Healthy Reefs

The CREWS provides CCMI with the opportunity to be at the forefront of coral reef science because it offers near real time information on the ocean environment around the robust reefs of Little Cayman. The project is led by the United States National Oceanographic and Atmospheric Administration (NOAA). CREWS gets its name from its success in modelling and alerting impacts on coral reefs from climate-related events such as, coral bleaching, seasonal upwelling, or approaching storms. This system is considered part of a NOAA Integrated Coral Observing Network (ICON) and is thus named ICON/CREWS.

The CREWS buoy system uses local information about weather and marine conditions that is continually gathered by a series of monitoring stations and buoys located across the Caribbean Sea as well as worldwide. The data is transmitted in real-time to NOAA for integration and analysis, while also being made available online to researchers, policy-makers, and to the public. ICON uses the data collected by CREWS in conjunction with satellite data and radar technologies to analyse and forecast regional oceanographic and atmospheric trends. The CREWS system has been successfully used in modeling and alerts of coral bleaching conditions both locally in the Cayman Islands and the Caribbean Sea. Over time, it is NOAA’s intent to expand the CREWS system by installing stations in more geographic regions and to further refine the systems capability to better predict the impact of climate patterns on coral reefs.

Originally installed in 2009, this monitoring location gave CCMI, the Cayman Islands, and the general public access to real-time weather information and records of local climate patterns over time. In October 2012, Hurricane Sandy unfortunately damaged CCMI’s monitoring system beyond repair. Almost one year later, a more rugged and robust monitoring buoy was installed in its place and remained in place until 2017, when recurring communications issues required it to be replaced.

Long Term Records to Strengthen Our Understanding of Coral Resilience

Coral reefs are the largest mass of construction workers on the face of the earth. They are natural architects in the shallow sea but only remain productive when juvenile corals are able to survive after recruitment onto the reef. At every dive location on the reef around Little Cayman, we see evidence of recruitment. This is a good sign for the future.

Using the AGRRA, Atlantic Gulf Rapid Reef Assessment protocol and collecting additional recruitment data, this project investigates the potential for juvenile corals to survive and replenish the local reefs. Results from this work will help generate an understanding of the mechanisms that are driving reef resilience.

AGRRA data on the benthic habitat and fish populations surrounding Little Cayman has been collected regularly since 1999. As CCMI researchers continue to collect this data annually, notes, reports, and peer reviewed journal articles are available online to scientists, policy-makers, and the general public. These surveys document patterns of local change over the last two decades and enable regional comparisons through the Healthy Reef Framework developed for evaluating the Mesoamerican Barrier Reef.

Key Results from the latest Technical Report (released 6 June 2020):

• There has been a gradual decline in coral cover in Little Cayman over the last 21 years, going from circa 24% to 20% coral cover. However, this change is not statistically significant (P = 0.092, R2 = 0.018; GLM). The slow rate of decline indicates that the reefs of Little Cayman are more resilient than reefs in other parts of the Caribbean where declines were rapid and reefs have not rebounded from global events (see Jackson et al. 2014).
• An overall coral cover of 20% is classified as “good” in terms of reef health. Over time, the health state in Little Cayman has fluctuated with an increasing number of sites classified as “poor” (5-10% coral cover) and fewer sites classified as “very good” (>30% coral cover). However, in 2019, none of the surveyed sites were “poor”, and the majority were either “good” (18-25%) or “good +” (25-30%), indicating a relatively stable reef system overall.
• Our results show that the composition of the coral community on the reef has changed over time, from reefs dominated by massive boulder corals, such as Orbicella spp, to smaller plating and branching corals such as Agaricia spp and Porites spp.
• Importantly, there was a significant trend of declining algal cover over the 21 years (P = 0.023, R2 = 0.041; GLM). This decrease in algal cover, again indicates a healthy reef that has not undergone a phase shift from coral to algae, as was previously documented on other reefs in the Caribbean (e.g. Carpenter 1990, Hughes 1994, Schutte et al. 2010, Jackson et al. 2014).
• In terms of fish communities, we found no significant trend in mean density (P = 0.373) or biomass (P = 0.795), suggesting that local regulations and marine protected areas are effectively maintaining fish populations.
• The density of all grouper species in the family Serranidae declined significantly over the 20 years (P = 0.009, R2 = 0.06; GLM), despite no change in mean biomass (P = 0.618, R2 = 0.002; Linear Regression), and no significant change in the average grouper size (P = 0.143, R2 = 0.019; GLM). The density of Nassau grouper, however, did not change over time (P = 0.143, R2 = 0.019; GLM), yet biomass increased significantly (P = 0.016, R2 = 0.089; GLM) as did the average fish size (P = 0.003 and R2 = 0.13; GLM).
• We found a significant trend of increasing parrotfish density over the 21 years (P = 0.043, R2 = 0.037; GLM), but no significant change in mean parrotfish biomass (P = 0.451, R2 = 0.005; GLM), which corresponds with a significant decrease in the average size of parrotfish (P < 0.001, R2 = 0.18; GLM). Thus, while the average number of parrotfish increased, the average size of each fish decreased, which may suggest an influx of juveniles into the community, indicative of a sustainable parrotfish population.
• Importantly, parrotfish density was found to positively correlate with coral cover (P < 0.05), indicating that sites with high densities of parrotfishes have higher percent coral cover. Likewise, overall algal cover was found to negatively correlate with overall herbivore density (P < 0.05), meaning that sites with higher densities of herbivorous fishes maintained lower percent cover of macro algae.
• Results from 21 years of AGRRA therefore indicate that whilst Little Cayman reefs are not immune to the impacts of local and global change, they have remained stable over time and appear to be more resilient than other Caribbean coral reef systems.

Full report available below.

2020- Coral Reef Resilience Over Two Decades at Little Cayman Island | Reef Report Card

2019- 20 Year Report on the Status and Trends of the Coral Reefs in the Cayman Islands 1999 – 2018

2015 – Project Overview

2013 – A Positive Trajectory for Corals at Little Cayman Island

2007 – Coral community decline at a remote Caribbean island: Marine no-take reserves are not enough

2003 – Status of coral reefs of Little Cayman, Grand Cayman and Cayman Brac