Metagenomics of Coral Reefs Under Phase Shift and High Hydrodynamics.

Pedro Milet Meirelles,Gilberto Menezes Amado-Filho,Sayaka Mino,Eduardo Siegle,Ronaldo Bastos Francini-Filho,Luciana Leomil,Diogo A Tschoeke,Ana Carolina Soares,Fabiano L Thompson,Luciana Reis Appolinario,Renato Tenan De Barros Almeida,Tomoo Sawabe,Paulo S Salomon,Isao Kudo,Ricardo Kruger,Louisi Oliveira,Rodrigo Leão De Moura,Cristiane C Thompson

doi:10.3389/fmicb.2018.02203

Abstract

Local and global stressors have affected coral reef ecosystems worldwide. Switches from coral to algal dominance states and microbialization are the major processes underlying the global decline of coral reefs. However, most of the knowledge concerning microbialization has not considered physical disturbances (e.g., typhoons, waves, and currents). Southern Japan reef systems have developed under extreme physical disturbances. Here, we present analyses of a three-year investigation on the coral reefs of Ishigaki Island that comprised benthic and fish surveys, water quality analyses, metagenomics and microbial abundance data. At the four studied sites, inorganic nutrient concentrations were high and exceeded eutrophication thresholds. The dissolved organic carbon (DOC) concentration (up to 233.3 μM) and microbial abundance (up to 2.5 × 105 cell/mL) values were relatively high. The highest vibrio counts coincided with the highest turf cover (∼55–85%) and the lowest coral cover (∼4.4–10.2%) and fish biomass (0.06 individuals/m2). Microbiome compositions were similar among all sites and were dominated by heterotrophs. Our data suggest that a synergic effect among several regional stressors are driving coral decline. In a high hydrodynamics reef environment, high algal/turf cover, stimulated by eutrophication and low fish abundance due to overfishing, promote microbialization. Together with crown-of-thorns starfish (COTS) outbreaks and possible of climate changes impacts, theses coral reefs are likely to collapse.

Highlights

Coral reefs are subjected to cyclic and episodic natural disturbances, but their recovery potential is affected by interacting factors that vary regionally and at ocean basin scales (Roff and Mumby, 2012)
The high hydrodynamics appear to contribute to the dispersion of microbes and coral disease among reefs
The high hydrodynamics may be considered an extra level of complexity while addressing coral reef microbialization and coral disease, not accounted for in previous studies

Summary

Introduction

Coral reefs are subjected to cyclic and episodic natural disturbances (e.g., storms), but their recovery potential is affected by interacting factors that vary regionally and at ocean basin scales (Roff and Mumby, 2012). The role of microbes in reef health is still underacknowledged and represents an emerging frontier to a full understanding of coral reef resilience (Knowlton and Jackson, 2008; Garren and Azam, 2012) It is not well understood how high hydrodynamics may affect reef microbial diversity. The microbial abundance and metagenomic diversity are not well known in high hydrodynamic reefs, such as those in Ishigaki (Okinawa). These reefs experienced intense and chronic coral stress due to frequent typhoons which can became catastrophic with global warming (Hongo et al, 2012; Harii et al, 2014)

Methods

Results

Discussion

Conclusion