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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.

Hurricanes triggering Earthquakes?

All the dead birds and fish and things distracted me from an interesting article I read on Wired Science the other day about the potential for hurricanes to trigger earthquakes.  It is a pretty good read so you should definitely go check it out.  But I just wanted to talk about it a bit here.  Now, keep in mind I am neither a climatologist or a geologist, so I won’t have as much scientific input on this matter, so anything I am saying here is based on my limited understanding of the material (in case you couldn’t tell you can read my other earthquake post or my hurricane posts here).  Either way, I wanted to share it with you, but again, I encourage you to go read the original piece.

The author, Brian Romans, aka Classic Detritus, introduces a topic put forth by researchers from the University of Miami (led by Shimon Wdowinski) – the idea is that a series of powerful tropical storms in Haiti in 2008 eroded and shifted enough sediment on a deforested landscape that it may have stressed the fault line and triggered the massively devastating 2010 earthquake.  When sediment is eroded, it needs to be deposited somewhere, and the researchers use models to show where the sediment was deposited and what kinds of stress impacts those shifting sediments were having on the fault.  The researchers concluded that this mass of shifting sediment acted as a trigger for the earthquake.  Romans, in the article, makes clear that the TRIGGER is not the same thing as the CAUSE.  Earthquakes occur when boundaries build up stress, and then that stress is released along a fault.  The researchers at UofM aren’t saying that hurricanes caused the earthquake, rather, that the shifting mass of sediment over an already stressed fault line due to excessive rainfall from tropical storms may have triggered the earthquake.

According the Romans, this isn’t even an entirely novel concept, as it has been proposed in peer-reviewed literature before.  But Romans does caution about causation.  In many fields of science, causation is often difficult to discern.  Just because events or data are related doesn’t mean one causes the other.  In fact, a common mantra is that correlation does not equal causation.  For example, take the Church of the Flying Spaghetti Monster’s stance on global warming.  Their argument is that as pirates (I think the more romantic version of swashbucklers, not the current AK47 wielding speed boat Indian Ocean pirates of modern times) have declined in numbers, average global temperature has increased.  (Wow, is this my first ever Chronicles mention of the Flying Spaghetti Monster?)

Anyway, I digressed slightly.  It is an interesting concept, and one that I had not even given a thought to before.  Is it possible that system processes on the Earth’s surface can affect things that go on within the Earth’s crust? Interesting questions.

1 comment to Hurricanes triggering Earthquakes?

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