Macroalgae inhibits larval settlement and increases recruit mortality at Ningaloo Reef, Western Australia.

Fiona J. Webster,Mike Van Keulen,Neil R. Loneragan,Russell C. Babcock,Tilmann Harder

doi:10.1371/journal.pone.0124162

Fiona J. Webster, Mike Van Keulen + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0124162

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Journal: PloS one	Publication Date: Apr 21, 2015
Citations: 107	License type: CC BY 4.0

Affiliation: Murdoch University, CSIRO Oceans and Atmosphere

Abstract

Globally, many coral reefs are degraded and demonstrate reduced coral cover and increased macroalgal abundance. While negative correlations between macroalgae and coral recruitment have commonly been documented, the mechanisms by which macroalgae affects recruitment have received little attention. Here we examined the effect of macroalgae on larval settlement and the growth and survival of coral recruits, in a field experiment over nine months. Exclusion treatments were used to manipulate herbivory and macroalgal biomass, while settlement tiles measured coral settlement and survival. After nine months the volume of macroalgae was up to 40 times greater in the caged treatments than in controls and the settlement of coral larvae on the undersides of tiles within caged plots was 93% lower than in the uncaged treatments. The growth and survival of coral recruits was also severely reduced in the presence of macroalgae: survival was 79% lower in caged treatments and corals were up to 58% smaller with 75% fewer polyps. These data indicate that macroalgae has an additive effect on coral recruitment by reducing larval settlement and increasing recruit mortality. This research demonstrates that macroalgae can not only inhibit coral recruitment, but also potentially maintain dominance through a positive feedback system.

Highlights

Coral reefs throughout the world are suffering from increased exposure to natural and anthropogenic disturbances, especially those associated with climate change [1,2]
There have been a number of studies which have found a negative correlation between the macroalgal abundance and coral recruits [5,7,13,14,15,16,17,18,19,20], the mechanisms driving these patterns and research on coral-algal interactions during the early coral life history phase has not received a lot of attention [17,21,22,23,24]
Larval settlement was severely reduced by in the presence of macroalgae, with 93% fewer larval recruits on the settlement tiles beneath the macroalgal canopy compared to open plots

Summary

Introduction

Coral reefs throughout the world are suffering from increased exposure to natural and anthropogenic disturbances, especially those associated with climate change [1,2]. Reefs which have suffered disturbance and coral mortality often demonstrate increased macroalgal abundance due to the ability of algae to dominant newly available space through rapid recruitment and growth [3,4]. Macroalgae Inhibits Coral Recruitment demonstrate reduced resilience and remain in a degraded state with macroalgae continuing to dominate the benthic substratum [7,8,9,10,11]. One of the reasons coral recruitment and post settlement survivorship remains little addressed is because of the challenges associated with studying coral recruits due to their small in size and tendency to settle in cryptic habitats [25]

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