Interspecific dominance does not exclude sub-dominant blennies from offshore petroleum platforms
Interspecific interactions can determine the abundance and distributions of animals. Seaweed blennies, Parablennius marmoreus, and tesselated blennies, Hypsoblennius invemar, are found in barnacle cavities on offshore petroleum platforms in the northern Gulf of Mexico. I measured the interspecific resource defense interactions between these fishes in aquaria. Seaweed blennies were dominant over tesselated blennies when equal-sized fishes were tested. No difference in dominance was found when tesselated blennies had a 10% advantage in size. However, tesselated blennies were able to successfully defend cavities against equal-sized competitors when given the advantage of prior residence. This prior residence advantage persisted despite seaweed blennies having the advantage of past experience. Seaweed blennies attain a larger size on petroleum platforms, but empty barnacle cavities are common in this environment. Tesselated blennies are able to colonize and successfully spawn because they can enter an empty barnacle cavity, gain the advantage of prior residence, and successfully defend this cavity.