It is a bright sunny day and the sea is finally calm enough for us to access the windward corner of Orona Atoll. Having surveyed 6 of the 8 atolls and islands, I feel ready to summarize and share my thoughts on coral disease in the Phoenix Islands Protected Area (PIPA).
Corals are just like people; they get sick and show signs of illness just like us. We get sick when our normal body performance is interfered with or modified by either presence of pathogenic micro-organisms such as bacteria, fungi and/or protozoans or abrupt changes in environmental conditions, such as temperature, high levels of nutrients and/or exposure to toxicants. Corals respond in a similar way.
|Example of black-band disease on a stony coral | Photo: Andy Bruckner, NOAA via|
However, low levels of disease are a natural part of almost all wildlife populations and nature’s way of weeding out the weak. When corals get exposed to pathogenic micro-organisms or environmental stress, the most obvious signs are tissue loss commonly seen as unusual whitening followed by algal growth on the recently dead areas. If conditions remain status quo and the coral is unable to mount a strong enough immune response to fight back, the whole coral may slowly die. While some of these types of diseases are known to be infectious (e.g. spread from colony to colony), and have been known to cause rapid and widespread mortality on reefs, some tissues diseases aren’t infectious. With the rising levels of coral disease across the Indo-Pacific and the threats of climate change and increased land-based pollution, coral disease has become a key concern for many researchers and coral reef managers.
|Example of yellow-band disease on a stony coral | Photo: Andy Bruckner, NOAA via|
I was very excited to be able to study the types and presence of diseases in one of the largest marine protected areas in the Pacific, and to assess the health of the corals. In Kanton I saw maybe three or four corals that were affected by lesions (per survey site) that were likely a general stress response rather than disease.
All the reefs we surveyed on Enderbury, Birnie, Rawaki, Manra and now Orona, have not shown any signs of disease. Actually, as we have moved south we have seen less and less disease. I could not help but be amazed by my findings. I kept thinking about how a large marine protected area, with almost no direct human impact that is recovering from a past bleaching event and currently experiencing warm water temperatures again, are largely free of disease… at least, so far. It will of course be important to keep an eye on how increasingly warm temperatures from the intensifying El Nino interact with disease and other stressors. But thus far, it is exciting that PIPA has a great story to tell about coral health, recovery and low rates of disease — and this gives me hope for future.
Yashika Nand joined WCS Fiji in 2010 as a Marine Scientist. She graduated with her Post-graduate Diploma in Marine Science specializing in coral reef ecology and biology with emphasis in climate change from the University of the South Pacific in 2008. She has previously worked for the Department of Fisheries in Fiji as the lead coral researcher. Yashika manages all data from WCS’ biological monitoring program, and helps integrate this into conservation planning in Fiji. Her expertise includes coral identification, coral health assessments and the aquarium trade fishery. She is currently doing a Masters in coral reef ecology, focusing on coral disease at the University of the South Pacific.