The invertebrate creatures that life on the coral reefs are in integral part of the vast and complicated ecosystem that has been referred to as the rainforest of the oceans. There is much about these ecosystems that we do not understand, and compiled with the complicated effects of human impact reefs makes it even more difficult to understand. However, after compiling years of data and the results inferred, it has been determined that there are key indicator species that can be used to determine the health of a reef. Almost as one would do with a canary in a mine shaft.
The species that have been determined by Reef Check to be indicator organisms based on economic (harvested for the aquarium trade) and ecological (balancing the algal growth) value are;
1) Banded coral shrimp (Stenopus hispidus)
2) Diadema urchins
3) Pencil urchin (Eucidras spp.)
4) Collector urchin/sea egg (Tripneustes sp.)
5) Triton (Charonia variegta)
6) Flamingo tongue (Cyphoma gibbosum)
7) Georgonian (sea fan, sea whip)
8) Lobster (Palinuridea)
While in our reef ecology class we reviewed and studied an article that studied and almost certainly concluded that the diadema (black spine) urchin was not only integral, but perhaps the most important, or key stone, invertebrate species within the coral reef ecosystem. Following a mass die out of diadema (aprox 95%) in 1984, the increase of alga was almost instantaneous. However, since the return of the diadema in recent years (since the mid 90s) they greatly reduced microalgal (from >60% to <5%) which in turn increased coral growth. The study was conducted throughout the Caribbean, but the discovery of the impact of the diadema was a place called Dairy Bull, in Jamaica. It was here that there as actually been an increase in coral cover in the past two decades (in vast contrary to the rest of the Caribbean), almost 100% more living coral and 90% less algal cover then it did in 1995. This coral growth is occurring even while overfishing is still a problem. This phase shift in coral growth appears to always be preceded by the recovering and increased population of the diadema urchin.
On the first dive located at, Buena Vista, we discovered invertebrate species in the low single digits only. This had also been a trend in most of the dive sites we had been to prior to our Reef Check dives. In addition to the lack of invertebrates, their was large amounts of coral disease and bleaching. Their was a large amount of algal proliferation, as well as a great over abundance of georgonians. The site just looked sick.
In contrary, the second dive site, Coral gardens, looked radically healthier. The amount of diadima urchins was around 50 and pencil urchins was even more then that. Also, reef urchins, which are not counted by Reef Check would have easily surpassed 200 if they had been counted. There were more flamingo tongues, and even two collector urchins, the georgonian count was also much lower. The coral substrate itself was vastly more abundant and disease and bleaching was far less prevalent. Also, there was significantly less algal proliferation. Both sites are legally allowed to be fished and the species discovered at each site were about even.
With out conducting a purely scientific study we can not make any fact based conclusions. However, from the data we gathered and what we were able to see just from being there supports the findings of the article we studied in class and the study it was based on. The diadema urchins, and other herbivores are indeed a keystone species. They are integral to the promotion of of healthy coral and increased coral growth. In addition to this, what we observed at another site, Hol Chan, also supports the article. While not a Reef Check site (so we did not study, just notice and observe), it is protected from fishing, which means far greater number of fish species. However the overall health of the site was less the that of Coral Gardens, and in parallel to that the amount of diadema we noticed was far less.
The coral reefs are an incredibly complex biosphere, and the more we study the more we learn. Reef Check, and the observations we make while conducting it, is an invaluable asset into this learning process. Just seeing that the two locations we studied were so different and the species we found in each site is an enormous help. The fact that what we found supports conclusions by other scientific data is large step forward in the understanding of healthy reefs. Hopefully, with time , the damage that has been done to the reefs can be stopped and the health of these underwater biosphere can be returned to their natural unparalleled state of beauty.