Impacts of water quality on Acropora coral settlement: The relative importance of substrate quality and light.

Coral larval settlement patterns are influenced by a vast array of factors; however, the relative roles of individual factors are rarely tested in isolation, leading to confusion about which are most crucial for settlement. For example, direct effects of the light environment are often cited as a major factor influencing settlement patterns, yet this has not been demonstrated under environmentally realistic lighting regimes in the absence of confounding factors. Here we apply programmable multispectral lights to create realistic light spectra, while removing correlating (but not obvious) factors that are common in laboratory settlement experiments.

Climate change doubles sedimentation-induced coral recruit mortality.

Coral reef replenishment is threatened by global climate change and local water-quality degradation, including smothering of coral recruits by sediments generated by anthropogenic activities. Here we show that the ability of Acropora millepora recruits to remove sediments diminishes under future climate conditions, leading to increased mortality. Recruits raised under future climate scenarios for fourteen weeks (highest treatment: +1.

Sediment characteristics influence the fertilisation success of the corals Acropora tenuis and Acropora millepora.

Elevated suspended sediment concentrations (SSCs) often impact coral fertilisation success, but sediment composition can influence effect thresholds, which is problematic for accurately predicting risk. Here, we derived concentration-response thresholds and cause-effect pathways for SSCs comprising a range of realistic mineral and organic compositions on coral fertilisation success. Effect concentration thresholds (EC: 10% fertilisation inhibition) varied markedly, with fertilisation highly sensitive to inshore organic-clay rich sediments and bentonite clay at <5 mg L.

Settlement patterns of the coral Acropora millepora on sediment-laden surfaces.

Successful recruitment in corals is important for the sustenance of coral reefs, and is considered a demographic bottleneck in the recovery of reef populations following disturbance events. Yet several factors influence larval settlement behaviour, and here we quantified thresholds associated with light attenuation and accumulated sediments on settlement substrates. Sediments deposited on calcareous red algae (CRA) directly and indirectly impacted coral settlement patterns.

Cumulative effects of suspended sediments, organic nutrients and temperature stress on early life history stages of the coral Acropora tenuis.

Coral reproduction is vulnerable to both declining water quality and warming temperatures, with simultaneous exposures likely compounding the negative impact of each stressor. We investigated how early life processes of the coral Acropora tenuis respond to increasing levels of suspended sediments in combination with temperature or organic nutrients. Fertilization success and embryo development were more sensitive to suspended sediments than to high temperatures or nutrient enrichment, while larval development (after acquisition of cilia) and settlement success were predominantly affected by thermal stress.

Mucous Secretion and Cilia Beating Defend Developing Coral Larvae from Suspended Sediments.

Suspended sediments produced from dredging activities, or added to the sediment budget via river runoff, are a concern for marine resource managers. Understanding the impact of suspended sediments on critical life history stages of keystone species like corals is fundamental to effective management of coastlines and reefs. Coral embryos (Acropora tenuis and A.

That sinking feeling: Suspended sediments can prevent the ascent of coral egg bundles.

Spawning synchrony represents a common reproductive strategy in sessile marine organisms and for broadcast spawning corals, buoyancy of egg-sperm bundles is critical to maximise fertilisation at the ocean surface. Here we demonstrate a novel threat to coral reproduction whereby buoyant egg-sperm bundles intercept and are "ballasted" by sediment grains on their journey to the ocean surface, preventing them from reaching the ocean surface and greatly reducing egg-sperm encounter rates. Empirical observations of this mechanism are successfully captured by a mathematical model that predicts the reduction in ascent probability and egg-sperm encounters as a function of sediment load.

Suspended sediments limit coral sperm availability.

Suspended sediment from dredging activities and natural resuspension events represent a risk to the reproductive processes of coral, and therefore the ongoing maintenance of reefal populations. To investigate the underlying mechanisms that could reduce the fertilisation success in turbid water, we conducted several experiments exposing gametes of the corals Acropora tenuis and A. millepora to two sediment types.