Ecological study of benthic communities in the continental shelf and upper slope in the Menorca Channel (North Western Mediterranean)
Technological development and increased availability of remotely operated vehicles and manned submersibles have significantly increased accessibility to deep environments revealing the presence of rich and diverse macrobenthic assemblages dominated by suspension feeders. These assemblages have been...
| Autor: | |
|---|---|
| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2016 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/403988 |
| Acesso em linha: | http://hdl.handle.net/10803/403988 https://dx.doi.org/10.5821/dissertation-2117-105812 |
| Access Level: | acceso abierto |
| Palavra-chave: | 504 |
| Resumo: | Technological development and increased availability of remotely operated vehicles and manned submersibles have significantly increased accessibility to deep environments revealing the presence of rich and diverse macrobenthic assemblages dominated by suspension feeders. These assemblages have been largely exposed to the impacts of fishing activities (especially bottom trawling) in the Mediterranean Sea. Consequently, it is currently urgent to increase knowledge on their distribution, as well as on the ecology and biology of the main species that constitute these macrobenthic assemblages in order to implement effective management and conservation measures. This thesis addressed the characterization of macrobenthic assemblages in the continental shelf and upper slope (40-360 m depth) of the Menorca Channel through a multidisciplinary approach at different ecological levels. Six macrobenthic assemblages mainly segregated by substrate and depth. Hard substrates hosted sponge grounds and coral gardens, whereas crinoid and brachiopod beds occurred on soft sediments. Highest diversity values were found in the shelf edge, probably as a consequence of the bottom heterogeneity and the constant hydrodynamic conditions. Gorgonians were one of the most important and diverse bioengineering organisms in the Menorca Channel, forming dense assemblages that extended over vast areas. Gorgonian assemblages on the continental shelf and upper slope were mostly monospecific, whereas shelf edge assemblages were highly multispecific. Small colonies were dominant throughout the studied bathymetric range, but in deeper environments intermediate and large colonies were more abundant. The good preservation state of most of the observed benthic assemblages and gorgonian populations is probably related to the low pressure of bottom trawling which is mostly concentrated in deeper areas of the continental slope. Paramuricea macrospina is the most abundant gorgonian species in the Menorca Channel. Throughout its distribution, three different chromatic forms were observed. Two forms occurred on the continental shelf, and a third occurred on the shelf edge. Colony shape, sclerite size and shape, and the genetic variability of mitochondrial markers were compared to elucidate if these chromatic forms represented different taxonomic units. Colony morphology barely changed among the three forms resulting as a high conservative character. Conversely, sclerite size and shape significantly differed amongst the three forms, possibly conditioned by genetic and environmental factors. However, no significant differences were observed in the studied mitochondrial markers. The reproductive cycle, energy storage and metabolic requirements of P. macrospina showed significant differences compared to Mediterranean coastal gorgonians. Its reproductive cycle was delayed 2¿3 months respect to shallow species, possibly following the late summer increase in seawater temperature occurring on the Mediterranean continental shelf. Moreover, internal brooding in P. macrospina contrasts with surface brooding in the congeneric Paramuricea clavata. Lipid content was lower and more constant in P.macrospina than in shallow species, and d13C and d15N composition showed almost no seasonal variation, suggesting that food availability in the continental shelf is lower but more constant than in shallower environments. The high oligotrophic conditions of the Balearic Sea apparently contrasts with the high abundance and diversity of active and passive suspension feeders observed in the Menorca Channel. Indeed, the downward particle fluxes quantified during two consecutive years in the Menorca Canyon were comparatively low within the Mediterranean context, reflecting the oligotrophic nature of the study area and the lack of continental inputs of particulate matter. Hydrodynamic settings and resuspenion appear to control TMF. |
|---|