Zostera marina is a seagrass species, commonly known as eelgrass, that is found on both coasts of the United States, as well as in Europe. Unfortunately, Zostera is disappearing all over the place, including right here in New York. This could have devastating impacts on animals that rely on eelgrass as foraging grounds, or, as is the case with scallops, use it as a refuge from predation. This is its story, as seen through the eyes of an aspiring graduate student...
Apparently, climate change might not be such a bad thing. Especially not if you are an exploited species of bivalve. Now I am not trying to be a climate change apologist, but too often we get caught up in this debate and science is 99% of the time on the side saying "It's bad." However, as I have learned in my own research with invasive species, there are always two sides to every coin. A warming ocean could be a benefit to numerous species, probably as many species as it might be of detriment. Obviously, there are a whole suite of ecosystem processes that are also affected, but in certain cases, it might not be so bad. At least not according to a paper in Marine Biology entitled "Strengthening recruitment of exploited scallops Pecten maximus with ocean warming." Its an interesting read. The essential idea is that over a long(ish) time period, the researchers were able to demonstrate a highly significant correlation between increasing temperature and increasing settlement and recruitment of juvenile scallops to a local scallop population. Shifts in recruitment can be attributed to temperature related shifts in feeding, gonad development and larval survival - and this impacts are more apparent in species who use environmental cues to induce development and spawning. Such is the case for many species of bivalves, including scallops, and so a warming ocean could potentially enhance scallop recruitment. There are some stats involved in their methods, but the basic results are pretty simple, over the past decade, scallop landings around the Isle of Man have been increasing. IN addition, mean springtime temperatures have been increasing (which cues development). I know what you all might be thinking, correlation does not equal causation (you know the one, mean global temperature has increased as the number of global pirates has decreased, meaning that the number of pirates somehow influences the climate), but that goes into their methods of using residuals and proxy values and all sorts of things. Basically, recruitment increase isn't significantly related to other things (spawning stock, dissolved oxygen, chlorophyll a), and is strongly related to temperature. They even examined a number of scallops during the three month conditioning period and the GSI - which indicates relative gonad development - was significantly higher in years when temperature was higher. So when temperature goes up, the scallops develop larger gonads and subsequently release more larvae which show up as strong recruitment classes.
So what does this mean for bay scallops? Well, there are plenty of issues with ocean warming and bay scallops - and one of particular concern is predator range expansion and new predators coming into the bay scallops range. In terms of recruitment, we haven't seen any patterns that would suggest this is the case in New York. However, there hasn't been many scallops here to spawn over the past 20 years until recently - due to the restoration efforts - and there needs to be a local spawning population in order to observe any of the patterns described from the paper. That said, bay scallop recruitment is not likely to be effected by ocean warming in terms of larger populations - although timing of first spawn might change, the number of times they spawn might change, etc, but it is my opinion that there are numerous variables that influence the size of recruitment classes in local scallop populations, particularly in the bay, which is already a dynamic environment.
Shephard, S., Beukers-Stewart, B., Hiddink, J., Brand, A., & Kaiser, M. (2009). Strengthening recruitment of exploited scallops Pecten maximus with ocean warming Marine Biology, 157 (1), 91-97 DOI: 10.1007/s00227-009-1298-7
TED is an awesome website with talks by hundreds of people from all disciplines, and you can see them all free. They are pretty good. You should check it out. This one in particular caught my eye. Edith Widder does ocean and deep sea research and uses submersibles - pretty awesome stuff. Enjoy!
A complete and utter failure? You decide. Last fall I had the bright idea to track overwinter survival and subsequent spring conditioning for scallops released in different habitats (eelgrass - their preferred habitat, see Thayer and Stuart 1974; Codium fragile - an introduced macroalgae which we think might serve as a suitable alternate substrate in the absence of eelgrass; and unvegetated, as a baseline for comparison). I have examined these habitats for growth in juvenile scallops and have already published some short term survival data (Carroll et al 2010, see earlier posts for a link). So my bright idea was to free release a fairly large number of scallops into these habitats at two field sites, one in Shinnecock Bay and one near Sag Harbor, NY. This is a method we have used in the restoration efforts, and a method that has been successful, so I figured that it would be no problem. I planted ~2500 scallops in each habitat at the 2 sites (~15,000 total scallops planted), not an insignificant number, at least not in my opinion back in November/December of 2009. In other planting sites, we typically don't monitor again after planting until the spring, so staying true to form, I did not actually go check on these scallops until last week. Much to my surprise (well, maybe not totally surprised) I didn't recover a single scallop in Shinnecock Bay. I surveyed all the habitats around my planting zone and didn't find a single live scallop, save for a couple natural 2 year olds. My dreams of having some uncaged growth and condition data failed! There wasn't even evidence of major predation, because I didn't even find empty or crushed shells. They were just all gone! A couple things are likely - either burial or transport - see Powers and Peterson's 2000 manuscript on scallop movement. Both are equally possible scenarios, as these sites in Shinnecock Bay were relatively shallow (~1m deep) and we had quite a crazy winter in terms of storms. Its just a shame. The only positive here is that at least my marker buoys were still firmly anchored at the sites! In fact, this picture is about the most exciting thing from the Shinnecock dives: (thats right, its my pink lemonade by the throttle while the boat is tied to the dock. Nice, right?)
I was hoping Sag Harbor would be slightly better. I mean, this was a deeper site, so things had to work out, right? Actually, I originally expected there to be scallops at Shinnecock (typically low energy sites) and not in Sag Harbor (strong tidal currents). In Sag Harbor, the scallops already drifted slightly down current from the planting area the date of planting, and despite the scallops looking good at the bottom, I figured strong currents and potential predation
would essentially eliminate them. Luckily, there was scallops to be found in Sag Harbor, although in much reduced densities. So, not enough scallops to monitor with enough replication to have confidence in the results, but at least all of the 7500 scallops here were not lost. What was lost, you ask? The Codium! It was all gone! My Codium planting area in Sag Harbor was completely devoid of Codium! So despite the semi-success of overwintering some of the scallops in Sag Harbor, my experiment here still failed! Awesome! I guess there's always NEXT year, I just don't know how my committee feels about that! I guess this season, I will just have to run juvenile growth experiments again, as soon as I get the juveniles.
At least I saw some cool stuff at Sag Harbor: Spider crab crawling out from a cinder block. Red beard sponge in eelgrass.
Surviving bay scallop, cryptically hidden on the bottom, save for its blue eyes! Juvenile lady crab.
Thayer, GW, & Stuart, HH (1974). The bay scallop makes its bed of seagrass Marine Fisheries Review, 36, 27-30
Powers, SP, & Peterson, CH (2000). Conditional density dependence: The flow trigger to expression of density-dependent emigration in bay scallops Limnology and Oceanography, 45, 727-732
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
Saw this video at the Benthic Ecology Meetings in Wilmington NC, it talks about benthic invertebrates to the tune of "Whatever you like" (whatever that is)... It was made by Jeremy Long of San Diego State University.
Also, check out my recent manuscript. 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
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!
Eelgrass is an important habitat for multiple marine species, including the bay scallop
Scallop on Artificial Eelgrass
This tethered juvenile bay scallop attached itself to my artificial eelgrass...
The decline of eelgrass meadows
Eelgrass, Zostera marina, is a flowering, marine vascular plant that remains submerged all the time. This is quite a feat for vascular flowering plants, and only a few dozen species world wide are capable of growing completely submerged in a marine environment. Eelgrass creates and extremely important habitat, its upright structures and complex root system create a 3-D living space for many different types of animals. It is (or was) the dominant habitat forming SAV (submerged aquatic vegetation) throughout much of the coastal waters in the northeastern United States. Unfortunately, for various reasons, eelgrass meadows have seen drastic declines, and in many locations eelgrass only exists in a mosaic of small patches. This is extremely bad news as many of the important, and formerly important, commercial and recreational fisheries of the northeast US are dependent on Zostera at some part of their life cycle as a nursery and foraging ground. Some of the species are finfish like tautog, bluefish, fluke, winter flounder, porgies, while others are shellfish such as blue mussels, hard clams, oysters, bay scallops, and blue crabs. Many of the aforementioned species support or once supported vibrant fisheries. Many of those fisheries have collapsed, also for various reasons. However, is it possible there is a link between the crash of the fisheries, the decline of Zostera and the failure for recovery on both ends?
Eelgrass, Zostera marina, a temperate seagrass species, providing a vital habitat for numerous marine species
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Scallops in eelgrass
Some adult bay scallops we planted in eelgrass for a free release survival experiment we conducted
If you live in coastal zones, urge your local and state representatives to push for environmental issues that you are concerned about. Ask for more stringent rules regarding the destruction of existing eelgrass. Encourage restoration programs to be set-up. Call your state and national representatives and ask them what they are doing to protect our precious resources. Practice safer boating and know the undersea terrain - i.e., don't drive your boat in very shallow water. Avoid clamming in eelgrass meadows.