Recruitment, growth, mortality and orientation patterns of Balanus trigonus (Crustacea: Cirripedia) during succession on fouling plates

Abstract

Succession studies on artificial substrates in the Bay of Santa Marta, Colombian Caribbean showed Balanus trigonus (Darwin) as one of the more prominent members of the fouling community. This fact prompted the interest for a closer examination of its biology. Four aspects were touched upon: recruitment, growth and mortality rates, and orientation with respect to the horizon line. Two hypotheses were tested. First, that orientation of individuals was random within the orientation range observed during succession, and second, that there was no relationship between orientation and age of the individuals. Larvae settling was found to occur throughout the year but with a well delimited peak in the dry season (January to April). The availability of competent larvae is reflected in the abundance of the species during succession. Growth and mortality proceed rapidly. Maximal growth (6.2 mm average carino-rostral distance) is reached in 20 weeks after settlement. Mortality is substantial: 50% of recruits, on average, died after 3-4 weeks from settlement. Orientation at settlement was found to be not random: for instance, 64% of individuals orientated between 0°-60° from the horizon. With age the orientation patterns at settlement changed statistically. Biological and ecological implications of these findings are discussed and comparisons made with other studies. It is concluded that Balanus trigonus could act as a model species for latitudinal comparisons in view of its wide distribution, adaptability and sessile habit.