Interactive climate change and runoff effects alter O<sub>2 fluxes and bacterial community composition of coastal biofilms from the Great Barrier Reef

Abstract

Global (i.e. ocean warming) and local (i.e. land runoff) anthropogenic disturbances affect coastal coral reefs worldwide. Terrestrial runoff, leading to reduced light and increased nutrient availability, may have interactive effects with ocean warming in promoting shifts in benthic communities. Because microbial biofilms rapidly reflect environmental changes, we investigated the quantitative (C, N and chlorophyll a contents) and qualitative (microbial community composition) parameters and metabolic responses (O 2 fluxes) of biofilms established on glass slides to combinations of manipulated water temperatures (26, 29 and 31°C) ) in a 28 d flow-through aquarium experiment. The findings revealed that, independent of light availability, a temperature of 31°C significantly decreased the 24 h net O 2 production and all of the quantitative parameters. Under high light, additive effects of 31°C and 1.4 µM nitrate reduced the 24 h net O 2 production. Terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes showed light-independent temperature-induced microbial community shifts driven by increases in the relative abundance of Oceanospirillum (Gammaproteobacteria) and decreases of Cyanobacteria. The relative abundances of diatom plastids increased in response to elevated nitrate only in high-lightexposed biofilms. Overall, high temperatures altered microbial biofilm community composition, biomass and productivity. Under predicted near-future inner reef scenarios (low light and high nitrate availability), biofilms become light-limited through sedimentation, while outer (high light and low nitrate availability) inshore reef biofilms remain nitrate-limited. Understanding the interactive effects of environmental changes on microbial biofilm communities may contribute to bioindicator development and improved coastal management strategies for coral reefs. Coral reefs harbour abundant microorganisms that predominantly exist as surface-attached communities (Costerton et al. 1995, Crump et al. 1998, Teske & Wooldridge 2001. Surface-colonising biofilms are complex communities comprising macromolecules and microorganisms embedded in an extracellular polymeric matrix (Mihm et al. 1981). These highly dynamic microbial biofilm communities respond rapidly to and are integrative of changing ambient environmental conditions (Paerl & Pinckney 1996, Snyder et al. 2005. Microbial biofilm communities also contribute significantly to biogeochemical nutrient cycling in aquatic ecosystems, such as coral reefs (Battin et al. 2003), and influence the settlement and metamorphosis of important reef building organisms, such as corals, therefore affecting the establishment, recovery and resilience of coral reefs (Wieczorek & Todd 1998, Webster et al. 2004). The immense surface area available for biofilm colonisation and development highlights the important contribution of biofilms to coral ecosystem functioning.Coral bleaching is promoted by increased SST (Hoegh-Guldberg 1999), and these effects may be exacerbated by ele...

Terrestrial Runoff Controls the Bacterial Community Composition of Biofilms along a Water Quality Gradient in the Great Barrier Reef

“…Our findings suggest that the parameters Chl a and DOC, both found at high concentrations inshore during the wet season, were the main drivers in spatiotemporal bacterial community shifts. This is in concordance with previous studies on biofilms from local aquaria studies (53) and midshelf reefs from the GBR (46) and temperate marine bacterioplankton (16,19,23).…”

“…Several microbial bioindicator studies repeatedly reconfirmed the aforementioned phylogenetic groups with similar responses (24,(51)(52)(53). Of particular relevance were the decreasing relative abundance of Alphaproteobacteria (mostly Roseobacter) and the concomitant increase in Bacteroidetes (mostly Flavobacteriaceae) detected in biofilms in response to increased water temperature (47,53), partial CO 2 pressure (pCO 2 ) (51), and nitrate (53).…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…Recently, it was shown that the abundance of surface-associated MRC bacteria is decreased while that of Bacteroidetes is increased in response to increases in environmental temperature or elevated partial CO 2 pressure (pCO 2 )-induced ocean acidification (322,324). Similarly, the abundance of planktonic Bacteroidetes also increases in response to increased temperature and/or CO 2 content (and thus decreased pH) in both mesocosms and natural seawater environments (850)(851)(852).…”

“…Environmental factors play important roles in determining microbial surface colonization events (47,60,(322)(323)(324). In general, the interaction of microbial cells with the substratum surface under specific physicochemical and nutritional conditions at the seawater-surface interface likely contributes substantially to the initiation and success of microbial surface colonization in marine environments.…”

Calcareous green alga H alimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps

“…After 3 h incubation under ambient light, incubation chambers were retrieved and a water subsample was directly analyzed for TA (as described above). Oxygen concentration was determined in each incubation chamber including two blank incubations per treatment (to correct for seawater production/respiration) with a hand-held dissolved oxygen meter (HQ30d, Hach) as described elsewhere (Uthicke and Fabricius 2012;Witt et al 2012). Light intensities of incubation conditions were recorded by two light loggers (Odyssey, New Zealand) each at control and seep site.…”