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Gera A.,Center Destudis Avanc Ats Of Blanes Ceab Csic | Pages J.F.,Center Destudis Avanc Ats Of Blanes Ceab Csic | Arthur R.,Center Destudis Avanc Ats Of Blanes Ceab Csic | Arthur R.,Nature Conservation Foundation | And 7 more authors.
Limnology and Oceanography | Year: 2014

We used the disturbance resulting from a once in a 100-yr storm on the northwest Mediterranean coast to examine the extent of the disturbance, the tolerance thresholds to burial, and the medium-term response of the long-lived Posidonia oceanica seagrass. Sediment burial at 12 surveyed areas was particularly strong in shallow meadows, with 23% of their surfaces buried, on average, under more than 10 cm of sediment. In contrast, less than 5% of the meadow was affected at deeper locations. At three sites, we tracked short-term mortality along a gradient of sediment burial. Survival response to burial was clearly nonlinear, with a significant threshold at 4–5 cm, beyond which shoot mortality was 100%. To track medium-term potential recovery, we established permanent plots subject to three sediment burial levels (0–5, 5–10, and. 10 cm burial) in four meadows. Where the initial shoot mortality was 100%, we recorded no shoot recovery over the 4-yr period. In the remaining plots, where some shoots remained alive, we detected either further mortality or shoot recovery of 7% per year on average. Extreme storm events can result in sudden catastrophic losses of seagrass cover in shallow P. oceanica meadows. In the long term and due to the long return time of such storms, the species may still be able to recover despite its low recovery potential. However, added anthropogenic stressors, including climate change, may seriously test the ability of long-lived shallow seagrass ecosystems to resist high-intensity natural disturbances and may be critical for its persistence. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc.

Garate L.,Center Destudis Avanc Ats Of Blanes Ceab Csic | Blanquer A.,Center Destudis Avanc Ats Of Blanes Ceab Csic | Uriz M.-J.,Center Destudis Avanc Ats Of Blanes Ceab Csic
Marine Ecology Progress Series | Year: 2015

Benthic sessile organisms in general, and sponges in particular, have developed an array of defense mechanisms to survive in crowded, resource and/or space-limited environments. Indeed, various defense mechanisms may converge in sponges to accomplish a defensive function in an additive or synergetic way, or to operate at different times during the sponge's life cycle. Moreover, sponges harbor highly diverse microbial communities that contribute in several ways to the host's success. Although some symbiotic bacteria produce chemical compounds that protect the sponge from predation, the possible deterrent function exerted by the calcareous coat of a sponge's endosymbiotic bacterium has not, to date, been explored. Hemimycale columella is an Atlanto-Mediterranean sponge, which produces bioactive metabolites and has been reported to host an intracellular bacterium with a calcite envelope. Calcibacteria accumulate in high densities at the sponge periphery, forming a kind of sub-ectosomal cortex. They have been suggested to provide the sponge with several benefits, one of which is protection from predators. In this study, we assess the relative contribution of the endosymbiotic calcibacteria and bioactive compounds produced by H. columella to defend the sponge against sympatric predators. Deterrence experiments have revealed that the sponge combines >1 defense mechanism to dissuade a large array of potential predators; this represents an example of the evolutionary fixation of redundant mechanisms of defense. The chemicals deterred Paracentrotus lividus, Chromis chromis, Oblada melanura, and Diplodus vulgaris, but not Parablennius incognitus and Coris julis, while the spherules of the symbiotic calcibacteria significantly deterred all predators assayed. © Inter-Research 2015.

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