Chaves-Fonnegra, Andia

Climate change has intensified thermal anomalies in coral reef ecosystems, contributing to coral bleaching and decline. As corals die, reef fragmentation increases, and species interactions in the benthos change. However, it is unclear which competitive interactions may prevail and structure future reef ecosystems. The aim of this thesis was to evaluate the effect of thermal anomalies on coral reef benthic competitive interactions. Photoquadrats in southeast Florida reef sites were assessed over 15-years to generate interaction metrics and determine effects on hard coral survivorship. A state-transition model was created to predict the resultant community across 100 years with thermal scenarios concordant with the IPCC RCP 4.5 and 8.5. Interaction doubled across three thermal anomaly events and ended up mainly composed of pairwise examples between Dictyota, Halimeda, Niphates erecta, and Erythropodium caribaeorum. Century projections confirm that soft coral and sponge interactions will increase through thermal anomalies. The survival of hard corals was more successful when colonies were in permanent or intermittent interactions than when colonies were solitary (indirect interactions). Living hard corals were mostly found interacting with the macroalgae, Dictyota, and sponge Aplysina cauliformis, while corals that died were mainly in interactions with the soft coral E. caribaeorum, and sponges N. erecta, C. delitrix, D. anchorata, and Ircinia campana. Future reefs will be composed of more interactions between soft corals and sponges as thermal anomalies intensify, which will result in a patchier and flatter community.

Sponges (Phylum Porifera) are hardy organisms persisting and predicted to become more dominant world-wide under climate change scenarios. However, we lack baseline knowledge on sponge biodiversity in transitional areas (subtropical to warm-temperate) that are more susceptible to climate change such as The Indian River Lagoon (IRL) (estuary) and Saint Lucie Reef (northern most coral reef) ecosystems in south Florida. The aims of this master’s thesis are to 1) evaluate if sponge assemblages reflect the previously defined ecotone between subtropical and warm-temperate biomes in the IRL (Chapter one), 2) determine how porifera communities are associated to their respective environment (temperature, water velocity, photosynthetically active radiation, carbonate chemistry, and nutrients) in the IRL and St. Lucie Reef (Chapter two), and 3) establish a distribution baseline for future studies aiming to assess Porifera range shifts during climate change (Chapter one and two). Porifera biodiversity surveys across the IRL and Saint Lucie reef were carried out at different spatial and time scales. Environmental parameters (ocean acidification, temperature and eutrophication) were obtained and compared for sites in Fort Pierce Inlet and St Lucie Reef. Chapter one results show that sponge assemblages do not reflect the previously defined ecotone between subtropical and warm-temperate biomes in the IRL, instead they structure in relation to the inlets (distance from the inlet). The most diverse sponge assemblages are found in Sebastian, Fort Pierce, and Jupiter Inlets, and are significant different among habitats; oyster reefs host a unique assemblage of excavating sponges.