Shell growth rate and habitat variability of the hydrothermal vent species Bathymodiolus thermophilus

Bathymodiolus species dominate the faunal assemblage of a variety of deep-sea reducing environments, where these symbiotic mussels are able to exploit different energy sources (H2S, CH4, H2) and cope with various physico-chemical constraints (temperature, acidity). Our knowledge of the environmental and biological drivers of the establishment of mussel assemblages is however still limited. In particular, the temporal patterns of settlement and growth need to be better constrained if we are able to appreciate their response to (natural or anthropogenic) disturbance.
To tackle these questions, we investigated shell growth rate of deep-sea hydrothermal bivalves using for the first time in situ chemical staining combined with high-resolution microincrement analysis and in situ chemical sensing. The staining chamber developed for this purpose allowed to characterize the growth rythmicity of Bathymodiolus thermophilus mussels from the V-vent site at 9°50’N on the East-Pacific Rise (EPR), while minimizing disturbance of the individuals in their habitat.
Bathymodiolus thermophilus revealed to grow according to a circalunidian rhythm, with one increment formed each lunar day, and a growth rate ranging between 4.2 and 1.1 cm y-1 with ontogenesis. The von Bertalanffy growth rate model built on these data allowed to ascribe an age of 10 years old for the largest shell collected (20.5 cm) at V-vent where mussel colonies were preserved after the 2005/2006 eruption. This growth model is consistent with the observed temporal pattern of recolonization of new habitats after the volcanic eruption at 9°50’N showing the rapid expansion of mussel populations between 2010 and 2012. The approach can be applied to other bivalve’s species as a suitable method for studying population structure and recruitment in the deep-sea.
The method can be used to analyze growth rate changes in relation to environmental constraints and energy limitation. Growth increments displayed tide-related variability at the scale of a complete tidal cycle (neap and spring tides). This tidal signature in shell is also visible at daily scale with the distinction of single and dual tide periods that characterize this region of the Pacific. As previously shown from temperature records, tide at diffuse flow modulates the fluid-seawater mixing ratio and is attributed to local changes of current speed and direction. In situ monitoring over several days with autonomous pH and sulfide sensors confirmed this tidal effect on habitat chemistry. A detailed analysis of S/T ratios also enables to identify sulfide depletion in the microhabitat variation over time. Shell growth variability will be further analyzed according to these environmental factors and sulfide consumption.

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First Name: 
Karine
Last Name: 
Nedoncelle
Telephone: 
00615967200
Affiliation: 
UPMC Univ Paris 06, LECOB UMR 8222, Benthic Ecogeochemistry Laboratory, OOB, 66650 Banyuls-sur mer, France
First Name: 
Franck
Last Name: 
Lartaud
Affiliation: 
UPMC Univ Paris 06, LECOB UMR 8222, Benthic Ecogeochemistry Laboratory, OOB, 66650 Banyuls-sur mer, France
First Name: 
Marc
Last Name: 
de Rafelis
Affiliation: 
UPMC Univ Paris 06, ISTeP UMR 7193, Biomineralization and Sedimentary environments Laboratory, 75252 Paris cedex 05, France
First Name: 
Leonardo
Last Name: 
Contreira-Pereira
Affiliation: 
UPMC Univ Paris 06, LECOB UMR 8222, Benthic Ecogeochemistry Laboratory, OOB, 66650 Banyuls-sur mer, France
First Name: 
Nadine
Last Name: 
Le Bris
Affiliation: 
UPMC Univ Paris 06, LECOB UMR 8222, Benthic Ecogeochemistry Laboratory, OOB, 66650 Banyuls-sur mer, France
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Ecological Interactions
Abstract ID: 
CBE5-135