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...
Thursday, September 16, 2010
Fishes respond poorly to seagrass loss
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
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.