Planktonic ingress of fiddler crab megalopae to the Newport River Estuary, NC: evidence for semilunar periodicity in Uca pugnax and species-specific sampling bias by hog’s hair larval collectors

Abstract

We examined the planktonic ingress of fiddler crab megalopae into the Newport River Estuary, NC, using hog's hair collectors to determine whether there were differences in pat- terns of ingress among the 3 Uca species in this estuary. In 2 consecutive summers, we docu- mented peaks in settlement of fiddler crab megalopae onto passive larval collectors at the quarter moons (neap tides), corresponding with longer durations of flood tides during darkness. However, molecular identifications revealed that over 80% of the megalopae settling on collectors were U. pugnax, even though there are millions of U. pugilator on sandflats within 1 km of the collection site and U. minax are common in the estuary. Plankton net samples taken on the same nights as collector settlement confirmed that megalopae of all 3 Uca species are common in the plankton. The proportions of species in the plankton and settling on collectors were significantly different. These differences may reflect species-specific differences in thigmotactic behavior, or may indi- cate differences in times of transport within a tide, since collectors reflect settlement at the end of rising tide while plankton nets sample the abundance at the time of maximum flood tide current. Thus, hog's hair collectors may not be an unbiased sampling method for fiddler crab megalopae.