Population structure and environmental niches of Rimicaris shrimps from the Mid-Atlantic Ridge

Abstract

Among the endemic and specialized fauna from hydrothermal vents, Rimicaris shrimps constitute one of the most important and emblematic components of these ecosystems. On the Mid-Atlantic Ridge, 2 species belonging to this genus co-occur: R. exoculata and R. chacei that differ in their morphology, trophic regime and abundance. R. exoculata forms large and dense aggregations on active vent chimney walls in close proximity to vent fluid emissions, whereas R. chacei is much less conspicuous, living mostly in scattered groups or solitary further away from the fluids. However, the recent revision of Rimicaris juvenile stages from the Mid-Atlantic Ridge shows that R. chacei abundance would be higher than expected at these early life stages. Here, we describe and compare the population structure of R. exoculata and R. chacei at the Snake Pit and Trans-Atlantic Geotraverse (TAG) vent fields. We show distinct population demographics between the 2 co-occurring shrimp species with a large post-settlement collapse in R. chacei populations suggesting high juvenile mortality for this species. We describe important spatial segregation patterns between the 2 species and their different life stages. Additionally, our results highlight distinct niches for the earliest juvenile stages of both R. exoculata and R. chacei, compared with all other life stages. Finally, we discuss the potential factors, including predation and competitive interactions, that could explain the differences we observed in the population structure of these 2 species.

Anatomy and Symbiosis of the digestive system of the vent shrimps Rimicaris exoculata and Rimicaris chacei revealed through imaging approaches

“…Another way of transmission may be proposed, as for terrestrial isopods, where juveniles eat the feces of the adults when ingesting food on litter (Wang et al, 2007). This may be the case for the R. exoculata where juveniles are recruited close to adults’ aggregations (Methou et al, 2022). However, R. chacei , juveniles are first mainly recruited in isolated patches, without adults or few (Methou et al, 2022).…”

“…This may be the case for the R. exoculata where juveniles are recruited close to adults’ aggregations (Methou et al, 2022). However, R. chacei , juveniles are first mainly recruited in isolated patches, without adults or few (Methou et al, 2022). This may then reduce digestive symbiont acquisition efficiency, leading to lower holobiont fitness, and may be a partial explanation of the observed population collapse of R. chacei .…”

“…Juveniles of R. exoculata also occur within these aggregations or adjacent to them (Hernández-Ávila et al, 2021; Methou et al, 2022). R. chacei shrimps live at close periphery of R. exoculata aggregations, and are sometimes observed hiding in crevices under the rocks, or behind mussels (Methou et al, 2022). They can occasionally form small aggregations, but are found in much lower densities than R. exoculata adults are.…”

“…They can occasionally form small aggregations, but are found in much lower densities than R. exoculata adults are. In contrast, numerous juveniles of R. chacei live in nurseries (Methou et al, 2020; Hernández-Ávila et al, 2021) suggesting that the relatively low adult number results from a population collapse during the recruitment process of this species (Methou et al, 2022). Such drop in abundance between life stages does not seem to exist in R. exoculata and raises questions on the possible underlying mechanisms.…”

“…Such drop in abundance between life stages does not seem to exist in R. exoculata and raises questions on the possible underlying mechanisms. The acquisition of symbiotic communities throughout each species recruitment process may play a major role in holobiont fitness (Methou et al, 2022).…”