Abstract
Caribbean coral reefs are in decline and the deployment of artificial reefs, structures on the sea bottom that mimic one or more characteristics of a natural reef, is increasingly often considered to sustain ecosystem services. Independent of their specific purposes, it is essential that artificial reefs do not negatively affect the already stressed surrounding habitat. To evaluate the ecological effects of artificial reefs in the Caribbean, an analysis was performed on 212 artificial reefs that were deployed in the Greater Caribbean between 1960 and 2018, based on cases documented in grey (n = 158) and scientific (n = 54) literature. Depending on the availability of data, reef type and purpose were linked to ecological effects and fisheries management practices around the artificial reefs. The three most common purposes to deploy artificial reefs were to create new dive sites (41%), to perform research (22%) and to support ecosystem restoration (18%), mainly by stimulating diversity. Ship wrecks (44%), reef balls© (13%) and piles of concrete construction blocks (11%) were the most-often deployed artificial reef structures and metal and concrete were the most-used materials. The ecological development on artificial reefs in the Caribbean appeared to be severely understudied. Research and monitoring has mostly been done on small experimental reefs that had been specifically designed for science, whereas the most commonly deployed artificial reef types have hardly been evaluated. Studies that systematically compare the ecological functioning of different artificial reef types are virtually non-existent in the Caribbean and should be a research priority, including the efficacy of new designs and materials. Comparisons with natural reef ecosystems are scarce. Artificial reefs can harbor high fish densities and species richness, but both fish and benthos assemblages often remain distinct from natural ecosystems. Studies from other parts of the world show that artificial reefs can influence the surrounding ecosystem by introducing non-indigenous species and by leaking iron. As artificial reefs attract part of their marine organisms from surrounding habitats, intensive exploitation by fishers, without clear management, can adversely affect the fish stocks in the surrounding area and thus counteract any potential ecosystem benefits. This study shows that over 80% of artificial reefs in the Caribbean remain accessible to fishers and are a risk to the surrounding habitat. To ensure artificial reefs and their fisheries do not negatively affect the surrounding ecosystem, it is imperative to include artificial reefs, their fisheries and the surrounding ecosystem in monitoring programs and management plans and to create no-take zones around artificial reefs that are not monitored.
Highlights
Since the 1970s, the amount of living coral cover on Caribbean coral reefs has been greatly reduced due to coral mortality caused by diseases (Gladfelter 1982; Aronson and Precht 2001), water pollution, hurricanes and periods with higher than average seawater temperature (Hughes 1994; Gardner et al, 2003; Jackson et al, 2014)
In the second half of the 20th century, observations of high fish densities on WWII wrecks resulted in an increase of artificial reef use in Japan and the USA (Lee et al, 2018) and increased fishing yields on these artificial reefs made the practice spread to the rest of the world (Lima et al, 2019)
The first record we found was an artificial reef made of 800 con crete construction blocks, which was deployed in the US Virgin Islands in 1960 for research purposes (Randall 1963)
Summary
Since the 1970s, the amount of living coral cover on Caribbean coral reefs has been greatly reduced due to coral mortality caused by diseases (Gladfelter 1982; Aronson and Precht 2001), water pollution, hurricanes and periods with higher than average seawater temperature (Hughes 1994; Gardner et al, 2003; Jackson et al, 2014). The first records of artificial reef use are more than 3000 years old (Riggio et al, 2000), they became common use in 18th century Japan (Lee et al, 2018) and spread to the USA and Europe in the 19th century (McGurrin et al, 1989; Fabi et al, 2011). Fish attraction was historically the main reason for artificial reef deployment (Polovina 1991), often to create new fishing grounds or to increase fishing efficiency (Lee et al, 2018), they were used for other purposes such as trawling obstacles for fisheries management and for coastal protection (Lima et al, 2019). The first record we found was an artificial reef made of 800 con crete construction blocks, which was deployed in the US Virgin Islands in 1960 for research purposes (Randall 1963)
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