Alligators in the abyss: The first experimental reptilian food fall in the deep ocean

Abstract

The high respiration rates of the deep-sea benthos cannot be sustained by known carbon supply pathways alone. Here, we investigate moderately-sized reptilian food falls as a potential alternative carbon pathway. Specifically, three individual carcasses of Alligator mississippiensis were deployed along the continental slope of the northern Gulf of Mexico at depths of ~2000m in early 2019. We posit the tough hide of alligators would impeded scavengers by limiting access to soft tissues of the alligator fall. However, the scavengers began consuming the food fall 43 hours post-deployment for one individual (198.2cm, 29.7kg), and the carcass of another individual (175.3 cm, 19.5kg) was completely devoid of soft tissue at 51 days post-deployment. A third individual (172.7cm, 18.5kg) was missing completely after 8 days, with only the deployment harness and weight remaining drug 8 meters away, suggesting a large elasmobranch scavenger. Additionally, bones recovered post-deployment reveal the first observations of the bone-eating Osedax in the Gulf of Mexico and are confirmed here as new to science. The findings of this study indicate the quick and successful utilization of terrestrial and aquatic-based carbon food sources in the deep marine environment, though outcome variability may be high.

The macrofaunal metropolis in the sediments around the first‐ever deep‐sea alligator fall

“…In this case, a temporary depression of alpha‐diversity during the sulfidic stage would mitigate enhancement of alpha‐diversity from enrichment alone, thus arriving at similar species richness as that of the background. Second, the food fall draws in scavengers and predators (McClain et al, 2019). These species may be agents of disturbance because enhanced abundance of higher trophic levels may lead to higher consumption of smaller species (Dayton & Hessler, 1972).…”

“…At a large spatial scale, food falls may support macrofaunal species atypical of the background and enrich gamma‐diversity. Although further work is required, the findings also indicate that species of Alligatoridae, abundant globally near coastlines (Balagera‐Reina & Velasco, 2019), are a viable carbon pathway to the deep not only for megafauna (McClain et al, 2019) but also for macrofauna. This energetic connection between land and the deep sea indicates conservation initiatives of the deep oceans must connect with those working on conservation of relevant terrestrial megafauna and ecosystems.…”

“…As part of a broader food fall experiment (McClain et al, 2019), sediment core samples were taken around one alligator fall. The carcass of Alligator mississippiensis (175.3 cm length, 19.5 kg; McClain et al, 2019) was obtained from the Louisiana Department of Wildlife and Fisheries, Alligator Management Program (LDWF Tag 898310). The alligator carcass was frozen immediately post‐mortem for later deployment.…”

“…Second, the food fall draws in scavengers and predators (McClain et al, 2019). These species may be agents of disturbance because enhanced abundance of higher trophic levels may lead to higher consumption of smaller species (Dayton & Hessler, 1972).…”

“…As part of the broader experiment, an additional alligator carcass, deployed 100 km from the carcass detailed here, was observed at 1-day post-deployment. At this time, giant isopods (Bathynomus giganteus) had already broken through the tough hide and were feeding on the flesh of the carcass(McClain et al, 2019). This observation indicates that it is possible that the soft tissue had been fully consumed within a few days, and the F I G U R E 1 Map of sampling site carcass may have been in skeletal form for some time prior to sediment sampling.…”