Abstract
A long-term (10 month exposure) experiment on effects of suspended sediment on the mortality, growth, and recruitment of the reef corals Montipora capitata and Porites compressa was conducted on the shallow reef flat off south Molokaʻi, Hawaiʻi. Corals were grown on wire platforms with attached coral recruitment tiles along a suspended solid concentration (SSC) gradient that ranged from 37 mg l−1 (inshore) to 3 mg l−1 (offshore). Natural coral reef development on the reef flat is limited to areas with SSCs less than 10 mg l−1 as previously suggested in the scientific literature. However, the experimental corals held at much higher levels of turbidity showed surprisingly good survivorship and growth. High SSCs encountered on the reef flat reduced coral recruitment by one to three orders of magnitude compared to other sites throughout Hawaiʻi. There was a significant correlation between the biomass of macroalgae attached to the wire growth platforms at the end of the experiment and percentage of the corals showing mortality. We conclude that lack of suitable hard substrate, macroalgal competition, and blockage of recruitment on available substratum are major factors accounting for the low natural coral coverage in areas of high turbidity. The direct impact of high turbidity on growth and mortality is of lesser importance.
Highlights
Sedimentation is a major detrimental factor on coral reefs (Johannes, 1975; Cortes & Risk, 1985; Grigg & Birkeland, 1997)
General linear models (GLM) were conducted using growth and mortality/partial mortality as dependent variables regressed against the predictors: species, turbidity, distance from shore, and macroalgae to explore the variation in coral growth and mortality
The sediment varied in composition from approximately 25–90% carbonate, and 10–75% terrigenous volcanics, by mass, with the fine-grain silts and clays being predominantly terrigenous in origin
Summary
Sedimentation is a major detrimental factor on coral reefs (Johannes, 1975; Cortes & Risk, 1985; Grigg & Birkeland, 1997). The classic work of Rogers (1983) and Rogers (1990) concludes that mean suspendedparticulate matter for reefs that are not impacted directly by human activities generally is less than 10 mg l−1 Concentrations above this value result in fewer coral species, less. Some coral species can tolerate short-term exposure (days) to suspended sediment concentrations as high as 1,000 mg l−1 while others show mortality after exposure (weeks) to concentrations as low as 30 mg l−1. Grain size and organic and nutrient-related sediment properties were key factors determining sedimentation stress in corals after short-term exposure. They found that silt-sized and nutrient-rich sediments can stress corals after short exposure, while sandy sediments or nutrient-poor silts affect corals to a lesser extent These results were followed up by Weber et al (2012) who postulated that the coral death was microbially mediated. We undertook a study to measure the impact of suspended particulate matter on coral recruitment, growth, and mortality for the two locally dominant reef flat coral species along a gradient of terrigenous sediment impact (Fig. 1)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
