Samplings were conducted in three sites, Bay Sansbois, Bay Batiste, and West Pointe à la Hache, located in the northeastern Barataria Bay. Bay Sansbois and Bay Batiste were sampled in May and October of 2015, and May of 2016, whereas West Pointe à la Hache was sampled only in May of 2016.

Fishes were sampled using multiple fishing gears (minnow traps, seines, trawls, and gill nets) and frozen upon capture. Minnow traps baited with dog food were placed in ponds, creeks, and the edge of the marshes. Trawl samplings (5-m otter trawl behind a vessel traveling ~2.5 knots) were carried out along the marsh channel while gill nets (Memphis Net and Twine: 1-1/2-inch, 3-inch, 8-inch deep) were set in creeks.  Seine net (Memphis Net and Twine: 25 ft long, 4 ft high, 1/4-in mesh) samplings were focused on ponds and creeks. For each specimen collected, a sample of the white tissue located on the dorsal region of the body was taken.

The most common marsh plant species were sampled in each site by clipping them at ground level. For this study, we analyzed only samples from fresh leaves. Phytoplankton was obtained from water sampled at the marsh main channel. Water samples were passed it through 105μm mesh screens to remove most zooplankton and large debris and then filtered through pre-combusted Whatmann GF/F glass-fiber filters. Chlorophyll was measured on the screened and unscreened water to determine how much of the phytoplankton were excluded by the screening.  We found that on average 93% of phytoplankton chlorophyll was included in our samples.  Detritus, which consisted of soil organic matter, was obtained from the upper 1-2cm of marsh soil. Microphytobenthos was extracted from the upper 1-2cm of marsh soil. Extraction methods are based on the protocol described by Levin & Currin (2012).

Terrestrial insects and spiders were collected using sweep nets along a transect from the border of the marsh to 20m inland, covering an area of approximately 40 m². Other invertebrates common to saltmarshes, including crabs, snails, and mussels, were sampled opportunistically by hand or indirectly through sampling techniques (e.g., seine nets) targeting other animal groups. After collection, crabs and mussels were dissected to extract soft tissue for stable isotope analysis.

Marsh rice rats were sampled using baited (oatmeal-peanut butter balls) Sherman live traps that were set overnight. Rats were euthanized with isoflurane and sampled for muscle tissue. Seaside sparrows were flushed into a continuous line of four to five, 12-m mist nets oriented perpendicular to the marsh edge. Netted individuals were briefly held in cloth bags until euthanized via thoracic compression. All individuals were immediately sampled for muscle tissue.

All isotope samples obtained were transported to the lab in coolers with dry ice and then sealed and stored in the freezer (-20°C). Samples were cleaned with distilled water, lyophilized for 48 hours, and then grounded to a fine pounder using pestle and mortar. Next, lipid extraction was conducted following chloroform-methanol practices (Folch et al. 1957).  Subsamples weighing 0.3-0.5 mg were packed into Ultra-Pure tin capsules and then sent to the Great Lakes Institute for Environmental Research Stable Isotope Analysis Facility for analysis of stable isotope ratios of δ13C and δ15N. The isotope analyses were carried out on a Thermo Finnigan DeltaPlus mass spectrometer (Thermo Finnigan San Jose, California, USA) coupled with an elemental analyzer (Costech, Valencia, California, USA).

Body size was measured for 59% of all animals sampled (52 taxa). Body mass was measured for the seaside sparrow and marsh rice rats whereas body length (e.g., total length for fish, carapace width for crabs) was measured for the remaining species.

References:

Folch J, Lees M, Sloane Stanley GH. 1957. A simple method for the isolation and purification of total lipides from animal tissues. Journal of Biological Chemistry 226: 497–509.

Levin LA, Carolyn C. 2012. Stable isotope protocols: Sampling and sample processing. UC San Diego: Library – Scripps Digital Collection. Retrieved from https://escholarship.org/uc/item/3jw2v1hh