High spatio-temporal variability in Acroporidae settlement to inshore reefs of the Great Barrier Reef.

Johnston Davidson,Murray Logan,Britta Schaffelke,Angus Thompson,Cristina Linares

doi:10.1371/journal.pone.0209771

Johnston Davidson, Murray Logan + Show 3 more

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https://doi.org/10.1371/journal.pone.0209771

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Journal: PloS one	Publication Date: Jan 30, 2019
Citations: 23	License type: CC BY 4.0

Affiliation: Australian Institute of Marine Science

Abstract

Recovery of coral reefs after disturbance relies heavily on replenishment through successful larval settlement and their subsequent survival. As part of an integrated study to determine the potential effects of water quality changes on the resilience of inshore coral communities, scleractinian coral settlement was monitored between 2006 and 2012 at 12 reefs within the inshore Great Barrier Reef. Settlement patterns were only analysed for the family Acroporidae, which represented the majority (84%) of settled larvae. Settlement of Acroporidae to terracotta tiles averaged 0.11 cm-2, representing 34 ± 31.01 (mean ± SD) spat per tile, indicating an abundant supply of competent larvae to the study reefs. Settlement was highly variable among reefs and between years. Differences in settlement among locations partly corresponded to the local cover of adult Acroporidae, while substantial reductions in Acroporidae cover caused by tropical cyclones and floods resulted in a clear reduction in settlement. Much of the observed variability remained unexplained, although likely included variability in both connectivity to, and the fecundity of, adult Acroporidae. The responsiveness of settlement patterns to the decline in Acroporidae cover across all four regions indicates the importance of supply and connectivity, and the vulnerability towards region-wide disturbance. High spatial and temporal variability, in addition to the resource-intensive nature of sampling with settlement tiles, highlights the logistical difficulty of determining coral settlement over large spatial and temporal scales.

Highlights

Replenishment of corals through recruitment is critical for the long-term resilience of reef communities facing exposure to pressures such as thermal bleaching, extreme weather events, outbreaks of coral predators such as the crown-of-thorns starfish, and disease [1, 2]
We have identified the main factors that we believe limit the utility of settlement tiles as a long-term monitoring method
We suggest that monitoring fecundity may provide a more direct assessment of environmental conditions limiting reproductive output of populations, while monitoring the density of juvenile corals is a better indicator of the success of the entire recruitment process

Summary

Introduction

Replenishment of corals through recruitment (here defined as successful settlement and metamorphosis of newly settled corals, hereafter “spat”, followed by post-settlement survival and growth) is critical for the long-term resilience of reef communities facing exposure to pressures such as thermal bleaching, extreme weather events, outbreaks of coral predators such as the crown-of-thorns starfish (currently referred to as Acanthaster cf solaris), and disease [1, 2]. Reefs close to the coast are subject to discharge from river systems, exposing coral communities to additional pressures such as increased turbidity, sedimentation, nutrient enrichment, pollutants and hyposalinity [3,4,5,6]. Of the MMP’s overall goals and objectives, and a description of the sub-programs are available at http://www.gbrmpa.gov.au/about-the-reef/howthe-reefs-managed/science-and-research/ourmonitoring-and-assessment-programs/reefrescue-marine-monitoring-program and http://eatlas.org.au/rrmmp. The Reef Rescue initiative had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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