Capacidad de carga y efectos del nivel de protección en tres AMPs de las Islas Baleares (Mediterráneo Noroccidental)

The monitoring of fisheries target species in three marine protected areas (MPAs) located in the NW Mediterranean provided important conclusions on management effects. The abundance, occurrence and biomass of large fish showed consistent and growing trends inside the MPAs. Fish diversity was also favoured by protection. Nevertheless, spatial variance of these indicators at a medium scale was often of the same order as that caused by time between different protection levels. The carrying capacity was determined for the first time in western Mediterranean MPAs in five out of six sites studied, and in all cases it was achieved within the first five years of protection. The observed values indicate that the system of the studied MPAs is representative of the general coastal environment of the Balearic Islands, but is far from the potential of other MPAs which are considered as hot spots in other localities. Likewise, this study shows that partially protected areas can also be fairly effective if their habitats fit with those required by target species and fishing modalities are suitably regulated or banned.El seguimiento de especies de peces vulnerables a la pesca en 3 AMPs del Mediterráneo Occidental ha permitido extraer conclusiones importantes sobre los efectos de la gestión. La abundancia y ocurrencia de peces grandes así como la biomasa presentaron patrones temporales consistentes y crecientes en las AMPs. Conjuntamente al incremento de biomasa, la diversidad de peces también aumentó con la protección. Sin embargo, la varianza de estos indicadores a mediana escala espacial fue a menudo del mismo orden que la producida por el tiempo y el nivel de protección. La capacidad de carga se ha establecido por primera vez en AMPs del Mediterráneo Occidental en 5 de los 6 sitios estudiados. En todos los casos esta situación se alcanzó dentro de los primeros 5 años de protección. Los resultados indican que el sistema de AMPs estudiado es representativo de la mayor parte de las costas de Baleares pero que está lejos del potencial de otras AMPs consideradas como hot spots en otros enclaves geográficos. Asimismo, este trabajo pone de manifiesto que las áreas de reserva parcial pueden ser muy efectivas si su hábitat se ajusta al de las especies que quieren protegerse y si las modalidades de pesca restringidas o prohibidas son las adecuadas

Results of the nested ANOVA comparing the mean size of <i>Arbacia lixula</i> between protection levels (reserve vs. non-reserve), habitats (boulders vs. vertical walls) and sites (nested within protection and habitat) over several years (1995 to 2005 and 2009–2010).

<p>Results of the nested ANOVA comparing the mean size of <i>Arbacia lixula</i> between protection levels (reserve vs. non-reserve), habitats (boulders vs. vertical walls) and sites (nested within protection and habitat) over several years (1995 to 2005 and 2009–2010).</p

Results of the nested ANOVA comparing the densities of <i>Paracentrotus lividus</i> between protection levels (reserve vs. non reserve), habitats (boulders vs. vertical walls) and sites (nested within Protection and Habitat) over time (1995 to 2005 and 2009–2010).

<p>Results of the nested ANOVA comparing the densities of <i>Paracentrotus lividus</i> between protection levels (reserve vs. non reserve), habitats (boulders vs. vertical walls) and sites (nested within Protection and Habitat) over time (1995 to 2005 and 2009–2010).</p

<i>Arbacia lixula</i> density over time.

<p>The number of <i>Arbacia lixula</i> (>1 cm diameter) per 10 m² (mean ± SE) over time at each site in the MIMR on a) boulder substrates and (b) vertical walls. Solid symbols represent sites within the reserve (R); open symbols represent sites in the nearby unprotected area (NR). Note the different scales of both types of habitat.</p

Multiple processes regulate long-term population dynamics of sea urchins on Mediterranean rocky reefs

We annually monitored the abundance and size structure of herbivorous sea urchin populations (Paracentrotus lividus and Arbacia lixula) inside and outside a marine reserve in the Northwestern Mediterranean on two distinct habitats (boulders and vertical walls) over a period of 20 years, with the aim of analyzing changes at different temporal scales in relation to biotic and abiotic drivers. P. lividus exhibited significant variability in density over time on boulder bottoms but not on vertical walls, and temporal trends were not significantly different between the protection levels. Differences in densities were caused primarily by variance in recruitment, which was less pronounced inside the MPA and was correlated with adult density, indicating density-dependent recruitment under high predation pressure, as well as some positive feedback mechanisms that may facilitate higher urchin abundances despite higher predator abundance. Populations within the reserve were less variable in abundance and did not exhibit the hyper-abundances observed outside the reserve, suggesting that predation effects maybe more subtle than simply lowering the numbers of urchins in reserves. A. lixula densities were an order of magnitude lower than P. lividus densities and varied within sites and over time on boulder bottoms but did not differ between protection levels. In December 2008, an exceptionally violent storm reduced sea urchin densities drastically (by 50% to 80%) on boulder substrates, resulting in the lowest values observed over the entire study period, which remained at that level for at least two years (up to the present). Our results also showed great variability in the biological and physical processes acting at different temporal scales. This study highlights the need for appropriate temporal scales for studies to fully understand ecosystem functioning, the concepts of which are fundamental to successful conservation and management

Results of the one-way ANOVA performed on log-transformed data for each study site comparing the data on <i>Arbacia lixula</i> density for the years before and after the storm (in parentheses), and the percent reduction (%).

<p>Results of the one-way ANOVA performed on log-transformed data for each study site comparing the data on <i>Arbacia lixula</i> density for the years before and after the storm (in parentheses), and the percent reduction (%).</p

Relationship between recruits and adults.

<p>Linear relationships between recruits (diameter <2 cm) and adult <i>Paracentrotus lividus</i> in the Medes Islands Marine Reserve on a) boulder substrates and b) vertical walls and in the Montgrí coast on c) boulder substrates and d) vertical walls over the study period for log-transformed data. Each point represents the adult density at a site and the recruit abundance for the following year.</p