PORTER, S.S.; ECKERT, G.; BYRON, C.; FISHER, J.; University of California, Berkeley; University of Alaska, Southeast; University of Wisconsin, Madison; Moss Landing Marine Laboratory: A comparison of light traps and plankton tows

We compared the efficiency of light-aggregation devices (light traps) and plankton tows for sampling crab larvae off the dock in Bartlett Cove, Glacier Bay National Park, Alaska. Three 10 hour light trap samples and three 5 minute plankton tows were compared each night of the study during three days in July and August of 2001 and July, August, and September 2002. Both methods captured both early and late stage larvae for all five major crab taxa present in the cove. However, light traps collected brachyuran megalopae that were not collected by the plankton tows, which suggests that the megalopae may evade plankton nets. The light trap technique was faster to use in the field and its selective method of sampling made it easier to process samples in the lab. The major disadvantage of the light traps was that they did not yield a quantitative measure of abundance, because the volume of water they sample could not be determined. However, the light traps did yield a relative abundance, which could be compared over space and/or time. This evaluation of light traps, a relatively novel sampling device for temperate marine invertebrate larvae, compared to plankton tows, a standardized method of collection, may aid future attempts to characterize the temporal and spatial distributions of planktonic crab larvae in Glacier Bay.