The global biogeography of reef morphology

Aim: The Caribbean and Indo-Pacific are separate biogeographical realms with distinct biogeographical and evolutionary histories, a 10-fold difference in biodiversity, and highly disparate sea-level histories. Since reef morphology often reflects interactions between biological activity and biogeographical history, including sea levels, the widths of shallow coral reef habitats are likely to differ markedly between realms, with ramifications for numerous ecosystem functions. Our goal, therefore, was to assess the impact of global-scale biogeographical and evolutionary histories on coral reef habitats. Specifically, are Indo-Pacific reefs wider than their Caribbean counterparts?. Location: Global. Time Period: Modern. Major Taxa Studied: Coral reefs. Methods: We used the Allen Coral Atlas, a global reef mapping system (3 m pixel resolution), to examine 3765 transects, 3 km long and 1 km apart, on 60 reefs across the two realms, quantifying shallow reef habitat widths (Inner and Outer Reef Flat, and Reef Crest) using ArcGIS. Results: Shallow reef habitat widths were strikingly similar between the Caribbean and Indo-Pacific. Estimated modal widths diverged by just 37 m; means by just 122 m. Although shallow reef zones appeared to be wider in the Indo-Pacific, habitat widths on atolls were almost identical across realms (means varying by less than 8 m). Main Conclusions: Our remote sensing approach provides a global description of the biogeography of coral reefs as biogenic structures. Furthermore, we can assess the relative importance of realm-wide differences in coral diversity and sea-level history on reef growth. The striking similarity of reef widths across realms suggests that reef growth (net reef accretion) is largely independent of coral diversity, or sea-level history, and that other factors may have played a major role in constraining shallow reef widths. These factors may include geomorphology (e.g. antecedent topography and historical accommodation space) and, once at sea level, self-limiting local hydrodynamics

A Synthesis of Climate Change and Coastal Science to Support Adaptation in the Communities of Torres Strait

[Extract] This report provides a synthesis of research on climate change and coastal science in the Torres Strait, and has been produced for the Australian Government's Marine and Tropical Sciences Research Facility (MTSRF). It identifies and summarises work to date on reef evolution, hydrodynamics and sedimentary environments throughout the Torres Strait. It describes the island dynamics at Boigu, Saibai, Masig, Poruma, Warraber and Iama Islands. Numerous studies relating to climatic change are reviewed and the most relevant regional predictions for climate change in the Torres Strait are presented. The potential physical and ecological impacts of these changes in the Torres Strait are also identified. Adaptation and mitigation measures are suggested and their outcomes and consequences are evaluated. The key principles from sustainable land use plans on the islands are summarised and knowledge gaps in the fields of both coastal and climatic science are identified to guide future research

Lagoon infilling by coral reef sand aprons as a proxy for carbonate sediment productivity

Sand aprons are distinctive landforms that offer important insights into sedimentary dynamics for reef platform development. Here we link temporal and spatial scales of 21 sand aprons in the southern Great Barrier Reef to understand their Holocene formation and evolution in response to relative sea-level changes, the depth of the Pleistocene base, and contemporary morphodynamics. Our results show that lagoon infilling is a function of reef size and is a self-limiting process controlled by hydrodynamics and relative sea-level changes. Lagoon infilling does not depend on the type of reef or degree of exposure to waves, but it could reflect past wave climates. Our carbonate productivity estimates based on lagoon infilling are remarkably similar to those inferred from habitat classification. Finally, we hypothesize that current carbonate productivity has slowed because of the effects of climate change

A morphometric assessment and classification of coral reef spur and groove morphology

Spurs and grooves (SaGs) are a common and important feature of coral reef fore slopes worldwide. However, they are difficult to access and hence their morphodynamics and formation are poorly understood. We use remote sensing, with extensive ground truthing, to measure SaG morphometrics and environmental factors at 11,430 grooves across 17 reefs in the southern Great Barrier Reef, Australia. We revealed strong positive correlations between groove length, orientation and wave exposure with longer, more closely-spaced grooves oriented easterly reflecting the dominant swell regime. Wave exposure was found to be the most important factor controlling SaG distribution and morphology. Gradient of the upper reef slope was also an important limiting factor, with SaGs less likely to develop in steeply sloping (\u3e 5°) areas. We used a subset of the morphometric data (11 reefs) to statistically define four classes of SaG. This classification scheme was tested on the remaining six reefs. SaGs in the four classes differ in morphology, groove substrate and coral cover. These differences provide insights into SaG formation mechanisms with implications to reef platform growth and evolution. We hypothesize SaG formation is dominated by coral growth processes at two classes and erosion processes at one class. A fourth class may represent relic features formed earlier in the Holocene transgression. The classes are comparable with SaGs elsewhere, suggesting the classification could be applied globally with the addition of new classes if necessary. While further research is required, we show remotely sensed SaG morphometrics can provide useful insights into reef platform evolution

Lagoon infilling by coral reef sand aprons as a proxy for carbonate sediment productivity

Sand aprons are distinctive landforms that offer important insights into sedimentary dynamics for reef platform development. Here we link temporal and spatial scales of 21 sand aprons in the southern Great Barrier Reef to understand their Holocene formation and evolution in response to relative sea-level changes, the depth of the Pleistocene base, and contemporary morphodynamics. Our results show that lagoon infilling is a function of reef size and is a self-limiting process controlled by hydrodynamics and relative sea-level changes. Lagoon infilling does not depend on the type of reef or degree of exposure to waves, but it could reflect past wave climates. Our carbonate productivity estimates based on lagoon infilling are remarkably similar to those inferred from habitat classification. Finally, we hypothesize that current carbonate productivity has slowed because of the effects of climate change