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Agencies monitoring coral health in West Maui

By Staff | Mar 10, 2016

A noticeably hazy sheen in the water is a telltale sign that freshwater is mixing with saltwater. PHOTO BY CURT STORLAZZI, USGS.

WEST MAUI – To address environmental concerns, scientists from the U.S. Geological Survey (USGS) are working with local organizations to determine if groundwater quality is affecting coral reef health.

Together with the state Department of Land & Natural Resources’ Division of Aquatic Resources on Maui, the National Oceanic and Atmospheric Administration’s Coral Reef Conservation Program, West Maui Ridge-to-Reef (R2R) Initiative, the U.S. EPA, and the Clean Water Branch of the state Department of Health, scientists are setting up instruments to analyze the composition of the seawater near the reefs close to shore.

Over a six-day period this month, USGS researchers will monitor seawater collected from the coral reefs at Kahekili Beach Park.

The water will be pumped through tubes leading from the reef to the beach. Every four hours, the scientists will take water samples and measure acidity and nutrient levels to calculate whether levels are higher than seawater further offshore.

An autonomous instrument will also be placed on the seafloor near the vent for the full six days to continuously measure the seawater composition. If residents or visitors see these instruments along the reefs, they are asked to not disturb them.

This research aims to discover whether a link exists between the quality of groundwater and the declining coral cover.

According to the agencies involved, a decline in the abundance of live coral and a rise in algal growth have been significant environmental concerns in West Maui since the late 1980s.

Too much algae can smother corals when competing for space, light and oxygen. Algae thrive when nutrients are abundant, but what boosts these nutrients levels?

Humans introduce a surplus of nutrients – such as phosphates and nitrates – into the environment when treating wastewater or using fertilizers in agriculture. These nutrients then trickle down through Maui’s porous volcanic rock, eventually mixing with the fresh groundwater below.

Underground streams of groundwater merge and run beneath the land and coastline until they eventually hit the ocean and bubble up through springs scattered on the seafloor called groundwater seeps.

Freshwater flowing from these seeps is more acidic (lower pH) and contains more nutrients than the surrounding seawater.

Corals living near these seeps appear to be more vulnerable to erosion by organisms such as urchins, bacteria and worms, which also flourish when an abundance of nutrients are in the water.