Are large colonies a "key factor" in the dynamics of gorgonian populations?

Abstract

Life cycle stages responsible for fluctuations in population sizes have often been described as fac­tors. In this study, a key factor approach was used to examine the dynamics of a shallow-water gorgonian popula­tion from 1983-1996 near La Parguera Gil the southwest coast of Puerto Rico. Gorgonian abundances increased from 8.1 to 99.6 colonies/m2 between 1983 to 1985 and gradually declined to 57.3 colonies/m2 in 1996. These variations in population size are largely attributable to recruitment, which increased from 2.1 to 44.9 colonies/m2 between 1983 to 1985, and declined thereafter. Survival. of recruit colonies which was generally higher after periods of high recruit­ment also played a contributing role in these population fluctuations. In contrast, survival of large colonies (2:10 cm in height) was essentially constant (about 94.1%/yr), and consequently had negligible effects on variations in abun­dances. These results demonstrate that large colonies are no! a key factor underlying fluctuations in gorgonian popu­lations. However, this assessment of large colonies differs if the results are examined in a different conceptual con­text. The combination of high and constant large colony survival, and variable reproductive success (recruitment and recruit survival) conforms to the interpretation of life history pattern. According to bet-hedging theory, large colonies are essential to the persistence of populations.