MSEL have investigated the competitive effects of macroalgae (Dictyota pulchella, Lobophora variegata, Halimeda opuntia and mixed algal communities) on coral growth, survival and fecundity. Fecundity was studied on colonies of the coral Montastraea annularis, while growth and survival were studied in Colpophyllia natans, Porites astreoides and Agaricia agaricites. We experimentally manipulated algal contact around the perimeter of M. annularis patches for the entire period of gamete development. Fecundity was measured as the diameter of eggs, the number of eggs per gonad and the number of gonads per polyp. We found that algal contact significantly reduced the diameter of eggs at both the coral-algal boundary and at the centre of coral patches. The presence of Dictyota spp. and a mixed algal community were shown to have more detrimental effects on egg diameter than L. variegata. Removal of algal contact immediately prior to gametogenesis increased the reproductive output of polyps directly adjacent to the cleared areas. In terms of growth and survival corals smaller than 10 cm in diameter were significantly more vulnerable to macroalgal competition. Furthermore, H. opuntia proved to have a more detrimental effect on C. natans, while A. agaricites resulted to be the best competitor against both H. opuntia and L. variegata.
Coral recruitment is critical to coral reef communities as it represents a crucial phase in the development of coral populations, important to the recovery of coral reefs affected by disturbance and mortality. Successful recruitment is important to the resilience of coral reefs, and degraded reefs often exhibit declining rates of coral recruitment through a poorly understood combination of reduced adult fecundity, decreased settlement, and higher rates of early mortality. Coral recruitment is a complex process involving gamete production, fertilisation, dispersal and development, settlement, early survival and growth. Colonisation of the benthos by invertebrates involves the three phases of (1) larval development, which includes planktonic dispersal, (2) testing of the benthos for microhabitat suitability, and (3) larval settlement on the substrate. Following larval settlement, coral spat exist as minute individuals for a period of time during which they are very difficult to detect by the observer and high mortality rates notoriously occur. Following settlement, recruitment itself is defined as the number of individuals passing from the settled phase to the stage when new members of the community become visible to be censused, after which time the individuals are commonly referred to as juveniles.
Sponges are well known because of the contribution to the functioning of coral reef ecosystems (i.e., bioerosion, competition, nutrient cycling, biodiversity, productivity). However, their role in the ecosystem may change as reef sustain greater levels of disturbance. Yet, how do sponges response to a number of perturbations and stressors, and moreover, how does this affect sponge-driven process in the ecosystem is poorly understood. MSEL is currently exploring at potential drivers on the structure of sponge population and communities (i.e., hurricanes, macroalgal competition and predation), looking at expanding our current knowledge on the ecosystem.