Table Mountain National Park Marine Protected Area

A Restricted Area is a part of a marine protected area also known as a "No-Take" area, in which all extraction and harvesting of marine plant and animal life is prohibited. There are six of these within the TMNPMPA.[5]

The remainder of the MPA is designated as a Controlled Area, where extraction and harvesting of marine life and other activities, are allowed on condition that one has a valid permit allowing one or more of the following specific activities: spear fishing, angling, scuba diving, snorkelling for mollusc extraction, boating, commercial diving, salvage operations, scientific research, commercial fishing, whale watching, shark cage diving or filming.[5]

The Table Mountain National Park Marine Protected Area includes the seabed, the water, and the airspace above it to an altitude of 1000 metres above sea level. The lateral boundaries of the controlled area on WGS84 are offshore of the high-water mark between Green Point at S33°54.075'; E018°24.037' and Bailey's Cottage, Muizenberg at S34°06.590'; E018°28.250', to a line drawn east (090°T) from the beacon at Bailey's Cottage to S34°06.590'; E018°33.413, south (180°T) to S34°24.444; E018°33.413, west (270°T) to S34°24.444; E018°15.000', north (000°T) to S33°54.075; E018°15.000, and east (090°T) to Green Point at S33°54.075'; E018°24.037'.[1]

• Karbonkelberg Restricted zone

  Offshore from the high-water mark between Oudekraal at S33°58.757'; E018°21.847' and Hout Bay at S34°03.660'; 018°20.252', west (270°T) from Hout Bay to S34°03.660'; E018°17.797', north (000°T) to S33°58.757'; 018°17.797'; and east (090°T) to Oudekraal at S33°58.757'; E018°21.847'.[1]

• Cape of Good Hope Restricted zone

  Offshore from the high-water mark between Hoek van die Bobbejaan at S34°18.393'; E018°24.258' and Schusters Bay Point, Scarborough, at position S34°12.271'; E018°22.194', south (180°T) from Schuster's Bay point to S34°16.490'; E018°22.194, to S34°18.393'; E018°23.500' and east (090°T) from position 34°18'.393S; 018°23'.500E to Hoek van die Bobbejaan at S34°18.393'; E018°24.258'.[1]

• Paulsberg Restricted zone

  Offshore from the high-water mark between Venus Pool at S34°17.744'; E018°28.020', and Smitswinkel Point at S34°16.549'; E018°28.464', east (090°T) from Smitswinkel Point to S34°16.549'; E018°29.000', south (180°T) to S34°17.744'; E018°29.000', and west (270°T) to Venus Pool at S34°17.744'; E018°28.020'.[1]

• Castle Rock Restricted zone

  Offshore from the high-water mark between Partridge Point at S34°15.480'; 018°28.344', and Millers Point at S34°14.100'; E018°28.508', east (090°T) from Millers Point to S34°14.100'; E018°29.300', south (180°T) to S34°15.480'; E018°29.300', and west (270°T) to Partridge Point at S34°15.480'; E018°28.344'.

• Boulders Restricted zone

  Offshore from the high-water mark between Rocklands, at S34°12.705'; E018°27.781', and Seaforth, Simonstown at S34°11.567'; E018°26.762', to S34°10.581'; E018°27.196'; east (090°T) to S34°10.581'; E018°27.781', and south (180°T) to Rocklands at S34°12.705'; E018°27.781'.

• St James Restricted zone

  Offshore from the high-water mark between the Kalk Bay Tidal Pool at S34°07.567'; E018°27.050' and the St James Tidal Pool at S34°07.123'; E018°27.568 south (180°T) from the St. James Tidal Pool to S34°07.567'; E018°27.568; and east (090°T) to the Kalk Bay Tidal Pool at S34°07.567; E018°27.050.[1]

The MPA is managed by Table Mountain National Park in conjunction with the Department of Agriculture, Forestry and Fisheries. TMNP is responsible for the administration, inshore law enforcement and educational activities.[7]

A total of 3.6% of the TMNP operational budget for annual recurring activity is allocated to marine management from 2015 to 2020, comprising R3,440,000 for 2015/6, R3,646,000 for 2016/7, R3,865,000 for 2017/8, R4,097,000 for 2018/9 and R4,343,000 for 2019/2020.[8]

• Hout Bay Harbour and slipway: Commercial fishing harbour and yacht club marina with public access slipway, S34°03'01.76" E018°20'42.97"
• Soetwater slipway: Public access slipway, S34°10.692' E018°20.684'
• Kalk Bay harbour: Commercial fishing harbour.
• False Bay Yacht Club: Member access marina and slipway, S34°11'32.57" E018°26'0.31"
• Simon's Town naval base: Government access harbour and slipways.
• Miller's Point slipway: Public access slipway, S34°13'49.63" E018°28'25.12"
• Rumbly Bay slipway: Public access slipway on the south side of Millers Point.
• Buffels Bay slipway: Public access slipway controlled by TMNP.

Fishing is allowed in the controlled zone of the MPA subject to permits, regulations, catch limits and seasons set by the Department of Agriculture, Forestry and Fisheries. However, it remains a contentious issue in the area. Subsistence fishers are prohibited from fishing in no-take zones and do not have the boats or technology necessary to safely travel past the no-take zone. For places where they are allowed to fish, they often have to apply for expensive permits. In addition, for those subsistence fishers that are illiterate, they must hire a literate third-party to fill out the application for them. Finally, it is often difficult for these subsistence fishers to prove they have the start-up capital or private boat needed to obtain a permit. [10]

Tension commonly exists between subsistence fishers and commercial fishers who are allowed to harvest rock lobster to measure the ecological growth rate of the species. This opportunity is not offered to subsistence fishers because they do not have the necessary gear.[11]

Other activities requiring permits include recreational scuba diving.[1]

Most of the recreational dive sites of Cape Town are in the Table Mountain National Park Marine Protected Area. A permit is required to scuba dive in any MPA in South Africa. These permits are valid for a year and are available at some branches of the Post Office.[1] Temporary permits, valid for a month, may be available at dive shops or from dive boat operators who operate in an MPA. A personal recreational scuba diving permit is valid in all South African MPAs where recreational diving is allowed. The business permit to operate recreational scuba business operations in an MPA is restricted to a specific MPA. Diving for commercial or scientific purposes is also subject to permit.

The MPA has a large number of rocky reef and wreck recreational dive sites which have been identified by position and named. Many of these have been partly or completely surveyed mapped and described in the travel guide for diving the Cape Peninsula and False Bay on Wikivoyage.[12] Some of them are listed here for the west coast of the peninsula from north to south, and for the east coast, also from north to south, roughly following the coastline:

An experimental octopus fishery was started in 2014 to gather data on octopus harvesting potential with a view to establishing a sustainable fishery and enhancing job creation and economic development in coastal areas. The deaths of whales trapped in octopus trap ropes led to protests and temporary suspension of the fishery pending scientific investigation of the experimental octopus fishery in False Bay in June 2019. Some of the fishing grounds involved are reefs in the controlled area of the MPA.[14]

New rules for the octopus fishery intended to reduce the risk of whale entrapment were published and the fishery reopened in November 2019.[15]

The City of Cape Town was founded at the northern end of the Cape Peninsula, a narrow mountainous strip of land at the most 11 km wide and just over 50 km long. The northern border is the coast of Table Bay, a large open bay with a single island, Robben Island, in its mouth.

A ragged coastline marks the western border along the Atlantic Ocean. A number of small bays are found along the coast with a single large one, Hout Bay, about half way along. Further south the peninsula narrows until it comes to an end at Cape Point. A range of mountains with Table Mountain at 1,085m at the northern end forms the backbone of the peninsula. The highest point of the southern peninsula is Swartkop, at 678 m, near Simon's Town.

The eastern side is bordered by False Bay, and this stretch of coastline includes the smaller Smitswinkel Bay, Simon's Bay and Fish Hoek Bay. At Muizenberg the coastline becomes relatively low and sandy and curves east to Gordon's Bay to form the northern boundary of False Bay. From Gordon's Bay the coastline swings roughly south, and zig-zags its way along the foot of the Hottentot's Holland mountain range to Cape Hangklip which is at nearly the same latitude as Cape Point. The highest peak on this side is Kogelberg at 1,269 m.

In plan the bay is approximately square with rather wobbly edges, being roughly the same extent from north to south as east to west (30 km), with the entire southern side open to the ocean. The area of False Bay has been measured at about 1,090 km², and the volume is approximately 45 km³ (average depth about 40 m). The land perimeter has been measured at 116 km, from a 1:50,000 scale map.

The bottom morphology of False Bay is generally smooth and fairly shallow, sloping gently downwards from North to South, so that the depth at the centre of the mouth is about 80 m. The bottom is covered with sediment which ranges from very coarse to very fine, with most of the fine sediment and mud in the centre of the bay. The main exception is a long ridge of sedimentary rock that extends in a southward direction from off the Strand, to approximately level with the mouth of the Steenbras River. The southern tip of this ridge is known to recreational divers as Steenbras Deep.

There is one true island in the bay, Seal Island, a barren and stony outcrop of granite about 200 m long and with an area of about 2 hectare. It is about 6 km south of Strandfontein and is less than 10 m above sea level at its highest point. There are also a number of small rocky islets which extend above the high water mark, and other rocks and shoals which approach the surface. Most of these are granite of the Peninsula pluton, but east of Seal Island they are generally sandstone, either of the Table Mountain series, or the underlying Tygerberg formation. Outside the bay, but influencing the wave patterns in it, is Rocky Bank, an extensive area of sandstone reef between 20 and 30 m depth.

A large granite reef, Whittle Rock, lies on the eastern edge of the MPA about halfway between the north shore and the mouth of the bay.

Strictly speaking, False Bay is part of the Atlantic Ocean which extends as far east as Cape Agulhas, but when in Cape Town, Atlantic generally refers to the western seaboard of the Cape Peninsula, and the east side is referred to as False Bay, or the Simon's Town side.

The Cape Peninsula shoreline in the case of (left) a 25m higher sea level that occurred around 5 and 1.5 million years ago, and (right) a 125m lower sea level at the time of maximum ice build-up during cold periods – the most recent being 20 000 years ago (after John S. Compton 2004)

The Cape Peninsula is a peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At its tip is the Cape of Good Hope. The peninsula forms the west side of False Bay. The three main rock formations are the late-Precambrian Malmesbury group (metamorphic rock), the Peninsula granite, a huge batholith that was intruded into the Malmesbury Group about 630 million years ago, and the Table Mountain group sandstones that were deposited on the eroded surface of granite and Malmesbury series basement about 450 million years ago. The sand, silt and mud deposits were lithified by pressure and then folded during the Cape Orogeny to form the Cape Fold Belt, which extends along the western and southern coasts.[16]

Almost 50% of the Cape Peninsula and Cape Flats area is covered by weakly cemented marine sands. Sea-levels fluctuated between −120 to +200m from present mean sea level during the Pliocene and subsequent Pleistocene ice-age between 2 million and 15000 years ago as a result of fluctuating global temperature and variable amounts of water accumulated in polar ice caps.[16] At times the sea covered the Cape Flats and Noordhoek valley and the Cape Peninsula was then a group of islands. Beach sands with shell fragments and estuarine muds were deposited and later overlain by calcrete-cemented dune sands as the sea retreated. "Dune rock" that was deposited during a Pleistocene interglacial period about 120,000 years ago is now being eroded in the sea-cliffs near Swartklip.[16] During glacial periods the sea level dropped to expose the bottom of False Bay to weathering and erosion. The last major regression, about 20,000 years ago, lowered the sea level to the present 130m isobath, which is south of Cape Point and Cape Hangklip, leaving the entire bottom of False Bay and a large part of the continental shelf to the west of the peninsula exposed. During this period an extensive system of dunes was formed on the sandy floor of False Bay.[16]

Over the last 2 million years of the Quaternary geological period, cool glacial periods (hypothermals) about 100,000 years long, have been the norm. Canada and northern Eurasia were covered by continental ice sheets kilometres thick, and the global effect was a lowering of sea level by some 130m because the sea was the source of the frozen water of these huge ice sheets. This means that False Bay and Table Bay were dry and covered by dunes for 90% of the last 2 million years. Warm interglacial periods (hyperthermals), have lasted only about 10 000 years and we are part way through the latest one which started about 6000 years ago. The coastline of False Bay, therefore, was usually across the mouth of the present False Bay. Robben Island was a hill on a coastal plain with the coast west of the island for most of the past 2 million years.[16] Sea level rises due to global warming may eventually increase this trend.

The large and small-scale relief of the coastal seabed is largely dependent on the local surface formation, where this is exposed above the generally sandy bottom. The granite areas are usually rounded corestone outcrops, influenced by the local jointing patterns, and can range between tall pinnacles, large low slab-like outcrops, and aggregations of boulders of a wide range of sizes. Usually a combination of these is present, often with sandy patches in local depressions, while the sedimentary facies present a more variable aspect, depending on the rock type, dip, strike, and thickness of the layers present. A very good estimate of underwater relief character can be made by observing the local topography above the water. An interesting local phenomenon is the contact zone between the intrusive granite of the Peninsula pluton and the older Malmesbury strata visible at the Sea Point shoreline.[16] The bottom off the west coast of the cape Peninsula between and beyond the rocky reef areas is largely fairly fine white quartzitic sand with some areas of coarser shelly sand. The bottom sediments of False Bay are more varied. On the west side of the bay there is a general tendency towards fine to medium quartzitic sand and coarser calcareous material, mostly mollusc shell fragments, with patches of a maerl of branching coralline algae fragments. There are also areas of very fine sand, almost mud, in the more sheltered Simon's Bay. Most of the intertidal zone of the peninsula is rocky shoreline, but there are several sandy beaches of varying extent.[17][18]

The Benguela current flows northward along the west coast, and Agulhas eddies move westwards along the south coast, bringing occasional warmer water into False Bay, along with drifting organisms from far upcurrent, which are often unsuited to the local conditions, and do not survive long. There are a few places in False Bay where they tend to end up. Currents in False Bay are generally weak, local, wind driven, shallow and not very predictable. Inshore currents in the MPA along the west coast also generally shallow and wind-driven.

Wind driven upwellings on the west coast are driven by strong south-easterly winds, which mostly blow in summer. Cold, clear, nutrient-rich water is drawn up from the deep to replace surface water driven offshore by Ekman transport, usually followed closely by algal blooms powered by the intense summer sunlight, which rapidly reduce water clarity and provide food for zooplankton. Lesser upwellings, also driven by south-easterly winds in summer, occur on the east side of False Bay near Cape Hangklip and Rooiels, where surface water temperatures can be 6 to 7 °C colder than the surrounding areas, and bottom temperatures below 12 °C.[19]^:10

Water temperature varies with the seasons. In summer False Bay is thermally stratified, with a vertical temperature variation of 5 to 9˚C between the warmer surface water and cooler depths below 50 m, while in winter the water column is at nearly constant temperature at all depths. The development of a thermocline is strongest around late December and peaks in late summer to early autumn.[19]^:8

The volume of fresh water runoff from rivers and stormwater drainage is low and mostly in late winter.

False Bay Bathymetry from SA Council for Geoscience

The Bathymetry of False Bay differs in character from the west side of the Cape Peninsula. The west coast seabed tends to slope down more steeply than in False Bay, and although the close inshore waters are also shallow, the 100 m contour is mostly within about 10 km of the west coast, while the entire False Bay is shallower than about 80 m.[20] The bottom of the bay slopes down relatively gradually from the gently sloping beaches of the north shore to the mouth, and is fairly even in depth from east to west except close to the shorelines, with three major features disrupting this gentle slope. These are the granite outcrops of Seal island and Whittle Rock, and the hard sedimentary rock of the Steenbras ridge. Just outside the bay, there is a large shoal area at Rocky Bank, and a long ridge extending south-west from Cape Hangklip, which channels cold, nutrient-rich water into the west side of the bay during upwelling events.[21]

Tidal range is moderate, with about 2 m range at spring tide on both sides of the peninsula, and tidal currents are negligible.

The climate of the South-western Cape is markedly different from the rest of South Africa, which is generally a summer rainfall region, receiving most of its rainfall during the summer months of December to February. The South-western Cape has a Mediterranean type climate, with most of its rainfall during the winter months from June to September.

The south westerly winds over the South Atlantic and Southern Ocean produce the prevailing south-westerly swell, which is strongest in the winter months, and which beats on the exposed Atlantic coastline and the east side of False Bay. The mountains of the Cape Peninsula provide protection on the east side of the peninsula from this wind and from the south westerly waves – a fact which influenced Governor Simon van der Stel in his choice of Simon's Bay as a winter anchorage for the Dutch East India Company’s ships for Cape Town.

Winter in the South-western Cape is strongly influenced by disturbances in the region between the circumpolar westerly winds and south-easterly trade winds, resulting in a series of eastward moving frontal depressions. These bring cool cloudy weather and rain on winds from the north west along the cold fronts which move in from the south west. The north westerly winter storms have wrecked many ships anchored in Table Bay over the centuries. Even today, in spite of technical advances and improved weather forecasting this still happens, though less frequently than in the past, and recently the salvage operations are more often successful. As the front passes, the wind shifts to south-westerly, and eventually south-easterly as the pressure rises, until the next front. The period between fronts tends to be in the order of a week, but can be highly variable.

During the summer the dominant factor determining the weather in the region is a high pressure zone, known as the South Atlantic High, located over the South Atlantic ocean to the west of the Cape coast. This high pressure zone moves seasonally, following the sun. The more southerly position of this high pressure zone in summer has the effect of blocking the cold fronts, and restricting them to pass mostly south of the continent. Winds circulating in an anticlockwise direction from such a system reach the Cape from the south-east, producing periods of up to several days of high winds and mostly clear skies. These south easterly winds are locally known as the Cape Doctor. They keep the region relatively cool and free of industrial pollutants. Because of the south facing aspect of False Bay, the west side of the bay is exposed to these winds, while Table Bay and the west coast of the peninsula experience an offshore wind. This wind pattern is locally influenced by the topography to the extent that gale-force winds may be blowing in one place, while a few kilometers away it may be almost calm.

The waves reaching the shores of False Bay and the Cape Peninsula can be considered as a combination of local wind waves and swell from distant sources. The swell is produced by weather systems generally south of the continent, sometimes considerably distant, the most important of which are the frontal systems in the South Atlantic, which generate wind waves which then disperse away from their source and separate over time into zones of varying period. The long period waves are faster and have more energy, and move ahead of the shorter period components, so they tend to reach the coast first. This is known to surfers as a pulse, and is generally followed by gradually shortening period swell of less power.

Local winds will also produce waves which will combine their effects with the swell. Offshore winds as a general rule will flatten the sea as the fetch (distance that the wind has blown over the water) is too small to develop waves of great height or length. Onshore winds on the other hand, if strong enough will produce a short chop.

South-easterly winds which blow offshore and along the coast on the west side of the Cape Peninsula and the east side of False Bay cause a movement of surface water offshore to the west of the coast. This movement of water away from the coast is compensated by the upwelling of deeper water. The upwelled water is generally cold and relatively clear. However, as the upwelled water has a high nutrient content, the upwellings are often forerunners of a plankton bloom known as a "red tide", which will drastically reduce visibility.

The local tides are relatively weak, and there are no strong tidal currents on the Atlantic coast or in False Bay. Maximum tidal range at Cape Town is approximately 1.86 m (spring tides), and at Simon's Town 1.91 m, with minimum ranges at both places of about 0.26 m (neap tides).

Average summer surface temperature of the Atlantic off the Cape Peninsula is in the range 10° to 13 °C. The bottom temperature may be a few degrees colder. Minimum temperature is about 8 °C and maximum about 17 °C. Average winter surface temperature of the Atlantic off the Cape Peninsula is in the range 13° to 15 °C. The bottom temperature inshore is much the same. Average winter surface temperature of False Bay is approximately 15 °C, and the bottom temperature much the same. Average summer surface temperature of False Bay is approximately 19 °C. The bottom temperature is 1° to 3 °C lower than it is in winter, and a distinct thermocline will usually develop between December and about May.

A shallow surface current may be produced by strong winds. Tidal currents are negligible. Cape Point may have stronger currents, where eddies from the Agulhas current frequently produce a light- to medium-strength current.

Turbidity has a strong influence on the penetration of light to depth, including the wavelengths that penetrate, and long-term turbidity can affect the growth of seaweeds which depend on sufficient light for photosynthesis. The depth distribution of the various species found in the waters of the MPA vary depending on the general turbidity of the water of the specific area.

There is a significant seasonal variation in sea conditions in the MPA. In summer the South Atlantic High moves south over the ocean to the west of the Cape Peninsula and brings south-easterly winds to the Cape Peninsula. On the west side of the peninsula these winds blow along the coastline and offshore, causing an offshore movement of surface water by Ekman transport. The offshore flow is compensated by upwelling of bottom water, and as the continental shelf is narrow and relatively steeply sloped in this area, the upwelled water is generally cold, clear, and rich in nutrients. Surface temperatures can drop by a few degrees over a matter of hours. When this water is illuminated by summer sunshine, there is generally a phytoplanktonic algal bloom, which will produce a sudden increase in microscopic biomass in the surface layer, until the turbidity of the water restricts penetration of light to the deeper levels. Visibility in the surface water can drop almost as fast at it improved on a clear day, and can reduce from tens of metres to less than 5 m in a few hours. Deeper water may remain clear, but relatively dark. The south-east wind also causes upwellings on the east coast of False Bay near Hangklip, but the upwelled water is not usually as cold, has a lower nutrient load, and may be turbid, so the effect is generally less marked. Nevertheless, the effect can be impressive phytoplankton blooms, known as red tides. The water in False Bay is constrained from westward flow by the Cape Peninsula, so these red tides can be relatively persistent.[22] The south easterly wind can push up a very rough wind wave, but the fetch is short and it usually dies down quite quickly, but while it lasts it can clear a large amount of benthic fauna off the shallower reefs, which may take weeks or months to find its way back.

In winter, the South Atlantic High moves north and the weather pattern is dominated by cold fronts formed over the southern ocean, The winds generally follow the pattern of light to strong north-westerly, swinging though south-westerly as the front passes overhead, and followed by relatively weak south-easterlies. North-westerly gales produce powerful wind waves which batter the west coast of the peninsula, but the east side waters may be calm, with a minor wind chop due to the short fetch. The westerly winds may also clean up the surface waters of the west side of False Bay, and as there is usually much lower insolation at this time of year, plankton does not usually bloom, and the water remains relatively clear.[22]

The westerly storms of the southern ocean also produce very large waves with a large amount of their energy propagating towards the north-east, and as these move away from their source they separate by wave-length, as the wave velocity is a function of the wavelength, with the longer, more powerful waves travelling faster and losing less energy as they travel. These become swells, and by the time they reach the Cape Peninsula the leading pulse is usually in the 13 to 15 second period band, occasionally up to 18 seconds. Depending on deep-water amplitude, they can break over some of the reefs outside Hout Bay at heights of up to 70 feet (21 m), making this a world-class big wave break.[23][24] Most of the energy of swells with a significant westerly component does not make it round the corner of Cape Point into the west side of False Bay. On the same day that big waves are breaking on the west coast, it may be calm enough for scuba diving from the shore in Simon's Town, on the False Bay coast on the other side of the peninsula.

Four major habitats types exist in the sea in this region, distinguished by the nature of the substrate. The substrate, or base material, is important in that it provides a base to which an organism can anchor itself, which is vitally important for those organisms which need to stay in one particular kind of place. Rocky shores and reefs provide a firm fixed substrate for the attachment of plants and animals. Some of these may have kelp forests, which reduce the effect of waves and provide food and shelter for an extended range of organisms. Sandy beaches and bottoms are a relatively unstable substrate and cannot anchor kelp or many of the other benthic organisms. Finally there is open water, above the substrate and clear of the kelp forest, where the organisms must drift or swim. Mixed habitats are also frequently found, which are a combination of those mentioned above.[27] There are no significant estuarine habitats in the MPA.

Rocky shores and reefs

Several layers of marine life may co-exist in apparent harmony

There are extensive rocky reefs and mixed rocky and sandy bottoms, with a significant number of wrecks, which are equivalent to rocky reefs for classification of habitat, as in general, marine organisms are not particular about the material of the substrate if the texture and strength is suitable and it is not toxic. For many marine organisms the substrate is another type of marine organism, and it is common for several layers to co-exist. Examples of this are red bait pods, which are usually encrusted with sponges, ascidians, bryozoans, anemones, and gastropods, and abalone, which are usually covered by similar seaweeds to those found on the surrounding rocks, usually with a variety of other organisms living on the seaweeds.[27]^:Ch.2

The type of rock of the reef is of some importance, as it influences the range of possibilities for the local topography, which in turn influences the range of habitats provided, and therefore the diversity of inhabitants. Granite reefs generally have a relatively smooth surface in the centimetre to decimetre scale, but are often high profile in the metre scale, so they provide macro-variations in habitat from relatively horizontal upper surface, near vertical sides, to overhangs, holes and tunnels, on a similar scale to the boulders and outcrops themselves. There are relatively few small crevices compared to the overall surface area. Sandstone and other sedimentary rocks erode and weather very differently, and depending on the direction of dip and strike, and steepness of the dip, may produce reefs which are relatively flat to very high profile and full of small crevices. These features may be at varying angles to the shoreline and wave fronts. There are far fewer large holes, tunnels and crevices in sandstone reefs, but often many deep but low near-horizontal crevices. In some areas the reef is predominantly wave-rounded medium to small boulders. In this case the type of rock has little influence.

The coastline in this region was considerably lower during the most recent ice-ages, and the detail topography of the dive sites was largely formed during the period of exposure above sea level. As a result, the underwater relief is mostly very similar in character to the nearest landscape above sea level. There are notable exceptions where the rock above and below the water is of a different type. These are mostly in False Bay south of Smitswinkel Bay, where there is a sandstone shore with granite reefs.[16]

Kelp forests

Dense kelp forest with algal understorey

Kelp forests are a variation of rocky reefs, as the kelp requires a fairly strong and stable substrate which can withstand the loads of repeated waves dragging on the kelp plants. The Sea bamboo Ecklonia maxima grows in water which is shallow enough to allow it to reach to the surface with its gas-filled stipes, so that the fronds form a dense layer at or just below the surface, depending on the tide. The shorter Split-fan kelp Laminaria pallida grows mostly on deeper reefs, where there is not so much competition from the sea bamboo. Both these kelp species provide food and shelter for a variety of other organisms, particularly the Sea bamboo, which is a base for a wide range of epiphytes, which in turn provide food and shelter for more organisms.[27]^:Ch.4 There are also places where the spined kelp Ecklonia radiata can be found east of Cape Point, and bladder kelp, Macrocystis pyrifera in sheltered areas west of Cape Point, often inshore of the Ecklonia forests.[28]

Sandy beaches and bottoms (including shelly, pebble and gravel bottoms)

Sandy bottoms at first glance appear to be fairly barren areas, as they lack the stability to support many of the spectacular reef based species, and the variety of large organisms is relatively low. The sand is continually being moved around by wave action, to a greater or lesser degree depending on weather conditions and exposure of the area. This means that sessile organisms must be specifically adapted to areas of relatively loose substrate to thrive in them, and the variety of species found on a sandy or gravel bottom will depend on all these factors. Sandy bottoms have one important compensation for their instability, animals can burrow into the sand and move up and down within its layers, which can provide feeding opportunities and protection from predation. Other species can dig themselves holes in which to shelter, or may feed by filtering water drawn through the tunnel, or by extending body parts adapted to this function into the water above the sand.[27]^:Ch.3

The open sea

The pelagic water column is the major part of the living space at sea. This is the water between the surface and the top of the benthic zone, where living organisms swim, float or drift, and the food chain starts with phytoplankton, the mostly microscopic photosynthetic organisms that convert the energy of sunlight into organic material which feeds everything else, directly or indirectly. In temperate seas there are distinct seasonal cycles of phytoplankton growth, based on the available nutrients and the available sunlight. Either can be a limiting factor. Phytoplankton tend to thrive where there is plenty of light, and they themselves are a major factor in restricting light penetration to greater depths, so the photosynthetic zone tends to be shallower in areas of high productivity.[27]^:Ch.6 Zooplankton feed on the phytoplankton, and are in turn eaten by larger animals. The larger pelagic animals are generally faster moving and more mobile, giving them the option of changing depth to feed or to avoid predation, and to move to other places in search of a better food supply. Plankton blooms following upwelling events are a characteristic of the west side of the peninsula in particular

Red tides

On the west coast of the peninsula and to a lesser extent the east side of False Bay, the south easterly winds can cause upwelling of deep, cold, nutrient rich waters. This generally happens in summer when these winds are strongest, and this in combination with the intense summer sunlight provides conditions conducive to rapid growth of phytoplankton. If the upwelling is then followed by a period of light wind or onshore winds, some species of phytoplankton can bloom so densely that they colour the water, most noticeably a reddish or brownish colour, which is known as a red tide.[27]

Depending on the species involved, these red tides may cause mass mortalities to marine animals for various reasons. In some cases the organisms may consume all the available nutrients and then die, leaving decaying remains which deplete the water of oxygen, asphyxiating the animal life, while others may simply become so dense that they clog the gills of marine animals, with similar effect. A third group are inherently toxic, and these may be particularly problematic as some filter feeding species are immune to the toxins but accumulate them in their tissues and will then be toxic to humans who may eat them.[27]

Red tides also have the effect of reducing light penetration. The reduction in illumination can range from a mild effect in the surface layers, to seriously reduced illunmination to considerable depth. Red tides may be small and localised and usually last for a few days, but in extreme cases have been known to extend from Doringbaai to Cape Agulhas, several hundred kilometres to both sides of Cape Town, and take weeks to disperse (March 2005).

Besides the resident species and several known migrants, the waters of the MPA are occasionally visited by vagrants carried in by the eddies of the Agulhas Current, which can bring tropical and subtropical specimens normally resident thousands of kilometres away.[29]

Number of marine animal species listed by phylum:[30][29][22]

• Poriferans: 28
• Cnidarians: 68
• Ctenophores: 4
• Platyhelmimthes: 4
• Polychaetes: 15
• Arthropods: 89
• Bryozoans: 32
• Molluscs: 242
• Brachiopods: 3
• Echinoderms:28
• Tunicates: 27
• Vertebrates:
  • Fish: 472
  • Reptiles: occasional vagrant turtles
  • Seabirds:
  • Marine mammals: 10

More than 300 species of seaweed are recorded from the Cape Peninsula and False Bay. Most of these in the MPA. These include kelp from three genera, Ecklonia, Laminaria and Macrocystis, and a range of other brown, green and red algae.[31][28] As previously mentioned the kelp forests provide shelter for a wide range of organisms, including other seaweeds, which form algal turfs and understoreys and live as epiphytes on the kelp plants and other sessile organisms. In the inshore shallow water Ecklonia maxima is common, and the plants grow to relatively small sizes to match the water depth. The waters are well illuminated and many other seaweeds live under the kelp canopy, to a large extent crowding out the sessile fauna. In slightly deeper water the Ecklonia reaches its maximum size and biomass per area. In this zone Laminaria pallida, the split-fan kelp, forms a secondary canopy, and under this an understorey of smaller seaweeds, including many species of encrusting and arborescent red seaweeds. In deeper water the Ecklonia do not thrive and are taken over by Laminaria. When there is insufficient light for Laminaria the algal turf is mostly red seaweeds, including many varieties of corallines.[27] Kelp beds are important to the life cycle of several animals. The sea urchin Parechinus angulosus feeds on kelp detritus, and browse the sporelings, keeping the rock surfaces relatively free of young kelp plants. Where there are sparse urchins, the kelp can establish more easily, and adult Laminaria fronds tend to sweep the underlying surfaces of some of the invertebrates which browse on the kelp. On deeper reefs, and on more steeply sloped rock surfaces there is less seaweed biomass as the light is insufficient.[27]

Endemism is the ecological state of a species being unique to a defined geographic location, such as an island, nation, country or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. The extreme opposite of endemism is cosmopolitan distribution. The MPA is small, and it is unlikely that there are any species endemic to only the MPA, but it may be the only or largest MPA within the known range of some endemic species. Some species are only recorded from the MPA, but this may be an artifact of the relatively high level of research and observation in this region.

At least two marine species that have become truly invasive affect this MPA - Carcinus maenas, the European shore crab, and Mytilus galloprovincialis, the Mediterranean mussel.[32]

The main ecological effect of the Mediterranean mussel invasion has been the increase in the extent of mussel beds in the region, crowding out other species which would otherwise occupy the reef surface, particularly the limpet, Scutellastra argenvillei The extended mussel beds also increase habitat available for infaunal species and provide more food for some species, particularly the African oystercatcher (Haematopus moquini).[32]