Mnemiopsis leidyi and juvenile Callinectes similis were collected in March – April 2022, and Beroe ovata was collected in November 2022, using a plankton net (50 cm diameter, 500 μm mesh) from Aransas Pass inlet at Port Aransas (27.8396° N, 97.0726° W). Palaemon pugio was collected using a plankton net from Corpus Christi Bay (27.8035° N, 97.0898° W) in Port Aransas in July 2021. Opisthonema oglinum and Lagodon rhomboides were collected using a seine (6.4 m wide by 1.2 m high with 5 mm square mesh) from Aransas Pass inlet at Port Aransas (27.8396° N, 97.0726° W) in August 2021 and Redfish Bay at Aransas Pass (27.8611° N, 97.07632° W) in May 2022, respectively.

The live animals of each species were divided into two treatments (control and experimental). Both treatments were fed a common diet of either live Artemia sp. nauplii (enriched with Alga-Mac 3050; Aquafauna Bio-Marine, Inc.) or commercial fish food, Otohime (EP1, Reed Mariculture, Inc.) during the acclimation period of 10 – 45 days. After acclimation (Day 0), both treatments received a common diet of Artemia or Otohime, and the diet of experimental treatments was supplemented with red drum eggs for a period of 10 – 94 days. Controls did not receive eggs. Three to eight tanks of study species were sampled at the end of acclimation (day 0). Three to eight replicate tanks (N) were sampled from each treatment 24 h and 2 – 10 days after the experimental treatment received eggs.

Mnemiopsis leidyi, B. ovata, and C. similis were held in rectangular tanks (26.7 cm long x 16.5 cm high x 16.5 cm wide), and P. pugio and fishes were held in circular tanks (12 cm in diameter, 6.4 cm deep) with recirculating filtered water. Within each rectangular tank, individuals of C. similis were held separately in round plastic containers (106.7 cm in diameter, 43.2 cm deep) with perforated lids to prevent aggressive contact. For the same reason, individuals of L. rhomboides were kept in separate perforated cylindrical enclosures (30 cm in diameter, 45 cm high) within each circular tank. Excess food and solid waste were siphoned daily from all tanks, and complete water changes were performed in rectangular tanks every 2 – 4 days. Environmental conditions were measured daily and were constant throughout the experiment (temperature: 21 – 24°C, salinity: 28 – 35 ppt, and photoperiod: 12-h light and 12-h dark).

Invertebrates removed from both treatments on sampling days were kept in clean sea water overnight to evacuate their guts and were sacrificed the following morning. For taxa with low dry weight, i.e., ctenophores, 3 – 4 individuals from each tank were pooled together to make a replicate. A single individual per tank of C. similis, and three individuals of P. pugio (subsamples, n=3) per tank were removed at each sampling day. Invertebrates were analyzed whole, except for C. similis, for which the exoskeleton was excluded. On each sampling day, one fish per tank was removed and immediately euthanized with tricaine methanesulfonate (MS-222). Euthanized fish were placed on ice where a fillet of dorsal white muscle tissue were collected. Subsamples (n = 5 – 21) of diets provided to both treatments (i.e., red drum eggs, Artemia, and Otohime) were collected throughout the experiments for each taxon. All samples were rinsed twice in distilled water and frozen at -80°C until analysis.

A known subsample (0.5 – 0.7 mg of crustacean and fishes, 4.9 – 5.2 mg of M. leidyi, 1.0 – 1.2 mg of B. ovata) of lyophilized and homogenized tissue was weighed into a tin capsule at the UTMSI Core Isotope Facility. A Thermo Fisher Scientific Flash Elemental Analyzer-Isolink coupled to a Thermo Fisher Scientific Delta V Plus Isotope Ratio Mass Spectrometry (Thermo Fisher Scientific, Waltham, MA USA) in continuous-flow (Helium) mode was used to determine carbon and nitrogen isotopic compositions. Isotope analysis produced δ13C and δ15N values in permil or parts per thousand as well as percent carbon and percent nitrogen in the sample.

Experiments took place at the Fisheries and Mariculture Laboratory of the University of Texas Marine Science Institute (lat. 27.8396111, lon. -97.0827222) ; University of Texas Marine Science Institute Core Isotope facility (lat. 27.83669, lon. -97.05250)