Locations: Gulf of Mexico Estuary near Port Aransas, Texas. FAML: pier at in Corpus Christi Channel, Port Aransas, TX, United States, Fisheries and Mariculture Laboratory of the University of Texas Marine Science Institute (lat. 27.8396111, lon. -97.0827222); MI: Mud Island in Aransas Bay, TX, United States (lat. 27.9362222, lon. -97.0217777)).

Methods and Sampling:
Carbon and Nitrogen stable isotope values were measured for samples of fish eggs, marine animals, and basal resources collected from the field as well as eggs, commercial fish food, Otohime (EP1, Reed Mariculture, Inc. and Artemia sp. nauplii (enriched with Alga-Mac 3050; Aquafauna Bio-Marine, Inc.) used in laboratory experiments.

Plankton net (500-µm mesh) samples were sorted immediately after collection (live material). Samples of jellyfish were collected using dip net. Animals were transferred to holding tanks to evacuate their guts for 4-5 hours. Fish were collected using cast net and seines. Fishes were immediately euthanized with lethal dose of MS-222. The euthanized fish were placed on ice and a fillet of dorsal white muscle tissue and liver were collected. Each sample was rinsed twice in distilled water and frozen at -80°C for subsequent analysis.

Basal resources were collected by pumping seawater from the Aransas Pass Channel adjacent to the University of Texas Marine Science Institute’s Fisheries and Mariculture Laboratory and filtering the seawater through sieves of five different mesh sizes to obtain five size fractions of plankton samples (i.e., 38-63 µm, 63-100 µm, 100-150 µm, 150-250 µm and 250-500 µm). Bottom sediment was collected with a dredge sampler. Those samples were passed through sieves of five different mesh sizes to obtain five size fractions mentioned above. The time between collection and analysis ranged from 2 months to a year.

For stable isotope analysis, each sample was lyophilized, homogenized, and weighed. A subsample of the lyophilized and homogenized tissue was analyzed for bulk stable carbon and nitrogen isotope ratios by mass spectrometry. Analyses of size-fractioned plankton samples were run separately for carbon and for nitrogen stable isotopes. The plankton samples and bottom sediments for carbon stable isotope analysis were acidified to remove carbonates. The nitrogen stable isotope analysis values of acidified samples were not significantly different from non-acidified samples of plankton and bottom sediment. Hence, the nitrogen stable isotope values of acidified samples were reported. Samples of eggs, commercial feed, and animals were not acidified. Isotope analysis produced δ13C and δ15N values as well as percent carbon and percent nitrogen in the sample.

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