Despite dark ominous clouds over the sea, we headed out into the lagoon at Ovalau lagoon to survey reefs on the southwest of the island.

Dark algal mats covering the surface of sand in Ovalau lagoon. Image by Sangeeta Mangubhai

Dark algal mats covering the surface of sand in Ovalau lagoon. Image by Sangeeta Mangubhai

I was not prepared for what I saw under the water. All around me were patch reefs scattered over sand that were covered in thick algae that smothered everything in its path. This is what I call ‘bad algae’ – it is algae that is toxic, outcompetes corals, outcompetes good algae, and prevents no new corals from coming into the area and settling. I recently learnt there are new studies from tabu areas in Fiji that are suggesting that if you have bad algae on reefs, fish larvae are less likely to settle in the area.

Green algae smothering surfaces in Ovalau lagoon. Image by Sangeeta Mangubhai

Green algae smothering surfaces in Ovalau lagoon. Image by Sangeeta Mangubhai

Algae can take over reefs if there are lots of nutrients that are entering the water, which they soak up and use to grow very fast. Algae can also become dominant if you remove too many herbivores who play an important role as ‘lawn mowers’ on the reef, keeping algae down to natural levels.

Filamentous algal mats smothering life in Ovalau lagoon. Image by Sangeeta Mangubhai

Filamentous algal mats smothering life in Ovalau lagoon. Image by Sangeeta Mangubhai

My plan is to start talking to other colleagues to learn more about these algae – what causes them to proliferate and become so dominant, and what actions are needed to reverse this worrying trend? And what are the consequences if we cannot get rid of the algae? I am going to hope that the lagoonal reefs I have seen are not beyond a critical tipping point – meaning that the reefs have not permanently changed from being coral-dominant to algae-dominant. It is clear from today we all need to do more to keep our reefs healthy and productive. Our reefs in Fiji are not limitless.