LIMPETS: Long-term Monitoring Program and Experiential Training for Students

Student Scientists on our Sanctuary Shores

Species

measurements being taken of sea life
“Despite the high prevalence of exposed sandy beaches along the coast of California, macrofauna communities of beaches have received little attention from marine ecologists!”

– Dr. Jenifer Dugan, Research Biologist, University of California, Santa Barbara

Why monitor mole crabs? In short, Pacific mole crabs are one of the most important herbivores on the beach, and they are a vital link in the sandy beach food web. They are prey for birds, mammals, and fishes, including endangered species such as the western snowy plover.

Mole crabs are hosts to a parasitic worm in the Phylum Acanthocephala. When birds and sea otters eat infected crabs, they too can become infected. We monitor these worms to learn more about the life cycle, seasonal cycles, and prevalence of the parasites in the populations of mole crabs along our coast. Learn more about these species below.

Pacific Mole Crab(Emerita analoga)
Pacific Mole Crab
Description:
Egg-shaped and small in size; carapace of females grows up to 35 mm, males up to 22 mm; gray or sand colored. Unlike many other crabs, mole crabs do not have claws or spines; have two pairs of antennae to gather food and oxygen
Distribution:
Along the Pacific Coast from Alaska to Baja California in the northern hemisphere and from Ecuador to Argentina in the southern hemisphere.
Habitat:
Live on exposed sandy beaches; spend most of their time buried in the shifting sand of the swash zone. The swash zone is the area between the highest and lowest reach of the waves.
Diet:
Suspension feeder; uses large, feathery secondary antennae to sieve food from the water; feeds primarily on small, drifting plant plankton (phytoplankton).
Fun Fact:
These are fast moving, rapidly burrowing crabs with excellent orientation and swimming abilities. They dig into the sand backwards and can bury themselves completely in less than 1.5 seconds.
Reason for Monitoring:
One of the most important herbivores on the beach, and a vital link in the sandy beach food web. Prey for birds, mammals, and fishes. Humans collect mole crabs for bait in recreational fishing. In southern California, approximately 2 million crabs were taken for bait in one year. Significant changes in mole crab populations can be an indicator of a larger problem in the ecosystem. Has shown potential as an indicator species for monitoring levels of contaminants and domoic acid in the waters off of California. Domoic acid is a neurotoxin produced by diatoms, a type of plankton. When mole crabs eat toxic plankton or contaminants, they become toxic to the birds, otters, and fish that eat them.
References:
Dugan, JE et al. 2005. Final Report for the Central Coast Regional Water Quality Control Board: Monitoring of Coastal Contaminants Using Sand Crabs (pdf).
Encyclopedia of the Sanctuary
Farallones Marine Sanctuary Association Fact Sheet: Pacific Mole Crab
Ferdin, ME et al. 2002. Emerita analoga (Stimpson) possible new indicator species for the phycotoxin domoic acid in California coastal waters. Toxicon 40(9):1259-65.