Aboard the Putiraja

Note: the following post is the latest in a series chronicling the ongoing expedition to the Raja Ampat Islands. Read more here.

The world’s oceans are getting warmer. But what does that mean for coral reefs?

After all, coral reefs grow in tropical oceans so they’re used to warm water, right? Well, this is true, partly, but when temperatures get hotter than normal and stay that way, corals begin to “bleach.” Climatic events like La Niñas cause ocean temperatures to rise above normal. In 2010, a La Niña event caused coral bleaching in reefs around the world, including many in Indonesia.

Temperature is also important to reefs on a day-to-day basis. Seasonal temperature cycles are a cue for reproduction in dozens of reef species — including corals — and they affect growth rates in everything from bacteria to fish. Cool water patches can be caused by local “upwelling” — a phenomenon in which cool, nutrient-rich water rises to the surface, creating a source of food and attracting an amazing amount of marine life.

So, to better understand local patterns of ocean temperatures in Misool, Purwanto and Muhajir have been putting out underwater temperature loggers in seven Misool reefs since 2009. The loggers are around the size of a small flashlight and record temperature readings every 30 minutes for an entire year.

Muhajir downloading temperature data from logger

On this expedition, we’ve been retrieving and downloading the loggers and comparing their data to temperature records from previous years. Interestingly, 2010 not only saw higher-than-usual summer temperatures; winter temperatures were also warmer than normal. It seems that 2011 has been a more normal year for ocean temperatures, which is good news for coral reefs. This year, we’ve seen a return to the usual annual pattern where temperatures drop to around 26°C (79°F) in July and August, coinciding with the south monsoon season.

We’re now approaching the warmest months of the year for Misool and temperatures are already warm — around 29.5°C (85°F). So far, we’ve seen a few coral colonies that are pale or slightly bleached, indicating that they are a little stressed by warm temperatures. As long as temperatures don’t get too high, we expect these corals to recover. However, this just goes to show how sensitive these reefs are to even small increases in temperature — even in “normal” conditions, they are already living pretty close to the highest temperatures they can tolerate.

The data we’re collecting on this expedition will help us understand differences between reefs and between coral species so we can see which types are most sensitive to increased temperatures. We can then use this information to identify reefs and species that may be more “resilient.” By protecting these resilient reefs from local threats like overfishing or anchor damage, we can hopefully help reefs survive climate change.

Explore further coverage of this expedition on nature.org and learn more about the Conservancy’s involvement in the game-changing Coral Triangle Initiative on Coral Reefs, Fisheries and Food Security.

(First image: The deck of the Putiraja, the expedition’s dive vessel. First image credit: TNC. Second image: Muhajir collecting data from a temperature logger. Second image credit: TNC.)

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