Size-specific life history pattern of a shallow-water gorgonian

Abstract

Size, rather than age, may be a more reliable indicator of survivorship and growth in colonial coral reef organisms. This study examined the size-specific demography of the shallow-water gorgonians Pseudopterogorgia spp. from 1984 to 1992 in Puerto Rico. Size-specific survivorship patterns were well-defined. Average (median) survivorship for large colonies (>10 cm tall) was relatively high (96.5%·yr −1) and constant (range: 91.8–100%-yr −1) while survivorship for small colonies (<6 cm tall) was low (62.0%·yr −1) and variable (range: 53.1–85.4% ·yr −1). Growth rates were largely unrelated to colony size; about 47% of colonies of all sizes grew into larger size classes per year. However, a significant positive relationship between survivorship and growth of small, but not large, colonies suggests an indirect size-specific growth effect. No strong age-specific effects were evident for colonies of equivalent sizes. Size-based population matrix models indicated that the combination of (1) low and variable survivorships of small colonies, and (2) high and constant survivorships of large colonies, lead to episodic variations in Pseudopterogorgia populations. The size-specific demography of Pseudopterogorgia can be viewed as an analog to the “bet-hedging” interpretation of life history pattern.