Abstract

The abundance of several highly exploited reef fish species in the GoM (groupers, snappers, triggerfishes, etc.) are high at artificial reefs (ARs) (Dance et al. 2011), but the functional role of ARs to these and other reef-associated species is not well understood. Studies investigating trophic interactions of fauna associated with ARs can yield valuable information on their function as habitat, in addition to the ecological roles of members within the biological community (Daigle et al. 2013). Gut content analysis has been used to reconstruct the feeding patterns of fauna on ARs, and can be used to discern complex trophic interactions when paired with dietary tracers (stable isotopes) (Wells et al. 2008 and Daigle et al. 2013). Trophic relationships can be determined from gut content analysis over a relatively short-term (hours to days), but has the potential to underestimate soft-bodied prey (due to differential digestion) (Michener and Lajtha 2008, Wells et al. 2008, Tarnecki et al. 2015). Natural stable isotopes of carbon (d13C), nitrogen (d15N), and sulfur (d34S) can be used to track energy flow through trophic pathways, determine an individual’s trophic position, and provide a long-term measure of diet (weeks to months) (Post et al. 2002, Michener and Lajtha 2008). Predator d13C ratios are useful for determining the contribution of organic matter from primary producers (fractionating by only 0.5 - 1.5‰) that differ in their d13C ratios (e.g. planktonic vs. benthic carbon), while nitrogen d15N ratios in a consumer (fractionating by 3-4‰ from its prey) can be used with primary producer d15N ratios to estimate trophic position (Michener and Lajtha 2008). Sulfur d34S ratios change little with trophic level, but significant differences in benthic sulfides (depleted d34S) and sulfates in the water column (enriched d34S) can be used to discern benthic vs. pelagic producers (Michener and Lajtha 2008, Wells et al. 2008). In this study, two heavily exploited species on ARs in the northwestern GoM were used as model species to compare the feeding ecology of one midwater (Gray Triggerfish Balistes capriscus n = 89) and one demersal (Red Snapper Lutjanus campechanus n = 279) predator at nearshore ARs. Objectives were to determine if differences exist between model species use of ARs as foraging habitat, and to examine spatial feeding patterns of Red Snapper across a north to south gradient along the Texas coast, and at inshore (with low relief reefs) and offshore (with high relief reefs) ARs via pairing species-specific stable isotope ratios of carbon (?13C), nitrogen (?15N), and sulfur (?34S) with gut content analysis.

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