As all of you Caribbean fiswatchers know, hamlets are a group of colourful coral reef fish found throughout the Caribbean. Ten species of hamlet have been discovered and each can be easily recognized by its own distinct colour pattern. In some areas, as many as seven varieties can be found on a single reef. However, most hamlet species are only found at specific locations. The blue hamlet, for example, is found only in the Florida region. How these very different looking, yet very closely related species came to be has been a a subject of debate among scientists. Data collected by divers and snorkelers as part of the REEF Volunteer Fish Survey Project were recently used in a large analysis to better understand the patterns of evolution in these and other marine fishes. Dr. Ben Holt from University of East Anglia (UK) and his colleagues Simon Fraser University in Canada recently published their findings in the scientific journal Global Ecology and Biogeography. 

It had previously been believed that these different species of hamlets evolved because of geographical separation. For example, it was thought that falling sea levels in the past could have divided the original species. Then, when levels increased, the differently evolved species were thrown back together. The new study found little evidence for this theory and instead suggests that hamlet color varieties could have evolved regardless of any physical separation. Using thousands of underwater surveys made by REEF volunteers, the researchers analysed distributions of the ten different hamlet species. They found that even widespread hamlet species are not found everywhere, and identified high density hotspots for each species. Because different species hotspots overlap and many species have more than one hotspot, the results do not support the theory that hamlets originated independently when they were geographically separated in the past. The research also showed how ecological factors, such as competition for food or habitat, may influence how different hamlet species co-exist. 

"Our findings suggest that ecology may better explain the evolution of hamlets than geographical separation," said lead author Dr Ben Holt of UEA's School of Biological Sciences. "Many scientists believe hamlets are beginning to evolve into a new species and this latest discovery will shed light on this process."

Ben goes on to say this about REEF volunteers and the value of their data in this study: "The success of this study is a great example of the value of citizen science and, specifically, the REEF volunteer survey project. It has been known for a long time that hamlets have distinct geographical distributions, and that this must be a clue to the origin of the many different colour types in this group. However, attempts by scientists to investigate these patterns are unavoidably held back by the huge scale of the costs and time required to survey a meaningful number of locations across the Caribbean. We are therefore extremely grateful to REEF and all the volunteer data collectors for providing this invaluable dataset. By analysing these data, we were able to look, not just at hamlet distributions but also at densities and at how different hamlets coexist on individual reefs, across the whole of the Caribbean. This has allowed us to draw some exciting conclusions about the hamlet system and I’m sure that there will be many more interesting discoveries regarding this group in the future. It is still very unclear how new species arise in the marine environment and the hamlet group represents one of the best opportunities to study these processes. Such work is important for the advancement of our knowledge of marine life, and consequently for our ability to value and protect it. This study represents a step towards understanding the evolution of the hamlet group and it would not be possible without the REEF volunteers. I would like to say thank you to all of them. Keep up the good work and, above all, keep having fun!"

The full citation of the paper is Holt, B., I Cote, and B Emerson (2010). Signatures of speciation? Distribution and diversity of Hypoplectrus (Teleostei: Serranidae) colour morphotypes. Global Ecology and Biogeography (published online 23 April 2010).

To see this and other scientific papers that have been published using REEF data, check out thePublications page on the REEF.org website here.