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, August 24, 2010
What would a Zostera blog be without a Zostera entry?
In the most recent issue of Marine Biology, there is a manuscript addressing the issue of 2 introduced species and their interactions with one another. Its an interesting read - one of the species is a commercially important bivalve, the Manila clam, which was introduced in the early 20th century and is now one of the most commercially harvested clams on the west coast of the US. The second is Zostera japonica, dwarf eelgrass, an introduced seagrass species which can establish itself on tidal flats. The idea is that this new seagrass species may be of detriment to the now commercially important manila clam. While there is certainly literature which suggests that seagrasses might enhance bivalve growth - see works involving hard clams and eelgrass by Elizabeth Irlandi and Mike Judge - it certainly stands to reason that eelgrass dampens water currents, and likely decreases the amount of food available to suspension feeders, particularly those distant from the edge of the seagrass (where the food availability might be enhanced). And so the team led by Chaochung Tsai aimed to investigate the impacts the invasive eelgrass had on the clams, and whether the clams might enhance the introduced grass. They chose 3 habitats - seagrass present, seagrass removed, and harrowed habitats. The presence of seagrass, while not necessarily impacting shell extension of the infaunal manila clam, did significantly negatively influence clam condition (tissue weight to shell volume ratio). On the flip side of the coin, while bivalves have been shown to influence eelgrass growth through nutrient additions - see the Peterson Lab publications - this apparently is not the case for the manila clams and dwarf eelgrass. In this experiment, clams did not enhance growth nor impact sediment porewater nutrients. In fact, the only positive effect of the introduced seagrass was on itself. Pretty interesting (and before I read it, unexpected) results.
Tsai, C., Yang, S., Trimble, A., & Ruesink, J. (2010). Interactions between two introduced species: Zostera japonica (dwarf eelgrass) facilitates itself and reduces condition of Ruditapes philippinarum (Manila clam) on intertidal flats Marine Biology, 157 (9), 1929-1936 DOI: 10.1007/s00227-010-1462-0
Irlandi, E., & Peterson, C. (1991). Modification of animal habitat by large plants: mechanisms by which seagrasses influence clam growth Oecologia, 87 (3), 307-318 DOI: 10.1007/BF00634584 Judge M, Coen L, Heck KL (1993). Does Mercenaria mercenaria encounter elevated food levels in seagrass beds? Results from a novel technique to collect suspended food resources Marine Ecology Progress Series, 92, 141-150
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
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.