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Sea cucumber (Stichopus horrens) as bioremediation agent against waste production in milkfish floating cages
Thesis Abstract:
The capacity of sea cucumber Stichopus horrens to mitigate pollution and its suitability for co-culture with milkfish were investigated in 120-day field study in oversea finfish cage farm in Carcar Bay, Carcar, Cebu from April 30 to August 28, 2009. Sea cucumbers were caged at 1.25, 2.5 and 5 individuals m-2 below milkfish floating cages. Survival and growth of experimental animals as well as the feed conversion ratio for milkfish were determined at the end of the experiment. The effects of the presence of sea cucumbers in the composition, abundance, and diversity of macroinfauna, amount of organic matter, and bacterial population in sediments were determined. Trend of reduced levels of organic matter in sediments were observed in cages with sea cucumbers, being significantly lower (p < .05) in cages with 5 sea cucumbers m-2 (14.34 ± 1.80%). Sedimentary bacterial loads were higher in cages with sea cucumbers although differences were insignificant compared with cages without holothurians (p > .05). Macroinfaunal community was likewise more diverse and abundant in cages grown with sea cucumbers (density = 16 × 105 m-2) than without (density = 7 × 105 m-2). The trend of decreasing levels of organic matter was a consequence of assimilation by sea cucumbers and removal of carbon by the microbial community. Stimulated growth of sedimentary bacteria means increased rate of mineralization and hastened removal of carbon from the sediments while enhanced abundance and diversity of macroinfauna implies a healthier and more stable ecosystem. These indicators of improved environmental conditions resulting from the activities of the sea cucumbers and the various interactions between the holothurians, bacteria, and other organisms in nutrient recycling and remineralization of organic matter suggest that S. horrens had functioned as a bioremediation agent below milkfish cages. Presence of sea cucumbers did not affect the growth and survival of milkfish. Survival of the holothurians was significantly higher in cages with least stocking density (p < .05) but growth did not vary significantly among stocking densities (p > .05). With the positive growth rates, it appears that co-culture of sea cucumber S. horrens and milkfish is viable and that the echinoderm has bioremediating environmental effect.