SETTLEMENT AND RECRUITMENT OF THE FIDDLER-CRABS UCA-PUGNAX AND U-PUGILATOR IN A NORTH-CAROLINA, USA, SALT-MARSH

Where larvae settle often is critical for determining the distribution and abundance patterns of later stages of sessile and sedentary marine invertebrates. However, selection of adult habitat by larvae at settlement might be less crucial for invertebrates that have motile benthic stages and have the option of further habitat selection after settlement. If movement after settlement is important in determining spatial patterns of later stages of motile invertebrates, then the distribution and abundance patterns of settling larvae will differ from those of older conspecifics. I tested this hypothesis by documenting the distribution and abundance patterns of settling larvae, juveniles, and adults of the fiddler crabs Uca pugilator and U. pugnax along an intertidal gradient in a North Carolina, USA, salt marsh. Benthic distribution and abundance patterns of conspecific settlers (megalopae and newly-metamorphosed crabs), juveniles, and adult crabs were very similar, but the 2 species generally were spatially separated in the marsh even at the earliest life stage. U. pugilator occupied the edge of the marsh next to a tidal creek, whereas U. pugnax was most abundant at higher marsh elevations. Because larvae settled in areas with older conspecifics, and the distribution and abundance patterns established at settlement were maintained throughout benthic life, post-settlement movement along a vertical gradient is not important in establishing where adults of these motile benthic species live.