ABOVE; A female crab sporting the "sponge" that consists of 

 about one million eggs. 



A female that survives to be a sponge 

 crab could end up in Harcke's lab where, 

 Harcke hopes, the chances of survival for 

 released eggs will be much improved. 



At the Crab Lab 



At the aquarium on Roanoke Island, 

 visitors mill about like ocean currents, peeking 

 at alligators, gazing at ocean life, having close 

 encounters with sea creatures at the "touch 

 tank" and, via closed-circuit TV, spying on the 

 osprey tending its raggedy nest outside. 



Away from all the activity is a utilitarian 

 little room aquarium-goers won't see. Along 

 one wall, a row of recycled bottles gurgles 

 with green and brown stuff, backlit by 

 fluorescent bulbs. 



In an aquarium sized for a kid's room or 

 a high school science lab, Number One squats, 

 wary, behind grass made of green curling 

 ribbon. 



Number One is a one-of-a-kind for the 

 aquarium — the first from the batch of blue 

 crabs raised last year. 



In a larger aquarium, two full-grown 

 females face each other. Last year, they 

 provided eggs for the project. 



Female crabs that have mated can retain 

 some sperm for a second batch of eggs, 

 Harcke says. She hopes these two may 

 develop eggs again this year. 



Scientists believe only about one of each 

 million or so crab larvae will grow to 

 adulthood in the wild. One has to wonder at 



the biological inefficiency 

 of such a system. But 

 Harcke explains the role of 

 these crab larvae, called 

 zoea, in the ecosystem. 



"Everything has a 

 niche," Harcke says. 

 Unable to swim, zoea float 

 passively with ocean 

 currents to areas of higher 

 salinity. Drawn toward 

 sunlight, they become 

 plankton — sacrificial 

 pawns in a game of 

 survival, providing food 

 for fishes and other sea 

 animals. 



Then a dramatic 

 change occurs. When zoea molt into 

 megalopae, they can swim — though not yet 

 beautifully — and propel themselves away 

 from the light to which they were at first 

 drawn. They also move toward areas of lesser 

 salinity, traveling back to the estuaries. 



Harcke explains that the endurance of 

 the megalopae is heightened by osmoregula- 

 tion, which allows them to tolerate higher 

 degrees of salinity until they get into more 

 favorable conditions in the estuaries, where 

 they will at last become something that looks 

 like minute, pinhead-size crabs. 



Each dramatic metamorphosis brings 

 new needs and food preferences. It's a 

 challenge for the scientist attempting to 

 provide sustenance for the blue crab from 

 larvae to adulthood. 



Working on the Food Chain 



Here's food for thought for anyone, say, 

 eating crab cakes in a seafood restaurant 

 while staring out at a sound like the Roanoke: 

 We know how we like to eat crabs — in 

 creamy bisques, as dips, as stuffing for 

 mushrooms or flounder. Some of us like them 

 whole, right after they shed, as soft-shell 

 crabs. And then there are crab cakes. 



But what do we know about what they 

 prefer to eat? Crabbers know how to bait a 

 crab pot, but what about how to feed crabs 

 that are newly hatched, planktonic members 

 of the food chain themselves? 



Harcke has learned a few things about 



the subject, and it wasn't easy. 



"I'm doing more work raising food than 

 growing crabs," Harcke jokes. 



Her goal is to increase the eggs' one-in- 

 a-million odds for survival. Keeping the zoea 

 out of predators' reach is the first step, but 

 they also have to be fed. Figuring out what 

 they eat in the wild was educated guesswork. 



The feeding experiments were meticu- 

 lous — 250 zoea were individually lifted by 

 pipette to one-liter beakers of artificial 

 seawater, where they were given a variety of 

 foods. At the end of five days, they were 

 gently sieved out, examined under a 

 microscope, counted, and determined to be 

 dead or alive. 



Harcke started with food that was easier 

 to come by. In beaker after beaker, zoea were 

 fed commercially available algae paste in 

 various forms. They responded with what 

 might be articulated as "give me something 

 else or give me death." 



Survival was zero until live algae were 

 introduced. They are the bottles of green 

 Tetrasehnas sp., and brown Chaetocerous sp. 

 and Isochrysis sp. bubbling away in the lab. 

 constantly aerated and grown using estab- 

 lished culture techniques. 



Combinations of live feed and algae 

 paste were compared so that feeding 

 procedures could be established. "It's like 

 setting up a buffet," Harcke says. 



Just as humans need a variety of foods 

 for balanced nutrition, so do blue crab larvae. 



In addition to the algae buffet, Harcke is 

 growing zooplankton called rotifers. To the 

 naked eye, they look like tiny dots. In a small 

 container of seawater, they look like 

 carbonation bubbles — except that the 

 rotifers are very small and don't zip straight 

 up. Under a microscope, they are round and 

 randomly mobile. 



So far, survival from the best buffet 

 combination was greater than 20 percent. 

 Less than impressed? Think of the one-in-a- 

 million odds the newly hatched crab larvae 

 get in nature. 



This coming year, Harcke will add 

 copepods — tiny crustaceans to make food 

 for other crustaceans — in hopes of boosting 

 survival even more for the lab crabs and, 

 possibly, for those in the wild. □ 



COASTWATCH 15 



