I arrived in Jamaica over a week ago with colleagues from Stony Brook University to continue our study investigating the effects of coastal development on adjacent coral reefs. The working hypothesis is that sediment and nutrient run-off from the land is higher around resorts and hotels than along coastlines that are covered by forest and scrub. High levels of sediment can smother corals and sponges, while increased nutrients promotes the growth of algae over coral. We are exploring if this actually happens by comparing the growth, distribution and recruitment of sponges, corals and other benthic organisms between an impacted location and two control, or non-impacted, locations.
The results so far have been very interesting. More sponges, and a greater diversity of species, are found on coral reefs located away from coastal development. In a 20 m2 area, for example, there can be over 150 sponges comprised of 40+ species in a control location, but less than 30 sponges consisting of about 10 species in the impacted location. Big difference.
For the recruitment experiment we measure the recruitment of sponges, corals and other organisms on terracotta tiles that have been anchored to the reef; terracotta tiles, 10×10 cm in size, are used as a substitute for reef substrate and means that we can remove and replace them to look at any temporal patterns without damaging the actual reef.
Again the results have been interesting but in a different way. Coral reefs on the northern coast of Jamaica are dominated by sponges while corals are often small and uncommon, so you would expect a lot of sponges recruiting to the tiles and few corals. But the reverse is true. Most tiles have about 20 very small corals (3 mm across) and no sponges. Possibly sponges release larva at a different time (these tiles were in the water from January to August), they may have naturally low levels of recruitment, or rely on fragmentation from predation or storm damage to generate and disperse new sponges. This recruitment study will continue for another 2 years with new tiles placed onto the reef every 6 months.
The growth study, like the other studies, is on-going and we will not have any results back for several years. So, stay-tuned!