Impacts of Sediments on Coral Energetics: Partitioning the Effects of Turbidity and Settling Particles

Abstract

Sediment loads have long been known to be deleterious to corals, but the effects of turbidity and settling particles have not previously been partitioned. This study provides a novel approach using inert silicon carbide powder to partition and quantify the mechanical effects of sediment settling versus reduced light under a chronically high sedimentary regime on two turbid water corals commonly found in Singapore (Galaxea fascicularis and Goniopora somaliensis). Coral fragments were evenly distributed among three treatments: an open control (30% ambient PAR), a shaded control (15% ambient PAR) and sediment treatment (15% ambient PAR; 26.4 mg cm−2 day−1). The rate of photosynthesis and respiration, and the dark-adapted quantum yield were measured once a week for four weeks. By week four, the photosynthesis to respiration ratio (P/R ratio) and the photosynthetic yield (Fv/Fm) had fallen by 14% and 3–17% respectively in the shaded control, contrasting with corals exposed to sediments whose P/R ratio and yield had declined by 21% and 18–34% respectively. The differences in rates between the shaded control and the sediment treatment were attributed to the mechanical effects of sediment deposition. The physiological response to sediment stress differed between species with G. fascicularis experiencing a greater decline in the net photosynthetic yield (13%) than G. somaliensis (9.5%), but a smaller increase in the respiration rates (G. fascicularis = 9.9%, G. somaliensis = 14.2%). These different physiological responses were attributed, in part, to coral morphology and highlighted key physiological processes that drive species distribution along high to low turbidity and depositional gradients.

Caribbean Near-Shore Coral Reef Benthic Community Response to Changes on Sedimentation Dynamics and Environmental Conditions

“…Sediment accumulation on coral surfaces, especially fine sediments, can produce significant adverse physiological responses as a consequence of energy relocation, required to achieve rejection of sediment particles through the production of mucus and ciliary action (Acevedo et al, 1989;Telesnicki and Goldberg, 1995;Woolfe and Larcombe, 1999;Fabricius, 2011). Coral abilities differ between species and coral morphologies, with branching, meandering, and large coral colonies being more tolerant to sediment accumulation (Rogers, 1990; Sedimentation rate Rho = −0.063 Rho = −0.093 Rho = 0.433 Rho = 0.001 Rho = 0.077 Rho = 0.256 Rho = 0.156 p = 0.6698 p = 0.8067 p = 0.0011 p = 0.4821 p = 0.2319 p = 0.0406 p = 0.1038…”

Evidence for rapid, tide-related shifts in the microbiome of the coral Coelastrea aspera

“…S2). Additional energetic costs in older corals are incurred from sediment shedding (Junjie et al 2014) and lesion healing as colonies grow and adopt a micro-atoll growth form (Scoffin et al 1997). The mucus layer is a critical, dynamic habitat for surface-colonizing bacteria (Ritchie 2006;Nakajima et al 2009), and such factors may have a profound effect on the energy available for mucus production.…”

Water Column Optical Properties of Pacific Coral Reefs Across Geomorphic Zones and in Comparison to Offshore Waters

“…On reef systems, the calcium carbonate skeletons of coral, as well as the structures of coralline algae, are broken down to fine particulate sand by physical and biological weathering [44][45][46]. Suspension of sediments through wind, wave, or other mechanisms increase the water column particulate load, limiting benthic PAR [14,47,48] in addition to other negative impacts on corals [49,50]. Particulate organic matter, i.e., detritus or marine snow, may remain suspended for long periods of time and can be produced on reefs from a variety of sources including coral mucus [51].…”