Make small but sustainable decisions

Why are marine ecosystems important?

Oceans cover 71 % of the Earth’s surface and are critical to the functioning of our planet. Marine ecosystems include a diverse range of habitats including rocky shores, seagrass beds, mangroves, kelp forests and the deep sea. These ecosystems provide an extensive number of ecosystem services, including carbon capture, nutrient cycling and renewable energy, that are critical tools in combatting climate change. It is also home to an incredible amount of biodiversity that is essential in maintaining resilient ecosystems that are able to adapt to environmental change, with over 12,000 species in South African waters alone. In South Africa, the marine environment provides a large number of jobs in industries such as fishing, aquaculture and nature-based tourism and plays a critical role in feeding a growing population. Marine ecosystems also hold great economic value, with coastal goods and services contributing a third to South Africa’s GDP, making it essential to sustainably manage marine resources. 

Threats to marine ecosystems

Perhaps the greatest and most immediate threat to marine ecosystems in South Africa is climate change. Our oceans absorb much of the excess heat and carbon dioxide in the atmosphere which has resulted in ocean warming and acidification. Even the smallest changes to temperature can cause significant changes to the physiology, reproduction and distribution of marine wildlife, altering the way species interact with each other and driving loss of biodiversity and ecosystem functioning. Ocean acidification also has significant consequences, particularly for calcifying species that include many commercially important shellfish, hindering their ability to build hard shells and altering respiration and feeding rates.  

Marine ecosystems, particularly coastal systems, are also at risk from land-based activities that result in marine pollution. For example, known as eutrophication, excess nutrients derived from fertilizers used in intensive land farming enter the marine environment through run-off, resulting in blooms of fast-growing algae that reduce light and oxygen availability. Urban development can also lead to excess sediment deposition in rivers and streams that then enters the ocean through run-off, decreasing water clarity and light availability. Coastal and urban development such as marinas or holiday resorts further results in significant habitat loss. Over 80% of marine plastic pollution originates from land-based sources and South Africa is ranked 11th on the list of highest contributors to plastic pollution in the ocean, recycling only 16 % of its plastic. Around 10 % of discarded plastic (~ 8 million metric tons a year) ends up in the ocean through our waterways. Marine wildlife is routinely entangled in plastics such as abandoned fishing nets and often swallow smaller items such as plastic bags, cotton buds and balloons. 

South Africa’s fishing industry is worth ~ R6 billion a year but is threatened by overfishing and illegal fishing, including poaching. Overfishing drives species loss and potentially extinction that can cascade through marine food webs given the reliance of many coastal birds and mammals on fish as prey. Consequences of overfishing are not limited to ecosystem effects, however, as many local communities rely on subsistence fishing and fishing as a source of income. 

What is the solution?

Although it can be overwhelming to read the many threats to our marine ecosystems, everyone can do their part in the fight to preserve our oceans. For example, reducing your carbon footprint by choosing to walk or cycle, reducing plastic consumption, recycling, reducing food waste and water consumption and buying sustainably sourced and local products are all part of the solution. Choosing to stay in environmentally friendly accommodation on your beach retreats and choosing to eat only green-listed fish are small decisions that have large impacts. By making small changes every day we can make a huge difference.  ‍

Dr. Abby Gilson, Coastal Research Group, Rhodes University‍

Dr. Abby Gilson is a marine ecologist working in the Coastal Research Group at Rhodes University. She is passionate about understanding the effects of climate change on biodiversity and ecosystem functioning, ensuring the sustainable use of marine resources. She specializes in rocky intertidal ecosystems, with a particular focus on macroalgal communities. Abby aims to understand how climate change stressors such as ocean warming and species range shifts affect macroalgae-herbivore interactions and the knock-on effects these changes have to ecosystem functioning.