Microbiome Shifts Associated With the Introduction of Wild Atlantic Horseshoe Crabs (Limulus polyphemus) Into a Touch-Tank Exhibit

Abstract

The Atlantic horseshoe crab ( Limulus polyphemus ) is a common marine aquarium species and model organism for research. There is potential monetary and conservation value in developing a stable captive population of horseshoe crabs, however, one major impediment to achieving captivity is a lack of knowledge regarding captive diseases. We utilized 16S rRNA gene amplicon sequencing to track changes in the microbiomes of four body locations in three wild-caught (tracked over 14 months in captivity) and three tank-acclimated (>2 years in captivity) adult L. polyphemus in a touch tank at Shark Reef Aquarium at Mandalay Bay in Las Vegas, NV. The wild population hosted diverse and distinct microbiomes on the carapace (260 ± 96 amplicon sequence variants or ASVs), cloaca (345 ± 77 ASVs), gills (309 ± 36 ASVs), and oral cavity (359 ± 37 ASVs), which were dominated by classes Gammaproteobacteria , Bacteroidia , and Alphaproteobacteria . A rapid decline in richness across all body locations was observed within 1 month of captivity, with tank-acclimated (>2 years) animals having <5% of the initial microbiome richness and a nearly completely restructured microbial community. Tank-acclimated horseshoe crabs possessed distinct microbiomes that were highly uneven and low in species richness on the carapace (31 ± 7 ASVs), cloaca (53 ± 19 ASVs), gills (17 ± 2 ASVs), and oral cavity (31 ± 13 ASVs). The carapace, oral cavity, and gills of the tank-acclimated animals hosted abundant populations of Aeromonas (>60%) and Pseudomonas (>20%), both of which are known opportunistic pathogens of aquatic animals and can express chitinases, providing a plausible mechanism for the development of the carapace lesion pathology observed in this and other studies. The cloaca of the tank-acclimated animals was slightly more diverse than the other body locations with Aeromonas , Enterococcus , Shewanella , and Vagococcus dominating the community. These results provide an important baseline on the microbiomes of both wild and tank-acclimated horseshoe crabs and underscore the need to continue to investigate how native microbial populations may protect animals from pathogens.

Sea stars resist wasting through active immune and collagen systems

“…As above, the genes in these modules perform functions related to immunity, collagen processes and cell adhesion, while the microbes were among those previously identified as associate with health status in SSW [ 33 ]. (iii) Considering animals that remained asymptomatic across the course of the study, we find stability and resilience in microbial community composition despite laboratory conditions including artificial seawater, in contrast with other laboratory studies of coral and horseshoe crabs [ 54 , 55 ], but consistent with the observations of a core microbiome for Pisaster ochraceus [ 56 ] and Pycnopodia helianthoides [ 57 ] in the field. Interestingly, all four studies, including the present study, find Spirochaetes to be the dominant microbes of asymptomatic stars for both P. ochraceus and P. helianthoides and across multiple geographical locations and tissues [ 33 , 56 , 57 ].…”

Testing cophylogeny between coral reef invertebrates and their bacterial and archaeal symbionts

“…This genus has been reported as a key member of the sponge microbiota, where it was the only taxon identified capable of performing the ammonia oxidation step in nitrification (Engelberts et al, 2020;Robbins et al, 2021) Microtrichaceae and Thermoanaerobaculaceae are less known as microbial symbionts but also showed strong cophylogenetic patterns. Although these bacterial families have been found in marine invertebrates previously (Friel et al, 2020;Sacristán-Soriano et al, 2020), no studies have yet assessed their functions within a host environment. Recent refinement of the taxonomic structure of Acidobacteria places Thermoanaerobaculaceae as a novel family in subdivision 23, members of which are characterised as thermophilic and neutrophilic anaerobes that may use sugars, organic acids and proteinaceous compounds as growth substrates (Dedysh & Yilmaz, 2018).…”

Functional and Compositional Changes in the Fecal Microbiome of a Shorebird during Migratory Stopover

“…Vibrio was one of the taxa that was associated with heavier birds and is known to be a main microbial producer of polyunsaturated fatty acids ( 37 ). Vibrio are also found in the horseshoe crab microbiome ( 46 ), so the increase could be due to dietary intake and benefit the host. Hosts could also be internally filtering for Vibrio , or both processes could happen in tandem.…”