Aliwal shoal is a subtidal, algal-dominated subtropical reef in the transitional region between the warm-temperate reefs of Pondoland and the tropical to subtropical reefs of Maputaland. The benthic communities are dominated by algae and sponges, but various soft and hard corals, echinoderms and ascidians are also present. The environment can be classified as marginal, in that it supports fauna of tropical, subtropical and warm temperate reefs. The diversity is comparable to similar latitude reefs of Australia. The adjacent coastline of KwaZulu-Natal has a humid subtropical climate with summer rainfall, and the freshwater and riverine sedimentary discharge into the region is significant and affects turbidity and plankton blooms. Most of this input is from the mKomazi River at the north of the MPA. A marine pipeline operated by Sappi Saiccor discharges just outside the MPA. The shoal is exposed to heavy wind-driven wave action, with an annual average swell height of . The following benthic taxa are recorded from the shoal: ;
Algae ;
Chlorophyta (green algae): :
Codium lucasii :
Ulva cf.
rigida ;
Rhodophyta (red algae): :
Amphiroa ephedraea :
Callophycus condominius :
Champia compressa :
Dichotomaria diesingiana :
Hypnea viridis :
Hypnea sp. :
Laurencia brongniartii :
Meristotheca papulosa :
Osmundaria serrata (ex
Vidalia serrata) :
Peyssonnelia capensis ;
Phaeophyta (brown algae) :
Dictyota dichotoma var.
intricata :
Exallosorus harveyanus :
Lobophora variegata :
Stypopodium multipartitum :
Zonaria subarticulata ;
Porifera :
Dragmacidon sanguineum :
Cliona orientalis :
Chondropsis sp. :
Fascaplysinopsis sp. :
Forcepia sp. :
Geodia sp. :
Hemiasterella vasiformis :
Oceanapia aff.
ramsayi :
Placospongia sp. :
Polymastia sp. :
Rhabderemia sp. :
Spheciospongia excentrica :
Spheciospongia globularis :
Spheciospongia vagabunda :
Suberites kelleri ;
Octocorallia (soft corals): :
Dendronephthya sp. :
Eleutherobia aurea :
Leptophyton benayahui :
Sinularia brassica ;
Gorgonians: :
Acabaria sp. :
Homophyton verrucosum ;
Anemones: :
Cerianthus sp. :
Heteractis magnifica ;
Zoanthids :
Palythoa natalensis ;
Black coral :
Antipathes sp. ;
Scleractinia (hard corals) :
Dendrophyllia sp. :
Favites sp. :
Montipora sp. :
Pocillopora damicornis :
Pocillopora verrucosa :
Stylophora pistillata :
Tubastraea micrantha ;
Annelida: :
Polychaeta ;
Arthropoda: :
Panulirus homarus ;
Bryozoa (Ectoprocta): :
Sertella sp. :Unidentified species 2 ;
Mollusca: :
Hyotissa hyotis :
Phyllidia varicosa ;
Echinodermata :
Diadema setosum :
Fromia sp. :
Linckia laevigata :
Linckia guildingi :
Mithrodia clavigera :Unidentified
crinoidea ;
Ascidiacea :
Sigillina sp. :
Sycozoa sp.
Benthic communities Three distinct benthic communities occur on the Crown reef, depending on topography, sediment cover and wave energy. The large shallow areas of the shoal have the highest abundance of
zooxanthellate hard corals, the encrusting zooxanthellate sponge,
Suberites kelleri and the hard corals
Stylophora pistillata and
Pocillopora spp., which appear to be tolerant of the high energy environment. This community has the lowest abundance of red foliose algae and occupies the reef top, inshore and offshore slopes of the northern, middle and southern regions at depths from . A second community inhabits the steep edges of the shoal and has larger proportion of
Polychaetes, the soft coral
Eleutherobia aurea, and the sponge
Spheciospongia globularis. This is the only community in which Suberites kelleri is absent. This community covers the high to medium relief inshore and offshore walls and broken edges of the middle and northern regions in the depth range. A third community lives deeper on the shoal and is dominated by
coralline and red foliose algae. This community covers the medium to low relief inshore and offshore slopes and broken edges of the middle, southern and far southern regions, and the top of the far southern region in the depth range.
Ecoregion The
Natal inshore ecoregion is transitional between the warm temperate reefs of
Pondoland to the south and the tropical/subtropical reefs of
Maputaland to the north. This is evident from the distribution of algae and corals. The corals of Aliwal shoal are less diverse than those of Maputaland, but more diverse than those of Pondoland, while the pattern for algal diversity show the opposite trend, being more diverse than Maputaland and less diverse than Pondoland. The high biomass of algae indicate an adequate supply of nutrients, while the relatively lower biomass of zooxanthellate corals indicate turbidity, light and temperature levels that are not optimum for these animals. The high occurrence of filter-feeding sponges, ascidians and polychaetes suggest that the suspended particulates causing the turbidity are adequate for their nutrition. ==Marine Protected Area (MPA)==