COOK ISLANDS MARINE PARK: Coral reef survey of Aitutaki, Manuae, Mitiaro, Takutea, and Atiu in the southern Cook Islands

Type Report
Title COOK ISLANDS MARINE PARK: Coral reef survey of Aitutaki, Manuae, Mitiaro, Takutea, and Atiu in the southern Cook Islands
Publication (Day/Month/Year) 2013
Publisher Government of the Cook Islands
From 28 July – 9 August 2013, a research team consisting of individuals from the Office of the Prime Minister of the Cook Islands, Te Ipukarea Society, Oceans 5, Pacific Islands Conservation Initiative, Cook Islands National Environment Service, and local volunteers travelled aboard the vessel Plan B of the Waitt Institute to conduct a rapid marine assessment of the fore reefs of the islands of Aitutaki, Manuae, Mitiaro, Takutea, and Atiu in the southern Cook Islands –– for the purpose of assessing the health of coral reefs within the proposed Cook Islands Marine Park.

The results of this assessment showed that coral communities on the fore reefs of Manuae, Mitiaro, Takutea, and Atiu were relatively healthy with good coverage of hard corals. Indicators of healthy reefs on these islands also included the dominance and high abundance of the coral-associated fish family Pomacentrids, high cover of crustose coralline algae, and low cover of macro-algae. Coral communities were very similar on these islands in terms of species composition (except Atiu), attributed to the dominance of a few species of hard coral –– such as the platy coral Astreopora expansa on steeper reef slopes –– which thus far appear to be unique to these islands. Despite low abundance of herbivorous fish species noted, this was unlikely the result of overfishing as human population is low on these islands and fishing activities have declined overall. On the other hand, Aitutaki’s reefs showed a significant decline in coral health, particularly on the fore reef.

Interestingly, coral reef disturbance (i.e., COTS infestation and coral disease) and recovery (based on coral colony size information) appear to have some geographical pattern, with both occurring in a southeastward direction from Aitutaki towards Manuae, Mitiaro, Takutea, and Atiu. Though limited historical information and baseline data exists for this chain of islands, seemingly these islands have gone through a cycle of disturbance with recovery well underway. Yet, a subsequent round of disturbance has commenced in this southeastward direction, with Aitutaki showing a significant decline in coral cover since the last fore reef survey in 2008, and Manuae (the next island in the chain) showing signs of stress related to coral disease and COTS predation.

Based on this pattern, we suggest that an outbreak of COTS and perhaps the prevalence of coral disease on Aitutaki could potentially cascade down the rest of the island chain. Hydrodynamic studies also support this pattern, particularly from December to March during the spawning months for most marine organisms in the region, where the predominant current flow is south to southeastward. In this regard, a bottomup control of nutrients in Aitutaki may reduce the impact of anthropogenic stressors such as COTS and coral disease on islands to the southeast. A more detailed study of coral disease and other diseases (i.e., Coralline

Lethal Orange Disease recorded on Aitutaki) would be critical to elucidate the causes and the extent of the damage and distribution in this group of islands. Indeed, connectivity studies and information from regular monitoring of these reefs will certainly help us understand how these islands influence each other, which would feed into an effective management plan for these delicate ecosystems within the Cook Islands Marine Park.

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