CITIES BENEATH THE SEA
Coral Reefs, Iingqaqa zekorale, *izixhobo zamaKhorali, Koraalriwwe
Living connected homes filled with life but sensitive to climate change
© Geoff Spiby
What are Coral Reefs?
Coral reefs are living cities that build themselves naturally over time by extracting and accumulating minerals (calcium carbonate) from the seawater to form hard skeletons. Corals are animals and the corals that make shallow coral reefs have tiny algae living in their tissue which capture energy from sunlight so that they can grow. Coral reefs may take thousands of years to build from the time the first coral polyp is laid down, but in South Africa, our cooler conditions only allow for a carpet of coral cover in shallow water rather than many layers of coral (accretive reef).
Coral ‘apartment blocks’ are colonial animals; meaning that each coral polyp is identical to every other coral polyp. The polyps work together as a colony in an endosymbiotic relationship with the zooxanthellae– the tiny algae inside each polyp that are able to turn sunlight into nutrients for the coral. In turn, corals provide a protective structure for the zooxanthellae and build up their calcium carbonate skeletons by removing minerals dissolved in the seawater.
South African coral reefs are located in the warm waters of the Indian Ocean, in Northern KwaZulu Natal. These are the southernmost coral communities on the African continent and one of the most biologically diverse places in South Africa. The coral reefs provide food and shelter for many animals.
Who lives on Coral Reefs?
On coral reefs, the corals and their associated algae are the main primary producers, although other autotrophs are also present. South African coral communities are dominated by soft corals but also have beautiful plate corals, branching staghorn corals, brain coral and honeycomb coral. Encrusting and small fleshy seaweeds attach to rock in between corals helping to create habitat and perform photosynthetic functions. Phytoplankton blooms are another source of primary production on coral reefs and, like in all light-filled ecosystems, form the foundation of coral reef food webs.
Herbivores are important parts of many ecosystems. Zooplankton are extremely small animals and larvae that feed on phytoplankton. Grazers like snails, urchins and herbivorous fish are important in keeping algae growth in check while key components of coral reefs include coral-eating fish like parrotfish and some butterflyfish. Omnivorous turtles feed on animals and seaweed with sponges being one of the favourite foods of hawksbill turtles.
Filter feeders grab tiny food particles in the form of plankton from the water and include seafans, sea squirts, feather stars, clams and soft corals. The high diversity of invertebrates and small fish attracts many different kinds of carnivores to coral reefs, including anemones, sea stars, predatory shrimps, cleaner shrimp, predatory fish (like kingfish and eels) and dolphins. Top predators like hammerhead sharks and reef sharks are signs of healthy ecosystems and these sharks prey on the various smaller fish species found on coral reefs.
Why are Coral Reefs important?
Coral reefs provide food and shelter for many animals. The intricate structure of coral reefs provides many different habitats for animals seeking shelter while some fish species eat the corals themselves. Global coral reef ecosystems host up to one-quarter of the known marine species in the world, while South African coral reefs host more than 1000 different species of fish. This abundance of fish life makes coral reefs a popular spot for fishers. Maintaining healthy coral reefs ensures food security for subsistence fishers and people relying on reefs for food.
The spectacular coral reefs and the colourful life associated with them attracts thousands of tourists to South Africa’s coral reefs in KwaZulu-Natal. There is a large scuba diving community in Sodwana Bay, injecting much-needed revenue into the tourism sector and local community.
Globally, coral reefs function as coastal ecological infrastructure– they protect the shore and humans from strong storms. The presence of reefs dampens the strength of storms, protecting the communities and people living near the beach.
How do we care for Coral Reefs?
Coral reefs are sensitive ecosystems because of their fragile habitat-forming three-dimensional structure and their vulnerability to climate change and water pollution. Coral reefs serve to provide benefits to marine species, humans and the economy yet there are several pressures affecting the health and survival of coral reefs.
Maintain healthy coral reefs- Climate change is a serious pressure on coral reefs. Rising sea temperatures can cause the zooxanthellae living in corals to die, leaving the corals white and bleached. Unfortunately, once a major coral bleaching event happens, there is little hope of full recovery for the coral reef and many corals die. When coral dies it is no longer able to provide food or shelter for other species which has significant economic effects on the people that depend on them for food, tourism and erosion mitigation. Increased ocean warming also results in a more acidic ocean with less oxygen. Ocean acidification, where carbon dioxide changes ocean chemistry by making it more acidic, is a serious threat to the ecological functioning of the oceans. A more acidic ocean erodes and dissolves shells of some plankton, crustaceans and molluscs while negatively affecting the ability of shallow reef-building corals to produce their skeletons. While individuals can make small impactful changes to reduce their carbon footprints collectively, climate change mitigation strategies require leadership from government and international cooperation. The solutions to climate change are known – but they must be implemented urgently. Managing other local-scale human activities that put additional pressure on coral reefs will give them the best chance of surviving climate change.
Protect coral reefs and manage fishing and diving: Many people rely on coral reefs for food, recreation and tourism opportunities. Overfishing has severe implications and has cascading effects on other trophic levels and may change the functioning of coral ecosystems. Ensuring that coral reefs continue to provide fish for the future and provide tourism opportunities relies on safeguarding corals in Marine Protected Areas like the iSimangaliso MPA.
Reduce and manage pollution –both chemical pollution and plastic waste can affect coral reef communities and the species reliant on them. Certain pollutants cause algal overgrowth, resulting in reduced oxygen which negatively affects marine life. Plastic pollution can severely affect the survival of birds, fish and mammals. Our individual choices and actions can affect the amount of plastic pollution on the coastline. We should choose to reduce our use and recycle what we can. Responsible practices by industry and government to reduce pollutants on the coastline should be encouraged to ensure healthy ecosystems for people and future generations. Pollution research can help us understand and manage pollution risks
How do we learn more about Coral Reefs?
South African coral reefs occur in the shallows of the northern part of KwaZulu natal. They are protected in the iSimangaliso Marine Protected Area and are a very popular tourist attraction. Learning to snorkel and to scuba dive can open up a whole new world for people exploring the sea. Coral reef scientists study a biologically diverse ecosystem that is under threat. Many coral reef scientists are trying to frantically study the impact that ocean warming will have on these sensitive ecosystems. Some are researching ways in which new corals can be grown in labs and replanted in the ocean. Coral reef scientists monitor the impact that coral bleaching will have on ecosystems, species and humans.
Dr Sean Porter
Coral reef scientist focused on the impacts of climate change and local stressors
Studied: Bachelor of Science, Honours (University of KwaZulu Natal), Doctor of Philosophy (University of Cape Town)
What is interesting about the ecosystem you are working in?
What is interesting to me about doing research on coral reefs is the biodiversity and complexity of these ecosystems and how they are able to literally create entire islands and land masses via a process known as biogenic accretion. In the most nutrient-poor waters, individual polyps form coral colonies which collectively form reefs by harnessing light energy using the algae inside them. An area of sea where there was once low biodiversity now becomes a rich ecosystem teeming with colourful biodiversity.
What are the challenges with working in your ecosystem?
The most obvious challenge is that most of the work has to be undertaken using SCUBA diving, which is an extremely inefficient and costly means of collecting data. Human capacity and expertise supported by reliable funding remain a huge general problem and constraint. One way of making the work a little easier is to undertake controlled laboratory experiments where one does not have to rely on SCUBA diving.
What are you working on and why is it important?
Most of my work focuses on climate change impacts on reefs and forecasting their responses to global warming and ocean acidification. I also do a lot of work on local pressures on reefs, especially pollution. This work is important as coral reefs contribute millions of dollars and rands in ecosystem services to coastal communities around the world and at home. In many places, coastal communities are completely reliant on Coral Reefs for food. Coral reefs also act as the proverbial canary in the coal mine in that they are very sensitive to the effects of climate change and thus offer an early warning sign of what is to come. Of all the ecosystems on the planet, coral reefs are likely to be the first to go extinct due to anthropogenic climate change. We can prevent this from happening if we urgently and drastically cut greenhouse gas emissions by moving to cleaner forms of renewable energy.