So anyone following my blog knows that I was actively involved in the bay scallop restoration efforts in Long Island. To refresh, scallop populations supported a vibrant fishery in NY until the mid 1980s, when populations crashed due to the first occurrence of a brown tide bloom, and recurrent brown tides pushed scallops to the brink of local extinction. The brown tide has not occurred in the Peconic Estuary since 1995 (although it still occurs on Long Island waters), so in 2006, restoration efforts started to help jump-start local scallop populations in the Peconics.
Commercial bay scallop landings and Brown tide occurrence
These efforts sought to boost spawning stock and concentrate high densities of scallops in close proximity to enhance fertilization and reproductive success. The idea was that low population densities of adults were limiting reproduction, which was subsequently limiting larval supply and recruitment. The restoration efforts sought to boost adult populations by establishing spawner sanctuaries using an array of lantern nets or by high density on bottom restoration. You can watch a number of videos on these efforts here, or watch the Fox News piece below:
The restoration efforts had been very successful – every year we see higher numbers of scallop spat than the year before (despite the same effort), and the results have translated to scallops on the bottom and to the fishery. Recently, our group was able to publish some of our findings in Marine Ecology Progress Series.
We were able to demonstrate at all sites annual increases in the mean spat per bag – that means, each year post-restoration, we saw greater numbers of baby scallops in our collectors. This occurred not only in our basins where we actively did restoration, such as Orient Harbor and Hallock Bay, but also in nearby basins with no active restoration efforts, such as Northwest Harbor.
A figure from our MEPS paper, illustrating the annually increasing densities of scallop spat in Orient Harbor. The cross denotes the site of a large lantern net spawner sanctuary.
In fact, scallop spat abundance increased up to 3000% of pre-restoration levels. This was despite that none of the environmental parameters had changed from the 10 years prior to restoration beginning to the 5 post-restoration years we examined for this study. Environmental variables could possibly influence the amount of larvae produced and larval survival. However, temperature, chlorophyll (a proxy for food), nitrogen, monthly rainfall and salinity were not different between the 2 time periods. This suggests that the restoration efforts played an important role in helping to increase the larval availability. In essence, we “primed the larva pump!”
Environmental variables for the pre-restoration period (1996-2006) and the post-restoration period (2007-2010).
Obviously, we were expecting these results and were very excited that we were able to eliminate other possibilities of increased larval supply. Additionally, the dates of peak settlement for the most part lined up with our estimates of spawning dates and settlement.
This doesn’t mean much, however, if it isn’t translating to the bottom, since we collect these scallops in spat collectors hanging in the water column. Many sources of mortality, but primarily predation, can occur from the time the scallop settles on the bottom to the time it can spawn and then contribute to the fishery. I focused most of my dissertation research on habitat and predation on scallops. Some of the cool things from that research suggests that patchy seagrass might not be detrimental to scallop populations and that an invasive species might be a suitable alternative habitat. So, despite limited seagrass in our restoration estuary, we have seen increases in scallops on the bottom.
On bottom increases in scallop densities post restoration
And in many of the basins, these increases in on bottom densities in the fall correlates with the increases in spat fall during the spring of that same year.
Relationship between seed scallop densities in the fall on the bottom in Orient Harbor and the spat per bag landings from the spring.
We are currently preparing this data for a manuscript, showing the subsequent increases in on bottom densities, fishery yield and the economic benefits of the restoration efforts. Hopefully, the success of this project and the information gathered will help other restoration efforts on Long Island, such as the Shinnecock Bay Restoration Project (which I have blogged about ) and elsewhere. I am hoping to turn some of the things I learned with this project (and the many various side projects) to my oyster work here in NC, although I also plan to keep working with scallops.
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!
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
(My best shark photo, sorry!) So I check out Underwater Times from time to time to see whats new in the underwater news world. So when I happened upon this article from the United Arab Emirates, it reminded me of a Science paper that came out a few years back that is near and dear to my heart. But first, the news article. Essentially, sharks are a major fishery in the Arabian Gulf. From 1985 to 2000, shark landings in the UAE ranged from 1350 to 1900 tons of sharks, and the UAE is a major exporter of shark fins to Asia. However, scientists and fishermen alike have started to notice that the loss of shark predators has impacted the ecology of the Arabian Gulf. This has lead to a study to be undertaken examining these impacts.
In the article, a sentence mentions how the loss of sharks on the Atlantic coasts has lead to a collapse in bay scallops. So you guessed right, this is where the 2007 Science paper which I find so particularly fascinating comes in. This paper, entitled “Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean,” by the late Ransom Myers and others detailed a study whose base conclusion was that the loss of sharks due to overfishing cascaded down the food web and resulted in the loss of bay scallops in North Carolina. They examined fisheries data for trends in individual species of elasmobranchs, the family of fishes to which sharks belong, from 1970-2005 between Cape Cod, MA and Cape Canaveral, FL. They were able to demonstrate strong decreasing trends in the abundance of great sharks, which are the apex predators. Over the same 35 year period, the populations of smaller elasmobranchs, including smaller sharks, skates and rays, were shown to be increasing. Many of these species, and the cownose ray in particular, are known consumers of benthic prey, including a variety of shellfish. In North Carolina, cownose rays move into the estuaries to feed in the summer, and were capable of removing entire bay scallop populations before they could spawn, and decimating populations to a point that densities were so low, that successful fertilization could not take place. By 2004, the North Carolina scallop fishery was gone. These mesopredators are also likely to be impacting the recovery of other shellfish species through consumption. Thus, the loss of sharks, even through by-catch, is likely to have devastating ecosystem impacts, not just in North Carolina, but likely in many coastal areas. (For other reasons why sharks matter, check out this website, this cool blog called Ya Like Dags, and the ongoing series of shark posts over on Southern Fried Science).
Myers RA, Baum JK, Shepherd TD, Powers SP, & Peterson CH (2007). Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science (New York, N.Y.), 315 (5820), 1846-50 PMID: 17395829
Another paper that came out of the Charles Peterson group (he was a co-author on the above Science paper) investigated restoration options for scallops in North Carolina. Obviously, cownose rays still prevent a major problem. One mode of restoration they examined was a way to protect adult scallops in a spawner sanctuary from predation by the rays. They were able to accomplish this via a fairly simple method of using PVC stakes into the sediment that reached out of the water at high tide, evenly spaced narrowly enough so that the rays could not fit inside. This method was capable of successfully maintaining dense populations of adult scallops during the period when the rays were in the estuary. Obviously, allowing populations of adults to survive to spawning is a major step in enhancing scallop populations.
Stephen R. Fegley,* Charles H. Peterson, Nathan R. Geraldi and David W. Gaskill (2009). Enhancing the Potential for Population Recovery: Restoration Options for Bay Scallop Populations, Argopecten irradians concentricus, in North Carolina Journal of Shellfish Research, 28 (3), 477-489 : 10.2983/035.028.0309
There is an interesting blog over on discovermagazine.com about the way sea walnuts (or ctenophores, or Mnemiopsis leidyi) feed (in addition to a cool video, which is posted below). Apparently, these organisms use their cilia to create almost undetectable currents, and they are then capable of catching unsuspecting prey with great efficiency. Due to their incredible ability to feed stealthily and efficiently, they have been particularly devastating invaders in European water bodies. When these comb jellies showed up in the Black Sea, they contributed to a food web collapse by consuming many of the fish larvae that would typically serve as the base of the food chain. In fact, gelatinous zooplankton are often considered productivity dead-ends; they consume productivity in the forms of other plankton, however, they offer little food value to other species. So the productivity is not transferred to other trophic levels, and food webs collapse. This is also becoming a problem in human impacted systems.
This blog made me remember some research some colleagues at the School of Marine and Atmospheric Science conducted. PhD student Marianne McNamara, under the tutelage of Darcy Lonsdale, investigated the impact of high abundances of ctenophores on larval bivalve mortality.
In their article “Shifting abundance of the ctenophore Mnemiopsis leidyi and the implications for larval bivalve mortality,” published earlier this year in Marine Biology, McNamara et al investigated how ctenophore abundance has changed, their digestion rates, and finally, their ability to control bivalve larvae. The data from this article is of particular importance for the hard clam restoration and management effort in Great South Bay, NY (their field sites), since the comb jellies may exert a strong predation pressure on hard clam larvae.
They conducted field surveys to investigate the abundance of ctenophores and other zooplankton. They enumerated and took volumetric measurements of the comb jellies, then looked at their gut contents. Finally, they conducted lab feeding experiments, and then used equations to calculate their ability to control bivalve larvae.
McNamara et al found high densities of ctenophores in the early summer, and larger ctenophores in the late summer, and when compared to the literature, densities were considerably higher than in previous decades. This is of particular importance, since bivalve veligers made up approximately 63% of the ctenophores’ gut contents, indicating this is a particularly valuable food source for the jellies. In addition, using their equations from densities and feeding rates, they predicted that at peak abundances, the ctenophores could consume over 94% of the bivalve veligers in Great South Bay. This is a particularly alarming figure. In addition, the peak abundances of ctenophores occurs earlier in the year (early summer) now than it did decades ago (in the fall), putting peak abundances of comb jellies in the water column at the same time as the bivalve larvae.
Clearly, this study illustrates the potential ecosystem impacts of increasing gelatinous zooplankton. While they have already been shown to be particularly harmful as invaders, it is now apparent that they can have impacts where they are native as well. It is likely that increasing human impacts leading to pelagic dominated production will lead to more ctenophores in coastal systems, which can prevent benthos from reestablishing in these areas. This might be the case in Great South Bay, where the hard clam populations are struggling to recover despite the Nature Conservancy’s efforts at replenishing them. Now I don’t know about their high end estimates, as one could imagine if ctenophores were capable of consuming essentially all of the bivalve veligers, then veligers and comb jellies wouldn’t be collected together in plankton tows. However, it is clear that ctenophores can possibly have a major impact on a local ecosystem.
McNamara, M., Lonsdale, D., & Cerrato, R. (2009). Shifting abundance of the ctenophore Mnemiopsis leidyi and the implications for larval bivalve mortality Marine Biology, 157 (2), 401-412 DOI: 10.1007/s00227-009-1327-6
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
For years, the “supply-side” ecology has been a common theme describing mechanisms for benthic species distributions and densities. In general terms, the amount and extent of a particular organism is driven by the supply of larvae to a given area. This larval supply can thus be seen as driving benthic community structure, especially for marine invertebrates – as their life cycles contain a planktonic larval stage which allows for dispersal over relatively long distances. Thus, many of these populations are considered “open” and their continuation is dependent on some large supply of larvae. This makes sense, and it has been demonstrated many times in the literature. However, this has often been demonstrated on hard bottom communities. Soft bottom benthos don’t always display similar patterns. A recent paper by Dr. Megan Dethier from the Friday Harbor Laboratory at the University of Washington, details an experiment conducted investigated very small, post set, infaunal recruits. Sampling these habitats is often difficult due to the 3-D nature of soft sediments. She was able to demonstrate that for a number of taxa she was working with, the strongest recruitment was not in areas where the largest adult populations existed. This suggests that for many of the soft bottom benthos she studied, the supply of larvae is not limiting the adult populations, but rather some post-settlement processes, such as predation, competition or abiotic stressors.
LEWIN, R. (1986). Supply-Side Ecology: Existing models of population structure and dynamics of ecological communities have tended to ignore the effect of the influx of new members into the communities Science, 234 (4772), 25-27 DOI: 10.1126/science.234.4772.25
Dethier, M. (2010). Variation in recruitment does not drive the cline in diversity along an estuarine gradient Marine Ecology Progress Series, 410, 43-54 DOI: 10.3354/meps08636
This is a particularly interesting article, because “supply-side” ecology doesn’t always hold true in soft bottom benthos. I have observed this first hand with the scallop restoration work on Long Island. Over 6 years, we have monitored larval supply of scallop spat at a number of different locations, and then each winter and spring, we conduct benthic surveys for juvenile densities. There isn’t always a match between sites where we had the highest numbers of post-set and the highest juvenile densities. The main causes for this mismatch is likely to be predation or physical factors.
On another project, I am investigating scallop settlement on artificial seagrass units. I design collectors to mimic seagrass, each collector has 10 artificial seagrass shoots. Half of the collector (5 shoots) is enclosed in a mesh bag (just under 1mm) and the other half exposed to predation. There is an order of magnitude difference between the number of available settlers (those inside the bags) when compared to those actual “recruits” (those scallops outside the bags). This low pattern of surviving recruits holds up regardless of location within the grass mats (either on small or large mats, at the center or the edge). This indicates to me that predation is a major contributing factor structuring the scallop populations, at least in the estuary in which I work, Hallock Bay, Long Island.
At 2 of the sites we surveys we found scallops at higher densities than anticipated based on the fall survey results, suggesting higher overwinter survival (which can be a problem – Tettelbach et al 1990), and higher densities overall. These are very good signs, indicating that the restoration effort is likely working (and here, last years harvest is also a good indication, but see Tettelbach and Smith 2009)! Below are some photos from the dives….
Eelgrass, Zostera marina, often considered the primary bay scallop habitat, although some of our new research indicates that other species might also facilitate scallop survival – Carroll et al 2010
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
Tettelbach, S.T., C.F. Smith, J.E. Kalady, T.W. Arroll and M.R. Denson. (1990). Burial of
transplanted bay scallops Argopecten irradians irradians (Lamarck, 1819) in winter. Journal of Shellfish Research, 9, 127-134
Tettelbach, S., & Smith, C. (2009). Bay Scallop Restoration in New York Ecological Restoration, 27 (1), 20-22 DOI: 10.3368/er.27.1.20
Yes, that is right. Failure. I guess it happens to everyone, and I half expected it by the way my recruitment experiment was going all summer. But I did get that glimmer of hope 6 weeks ago, when I did find a handful of scallop spat on my recruitment squares, and both 4 weeks ago and last week when I saw numerous scallops in our local spat collectors. Alas, no recruits on my squares. That old adage of “If you build it, they will come” does not seem to be ringing true for scallop spat in my grass mats.
Now, I don’t want to make this all bad, because clearly highly mobile macrofauna have had no problems discovering or inhabiting my artificial grass mats. In fact, with the water relatively clear last week, I saw numerous species, including tomcod (which I had not seen in Hallock in all my dives there), largish sea bass, and the usual suspects (killifish, pipefish, sticklebacks, cunner, blackfish, porgies). So the whole “if you build it, they will come” theory behind creating artificial habitats or restoring habitats may ring true for certain mobile organisms. However, habitat value aside, no habitat can encourage organsisms to come if those organisms can not get there. Simple. If the supply is low, which I have reason to expect that it is (judging by the almost complete absence of adult scallops from the bay, among other things), it cannot be compensated by available habitat. However, it is still quite possible that I am simply missing the spat on my collecters, since collecting approximately 1 square meters worth of recruitment squares (~500 shoots) out of ~119 square meters of areas (~59000 shoots) may just be too small an amount to see anything. Finding scallop spat on natural grass is akin to finding a needle in a haystack, so why would my mats have been any different? And yes, the number of squares I collect seems low relative to the total area, but over the course of the whole summer, I collected ~5 square meters worth of artificial grass mats, with essentially the same result every time, nothing. Given the amount of hours it takes to locate and collect the squares, then process them, it is alot of work, trust me on that. It just seems to me that supply is very low. Even in the collectors we aren’t getting that many, 10-20 per collector, and those are on a mesh that has more surface area than my recruitment squares and are enclosed and thus less likely to be preyed upon. My recruitment squares also don’t have that luxury, and I did this on purpose. Maybe next year I will do a predicted vs apparent recruitment survey. I know I am missing some, since we did collect one large seed ~30mm on one of my squares, but not attached to my grass. At least this is a good sign that there are probably some seed out there, and I am hoping in November to do some bottom surveys to find out.
So, a few posts back I was disappointed in the lack of scallop spat on my mats and in Hallock Bay in general. We had not really seen any in our collectors which we use to monitor spat in any of the collections, and so I was not so upset that I wasn’t finding them on my mats, just figuring they weren’t around. I was a little worried though, since scallop recruitment is a part of my research, and I was already thinking about possibilities of new locations for next year. I was ready to give up on the recruitment thing all together, since it is a lot of work to make the recruitment squares, to search for the squares within the mats, and to put new squares back on, not to mention I didn’t want to keep wasting fuel for fruitless boat trips to my site. However, after much deliberation, I decided to make a new set of squares over the weekend to put one more set out there, just to be sure I wouldn’t miss it.
Well we went to the site on Monday to collect my 3rd set of recruitment squares and to replace them with the 5th (and final) set. I also keep a set of spat collectors at the center of my array to make sure scallops are recruiting to the area using a known method for sampling them. I always process the spat collectors first, just so I have an idea of what to expect on my squares. Guess what?
Scallop spat in my collectors!! This was exciting. It wasn’t a lot, only 16 total out of 3 bags, but I honestly didn’t think I would see any. I still wasn’t sure what to expect on my mats, but at least I was happy there were spat in the area. After processing all the recruitment squares, I did have spat on the mats! Success!! Well, kind of – we only found 4 total spat on the squares, not quite numbers that I can use for any kind of stats. However, now I know that if there are spat in the area, they will potentially settle on my mats, which was very refreshing to find.
Oh, and there is better news, the spat that we found was mostly small – 2-4mm. This is good, because it means the spawn happened relatively recently, and will probably show up on my next set of collectors. Second, and more exciting, is what we found today – in our spat monitoring we have 5 sites within Hallock Bay where we have sets of collectors, and we found spat at all of them, and in decent numbers (some bags over 20 scallops) and again, many were small. So I am keeping my fingers crossed that I will see much better numbers on my mats during my next collection!
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!