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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.

Silly spider crabs…

I have been doing some field work the past few weeks, one of the reasons for infrequent postings, so I apologize.  This week, I saw some cool things.  Well the things I saw were not so cool – they were spider crabs, and I see them ALL THE TIME.  (In fact, I’d be more surprised to not see any spider crabs.)  But it was what I saw the spider crabs DOING this week that was so cool.

While snorkling at a site in Heady Creek, Shinnecock Bay, NY, I came across this creepy (and dead) bluefish.  It was pretty big, and it was being picked at by a spider crab.  I know that spider crabs are typically considered scavengers, and this particular crab is no different. But its one thing to watch spider crabs picking on a dying whelk. Its something different, or rather, interesting to see them doing on this bluefish. Maybe its just funny, as I typically wish there were more large fish to consume all the spider crabs, as they eat bivalves, including my precious scallops.

And then I saw this amazing site – a spider crab, while clinging to one of my spat bags, was also clinging to a sea nettle, my assumption is to eat it. And after reading about ctenophores found in dogfish stomachs, and a recent article in Science about bearded gobies consuming jellies, it makes me think “Ecological dead-end my ass!” Well, lets not get too ahead of ourselves, but still interesting to see this today (and according to the Smithsonian Marine Station, spider crabs do eat jellies):

Plus they were just crawling all over things, including my recruitment tiles and into the eelgrass canopy (hey I thought only mud crabs did that)!

Spider crab crawling up eelgrass

Spider Crab on my recruitment tile

These little guys do some pretty interesting things.  From typically scavenging, consuming vegetation, carrion and detritus, to possibly actively hunting – including on shellfish and probably jellies, maybe we need to reconsider the role of spider crabs in our coastal ecosystems. Maybe…

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