As recent bleaching events have shown, warming ocean waters pose a great threat to the existence of natural wonders like the Great Barrier Reef, but they aren’t the only factor that needs to be taken into account. Scientists have discovered that abnormal flows of nutrients can compound the risk of bleaching in already vulnerable corals, a finding that could shape future approaches to conserving the at-risk organisms.
Generally speaking, coral reefs exist in environments with low levels of naturally occurring nutrients, but ocean currents along with man-made sources like stormwater runoff can wash things like nitrogen and phosphorous into the area. While this was already known to scientists, it has been difficult to investigate the effects of these nutrients in isolation, with researchers instead only studying them in combination with heat stress.
The authors behind the new study, from the King Abdullah University of Science and Technology and the University of Queensland in Australia, found a way around this. The team turned to long-living corals in the Red Sea for its study, as this is one of the only marine environments in the world where nutrient stress and heat stress impact corals independently of one another.
By examining the skeletal cores of the old corals, the team was able to investigate the causes of historic bleaching events. This revealed that only on occasions where both high temperatures and excessive nutrient flows occurred at the same time were the conditions right for these severe bleaching events.
This evidence that excess nutrients can exacerbate the effects of heat stress and trigger severe bleaching provides another piece of a very complicated puzzle. But the scientists hope that this new information can increase the effectiveness of conservation strategies, with most coral reefs facing a fight for survival as ocean waters continue to warm and become more acidic.
“Incorporating nutrient-supplying ocean currents into coral bleaching forecasts will enhance those predictions that are based on temperatures alone,” says Professor John Pandolfi from the ARC Centre of Excellence for Coral Reef Studies at the University of Queensland. “Our research suggests that projections of coral reef futures should move beyond solely temperature-based stress to incorporate the influence of ocean current systems on coral reef nutrient enrichment, and thus susceptibility to bleaching.”
The research was published in the journal Science Advances.
