Diving the south coast of South Africa/Dalgleish Bank

Understand

Dalgleish Bank is a relatively deep dive site far enough offshore not to be influenced much by inshore conditions, and may have good visibility relatively often for this region. It has a high level of biodiversity and endemicity, and the reef edge dropoffs can be topographically spectacular. The top of the reef extends nearly 2 km east to west, and probably about 600 m north to south, roughly parallel to the coastline.

Position A fairly large reef about 11 km offshore of Buffelsbaai, or 15.5 km, (about 8.3 nautical miles) bearing 218°T from Knysna Heads This site is not in a Marine Protected Area. A permit is not required.

Name It seems likely that the bank is named after Commodore James Dalgleish, who was a hydrographer and Chief of the South African Navy.

Depth Maximum depth is about 80 m off the northwestern wall, and the top of the shallowest part of the reef is about 29 m. Average depth of a dive, excluding decompression, is likely to be about 35 to 40 m, depending on whether you stay on the top or make an excursion down the dropoff.

Visibility Visibility can be excellent, as the site is far enough away from the shoreline to not be affected much by the tidal outflow of Knysna lagoon or any of the nearby rivers, but the bank has not been dived enough to predict conditions with any confidence. In December 2021 the visibility was good and the water temperature warm from top to bottom, while in early February 2022, a warm (16°C) turbid (3 to 6 m viz) layer of some 8 to 15 m depth overlaid a much clearer (20 m viz) and colder (8°C) bottom water. In early February 2023 conditions were very similar to the same time in 2022.

Topography A fairly flat topped expanse of hard sedimentary rock, with a dropoff around the edge, which is quite sheer in places, and the edges and top surface are cut in places by deep and occasionally narrow gullies. The top surface slopes gradually over much of the area, with occasional near vertical steps up to a few metres high.

Getting there

This is a boat access dive as it is several kilometers offshore. The site is about 10.8 nautical miles (20 km)from the slipway on Leisure Island and much the same distance from the Knysna yacht club in Knysna lagoon, or about 8.4 nautical miles (15.5 km) from Knysna heads. There are no realistic alternatives for a day boat. In an emergency the harbour at Mossel Bay could be used, but it is 75 km to the west.

See

A good site for colourful invertebrates, and when not too cold, abundant reef and pelagic fish.

Marine life

Dalgleish Bank is in the middle of the warm temperate inshore Agulhas ecoregion, which extends from Cape Point to the Mbashe River, and is the major marine ecoregion of the south coast. Upwelling on the south coast of South Africa is largely driven by the Agulhas current and the continental shelf. This form of upwelling forces cold deep water up onto the continental shelf, but not necessarily above the thermocline. In the region east of the Agulhas bank, wind enhanced upwelling, occurring mainly in summer, augments the current driven upwelling bringing the colder deeper waters to the surface. This enhances biological productivity by supply of nutrients to the euphotic zone (where plants have sufficient light to flourish) which fuels phytoplankton production, and rocky shores that are supplied with the nutrient rich water support rich algal biomass. This ecoregion is also the centre of endemicity for South African waters, and a relatively high percentage of endemic species can be expected. The reef has not been extensively dived, and it is likely that undiscovered species will be found, particularly among the organisms without a planktonic stage. Invertebrates that are relatively common at this site include basket stars, a finely branched orange or brown sea fan, noble corals and other hydrocorals, and in the deeper areas, deewater urchins, a few species of gorgonian and other soft corals, and colonies of yellow zoanthids. Sponges are everywhere. Elegant feather stars are present but sparse. There appear to be quite a variety of white dorid nudibranchs with dark brown or black spots, known to divers as "Dalmatians" which represent several genera and species, some probably undescribed. Also a fair number of the frilled nudibranch Leminda millecra The shallower areas on the top of the reef support a fairly sparse spiny kelp forest, and a fairly diverse but n

Do

Dive at one of the listed drop points, or explore another area and let us know what you find. 1 Katja's Wall: S34° 11.737', E22° 57.186', Southwestern edge of reef top. 40 m at drop with dropoff to 60 m at the bottom of the wall and 35 m local minimum. 2 West Pinnacle: S34° 11.610', E22° 57.144', Top of the reef, at the west end. 32 to 37 m. 3 South Gully: S34° 11.773', E22° 57.293', Southern edge of the reef top. Depth at drop 42 m. 35 to 45 m. Flattish reef top with some deep gullies and ledges. 4 Stefan's Koppie: S34° 11.603', E22° 57.459', Top of the reef, roughly central. Depth at drop 30 m, Reef depth in vicinity 29 to 32 m. Relatively shallow and mostly fairly flat low profile reef, but good rugosity and high biodiversity. Lots of small Ecklonia radiata (spiny kelp). None of the brown Dalgleish sea fans, maybe too shallow. 5 East Point: S34° 11.541', E22° 58.297', Northern edge of the reef top. Depth at drop 40 m, 38 m deep on flattish top with a steep dropoff to 65 m a short distance away. 6 Josh's Drop: S34° 11.570', E22° 57.178', Top of the reef, northwest end. Depth at drop 34 m, 33 to 35 m. 7 Grant's Wall: S34° 11.630', E22° 58.076', Southeastern edge of the reef top. Depth at drop 40 m, 39 m on top with a dropoff to 55 m. 8 West Wall: S34° 11.674', E22° 56.993', Depth at drop 45 m, bottom of wall 80 m 9 Ben's Beach: S34° 11.733', E22° 57.301', Depth at drop 36 m, bottom of gully 50 m. Medium to high profile sandstone reef, with ridges and gullies. 10 Sam's Drop: S34° 11.606', E22° 57.061', Depth at drop 38 m 11 Johan's Ridge: S34° 11.746', E22° 57.419', Depth near drop about 36 to 40 m 12 Wednesday Drop: S34° 11.577', E22° 57.100', Depth about 36 to 38 m. Moderate profile reef top with small ridges and gullies. 13 Hole-in-the-Wall: S34° 11.408', E22° 58.124', Depth at drop about 37 m near the top of the wall. Zigzag dropoff edge of vertical wall with a few moderate profile gullies in the flattish reef top. Swim-through under a slab boulder at