Country’s coral cover reduced, protected area shows greater resilience than outside | THE DAILY HERALD

COLE BAY–Hurricanes Irma and Maria caused reduction in coral cover on St. Maarten reefs; however, reef health improved due to a decrease in coral bleaching, according to scientifically analysed reef monitoring following the Global Coral Reef Monitoring Network (GCRMN) guidelines.

Coral cover (hard corals) has been significantly reduced from 6.1 per cent to 3.7 per cent since the hurricanes, “which is unfortunate, but expected, considering the intensity of Irma,” said Nature Foundation Projects Officer Melanie Meijer zu Schlochtern.

Coral cover is still higher than observed in 2016 (3.5 per cent). Scientific research found that coral cover mostly declines the year after large hurricanes, therefore Nature Foundation is concerned to observe a larger reduction of coral cover for this year.

The strong surge and swells of the storms caused gorgonian corals (soft corals) and fleshy algae to be ripped off from the reefs, leading to more exposure of coral recruits, sponges and calcareous coralline algae (CCA).

Higher carnivorous-fish biomass was found on the reefs after the hurricanes. This increase of larger fish, especially groupers and snappers, was found to be extraordinarily high in the Marine Protect Area’s mostly healthy reefs, such as Proselyte Reef and Mike’s Maze. Herbivorous fish biomass did not change significantly after the hurricanes, but fewer fish species were found.

“More accessible CCA can be profitable, as it is used by juvenile corals to settle on in the future and these juveniles can grow into larger corals and build our next generation of coral reefs. Larger pelagic fish can travel long distances. They may look for the best shelter against the impacts of the hurricanes and therefore moved to the reefs with the highest coral cover to find their needs,” stated GCRMN data analyst Achsah Mitchell.

The decrease in coral bleaching could be favourable for the health of the corals and probably is caused by the lower sea-water temperatures and the decreased visibility after the storms.

“We are worried about the higher algae cover. This could deteriorate our coral reefs even more,” said Meijer zu Schlochtern.

Macro algae cover increased after the hurricanes. This high algae cover threatens coral recruitment and coral growth.

Caribbean coral reefs have been deteriorated to a macro algal state due to several factors such as the die-off or overfishing of herbivores (such as parrotfish), climate change, human and natural disasters. Water quality had decreased on all the reefs three months after the hurricanes; water visibility was reduced by about 16 metres.

The results of St Maarten’s reef monitoring also show the significance of protecting reefs, as coral reefs in the Marine Protected Area performed better and are healthier, with higher coral, gorgonian coral, CCA and sponge cover compared to other St Maarten reefs outside the protected area. Reefs outside of the Marine Protected Area had significantly more macro algae cover than reefs within the park.

Also, greater densities of coral recruits, which indicate a greater number of healthy and reproducing corals, were found. Moreover, carnivorous fish and herbivorous fish had a greater biomass within the Marine Protected Area.

“If we do not protect our coral reefs’ health, fish biomass and coral cover will decrease and our reefs will shift to a macro algae state. Algae cover was the lowest inside the Marine Protected Area, showing us the effectiveness of protecting our coral reefs. Our results demonstrate clearly the importance of our Marine Protected Area ‘Man of War Shoal’ for our fish stocks and coral reef preservation” stated Meijer zu Schlochtern.

The entire country benefits from reefs with higher coral cover and lower macro algae and these reefs are also more resilient regarding disaster events such as Hurricane Irma.
“The reefs in the Marine Protected Area showed greater resilience to hurricanes than reefs outside the protected area. Especially the lower macro algae cover makes reefs better suited for coral growth and recruitment and would therefore have a higher resilience for hurricanes and other threats. I recommend increasing coral reef protection, management and monitoring, especially within the Marine Protected Area,” explained Mitchell.

Nature Foundation monitors the country’s coral reefs scientifically every year, using the GCRMN method to determine the health, composition and state of St. Maarten reefs. With financial support made available by the Dutch Caribbean Nature Alliance the foundation was also able to monitor and analyse the reefs after the hurricanes in 2017.
Several dive sites in the Man of War Shoal Marine Protected Area and other important dive sites around the island were monitored pre-hurricanes in August and post-hurricanes in December 2017. The full report can be accessed through the Foundation’s website .

Source: The Daily Herald