A multi-scale biophysical model to inform regional management of coral reefs in the western Philippines and South China Sea

The health and functioning of coral reef ecosystems worldwide is in decline, and in the face of increasing anthropogenic stress, the rate of decline of these important ecosystems is set to accelerate. Mitigation strategies at regional scales are costly, but nevertheless critical, as reef systems are highly connected across regions by ocean transport of both larval propagules and pollutants. It is essential that these strategies are informed by sound science, but the inherent complexity of coral reef systems confers significant challenges for scientists and managers. Models are useful tools for dealing with complexity and can inform decision making for coral reef management. We develop a spatially explicit biophysical model for a general coral reef system. The model couples dynamics from local (102 m) to regional (106 m) scales, and explicitly incorporates larval connectivity patterns derived from sophisticated larval dispersal models. Here, we instantiate and validate the model for coral reefs in the Philippines region of the South China Sea. We demonstrate how the model can be used in decision support for coral reef management by presenting two examples of regional-scale scenario projection relating to key management issues in the Philippines: (i) marine reserve design and the recovery of fish stocks; and (ii) synergistic effects between coral bleaching and poor water quality. These scenarios highlight the importance of considering multiple stressors to reef health and patterns of larval connectivity in regional-scale management decisions

Modelling coral reef futures to inform management: can reducing local-scale stressors conserve reefs under climate change?

Climate change has emerged as a principal threat to coral reefs, and is expected to exacerbate coral reef degradation caused by more localised stressors. Management of local stressors is widely advocated to bolster coral reef resilience, but the extent to which management of local stressors might affect future trajectories of reef state remains unclear. This is in part because of limited understanding of the cumulative impact of multiple stressors. Models are ideal tools to aid understanding of future reef state under alternative management and climatic scenarios, but to date few have been sufficiently developed to be useful as decision support tools for local management of coral reefs subject to multiple stressors. We used a simulation model of coral reefs to investigate the extent to which the management of local stressors (namely poor water quality and fishing) might influence future reef state under varying climatic scenarios relating to coral bleaching. We parameterised the model for Bolinao, the Philippines, and explored how simulation modelling can be used to provide decision support for local management. We found that management of water quality, and to a lesser extent fishing, can have a significant impact on future reef state, including coral recovery following bleaching-induced mortality. The stressors we examined interacted antagonistically to affect reef state, highlighting the importance of considering the combined impact of multiple stressors rather than considering them individually. Further, by providing explicit guidance for management of Bolinao’s reef system, such as which course of management action will most likely to be effective over what time scales and at which sites, we demonstrated the utility of simulation models for supporting management. Aside from providing explicit guidance for management of Bolinao’s reef system, our study offers insights which could inform reef management more broadly, as well as general understanding of reef systems

A multi-scale biophysical model to inform regional management of coral reefs in the western Philippines and South China Sea

The health and functioning of coral reef ecosystems worldwide is in decline, and in the face of increasing anthropogenic stress, the rate of decline of these important ecosystems is set to accelerate. Mitigation strategies at regional scales are costly, but nevertheless critical, as reef systems are highly connected across regions by ocean transport of both larval propagules and pollutants. It is essential that these strategies are informed by sound science, but the inherent complexity of coral reef systems confers significant challenges for scientists and managers. Models are useful tools for dealing with complexity and can inform decision making for coral reef management. We develop a spatially explicit biophysical model for a general coral reef system. The model couples dynamics from local (102 m) to regional (106 m) scales, and explicitly incorporates larval connectivity patterns derived from sophisticated larval dispersal models. Here, we instantiate and validate the model for coral reefs in the Philippines region of the South China Sea. We demonstrate how the model can be used in decision support for coral reef management by presenting two examples of regional-scale scenario projection relating to key management issues in the Philippines: (i) marine reserve design and the recovery of fish stocks; and (ii) synergistic effects between coral bleaching and poor water quality. These scenarios highlight the importance of considering multiple stressors to reef health and patterns of larval connectivity in regional-scale management decision

Success in Competition for Space in Two Invasive Coral Species in the western Atlantic – Tubastraea micranthus and T. coccinea

Invasion success by an alien species is dependent upon rate of reproduction, growth, mortality, physical characteristics of the environment, and successful competition for resources with native species. For sessile, epibenthic marine species, one critical resource is space. We examined competitive success in two invasive Indo-Pacific corals involved in competition for space in the northern Gulf of Mexico-Tubastraea coccinea and T. micranthus-on up to 13 offshore oil/gas platforms south of the Mississippi River. Still-capture photos of thousands of overgrowth interactions between the target corals and other sessile epibenthic fauna were analyzed from ROV videos collected at 8-183 m depth. T. micranthus was observed overgrowing >90% of all sessile epibenthic species which it encountered. Frequencies of competitive success varied significantly between platforms. T. coccinea was competitively superior to all competitors pooled, at the 60% level. There was little variability between T. coccinea populations. T. coccinea encountered the following species most frequently-the encrusting sponges Xestospongia sp. (with the commensal Parazoanthus catenularis), X. carbonaria, Dictyonella funicularis, Mycale carmigropila, Phorbas amaranthus, and Haliclona vansoesti-and was found to be, on average, competitively superior to them. Both T. micranthus and T. coccinea appear to be good competitors for space against these species in the northern Gulf of Mexico. Competitive success in T. micranthus was highest in the NE part of the study area, and lowest in the SW area near the Mississippi River plume. T. coccinea's competitive success peaked in the SW study area. This suggests that variation in competitive success both within and between populations of these species may be due to differences in local environmental factors

Larval settlement and juvenile development of sea anemones that provide habitat for anemonefish

Sea anemones that host obligate symbiotic anemonefish are ecologically important throughout many coral reef regions of the Indo-Pacific. This study provides the first quantitative data on larval settlement rates and juvenile development of two species of host sea anemone, Heteractis crispa and Entacmaea quadricolor. Larvae were reared from broadcast spawned gametes of sexually reproductive male and female anemones collected from the Solitary Islands Marine Park, NSW, Australia. Prior to the start of the experiments, H. crispa larvae were reared for 3 days after spawning in March 2004 and E. quadricolor larvae were reared for 4 days after spawning in February 2005. Larval settlement onto biologically conditioned terracotta tiles in outdoor flow-through seawater aquaria was first recorded 4 days after spawning for H. crispa and 5 days after spawning for E. quadricolor. Peak settlement occurred 10 days after spawning, with a mean of 33.4 and 50.3% of the original groups of 350 larvae in replicate tanks settling for H. crispa and E. quadricolor, respectively. Tentacles arose as outpocketings of the oral region, at first appearing as small rounded buds. These buds elongated to form long, thin, tapering tentacles in H. crispa, whereas E. quadricolor tentacles had slight bulbs below the tips. Juvenile anemones, especially H. crispa, were found to have very different colouration and markings when compared with adult anemones, and therefore the descriptions and images provided here will enable correct identification of juvenile recruits