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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.

It’s not the size of the boat (or barnacle), but it’s the motion in the ocean (literally)

A clump on barnacles on one of my cinder blocks in Shinnecock Bay, NY

If you ever needed to know one thing about barnacles, its that they have large penises.  Sure, you might be thinking barnacles are so small.  But relative to total body size, they have the largest penises.  It is a result of living a sessile life, remaining attached to the spot which they settled as larvae.  Since they are unable to move to mate, they had to develop a different strategy. Hence, the large penises.

Former Stony Brook University Department of Ecology and Evolution student J. Matthew Hoch (now at the Southeast Environmental Research Center at Florida International University) spent his time here researching barnacle penis morphology.  Some of his findings were published in the most recent issue of Marine Biology.

Some of his interesting findings were that both wave action (yes! the motion in the ocean… this makes SO much more sense to me now) and population density can have significant impacts on penis morphology.  His study organism, the Atlantic acorn barnacle, Semibalanus balanoides, is known to have a penis with a exoskeleton with “accordion-like folds” that allows it to stretch to many times its relaxed length in order to find a mate.  This is useful due to their sessile lifestyle, and makes copulation with their neighbors much easier.

What Hoch found was that population density has an impact on overall penis length.  Barnacles which were sparsely populated had more of the folds in the penis, indicative of having a greater fully stretched length.  This is presumably an adaptation to low population densities, allowing for the chance of successful mating. Those barnacles in crowded conditions had fewer folds, indicating that they are likely to have less ability to stretch (and also less need to do so).

And now the motion in the ocean part.  Barnacles on wave exposed shores grow larger and their penises grow thicker/wider.  They aren’t necessarily longer than those that live in protected sites, nor do they have more folds allowing them to stretch greater distances.  They just have thicker penises.  This is likely a result of the water action.  These barnacles have to have thicker penises for more support, making them less likely to break in the wave action and more likely to produce successful mating attempts.

All in all, it was an interesting read, seeing how barnacles adapt reproductive mechanisms to their surroundings.  In case you want to learn more about this research, Dr. Hoch did a write up last year fr the Deep Sea News site, and his work has also been highlighted on the NewScientist.
J. Matthew Hoch (2010). Effects of crowding and wave exposure on penis morphology of the acorn barnacle, Semibalanus balanoides Marine Biology, 157, 2783-2789 : 10.1007/s00227-010-1536-z

8 comments to It’s not the size of the boat (or barnacle), but it’s the motion in the ocean (literally)

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