New Publication: Kenyan and Mozambican coral reef ‘carbonate budgets’ contribute to international picture of corals under sea-level rise.

SPACES coral reef surveys have contributed to an international picture of how reefs might be able to grow to keep up with sea-level rise, recently published in Nature.

The growth of coral reefs is strongly influenced by the amount and types of coral living on the reef surface, but across both regions this growth is now being hampered by combinations of coral disease, deteriorating water quality and fishing pressure, along with severe impacts from “coral bleaching” caused by climate change. By counting the organisms responsible for building up and eroding reefs, SPACES team members Chris Perry and Fraser Januchowski-Hartley have been able to calculate the ‘carbonate budget’ and estimate how quickly reefs can grow towards the surface (the ‘accretion rate’).

In the figure below, the Mozambican (17) and Kenyan (18) SPACES sites can be seen in comparison to reefs from around the Indian ocean and Western Atlantic. The poorest reefs in […]

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Artisanal fisheries in Cabo Delgado, Mozambique: rural vs urban fishing centers

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This working paper investigates the relationship between gear, catch and income generated by the fishers in different seasons. SPACES researchers collected data using fish catch surveys at landing sites in Pemba town, Vamizi and Lalane. A standard questionnaire was used to collect the effort and location of the fishery. The fishery shows a wide range in both gears and profitability, and the surveys in conjunction with ecological surveys conducted by other SPACES team members revealed higher catch per unit effort (CPUE) values in Vamizi and Lalane when compared to Pemba, associated with higher fish diversity and fish biomass at Vamizi and Lalane when compared to Pemba. This suggests that the near shore coral reef environment in Pemba is overexploited.

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Changing dynamics of reef framework production in the Western Indian Ocean – Fraser Januchowski-Hartley et al.(1.2 MB)

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Fraser Januchowski-Hartley’s presentation at the 2015 WIOMSA symposium on carbonate budget and current coral condition at SPACES sites, Mombasa, Shimoni, Vamizi, and Pemba.

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Linking reef ecology to island building: Parrotfish identified as major producers of island-building sediment in the Maldives. Geology 2015

Abstract

Reef islands are unique landforms composed entirely of sediment produced on the surrounding coral reefs. Despite the fundamental importance of these ecological-sedimentary links for island development and future maintenance, reef island sediment production regimes remain poorly quantified. Using census and sedimentary data from Vakkaru island (Maldives), a sand-dominated atoll interior island, we quantify the major sediment-generating habitats, the abundance of sediment producers in these habitats, and the rates and size fractions of sediment generated by different taxa. The estimated annual sediment production is 685,000 kg (or 370 m3), ∼75% of which is produced on the narrow outer reef flat, despite composing only 21% of the total platform area. Approximately 65% of the platform acts solely as a sediment sink. Census data identify parrotfish as the major sediment producers, generating >85% of the 5.7 kg m–2 of new sand-grade sediment produced on the outer reef flat each year. Halimeda (macroalgae) produce a further 10%, most as gravel-grade material. Comparisons between production estimates and sedimentary data indicate that reef ecology and island sedimentology are tightly linked; reef flat and lagoon sediments are dominated by coral and Halimeda, although fine- to medium-grained coral sand is the dominant (∼59%) island constituent. The generation of sediment suitable for maintaining this reef island is thus critically dependent on a narrow zone of high-productivity reef, but most especially on the maintenance of healthy parrotfish populations that can convert reef framework to sand-grade sediment.

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Remote coral reefs can sustain high growth potential and may match future sea-level trands. Nature Scientific Reports 2015

Abstract

Climate-induced disturbances are contributing to rapid, global-scale changes in coral reef ecology. As a consequence, reef carbonate budgets are declining, threatening reef growth potential and thus capacity to track rising sea-levels. Whether disturbed reefs can recover their growth potential and how rapidly, are thus critical research questions. Here we address these questions by measuring the carbonate budgets of 28 reefs across the Chagos Archipelago (Indian Ocean) which, while geographically remote and largely isolated from compounding human impacts, experienced severe (>90%) coral mortality during the 1998 warming event. Coral communities on most reefs recovered rapidly and we show that carbonate budgets in 2015 average +3.7 G (G = kg CaCO3 m−2 yr−1). Most significantly the production rates on Acropora-dominated reefs, the corals most severely impacted in 1998, averaged +8.4 G by 2015, comparable with estimates under pre-human (Holocene) disturbance conditions. These positive budgets are reflected in high reef growth rates (4.2 mm yr−1) on Acropora-dominated reefs, demonstrating that carbonate budgets on these remote reefs have recovered rapidly from major climate-driven disturbances. Critically, these reefs retain the capacity to grow at rates exceeding measured regional mid-late Holocene and 20th century sea-level rise, and close to IPCC sea-level rise projections through to 2100.

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