Temporal variations of the Mid-Atlantic hydrothermal vent communities from the Lucky Strike vent field
Cuvelier, D. (2011). Temporal variations of the Mid-Atlantic hydrothermal vent communities from the Lucky Strike vent field. PhD Thesis. Universidade dos Açores. Departamento de Oceanografia e Pescas: Horta. 199 pp.
The first Mid-Atlantic hydrothermal vents were discovered in 1985 (Rona et al., 1986), almost 10 years after the first hydrothermal vent discovery at the Galápagos Rift (Lonsdale, 1979). Over three decades of research on these extreme deep-sea ecosystems has improved our knowledge on the mega-and macrofauna inhabiting these peculiar habitats substantially. Less is known about the community structure and the spatial and temporal distributions of the fauna in relation to abiotic andbiotic factors. Ecological time-series studies of temporal variation are indispensable to comprehend the functioning of an ecosystem. However, such studies at hydrothermal vents are scarce and mostly restricted to well-known and more accessible sites in the East Pacific Ocean (EPR and NEP). Imagery analysis is an important tool to assess temporal variation at these often remote and extreme ecosystems both under conitions of continuous venting (Hessler et al., 1985, 1988; Fustec et al., 1987; Sarrazin et al., 1997; Desbruyères, 1998) and post-eruptive nascent vent development (Tunnicliffe et al., 1997; Shank et al., 1998a; Tsurumi & Tunnicliffe, 2001; Shank et al., 2003; Nees et al., 2008; Marcus et al., 2009). Until now, only one single long-term temporal dynamics study is available for the Mid-Atlantic Ridge (MAR), where decadal-scale changes were assessed at the TAG sulfide mound (Copley et al., 2007a). The study presented here is the first high-resolution long-term variations study on the Mid-Atlantic Ridge, investigating both long-term (>10 years) variations in community structure as well as dynamics on shorter time-scales (1 to 4 years). In this dissertation, assemblage distribution patterns and zonation on the Eiffel Tower edifice (part of the Lucky Strike vent field, south of the Azores, situated at a mean depth of 1700m) is assessed by use of image analyses. The protocol wielded is described, which then was elaborated to allow comparisons between the years and to study 14 years of community dynamics. Trends in temporal variations are described. Overall decadal-scale constancy appears to persevere, however on smaller time and spatial scales, changes do occur. A succession model is proposed and a quantification of the rate of change at the slower-spreading MAR is evaluated and compared to that of faster-spreading ridges (NEP). While imagery analysis was used to unravel main temporal and spatial variation trends, discrete biological samples and physico-chemical measurements were analysed to better comprehend the discrepancies observed. Microhabitats were characterised by the extent of fluctuations in environmental variables, while temperature was identified as being a more limiting factor, separating the mussel-based assemblages from the shrimps. In addition, species lists from past and on-going sampling during the French cruises, stored in the Biocean database (Fabri et al., 2006), were analysed to identify changes over time within the Lucky Strike vent field. Based on the data at hand, no significant differences in species composition between different edifices and years were revealed. This dissertation allowed us to gather new insights on the ecosystem functioning of Mid-Atlantic hydrothermal vents. Larger-scale applications and extrapolation of these results and models are proposed, for which the collection of new data is needed.