Preview

PDF 4Mb

Ocean acidification is a threat to marine ecosystems globally. In shallow-water systems, however, ocean acidification can be masked by benthic carbon fluxes, depending on community composition, seawater residence time, and the magnitude and balance of net community production (NCP) and calcification (NCC). Here, we examine how six benthic groups from a coral reef environment on Heron Reef (Great Barrier Reef, Australia) contribute to changes in the seawater aragonite saturation state (Ωa). Results of flume studies using intact reef habitats (1.2 m by 0.4 m), showed a hierarchy of responses across groups, depending on CO₂ level, time of day and water flow. At low CO₂ (350-450 μatm), macroalgae (Chnoospora implexa), turfs and sand elevated Ωa of the flume water by around 0.10 to 1.20 h^-1 - normalised to contributions from 1 m² of benthos to a 1 m deep water column. The rate of Ωa increase in these groups was doubled under acidification (560-700 μatm) and high flow (35 compared to 8 cm s ^-1). In contrast, branching corals (Acropora aspera) increased Ωa by 0.25 h^-1 at ambient CO₂ (350-450 μatm) during the day, but reduced Ωa under acidification and high flow. Nighttime changes in Ωa by corals were highly negative (0.6-0.8 h^-1) and exacerbated by acidification. Calcifying macroalgae (Halimeda spp.) raised Ωa by day (by around 0.13 h^-1), but lowered Ωa by a similar or higher amount at night. Analyses of carbon flux contributions from benthic communities with four different compositions to the reef water carbon chemistry across Heron Reef flat and lagoon indicated that the net lowering of Ωa by coral-dominated areas can to some extent be countered by long water-residence times in neighbouring areas dominated by turfs, macroalgae and carbonate sand.

Item Type:	Refereed Article
Keywords:	acidification, aragonite, benthos, carbon flux, community composition, coral reef, dominance, hierarchical system, marine pollution, residence time, saturation, seawater, water column, water flow
Research Division:	Biological Sciences
Research Group:	Ecology
Research Field:	Marine and estuarine ecology (incl. marine ichthyology)
Objective Division:	Environmental Management
Objective Group:	Marine systems and management
Objective Field:	Marine biodiversity
UTAS Author:	Tilbrook, B (Dr Bronte Tilbrook)
ID Code:	118976
Year Published:	2013
Web of Science® Times Cited:	55
Deposited By:	Zoology
Deposited On:	2017-07-24
Last Modified:	2017-10-16
Downloads:	143 View Download Statistics