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Dietary plasticity in three populations of the scavenger Lethrinus mahsena in a Kenyan coral reef ecosystem as revealed by gut contents and trophic markers
Kinds, A. (2011). Dietary plasticity in three populations of the scavenger Lethrinus mahsena in a Kenyan coral reef ecosystem as revealed by gut contents and trophic markers. MSc Thesis. Faculty of Sciences, Ghent University/Kenya Marine and Fisheries Research Institute: Gent and Mombasa. 40 pp.
Thesis info:
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Documenttype: Doctoraat/Thesis/Eindwerk
Trefwoorden
    Acids > Organic compounds > Organic acids > Fatty acids
    Biomarkers
    Diets
    Isotopes > Stable isotopes
    Reefs > Biogenic deposits > Coral reefs
    Stomach content
    Echinoidea [WoRMS]; Lethrinus mahsena (Forsskål, 1775) [WoRMS]
    Nyali [Marine Regions]
    Marien/Kust
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Abstract
    Overgrazing of seagrasses by sea urchins is known to be one of the key threats to seagrass habitat. What causes these outbreaks of sea urchins (mainly Tripneustes gratilla) is not yet fully understood, but it has been suggested that overfishing of sea urchin predators could be major driver. This study explored feeding patterns and dietary plasticity of a heavily fished urchin predator, Lethrinus mahsena. The diet of L. mahsena from three locations along the southern Kenyan coast (Nail, Shelly and Vipingo) was assessed using three different techniques: gut content analysis, fatty acid analysis and stable isotope analysis. The general diet of L. mahsena was dominated by crabs, fish and squid. Sea urchins made up only a small fraction of the gut contents in Nail and Vipingo, whereas in Shelly it was the second most important prey item. Based on both frequency of occurrence of preys and gravimetric data, the Shelly population was separated from the Nyali and the Vipingo populations. Also fatty acid and stable isotope data defined the Shelly population as a distinct group. However, this separation may be a reflection of different feeding habitats (seagrass beds vs. reef flats) rather than a difference in prey preference. Since fatty acid profiles of sea urchins did not reveal specific ‘urchin’ biomarkers, we were unable to assess the importance of sea urchins in the long term diet of L. mahsena. However, the relative trophic position of fish from Shelly was significantly lower than for the other populations, which may be related to the higher incidence of sea urchins (herbivores) in Shelly stomachs.
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