Many factors have been related to the deterioration of Caribbean coral reefs. Among those factors, about 35 years ago a disease known as "white-band" almost drove two of the most prominent corals to extinction: Acropora palmata and A. cervicornis.
Until the 1980s, stony corals clearly dominated the reef landscape, and bioeroding sponges of the genus Cliona were less than rare organisms. Five species of those sponges simultaneously incrust and excavate coralline substrates, and are capable of killing corals in the process. In 2000 we started a series of investigations to:
a) reconstruct the most likely scenario of the colonization of the reef by these sponges,
b) describe the mechanisms of interaction between sponges and other sessile organisms,
c) evaluate the effect of that interaction in the composition and structure of the reef landscape, and
d) evaluate differences in the dynamic of this phenomenon in the short, medium and long term.
To achieve these goals, we marked and monitored coral colonies in interaction with clionas, we studied the distribution and abundance of these sponges in selected reefs, and we performed experiments to determine some details of the physical and chemical processes operating in the sponge-coral interaction. Data collected so far suggest the following scenario: after acroporids die-off due to the disease, two of the clionid sponges took advantage of the liberated coralline substrate and have since been progressively increasing their abundance in the reefs. Clionas undermine and erode the coral exoskeleton, killing the living coral tissue in the process, apparently using allelopathic chemicals. Moderately polluted waters seem to favour growth and abundance of some of these sponges, while changes in temperature seem to affect others.
Although the short-term dynamics of these interactions showed an aggressive advance of the sponges at the expense of corals, over time this overtake slows down and sponges might retreat or die. Eventually, when there is no more adequate coralline substrates available, or when most of them are colonized by other organisms, the process reaches a certain stability. However, in the medium term, corals are not capable to regain the space lost to the sponge, and wherever the sponges retreat or die algae flourish. Besides dispersed by sexual reproductive events, some of these sponges can also colonize other sectors of the reef, by means of being transported in coral fragments during storms. Some of our initial hypothesis were confirmed, while others had to be reformulated. The dynamics of the interactions between clinoid sponges and stony corals on a given reef depends on the time such interactions have been taking place.
ABOUT THE SPEAKER:
Mateo López-Victoria is an Associate Professor from Pontificia Universidad Javeriana (Colombia). He is a marine and island ecologist whose research primarily focuses on ecological processes on coral reefs (i.e., competition for space, population dynamics, structure of reefs under sub-optimal conditions). His current research projects are in the fields of conservation and restoration, combining scientific and engineering methods.
Marine Biologist – Universidad del Valle (Cali, Colombia)
Magister Scientiae in Marine Biology – Universidad Nacional de Colombia
Dr.rer.nat. in Biology – Justus-Liebig University (Giessen, Germany)
Currently Associate Professor, Biology Program – Conservation & Restoration, Department of Natural Sciences and Mathematics, Pontificia Universidad Javeriana – Cali (Colombia)