According to the CCMI, globally, coral reefs face increased threats from climate change and human development, including the widespread prevalence of diseases such as stony coral tissue loss disease in the Caribbean. While Little Cayman’s reefs are subject to the same global pressures that reefs elsewhere face, CCMI’s latest surveys indicate that local protections are mitigating the impact of these threats and that Little Cayman’s fish populations have shown significant signs of recovery. The 2021 studies also conclude that coral reefs remain vulnerable, as evidenced by decreased coral recruitment and reduced coral size (CCMI has just released the results of its 2021 Rapid Reef Assessment studies). Atlantic and Gulf Region (AGRRA) of 2021, which the CCMI research team has conducted annually since 1999).
Despite the challenges, CCMI says Little Cayman’s coral reefs continue to show resilience, especially within Marine Protected Areas (MPAs), proving the importance of local protective laws.
Positive results from CCMI surveys indicate an increase in overall fish density, biomass and species richness after 2016, an apparent ripple effect of improved local protections aimed at the recovery of the Nassau grouper population. This means we are seeing more fish, bigger fish and a greater diversity of species than in previous years. Major increases in 2020 and 2021 may be further influenced by COVID-19 and reduced overall activity on the reef.
CCMI survey data also shows that while fish biomass (total fish population weight) fluctuates from year to year, there is significantly higher biomass inside marine protected areas. (AMP) throughout these fluctuations. This suggests that while areas inside and outside MPAs are impacted by environmental change, this impact is mitigated inside MPAs, allowing more fish and larger fish to thrive. In 2021, fish biomass was 40% higher inside MPAs than outside.
For many years, CCMI researchers have observed a decline in grouper density (quantity of fish), despite areas of no-take at Nassau grouper spawning aggregations in season from 2003 until Cayman Islands to enact greater protections in 2016 aimed at restoring the population. Local protections include a general seasonal closure of the Nassau grouper fishery, catch limits, gear restrictions and size limits. The effects of these protections were reflected in the 2021 CCMI surveys, as the population density of grouper (all grouper species) continues to rebound.
Parrotfish density has increased by 47% between 1999 and 2021, which is also a positive indicator of reef health, as they are key algae-eating herbivores, competing for space on the reef. with coral. The effects are reflected in the general health of the reefs since 90% of the reefs studied were classified as “good” (40%), “good +” (40%) or “very good” (10%) . cent) state based on coral cover. This is an encouraging indicator, as fewer sites were rated as “fair” than in recent years, and no sites were rated as “poor”.
However, while coral cover remains relatively high, aided by recovering fish populations, data from the 2021 CCMI survey also demonstrates the vulnerability of corals to increasing threats from climate change and disease, as they have a slow growing and unable to move (as many fish can do to take refuge from stressful events), they are not able to bounce back or react as quickly to stressful events.
There was a species change of corals that dominate the reefs of Little Cayman, from the largest species of boulder corals to smaller, faster growing ones. This abandonment of boulder coral species reflects a trend observed throughout the Caribbean region. The 2021 surveys also recorded a 60% decrease in the size of the corals studied, reflecting the change in coral species. The shift from larger to smaller species impacts the overall function of coral reefs, as large boulder species build the massive reef structure that is so needed and provides the critical wave break that protects coral reefs. coasts of Little Cayman from storms, which are becoming increasingly powerful as a result of climate change.
The vulnerability of coral species on reefs is compounded by 2021 survey data which shows that new coral recruits, or baby corals, have declined by 83 percent from 2006 to 2021. In this framework, the researchers also find that among the species of recruits recorded, there are almost no Orbicella species recruits and not Montastrea Species recruits after 2017, both of which are important boulder corals. If the local adult population experiences a mortality event, such as bleaching or disease, low recruitment means coral reefs are unlikely to recover quickly.
Local protections and low human impact have undoubtedly shielded Little Cayman from the edge of global pressures that heavily affect reefs around the world; however, changes continue to occur that put the reefs at increasing risk. Understanding how low coral recruitment and declining coral size can be mitigated is crucial for coral reef ecosystem management. The resilience of coral cover and fish populations is good news that can largely be attributed to the success of MPAs and the protection of specific species in the Cayman Islands.
CCMI’s surveys of the Little Cayman Reefs indicate that with appropriate management policies, coral reefs may be able to recover and demonstrate resilience in the face of increasing pressures from regional and global threats. Studying coral resilience mechanisms is key to understanding how corals can survive under climate change and future threats.
For more information about CCMI, upcoming events, and how to help protect Cayman’s reefs, visit www.reefresearch.org.