Life-history trade-offs among four sympatric seabreams

Abstract

Fish life history is shaped by environmental and ecological circumstances but constrained by phylogeny. Life-history trade-offs can be exposed in a comparison of closely related species with similar niches. We compare the life histories of four closely related and similar-sized, sympatric, omnivorous seabreams (Sparidae) that share the same physical habitat, namely the steentjie Spondyliosoma emarginatum, hottentot Pachymetopon blochii, white stumpnose Rhabdosargus globiceps and Fransmadam Boopsoidea inornata. Samples of each species were obtained in every season from the southwestern Cape, South Africa, to obtain measures of length, mass, gonadosomatic index (GSI) and condition. Large variations in sex ratio, GSI, and spawning season length (SSL) among species are described. Differences in patterns of sex-specific GSI and condition point to different mating systems. Spondyliosoma emarginatum is a nest-guarding, short-lived, protogynous hermaphrodite. Pachymetopon blochii is a resident group-spawner. Rhabdosargus globiceps is a moderately long-lived migrant group-spawner, with a sex ratio closest to 1:1. Boopsoidea inornata is a polygamous, long-lived resident with low annual fecundity. Trade-offs are apparent between annual fecundity and longevity, parental care and male GSI, parental care and SSL, migration and SSL, hermaphroditism and migration, and hermaphroditism and bet-hedging. The cost of sequential hermaphroditism in marine fish is considered in terms of reproductive success in highly variable environments.

Keywords: Boopsoidea inornata, fecundity, longevity, mating system, Pachymetopon blochii, Rhabdosargus globiceps, sequential hermaphroditism, Spondyliosoma emarginatum