Seasonal dynamics of molluscan assemblages associated with littoral soft bottoms of the NW Alboran Sea (Western Mediterranean Sea)

Abstract

Molluscan assemblages inhabiting subtidal soft bottoms in the northwestern Alboran Sea were studied to analyse temporal changes in structure and composition. A total of 117 samples were collected seasonally using a small rock dredge at 10 sampling stations, yielding 210 mollucan species. The assemblages occurring on the different soft bottoms were well-sorted fine sands assemblage (SFBC), mixed coarse sands assemblage (MX), muddy bioclastic sands assemblage (DE) and coastal bioclastic sands assemblage (DC), and all displayed high species richness values throughout the year. Different seasonal dynamics were observed and ecological indices were influenced by dominant species, especially the bivalve Spisula subtruncata at the shallow stations and the gastropods Calyptraea chinensis and Nassarius reticulatus at the deeper stations. SFBC displayed maximum abundance (N), species richness (S) and Shannon–Wiener diversity (H′) in autumn, DE and MX displayed maximum N and S in spring but maximum H′ in autumn (DE) and winter (MX), and finally DC displayed stable values of ecological indices throughout the year with minima in spring. Seasonal changes in the deep assemblages (25 m) were not significant and therefore less acute than those of shallower ones (5, 15 m), probably due to a lower influence of the environmental conditions and a higher habitat complexity. Seasonal patterns were somewhat different from those observed in more northern areas of Europe, where maximum abundance and species richness is usually concentrated at the end of summer. This original information will provide a baseline to understand the dynamics of benthic communities in this area.

Keywords:

• Molluscs
• assemblages
• soft bottoms
• diversity
• seasonal dynamics

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

We would like to express our sincere gratitude to José S. Guirado, Fernando Ortega and Rafael Barba (Dirección General de Gestión del Medio Natural) for their help and continuous interest; to José Fraidias (Junta de Andalucía) and Diego Luis Gancedo (EGMASA) for the use of the ship AMA 8; to the captain and crew of the vessel AMA 8 for their cooperation during the sampling campaign; to the colleagues of our department, mainly to Dr J. Enrique García-Raso and J. Enrique García Muñoz (members of this project) for their help at different stages of this research, and to Terence Edwards for English revision of this manuscript. Comments from two anonymous reviewers improved a previous draft of this paper. This work was supported by the ‘Consejería de Medio Ambiente de la Junta de Andalucía’ (contract with the University of Málaga; reference 807/46.2284).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark