Setting priorities for conservation at the interface between ocean circulation, connectivity, and population dynamics

Abstract

Population persistence in the marine environment is driven by patterns of ocean circulation, larval dispersal, ecological interactions, and demographic rates. For habitat‐forming organisms in particular, understanding the relationship between larval connectivity and meta‐population dynamics aids in planning for marine spatial management. Here, we estimate networks of connectivity between fringing coral reefs in the northwest shelf of Australia by combining a particle tracking model based on shelf circulation with models of subpopulation dynamics of individual reefs. Coral cover data were used as a proxy for overall habitat quality, which can change as a result of natural processes, human‐driven impacts, and management initiatives. We obtain three major results of conservation significance. First, the dynamics of the ecological network result from the interplay between network connectivity and ecological processes on individual reefs. The maximum coral cover a zone can sustain imposes a significant nonlinearity on the role an individual reef plays within the dynamics of the network, and thus on the impact of conservation interventions on specific reefs. Second, the role of an individual reef within these network dynamics changes considerably depending on the overall state of the system: a reef's role in sustaining the system's state can be different from the same reef's role in helping the system recover following major disturbance. Third, patterns of network connectivity change significantly as a function of yearly shelf circulation trends, and nonlinearity in network dynamics make mean connectivity a poor representation of yearly variations. From a management perspective, the priority list of reefs that are targets for management interventions depends crucially on what type of stressors (system‐wide vs. localized) need addressing. This choice also depends not only on the ultimate purpose of management, but also on future oceanographic, climate change, and development scenarios that will determine the network connectivity and habitat quality.

Cross-shelf Heterogeneity of Coral Assemblages in Northwest Australia

“…Although the region has experienced levels of heat stress typically associated with coral bleaching and mortality [47,82], these effects may have been mediated by local factors in the Dampier Archipelago, resulting in unexpected distribution patterns. Environmental factors not investigated in this study, including substrate type, nutrient influx and hydrodynamic patterns, may have influenced the distribution of species and resilience of coral reefs in the Dampier Archipelago [100,101].…”

Recurrent coral bleaching in north-western Australia and associated declines in coral cover

“…Because areas of high and low seasonal and interannual SST variability exist in the western Pilbara, and to coincide with patterns of bleaching in the period between 2011 and 2016, it may be possible to optimise future management strategies by understanding how these patterns may affect the overall system resilience. For example, spatio-temporal refugia provided by such variability, which appears to be greater than that on Australia's other tropical coasts, may interact with ecosystem properties such as regional connectivity to affect resilience (Boschetti et al 2017). An understanding of connectivity regimes among coral populations within the region is emerging on the basis of both hydrodynamic modelling (Feng et al 2016;Boschetti et al 2017) and genetic studies.…”

“…For example, spatio-temporal refugia provided by such variability, which appears to be greater than that on Australia's other tropical coasts, may interact with ecosystem properties such as regional connectivity to affect resilience (Boschetti et al 2017). An understanding of connectivity regimes among coral populations within the region is emerging on the basis of both hydrodynamic modelling (Feng et al 2016;Boschetti et al 2017) and genetic studies. Particle-track modelling shows that reefs to the north of Barrow Island have a low connectivity with those to the south (Feng et al 2016), which was corroborated in a recent coral population-genetic study of Cyphastrea microphthalma, which showed low levels of differentiation among some Pilbara reefs (Evans et al 2019).…”

Oceanography and Marine Biology

“…This inference is supported by hydrodynamic particle dispersion modelling, which shows that Ningaloo probably receives larvae from the reefs farther north (Feng et al 2016). Furthermore, the amount of larvae that are transported to Ningaloo varies from year to year, and supply varies among individual reefs, such that recovery times of many reefs are likely to be decades or longer (Boschetti et al 2019).…”

“…The faster rates of warming yielded by downscaled models and evidence from coral cores mean that this might occur sooner. Exacerbating the likely increase in the frequency of bleaching is the potential for reduced supply of larvae from weaker currents, because the coral reefs to the north are likely to be sources of larvae for Ningaloo (Boschetti et al 2019), and coral abundance on these reefs has already been significantly reduced (Gilmour et al 2019.…”