Equilibrial blenniid assemblages on offshore petroleum platforms

Abstract

Ecological assemblages may be viewed as lying along a continuum between equilibrium and non-equilibrium. I investigated the position on this continuum of an assemblage of blennies found on offshore petroleum platforms in the northern Gulf of Mexico. I conducted visual censuses of four species of blennies on 13 different platforms. Several species displayed a distinct vertical zonation with Scartella cristata  confined to the upper 5m and Parablennius marmoreus  limited to 10–15 m depths. I used Morisita’s index (I_M) to assess blenniid assemblage similarity andcompared values to a null model of randomly generated data. Comparisons indicated that platforms were similar in blenniid assemblage structure. Tropical Storm Danny passed over my study site after data collection had begun in 1997. Pre- and post-storm I_M’s indicated that this disturbance did not affect these blenniid assemblages.