Predators and the Distribution and Abundance of Blennies on Offshore Petroleum Platforms

Abstract

Predation may be important in structuring fish assemblages but studies of the intensity of predation on marine fish assemblages are uncommon. Predator avoidance behavior was used to identify the predators of an assemblage of blennies found on offshore petroleum platforms in the northern Gulf of Mexico. The distribution of predators was then compared with the distribution of 3 species of blennies to see if predation intensity was related to the vertical zonation of blennies. Predator approaches and blenniid activity were compared in low and high surface current events. Results did not support a hypothesis of predation controlling the distribution and abundance of blennies. Also, predators were less abundant and blennies increased their activity when a surface current was present. 'Enemy free space' created by surface currents may help explain why predation is not important in structuring these blenniid assemblages.

Interspecific dominance does not exclude sub-dominant blennies from offshore petroleum platforms

“…Only male P. marmoreus hold territories and defend barnacle cavities; however, both sexes of H. invemar defend cavities and hold territories (Rauch 1996). The abundance and distribution of these blennies is consistent from platform to platform (Rauch 2003) and predation does not produce the observed patterns of zonation (Rauch 2004). Herein I evaluate the importance of interspecific competition in governing the zonal distribution of H. invemar and P. marmoreus on offshore petroleum platforms.…”

“…Blennies in this soft-bottom habitat are incapable of leaving a platform and most maintain territories around empty barnacle cavities, which provide a spawning site and a refuge from predation (Smith-Vaniz 1980;Gallaway and Lewbel 1982;Rauch 2004). H. invemar are found throughout the water column down to 15 m but the abundance of these fishes decreases with increasing depth (Rauch 2003).…”