engleski

THE STATUS OF MEDITERRANEAN SYMBIOTIC CORALS IN THE FORTHCOMING “TROPICALIZATION”

There are reasonable concerns that climate change could reduce marine biodiversity in the Mediterranean Sea. Warmer sea temperatures are also associated with the spread of invasive species and marine diseases. Due to the increased frequency of above-average temperatures and the occurrence of warm-water organisms, the Mediterranean Sea is under a process known as tropicalization. Mass mortality of marine invertebrates is becoming more common in temperate seas. Several episodes of mass mortalities, affecting populations of corals and other sessile invertebrates, have been recorded over the past 20 years in the Mediterranean Sea. Symbiotic coral species suffered the most extensive damages during the mass mortality events. Current hypotheses about the causes of coral mass mortality events mostly focus on their relationship with the occurrence of distinctive climatic anomalies during the late summer and early fall (exceptionally high and constant temperatures for over one month) usually related to the local hydrological conditions. Mortality events of the scleractinian corals Cladocora caespitosa (Linnaeus, 1767), Madracis pharensis (Heller, 1868) and Balanophyllia europaea (Risso, 1826) were recorded in the Mediterranean Sea. Coral mortality resulted from polyp bleaching (massive zooxanthellae loss) and polyp tissue necrosis, leaving the calyx rim deprived of tissue coverage. The highest mortality rates were registered after the exceptionally hot summers of 2003, 2007, 2008, 2009, 2011 and 2012, when up to 30% specimens of C. caespitosa and M. pharensis colonies were affected and more than 40% of the B. europaea specimens died, all caused by bleaching events and polyp tissue necrosis. In most cases bleaching has been attributed to elevated temperature. However, some populations could recover after bleaching events. These possible coral recoveries provide clear evidence as to how corals can adapt to stressors and thus to potentially future climate change. Unfortunately, nothing is still known of the inherent variability of key environmental factors that regulate coral fitness (like sea temperature, light, symbionts, food) or how this variability drives sensitivity to bleaching-induced mortality. Taking into account the global warming context in the Mediterranean Sea, monitoring programs of physical-chemical parameters and vulnerable coral populations should be rapidly set up.

MEDITERRANEAN SYMBIOTIC CORALS

nije evidentirano