Abstract
Abstract. Submarine canyons are known as one of the seafloor morphological features where living cold-water coral (CWC) communities develop in the Mediterranean Sea. We investigated the CWC community of the two westernmost submarine canyons of the Gulf of Lions canyon system: the Cap de Creus Canyon (CCC) and Lacaze-Duthiers Canyon (LDC). Coral associations have been studied through video material recorded by means of a manned submersible and a remotely operated vehicle. Video transects have been conducted and analyzed in order to obtain information on (1) coral bathymetric distribution and density patterns, (2) size structure of coral populations, and (3) coral colony position with respect to the substrate. Madrepora oculata was the most abundant CWC in both canyons, while Lophelia pertusa and Dendrophyllia cornigera mostly occurred as isolated colonies or in small patches. An important exception was detected in a vertical cliff in LDC where a large L. pertusa framework was documented. This is the first record of such an extended L. pertusa framework in the Mediterranean Sea. In both canyons coral populations were dominated by medium and large colonies, but the frequent presence of small-sized colonies also indicate active recruitment. The predominant coral orientation (90° and 135°) is probably driven by the current regime as well as by the sediment load transported by the current flows. In general, no clear differences were observed in the abundance and in the size structure of the CWC populations between CCC and LDC, despite large differences in particulate matter between canyons.
Highlights
Occurrence, distribution and abundance of CWC species are strongly influenced by several abiotic factors such as seawater temperature and density, aragonite saturation state, oxygen concentration, presence of appropriate substratum, and water flow regimes (Dullo et al, 2008; Davies et al, 2008; Orejas et al, 2009; Roberts et al, 2009a)
A total of 4447 linear m of sea bottom have been explored in Cap de Creus Canyon (CCC), in which a total of 790 colonies of Madrepora oculata, 16 colonies of Lophelia pertusa, and 62 colonies of Dendrophyllia cornigera were recorded in 7 of the 10 explored sites (Fig. 2, Table 2)
A total of 8362 linear m of sea bottom have been explored in Lacaze-Duthiers Canyon (LDC), in which a total of 555 colonies of M. oculata, 97 colonies of L. pertusa, and 6 colonies of D. cornigera were recorded in 6 of the 8 explored sites (Fig. 2, Table 2)
Summary
Occurrence, distribution and abundance of CWC species are strongly influenced by several abiotic factors such as seawater temperature and density, aragonite saturation state, oxygen concentration, presence of appropriate substratum, and water flow regimes (Dullo et al, 2008; Davies et al, 2008; Orejas et al, 2009; Roberts et al, 2009a). Each canyon presents unique characteristics (Wurtz, 2012) with large differences in the sediment fluxes and hydrodynamic features (Palanques et al, 2006; Canals et al, 2009) that make the availability of food to CWC largely variable among canyons Such differences affect the abundance and species composition of the fauna (Gili et al, 2000), and could result in different suitability and stability of coral habitats, inducing differences among their populations. Video analysis methods have been employed to compare the state of CWC populations in the Cap de Creus Canyon (CCC) and Lacaze-Duthiers Canyon (LDC), in the Gulf of Lions Both canyons present well-developed CWC communities, but differ in terms of main hydrodynamic features and particulate fluxes (Palanques et al, 2006, 2012; Ogston et al, 2008; Sanchez-Vidal et al, 2009; Pasqual et Lacaze-Duthiers Canyon (LDC). Since protection measures will be put in place in both the studied canyons (Madurell et al, 2012; Watremez, 2012), the results of this study will represent a before-protection assessment for monitoring programs aiming to evaluate the effectiveness of protection measures
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