A decadal analysis of bioeroding sponge cover on the inshore Great Barrier Reef

Nicole S Webster,Mia O Hoogenboom,Blake D Ramsby,Angus Thompson,Steve Whalan

doi:10.1038/s41598-017-02196-z

Abstract

Decreasing coral cover on the Great Barrier Reef (GBR) may provide opportunities for rapid growth and expansion of other taxa. The bioeroding sponges Cliona spp. are strong competitors for space and may take advantage of coral bleaching, damage, and mortality. Benthic surveys of the inshore GBR (2005–2014) revealed that the percent cover of the most abundant bioeroding sponge species, Cliona orientalis, has not increased. However, considerable variation in C. orientalis cover, and change in cover over time, was evident between survey locations. We assessed whether biotic or environmental characteristics were associated with variation in C. orientalis distribution and abundance. The proportion of fine particles in the sediments was negatively associated with the presence-absence and the percent cover of C. orientalis, indicating that the sponge requires exposed habitat. The cover of corals and other sponges explained little variation in C. orientalis cover or distribution. The fastest increases in C. orientalis cover coincided with the lowest macroalgal cover and chlorophyll a concentration, highlighting the importance of macroalgal competition and local environmental conditions for this bioeroding sponge. Given the observed distribution and habitat preferences of C. orientalis, bioeroding sponges likely represent site-specific – rather than regional – threats to corals and reef accretion.

Highlights

Loss of coral cover has led to dire predictions for the future of coral reef ecosystems[1,2,3], including the Great Barrier Reef (GBR)[4]
C. orientalis percent cover was lower than previously reported from Orpheus Island (>6%)[20], possibly due to a greater area surveyed or the untargeted design in the current study
When absences are included, the average percent cover of C. orientalis on the inshore GBR was 0.14% (±0.51 SD), which is comparable to the average cover of C. delitrix in the Florida Keys, USA (~0.1%)[45] and southeast Florida (~0.08%)[46], but lower than C. delitrix cover in Colombia (~2%)[47]

Summary

Introduction

Loss of coral cover has led to dire predictions for the future of coral reef ecosystems[1,2,3], including the Great Barrier Reef (GBR)[4]. A number of processes compromise coral health and the broader health of coral reefs, including increased sea surface temperatures, ocean acidification, pollution, cyclones, and crown of thorns starfish outbreaks[4, 5]. All of these stressors are predicted to intensify over coming decades, potentially shifting the coral reef benthic community from coral-dominated systems to those dominated by less-sensitive species[6, 7]. Poor water quality is associated with low light conditions that may negatively impact growth of photo-symbiotic bioeroding sponges such as C. orientalis and C. varians[28, 29]

Methods

Results

Conclusion