A multiple-choice feeding-preference experiment utilising seagrasses with a natural population of herbivorous fishes

Abstract

We examined fish food preferences among the 9 most frequent seagrass species from Kenyan lagoonal areas. We tested the hypothesis that grazing fish prefer 'pioneering' seagrass species rather than 'climax' species. The experiment was conducted in situ in the Watamu Marine National Park (Kenya), with a natural population of herbivorous fish. The only fish observed eating seagrass leaves was Calotomus carolinus (family Scaridae), the second most abundant fish of the family in the park. The 3 variables tested (biomass eaten, % of leaf eaten and leaf marks) revealed that there was a clear preference for 'pioneering', short-lived species such as Cymodocea rotundata and Syringodium isoetifolium over 'climax', long-lived species such as Enhalus acoroides and Thalassodendron ciliatum (Friedman's test, p < 0.005). The good correlation found between total carbon content and leaf marks indicated that fishes also prefer low 'carbon-fiber' plant species instead of high carbon content species. This study ascertains the feeding behaviour of fish species and suggests new ways of understanding the complicated relationships that bind herbivores and seagrasses, highlighting the role of grazing fish in influencing seagrass abundance and distribution.