Multitrophic integration of the tropical red seaweed Solieria filiformis with sea cucumbers and fish

Abstract

Integrated multi-trophic aquaculture systems can be very complicated as they involve interactions between different fed and extractive organisms, where each organism can have different peaks of nutrient production or absorption and assimilation during the day. Integrated seaweeds must be able to absorb nutrients under a wide range of conditions, making seaweed selection and the effects of its integration a high importance subject, particularly for tropical, poorly studied species. This study evaluated ammonium and phosphate absorption in light and dark conditions and their biochemical implications using Solieria filiformis, a promising tropical seaweed species, and its performance when integrated with fish and sea cucumbers. Nutrient pulses were added under laboratory conditions, and integration was evaluated through a cascade design in a recirculation aquaculture system (RAS), including fish and sea cucumber with tanks connected through their effluents. S. filiformis had high absorption rates under light and dark conditions either in single or combined pulses during the day. In general, controls without nutrient additions showed lower growth rates, lower Chl a, and a constant decrease in phycoerythrin, but light, dark, or combined nutrient pulses did not differ. In the integration experiments, seaweeds without enriched nutrient effluent had significantly lower growth rates, fewer ramifications, and were brittle. Flexibility improved with the integration of sea cucumbers, and, with fish, branches were thinner and more abundant. S. filiformis has been proven as an effective species to be considered for integration with fish and sea cucumbers in tropical environments.