Islands Ecology

The authors would like to thank the Swedish Research Council (grant no. 2006-5571 to T.D.), the Icelandic Research Fund (Rann í s; grant no. 070236041 to F.G.), and the Riksmusei V ä nner for fi nancial support. We also thank Dr. Leifur A. S í monarson and Dr. Margr é t Hallsd ó ttir for help acquiring sediment samples from Hr ú tagil in M ó kollsdalur, and Oddur Sigur ð sson for taking us to the Sel á rgil outcrop. Christian Pott is thanked for taking the image of Q. furuhjelmii. Two anonymous reviewers and Bruce Tiffney provided helpful comments to the manuscript.

RÉSUMÉ : Le milieu marin de la rive sud-méditerranéenne accuse un retard en matière de maintien et de protection de la biodiversité par rapport au domaine continental. Les surfaces réservées aux aires marines protégées sont limitées, et les niveaux de protection sont dérisoires. Devant l’ampleur de la dégradation des écosystèmes marins affectant l’ensemble des pays riverains de la Méditerranée dont l’Algérie, la nécessité de sauvegarder les espaces littoraux et insulaires d’intérêt écologique majeur n’est plus à démontrer. La présente étude menée au niveau de l’île de Rechgoun s’inscrit dans ce cadre visant à caractériser l’habitat, d’évaluer ses potentialités écobiologiques renfermant des espèces végétales et animales remarquables par leur endémisme, leur rareté, et leur vulnérabilité, et disposant d’un statut national voire régional, mais subissant de fortes pressions anthropiques qui indiquent avec force la nécessité et l’urgence d’enclencher des mesures de protection du site insulaire en question. L’île de Rechgoun répond parfaitement à l’ensemble des critères de sélection des aires marines protégées, reconnus et admis par les instances régionales, voire internationales auquel s’ajoute la ressemblance des niches écologiques avec un site similaire déjà classé en l’occurrence les îles Habibas au nord-est d’Oran. Tout ceci  renforcera le nombre d’espaces protégés exclusivement marins en Algérie, et par voie de conséquence, le réseau des aires marines protégées dans la partie sud de la Méditerranée avec comme incidences majeures, le maintien d’un pôle de biodiversité, et la reconstitution des stocks halieutiques à forte valeur marchande.
MOTS CLÉS : Ile Rechgoun,  Aire marine protégée, Espaces insulaires, Biodiversité, Endémisme, vulnérabilité. Méditerranée, Algérie.

ABSTRACT: The marine environment in the Mediterranean shows a delay maintenance protection of the biodiversity compared to continental field. The surfaces reserved for marine protected areas are weak, and the levels of protection are ridiculous. In front of the extent of the erosion of the marine ecosystems affecting the whole of the countries on the Mediterranean who’s Algeria, the need for safeguarding littoral and insular spaces of major ecological interest is not any more to show. The presents study led to the level of the Rechgoun island lies within this scope sant to characterize the habitat, to evaluate its ecobiological potentialities containing of the vegetable and animal species remarkable by their endemism, their scarcity, and their vulnerability, and having an even regional national statute, but undergoing strong anthropic pressures which indicate with force the need and the urgency to engage protection measures of the insular site in question. The Rechgoun island answers perfectly the whole of the marine criteria of selection of marine protected areas, recognized and admitted by the regional authorities,  even international to which the resemblance of the ecological niches is added to a similar site already classified in fact the Habibas islands  to north east of Oran. All this will reinforce the number of exclusively marine spaces protected in Algeria, and consequently, the network of  marine protected areas in the southern part of the Mediterranean with like incidences major, the constitution, the maintenance of a pole of biodiversity, and the reconstitution of halieutics stocks to strong commercial value.
KEY WORDS: Rechgoun Island, Marine protected areas, Insular spaces, Biodiversity, Endemism, Vulnerability. Mediterranean, Algeria.

The distribution and biogeography of marine prosobranch gastropods from four oceanic islands and six seamounts off Brazil are investigated. The study is founded on an inventory of all Recent species known to occur in Atol das Rocas, Fernando de Noronha, Trindade and Martin Vaz Islands and the seamounts at the Vit6ria-Trindade Seamount Chain, and deposited in several collections in Brazil, the U.S. and abroad. The species composition was determined for each island, and the relationships among assemblages from each island, and between islands and those from other land masses investigated. Evaluation of the modes of development in insular species made it possible to determine whether the assemblages are dominated by species with particular developmental strategies allowing for selective larval dispersal and eventual colonization of insular habitats. A total of 297 species was examined, equivalent to about 40 % of the number of species known from the Brazilian coast. Cluster analyses of similarity indicate that assemblages from Rocas and Noronha are more related to each other than to those of any other study locality, probably due to geographic proximity and some ecological affinities. Similarities also suggest that, at the seamount chain, a 'stepping stones' effect should occur among the seamounts close to coast. The total number of species decreases with distance from the coast along the chain. Rates of endemisrn are relatively high (9 to 16 %) in the four islands, in spite of their young age and small insular areas. Similar values were determined for exclusively Brazilian species present in the islands. Vl7idely distributed western Atlantic tropical species are prevalent in each of the four islands. Species present in biogeographic units other than the western Atlantic were poorly represented. The effectiveness of a mid­-Atlantic barrier is confirmed by small percentages of amphi-Atlantic species, and by reduced similarities between study localities and Ascension Island. Frequencies of planktotrophic species among islands and seamounts were not significantly different from those with lecithotrophic development, suggesting that distances are not large enough to constitute a filter in regard to developmental strategies. However, species with broad, extra-western Atlantic distribution present in the four islands were preponderantly planktotrophic. Conversely, lecithotrophy was prevalent in the groups of restricted or en­demic species, indicating that speciation rates should be higher for species without the high dispersal abilities associated with feeding, long-lived planktonic stages. Finally, the species per family ratios in the the four islands did not support the hypothesis that oceanic islands can act in general as refugia for invertebrate faunas during periods of lowered sea-level. Some isolated cases, however, do indicate that these localities have sheltered particular groups of species that underwent extinction elsewhere.

Dating the subsidence history of the North Atlantic Land Bridge (NALB) is crucial for understanding intercontinental disjunctions of northern temperate trees. Traditionally, the NALB has been assumed to have functioned as a corridor for plant migration only during the early Cenozoic, but recent fi ndings of plant fossils and inferences from molecular studies are challenging this view. Here, we report dispersed pollen of Quercus from Late Miocene sediments in Iceland that shows affi nities with extant northern hemispheric white oaks and North American red oaks. Older (15 to 10 Ma) sediments do not contain pollen of Quercus suggesting it arrived after that time. Pollen from the 9 -8 Ma Hr ú tagil locality is indistinguishable from morphotypes common among white and red oaks. In contrast, pollen from the 5.5 Ma Sel á rgil locality has a tectum that is at present confi ned to North American white and red oaks, indicating a second episode of migration to Iceland. These fi ndings suggest that transatlantic migration of temperate plant taxa may not have been limited by vast areas of sea or by cold climates during the Miocene. Furthermore, our results offer a plausible explanation for the remarkably low degree of genetic differentiation between modern disjunct European and North American oaks.