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

Highlights

• Native tropical seaweeds were evaluated for food and cultivation in Costa Rica.

• Modes of use tried indicate potential to substitute up to 15% of food with seaweeds.

• Several species showed adequate cultivability and yields with no need to fertilize.

• Seaweed plantings attracted biodiversity with potential to enhance fisheries.

• Methodology implemented may be of use to others in tropical developing countries.

Abstract

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 involved many 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 a mean 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.

Introduction

Needed increases in world food production are hindered by growing land and water shortages and by climate change (Falkenmark et al., 2009, OECD/FAO, 2012, UNU, 2012); however, at sea space abounds and food production does not require any freshwater (Radulovich, 2011). The use of seaweeds (macroalgae)—the only existing choice for primary production at sea—for human food and other applications, has grown to ~ 21 million tonnes (Mt) on a fresh weight basis annually, of which ~ 20 Mt are cultivated at sea, the rest is from natural harvests (FAO, 2012, FAO, 2013). It is considered that 76% of world seaweed production and 88% of its value are for direct food consumption (Chopin, 2012). However, 99.8% of cultivated production happens in only nine countries, of which eight are Asian (four of them tropical: Indonesia, Philippines, Malaysia and Vietnam), and one African (Tanzania, particularly Zanzibar); the remaining 15 tropical countries with some cultivation reported produce a combined yearly total of only ~ 32,000 t (FAO, 2012).

Although tropical seaweeds have amply demonstrated ‘cultivability’ and productivity, and their nutritional adequacy and edibility as human food have also been shown, at least at the laboratory level (e.g., Black, 1952, Matanjun et al., 2009, McDermid and Stuercke, 2003, Reed, 1907, Robledo and Freile, 1997), most of the limited cultivation experience outside Asia is for hydrocolloid uses, as it is, e.g., for Zanzibar (Msuya, 2011). In all countries of tropical Latin America, the Caribbean and most of Africa seaweeds are essentially an ignored resource, and scant or no cultivation is reported for any purpose much less for food (FAO, 2012).

Given the overarching opportunity this may represent, it was considered convenient to evaluate seaweeds as a food source, including their cultivation and effects on biodiversity in Costa Rica, a country with coasts on both the Pacific ocean and the Caribbean sea and an abundance of native seaweed species (Fernández-García et al., 2011, Wehrtmann and Cortés, 2009). Since there is a generalized lack of proven methodology to follow, it was necessary to establish and implement an agriculture-like protocol to conduct this work, thus expanding aims into generating specific experience which can be of use in the context of coastal tropical developing countries seeking solutions at sea to their food-production limitations.