Emergence on the continental shelf: Differences among species and between microhabitats

Abstract

Emergence, the phenomenon in which a normally benthic individual leaves the seabed, enters the water column, and then returns to the seabed, is widespread among taxa and among environments and can be important to such issues as benthopelagic coupling and benthic-community organization. Emergence is far from completely understood, particularly in shelf environments. We studied a sandy site on the north Florida shelf (30°22.65'N, 86°38.69'W, 20 m depth) and focused on harpacticoid copepods, known to be important emergers. To test for differences among shelf species in the proportion of the population that emerged daily, we used an approach that allowed us to perceive proportions as small as ∼1 % and found that species ranged from ∼1 to ∼80% in percentage emergence. Of 3 adaptations proposed in the literature to explain differences among species in emergence, we found that one, the average area of the cephalosome in dorsal view (a correlate of swimming ability), explained a significant and nontrivial amount of the variability. In addition, microhabitats (sediment ripple crests and troughs) significantly affected emergence in 3 species. Within microhabitats, emergence behavior did not appear to be a response to intraspecific crowding. Our results suggest that the number of harpacticoids that emerge from a locality can be quite variable and depends on both the type of microhabitat and the identities of the species present. © Inter-Research 2006.