by Liz Leavens
Published Summer 2007

• Dungeness zoea
• Dungeness megalopa
• One year old Dungeness
• Adult Dungeness, 6 inches

True crabs, such as Dungeness crabs, go through an intricate life cycle. They molt, or shed their skin many times as planktonic larvae floating in the water column and undergo a metamorphic molt to what is called the megalopae stage. To learn more about this, one needs only to sit down with the recipient of a Padilla Bay NERR Graduate Research Fellowship award, Elizabeth Harvey.

With her Bachelor's in Marine Science from the University of Maine under her belt, Liz is pursuing a Master's degree in Environmental Science from the Huxley College of the Environment at Western Washington University in Bellingham. With guidance from her graduate advisor, Director of Shannon Point Marine Center, Dr. Stephen Sulkin, Ms. Harvey has developed a research project addressing the effects that large algae or "macroalgae" in high densities may have on true crabs.

During the megalopae stage in their life cycle, true crabs settle from the water into a habitat suitable for juvenile existence. Previous research has shown that megalopae prefer settlement in complex habitats such as eelgrass, oyster beds, and high-density macroalgae. Yet, certain chemicals, such as dopamine, associated with the decaying of some macroalgal species are toxic to invertebrates. Along with this, macroalgae often creates low-oxygen conditions harmful to the aquatic community, including juvenile crabs. So, researchers question why megalopae settle in a habitat that is potentially detrimental to their survival.

Liz conducted her research in both the laboratory and the field. Megalopae were collected from Padilla Bay and the surrounding area and brought back to the lab to observe settling behavior (macroalgae versus sediment) and dopamine effects. Field studies took place within the Padilla Bay Reserve. Crabs were collected from high-density macroalgae and the sediment underneath for comparison. Quantity and size variation of the crabs was recorded.

Preliminary research from the summer of 2006 showed there were more crabs in the macroalgae than in the sediment beneath. This trend held true for two of the collection days when the macroalgae was in full bloom. Twelve days later on the third sampling date, there were very few crabs in either the decaying macroalgae or the sediment. Lab results also show that dopamine had an adverse effect on the crabs used in the study.

This research indicates that the environment under macroalgae is not suitable for juvenile crabs. So why do they settle there? We're still wondering.