How climate change is affecting the oceans and coral reefs and what we can do about it.
It is no secret the world is getting warmer with the influence of the changing climate being demonstrated through numerous extreme weather events across the globe. But what does a changing reef mean for our oceans and coral reefs?
Climate change is having an effect on ecosystems all over the planet. Forests, farms, freshwater sources and possibly most importantly for us, economically. However, the oceans remain at the centre of the effect, the ‘canary on the coalmine’. They absorb huge amounts of carbon but dramatic changes are already afoot across our planet’s marine systems.
These changes are likely to accelerate with the associated global warming that has been clearly evident since the 1950’s.
Scientists are racing against the clock for solutions to the threat of climate change, and reducing our global carbon emissions is crucial if ocean ecosystems, especially coral reefs are to have any long term chance of survival.
The good news: Oceans as a Carbon Sink
Early in the 18th century English chemist William Henry developed ‘Henry’s Law’ which governs the relationship between liquids and gases. The law states that when a liquid and a gas are in contact, they will achieve equilibrium with each other.
This law has implications for scuba divers in relation to decompression sickness (DCS) as increased gas pressure underwater leads to an increase in the partial pressure of gases within the tissue of your body. Henry’s law also has implications for the world’s oceans.
The effects of increasing climate emissions would be far more serious without the oceans. Across the world’s oceans there is a continual cycle of equilibration of dissolved carbon dioxide in water with carbon dioxide in the atmosphere.
Carbon dioxide readily dissolves in water and the oceans provide a huge reservoir of carbon. About 40% of the carbon emitted into the atmosphere is absorbed by the oceans. What that means is the oceans are an enormous mitigating force against the effects of climate change. Without this, the the world would be warming at a much faster rate and the consequent negative effects would be far greater than is currently being felt around the globe.
The bad news: Oceans as a Carbon Sink
Ocean acidification is the quiet achiever in the climate change ranks falling behind often discussed challenges such as coral bleaching. But what is ocean acidification?
For millions of years the chemistry of the oceans has remained fairly stable. In this stability a diverse and abundant marine environment has developed, evolved and flourished.
Research into the changing conditions over the last 100 years or so is revealing alarming trends and changes in this ancient balance. The chemistry of the oceans is changing as the pH drops and the oceans become more acidic.
An average surface ocean pH has been reduced by an average of 0.1 unit however this small figure actually represents a 25% increase in the acidity of the oceans.
This may not seem like a great deal, but it has major implications of the make up of the oceans and the animals that live there. Many ocean creatures use calcium carbonate to create their skeletons.
Hundreds of species of coral, fish and invertebrates use calcium carbonate as the building blocks of their existence. Millions of phytoplankton and zooplankton species create calcium carbonate matrices as part of their development.
These creatures are the basis of food webs across the globe. If the ocean is more acidic, their skeletons become harder to create, may be more brittle and dissolve more easily. This does not augur well for the future of coral reefs as we know.
Coral itself is an amazing creature. An upside down jellyfish that has learned how to not only fix itself to the seafloor and secrete a hard, calcareous limestone skeleton, but over millions of years it has recruited tenants.
Symbiotic algae called zooxanthellae live inside the coral’s tissue. These algae photosynthesize sunlight and create sugars that provide food for the coral. In some incidences up to 90% or more of the coral’s food.
When the water becomes too warm, or the UV radiation becomes too intense, these symbionts over metabolise, and instead of helping the coral, they actually cause tissue damage. Consequently, the coral needs to expel the symbionts it doesn’t want to, but it needs to to survive in the short term.
Research has shown that coral reefs are particularly sensitive to increases in ocean temperature. Bleaching events are happening more often and on a wider scale.
In Koh Tao we experienced a severe coral bleaching event in 2010. Since then, many of the world’s coral reefs have experienced widespread bleaching, with a global mass bleaching event recorded between 2015-17.
During this event, the effect on Koh Tao was relatively limited (compared with other locations) and hopefully the next bleaching event is many years away. But there is little doubt that bleaching events are likely to become more frequent and potentially more severe.
With shorter gaps between events the challenge is for reefs to be granted enough time to recover.
Rising sea levels are having a detrimental effect on the health of mangroves and seagrass ecosystems. These habitats provide important complementarity to coral reefs. Many coral reef associated animals and organisms spend juvenile phases of their lives in coastal areas dominated by mangroves and seagrass.
Rising sea levels and warmer waters are both having negative effects in these associated ecosystems. Seagrass, similar to coral requires access to sunlight to photosynthesise. If sea levels rise so that these ecosystems become too deep, their survival will no doubt be threatened.
Turtles: Threats to iconic species
Sea turtles are ancient animals that have roamed the oceans for millions of years. Despite this rich history, climate change and the expansion of human populations is having a detrimental effect on turtle populations around the globe.
Increasing temperatures not only affect the oceans, but also the sand in which turtles nest. The temperature of the incubating sand for the turtle eggs determines the gender of the turtles. Cooler temperatures result in male species, warmer temperatures result in females.
With changes to the gender balance predicted, scientists believe the future genetic diversity for turtles could be under threat. Not to mention the loss of habitat these creatures are experiencing as mangroves and especially seagrass and coral reefs are degraded and transformed forever.
Food Web Disruptions
We have already discussed the effect of warmer oceans and important food sources such as zoo and phytoplankton. When it comes to food webs, the impact of changing abundance and distribution of these base organisms will create ripples across entire ecosystems.
As individual species are compromised, others in the chain begin to feel the effects of dwindling supply and either adapt or die out forever.
Not only are species lost, but patterns change as those mobile species migrate to new locations where conditions may be more suitable. Recent studies suggest hundreds of species of ocean fish may migrate towards the poles in search of cooler ocean conditions.
Making a positive difference to the health of our oceans and all ecosystems
Solutions to the global crisis facing reefs and ecosystems are both individual, local, regional and global.
Reduce carbon emissions
Regardless of anything else we do, a global reduction in carbon emissions is essential to keep ecosystems from collapsing altogether. This requires a collective effort from individual actions to national commitments by governments all around the world.
From an individual perspective, every light you turn off, every flight you don’t take and every person you encourage to be more environmentally friendly contributes to reduce carbon emissions.
Active reef restoration refers to the active interventions undertaken by people and businesses across the globe. This takes many and varied forms from growing and outplanting coral in nurseries, to sexually propagating new corals from eggs.
Businesses and community groups in Koh Tao are leading the way in implementing conservation measures to improve the health of coral reefs locally. Whilst active reef restoration has big impacts in small areas, by training people up and getting them involved in the process, increases the impact exponentially.
Become a coral reef conservation champion
There are many training courses and PADI conservation programs that enable you to spread the word, expand the reach of your message and do your bit to lead by example.
By distilling information you provide people with knowledge and awareness to create behavioural change to make a difference.
‘In the end we will conserve only what we love,
We will love what we understand, and
We will understand only what we are taught’
Marine Scientist? Take the next step
Marine science leaders around the globe are working to find locally relevant and globally up-scalable solutions to improve the resistance and resilience of coral reefs.
Programs like marine resource management and the reef check ecodiver provide ideal practical starting points for people wishing to graduate into the field of marine science.
For example, scientists in Australia and Hawaii are working together to breed heat resistant zooxanthellae to enable corals to survive in warmer temperatures. Who knows, the solutions are many and varied. They are there waiting to be discovered and there’s no reason why it couldn’t be you.
Nathan Cook M.Sc
PADI MI 479720