| Title | Long-term monitoring of the shallow water benthic communities of Olifantsbos within Table Mountain National Park MPA |
|---|---|
| Authors |
Haupt, Tanya Janson, Liesl Williams, Lauren Williamson, Ricardo |
| Publisher | Department of Forestry, Fisheries and the Environment (2026) |
| Contributors |
Contact Person: Haupt, Tanya Other: Williamson, Carlo Related Person: Kirkman, Stephen |
| Abstract | Benthic invertebrate communities, particularly sessile and semi-motile organisms like sponges, cnidarians and echinoderms, are effective for assessing long-term change, since they respond to factors such as marine pollution or climate change through measurable changes within populations over weeks to years. Exploratory research on these communities and their habitats has contributed substantially to increased understanding of benthic biota, and to the establishment of Marine Protected Areas (MPAs). However, very few repeat observations in the same areas are available to assess changes in benthic community structure and function over time. With long-term monitoring being a key DFFE mandate, such data availability is becoming increasingly important to assess the credibility of management strategies within MPAs. The key objective of this study was to establish long-term monitoring of the sessile and semi-motile benthic invertebrate communities occurring at various depths in a biodiversity rich area inside Table Mountain National Park (TMNP) MPA - Olifanstbos. The inshore area of Olifantsbos forms part of the Cape of Good Hope restricted zone and the survey was conducted using underwater imagery across four depth categories: 15 – 30 m, 31 – 50 m, 51 – 70 m and 71 – 90 m. Environmental data were also collected such that depth, habitat type and temperature can all be examined as possible drivers of species diversity and richness. Preliminary analyses show that macroalgae dominates the shallowest depth (15 - 30 m) and possibly accounts for the low abundance of observable benthic organisms occurring on and in between rocks - the dominant substrate type at this depth. Sponges are also common at these shallower depths and are the only taxonomic group prevalent across all depth bins. Species richness peaks between 31 and 70 m where a diverse assemblage of cnidarians dominate. The highest species richness and abundance occurs between 51 - 70 m, likely reflecting the presence of mixed habitat types found at these depths. The deeper depths of 71 - 90 m are comprised mainly of sediment where burrowing organisms dominate. This initial study forms a baseline upon which further monitoring will be conducted every two to three years. |
| Methods | A grid of 6.5 x 2 km overlaid the Olifanstbos area with each cell (i.e. station) being 250 x 250 m in size. The area was divided into four depth categories: 15 – 30 m, 31 – 50 m, 51 – 70 m and 71 – 90 m and stations sampled in each depth bin were randomly selected. Using a drop camera system deployed from a winch off a small boat, the numbers of stations sampled in each depth category were six between 15 – 30 m, six between 31 – 50 m, nine between 51 – 70 m and seven between 71 – 90 m. The GoPro camera attached to the drop camera frame was set to record still images every second and at each station +- 20 drops (i.e. once frame reaches the seafloor) were conducted whilst circling within the general vicinity of the central co-ordinate (i.e. staying within the 250 x 250 m radius). Once on the seafloor, the drop camera was held in position for 60 seconds and brought up ~five metres from the sea floor between drops. Detailed metadata sheets ensured accurate records of operations (e.g. depth, bottom times, etc.) and a temperature logger attached to the drop camera frame allows for correlation with environmental conditions. The data available are JPEG images of photoquadrats obtained using a circular frame with a radius of 350 mm (diameter = 700 mm). The data provided for each station are raw images from the time the drop camera leaves the boat till when it is brought up. A csv file capturing metadata (i.e. operational details) are provided for each station. Temperature logger data were collected, but excluded due to incomplete coverage and data quality limitations. Access to the raw data may be provided upon request. |
| Data | |
| Temporal extent | 23 Aug 2024 – 23 Oct 2024 |
| Geographic extent |
Olifantsbos, Table Mountain National Park Marine Protected Area (MPA), South Africa
North: -34.2524 |
| Keywords | ANIMALS/INVERTEBRATES , BIOLOGICAL CLASSIFICATION , CNIDARIANS , ECHINODERMS , Invertebrate Abundance and Distribution (emerging) , SOUTH ATLANTIC OCEAN , SPONGES , Taxonomic/phylogenetic diversity |
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