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Fatty acids (FA) play a vital role in coral physiology, metabolism and stress resistance. Optimal health requires a balance of fatty acids, and more specifically essential polyunsaturated fatty acids (PUFA), for efficient biochemical and physiological functioning. Therefore, it is necessary to fully assess and evaluate the viability of FA as biomarkers for monitoring the health of coral populations. This study explores seasonal and spatial variation in the abundance of 17 FA in the coral Acropora tenuis, along two water quality gradients on the central Great Barrier Reef. Ratios of key FA varied similarly along the two water quality gradients and were highest in corals from comparatively good water quality conditions. Strong differences in PUFA composition were found between wet and dry seasons, with high percentage n-3 PUFA defining the dry seasons (June 2013 and October 2013) and high percentage n-6 PUFA defining the wet seasons (February 2013 and 2014). Saturated FA and monounsaturated FA concentrations varied with season, positively correlated with Symbiodinium density, and had highest concentrations in corals exposed to relatively poor water quality. Overall, results demonstrate that essential FA and their derived ratios support FA as a potential indicator of coral holobiont health; however, strong seasonal variation may negate FA and their derived ratios as water quality indicators. [ABSTRACT FROM AUTHOR]

Outbreaks of the crown-of-thorns seastar (CoTS) represent a major cause of coral loss on the Great Barrier Reef. Outbreaks can be explained by enhanced larval survival supported by higher phytoplankton availability after flood events, yet little is known about CoTS larvae feeding behaviour, in particular their potential for selective feeding. Here, single- and mixed-species feeding experiment were conducted on CoTS larvae using five algae (Phaeodactylum tricornutum, Pavlova lutheri, Tisochrysis lutea, Dunaliella sp. and Chaetoceros sp.) and two algal concentrations (1000 and 2500 algae.mL-1). Cell counts using flow-cytometry at the beginning and end of each incubation experiment allowed us to calculate the filtration and ingestion rates of each species by CoTS larvae. In line with previous studies, CoTS larvae ingested more algae when the initial algal concentration was higher. We found evidence for the selective ingestion of some species (Chaetoceros sp., Dunaliella sp.) over others (P. lutheri, P. tricornutum). The preferred algal species had the highest energy content, suggesting that CoTS selectively ingested the most energetic algae. Ultimately, combining these results with spatio-temporal patterns in phytoplankton communities will help elucidate the role of larval feeding behaviour in determining the frequency and magnitude of CoTS outbreaks. [ABSTRACT FROM AUTHOR]

The reduction in benthic light from natural sediment resuspension events, dredging activities and clouds was quantified over multiple time periods (days to weeks) from a 3-year in-situ field study in the inshore turbid-zone coral communities of the Great Barrier Reef. The results were then used to examine the tolerance levels of three coral species and a sponge to light reduction and associated changes in spectral light quality (in conjunction with elevated sediment concentrations) in a 28-day laboratory-based study. All species survived the exposures but sub-lethal responses involving changes in pigmentation, lipids and lipid ratios were observed. A pocilloporid coral was the most sensitive taxon, with a 28-d EC10 value for bleaching (dissociation of the symbiosis) of 2.7 mol photons m2 d−1. The possibility of such light reduction levels occurring naturally and/or during maintenance dredging activities was then examined using the 3-year in-situ field study as part of a risk assessment. • Inshore corals naturally experience periods of low light impacting their physiology. • Sensitive pocilloporid corals could potentially be used as an indicator of low light effects. • Dredging programs should include measurements of light availability as a key pressure-parameter. [ABSTRACT FROM AUTHOR]