Blue Planet | Episode 3 | Coral Reefs

It is difficult to disagree that coral reefs are of global importance – the most biodiverse, the most colourful, and often associated with tropical paradise. As well as aesthetic beauty, reefs possess huge biological and socioeconomic value. They are the primary source of food for up to a billion people, act as natural storm barriers, bring in millions via tourism, have potential in medical research and provide a nursery for species from all over the rest of the ocean (1). They are home to 25% of all known marine species.

Corals bleached completely white.
Bleaching at Green Island, Northern Great Barrier Reef, during the 2017 event. Photo by Andrew Ball.

It is therefore extremely concerning that reefs are in the worst state they have ever been in. The programme was not exaggerating how serious this is. No reef anywhere on Earth is what it was 20 years ago, and is barely recognisable from 100 years ago. One important consideration in ecological science is setting a baseline – a ‘pristine’ environment, or a ‘fully grown’ fish – to act as a control with which to assess the extent of change. This is usually a nearby area, or the same location a few months or years before. What is problematic is that these baselines change generation to generation (2).

As a young person, the places I have dived and snorkelled that I consider ‘amazing’ would be considered degraded to senior divers who started diving 50 years ago. On a fieldcourse in Bermuda this summer I was struck by the beauty of an offshore reef we visited to measure coral cover – I was surprised to hear the scientists working at BIOS considered this site degraded. The same issue occurs with fisheries, where what is considered a ‘big fish’ by one generation would have been considered a juvenile by a great grandparent. The programme’s spectacular footage from French Polynesia represents the kind of community that most coral reefs would have possessed at one time – today represented by very few extremely remote places. It is thought that before human interference, apex predators like groupers and sharks would have made up the majority of biomass in a reef community (3). Perspective is powerful, and as scientists we must select ours carefully.

A small fish swimming above a coral, with white tips from bleaching.
Early signs of bleaching on an Acropora sp. Corals are keystone species, and their deaths have far-reaching consequences for the rest of the marine ecosystem which depends on them. Photo by Andrew Ball.

Additionally, the corals on which the entire reef ecosystem depends are imperilled worldwide. The largest living structure on Earth, the Great Barrier Reef, bleached two consecutive years in 2016 and 2017 – the first time this has ever happened – in the worst bleaching event in its history. Corals in the Caribbean have declined by 40% in the last five decades (4). Something that I have found as fascinating as shocking considering contemporary life on Earth in the context of its entire history. This decline is a geologically significant event – such large formations dying en mass in a blink of an eye in terms of Earth history is an unusual freak event. The science is increasingly showing that humans are the most influential species of vertebrate in the history of life on Earth.

There have been encouraging suggestions of long-term adaptability – some of the research coming from the Coral Reef Lab at NOC. Some reefs in the Middle East have showed less extreme responses to bleaching. However, I attended a seminar by Dr. Leonard Nurse of University of the West Indies in Barbados a few weeks ago, who is involved in Caribbean coastal management and the Intergovernmental Panel on Climate Change. He made no qualms about mentioning that “no evidence exists that corals can adapt to unabated thermal stress over decadal timescales”.

Change is occurring at both regional and global scales, and although reefs are already declining globally, regional management, intergovernmental climate change agreements and robust science are key to boosting reef longevity and resilience. Seeing the enormous engagement and widespread reaction to the Blue Planet episode is extremely encouraging, and I look forward to seeing a new generation inspired to understand and protect these beautiful habitats.

1. Pascal, N. et al. Economic valuation of coral reef ecosystem service of coastal protection: A pragmatic approach. Ecosyst. Serv. 21, 72–80 (2016).
2. Roberts, C. The Unnatural History of the Sea. (Island Press/Shearwater Books, 2008).
3. Friedlander, A. M. & DeMartini, E. E. Contrasts in density, size, and biomass of reef fishes between the northwestern and the main Hawaiian islands: the effects of fishing down apex predators. Marine Ecology Progress Series 230, 253–264 (2002).
4. Gardner, T. A., Côté, I. M., Gill, J. A., Grant, A. & Watkinson, A. R. Long-Term Region-Wide Declines in Caribbean Corals. Science (80-. ). 301, 958–960 (2003).

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