That was the title of a talk I saw at the benthic ecology meeting this past March by Paul Bologna of Montclair State University. The premise was that due to a variety of anthropogenic stressors, the coastal environments are changing and leading to declines for a number of seagrass species. As a result, he suggests that more opportunistic seagrass species, such as Ruppia maritima, more commonly known as widgeon grass, may become the winner by default. Bologna argues that this poorly studied species may come to dominate the anthropogenically influenced “new” environments, and makes a call for more research into widgeon grass dominated communities to offer a clue of the potential future of our coastal ecosystems.
So it got a few of us in the Peterson lab thinking about Ruppia. I have seen it only a few times in all my time on Long Island, but I know its here. The first time I saw it was in Great South Bay. I also remember seeing this little grass in Cedar Beach Creek in Southold, NY a few summers ago, but not since. But one site where we know it is present in a small, persistent pond in the salt marsh (i.e., it is a pool of water that remains even as the tide goes out and has been there in the same form, for at least the last 9 years) at Scallop Pond in Southampton, NY.
Flowering Ruppia in a salt marsh pond at Scallop Pond
So we know that widgeon grass persists in this little body of water in the salt marsh essentially year-round (well at least we have seen it there in both November and March, I am making an assumption right now about Dec-Feb). This species is known to be tolerant of fluctuating temperature and salinity, and the grass that persists here likely isn’t any different. Since Ruppia is a widespread seagrass species, it experiences a temperature extremes throughout its range – from near freezing to temperatures as high as 35C (approaching 100 degrees Fahrenheit). In such a small, shallow body of water as shown above, the temperature can reach these extremes over the course of one year, so this particular population needs to be particularly resistant to temperature swings. We would like to learn more about this, so we placed some temperature loggers out at the site in the early spring with the hopes of leaving them out for a year. Since salinity can similarly vary, we are going out on a weekly basis to measure salinity with a YSI monitoring probe (they make loggers which we can leave out for extended periods, but unlike temperature loggers which run ~$100, in situ probes that record salinity are on the order of thousands of dollars). We are trying to get a good handle on the potential tolerance of this species here in New York waters.
Species range for Ruppia maritima in the US and Canada, from the USDA
Why? Well as Dr. Bologna argues, as we continue to stress the environment, dominant seagrass (such as eelgrass, Zostera marina, in New York) species are declining. These species provide a variety of ecosystem services. Widgeon grass, which is apparently more tolerant and opportunistic, can potentially move in and become a dominant seagrass species in stressed ecosystems. The problem with this is that widgeon grass is much smaller in size (shorter, skinner blades), and so they might not provide the same ecosystem services as larger species like eelgrass. However, we don’t really know the answers to the questions about ecosystem services. This is an area which requires considerable research. As a structure forming species, it should provide habitat, and I saw a bunch of juvenile fish (likely some species of killifish) swimming around the Ruppia today. However, other services, such as particle trapping and wave attenuation, may be non-existent in Ruppia meadows.
Hopefully, our lab can help answer some of these questions in the future…
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.
Hard clams ability to alleviate eelgrass stress
(You can see the rest of the slideshow JCarroll- CommunityEcology-Apr12-845am)
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.
Scott Marion, seagrass researcher at VIMS
Hopefully, we can save seagrasses from the countdown to extinction.
Short, FT, Polidoro, B, Livingstone, SR, Carpenter, KE, Bandeira, S, Bujang, JS, Calumpong, HP, Carruthers, TJB, Coles, RG, Dennison, WC, Erftemeijer, PLA, Fortes, MD, Freemen, AS, Jagtap, TG, Kamal, AHM, Kendrick, GA, Kenworthy, WJ, Nafie, YAL, Nasution, IM, Orth, RJ, Prathep, A, Sanciangco, JC, van Tussenbroek, B, Vegara, SG, Waycott, M, & Zeiman, JC (2011). Extinction risk assessment of the world’s seagrass species Biological Conservation : 10.1016/j.biocon.2011.04.010
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
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.
Green Crab - Invader!
In the marine realm, there are numerous invaders from all taxa – from plants and algae, to tunicates, crabs, mollusks, and all the way up to fish and birds. Some of the species have been here for centuries- such as the green crab, Carcinus menas, on the east coast, and the mute swan, Cygnus olor. Still, others are much more recent, such as the Asian shore crab, Hemigrapsus sanguineus, the Chinese mitten crab, Eriocheir sinensis, the lionfish, Pterois volitans,(which I’ve recently blogged about many times), and the tunicate Didemnum vexillum (which I blogged about here). Regardless of species, and length of time since invasion, these species have potential to be harmful to their new environments. The East Coast of the US is particularly hard hit by these species.
Map of invasive problem regions
Map of origins of marine invaders
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
So I frequent the UnderwaterTimes almost daily. I like to find out what’s going on in underwater related news. So imagine my excitement at this article today:
“Fake seagrass could help boost fish numbers”
The premise of the article states that scientists in New Zealand are using artificial seagrass to help boost fish stocks. Seagrass is an extremely vulnerable marine habitat, with worldwide losses. In some places where lush underwater meadows used to exist, the grass has been replaced by barren sediments. This can have an impact on fish stocks, as many marine species utilize seagrass as a habitat for at least some portion of their life cycle. So it comes as no surprise that scientists want to try to replenish fish stocks by enhancing seagrass. This is apparently what they are trying to do in a bay in New Zealand. Although, I imagine that the researchers are actually using ASUs to test affects of fragmentation on local fisheries species and not to actually be used to enhance species, it is interesting none-the-less.
I have a certain affinity for all things fake seagrass. Why? Well, a portion of my dissertation research involves using artificial seagrass units (ASUs) to investigate the impacts of patch size and shape (perimeter, area, and P:A ratios) has on scallop recruitment, survival and growth. As I mentioned already, seagrasses are important habitats, and bay scallops have long been known to associate with seagrass. Scallop populations are currently undergoing varying degrees of restoration (depending on location) but with restoration comes certain issues – namely, how are these little guys going to be affected by declining seagrass. In many areas where scallop populations crashed, seagrasses have also diminished in extent. Since seagrass is important for scallops, a decline in seagrass cover can have implications for scallops and their restoration. For my work, I use 2 sizes of seagrass mats, 8.5 and 17 square meters, and 2 shapes – a circle and 4 pointed star to maximize perimeter. Just in case those numbers don’t mean much to you, the small circles are just over 3 meters in diameter, the large circles around 5 meters across. The large star is 7 meters from tip to tip. These ASUs have 500 shoots per meter, consisting of 4 blades of polypropelene ribbon. It was quite the undertaking, and required many beer and pizza nights for fellow grad students, as well as help from local schools and scout troops.
I have generated some interesting, and unexpected, data. There is a wealth of literature out there about the impacts of fragmented seagrass habitats, patch configuration, edge effects, etc, that has been accumulating over the last 15 or so years. Going into the experiments, I had a pretty good idea about what I would expect to see – more scallop recruits along the edges of the mats, but higher predation at the edge. Growth to be slowest in the centers of the mats, etc. However, not everything happens the way I planned or anticipated. In particular, I have been working up some of my recruitment data, and I did not see a “settlement shadow” or edge effects due to predation. What is a “settlement shadow?” Essentially, bivalve larvae can be assumed to be passive particles, moving at the mercy of the currents. As a current comes into a seagrass meadow, the flow is attenuated. Particles settle out along the edge, and become diminished with distance into the meadow. Hence, recruitment is expected to be highest along the edges of seagrass meadows (and, also, the edges of my ASUs). On the opposite end of the spectrum, survival is expected to be the lowest along the edge, since predators are likely to have more access along the edges, and thus predator encounter with scallops should be higher. However, this isn’t what I saw. The reason? The dominant predator in my particular system is a small mud crab – not likely to be impeded by seagrass structure and essentially ubiquitous throughout the ASUs. This tells me the dominant process structuring post set scallop communities on my grass mats is predation, and the predator is apparently not impacted by fragmentation. This could have implications for restoration. I haven’t finished all the analysis yet, but it was pretty interesting. I just presented some of this work at a graduate symposium last week, and plan on presenting it again at the National Shellfish Association annual meeting in March.
Well it has been a few weeks since I’ve posted on some research articles. But then the Journal of Experimental Marine Biology and Ecology published a manuscript about cod responses to expanding seagrass meadows. In addition, a paper out of Japan earlier this year talks about the loss of fish species with the loss of an eelgrass meadow. Combined, these point out the obvious, many finfish are dependent on seagrasses for habitat. However, its not just typical seagrass-associated species that are affected by the loss of seagrass.
First, what happens when seagrasses disappear? There is a wealth of literature that suggests disappearing seagrasses has many negative consequences for both resident and transient species. Many species, including numerous commercially important species, utilize seagrass as a habitat for at least some portion of their life cycle. A paper by Yohei Nakumura examining seagrasses next to l reefs demonstrated that seagrass loss has an impact on the abundance and diversity of fishes, including reef associated species. A series of disturbances, particularly typhoons, decimated a seagrass meadow near a reef, to the point where in 2009, the seagrass meadow had totally disappeared. This caused a 80% reduction in the number of species and a 90% reduction in the total number of individual fish along transects at the same site before and after the disappearance. In addition, they monitored a nearby undisturbed site as a reference, and there was no difference in the abundance or diversity of fishes over the same time period. Many of the fishes that disappeared weren’t just seagrass residents, but also coral dwellers. In fact, the only species that didn’t seem affected were some gobies. The reason for the loss of fish might not be the eelgrass itself, although the habitat does provide shelter from predators, but could also be due to loss of food for many of the fish – tiny crustaceans that live amongst the seagrass.
A more recent paper involves the increase in abundance of juvenile cod in areas where seagrass is recovering and expanding. First, I know what you are all thinking, I love cod and eelgrass associations! And second, it is great news to hear that seagrass is recovering in some areas (I can talk more about this later). Apparently, there are seagrass meadows in Newfoundland, Canada, that are recovering and expanding over the past decade. These habitats are nursery grounds for both Atlantic cod and Greenland cod. So, one might imagine that an increase in seagrass would be beneficial to these species. Using biweekly seines to monitor changes in fish abundance, Warren and others were able to demonstrate dramatic increases in young of the year cod in the seagrass habitats, in particularly in those “recovering” habitats. This increase also occurred rapidly with expanding seagrass meadows. This suggests that these fish are capable of recovering quite quickly if enough suitable habitat exists. However, it also suggests that since juvenile cod might respond so rapidly, that any negative changes in seagrass cover can be detrimental to stocks. Combined with the Japanese study, the literature indicates that fish populations may lack resiliency to seagrass loss, and illustrate the need for water quality monitoring and management, as well as seagrass restoration. Otherwise, the news that cod stocks might recover, might be just internet fodder.
Nakamura, Y. (2010). Patterns in fish response to seagrass bed loss at the southern Ryukyu Islands, Japan Marine Biology DOI: 10.1007/s00227-010-1504-7
Warren, M., Gregory, R., Laurel, B., & Snelgrove, P. (2010). Increasing density of juvenile Atlantic (Gadus morhua) and Greenland cod (G. ogac) in association with spatial expansion and recovery of eelgrass (Zostera marina) in a coastal nursery habitat Journal of Experimental Marine Biology and Ecology DOI: 10.1016/j.jembe.2010.08.011
In the most recent issue of Marine Biology, there is a manuscript addressing the issue of 2 introduced species and their interactions with one another. Its an interesting read – one of the species is a commercially important bivalve, the Manila clam, which was introduced in the early 20th century and is now one of the most commercially harvested clams on the west coast of the US. The second is Zostera japonica, dwarf eelgrass, an introduced seagrass species which can establish itself on tidal flats. The idea is that this new seagrass species may be of detriment to the now commercially important manila clam. While there is certainly literature which suggests that seagrasses might enhance bivalve growth – see works involving hard clams and eelgrass by Elizabeth Irlandi and Mike Judge – it certainly stands to reason that eelgrass dampens water currents, and likely decreases the amount of food available to suspension feeders, particularly those distant from the edge of the seagrass (where the food availability might be enhanced). And so the team led by Chaochung Tsai aimed to investigate the impacts the invasive eelgrass had on the clams, and whether the clams might enhance the introduced grass. They chose 3 habitats – seagrass present, seagrass removed, and harrowed habitats. The presence of seagrass, while not necessarily impacting shell extension of the infaunal manila clam, did significantly negatively influence clam condition (tissue weight to shell volume ratio). On the flip side of the coin, while bivalves have been shown to influence eelgrass growth through nutrient additions – see the Peterson Lab publications – this apparently is not the case for the manila clams and dwarf eelgrass. In this experiment, clams did not enhance growth nor impact sediment porewater nutrients. In fact, the only positive effect of the introduced seagrass was on itself. Pretty interesting (and before I read it, unexpected) results.
Tsai, C., Yang, S., Trimble, A., & Ruesink, J. (2010). Interactions between two introduced species: Zostera japonica (dwarf eelgrass) facilitates itself and reduces condition of Ruditapes philippinarum (Manila clam) on intertidal flats Marine Biology, 157 (9), 1929-1936 DOI: 10.1007/s00227-010-1462-0
Irlandi, E., & Peterson, C. (1991). Modification of animal habitat by large plants: mechanisms by which seagrasses influence clam growth Oecologia, 87 (3), 307-318 DOI: 10.1007/BF00634584
Judge M, Coen L, Heck KL (1993). Does Mercenaria mercenaria encounter elevated food levels in seagrass beds? Results from a novel technique to collect suspended food resources Marine Ecology Progress Series, 92, 141-150
Well, now I’ve seen everything. Well maybe not everything, but in all my NY diving, I had never seen this: eelgrass on an exposed, essentially oceanic sandy, rocky bottom, and a school of YOY cod. I have heard about eelgrass in these locations. I have heard that there have been increasing cod landings in NY over the past 2 winters. I have even read that juvenile cod utilize eelgrass. But I had never actually seen it until last week, when we dove along the south-western corner of Fisher’s Island.
We were out there for the day looking at some eelgrass for some new projects we are working on in the lab and in addition to collect samples for genetic analysis for a colleague’s (Jamie Brisbin‘s) research. After we were done at our site for the day, we decided to take a quick drop in along the exposed southern shore where the grass was supposed to be extremely tall and growing in a relatively rocky habitat. It was a pretty cool site – I saw typically rocky subtidal macroalgae – kelps, fucoids, coralline – with patchy eelgrass mixed in. It was pretty exciting and cool to see (although my picture below hardly does it justice).
But while I was down there, I was surrounded by what appeared to me to be young of the year (or at the most young juvenile) cod. I am in no means a fish biologist, so I might be off a bit in estimating their age, but they were definitely gadiforms, and I am fairly confident they were Atlantic cod, Gadus morhua. The distinguishing feature for me was the 3 dorsal fins. Either way, I was surprised to be surrounded by this school, although again, these pictures do them no justice. I found it difficult to get good photos – it was late in the day, the water was surgey (I just made up a word I think), and I just couldn’t get very close, so I was limited by the capabilities of my Sea and Sea camera. That didn’t stop me from trying, mind you. I was swimming, hands extended in front of me and (don’t try this at home) holding my breath while diving and snapping away. Everytime I let out a breath, they would swim away. This is poor diving practice, and I wasn’t holding my breath for long – just slightly longer than my normal breathing rhythms – it was just my best chance at getting any shots at all.
But then I realized, wow, these are a bunch of young cod and they are staying in this area where there is eelgrass. And I remembered an article I read about YOY cod and survival in eelgrass meadows. And since my experiences with eelgrass have always been in lagoonal-type estuaries where we don’t see cod (although we do see their cousins Atlantic tomcod and hake), I was excited to see both eelgrass and cod in the same place (mind you, I had never seen cod while diving either). So I was sitting on the bottom, trying to follow this school of fish and get any good pictures, and thought this is what that paper was talking about. I will detail the paper below.
The basic idea behind the paper by Ann Marie Gorman et al in 2009 was this idea of habitat patch size and edge effects on juvenile cod. I was particularly interested in this paper because the impacts of eelgrass patch morphometrics is something I have spent considerable time working on in regards to bay scallops – my research organism. So any manuscript pertaining to seagrass patch effects I try to read. This paper was pertaining to Atlantic cod, predatory mortality, and edge effects, all things of significance to my research. Since young of the year cod utilize coastal eelgrass habitats as nurseries and predation refuges, varying sizes of patches can have considerable impacts on juvenile survival. The group investigated different size patches, as well as within patch location (along the patch edge, 5 and 10 meters into the patch and into the unvegetated sediment outside the patch), and how those two factors affected the survival of tethered age-0 cod. Obviously, there are all sorts of potential artifacts with tethering mobile individuals in survival studies, however, because they are mobile, there is no other way to look at predatory mortality as specific locations within a given habitat. They observed a relationship which demonstrated lowest survival at intermediate patch sizes and highest survival at the largest patch sizes. And interestingly, they had lowest survival of tethered scallops along the eelgrass patch edge than either within the patch or in the barren habitat – and this survival increased with distance from the edge in both directions. This has been observed in other seagrass habitats, so I bought this. It solidifies the hypothesis that predators in seagrass habitats patrol along the edge of the seagrass, where prey densities are likely to be higher than in unvegetated habitats, and more easily accessible than within the seagrass patch. An interested read for those interested in spatial and landscape ecology, impacts of habitat patchiness on survival, or finifsh predation.
Gorman, A., Gregory, R., & Schneider, D. (2009). Eelgrass patch size and proximity to the patch edge affect predation risk of recently settled age 0 cod (Gadus) Journal of Experimental Marine Biology and Ecology, 371 (1), 1-9 DOI: 10.1016/j.jembe.2008.12.008
Research to Assess and Tackle Issues of Seagrass Die-Off in Local Waters
Cold Spring Harbor, NY — May 1, 2009 — Seagrass has received a significant boost thanks to a $500,000 research grant (H.R. 1105, the Omnibus Appropriations Act of 2009) co-sponsored by Congressman Timothy Bishop (NY-01) and Congresswoman Rosa DeLauro (CT-03). These overlooked, but essential underwater flowering plants, form dense stands in shallow salt-water bays and harbors, and provide critical habitat for local fish and other marine life.
Read the rest here.
We all know the story here, at least if you have been following my blog, but seagrasses are vital ecosystems that serve important nursery and foraging habitats for many fin and shellfish. Many of the species are also of economic importance, which is garnering eelgrass more attention. This is big news for Long Island, since there are numerous critical gaps in the information necessary to successfully manage and restore eelgrass. And, while there may be other suitable habitats in the Peconics for my study organism, the bay scallop, eelgrass is the preferred habitat.
To learn more about seagrasses, and eelgrass in particular, check out Seagrass.LI. Also, check out this new blog by a marine biologist from Canada.
At the Cornell Cooperative Extension of Suffolk County’s Marine Environmental Learning Center works a team of eelgrass restoration experts. They have been actively working to restore eelgrass meadows to their past glory throughout the Peconic Estuary, and more recently have been working in Long Island Sound and in the South Shore estuaries. About twice a year they release a newsletter that highlights some of the work they are involved in. The current newsletter also highlights the scallop restoration project being undertaken in Suffolk County, a project which I am involved, and a project that allows me to conduct much of my bay scallop research.
to read the current newsletter.
Also, if you would like to visit their website, click here
I have worked with this group in the past, and all members are very knowledgable in habitat restoration. They have experienced success in many of their transplant and restoration sites, and even developed their own methods for restoration. Now that the importance of eelgrass for many species has been ackowledged by the state of New York, which recently held a meeting of national and international seagrass experts to create an “eelgrass task force” to identify areas of research that are important to understand the dynamics of eelgrass survivng on Long Island and how best to protect it, the job of both the Cornell seagrass restoration team and Dr Brad Peterson’s (of Stony Brook University) Seagrass Rangers, a team of graduate students to which I belong, has never been more important.
To see the seagrass ecology lab website, click here.