP cell densities, >2000 per ml, caused rapid 100% mortality of bay scallops, within 10-24 hours. This is clearly problematic, as blooms occur when scallop larvae are expected to be in the water, so this has potential to be devastating to the restoration effort.
Figures from Gobler et al 2008 and Tang and Gobler 2009
If we extrapolate based on these results, we would expect extremely low recruitment and abundance of bay scallops. In fact, the Gobler et al paper from 2008 says exactly that: “Our results demonstrate that the failure of this population to recover could be due, in part, to recent outbreaks of C. polykrikoides blooms in this system.” Wow. Has that for scaling up! What’s the problem here? Well, first and foremost, the statement is fundamentally false. Anyone who has been following this blog can attest to the fact that scallop populations are indeed recovering. The most recent literature shows over 13-fold increases in on bottom densities of scallops in restored basins – see Tettelbach and Smith, 2009. And a manuscript we are currently finishing shows even better results. Landings have been increasing as well, as demonstrated here:
Data from Steve Tettelbach
In addition, as an unexpected natural experiment of sorts this summer, I was able to observe scallop recruitment in the presence of C. polykrikoides, which means the scallop larvae survived, remained competent, settled, grew, and survived all in the presence of this harmful algal blooms. This is preliminary data still, and remember, I was not looking for this relationship. In fact, I was simply interested in monitoring scallop recruitment in Shinnecock Bay, a south shore lagoon, with healthy eelgrass populations (and eelgrass is the preferred scallop habitat, although other habitats are also important). That was my goal. Being interested in all things, I thought it would be useful to have an idea of size fractionated chlorophyll analysis for each of my Shinnecock Bay study sites, to see what the differences might be across the bay. Additionally, I collected water that I fixed with Lugol’s so I could have an idea what the phytoplankton community looked like. As a part of this process, I was able to get CP cell densities at the same sites which I collected scallop recruits.
So what gives? Well, I think that its clear that lab experiments can’t be so easily extrapolated to the ecosystem level. And maybe, we shouldn’t even attempt to extrapolate these data to ecosystem scale processes. Lab experiments are good because they are extremely reproducible, can rapidly generate data, regulate all independent variables, and are lend toward easy replication. However, they have limitations in both spatial and temporal scale, realism and generality. So while larvae in 10 ml of high concentrations of CP all die within 24 hours in the lab, the likelihood that that kind of exposure happens in the field is extremely unlikely. Even the 5-l bucket experiments were unrealistic. The lab experiments failed to incorporate physical and biological characteristics of the system. Things such as larval availability, larval behavior, algal behavior, water column depth, variations in temperature, daylight, salinity, the community, etc, are all ignored in the lab experiments.
However, by its very nature, CP is difficult to study in the field. It is a spatially aggregating, chain forming species – so that over the spatial extent of the bloom you can experience cell densities that vary by orders of magnitude. It also undergoes diel vertical migration, so that it is at the surface during the day and the bottom at night (where exactly they go at the bottom is another story). It just can’t be controlled in the field and its spatial extent and bloom density is highly variable and unpredictable. So figuring out the problems with the lab exposures is not as simple as placing some scallops out in the field. So its a question that is not easily solved, which is probably why it is still being debated after decades.
Image from C. Gobler
In case you couldn’t tell, I am a field ecologist by trade, so I am obviously a little biased. But I do personally believe that lab experiments, while important, have limited utility in ecological studies without appropriately scaled field studies to corroborate the results. Many times, microcosm studies don’t. I am not as bullish on lab studies as Stephen Carpenter (1996) who suggests “an ecologist who isolates organisms in bottles may not be working on communities and ecosystems in any relevant sense.” I think that microcosms and lab experiments have their place – and that they provide valuable information for ecological studies, and I do employ them on a limited basis. It is just in my strong opinion that their value becomes limited without field testing the results.
Either way, it is certainly an interesting debate. Both sides have valid arguments – reproducibility, replication, control in lab experiments, the realism, relevant scales, and generality in field and natural experiments. The ideal combination of lab and field experiments depends on the questions asked and species studies. But it is clear that at times, the field observations don’t match what would be expected from lab experiments. This doesn’t mean either side is wrong, but illustrates the need to utilize both practices.
EDIT – This blog post is not intended to suggest harmful algae don’t have impacts in the field. There are plenty of examples from the field of harmful algae having impacts on fauna – including the recent sardine die-off in California. Rather, it is only to illustrate disconnects between field and lab observations.
Carpenter, S. (1996). Microcosm Experiments have Limited Relevance for Community and Ecosystem Ecology Ecology, 77 (3) DOI: 10.2307/2265490 Gobler, C., Berry, D., Anderson, O., Burson, A., Koch, F., Rodgers, B., Moore, L., Goleski, J., Allam, B., Bowser, P., Tang, Y., & Nuzzi, R. (2008). Characterization, dynamics, and ecological impacts of harmful Cochlodinium polykrikoides blooms on eastern Long Island, NY, USA Harmful Algae, 7 (3), 293-307 DOI: 10.1016/j.hal.2007.12.006 Tang, Y., & Gobler, C. (2009). Cochlodinium polykrikoides blooms and clonal isolates from the northwest Atlantic coast cause rapid mortality in larvae of multiple bivalve species Marine Biology, 156 (12), 2601-2611 DOI: 10.1007/s00227-009-1285-z Tettelbach, S., & Smith, C. (2009). Bay Scallop Restoration in New York Ecological Restoration, 27 (1), 20-22 DOI: 10.3368/er.27.1.20
New species get introduced into novel habitats almost like clockwork in the modern era. These are termed introduced or exotic species. Typically, these introductions are the effect of anthropogenic activity. Sometimes, these species become nuisances – spreading in their new habitats via natural processes, and creating problems for native species. These nuisance exotics are called invasive species.
So how do they get here? From a variety of ways, but perhaps most famously via ships’ ballast dumping. Ballast is simply material used by ships to control and maintain buoyancy and stability. Typically this is water, pumped into ballast tanks from the port the ship is sitting in at the time. This ballast water gets pumped in or out depending on the weight of the cargo on this ship, and so you can imagine how water could be transferred across whole oceans, bringing with it any species that happened to get sucked in to the ballast tank. This is a major source of marine invaders – including the now infamous zebra mussel, Dreissena polymorpha, which has become especially problematic throughout fresh waters of the Mississippi River, the Great Lakes, and the east coast. However, invasives can also come from aquaculture gear and species – especially as native species are fished out and replaced with non-natives to keep up food production. In addition to these non-native species used in aquaculture, other species hitch rides on them.
How Ship's Ballast works
However, as you can see above, it is possible that all invasive species are not created equal – that is, maybe not all invasives are so bad. Green fleece, known as Codium fragile, has been introduced to the east coast of America for decades. Originating from Japan, it has typically viewed as bad – it is a buoyant species which needs hard substrates to attach, including living shellfish. It got the nickname “oyster thief” since it would attach to oyster shells, and whenever a storm or strong current event occurred, the buoyant macroalgae would be swept away, dislodging oysters and taking them away from reefs and culture sites. It is clear why this is considered a problematic species.
And yet, some recent research has shown that maybe Codium isn’t all that bad. Research which I have participated in has demonstrated that Codium may act as a viable alternative habitat for native bay scallops. Why? Bay scallops have evolved a strong association with seagrasses, and the Codium canopy likely provides the same upright structure to scallops. We observe scallops frequently in association with Codium in Long Island bays, and a study conducted showed that survival of free-released and tethered scallops was the same in eelgrass and Codium, suggesting that the invader offers a similar predation refuge. This was published last year in Marine Biology (See Carroll et al, 2010, below).
From Carroll et al 2010
In addition, I have taken the research further. The aforementioned paper talked about survival on a relatively short time span – 1 week. In order to examine the longer term effects on growth I conducted a caged field experiment the past two summers at 2 field sites with eelgrass, Codium, and unvegetated sediments in close proximity to each other. The general findings have been that scallops in Codium grow at rates similar to scallops in eelgrass, however, there are site-specific differences. There are also no differences in mortality between the habitats – suggesting that dense stands of Codium aren’t having as detrimental impact of low dissolved oxygen as I originally thought. This work isn’t published yet, as I am working on a method to find the stoichiometry of the tissues, but some of the results are in the presentation I gave at CERF 2009 here: Thursday_SCI-045_1115_J.Carroll
Moon snail crawling over Codium
However, I am not the only one who sees “positive” impacts of Codium. In the most recent issue of Marine Ecology Progress Series, a team of Canadian researchers, led by Annick Drouin, higher abundance and diversity of the faunal community in eelgrass meadows invaded by Codium fragile. Using a variety of sampling methods and field manipulations, the team demonstrated higher abundance and diversity of invertebrate organisms on Codium, and in eelgrass meadows invaded by Codium, than those without Codium. The pattern of fish abundance and diversity was not different – likely because they are highly mobile and can move easily between structured habitats. It is likely that Codium just generates MORE habitat, as it is branching and canopy forming. The important thing here is the ecological implication – the lack of a negative effect on native species by the presence of this “invader.” Perhaps Codium might not be so bad after all, especially as eelgrass is declining in many regions.
Figure from Drouin et al 2011
It is possible, then that “invasive” vegetation species in the marine environment may not always be bad. In many cases, invasives may be beneficial. Numerous studies (including the ones above with Codium) have demonstrated a positive effect of invasive algal species on native fauna. Typically, the vegetation is habitat forming, and invades areas where native habitat forming vegetation has already been lost. In essence, it is replacing a lost habitat, and creating a new habitat which is functionally similar to the species which declined/disappeared. That being said, invasive algal species can be detrimental to native macrophytes through competition. However, the benefit is in enhancing native fauna, which has potential fisheries ramifications. This requires further investigation, but it is entirely possible that non-native macroalgal species might have a positive effect on a number of native fauna.
Mud crab in Codium canopy
Pipefish chillin' in Codium canopy
The above photos, and the one of the moon snail farther up the page, are all illustrations of native species of Long Island associating with the invasive Codium fragile. Now, again, there are certainly detrimental effects of invasive species, so I am not trying to be too much of an apologist for them here. However, in the absence of eelgrass, it is entirely likely that the upright, canopy forming structure of Codium creates a habitat suitable to many seagrass associated fauna. As eelgrass is declining, invasive macrophytes might be important replacement habitats for a variety of native species. Understanding how these species affect native species will be key for management of estuaries moving forward. Particularly, once established, invasives becoming increasingly expensive and difficult to remove. If some invaders might be of benefit, that relationship needs to be well understood. Hey, invasives could help bring back the bay scallop in NY (and likely is having an impact), providing a habitat as eelgrass has disappeared from many Long Island areas. Who knows where else they might be beneficial.
There will be those of you out there who disagree. I don’t blame you. Calling an “invader” beneficial certainly goes against conventional wisdom. When we first introduced the idea of Codium as a potential scallop habitat to a shellfish crowd, we were scoffed at. However, the data don’t lie. And more research points to cases where invasives may actually facilitate natives.
Drouin, A., McKindsey, C., & Johnson, L. (2011). Higher abundance and diversity in faunal assemblages with the invasion of Codium fragile ssp. fragile in eelgrass meadows Marine Ecology Progress Series, 424, 105-117 DOI: 10.3354/meps08961 Carroll, J., Peterson, B., Bonal, D., Weinstock, A., Smith, C., & Tettelbach, S. (2009). Comparative survival of bay scallops in eelgrass and the introduced alga, Codium fragile, in a New York estuary Marine Biology, 157 (2), 249-259 DOI: 10.1007/s00227-009-1312-0
Well, it actually kind of is impressive. A documentary was broadcast on British Channel 4 (don’t ask me, I have no idea) about a science experiment conducted on an elephant carcass to examine what happens after death. While I can’t access the full video (I’ve tried, but you can too here), I was able to get a trailer off Youtube:
It seems pretty impressive, and I am bummed I haven’t been able to watch the full show. Hopefully sometime soon it will become available.
But reading the article got me to thinking about whale falls. I mean if you think what happens to this dead elephant is impressive, just imagine what the ultimate fate is for dead whales, some of which are 10 times the size of elephants. These are called whale falls, as the whales carcass sinks to the bottom of the deep sea. The process isn’t nearly as rapid as the above video, and whale falls undergo a series of successional communities, supporting life for years after the whale has died. (That’s not to say the elephant carcass doesn’t support some sort of community for longer time periods, I am guessing there is all sorts of microbial activity that is affected by the nutrient pulse long after the elephant’s bones have been picked clean, it just doesn’t make for good television).
Whale falls are rather impressive deep sea features. But to imagine how impressive these things are, we first need to consider the deep sea floor. We are talking about life at the bottom of the ocean here – there is no light (with the exception of any biogenic light). There is also little food on the bottom. One reason, of course, is that with no light, there are no producers. Most of the organisms that inhabit the deep sea floor have adapted to life with a small drizzle of organic particles from the surface waters. This rain of detritus (wouldn’t that be an awesome band name?) is known as the biological pump, and is one of the mechanisms of carbon sequestration in the deep sea. This is great in shallow waters, where this productivity reaches the bottom. However, due to simple sinking, horizontal transport, and use, only about 1% of the surface organic matter reaches a depth of 1000 meters, and much of the stuff that reaches the bottom are refractory particles – essentially particles that are barely usable.
Image from earthobservatory.nasa.gov
But species have adapted to this environment. In fact, there is a surprising amount of diversity found on the deep sea floor. There are a some theories as to why this might be the case such as the stability time hypothesis which states that organisms, given enough time, will become specially adapted to very narrow niches (although this theory is less supported now). Another hypothesis is that of intermediate disturbance – disturbances reset the clock, so to speak, allowing more species to compete and prevents preventative exclusion. At some intermediate level of disturbance there is expected to be the maximum amount of species. Some of this is also likely attributed to the wide array of habitats, including the muddy abyssal plains, hyrdothermal vents, seeps, seamounts, and canyons. Regardless, there is a lot of diversity on the deep sea floor. (In fact, you can learn about many of these things over on Deep Sea News, if you aren’t already following them, you should!)
Image from PLOS one
So now, picture you are out on this deep sea floor, where there is a high diversity of organisms, but low abundances. There is limited food. Then this giant whale carcass comes crashing down. I am sure you can imagine what happens, but first, a little more about whales, and their importance to the benthos. Their mere actions in the water column might be vital to the global carbon pump. Whale waste contains high concentrations of nitrogen and iron. These recycled nutrients enhance phytoplankton activity, known as the “whale pump,” which, in turn, stimulates the biological pump. Granted, there are complex interactions going on, but simply, whale excrement facilitates alga growth, which in turn, facilitates flux to the bottom. So whales are already good. But what happens when that whale dies? Well, we know they (mostly) sink to the seafloor, and deliver all that carbon sequestered in their tissues to the bottom.
Image ChEss website
Now the whale is on the bottom. The impact on the sea floor is immense. One whale carcass is close to the equivalent of 1000 years worth of marine snow falling at once. Now, there is tens to a hundred tons of organic matter and nutrients, a veritable all-you-can-eat buffet of sorts. Which reminds me of an expression I was told the other day – How do you eat a whale? Give up? One spoon at a time! Ok, ok I digress. It becomes a site teeming with life, and a biodiversity hot spot. Professor Craig Smith at the University of Hawaii has made a career of investigating these deep sea features. Some of the organisms found at whale falls are also found at hydrothermal vent systems, leading some researchers to believe that these communities act as stepping stones, allowing dispersal of organisms between vents. There is also a succession of animals which colonize and utilize whale falls, so if you visit a whale fall over a period of time you might find entirely different communities. There are even worms that eat whale bones! This is a truly amazing progression of carbon and nutrient transfer from one giant organisms to thousands of deep sea floor animals.
Image from MBARI
So, that is impressive. Granted, I’ll give you the entire elephant being devoured in days. But whale falls can support entire different communities of organisms for years. And while I am sure I have gotten some of the information a little wrong, there are definitely sites you should check out to learn more, such as MBARI, Dr Craig Smith’s site, and Deep Sea News. There is also a really nice write-up about whale falls at the Audubon Magazine.
Editor’s Selection IconWell I haven’t done a Research Blogging post in a very long time. But I was inspired by this news release I read today about crabs spilling onto the Antarctic peninsula with warming waters. On a recent voyage to Antarctica, marine biologists collected digital images of these deep water predators moving closer to shallow coastal waters which have been excluded from for potentially millions of years, because the shallow coastal waters, until recently, have been too cold to support these predators. This can be devastating to the coastal shelf community in Antarctica, which has adapted no defenses in the absence of these predators – many organisms here have thin shells or don’t burrow into sediments.
My friend and fellow Southampton College alum, Molly, recently blogged about this issue. She is currently doing graduate work at the University of Alaska Fairbanks on snow crabs, so she loves crabs (as her blog title suggests). The idea is that, as the above article states, these crabs are moving closer to the Antarctic shelf, and this can have devastating impacts on the local fauna there. It was highlighted in a National Geographic article in 2008.
According to research, the Antarctic coastal shelf experienced a cooling trend starting around 40 mya, and the waters, due to the cooler temperatures, essentially became devoid of many types of predators. The subsequent community had evolved over those millions of years in the absence of major durophagous predators – known for their shell crushing abilities. The major predators in these bottom waters are slow moving invertebrates, and the community developed over time accordingly. Now as surface waters are warming, crabs are able to enter these new areas from the depths, and can have potentially harmful impacts.
At first, this might seem counter-intuitive – typically bottom waters, and the deep ocean, are very cold, and the water warms as you get shallower. This is not the case on the Antarctic shelf, where the shallow waters are actually colder than the surrounding deep waters. This is due to the cold Antarctic circumpolar current, which runs clockwise around Antarctica, isolating its cold water and continental shelf from crabs and fish with bony jaws.
However, the absence of crushing predators was not due to geograhic isolation of the Antarctic continental shelf (although Antarctica is oceanographically isolated, the barriers of biological invasion in this case are physiological, according to Richard Aronson, professor of biology at the Florida Institute of Technology, and others in 2007). Physiologically, the crabs are unable to process magnesium in their blood at the normal shelf water temperatures, resulting in narcotic effects. So the crabs, for millions of years, had stayed away. The resulting shelf community, consisting of epifaunal suspension feeders, lacked the typical defense mechanisms seen in other benthic environments where soft bottom bethos have been evolving with predators in an evolutionary arms race. As already mentioned, the archaic communities of the Antarctic shelf, consist of animals with thin shells which don’t burrow. So one could imagine that if these crab predators were allowed to move into these coastal waters, it could have devastating consequences on the community there.
This is not a crab you would encounter in the Antarctic, however, it is as close a figure to the "arms race" - crab claws, thick clam shell - as I could find on the interwebs.
Range expansions are something that are particularly interesting to me. The lifting of physiological barriers due to temperature will allow biological invasions of numerous species. How these species interact with native species is of great concern. In particular, predator-prey relationships between novel predators and naive prey can restructure communities in warming oceans. Despite its perceived isolation, this research suggests that Antarctica will not be immune to these impacts (and it fact, polar regions are likely to experience a greater magnitude of temperature change).
And the real news here, is not only is there evidence the crabs are moving closer to these shallow shelf communities, but that it is occurring at a much more rapid rate than anticipated.
A quote by Dr. Aronson from the new article: “If you look at the warming trends on the peninsula, you would expect that the crabs would come back in 40 or 50 years,” Aronson said from his office in Melbourne, Fla. ”But boom, they’re already here. This is the last pristine marine system on Earth and it could get destroyed”.
This is big and bad news for the Antarctic bottom communities. Clearly, this is something that should be monitored closely. But it is not in any means an Antarctic phenomenon. In many regions where warming is taking place, range expansion of novel predators can occur. This is something all benthic communities could experience in the near future.
Aronson, R., Thatje, S., Clarke, A., Peck, L., Blake, D., Wilga, C., & Seibel, B. (2007). Climate Change and Invasibility of the Antarctic Benthos Annual Review of Ecology, Evolution, and Systematics, 38 (1), 129-154 DOI: 10.1146/annurev.ecolsys.38.091206.095525
Aronson RB, Moody RM, Ivany LC, Blake DB, Werner JE, & Glass A (2009). Climate change and trophic response of the Antarctic bottom fauna. PloS one, 4 (2) PMID: 19194490
Thatje, S., Anger, K., Calcagno, J., Lovrich, G., Pörtner, H., & Arntz, W. (2005). CHALLENGING THE COLD: CRABS RECONQUER THE ANTARCTIC Ecology, 86 (3), 619-625 DOI: 10.1890/04-0620
Thatje, S., Hall, S., Hauton, C., Held, C., & Tyler, P. (2008). Encounter of lithodid crab Paralomis birsteini on the continental slope off Antarctica, sampled by ROV Polar Biology, 31 (9), 1143-1148 DOI: 10.1007/s00300-008-0457-5
Because I couldn't have a climate related article without citing the Church of the Flying Spaghetti Monster
I don’t like doing this often, because I would rather add my own content than just send you elsewhere. But some of this stuff is just TOO GOOD! Plus it gives me an opportunity to show some of my photos. So I guess this type of entry isn’t all bad. Btw, I took these photos while on a dive trip to Fiji. Enjoy!
I am a marine biologist that is currently attending graduate school at the School of Marine and Atmospheric Sciences, Marine Sciences Research Center, of Stony Brook University, New York. I am very interested in marine ecology and have been focusing my studies on bay scallop interactions with their habitats. I plan to investigate various anthropogenic impacts on bay scallop populations for my PhD dissertation. This blog will highlight the details of my graduate research, from bay scallop-eelgrass interactions as previously mentioned, to alternative habitats for scallops, such as Codium, to trophic cascades, and more. Enjoy!
Is a useful experimental tool to mimic natural seagrass while controlling many factors, such as density, canopy height, leaf number, which are usually confounding in natural eelgrass meadows.
Scallops seem to love this stuff!