Abstract:
Concerns relating to continued habitat degradation in the coastal areas around Anguilla, combined with the recognition that ecological data is essential before effective management decisions can be made, led to the initiation of the Anguilla Marine Monitoring Programme in 2007. Now in its tenth year, surveys are undertaken at fifteen sites around the island that collect a suite of data on fish, plants, algae, corals, and other invertebrates, and represents the first time series dataset for the island. This report examines five primary variables identified as crucial when establishing habitat health in both coral reef and seagrass areas: coral cover; algae cover; fish species diversity; overall fish abundance; and size of commercially and ecologically important fish families. A small number of other variables are also examined as related to habitat health. Over the study period, an 11% drop in coral cover was recorded, with a mean value across all sites combined falling from 5.6% to 5.1%, and algae cover increased by 9.5%, from 14.2% to 15.0%. The most common coral species was Porites astreoides, although it has decreased in frequency by 45% since this work began. The massive reef building species, Acropora palmata today only accounts for 2% of coral colonies recorded. Fish species number decreased across all sites by 21% with a mean count of 48 at each site at the beginning of the survey, dropping to 38 by 2016. Fish abundance also decreased with a reduction of 27% from a mean of 621 individuals counted per survey to 451. Similarly, commercially and ecologically important fish family sizes decreased by 24% over the study period, with a mean of 10.6 cm lowering to 8.1 cm. This trend in fish size could be seen amongst all families analysed, with Acanthuridae, Scaridae and Serranidae decreasing by 31% (9.5 cm to 6.5 cm), 9% (11.5 cm to 10.4 cm), and 54% (17.5 cm to 8.1 cm) respectively. In terms of seagrass sites, overall plant/algae cover increased by 15% from 66.4% to 78.2%, although this was seen to be due primarily to increases in the invasive seagrass Halophila stipulacea and weedy algal species Dasycladus vermicularis. Percentage cover of the native seagrass Thalassia testudinum declined by 21% from 56.2% to 44.6%. These results illustrate that Anguilla’s coastal coral reef habitat are in an increasingly poor state of health, having been in continual decline since the 1970’s. Seagrass beds in Anguilla are also in decline, although currently still in a relatively healthy state. As many of the stressors influencing habitat health are regional in nature, management measures are unlikely to be able to reverse these negative trends, although local mitigation measures may help to slow them. It is recommended that existing marine parks be used to preserve relic populations, with restrictions applied to extractive and/or damaging practices. It is also recommended to introduce minimum landing sizes for key reef fish species, regulation of all septic tanks in coastal areas, introduction/enforcement of development setbacks, and minimization of any sources of terrestrial runoff. If marine habitat health continues to decline, beach erosion will increase, coastal fisheries will collapse, and almost all livelihoods around the island will be negatively impacted.
