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Dungeness larvae: key to better understanding of population?
By Jacq Zier
Special to the Sounder/Journal
Dungeness crab is one of the most important fisheries in the Salish Sea. In Washington State alone, the fishery has an annual average value of about $20 million. Unfortunately there’s a little more work to do to better understand crab reproduction so we can make sure the population thrives while we serve up this delicious crustacean for dinner.
Researchers from SeaDoc and the UC Davis Bodega Marine Laboratory in California are looking for local Dungeness crab larvae, called megalopae, to better understand population dynamics and crab fishery cycles. Ultimately this will help us understand what oceanographic conditions are good for crab catching as well.
The SeaDoc Society is looking for help from sharp-sighted beachgoers in finding Dungeness crab megalopae for this study. The tiny megalopae are 5-8 mm in length and look like a very small floating crab about the size of a pencil eraser. They might be spotted swarming near the surface of the water by people walking on beaches or docks.
The making of megalopae begins when a female Dungeness crab releases a pheromone before she molts. Dungeness crabs can mate nearly year round, but only while females are soft-shelled.
When a keen male picks up her scent, he lifts her up with his claws – carrying her around for hours sometimes – to make sure he is there the instant she begins to molt. Once she has sloughed off her old shell, he deposits his sperm, which she stores until her 2.5 million eggs are fully developed and fertilized.
Afterwards, the male protects his mate from other suitors for several days by carrying her around with him. A female can store sperm for up to two years and may use sperm from one mating event for several batches of eggs.
In the following months, the eggs hatch and embark on a metamorphosis through different larval stages. They first resemble small, planktonic shrimp while in the zoea stages.
These larvae then undergo months of development in the ocean before they flock to sites close to the shore for a final larval stage known as the megalopae.
Megalopae resemble tiny crabs and eventually move to live on the sea floor. It will take three to four more years for these crabs to mature to a harvestable size.
A permit is required for megalopae collection, so please call the SeaDoc Society office (360-376-3910) to report megalopae sightings.
Jacq Zier, a 4th year student at Colgate University, is a 2011 graduate of Orcas Island High School. As a SeaDoc summer intern in 2013 she published an article on harbor seals in the Encyclopedia of Puget Sound and conducted research on threatened and endangered species in the Salish Sea. This summer she is writing a scientific monograph on harbor porpoise.