Maui corals show decreased resilience due to human contaminants
A University of Hawai‘i study reveals that pharmaceutical and industrial pollutants are altering coral metabolomes, leaving reefs less able to survive stressors.
Maui corals show decreased resilience due to human contaminants
Human activities are fundamentally changing the chemical composition of coral reefs around Maui, Hawai‘i, according to a study led by the University of Hawai‘i at Mānoa and published in Nature Communications. Researchers found that 25 contaminants from pharmaceutical, industrial, and agricultural sources have accumulated in the soft tissues of local corals.
The research team, which included experts from the Woods Hole Oceanographic Institution, Princeton University, and various Australian institutions including the University of Newcastle and the University of New South Wales, tested the metabolomes—the pool of chemicals within tissues—of 380 rice corals (Montipora capitata) and lobe corals (Porites lobata). These samples were collected from 16 sites across south and west Maui.
The study revealed that human activities within the marine ecosystem and the adjacent watershed altered these metabolomes. In areas with higher levels of ecosystem disturbance, corals showed an increase in contaminant accumulation and a corresponding decrease in energy and nutrient reserves.
Zach Quinlan, a research biologist at the Hawai‘i Institute of Marine Biology and lead author of the study, noted that the trends were almost identical across both coral species. This was unexpected because the two species possess different life strategies.
"This demonstrates how strong of a forcing these anthropogenic activities really are,"
Zach Quinlan, research biologist at the Hawai‘i Institute of Marine Biology, via soest.hawaii.edu
The researchers identified two primary mechanisms that reduce coral resilience. First, the corals accumulate anthropogenic molecules such as industrial byproducts and pharmaceuticals. Second, the pressure from human activities forces the corals to use their own nitrogen and energetic reserves to cope.
This depletion of resources makes the corals significantly less resilient to environmental stressors, including acidic waters or warmer temperatures. The study suggests a direct relationship between anthropogenic disturbance, the accumulation of dangerous contaminants, and overall coral health.
The team validated these findings by looking at historical coral cover trends from five of their sampled sites. They found that the sites experiencing the most severe declines in coral cover following the 2016 bleaching event were the same sites with the most impacted metabolomes. In these areas, stress chemicals were enriched while energy and nitrogen reserves were reduced.
Megan Donahue, the director of HIMB and senior author of the paper, said the study shows how many anthropogenic contaminants are escaping into marine ecosystems.
"We see increasing evidence that anthropogenic contaminants have broad cumulative impacts, undermining the resilience of coastal ecosystems,"
Megan Donahue, HIMB director, via soest.hawaii.edu
Beyond the specific contaminants found in the Maui study, broader human threats to reefs include destructive fishing practices such as cyanide and blast fishing, as well as mining for building materials and the collection of live corals for the jewelry and aquarium trades. Land-based runoff from sewage treatment plants, deforestation, and coastal development can also introduce oil, chemicals, and insecticides into the water.
Such pollution can promote the growth of algae that smothers corals. Furthermore, oil spills can damage floating eggs and sperm during spawning, disrupting reproductive success. Climate-driven threats, fueled by the burning of fossil fuels and deforestation, continue to increase ocean temperatures and trigger more frequent bleaching events.
The researchers propose that monitoring the metabolomes of coastal seafloor species can serve as a powerful tool for tracking the hidden impacts of human disturbance on marine life.
Quinlan and his team are now moving into controlled experiments. They are searching for methods to enrich the nitrogen and energy reserves in coral tissue to determine if these increases can produce more resilient corals.
