The effects of a stressed inshore urban reef on coral recruitment in Suva Harbour, Fiji.

Ronal Lal,Antoine D R N’Yeurt,Ralph H Riley,Stuart Kininmonth,Ciro Rico

doi:10.1002/ece3.4641

Abstract

A relic inshore reef ecosystem adjacent to the Fijian capital of Suva and another remote inshore reef were monitored monthly from July 2014 to July 2015 for coral recruitment, sedimentation rates, coral cover, temperature, and light intensity. Despite a major sewage spill in Suva Harbour in December 2014, the municipal inshore site exposed to constant anthropogenic activity, recorded no significant differences in coral spat abundance (except for the family Poritidae) on artificial substrata compared to the remote inshore site. Total yearly spat abundance was 106 on municipal reef and 132 on remote reef, while average daily sediment trap collection rates (g cm2/day) were significantly higher in the municipal site for the entire duration of monitoring. Total annual particulate organic matter content in sediment was also significantly higher in the municipal site (107.51 g cm2), compared to the remote site (43.37 g cm2). Mean light intensity was significantly lower for the municipal site (69.81 lum/ft2) compared to the remote site (239.26 lum/ft2), with Photosynthetically Active Radiation also lower for the former (800–1,066.66 µmol m−2 s−1) compared to the latter (3,266.66–3,600 µmol m−2 s−1). The lack of significant differences in coral spat recruitment rates suggests that settling larvae may be unable to distinguish between sub‐optimal and optimal sites probably as a consequence of interference with coral settlement cues arising from anthropogenic development.

Highlights

The reproductive capacity of a reef ecosystem is vital to its sustain‐ ability (Bauman et al, 2015)
Our results indicate that environmental stressors such as sedimen‐ tation and sewage pollution do not necessarily result in a reduc‐ tion in coral cover, or a change in the recruitment rate of coral spat
Most field studies investigating the effects of sewage pollution on coral reef ecosystems have been short‐term and limited in scope (Pastorok & Bilyard, 1985), and report that sewage‐stressed eco‐ systems typically experience a decrease in coral cover, taxonomic richness, water clarity, larval recruitment, and decreased calcifica‐ tion rate as a result of the sewage effluent (Laws & Redalje, 1982)

Summary

Introduction

The reproductive capacity of a reef ecosystem is vital to its sustain‐ ability (Bauman et al, 2015). The recruitment of coral juveniles is considered a major determinant of community structure in marine ecosystems and is recognized as a fundamentally important influ‐ ence affecting the distribution and abundance of reef organisms (Babcock & Mundy, 1996; Harriott, 1992). Specific coral larval settlement cues involving reef acoustics, chemical‐algal signals, reef surface parameters, and light are vital in influencing the orienta‐ tion of coral planulae toward healthy reefs for settlement (Strader, Davies, & Matz, 2015; Tebben et al, 2015; Vermeij, Marhaver, Huijbers, Nagelkerken, & Simpson, 2010). Major urban and indus‐ trial infrastructures may mask or distort acoustic cues through noise, disrupt and interfere with chemical signals through sediment and toxic pollutant influx, inhibit light availability through high turbid‐ ity, induce sediment smothering of settlement‐cue‐surfaces, that is, coralline algae, and mislead planulae larvae toward settling near developed coastal areas hosting high intensity artificial light stimuli (Bauman et al, 2015; Codarin, Wysocki, Ladich, & Picciulin, 2009; Davies, Coleman, Griffith, & Jenkins, 2015; Leduc, Kelly, & Brown, 2004; Munday et al, 2009; Perez III, Rodgers, Jokiel, Lager, & Lager, 2014; Slabbekoorn et al, 2010; Tebben et al, 2015)

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Conclusion