Monitoring our coastal invertebrates

Holidaymaker Garth Winfield examines brown mussels

The rocky shores, sandy beaches and estuaries of KwaZulu-Natal support a multitude of invertebrates (animals without an internal backbone). Many of these organisms are inconspicuous, requiring patience and a closer look to discover. Without these organisms, our shoreline would contain little more than algae-covered rocks frequented by a small number of fish.

Unfortunately, these organisms are particularly vulnerable to over-harvesting. In KwaZulu-Natal alone, between 10 000 and 11 000 people buy permits to collect mussels, crayfish, oysters and other shellfish each year. This could potentially have a large impact on our coastal resources.

The most popular coastal invertebrates collected in KwaZulu-Natal are brown mussels. The filter-feeding brown mussel is an integral component of the rocky shore ecosystem. It forms extensive beds on rocky reefs which provide a habitat for many other organisms such as marine worms, snails, crabs and shrimps. Predatory fish also feed on the organisms living in the mussel beds.

Mussels also help to clarify coastal waters by taking up small food particles suspended in the water. In KwaZulu-Natal, rivers carry large amounts of terrestrial plant material down to the coastal zone each year. The plant material is broken down to smaller pieces by wave action and mussels eventually take up these particles. In turn predatory fish, snails and octopus prey on mussels, which form an important link between the marine and terrestrial food webs.

Assistant scientist Erika Steyn records invertebrate populations

In the 1990s, legal “sports” mussel collectors (not permitted to sell their catches) severely overexploited mussel beds at Umhlanga and Umdloti, north of Durban. It was estimated that they caused as much damage to mussel beds as unregulated subsistence collectors in northern KwaZulu-Natal, who collect mussels to support their basic food needs.

ORI conducts periodic coastal surveys, but due to logistics, it is not possible to monitor all KwaZulu-Natal resources on a regular basis. The shore patrols conducted by the Ezemvelo KwaZulu-Natal Wildlife officers along the coast reveal where people collect organisms, but the data collected through the surveys and by the volunteers is superior in regard to how many organisms are taken.

Clearly, the support and integrity of local fishers and invertebrate collectors is essential for effective fishery management in KwaZulu-Natal. Over the last 40 years, a small group of anglers and shellfish collectors from all over South Africa have given of their time to fill in questionnaires or measure mussels and crayfish. These are our citizen scientists, everyday people who would like to make a difference. They care for the ocean and want to share it with their children and grandchildren. 

Subsistence harvesters collect mussels and octopus at low tide

Would you consider joining them? If you would like to become involved in this programme, please contact ORI at 031 328 8222 or complete a survey. Remember that if you plan to collect any marine resources from the sea, you need a permit. Marine collection permits can be bought at any post office and a marine recreational activity information brochure containing information about bag limits, size limits and gear restrictions applicable to each species can be downloaded from the Department of Agriculture, Forestry and Fisheries website. 

Note that there are some regulations not specified in this brochure that apply in KwaZulu-Natal, such as: it is illegal to collect brown mussels and Cape rock oysters on the mollusc permit in this province. You require a species-specific permit to collect these animals. It is also illegal to collect marine worms in KwaZulu-Natal, as this can be a highly destructive activity.