Spatial patterns of microbial communities across surface waters of the Great Barrier Reef

Pedro R Frade,David G Bourne,Camille Mellin,Nicole S Webster,Bettina Glasl,Ester A Serrão,Samuel A Matthews,Kennedy Wolfe,Peter J Mumby

doi:10.1038/s42003-020-01166-y

Abstract

Microorganisms are fundamental drivers of biogeochemical cycling, though their contribution to coral reef ecosystem functioning is poorly understood. Here, we infer predictors of bacterioplankton community dynamics across surface-waters of the Great Barrier Reef (GBR) through a meta-analysis, combining microbial with environmental data from the eReefs platform. Nutrient dynamics and temperature explained 41.4% of inter-seasonal and cross-shelf variation in bacterial assemblages. Bacterial families OCS155, Cryomorphaceae, Flavobacteriaceae, Synechococcaceae and Rhodobacteraceae dominated inshore reefs and their relative abundances positively correlated with nutrient loads. In contrast, Prochlorococcaceae negatively correlated with nutrients and became increasingly dominant towards outershelf reefs. Cyanobacteria in Prochlorococcaceae and Synechococcaceae families occupy complementary cross-shelf biogeochemical niches; their abundance ratios representing a potential indicator of GBR nutrient levels. One Flavobacteriaceae-affiliated taxa was putatively identified as diagnostic for ecosystem degradation. Establishing microbial observatories along GBR environmental gradients will facilitate robust assessments of microbial contributions to reef health and inform tipping-points in reef condition.

Highlights

Microorganisms are fundamental drivers of biogeochemical cycling, though their contribution to coral reef ecosystem functioning is poorly understood
Modelled estimates of the environmental conditions of surface seawater retrieved from the eReefs hydrodynamic and biogeochemical model (GBR1, https://research.csiro.au/ereefs/models/modeloutputs/gbr1/) for the microbial case study (n = 37) and Long-Term Monitoring Program (LTMP) (n = 109) sites, covered 16 environmental variables known as potential drivers of microbial community variation
Organic and inorganic nutrients decreased in concentration with increasing distance from the shore (Fig. 2 and Supplementary Fig. 1; inshore macroalgae communities (In-MA) and In-Porites > Mid-Mixed and outershelf tabular and corymbose hard coral (Out-Tab) > Out-Soft and Out-Digit)

Summary

Introduction

Microorganisms are fundamental drivers of biogeochemical cycling, though their contribution to coral reef ecosystem functioning is poorly understood. Protection from fishing has led to improved reef health through the promotion of microbial diversity as opposed to the growth and rapid development of opportunistic microbial pathogens in reefs open to fishing pressures[20] These findings were validated in a field experiment simulating overfishing and nutrient pollution, which interacted with sea surface temperatures to drive changes in coral microbiomes and an increase in coral mortality[21]. The health and condition of corals, and resilience of reefs to environmental stressors more broadly, is inherently linked to microbial functioning in these ecosystems Pressures such as overfishing and nutrient pollution can contribute to the top down and bottom up processes that drive phase-shifts from coral-dominated to macroalgaldominated reef ecosystems[22,23]. Positive microbial responses to the photosynthates leached from algae may increase the vertical attenuation of light, thereby suppressing coral calcification and elevating stress on the coral[28]

Methods

Results

Conclusion