Data from marine citizen scientists reveal how fish biodiversity patterns across the Caribbean are linked to sea temperature.

A study published today in the Journal of Biogeography has utilised the power of the people in the form of “citizen science” to produce a new map of marine fish biodiversity across the Caribbean and tropical western Atlantic.

A marine citizen scientist collecting data for the REEF fish survey project. Credit Jeffrey D Haines.

The work, performed by scientists from the Center for Macroecology, Evolution & Climate in Denmark and the Marine Biological Association, studied a huge data base collected by volunteer SCUBA diving enthusiasts to produce the map and find that fish biodiversity is strongly linked to sea temperatures. However, results also show that while fish biodiversity is higher in warmer waters, the very hottest sites in fact have fewer species than sites with intermediate temperatures, something not shown before in previous studies. These results will be of concern given the rising water temperatures in the region.

This ground-breaking research is based on data collected by thousands of marine citizen scientists working within the Reef Environmental Education Foundation’s (REEF, www.reef.org) SCUBA diving based fish survey project. These volunteers have been recording data on the fish species they see during dives for over 25 years and inputting their records into REEF database. This work has enabled researchers to compare different coral reefs and other coastal sites across this tropical region for the first time. The resulting map shows high diversity areas in the Dutch Antilles and the Florida Keys, whereas relatively few species were found in Bermuda, the Gulf of Mexico and Northern Florida.

In order to examine potential explanations for these patterns the research team looked at potential environmental factors that might be associated with them, including natural factors, such as temperature, salinity and depth, and human-based factors, such as population density. Analysis proved the number of fish species recorded at a site could be predicted by how warm the water was at that site, and, to a lesser extent, how deep the site was. While a positive relationship between temperature and biodiversity has been demonstrated in previous research of global patterns, the fine scale detail provided by this huge citizen science dataset facilitated the discovery of important details of this relationship within the wider Caribbean. Senior author Dr Ben Holt said:

"Rather than being a simple relationship, whereby warmer waters equal more fish species, the relationship seen in the REEF data was “hump-shaped”; warmer sites tend to have more species up to an optimal temperature of around 27oC and then the hottest sites become less diverse.”

Further analysis suggests that this result may be partly driven by a fewer species being adapted to the warmest temperatures. The findings of this study will inevitably be of concern given the fast rising temperatures of Caribbean water but the research team urge caution extrapolating their results based on future climate predictions. Dr Holt said:

“The efforts of citizen scientists have provided an invaluable opportunity to study spatial patterns of marine biodiversity. Their data suggest that the hottest reefs are not the most biodiverse but it does not necessarily mean that the diversity of any particular site will change as seawater temperatures change. This is an important area for further research given the importance of these habitats within the Caribbean and around the world.”

Dr Holt is currently based at the Marine Biological Association of the UK in Plymouth and can be contacted on 0786 6862865 or benhol@mba.ac.uk
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May 1, 2017 By guba