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The Decline of Seagrass Meadows

Zostera! 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?

Bay Scallop on Eelgrass

Argopecten on Zostera! Bay Scallops, Argopecten irradians , have developed a very close relationship with eelgrass, Zostera marina. As larvae, they are passively transported, and tend to settle in eelgrass meadows when the current is dampened by the 3D structure of the seagrass. This same 3D structure provides post-set juvenile scallops a spatial refuge from predation. Even as larger juveniles and adults, scallops are capable of, and have been shown to, actively select eelgrass habitats.

Other species also use eelgrass

grass shrimp A number of other species utilize eelgrass as a habitat. Included are grass shrimp, like the Palaemonetes pugio, other decapods such as blue crabs, bivalves such as hard clams, gastropods (snails), and numerous fish species, including winter flounder, tautog and cod.

To start things off

Well, I realize that I started this blog and never put any updates into it… Oops… It has been a busy summer filled with long days on and in the water, but with some excitement as well… I finally put my artificial seagrass mats out in the field in July, which was a very exciting day… The idea behind the artificial mats is that the local estuarine habitats are changing from once dense meadows of eelgrass to small isolated patches… Nobody is really sure the impacts of this changing habitat, and rather than disturb the already stressed existing eelgrass, we chose to make our own artificial mats… This also allows us to make them all the same, in terms of number of shoots, blades, etc :

Once they were in the water, they looked great… The ribbons stood upright… They were quickly colonized by small fish like silversides and killifish… Soon the mats were colonized by other fish, like pipefifh, tautogs, cunner, and even some small flounder and sea bass, and many invertebrates, including grass shrimp, mud crabs, spider crabs, blue crabs and whelks… The mats also experienced epiphytic algal and bacterial growth and also received a fair amount of drift algae… All in all, it was very impressive and far exceeding my expectations:

I placed scallops out in these mats, 10 to a bag, to prevent predation, in order to measure scallop growth… They have been growing well, around 25 millimeters (around one inch) in 8 weeks time… These are about triple the size of when I put them in (averaging around 11-12 mm, and now between 35-40mm)… These are very exciting results, although I don’t have pictures right now to show… I attempted a predation experiment with tethers, however, this wasn’t very successful, as I had extremely high mortality that I could not attribute to predation…

I have also worked on spat collectors located in various locations throughout the Peconic Estuary, with some fairly exciting results… This is part of a large bay scallop restoration effort undertaken by Suffolk County and the Cornell Cooperative Extension of Suffolk County… This effort includes researches from various parts of Long Island, as well as dozens of local volunteers, to spawn scallops in captivity, grow them out in field settings and hang millions of them in lantern nets in close proximity in the hopes that having that many close together will enable them to spawn in the wild and allow larvae to recruit throughout the bays… This is the first full year with the high density of scallops in these lantern nets, although various other spawner sanctuaries have been set up for the past few years… All the data is still coming in, so nothing concrete yet, but there are some real positive signs that this type of method might be working…

Finally, I am also investigating the effectiveness of alternative habitats… I have looked at free planted and tethered scallops in alternative habitats for the past 2 summer seasons… Stay tuned for the results…

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