Coral reef ecosystem collapse in Puerto Rico: Combined impacts of long-term local anthropogenic factors and climate change

Abstract

Coral reefs are under increasing threats that have undermined their resistance ability to disturbance, their ecological functions and their ecosystem resilience. A combination of long-term impacts by natural factors (i.e., hurricanes, meso-scale gyres), a sort of local human factors (i.e., water quality degradation, sediment- and nutrient-loaded runoff, overfishing), and climate-related factors (i.e., sea surface warming, bleaching) have resulted in net coral decline trends along the wider Caribbean region. This study is aimed at addressing long-term ecological change in coral reef benthic communities across different coral reefs in Puerto Rico (PR). This presentation is focused in Playa Carlos Rosario, Culebra Island, with 12 years of data. Coral species richness declined by a mean factor of 54% during the period of 1997 to 2009. Percent living coral cover plummeted by 81%, or an annual mean of 6.8% loss. Coral cover loss following the 2005 unprecedented sea surface warming and mass bleaching event was 66%. Total algal cover has increased by a factor of 91%, but macroalgal cover has increased by 1,064%, or a mean annual increment of 89%. This suggest unequivocal impacts by recurrent sediment- and nutrient-loaded runoff pulses, in combination with recurrent impacts from meso-scale gyres that can increase background chlorophyll a concentrations by a 5-10 fold factor. Coral:macroalgal ratios have declined by 97%. Mortality trends in Montastraea annularis spp. complex has averaged 70% during the same period and 48% since 2005. These trends are widespread through different locations in PR, suggesting that coral reefs are in the peril of an ecosystem collapse. There is a need to develop mathematical models to predict what would be the future of Caribbean-wide coral reefs in the face of climate change impacts.