Javier Urra

Molluscan assemblages in littoral soft bottoms of the Alboran Sea (Western Mediterranean Sea)

Abstract The structure of the molluscan assemblages inhabiting the subtidal bottoms off the west coast of Malaga province (southern Spain) and their relation to sediment characteristics were analysed with both univariate and multivariate parameters. Five significantly different molluscan assemblages were identified and assigned to ‘sables fins bien calibrés’ (SFBC, well sorted fine sands); ‘détritique côtier’ (DC, coastal bioclastic sands); ‘détritique envasé’ (DE, muddy bioclastic sands); and ‘coralligène’ (CO, coralligenous) biocoenoses of Pérès and Picard classification. A total of 234 molluscan species were identified, with gastropods as the dominant group (135 species). An increase of diversity and evenness with depth has been observed, with the highest values for both indexes on a rocky outcrop, and the lowest in the shallower fine sand assemblage dominated by few species. The different molluscan assemblages inhabiting these sublittoral bottoms were conditioned by depth, percentage of gravel and percentage of clay. A large proportion of tropical West African species is found in the area, some of them reaching their distributional limit towards the Mediterranean Sea. The southern Iberian coasts, in the confluence of Atlantic and Mediterranean waters and between Africa and Europe, are therefore highlighted as one of the areas with highest molluscan species richness in Europe, and require a conservation policy in order to preserve this unique European biodiversity heritage.

A species rich molluscan assemblage in a coralligenous bottom of the Alboran sea (south-western Mediterranean): intra-annual changes and ecological considerations

The composition and structure of a molluscan assemblage inhabiting an outcrop with a coralligenous community was studied in southern Spain. A total of 117 molluscan species were identified, with gastropods as the dominant group. Calyptraea chinensis was the dominant species and the family Conidae presented the highest number of species. The Shannon ― Wiener diversity index and the Evenness showed non-significant changes between cold and warm months, displaying high values (∼4 bits and ∼0.8 bits respectively). Some of the dominant and/or frequent species are strictly associated with coralligenous-building organisms, such as Neosimnia spelta with gorgonians. Regarding trophic guilds, carnivores are the dominant group, followed by filter feeders due to the high abundance of C. chinensis. Regarding biogeographical distributions, most of these species (<95%) are widely distributed in European waters, the number of strictly Mediterranean species being very low. The Alboran Sea represents the distributional limit towards the Mediterranean for some species found in this bottom, such as the Atlantic Bela powisiana. Rocky-coralligenous bottoms are scarce in the western Alboran Sea but support a high species richness molluscan assemblage, displaying higher diversity values than the surrounding soft bottoms and increasing the biodiversity at local scale. This high biodiversity is partly explained by the coexistence of different taxa with contrasting biogeographical affinities promoted by the geographical location of the area. Due to this, conservation efforts should be required to protect this stretch of coastline where one of the most biodiverse invertebrate assemblages along the European coasts can be found.

Biodiversity and biogeographical patterns of molluscan assemblages in vegetated and unvegetated habitats in the northern Alboran Sea (W Mediterranean Sea)

This paper evaluates the influence of habitat heterogeneity, inter-habitat connectivity, and biogeograhical patterns in the context of a biodiversity hotspot in an Atlantic-Mediterranean marine transition area. We analyzed some biological and ecological aspects of molluscan assemblages inhabiting different habitats located in the northwestern Alboran Sea, in order to elucidate the inter-habitat connectivity among coastal habitats, and to understand the contribution of each habitat to the integrity of the infralittoral ecosystem. The assessment of molluscan assemblages was performed by combining information regarding (1) feeding guilds, to analyze trophic strategies; (2) microhabitat preference, to study the link between habitat heterogeneity with biodiversity; and (3) biogeographical affinities, to identify distributional patterns of molluscs. A total of 354 molluscs were identified, with vegetated habitats harbouring the highest number of species. A wide variety of trophic strategies were observed, with infaunal filter feeders, specialized carnivores living on sessile invertebrates and microalgal grazers dominating the assemblages. Most of the species have a wide distribution while few strictly Mediterranean species have been collected. The presence of subtropical species highlights the uniqueness of this area in European seas. The high β-diversity value obtained is indicative of high habitat heterogeneity and a high amount of uncommon species, some of them displaying their sole European populations. The different assemblages enrich the global taxocoenosis through complementarity, with an important inter-habitat connectivity reflected by the different temporal ordination of samples according to both micro-habitat affinities and feeding guilds. This work highlights the balanced contribution of soft and vegetated bottoms as reservoirs of biodiversity.

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.

Sublittoral soft bottom assemblages within a Marine Protected Area of the northern Alboran Sea

pablo marina, jose’ l. rueda, javier urra, carmen salas, serge gofas, j. enrique garci’a raso, francina moya, teresa garci’a, nieves lo’ pez-gonza’ lez, rau’ l laiz-carrio’ n and jorge baro Centro Oceanografico de Malaga, Instituto Espanol de Oceanografia, Puerto Pesquero s/n, 29640 Fuengirola, Malaga, Spain, Departamento de Biologia Animal, Universidad de Malaga, Campus de Teatinos s/n, 29071 Malaga, Spain

Reproduction and Population Structure of Acanthocardia tuberculata (Linnaeus, 1758) (Bivalvia: Cardiidae) in Southern Spain: Implications for Stock Management

ABSTRACT The cardid bivalve Acanthocardia tuberculata is harvested in southern Spain and on the Atlantic coast of Morocco for the Spanish canning industry. The reproductive cycle and population structure of this species were studied in southern Spain from June 1999 to May 2000, using histology and condition indices, as well as modal size classes in length-frequency distribution analysis. The samples were collected monthly during autumn and winter months and fortnightly during spring and summer months. A total of 4,047 specimens were examined, from which 3,539 specimens were processed for biomass analyses and 508 for the study of the gametogenic cycle. Shell lengths of individuals ranged from 6 to 76 mm (48.15 ± 15.15 mm, mean ± SD), and the sex ratio was 1:1. The reproductive cycle of A. tuberculata showed an annual pattern, with an extended sexual activity from January to July, during which successive spawning events were observed, and with a clear-cut resting period from September to November. Small-size individuals are recruited into the population from June to December. No correlations were found between the environmental variables (sea water temperature and concentration of chlorophyll a) and the condition indices, which could be explained by the presence of upwellings in the area that introduce random fluctuations of these environmental variables. To improve management of the wild stock, a closed season during June–July was proposed together with a minimum harvest size of 45 mm.

First records of Posidonia oceanica flowering at its westernmost distributional limit (Málaga, Alboran Sea)

Abstract Flowering events of Posidonia oceanica (over two consecutive years) are reported for the first time in meadows located close to its westernmost distribution limit (Málaga, southern Spain). Shoots with inflorescences were found in fragmented meadows (patches between 1–130 m2) at a mean depth of 2.5 m. In March 2009, flowering was only observed in Calaburras (0–28 inflorescences m-2) and not in Calahonda. In November 2009, massive flowering events were observed in both Calaburras (4–144 inflorescences m-2) and Calahonda (8–184 inflorescences m-2). On this occasion, developing fruits were also observed. From 2003 to 2009, mean annual water temperatures increased in this area, with maximum values in late summer and autumn of 2007 and 2008, and these warm waters may have induced the massive flowering events. Flowering in these P. oceanica meadows located close to the Atlantic Ocean may imply favourable environmental conditions and a good health status, which should be considered in improving conservational strategies for these meadows.

Exploitation status and stock assessment of the smooth clam Callista chione (Linnaeus, 1758) in the northern Alboran Sea (GSA01-W Mediterranean Sea)

The smooth clam, Callista chione (Linnaeus, 1758), is a venerid bivalve widely appreciated in southern Spain where it represents the top commercial bivalve species in terms of landings and economic value. In this area, a total of 223 artisanal boats (68% of the artisanal fleet) are involved in shellfishing targeting bivalve molluscs, including the smooth clam. The artisanal mechanised dredging that targets C. chione in the northern Alboran Sea is described and the current exploitation status of its populations is analysed. A surplus-production model was run using ASPIC and used to assess the temporal variation in the levels of fishing for this bivalve throughout the study period (2002-2015), as well as to suggest conservation reference points that could guarantee the sustainable exploitation of this resource. During the study period, the maximum C. chione catch was registered in 2003 (306 t) and the minimum in 2006 (93 t). The ASPIC model for C. chione stock suggests that a Maximum Sustainable Yield (MSY) of 216 t could be produced from a total stock biomass of 983 t (Bmsy) at a fishing mortality rate of total biomass of 0.22 (Fmsy), with B/Bmsy and F/Fmsy values of 1.34 and 0.82, respectively, indicating that the stock is approaching good status.

First Record of Doris verrucosa Linnaeus, 1758 (Mollusca: Heterobranchia: Nudibranchia) in the bay of Tunis, Tunisia (Central Mediterranean)

Recent observations on molluscan assemblages associated with photophilous algae on rocky substrates located in the Rades Basin (Tunis Bay), have showed an established population of the nudibranch mollusc Doris verrucosa Linnaeus, 1758. This species inhabits shallow rocky environments of the western Mediterranean basin, and its presence in Tunisia was doubtful.