Volunteer Day Recap: Limu Sampling in South Maui

Testing limu (marine algae) to learn about pollution sources in South Maui Waters

Since 2019 Maui Reefs has analyzed several types of limu (marine algae) that can indicate the presence of freshwater nutrient pollution along Kahului and the West and South Maui coastline. Studies conducted in previous years showed pollution was a concern in these areas, so we wanted to see if nitrogen (a fertilizer) was still in those waters and, if so, where that pollution might be coming from.

To help answer these questions, a group of Maui Reef volunteers went out on February 11 to collect samples from 12 sites along the South Maui coast. The specimens that will be tested by the University of Hawaiʻi at Mānoa for nitrogen, which can indicate potential pollution problems when found in excessive amounts

Like many plants, limu will absorb nitrogen as they need certain amounts to grow. When limu is analyzed for nitrogen, we can tell if nitrogen levels are too high for normal conditions. When too much nitrogen is present in the water, it harms reefs by causing algae to grow too quickly and to dangerously large sizes. Too much algae can smother a reef and severely reduce the oxygen needed to survive. Further analysis can also help determine if the nitrogen source is related to sewage or if it is coming from a natural source.

In order to spot patterns and trends in conditions, we generally need to have 3 year’s worth of data. Although Maui Reefs sampled limu in 2019, 2023, and 2024, not all sites were sampled each year. But, with the help of our amazing volunteers, we were able to quickly collect more samples than we have ever done in a single day! Now, we have a larger base of information  to build off of as we look to collect more samples in the coming months and analyze the new and old data to see what is happening in the waters off of South Maui.

Mahalo nui to all of our wonderful volunteers who made this work possible!