Habitat fragmentation is one of the most obvious changes in nature and for that reason this study aimed to find the relation between the habitat fragmentation and the community inhabiting fragmented habitat. As a model habitat, important and endangered Posidonia oceanica meadows were used. These endemic habitats are wide spread throughout the Mediterranean playing important multiple roles as habitat providers, carrying function of ecosystem engineers, nursery areas, primary producers and sediment stabilizers. Effect of fragmentation of the P. oceanica meadows was studied on two groups of bivalve larvae endemic Mediterranean species Pinna nobili and widespread scallops of Pectinidae family. These species were chosen for their different life strategies and movement capabilities. On five sites around the Mallorca Island in Spanish Mediterranean, larval collectors were set to provide artificial surface for larvae settlement. Collectors were submerged during 3 month sampling period between July and September 2009. Data on numbers, species composition and post-settlement presence of larvae on the collectors was collected. At the same time, various environmental and habitat descriptors were collected about the temperature, waves, P. nobilis adult population, P. oceanica meadow characteristics (demography and density) and fragmentation. Fragmentation was described based on the number of gaps, gap area, perimeter and perimeter/area ratio. Highest numbers of larvae were found at Pollença and Magaluf. While there was no observed correlation between the settlement of larvae and any of the monitored parameters in case of Pectinidae, there was correlation in case of settlement of P. nobilis larvae and P. oceanica meadow demographic data. Post-settlement survival of P. nobilis larvae varies little between the study locations (42-61%). In the case of fan shell, survival doesnt correlate with any of the studied parameters, for Pectinidae species larvae post-settlement presence on the collectors was highly correlated with the fragmentation parameters, namely perimeter lengths and perimeter/area ratio. For these parameters are probably best to describe fragmentation in case of this type of study. |
