Temporal and spatial patterns of growth and survival of invertebrate and algal populations of a North Carolina continental shelf community

Abstract

This study was undertaken to document temporal and spatial population variability in a seaweed-dominated, continental shelf community off North Carolina. Perennial, foliose seaweeds, particularly the dominant species, exhibited large seasonal and year-to-year population variability, with peak abundance during periods of warm water temperatures and high percentage incident irradiance. Reduction of erect vegetative portions to resistant perennating structures by the dominant species during periods unfavourable for growth might explain their northerly extension into the seasonally stressed Carolina waters. Annual algal species rapidly grew and completed their life-cycle during the spring through early summer, presumably during periods favourable for growth (e.g. increasing irradiance and temperature, reduced turbulence). Further, these species exhibited dramatic year-to-year fluctuations in abundance. The resistant vegetative morphology of the crustose algae permitted year round survival at the study site, even in areas of high physical disturbance. Both seaweed and invertebrate species exhibited distinctive spatial distribution patterns which appear to be associated with seasonal variations in storm surge and strong currents. The results of this study suggest that the spatial, seasonal and year-to-year variations in abundance of organisms (particularly the algae) are, in part, a reflection of the fluctuating environmental conditions (e.g. annual temperature and light variations and seasonal storm surge) characteristic of this continental shelf community.