Great Barrier Reef decline over the last 90 years and how to save them!

Introduction

The Great Barrier Reef, home to the largest coral reef system and thousands of species of organisms, faces threats of climate change, pollution, and fishing, bringing its health into great concern. The decline of reefs due to changes in the way they build and the species that inhabit them risk the food and livelihood of hundreds of millions of people. This study examines data collected over the past 91 years to better understand the survival of coral reefs, exploring the documented environmental conditions surrounding coral reefs, community structures of organisms there, and highly accurate mapping of the reef. 

Methods

The researchers selected a reef that had been subject to study a number of times in the past, dating back to a quadrat-based survey that ran from 1928 to 1929. They observed coral and marine species biodiversity, supplementing their work with photographs. Areas previously studied were photographed and these photographs edited into one continuous mosaic. Comparing that mosaic (and the species it featured) to reports from previous expeditions allowed the researchers to determine the nature and extent of major trends in the reef.

Results

The barrier reef has seen the worsening of coral cover, colony size, and species diversity over the last 90 years. Coral cover and colony size have declined, with no corals in many intertidal areas named for their dominant reef-building coral. There has been a drastic fall in species richness. Revisiting 13 sites from 1954 found that many species of coral were near extinction and all the sites saw their population decline to half. Corals forms have changed from hard corals to soft corals and from branching corals to massive corals. Many invertebrates that called these intertidal coral colonies home have vanished.

 Figure 1: Dead coral reefs near Low Island

Discussion

In the past, coral cover has been used as an indicator for reef health as it strongly predicts the capacity of a reef to track sea-level rise and resist drowning. However, species diversity and richness are crucial indicators of reef health. In addition to lower coral cover and size, there has also been a huge drop in species diversity and richness since 1928. This lower diversity is likely as a result of chronic stress and disturbances. These conditions select for coral species which are disturbance resistant and slow-growing, such as soft corals and massive corals. Coral now takes longer to recover following a disturbance such as a cyclone. Additionally, coral reefs which fail to reassemble a diverse community have higher vulnerability and sensitivity to future disturbances. Low Island has failed to reassemble a diverse community and is more susceptible to both drowning and cyclones than it was in the past. Reports since 2000 suggest identical effects in inshore and offshore reefs globally. Hence, the decline of reefs on low isles provides an unfortunate story for coral reefs globally. 

Potential Solutions

Solving the Coral reef problem requires pollution control, better fishing policies, reducing CO2 emissions and extreme temperatures. Better fishing practices improve reef health by preventing overfishing of keystone species crucial to the local ecosystem(Health Fisheries). One example is the decline of shark populations(keystone species) due to overfishing. It has lead to an increase in mid-level feeders, a decline in herbivores and an increase in algae, which harms the coral reefs(Earthsky). Extreme high temperatures due to climate change can potentially destroy 90% of the reefs. Scientists like Daniel Harrison believe that reducing CO2 is insufficient. Instead, they propose reducing reef water temperatures by making clouds brighter and reflecting more sunlight in a process called Marine Cloud brightening(Temple, J.).

Figure 2: Impact of overfishing and loss of species diversity on coral reefs

Figure 3: Mechanism of action of Marine Cloud brightening

Sources:

1. Fine, M., Hoegh-Guldberg, O., Meroz-Fine, E. et al. Ecological changes over 90 years at Low Isles on the Great Barrier Reef. Nat Commun 10, 4409 (2019). https://doi.org/10.1038/s41467-019-12431-y
2. Bar-Ilan University. “Longest coral reef survey to date reveals major changes in Australia’s Great Barrier Reef.” ScienceDaily. ScienceDaily, 27 September 2019. <www.sciencedaily.com/releases/2019/09/190927074930.htm>.
3. Chemical & Engineering News. “Climate Change Is Destroying Our Coral Reefs. Here’s 3. How Scientists Plan to Save Them.” Accessed February 11, 2020. https://cen.acs.org/environment/climate-change/Climate-change-destroying-coral-reefs/98/i6.
4. Healthy Fisheries. (n.d.). Retrieved from https://coral.org/what-we-do/healthy-fisheries-for-reefs/
5. Earthsky, Researchers find coral reefs at risk when sharks overfished. (n.d.). Retrieved February 12, 2020, from https://earthsky.org/earth/researchers-find-coral-reefs-at-risk-when-sharks-overfished
6. Temple, J. (2017, April 20). Are brighter clouds the best bet for the Great Barrier Reef? Retrieved February 12, 2020, from https://www.technologyreview.com/s/604211/scientists-consider-brighter-clouds-to-preserve-the-great-barrier-reef/

Article Source

https://www.sciencedaily.com/releases/2019/09/190927074930.htm -Online article

https://www.nature.com/articles/s41467-019-12431-y Actual Study article references