Sea Urchins Predation Facilitates Coral Invasion in a Marine Reserve

Macroalgae is the dominant trophic group on Mediterranean infralittoral rocky bottoms, whereas zooxanthellate corals are extremely rare. However, in recent years, the invasive coral Oculina patagonica appears to be increasing its abundance through unknown means. Here we examine the pattern of variation of this species at a marine reserve between 2002 and 2010 and contribute to the understanding of the mechanisms that allow its current increase. Because indirect interactions between species can play a relevant role in the establishment of species, a parallel assessment of the sea urchin Paracentrotus lividus, the main herbivorous invertebrate in this habitat and thus a key species, was conducted. O. patagonica has shown a 3-fold increase in abundance over the last 8 years and has become the most abundant invertebrate in the shallow waters of the marine reserve, matching some dominant erect macroalgae in abundance. High recruitment played an important role in this increasing coral abundance. The results from this study provide compelling evidence that the increase in sea urchin abundance may be one of the main drivers of the observed increase in coral abundance. Sea urchins overgraze macroalgae and create barren patches in the space-limited macroalgal community that subsequently facilitate coral recruitment. This study indicates that trophic interactions contributed to the success of an invasive coral in the Mediterranean because sea urchins grazing activity indirectly facilitated expansion of the coral. Current coral abundance at the marine reserve has ended the monopolization of algae in rocky infralittoral assemblages, an event that could greatly modify both the underwater seascape and the sources of primary production in the ecosystem.

External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea

Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009 2010 and 2010 2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009 2010 and 2010 2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009 2010 that triggered a pronounced sea surface cooling compared to winter 2010 2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009 2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010 2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009 2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010 2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.

Circulation of a Meaban-like virus in yellow-legged gulls and seabird ticks in the western Mediterranean Basin

In recent years, a number of zoonotic flaviviruses have emerged worldwide, and wild birds serve as their major reservoirs. Epidemiological surveys of bird populations at various geographical scales can clarify key aspects of the eco-epidemiology of these viruses. In this study, we aimed at exploring the presence of flaviviruses in the western Mediterranean by sampling breeding populations of the yellow-legged gull (Larus michahellis), a widely distributed, anthropophilic, and abundant seabird species. For 3 years, we sampled eggs from 19 breeding colonies in Spain, France, Algeria, and Tunisia. First, ELISAs were used to determine if the eggs contained antibodies against flaviviruses. Second, neutralization assays were used to identify the specific flaviviruses present. Finally, for colonies in which ELISA-positive eggs had been found, chick serum samples and potential vectors, culicid mosquitoes and soft ticks (Ornithodoros maritimus), were collected and analyzed using serology and PCR, respectively. The prevalence of flavivirus-specific antibodies in eggs was highly spatially heterogeneous. In northeastern Spain, on the Medes Islands and in the nearby village of L'Escala, 56% of eggs had antibodies against the flavivirus envelope protein, but were negative for neutralizing antibodies against three common flaviviruses: West Nile, Usutu, and tick-borne encephalitis viruses. Furthermore, little evidence of past flavivirus exposure was obtained for the other colonies. A subset of the Ornithodoros ticks from Medes screened for flaviviral RNA tested positive for a virus whose NS5 gene was 95% similar to that of Meaban virus, a flavivirus previously isolated from ticks of Larus argentatus in western France. All ELISA-positive samples subsequently tested positive for Meaban virus neutralizing antibodies. This study shows that gulls in the western Mediterranean Basin are exposed to a tick-borne Meaban-like virus, which underscores the need of exploring the spatial and temporal distribution of this flavivirus as well as its potential pathogenicity for animals and humans.

A wolf in sheep"s clothing: carnivory in dominant sea urchins in the Mediterranean

Arbacia lixula and Paracentrotus lividus are the dominant sea urchins in the Mediterranean sublittoral, where they are key structuring species due to their grazing activity. It has been commonly accepted that competition between both species is minimized by specializing in different algal foods. A. lixula is considered to feed mainly on encrusting coralline algae, while P. lividus prefers fleshy macroalgae. We used stable isotope analysis to test if these species occupy different trophic positions at 3 locations in the western Mediterranean and one in Macaronesia. Our results show unambiguously that A. lixula always occupies a higher trophic level than P. lividus, with a δ15N comparable in some locations to strict carnivores such as Actinia schmidti or Marthasterias glacialis. A temporal monitoring at one locality showed that this signature of a higher trophic level is consistent throughout the year. These results are incompatible with the current belief of an herbivorous diet for A. lixula and suggest that it must be considered an omnivore tending to carnivory in Mediterranean ecosystems, feeding at least partially on sessile animals such as Cirripedia, Hydrozoa or Bryozoa. A parallel analysis of gut contents showed a predominance of vegetal items in both species, although A. lixula consistently had a higher abundance of animal components than P. lividus. Our results challenge the validity of using gut content observations alone for characterizing the trophic behaviour of omnivorous marine invertebrates that feed on a variety of food sources with different digestibility.

Natural or naturalized? phylogeography suggests that the abundant sea urchin arbacia lixula Is a recent Colonizer of the Mediterranean

We present the global phylogeography of the black sea urchin Arbacia lixula, an amphi-Atlantic echinoid with potential to strongly impact shallow rocky ecosystems. Sequences of the mitochondrial cytochrome c oxidase gene of 604 specimens from 24 localities were obtained, covering most of the distribution area of the species, including the Mediterranean and both shores of the Atlantic. Genetic diversity measures, phylogeographic patterns, demographic parameters and population differentiation were analysed. We found high haplotype diversity but relatively low nucleotide diversity, with 176 haplotypes grouped within three haplogroups: one is shared between Eastern Atlantic (including Mediterranean) and Brazilian populations, the second is found in Eastern Atlantic and the Mediterranean and the third is exclusively from Brazil. Significant genetic differentiation was found between Brazilian, Eastern Atlantic and Mediterranean regions, but no differentiation was found among Mediterranean sub-basins or among Eastern Atlantic sub-regions. The star-shaped topology of the haplotype network and the unimodal mismatch distributions of Mediterranean and Eastern Atlantic samples suggest that these populations have suffered very recent demographic expansions. These expansions could be dated 94-205 kya in the Mediterranean, and 31-67 kya in the Eastern Atlantic. In contrast, Brazilian populations did not show any signature of population expansion. Our results indicate that all populations of A. lixula constitute a single species. The Brazilian populations probably diverged from an Eastern Atlantic stock. The present-day genetic structure of the species in Eastern Atlantic and the Mediterranean is shaped by very recent demographic processes. Our results support the view (backed by the lack of fossil record) that A. lixula is a recent thermophilous colonizer which spread throughout the Mediterranean during a warm period of the Pleistocene, probably during the last interglacial. Implications for the possible future impact of A. lixula on shallow Mediterranean ecosystems in the context of global warming trends must be considered.