Abstract
Rimicaris exoculata, the ‘blind shrimp,’ is the most abundant species living on active hydrothermal edifices at deep-sea vents of the Mid-Atlantic Ridge. Its unusually enlarged branchial chamber houses a dense ectosymbiotic community of chemoautotrophic bacteria. Long debated, shrimp nutrition has been proven to be a kind of osmotrophy, whereby small organic molecules produced by the symbionts pass through the integument of the shrimp directly into the circulatory system, rather than through the digestive system. The broad phylogenetic and metabolic diversity of this epibiotic community suggests a highly flexible and adjustable microbial consortium, adapted to the chemically contrasting environments inhabited by the shrimp. To cope with the highly fluctuating oxygen and temperature conditions of its habitat,R. exoculatapossesses hemocyanin with a strong oxygen affinity, and has developed both molecular and behavioral responses to heat stresses. IfR. exoculatais able to detect very dim light or chemical compounds emitted by vents, the relatively small visual and olfactory areas in the brain, along with the disproportionately enlarged higher centers, argue for a significant involvement of navigational skills using learning and place memory to orient itself within its aphotic environment. This shrimp undergoes unconventional larval development, with a primary lecithotrophic stage followed by an extended planktotrophic period, allowing a huge potential for dispersion. In light of mining licenses posing a threat for deep-sea environments, this species is a model still to be studied to better understand life in extreme deep-sea ecosystems at the global scale of an ocean.
Highlights
In deep-sea hydrothermal ecosystems, deprived of photosynthetic activity, chemoautotrophic bacteria fueled by hydrothermal fluid reduce compounds to sustain a complex and dense food web
Fluorescent in situ hybridization (FISH) observations allowed intersecting data of morphology and molecular biology, confirming the predominance of Campylobacteria with thick and thin filamentous morphologies and Gammaproteobacteria related to some thin filamentous morphologies and rods (Fig. 5d, Hügler et al 2011, Guri et al 2012, Liu et al 2019)
Tional crustacean C-type lectins (CTLs), rRCTL did not affect the located in the midgut, devoid of cuticle, and is normal growth of the bacteria that had been recruited not submitted to the molt cycle
Summary
The discovery of hydrothermal vents in 1977 on ocean ridge crests off the Galapagos Islands was quickly followed by vent discoveries along the East Pacific Rise (EPR) (Lonsdale 1977, Corliss et al 1979). 1995 2007 selves near the source of hydrothermal fluid (Van Dover et al 1988, Renninger et al 1995), resulting in a teeming swarm oriented against the current of vent fluids (Copley et al 1997) These dense aggregations were prowith the exception of the shallowest sites: Menez posed to form in response to physical constraints. The thermal environment within the aggregations has been well documented, with reported temperatures ranging from 2.8 to 32°C (Van Dover et al 1988, Segonzac et al 1993, Desbruyères et al 2001, Geret et al 2002, Zbinden et al 2004, Schmidt et al 2008a), measurements taken within a few centimeters of the shrimp aggregations (Zbinden et al 2004, Schmidt et al 2008a) do not exceed 18°C. In situ measurements of temperature, pH, ferrous iron and sulfide concentrations within the aggregations reflect the moderate contribution of hydrothermal fluid in the mixing with seawater (Zbinden et al 2004). The importance of flow rate, chemical composition and/or temperature of the hydrothermal fluid, or even duration of activity of the site, remains to be determined (Schmidt et al 2008b)
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