Resumen de Demographics and population ecology of the range-expanding zooxanthellate coral oculina patagonica in the mediterranean sea
Shallow-water rocky ecosystems in temperate areas are dominated by macroalgae, whilst zooxanthellate corals are extremely rare. In an era of global change, sea warming plays a crucial role in the widespread phase shifts from coral- to algal-dominance in tropical coral reef ecosystems, and in the poleward spread of some tropical and subtropical zooxanthellate corals into algal-dominated temperate areas. In this PhD Thesis, we examine the demographics and population ecology of the range-expanding zooxanthellate coral O. patagonica along the Iberian coast in the temperate Mediterranean Sea to contribute understanding the interaction among the main intrinsic and extrinsic factors in modulating the species’ dynamics. First, we document that this species is experiencing an invasive behavior that challenges the current conceptual framework, by providing evidence it is able to form encrusting bioconstructions and drive a phase shift from macroalgal- to coral-dominated states, and experience an invasive behavior at both population outbreak and geographical distribution range levels. Second, we document that a severe and recurrent pattern of partial mortality on coral colonies occurs under low seawater temperature conditions during winter, constraining coral growth at high-latitudes. Third, we document the spatial variation in the demographics of O. patagonica by examining 314 locations along ~1300 km Iberian coast that provides a detailed baseline quantitative dataset. Our results indicate that coral populations were non-stable and growing. However, the species’ demographics showed a marked ‘abundant-center’ pattern that is related to zonal differences in coral population growth that correlate with key environmental variables. The success of coral colonies and populations appear to be generally constrained by low ST and light conditions. The positive effects of algal-depleted reefs and sea urchin herbivory on coral population growth indicate that open space availability is a crucial factor enhancing its proliferation. Artificial reefs also foster the population growth and the expansion of its geographical distributional range. The broad spread of O. patagonica across the Mediterranean, and its invasive behavior at both distributional range shift and population outbreak levels, is consistent with the ongoing process of zooxanthellate coral-mediated tropicalization of shallow-water rocky ecosystems documented in other subtropical and temperate areas under current global change.
