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MEPS prepress abstract   -  DOI:

Trophic partitioning among seasonally resident predators in a temperate estuary

Jeffrey D. Plumlee*, Creed Branham, Savannah Ryburn, F. Joel Fodrie

*Corresponding author:

ABSTRACT: Many migratory coastal shark species enter temperate estuaries seasonally, tracking suitable environmental conditions (i.e., temperature) and food resources. Understanding the functional role migratory sharks play in coastal food webs depends on information regarding the distinctness among predators’ trophic ecology. We examined the trophic ecology of four species of coastal sharks (Atlantic sharpnose, n = 22; bonnethead, n = 29; blacktip, n = 8; blacknose, n = 28) that migrate into temperate coastal ecosystems during the summer. We quantified their trophic relationships using bulk stable isotope ratios (δ13C, δ15N, and δ34S) measured in two tissue types representing long-term (red blood cells; 8 – 10 months) and short-term (blood plasma; 10 – 13 weeks) metabolic turnover. The primary carbon sources for the four shark species determined via stable isotope mixing models were consistently phytoplankton (65.8% ± 4.8% SD) and microphytobenthos (18.6% ± 5.4%) regardless of tissue type. However, interspecific isotopic niche overlap was species-specific and ranged widely (0 – 92%). The niche space occupied exclusively by one species also varied considerably but was lowest for blacktips (< 20%) and highest for bonnetheads (> 90%). Isotopic niche size estimated using short-term tissues was substantially larger for three of the four species (Atlantic sharpnose 41% increase, blacknose 140%, blacktips 159%) than long long-term tissues. These data suggest variable species-specific trophic redundancy and increasing overlap in the summer months indicated by larger isotopic niches. As coastal habitats become increasingly altered, understanding the functional diversity of predators is vital for prediction and assessment of resulting ecosystem-level change.