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, September 28, 2010
The impacts of top predator declines...
(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
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.