The consequences of seasonal reproductive strategies for the interpretation of settlement trials

Many temperate marine organisms, including the boreo‐arctic barnacle Semibalanus balanoides, have well‐delineated reproductive seasons. The aim of this study was to examine the consequences of small changes in deployment time of settlement experiments within such a settlement season upon long term demographic parameters. Repeat deployments of settlement tiles were made at 1‐week intervals for six weeks during the April 1996 S. balanoides settlement season in the Clyde Sea, UK. The colonies were harvested in November 1996 and density, mortality, fecundity, morphology, and dry weight of eggs, somatic tissue and shell determined. There were non‐linear relationships between density (D) and deployment time (W) (D = 1.11+1.38W‐0.24W ²), and between morphology (M) and deployment time (M = 21.2 + 0.54W‐0.13W ²). There were linear relationships between mortality (L) and deployment time (L = 61.49 ‐ 7.99 W), body weight (B) and deployment time (B = 0.0050 + 0.0012W), shell (S) dry weight and deployment time (S = 0.17 + 0.02W). Egg dry weight did not vary significantly with deployment time. This study demonstrates how small changes in deployment time of settlement can have substantial consequences on the long‐term demographic processes within single species populations. The relationships between deployment, density and other demographic parameters are discussed, as are strategies for dealing with the confounding effects of reproduction.