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

Habitat and Scale Shape the Demographic Fate of the Keystone Sea Urchin Paracentrotus lividus in Mediterranean Macrophyte Communities

Demographic processes exert different degrees of control as individuals grow, and in species that span several habitats and spatial scales, this can influence our ability to predict their population at a particular life-history stage given the previous life stage. In particular, when keystone species are involved, this relative coupling between demographic stages can have significant implications for the functioning of ecosystems. We examined benthic and pelagic abundances of the sea urchin Paracentrotus lividus in order to: 1) understand the main life-history bottlenecks by observing the degree of coupling between demographic stages; and 2) explore the processes driving these linkages. P. lividus is the dominant invertebrate herbivore in the Mediterranean Sea, and has been repeatedly observed to overgraze shallow beds of the seagrass Posidonia oceanica and rocky macroalgal communities. We used a hierarchical sampling design at different spatial scales (100 s, 10 s and <1 km) and habitats (seagrass and rocky macroalgae) to describe the spatial patterns in the abundance of different demographic stages (larvae, settlers, recruits and adults). Our results indicate that large-scale factors (potentially currents, nutrients, temperature, etc.) determine larval availability and settlement in the pelagic stages of urchin life history. In rocky macroalgal habitats, benthic processes (like predation) acting at large or medium scales drive adult abundances. In contrast, adult numbers in seagrass meadows are most likely influenced by factors like local migration (from adjoining rocky habitats) functioning at much smaller scales. The complexity of spatial and habitat-dependent processes shaping urchin populations demands a multiplicity of approaches when addressing habitat conservation actions, yet such actions are currently mostly aimed at managing predation processes and fish numbers. We argue that a more holistic ecosystem management also needs to incorporate the landscape and habitat-quality level processes (eutrophication, fragmentation, etc.) that together regulate the populations of this keystone herbivore

Genetic connectivity and diversity as a tool to assess the effectiveness of Marine Protected Areas.

The design and management of Marine Protected Areas (MPAs) and MPA networks should take into account the spatial distribution patterns and connectivity among populations of the target species, as a key element in biological conservation. Connectivity is the exchange of individuals among populations through the passive transport and/or active movement of individuals at whatever life stage. Well-connected and highly diverse populations are more resilient to natural and anthropogenic environmental impacts. In the context of MPA monitoring, genetic analyses are considered a powerful tool for assessing population diversity and connectivity patterns at different temporal and spatial scales. In this poster presentation the guidelines to apply genetic analyses as a monitoring tool for MPAs are presented. Two case studies in which genetics tools were used to assess connectivity patterns between protected and unprotected areas in the Western Mediterranean Sea were provided. In these case studies, two widely distributed intertidal limpets, Patella rustica and Patella caerulea, and a commercially renowned coastal fish, the saddled sea bream Oblada melanura, were considered. The results of these studies provide MPA managers with good examples on how to apply these guidelines and obtain the information needed to address specific species conservation issues

Propagule dispersal and larval patch cohesiveness in a Mediterranean coastal fish

The assessment of fish dispersal is fundamental for both conservation and management of fishery resources as it provides crucial information for the establishment of more effective marine protected areas (MPAs) and networks of MPAs. In this study, we investigated the elemental composition of otoliths in early life stages of the saddled sea bream Oblada melanura (Linnaeus, 1758) (Perciformes: Sparidae) in order to obtain information on its propagule (egg and larva) dispersal in the south-western Mediterranean Sea. Specifically, using pre-settlement individuals we investigated (1) larval patch cohesiveness during the last phase of larval life; and with early post-settlement individuals we investigated (2) the number of potential natal sources, and (3) propagule dispersal distances. Results indicated that different larval patches can merge in the pelagic environment after having travelled separately for some days. In total, 7 natal sources were found to replenish, with different proportions, almost all sampling sites along a stretch of coastline of similar to 180 km, suggesting that propagule dispersal can extend at least up to similar to 90 km. This information provides important insights for understanding fish dispersal processes and supports the appropriate establishment of spatially explicit conservation strategies such as MPAs and MPA networks in the south-western Mediterranean Sea