Tropical seaweeds for human food, their cultivation and its effect on biodiversity enrichment

As a response to growing land and freshwater shortages and climate change, the use of seaweeds as food, their cultivation at sea and its effect on biodiversity are being researched on both the Caribbean and Pacific coasts of Costa Rica. Native species, more plentiful on the Caribbean coast, were collected and pre-selected based on existing information and on criteria including ubiquity, abundance, growth and palatability. These species were then evaluated as food and subjected to floating long-line cultivation using vegetative propagules. After establishing postharvest procedures, use as food involvedmany preparations to be eaten fresh or after drying, including a dry-ground meal. Ten of these species, which had nutrient contents within expected values including 9.8% crude protein on a dry weight (dw) basis and high iron, were considered adequate as food, both directly and as part of recipes in quantities not exceeding 20% dw of a given dish. Higher concentrations either ‘overwhelmed’ traditional recipes or their taste was rejected by tested consumers. Near-coast cultivation was in general a simple matter, easily transferred to artisanal fishers. To a great extent due to herbivory and theft of ropes, yield (ranging from 51.7 to 153.2 t ha⁻¹ yr⁻¹ on a fresh weight basis) was quantified for only five species with amean of 9.3 t ha⁻¹ yr⁻¹ dw, equivalent to 0.91 t ha⁻¹ yr⁻¹ of crude protein—very similar to yields of two grain crops per year. Species of Codium, Gracilaria, Sargassum and Ulva were considered adequate both for use as food and cultivation. Cultivated seaweed plots rapidly attracted biodiversity, including a significantly larger number of fish species and individuals than nearby control areas. Based on this we postulate the need to further explore a ‘biodiversity enrichment’ service from seaweed cultivation and any effect of this on fisheries enhancement. While noting areas in which further research and international collaboration are needed, it is concluded that tropical seaweeds, besides their many other uses, can at this stage substitute up to 15% of food on a dry weight basis, their cultivation is simple, and effects on biodiversity are a previously undocumented advantage. Given the lack of experience in most of the world excepting some Asian countries, the agriculture-like approach followed here may be of use to others in tropical developing countries who wish to explore seaweed cultivation at sea, for food and other products and for environmental/biodiversity services.