Bacterial Biofilm Communities and Coral Larvae Settlement at Different Levels of Anthropogenic Impact in the Spermonde Archipelago, Indonesia

Pia Kegler,Muhammad Lukman,Sebastian C A Ferse,Andreas Kunzmann,Yustian R Alfiansah,Christiane Hassenrück,Hauke F Kegler,Astrid Gärdes

doi:10.3389/fmars.2017.00270

Abstract

Populations on small islands surrounded by coral reefs often heavily depend on the services provided by these reefs. The health and recovery of reefs are strongly influenced by recruitment of coral larvae. Their settlement relies on cues such as those emitted from bacterial communities forming biofilms on reef surfaces. Environmental conditions can change these bacterial community compositions (BCC) and may in turn affect settlement of coral larvae. At three small inhabited islands in the Spermonde Archipelago, Indonesia, with different distance from the mainland, BCC and coral recruitment were investigated on artificial ceramic tiles after 2-8 weeks exposure time and on natural reef substrate. Water parameters showed a clear separation between inshore and near-shore/mid-shelf sites, with distinct benthic communities at all three sites. No coral recruitment was observed at the inshore site with highest natural and anthropogenic stressors. At the other two sites coral recruitment occurred on natural surfaces (recruits per 100 cm2: 0.73 ± 1.75 near-shore, 0.90 ± 1.97 mid-shelf), but there was no significant difference between the two sites. On artificial substrates coral recruitment differed between these two sites, with tile orientation and with exposure time of the tiles in the reef. The most abundant bacteria on both substrates were Gammaproteobacteria, Alphaproteobacteria and Cyanobacteria. BCC was strongly correlated with water quality and significant differences in BCC between the inshore site and near-shore/mid-shelf were found. On artificial substrates there was a significant difference in BCC also with exposure time in the reef. Our study highlights the value of taking both BCC and coral recruitment into account, in addition to the environmental conditions, when considering the recovery potential of coral reefs.

Highlights

Coral reefs worldwide are declining due to a multitude of anthropogenic stressors that frequently act in combination (Burke et al, 2012)
NOx differed only between mid-shelf (BD) and inshore (LL), suspended particulate matter (SPM) differed only between near-shore (BL) and inshore (LL), while significant differences in PO4, Si, and Chl. a concentration were observed between inshore (LL) and both of the other islands
While no clear correlation between recruitment of larvae and bacterial community compositions (BCC) could be determined, this study showed that both are altered by habitat and environmental conditions

Summary

Introduction

Coral reefs worldwide are declining due to a multitude of anthropogenic stressors that frequently act in combination (Burke et al, 2012). Reefs often surround small islands along the coasts, providing essential livelihoods for the inhabitants of these islands (Cinner, 2014), while being subjected to combined influences from the mainland and the islands themselves (Baum et al, 2015). Mostly inhabited small islands fringed by coral reefs provide the unique possibility to study reefs subjected to various natural and anthropogenic influences, mainly related to the city of Makassar with 1.5 million inhabitants (Sawall et al, 2012, 2013; Polónia et al, 2015), resulting in an environmental gradient with increasing distance from the city (Cleary et al, 2005; Polónia et al, 2015; Teichberg et al, 2017). Over the past decades studies in Spermonde have shown declining coral cover, habitat degradation, and reefs impacted by blast fishing activities (Edinger et al, 1998; Pet-Soede and Erdmann, 1998)

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