By: Victor Bonito, Director, Reef Explorer Fiji
Over the last three years, coral reefs worldwide have suffered unprecedented damage to coral communities from abnormally warm seawater temperatures. When the US National Oceanic & Atmospheric Administration (NOAA) announced the third global coral bleaching event in October 2015, shallow reef areas along Fiji’s Coral Coast had already experienced two back-to-back years of widespread coral bleaching. Before we received the depressing news about our local reefs, we decided to take action and incorporate lessons learned from previous bleaching events and seawater temperature monitoring efforts.
In late 2015, our Reef Explorer project team and local youth clubs established five new coral nurseries across our local reefs. We stocked the nurseries with a good diversity of coral species propagated from numerous donor colonies that we suspected had good thermal (heat) tolerance due to their size and placement on the reef. While we chose them for a purpose, we never thought that our corals would be put to the test so soon.
Throughout January 2016, nearly all the corals propagated in the five nurseries (consisting primarily of 34 species in 13 genera / 7 families). Several months earlier, these corals were thriving, growing rapidly, and looked healthy in color despite the high temperatures the loggers deployed). Corals on the reef areas surrounding our nurseries also looked healthy into the warm season, despite the extreme seawater temperatures throughout the month of June.
On the weekend of February 6th, 2016, however, seawater temperatures spiked too high and corals and other marine life began to die. Shallow reef areas along the Coral Coast suffered from mass fish kills on several days during the mid-day low tides. Most hard and soft corals bleached with many dying during the first few days. Seawater temperature remained high throughout the month of February until Cyclone Winston, which brought so much destruction to many areas in Fiji, helped cool seawater temperatures by several degrees at the end of the month, providing relief for the surviving corals. Just as the seawater was starting to heat up to extreme levels later in March, Cyclone Zena passed by Fiji cooling the seawater again. But the damage had already been done – extensive stands of colorful corals and fish had been turned into coral graveyards at a scale that no one had seen before.
Our Reef Explorer team conducted rapid surveys of the reef areas surrounding three of our nurseries and assessed the impacts of the bleaching event on our nursery corals. The coral bleaching event severely bleached most of the live coral on the shallow reef areas and ultimately killed 50% or more of the hard and soft coral cover on the reef surrounding the nurseries. As if the bleaching was not enough of an assault, a new cohort of coral-eating crown-of-thorns starfish moved onto the reef and moved around voraciously eating the remaining preferred coral species. While most (70-80%) of the nursery corals also bleached to some extent during this extreme thermal event, our team’s assessment found that only 19% of the 7830 corals we propagated ultimately died (range 6% – 33%) by the end of the bleaching event.
It was hard not to cry in our masks as we swam through the devastation that had occurred on the reef before our very eyes over a matter of weeks. The 6,058 corals that survived were able to transplanted back to the reef, giving us hope for the future of our reef. Some of the coral species we propagated came in a wide assortment of colors – bright purple, green, blue, and cream colored varieties. As our team reattached the new coral colonies back to the reef, we made a concerted effort to intermix various colonies of the same species in close proximity of each other in various patches on the reef. Our goal is to promote the reproductive success of the more heat-tolerant strains of corals when they spawn. We hope that our gardening will assist coral populations on the reef to more rapidly adapt to the warming ocean temperatures.
While coral reefs worldwide have been largely impacted by coastal populations and development, now the impacts of global climate change threaten even reefs being protected from severe human impacts. Though we are not certain of their fate in the long run, we feel a certain hope for the future of our reefs from the coral gardens we planted this year. While our global community works to address climate change, we are optimistic that the impacts of our local corals will be resilient, able to acclimate and adapt to our warming oceans, and may continue to support coastal populations as they have since time immemorial.
This project was supported by Biotherm Water Lovers via Mission Blue.