Elemental ratios and lipid classes in a coral reef food web under river influence

• Published in: Progress in oceanography 2018-05, Vol.164, p.1-11
• Main Authors: Carreón-Palau, Laura, Parrish, Christopher C., Pérez-España, Horacio, Aguiñiga-Garcia, Sergio
• Format: Article
• Language: English
• Subjects: C:N ratio; Coral reefs; Food web; Lipid classes; Nitrogen; Nutritional condition; Nutritional quality; PNSAV; Triacylglycerols
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2018.03.009

[Display omitted] •Low C:N ratios revealed nitrogen enrichment in primary producers.•Phytoplankton and zooxanthellae have higher TAG followed by sea grass, mangrove, and macroalgae.•In the rainy season energy storage increased in primary consumers and top predators.•In the rainy season the habitat providing coral decreased its nutritional condition.•Zooplankton does not satisfy the energy demand of M. cavernosa during rainy seasons. Coral reefs in the Caribbean and Gulf of Mexico are increasingly suffering from anthropogenic nutrient inputs principally from fertilizers as identified by their δ15N signatures. To determine if primary producers are passively affected by anthropogenic nitrogen enrichment in a coral reef community, carbon: nitrogen ratios (C:N mol mol−1) were measured. The C:N ratio was used as a proxy for nitrogen enrichment in primary producers when the ratio decreases, and for lipid plus carbohydrate in terms of C, and protein in terms of N in primary producers and consumers. Lipid classes and the triacylglycerol to sterol (TAG:ST) ratio were used to evaluate energy storage as an indication of nutritional quality in the six most abundant primary producers, and of nutritional condition in ten ubiquitous consumers in a coral reef in the Gulf of Mexico under river influence. A low C:N ratio revealed nitrogen enrichment in primary producers. Among the lipids, high TAG proportions were detected in phytoplankton and zooxanthellae suggesting that they have a higher nutritional quality in terms of energy, followed by sea grass, mangrove, and macroalgae. During the rainy season TAG:ST increased in primary consumers such as echinoderms, and top predators such as the perciform fish Bodianus rufus, Ocyurus chrysurus and Caranx hippos, suggesting an increase in energy storage. In contrast, TAG:ST decreased in the principal habitat providing coral Montastrea cavernosa, along with a decrease in the phospholipid proportion suggesting a poor nutritional condition. There were three species with no change in their TAG:ST ratio: the sponge Aplysina sp., the masked goby Coryphopterus personatus and the surgeon fish Achanturus chirurgus. The lower value of TAG, TAG:ST ratio and phospholipid proportion in the coral M. cavernosa suggests that the reported abundance of zooplankton does not satisfy the energy demand of M. cavernosa during the rainy season.