Expedition update: Opal Reef

Today we surveyed south and main Opal reef, adding to the data we collected from the first expedition. However, unlike on our September visit, today we had poor visibility (only around 10 metres). This reflects how dynamic reef systems can be; tides, weather and seasons all play a role in the water clarity. As the water warms during the summer months, the amount of algae living in the water column increases, adding to the particulates in the water. While surveying, it was quite interesting to find that despite being in the marine park zone, we did not see many fish. Particularly at Main Opal Reef, there were distinct patches of degraded coral life; portions of coral colonies were overgrown by blue-green algae (cyanobacteria) and macroalgae dominated the benthos. On the other hand, South Opal Reef was quite scenic especially in the channel that separated the two reefs. Here there were extensive patches of branching corals giving refuge to small reef fish and coral overhangs giving shade to a school of Striped Sweetlips.