Revealing organic carbon sources fueling a coral reef food web in the Gulf of Mexico using stable isotopes and fatty acids

Abstract

Carbon and nitrogen stable isotopes and fatty acids (FAs) revealed primary producer organic carbon sources that fuel a coral reef food web with river influence. A stable isotope mixing model was used to assess the relative contribution of six different primary producers to nine of the most ubiquitous invertebrate and fish consumer's bulk carbon. Mangrove and phytoplankton were difficult to differentiate in some consumers; likely solutions involved one or the other but not both at the same time. FA concentration in upper trophic levels was corrected for the primary producer's relative contribution according to the mixing model, and FA retention was evaluated using a calculated trophic retention factor (TRF). The C 18 FAs, 18:2v6 and 18:3v3, were plentiful in mangrove, sea grass, and green algae, but decreased across trophic levels with a TRF # 1, probably due to decomposition of drifting leaves and then consumer metabolism. In contrast, macroalgae and phytoplankton FAs, 24:1v9, and highly unsaturated fatty acids (HUFAs), arachidonic acid (ARA) 20:4v6, docosapentanoic acid (DPA) 22:5v3, and docosahexanoic acid (DHA) 22:6v3, showed trophic accumulation (TRF . 1), while eicosapentanoic acid (EPA) 20:5v3 had similar concentrations across trophic levels (TRF 5 1), suggesting the following degrees of HUFA retention: DHA . ARA . EPA. This study indicates that phytoplankton are the major source of essential dietary nutrients for all fish, and that dietary energy from mangroves is transferred to juvenile fish Caranx hippos, while sea grass nonessential FAs are transferred to the entire food web. Moreover, among the species studied, the sea urchin Echinometra lucunter is the major consumer of brown and green algae, while red algae were also consumed by the surgeon fish Acanthurus chirurgus.Coral reefs are located along the coastlines of over 100 countries and provide a variety of ecosystem goods and services. Reefs serve as a major food source for many developing nations, they provide barriers to high wave action that buffer coastlines and beaches from erosion, and they supply an important revenue base for local economies through fishing and recreational activities. This is the case of the Veracruz Reef System National Park (Parque Nacional Sistema Arrecifal Veracruzano: PNSAV) located in the southwest Gulf of Mexico. The PNSAV was declared a marine protected area in 1992 because of its high biodiversity. However, the PNSAV is under considerable pressure from fisheries, tourism, and from intense traffic of large ships to Veracruz harbor. Also, it receives rates of sedimentation ranging between 0.006 and 2 kg m 22 d 21 , turbidity, and organic matter related to the three rivers flowing into the PNSAV: La Antigua in the north, Jamapa in the middle, and Papaloapan in the south (Pérez-Españ a and Vargas-Herná ndez, 2008). The myriad sources of organic matter in the oceans depend on the intensity of the autochthonous signal and the proximity and magnitude of inputs from coastal higher plants and transport by rivers. Pri...

Reconciling the role of organic matter pathways in aquatic food webs by measuring multiple tracers in individuals

“…Terrestrial vegetation, particularly grasses and herbaceous plants, had high ALA, in line with results for trees from diverse biomes (mangroves [Carreon-Palau et al 2013], alder and hemlock [Volk and Kiffney 2012]). Terrestrial vegetation, particularly grasses and herbaceous plants, had high ALA, in line with results for trees from diverse biomes (mangroves [Carreon-Palau et al 2013], alder and hemlock [Volk and Kiffney 2012]).…”

Diversity of trophic niches among herbivorous fishes on a Caribbean reef (Guadeloupe, Lesser Antilles), evidenced by stable isotope and gut content analyses

“…Recently, Plass-Johnson et al (2013) recommended a mean nitrogen enrichment equal to +2.3‰ for parrotfishes, due to their diet consisting of both low and high-proteins foods. The use of stable isotope analyses has considerably increased over the last decades to discriminate different trophic groups in food web studies (Cocheret de la Morinière et al 2003, Carassou et al 2008Wyatt et al 2012), compare trophic niches in a fish community (Ho et al 2007, Frédérich et al 2009, Nagelkerken et al 2009, Layman and Allgeier 2012, Lamb et al 2012, show ontogenetic changes in diet (Cocheret de la Morinière et al 2003, Kolasinski et al 2009, Carreón-Palau et al 2013, Plass-Johnson et al 2013 or plasticity of feeding habits (Ho et al 2009). Coupling digestive content and stable isotopes analyses represents a powerful tool to determine trophic niches.…”

Lipids in Marine Ecosystems

“…Carreón-Palau et al [123] used bulk 13 C and 15 N to apportion primary producer sources of organic carbon in a coral reef food web. The most probable solution was calculated using an isotopic mixing model: Stable Isotope Analysis in R (SIAR) which is available as an open source R package.…”

“…Carreón-Palau et al [123] calculated trophic retention factors (TRFs) for fatty acids in a coral reef food web with river influence in the Gulf of Mexico. These factors were calculated in a manner similar to that used for trophic magnification factors (TMFs) of contaminants.…”