The nutritional quality of non-calcified macroalgae in Guadeloupe (Lesser Antilles) evaluated by their biochemical composition

Abstract

Uncor rected proof sNot fo r Distr ibutio n IntroductIon Climate change, marine pollution and overfishing on reef environments have led to an increasing colonization of macroalgae which compete with corals for space. This coral—algal phase shift is identified as a major threat for coral reefs (Hughes 1994). Cover and biomass of benthic macroalgae increase concurrently with coral loss, resulting in a shift from communities dominated by corals to communities dominated by macroalgae (Done 1992, McManus and Polsenberg 2004). This change has been attributed to an increasing input of nutrients in the ocean due to land—based pollution (agriculture, wastewater), a fragilization of the reef ecosystem due to climate changes (bleaching events, diseases) and the loss of major herbivorous organisms due to overfishing (Hughes 1994, McManus and Polsenberg 2004). Herbivorous fishes and urchins are key taxonomic groups to control and reverse this phenomenon (Bellwood et al. 2004, Ledlie et al. 2007). In the Caribbean, the principal herbivorous fishes are parrotfishes (Scaridae) and surgeonfishes (Acanthuridae). These groups are widely harvested and consumed in the whole region. Other herbivorous reef organisms are sea urchins, like Diadema antilarum. However, that species suffered from a massive mortality by epizootic disease between 1983 and 1984 (Lessios et al. 1984), leading to a severe depletion of their populations. Herbivorous fishes and sea urchins principally consume early life stages of macroalgae, maintaining an algal turf on coral reefs (Lubchenco and Gaines 1981, Burkepile and Hay 2010). With a loss of grazing pressure, macroalgae reach mature forms which are difficult to remove when established. Mature forms of macrolgae are generally avoided by herbivorous organisms due to their morphological and physiological strategies against herbivory such as calcification or synthesis of repellent molecules (Lubchenco and Gaines 1981, Norris and Fenical 1982, Lewis 1985, Hay 1991). Dietary behaviors of herbivorous fishes have been studied for a long time due to their ecological role in the regulation of macroalgae (Ogden and Lobel 1978, Lewis 1985). Several studies were conducted to determine food preferences of herbivorous fishes with direct observations in the field (McAfee and Morgan 1996, Kopp et al. 2010), experiments of cage exclusion (Burkepile and Hay 2011), feeding preferences assays using transplant experiments (Lewis 1985, Paul and Hay 1986, Mantyka and Bellwood 2007), gut content analyses (Randall 1967) or stable isotopes analyses (Plass—Johnson et al. 2013, Dromard et al. 2015). Some macroalgae are unanimously cited as preferred species for herbivorous fishes, like Acanthophora spicifera (Littler et al. 1983, Lewis 1986, Paul and Hay 1986) or Padina (Ogden 1976, Lewis 1985, Paul and Hay 1986, Mantyka and Bellwood 2007). Some species are differently consumed according to site or the phyla. For example, Laurencia spp. seems to be widely consumed by herbivorous fishes in Australia (Mantyka and Bellwood 2007), while this species appears to be avoided by fishes in the Caribbean (Ogden 1976). In the Caribbean, Laurencia is a preferred macroalgae for the queen conch Strombus gigas (Lapointe et al. 2004). Finally some macroalgae genera, such as Dictyota spp. and Caulerpa spp., seem to be avoided by herbivorous fishes (Paul and Hay 1986). Food preferences for herbivorous fishes can be explained by several factors, including algal structure, chemical defenses, and nutritional quality. It has been suggested that the probability of being eaten changes as a function of seaweed morphology. Indeed, filamentous algae and sheet—like algae are more likely to be consumed than calcareous macroalgae (Steneck and Watling 1982, Littler et al. 1983, Paul and Hay 1986, Hay 1991). Food choices can also be explained by the chemical defenses of macroalgae. Some species are able to synthetize repellent molecules, which deter herbivores and inhibit grazing by influencing their palatability (Paul and Hay 1986, Targett et al. 1986, Hay and Fenical 1988). Finally, THE NUTRITIONAL QUALITY OF NON—CALCIFIED MACROALGAE IN GUADELOUPE (LESSER ANTILLES) EVALUATED BY THEIR BIOCHEMICAL COMPOSITION