Martin Posey lifts a hunk of rock 

 collected by the submersible' s robotic 

 arm. 



morphology, and all of a sudden it 

 goes bananas; the algae become very 

 abundant." 



Set in motion by coastal storms 

 such as northeasters, sediments in the 

 extensive sand flats provide too harsh 

 an environment for attached animals. 

 Moving grains of sediment are as 

 big as bowling balls to microscopic 

 larvae trying to attach to a flat 

 hardbottom, says Riggs. 



On land, plants grow in soil and 

 gather nutrients from the ground. In 

 the ocean, the rock provides the 

 stable medium on which attached 

 plants flourish, and the nutrients are 

 absorbed from the surrounding 

 waters. 



"One of the things we're trying to 

 get a handle on is how much sand is 

 out there, how it's moving and how 

 mobile it is. We don't know whether 

 it moves in decades or moves with 

 each storm," Riggs says. "There are 

 many places where the scarps are 

 totally buried." 



One way to increase biomass — 

 the amount of living matter — is to 

 remove the sand, re-expose the rock 

 and use the sediment as a source of 

 beach renourishment, he says. 



"Now the worm people squirm 

 like crazy when I say that," says 

 Riggs, adding that the sand substrate 

 is important for worms and micro- 

 algae. 



"There've been a few biologists 

 and geologists poking around on 



hardbottoms for a long time, but they 

 didn't talk together," says Riggs. 

 "Now when we go down and look at 

 this stuff, we argue like crazy, and 

 the biologists say, 'Wow, maybe 

 there's something to the substrate 

 control.' And the geologists say, 

 'Wow, look at the role the animals 

 are playing in the bioerosion.' It turns 

 out the animals are very important, 

 just chewing the hell out of these 

 rocks. ... If I had to guess right now, I 

 would say that some of those rock 

 scarps out there are receding at the 

 rate of a foot per decade. For a hard 

 rock, that's pretty fast." 



"There are a lot of fish that use 

 the hardbottom areas to feed or as a 

 refuge from bigger fish — a place to 

 hang out — and they leave these 

 areas at night to feed in the surround- 

 ing sand," says Ambrose. "So what 

 we expect to see ... is sort of a halo of 

 low food abundance around these 

 hardbottoms. 



"In other words, the fish don't go 

 out forever because the farther they 

 go out, the more likely they're going 

 to become somebody's dinner," he 

 says. "If the further we get away 

 from these hardbottoms, the more 

 food we find, then we know that 



The existence of hardbottoms has been no secret. 

 For decades fishermen have pursued the irregular topography with 

 depth-finders, then anchored above these fertile fishing holes, hauling 

 in grouper as long as their arms span. 

 But as pressure has increased on these bountiful bottomlands, 

 the catch has shrunk in size and quantity. 



Another significant area of 

 biological study is the benthic — or 

 ocean bottom — sand community in 

 the periphery of hardbottoms. Hard- 

 bottom reefs were once thought of as 

 islands that sustained themselves, but 

 it turns out that 

 the surrounding 

 sand flats or 

 "softbottom" 

 areas may be 

 critical in 

 sustaining the 

 system's 

 foraging fauna. 

 Maybe these 

 worms and 

 microorgan- 

 isms are 

 significant to 

 the food chain 

 of reef species, 

 says Ambrose. 



they're foraging a lot nearby and not 

 so much far away." 



Designating reef reserve areas may 

 become necessary to allow long-lived 

 and older reproductive-age fish of 



Continued 



(Left to right) Will Ambrose, Paul Renaud and Martin Posey 

 in the lab. 



COASTWATCH 5 



