Is there a link between the type of habitat and the patterns of abundance of holothurians in shallow rocky reefs?

[EN] The presence of a mosaic of habitats, largely determined by sea urchin grazing, across shallow rocky reefs may potentially influence in differences in the distribution patterns of invertebrates. The aim of this paper was to assess, using a correlative approach, whether the type of habitat influences the abundance patterns of holothurians in the eastern Atlantic. We hypothesized that abundances of large (> 10 cm) holothurians varied among four types of habitat (3 vegetated habitats with low abundances of the sea urchin D. antillarum versus ?barrens? with hyperabundances of sea urchins), and that these differences were consistent at a hierarchy of spatial scales, including two islands and several replicated sites within each type of habitat and island. Three species of large holothurians were found, accounting for a total of 300 specimens. We found remarkable differences in abundances of holothurians between the ?barrens? and the three vegetated habitats. This pattern was strongest for the numerically dominant species, Holothuria sanctorii. Total abundances of holothurians were between 5 ? 46 times more abundant in ?barrens? compared with the vegetated habitats. Inter-habitat differences were species-specific with some inconsistent patterns from one island to the other. The total abundances of holothurians tended to increase with the abundance of sea urchins within ?barrens?. Our study suggests that there may be a link, at least for the dominant species Holothuria sanctorii, between the distribution and abundances of large holothurians and the habitat across shallow-waters of the eastern Atlantic.

Relaciones jerárquicas intra e interespecíficas entre Parablennius parvicornis y Mauligobius maderensis

Se estudia la relación de dominancia entre dos especies de peces (Parablennius parvicornis y Mauligobius maderensis) que conviven en los charcos del intermareal rocoso de las Islas Canarias. Ambas especies mostraron un patrón de jerarquía lineal basado en ataques. Se discute la jerarquía interespecífica y el cambió de rol al enfrentarse individuos de la misma especie e individuos de especies diferentes. Parablennius parvicornis mostró un comportamiento de cooperación intraespecífica y de codominancia frente a Mauligobius maderensis.It is studied the relationship of dominance between two fish species (Mauligobius maderensis and Parablennius parvicornis) which coexist in the same intertidal pools at the rocky shore of the Canary Islands. Both species showed a pattern of linear hierarchy based in attacks. It is discussed the intraspecific hierarchy and variations in the role of individuals when confronted against coespecifics or individuals of a different species. Parablennius parvicornis showed intraspecific cooperation and codominance against Mauligobius maderensis.

El erizo de mar Diadema antillarum Phillipi, 1845 influye sobre la diversidad y composición de la comunidad de mega-invertebrados vágiles en fondos rocosos del Archipiélago Canario

Abstract.- The effect of the sea urchin Diadema antillarum density over the diversity and composition of the mobile megainvertebrate community (> 2 cm) inhabiting shallow rocky reefs off the Canary Archipelago (eastern Atlantic) is described. Specifically, it was predicted that (1) high densities of D. antillarum produce a low diversity of the mobile megainvertebrate community, and (2) the composition of this community changes between rocky bottoms (= reefs) under different densities of D. antillarum. The presence of megainvertebrate taxa, and the density of D. antillarum individuals were recorded visually using 2 x 2 m quadrats (n = 16 replicates) in each of 24 locations (three locations in each of the eight main islands of the archipelago), which were visited in four occasions between February-2003 and October-2004. Thritythree taxa of mobile mega-invertebrates were observed. We registered a decline in the richness of such assemblages with increasing densities of D. antillarum (rs = -0.20; P<0.001). Species richness fluctuated considerably (0-16 species) in those locations with low densities of D. antillarum (< 2 ind. m-2). However, species richness was always low (< 9 species) in those locations with high densities of D. antillarum (> 8 ind. m-2). A CAP ordination analysis showed significant differences in the composition of the mega-invertebrate community between rocky bottoms under different densities of D. antillarum, and we registered a negative correlation between the presence of some taxa and the densities of sea urchin. Consequently, the sea urchin D. antillarum influences the diversity and composition of the mobile mega-invertebrate community on rocky bottoms off the Canary Archipelago. Resumen.- Se describe el efecto de la densidad del erizo Diadema antillarum sobre la diversidad y composición de la comunidad de mega-invertebrados vágiles (> 2 cm) que habita fondos rocosos del Archipiélago Canario (Atlántico oriental). Específicamente, se predijo que (1) las altas densidades de D. antillarum producen una baja diversidad de la comunidad de mega-invertebrados vágiles, y (2) la composición de las comunidades de mega-invertebrados varía entre fondos con diferentes densidades de D. antillarum. La presencia de especies mega-invertebradas, y la densidad de individuos de D. antillarum, se registraron visualmente en cuadrados de 2 x 2 m (n = 16 réplicas) en un total de 24 localidades (tres localidades en cada una de las ocho islas principales del archipiélago), visitadas en cuatro ocasiones entre febrero-2003 y octubre-2004. Se observaron 33 taxones de mega-invertebrados vágiles. Se registró una relación inversa entre la riqueza específica y la densidad de D. antillarum (rs = -0,20; P<0,001). En localidades con bajas densidades de D. antillarum (< 2 ind. m-2), la riqueza de especies fluctuó considerablemente, entre 0-16 especies. Sin embargo, en localidades con altas densidades de D. antillarum (> 8 ind. m-2), la riqueza de especies fue siempre baja (< 9 especies). Un análisis de correspondencia canónicas (CAP) mostró diferencias significativas en la composición de la comunidad de mega-invertebrados entre fondos sometidos a diferentes densidades de D. antillarum, y se detectó una correlación negativa entre la presencia de ciertas taxa y las densidades de D. antillarum. Consecuentemente, el erizo D. antillarum influye sobre la diversidad y composición de la comunidad de mega-invertebrados vágiles en fondos rocosos del Archipiélago Canario.

Homing behaviour of Parablennius parvicornis (Pisces: Blenniidae)

The homing ability of the rockpool fish Parablennius parvicornis was studied at the rocky shore of Gran Canaria (Canary Islands, Spain). Fish were displaced from the original rockpool during low tide to another pool 74 metres away. The return of the first blenny occurs directly after the first tide while one week later 40% of the blennies had returned to the original pool. This paper discusses the homing behaviour of this species. RESUMEN: Se estudian las habilidades de retorno (homing) de la barriguda Parablennius parvicornis en una región de la costa rocosa de la isla de Gran Canaria (Islas Canarias, España). Los peces fueron desplazados desde su charco original, durante la bajamar, a otro charco que distase 74 metros. El retorno de la primera barriguda ocurrió después de la primera marea, mientras que tras una semana habían regresado el 40% de los peces originalmente desplazados. En este artículo se discute el comportamiento de retorno de esta especie

Contribution to the biology and fishery of the deep-water red crab, Chaceon Affinis (A. Milne-Edwards & Bouvier, 1894) (Decapoda, Brachyura, Geryonidae) in deep waters of the Canary Islands (Central-East Atlantic)

[EN] This crab was captured in the whole range of depths sampled, although its highest abundance was found between 600 and 800 m, on muddy-rocky bottoms. Moreover, significant differences were observed in the average weight and length, according to depth of capture, island of origin, and date of survey. In general, the b parameter of length-weight relationship indicates a negative allometric growth pattern, although in some cases it was not statistically different from isometry, particularly in males. Males were heavier, larger, and more abundant in catches than females.

Problemática ambiental en la isla de La Graciosa: ¿Hay déficit de arena actual en sistemas playa-duna?

[ES] La isla La Graciosa está situada al noroeste de Lanzarote y tiene una extensión de 27,05 km2. Se trata de un área que presenta un alto valor ecológico pues está protegida a través de diferentes figuras tales como: Parque Natural y Reserva Marina del Archipiélago Chinijo, Reserva de la Biosfera de Lanzarote, Zona de Especial Protección de aves (ZEPA) y Zona de Especial Conservación (ZEC), entre otras. En la isla hay varios sistemas playa-duna tanto en la mitad nororiental de la isla (Las Conchas, Lambra y El Jablillo) como en su parte meridional (Barranco de Los Conejos, Las Caletas, El Salado y Francesa). Algunas de las playas muestran evidencias de un déficit sedimentario pues tienen una reducida o nula entrada de sedimentos arenosos al sistema y/o muestran procesos erosivos que hacen aparecer el substrato rocoso. Además, se observa en el interior de la isla la estabilización de los mantos eólicos por la vegetación. Estos ambientes eólicos costeros son esenciales, tanto para la preservación de los ecosistemas protegidos, como para la actividad turística insular. En este contexto se están desarrollando investigaciones multidisciplinares para elaborar un diagnóstico científico de esta problemática ambiental, determinando si las causas de este déficit sedimentario son naturales o antrópicas, y proponer soluciones al respecto.

Does depth and sedimentation interact with sea urchings to affect algal assemblage patterns on eastern atlantic reefs?

[EN]A range of factors may affect the composition and abundance of macroalgae on subtidal rocky reefs. We experimentally determined the interactive effect of the occurrence of the long-spine sea urchin, Diadema antillarum, depth and sedimentation levels on macroalgal assemblage structure on eastern Atlantic rocky reefs. Specifically, we manipulated sea urchin densities (removal of all individuals vs. untouched controls at natural densities) on rocky reefs devoid of erect vegetation, and predicted (1) that removal of sea urchins would differently affect macroalgal assemblage structure between deep (16-18 m) and shallow (8-9 m) reef strata, and that (2) the effect of sea urchin removal on macroalgae would be altered under different scenarios of sedimentation (ambient vs. enhanced). Experimental circular plots (2 m in diameter) were set up at 3 locations at Gran Canaria (Canarian Archipelago), and were maintained and monitored every 4 wk for 1 y. At the end of the experimental period, the structure of the algal assemblages differed between urchin treatments and depth strata, with a larger cover of turf and bushlike algae where urchins were removed and at the shallow reef stratum. More important, differences in algal assemblage structure between urchin treatments were irrespective of sedimentation levels, but shifted from the shallow to the deep stratum. This interactive effect was, in turn, observed for bushlike algae, as a result of a larger magnitude of response (i.e., larger cover) in the shallow stratum relative to the deep stratum, but was not detected for either turf or crustose coralline algae. These results highlight the importance of sorne physical conditions (here, differences in depth) to interact with biotic processes (here, urchin abundance) to create patterns in the organization of subtidal and benthic assemblages

Neogene and Pleistocene fossil brachiopods of the Eastern Islands. Current appointments.

[EN] Numerous specimens of fossil brachiopods have been found in the different fossiliferous outcrops of the Canary Islands. These fossils have been found in the deposits of Mio-Pliocene age of the eastern Canary Islands, described and illustrated in the work of Meco et ali. 2005 and in the outcrops interpreted as a tsunami deposits  in Piedra Alta, Lanzarote, belonging to the Marine Isotope Stage 11 dated to circa 330 ka. 4 species of fossil brachiopods have been identificated: Terebratula sinuous Brocchi 1814, Lacazella mediterranea Risso 1826 Terebratulina caputserpentis (Zbyszewski, 1957) and Thecidium cf . digitatum (Sowerby 1823). These fossils provides stratigraphic and paleoclimatic taxonomic information. Furthermore, in order to compare the fossil brachiopods with present in the Canary Island, a reference collection is defined with specimens obtained from marine sediment surveys at Gran Canaria, La Palma and El Hierro, identifying 3 species: Argyrotheca barrettiatia (Davidson, 1866), Megerlia truncata (Linaeus 1767 ) and Pajaudina atlantica (Logan 1988).