Shallow Rocky Reefs


Shallow rocky reef, Vlak rotsagtige rif, Ingxondorha ezincinane ezinamatye, Amadwala angajulile

Colourful reefs with seaweeds that harness energy from the sun to feed animals and us

© Steve Benjamin

What are Shallow Rocky Reefs?

Shallow rocky reefs are bright sunlit reefs that grow on hard rocky seabeds. In South Africa, these shallow reefs are found at sunlit depths usually between 10 and 30 m. They occur on rocky areas that are not productive or cold enough for kelp forests but too cool and low in nutrients for corals. 

The underlying rock structure provides a point of attachment for seaweeds and invertebrates (animals without backbones) like sponges, anemones, soft corals, sea fans and seasquirts). These colourful seaweed and animal gardens of host diverse communities of fish and other animals.

Who lives on Shallow Rocky Reefs?

Despite the depth of shallow rocky reefs, light reaches the seabed and is used by seaweeds that can make food from sunlight. These are called primary producers. Seaweeds attached to the rocky seabed and microscopic algae called phytoplankton- use sunlight to photosynthesise. Shallow rocky reefs support red, green and brown seaweeds. Common green seaweeds include the wedge-weed, golf-ball like codium seaweeds and strap seaweed. Red seaweeds include beautiful forms of coralline algae like the stiff jointed horse-tail seaweed and many forms of jelly-like or branching red seaweeds. More brown seaweeds are prevalent in the Western Cape but turkey tail seaweed, lobe fan seaweeds and many others occur on shallow reefs on the South and East Coast. 

The presence of seaweeds means that grazers are common on shallow rocky reefs. The species of herbivores present changes depending on the ecosystem’s position along the South African coastline, and those in the cold Atlantic Ocean differ from those in the Indian Ocean. 

Interspersed with seaweeds are sessile filter feeders. Soft corals and fan corals are important in providing points where other animals can attach. Other filter-feeding animals on Shallow Rocky Reefs include worms (like Christmas tree worms and tubeworms), barnacles, mussels, sponges and sea squirts (redbait). There is always something new to see when exploring shallow reefs.

Common animals from the sunlit reefs on the East Coast include octopus and east coast rock lobster. Many important fish use the habitats provided by seaweeds, redbait and other invertebrates for food and shelter. Some valuable fish from shallow rocky reefs include blacktail, zebra, roman, galjoen, fransmadam, strepie (also known as karanteen) and bronze bream. This high diversity of fish and crustaceans attracts larger predatory species like sharks and rays. Pregnant ragged-tooth sharks aggregate on sunlit reefs on the South and East Coast and spotted gully sharks frequent this ecosystem type on the southwestern coast.

Why are Shallow Rocky Reefs important?

Shallow rocky reefs host diverse fish communities-many of which are important to subsistence, small scale and recreational anglers. Their closeness to shore increases their importance to coastal communities that harvest the many fish and invertebrates on rocky reefs as a supplementary food source. Such fishing is an important part of many cultures. Recreational fishers also enjoy and value these ecosystems and resources. Ensuring reefs remain healthy is important for food security, cultural practices and identity and recreation.

Shallow rocky reefs are important for ecotourism. Aliwal shoal Marine Protected Area is a shallow reef that through scuba diving, shark tourism, and other ecotourism ventures contributes to the South African economy, provides jobs and opportunities for the communities living nearby.  In northern KwaZulu-natal, the Tsonga communities harvest redbait from shores and shallow reefs. Shallow rocky reefs in the Eastern Cape support fish like blacktail which is an important food species for many coastal communities. East coast rock lobster and oysters are also important resources found in this zone.

How do we care for Shallow Rocky Reefs?

Shallow Rocky Reefs are under pressure from human activities. This is because of their close proximity to shorelines. 

Manage and reduce pollution – Shallow Rocky Reefs are sensitive to pollution from waste disposal, plastic pollution and human activities (like pipelines). Taking care of the way that we dispose of trash is essential for maintaining the health of these spectacular ecosystems and those who rely on them. Industries/activities that damage ecosystems should be regulated and managed, ensuring minimal harm comes to Shallow Rocky Reefs.

Manage fisheries resources and present overharvesting- The proximity of these ecosystems to shores means that they are easily accessible and used by people for fishing. Fish populations should be carefully managed to avoid population collapse through overfishing. Fishers need to adhere to fishing regulations designed to support sustainable fisheries in the long term

Protect portions of abyssal ecosystem types in Marine Protected Areas (MPAs): Within MPAs activities that damage the seabed are limited. Protecting the seaweeds and animals that are integral to the functioning of rocky shelves and are extremely sensitive to damage. These areas also protect important fish populations from overharvesting, allowing them to breed and grow safely. Shallow reefs are protected in a number of coastal Marine Protected areas. These include popular tourist spots like Table Mountain National Park MPA, De Hoop MPA, Sardinia Bay MPA, Trafalgar MPA and the Cape Vidal section of the iSimangaliso MPA.

How do we learn more about Shallow Rocky Reefs?

Scientists, who study Rocky Shores, work in an exciting environment that sustains large Shallow Rocky Reefs can be visited by snorkelers and scuba divers across the South African coastline. Popular spots include deep dive sites in the Western Cape and Protea Banks in KwaZulu Natal.

Dr Tanya Haupt

Production Scientist DFFE

Studied: Doctor of Philosophy (Stellenbosch University)

What is interesting about the ecosystem you are working in?

Shallow water reef ecosystems are comprised of a diverse range of fixed of sessile and semi-motile reef invertebrates like sponges, corals and echinoderms (e.g. sea stars, urchins and sea cucumbers). Despite making up a large percentage of reef life and providing habitats and food for commercial species, these species have largely been underrepresented and unmonitored compared to commercially important species (e.g. abalone and rock lobsters).

What are the challenges with working in your ecosystem?

In South Africa, baseline data for sessile and semi-motile reef invertebrates are lacking for many MPAs and associated areas. Data on species diversity, richness, distribution patterns and range overlaps are required to better understand the functioning of whole benthic ecosystems (i.e. not only commercially important ones). One of the main reasons that reef habitats are generally unexplored is firstly, unlike rocky shores or estuaries, they are difficult to access and require special resources and skills such as diving, all of which can also be costly. When sampling is possible, it is usually limited to diving depths of less than 30m. However, researchers worldwide now utilize underwater imagery equipment to survey the marine environment across a range of depths. These tools are generally non-destructive and provide an excellent means to conduct baseline assessments using standardized protocols which allow for long-term monitoring of benthic ecosystems.

What are you working on and why is it important?

I am focused on shallow water benthic (seafloor) ecosystems, specifically targeting sessile and semi-motile reef invertebrates within Marine Protected Areas (<100m).

Benthic monitoring is a relatively sensitive, effective and reliable technique that can detect subtle changes that serve as an early indicator before more drastic environmental changes occur. Through detectable changes within populations over weeks and years, benthic monitoring is also able to assess changes over longer periods of time due to marine pollution or climate change. And because benthos are made up of largely sessile organisms,( i.e. they cannot move) they must either tolerate, adapt, or die. The other advantages that make them model organisms to monitor change is that they are resident year round, are naturally abundant and diverse and most are not fished or intentionally managed by man. Lastly, there are wonderful creatures with a wide variety of lifestyles making them fun to study!

Mzansea: revealing south Africa's marine ecosystems Logo

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