Presence of Symbiodinium spp. in macroalgal microhabitats from the southern Great Barrier Reef

Coral reefs are highly dependent on the mutualistic symbiosis between reef-building corals and dinoflagellates from the genus Symbiodinium. These dinoflagellates spend part of their life cycle outside the coral host and in the majority of the cases have to re-infect corals each generation. While considerable insight has been gained about Symbiodinium in corals, little is known about the ecology and biology of Symbiodinium in other reef microhabitats. This study documents Symbiodinium associating with benthic macroalgae on the southern Great Barrier Reef, including some Symbiodinium that are genetically close to the symbiotic strains from reef-building corals. It is possible that some of these Symbiodinium were in hospite, associated to soritid foraminifera or ciliates; nevertheless, the presence of Symbiodinium C3 and C15 in macroalgal microhabitats may also suggest a potential link between communities of Symbiodinium associating with both coral hosts and macroalgae

The promiscuous larvae: flexibility in the establishment of symbiosis in corals

Coral reefs thrive in part because of the symbiotic partnership between corals and Symbiodinium. While this partnership is one of the keys to the success of coral reef ecosystems, surprisingly little is known about many aspects of coral symbiosis, in particular the establishment and development of symbiosis in host species that acquire symbionts anew in each generation. More specifically, the point at which symbiosis is established (i.e., larva vs. juvenile) remains uncertain, as does the source of free-living Symbiodinium in the environment. In addition, the capacity of host and symbiont to form novel combinations is unknown. To explore patterns of initial association between host and symbiont, larvae of two species of Acropora were exposed to sediment collected from three locations on the Great Barrier Reef. A high proportion of larvae established symbiosis shortly after contact with sediments, and Acropora larvae were promiscuous, taking up multiple types of Symbiodinium. The Symbiodinium types acquired from the sediments reflected the symbiont assemblage within a wide range of cnidarian hosts at each of the three sites, suggesting potential regional differences in the free-living Symbiodinium assemblage. Coral larvae clearly have the capacity to take up Symbiodinium prior to settlement, and sediment is a likely source. Promiscuous larvae allow species to associate with Symbiodinium appropriate for potentially novel environments that may be experienced following dispersal

Ocean acidification influences the biomass and diversity of reef-associated turf algal communities

Projected ocean acidification will have a detrimental impact on coral reef ecosystems, where fleshy algae are expected to replace corals. Of particular importance to reef ecosystems are fleshy turf algal communities, which have the potential to overgrow corals; few studies have investigated the community structure and diversity of turfs to climate change. Here, we assessed the response of reef-associated turf algal communities from the Great Barrier Reef, Australia to three levels of ocean acidification. Biomass of turf communities was positively affected by increases in carbon dioxide (CO2), where turf communities grown under high CO2 had the greatest biomass. No effect of CO2 was found on mean turf organic content or genus richness. By contrast, turf community evenness and diversity (H′) increased under medium and high CO2 treatments. Our results indicate that increased turf growth under high CO2 will aid the overall expansion and growth of fleshy macroalgae in coral reef ecosystems, as opportunistic algae may have an advantage over other reef-associated species. Changes in turf community diversity will help provide insight into how macroalgal communities may be structured in the future, highlighting genera primed to take advantage of the changes in ocean chemistry associated with ocean acidification.No Full Tex