Summary

Report of study by a team of Australian marine scientists to assist in the assessment of damage to the coral reefs of the Maldives following the 26 December 2004 tsunami.

Description

Prepared by an Australian Government Mission and the Maldives Marine Research Centre

Full report [PDF file - 1.68MB]

Executive Summary

In response to a request from President Gayoom of the Maldives, the Australian Prime Minister Mr Howard committed a team of Australian marine scientists to assist in the assessment of damage to the coral reefs of the Maldives following the 26 December 2004 tsunami.

The team was formed by scientists from Australia's leading marine science agencies (CSIRO, Australian Institute of Marine Science, Great Barrier Reef Marine Park Authority and James Cook University), and included expertise in coral and coral reef fish ecology, reef health assessment, reef management, reef and island geomorphology and baitfish assessment. AusAID provided co-ordination and funding for the team's mission, and an AusAID officer accompanied the team to the Maldives.

The Australian team joined with scientists from the Maldivian Marine Research Centre in a 17 day mission with the following major objectives:

1. Conduct a rapid assessment of coral reef health, including the nature and extent of any damage to corals and associated reef ecosystems caused by the tsunami,
2. Examine the geomorphology of islands and associated reef systems to determine the nature and extent of any structural damage or changes resulting from the tsunami,
3. Examine the impacts of the tsunami on baitfish populations resident in atoll and coral reef lagoons,
4. Develop recommendations for work to be conducted following the mission's rapid assessment where this is required to fully understand the impacts of the tsunami on Maldivian coral reef systems.

Coral and Coral Reef Health

One hundred and twenty four reef sites were surveyed in seven atolls, covering about 170 km of reef margin, with additional information from 65 tourism dive sites. Although there was damage to coral and movement of sediments in all regions these perturbations varied in extent and intensity. Even so, surveys generally indicated that direct damage to reefs from the tsunami was minor. However, the reefs of the Maldives are in the early stages of recovery from the massive bleaching in 1998 and the most significant consequence of the tsunami may be to hamper this process. Many survey sites had a light coating of sand. Small coral recruits are most vulnerable to smothering by sand and rubble and even a light coating of sand may make reef surfaces unsuitable for future settlement. In general little is known of the biodiversity or prior ecosystem status and past changes on coral reefs of the Maldives. This complicated the assessment of the effects of the tsunami and, given the economic importance of coral reefs to the nation, this is a gap.

The mission was hampered by a lack of adequate historical data on the biodiversity and ecosystem status of, and past changes to, coral reefs of the Maldives. Given the economic importance of coral reefs to the nation, this is a critical gap. Our strong view is that the biodiversity and resilience of coral reef ecosystems needs to be safeguarded through a network of protected areas, and there is a need to increase national capacity in coral reef science so as to continue and extend existing monitoring programs for reef resources.

Reef and Island Geomorphology

An assessment of the geomorphology of reef flats, shorelines and islands of 19 inhabited and uninhabited islands of Laamu and Thaa Atoll was undertaken. The tsunami approached islands from the outside of the atoll, including on the western side. Despite significant damage to buildings, the tsunami had less impact on the reef flats, islands and beaches than was expected:

• Reef flats on the outside of atolls were minimally impacted.
• Beaches exposed to the tsunami experienced limited erosion, and some toppling of vegetation that may increase the likelihood of further seasonal erosion.
• The ends of islands suffered more extensive erosion.
• The island surface and soil structures of the islands remained relatively intact, and there were no major accumulations of reef sand or shingle.
• On the beaches on the lagoon side of the atolls, scour pit formation caused significant erosion and deposition of sediment on the adjacent reef flats, except on islands where the water did flow right across the island.
• One case of an island breaching was documented. The importance of shoreline vegetation for erosion prevention was significant in all environments.

Much of the building damage was caused by scour under and around structures, and by physical damage by debris. On coral walls without rendering, water entering cracks led to rapid collapse of walls. Increased groundwater pressures probably caused some lifting of solid floors. Huraa on North Mal� Atoll was visited where one area of collapse of the ground was probably assisted by the tsunami, but a cavity or area of loose sand beneath a cemented layer, which led to the collapse, is not unusual.

Bait and Fisheries Assessment

To assess the impact of the tsunami on reef-associated fisheries (bait and reef fisheries) surveys of the perceptions of fishers active in Laamu, Thaa and Baa atolls and at Mal� fish market were undertaken. Islands in Laamu and Thaa Atolls were highly impacted by the tsunami, whereas Baa atoll was only moderately and Mal� only lightly impacted.

The study found that fishers in the pole-and-line fishery in the southern atolls (Laamu and Thaa) noticed few effects. Most had returned to fishing and their income was similar to that before the tsunami. In Baa Atoll, fewer fishers had returned to fishing and more were still involved in the reconstruction of their islands. Reef fisheries in Baa Atoll and in Mal� had reduced effort as nearby resorts had low occupancy and thus demand was low.

A high proportion of pole-and-line tuna fishers landing in Mal� felt the bait fishery was poor and had declined since the tsunami. However, these fishers believed that poor bait fish catch rates were due to seasonal fluctuations rather than tsunami effects. It was impossible to assess the accuracy of fisher perceptions due to a lack of fishery data on their catch, effort and species composition. While surveys are useful in obtaining a rapid early assessment of major impacts, it will not detect more subtle or longer term effects of the tsunami on fishery productivity.

Key Recommendations

The existing Maldives coral reef monitoring program needs to be expanded to cover more reefs and allow detailed examination of the impacts of the tsunami on fragile coral populations and associated ecosystems currently rebuilding after the massive coral bleaching event of 1998.

To facilitate increased monitoring of reef resources, there is a critical need to increase national capacity in coral reef science (including fisheries).

The biodiversity and resilience of coral reef ecosystems needs to be safeguarded through a network of protected areas.

More detailed examination of the geomorphic effects of the tsunami on a small number of islands should be undertaken as soon as possible.

A simple monitoring program of island shorelines at selected sites should be implemented, in order to better understand seasonal and long term trends, as well as the effect of major events such as a tsunami.

The important live bait fishery and the valuable reef fish fisheries need to be incorporated in the national fishery data collection system in order to be able to detect the effects of major environmental perturbations or excessive catch.