Protecting the 'Beautiful, Savory Swimmer'

Richard Forward's Blue Crab Research Crucial to Saving Habitats and to Setting Sustainable Catch Limits p.4

  Forward’s studies of postlarvae migrations, conducted with Tankersley and former doctoral student Jim Welch, have yielded similarly useful and illuminating information. “In many ways, this is where we’ve made the most progress, and where we really know something about crab behavior,” he says. “Through years of studies, we’ve figured out the behaviors and environmental cues involved in postlarvae migration, which is critical for predicting the best conditions for flood-tide transport into the estuaries.”

  Their research has revealed that megalopae sit on the bottom until they detect an increase in salinity that occurs as the flood tide, or rising tide, begins. Spurred by this stimulus, they jump off the bottom and move up into the water column, swimming with the current for as long as they sense water turbulence. When the tide ends and the water begins to calm, the megalopae move back to the bottom, conserving their energy rather than expending it unnecessarily by swimming against the outgoing ebb tide. The behavior occurs only at night, Forward says. Daylight appears to inhibit it.

   To determine approximately how many megalopae migrate into an estuary each night during summer and fall, Forward and doctoral student Matthew Ogburn submerge hog’s hair collectors— long tubes made of material resembling air vent filters—near Beaufort Inlet at the Duke Marine Lab. Each morning, they count the number of post larvae that have settled in the collectors overnight.

   “The collectors are like postlarval hotels,” Forward quips. “You see how many megalopae have settled there the previous night on their way to the nursery grounds.”

  Using this data, he has devised a graph in which the relative number of postlarvae that settle in collectors during one season is plotted against the commercial fisheries’ catch that takes place two years later. “It’s not a perfect relationship, but the graph does indicate that if you get good settlement, two years later you will have a large adult population,” he says.

   Innovative research like that—which both advances scientists’ basic understanding of crab ecology while having practical applications for fisheries management—is one reason why the easy-going Southern California native is widely respected by his peers.

  “Much of what we know today about how organisms in their early larval stages and some adult stages migrate through the estuaries and sounds is due to Dick’s research,” says frequent collaborator Luettich of UNC-CH’s Institute of Marine Sciences.

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