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...
Tuesday, October 14, 2008
Failure to launch, er, or settle, or recruit...
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.
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.