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

Abstract

Among the endemic and specialized fauna from hydrothermal vents, Rimicaris shrimp surely constitutes one of the most important and emblematic component of these ecosystems. In the Mid Atlantic Ridge, two species affiliated to this genus co-occur: Rimicaris exoculata and Rimicaris chacei that differ by their morphology, their trophic regime as well as by their abundance. The first forms large and dense aggregations on active vent chimney walls in close proximity to vent fluid emissions, whereas the second is recognized as 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 show that R. chacei abundance would be higher than expected at these early life stages. Here, we describe and compare the population structures of R. exoculata and R. chacei at the Snake Pit and TAG vent fields. We show widely distinct population demographics between the two co-occurring shrimps with a large post settlement collapse in R. chacei population suggesting a large juvenile mortality for this species. We also observe important spatial segregation patterns between the two 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 to all the other life stages. Finally, we discuss the potential factors - predation and competitive interactions among others - that could explain the differences we observe in the population structure of these two species.

Symbiont Community Composition in Rimicaris kairei Shrimps from Indian Ocean Vents with Notes on Mineralogy

“…Chemosynthetic metabolisms found in these symbiotic communities are diverse, including oxidation and dismutation of sulfur compounds and the oxidation of hydrogen, methane, or iron ( 8 , 22 , 23 , 27 , 28 ). This metabolic flexibility of the bacterial partners certainly has an important role in the ecological success of R. exoculata within Atlantic hydrothermal ecosystems, enabling these animals to colonize a wide range of vent fields with contrasting chemical profiles, all along the Mid-Atlantic Ridge (MAR), where they live in dense swarms close to the vent fluid emissions ( 20 , 29 , 30 ).…”

“…Aside from R. exoculata , symbiosis in other closely related alvinocaridid shrimps have received little attention compared to that given to other animal groups with chemosymbioses ( 2 , 31 – 34 ). At present, the only other alvinocaridid shrimp with characterized cephalothoracic bacterial communities is Rimicaris chacei ( 35 ), which cooccurs with R. exoculata in several vent fields on the northern MAR ( 29 ). This limits our capacity to compare the symbiotic adaptation of different lineages within the family and how the symbiont population may be linked to environmental factors in other vents around the world—even recently discovered and poorly known groups like Kiwa squat lobsters have symbioses characterized in more species across a wider geographic area ( 15 , 36 , 37 ).…”

Reproduction in deep-sea vent shrimps is shaped by diet and phylogeny, with rhythms unlinked to surface production

“…kairei brooding females present a rather low size-specific fecundity and a large mean egg size for this family. These variations mirror differences observed in benthic post-settlement stages of these two lineages, with significantly smaller body size for settled juveniles, as well as much larger relative proportions of juveniles in populations of R. chacei [29], [32]. Higher egg numbers per brood in R. chacei might thus contribute to its high supply of settlers despite an apparently lower breeding population size than R. exoculata in northern MAR vent fields.…”

“…The majority of R. exoculata ovigerous females were collected in dense aggregates close to vent orifices with only two ovigerous females taken outside these assemblages. On the other hand, ovigerous females of R. chacei were collected either in hidden aggregates where large populations of their adults have been retrieved [32] or within dense aggregates of R. exoculata. As highlighted previously [39], ovigerous females of R. exoculata were almost absent from samples collected outside this period of the year -i.e., January to April -despite more than 30 years of sampling efforts along the MAR (figure 4a).…”

“…Species with different trophic regimes often co-occur on same vent fields, for example R. exoculata which rely on symbiosis and the mixotrophic R. chacei, allowing for a straight-forward comparison of species. The symbiotrophic species such as R. exoculata and R. kairei exhibit greatly inflated cephalothorax and live in large aggregates around the hot fluid flows [28]- [31], whereas mixotrophic species such as R. chacei [27]- [29] lacks the inflated cephalothorax and lives in small groups [32].…”