Hard Corals of the Darwin Region, Northern Territory, Australia
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HARD CORALS OF THE DARWIN REGION, NORTHERN TERRITORY, AUSTRALIA. JACKIE WOLSTENHOLME I ZENA D. DINESEN 2 AND PHILIP ALDERSLADE 3 I Museum of Tropical Queensland, 70-84 Flinders St, Townsville, QLD 4810, Australia. 2 Great Barrier Reef Marine Park Authority, P.O. Box 1379 Townsville, QLD 4810, Australia. 3 Museum and Art Gallery of the Northern Territory, P.O. Box 4646, Darwin, NT 0801, Australia. ABSTRACT A species list of hard corals recorded in subtidal and reef flat habitats of the Darwin region is presented. This is the first published list of the species of corals from the Darwin area, with a total of 125 scleractinian and non-scleractinian calcareous coral species belonging to 17 families and 47 genera, including one hydrozoan and one octocoral. The Faviidae is the family represented by the highest number of genera and species while relatively high numbers of species from the families Acroporidae and Poritidae are also present in the Darwin region. Similar numbers of species are recorded from the reef flat and the subtidal zone. Fewer species, but similar propor tions of all major genera, are recorded from each family in Darwin compared with the east and west coasts of Australia. KEYWORDS: Corals, Australia, Darwin, Cnidaria, check list. INTRODUCTION 1990). The distribution of deep water hermatypic corals is restricted by the low lev Darwin Harbour is a relatively shallow els of light penetration through the turbid wa tropical estuarine system which is naturally ters (Hooper 1987). The substratum of habitats turbid with a hIgh rate of sedimentation and a in which corals live is composed of dead coral, large diurnal tidal amplitude of 8 m maximum calcareous sand with clasts of coral rubble, and spring tidal range (Michie 1987). The high some terrestrially derived mud (Michie 1987). levels of suspended sediment in Darwin Har Very few nearshore reefs have been investi bour are derived from wet season runoff, and gated biologically in north-west Australia wind and wave resuspension (Wrigley et al. (Hooper 1987). The only published estimate of 1990). The major coral beds in this region are the number of coral species occurring in Dar sparsely distributed across the extensive inter win Harbour records 30 species of hard corals tidal reef flats, to a depth of 10 metres within from Channel Island to Lee Point (Low Choy the Harbour, and to greater depths in subtidal 1983 in Hooper 1987). regions outside the Harbour (Hooper 1987). The aim of this study was to prepare a check The increasing depth of the distribution of cor list of the hard corals present in Darwin Har als is probably related to the increasing depth bour in preparation for a handbook which will of the photic zone as water moves through the provide full descriptions of the species that oc middle Harbour to the ocean (Wrigley et al. cur in the region. In: Hanley, 1.R., Caswell, G., Megirian, D. and Larson, H.K. (eds) Proceedings of the Sixth International Marine Biological Workshop. The marine flora andfauna ofDanvin Harbour, Northern Territory, Australia. Museums and Art Galleries of the Northern Territory and the Australian Marine Sciences Association: Darwin, Australia, 1997: 381-398. 381 J. Wolstenholme. Z.D. Dinesen and P. Alderslade MATERIALS AND METHODS RESULTS The list of species presented in this paper is As a result of the field surveys of the hard based on corals collected in subtidal and reef corals of the Darwin region, we found 123 spe flat habitats in or near Darwin Harbour. The cies from 45 genera and 15 families of Harbour refers to all sites within Port Darwin, scleractinian corals, one hydrozoan, Millepora and extends from West Point to Lee Point. Col sp. and the octocoral Tubipora musica. This lection sites are listed for each sample in the record includes all common species and many species list (see Results) and locations of sites less common species, although it is unlikely are indicated by triangles in Figure 1. Two sites that the list is exhaustive because some rarer north of the Harbour, North West Vernon Is species may have been overlooked or not present land and the reef off Gunn Point Beach, were at the sites surveyed. The full species list, in also sampled. Subtidal corals were collected cluding museum registration numbers of each during ten dives conducted during the Sixth specimen and collection sites is given below. International Marine Biological Workshop, in Darwin, in July 1993. Dive sites were chosen to sample the full range of coral habitats in the DESCRIPTION OF CORAL HABITATS IN Darwin region, to maximise the number of spe THE DARWIN REGION cies collected. The majority of specimens col lected on reef flats were sampled during exten The intertidal and subtidal substrata around sive surveys at extreme low tides in November/ Darwin on which corals are living mainly con December 1982. All corals collected were pho sist of rocks, unconsolidated and consolidated tographed prior to their removal, with the ex rubble, sand and mud. The intertidal reef flats ception of the fungiid Heliofungia actiniformis, are a mixture of low profile, silty, aggregations which was photographed but not collected. or rock and coral rubble, and elevated rock Specimens were identified, using Veron and platforms with pools and lagoons that never Pichon (1976,1980,1982), Veron 1985, Veron dry. Dudley Point was the most extensively sur 1986, Veron, et al. (1977), Veron and Wallace veyed intertidal region. The coral cover here is (1984), Hoeksema (1989), Koh and Chou (1989), noticeably richer on the outer parts of the reef Lamberts (1982), Nemenzo (1981) and Veron and in the shallow channel between the reef and (1990). Specimens which are apparently a dis the headland. The dry areas are dominated by tinct species but are not described in these refer large Symphyllia heads and numerous faviids. ences are listed as Porites sp. 1, Montipora sp. Although some colonies of Acropora are often 1, Montipora sp. 2, Montipora sp. 3 and exposed, most occur in the rock pools and the Acropora sp. 1. Specimens which were uniden channel, as do corals of many other genera such tifiable to species are listed using the genus, e.g. as Porites, Goniopora and Turbinaria. The lat Millepora sp. ter is most common in the areas that are only All samples are lodged at the Museum and uncovered at the lowest tides, on the reef mar Art Gallery of the Northern Territory (NTM), gins and the channel entrance. Darwin (registration numbers prefixed NTM C) The substratum at the dive sites within the or at the Museum of Tropical Queensland Harbour carried the highest sediment loads and (MTQ), Townsville (registration numbers pre had less rubble or other solid substratum. Large fixed QM G). Collectors, habitat, and registra colonies of Symphyllia and medium to large tion details for the specimens are listed in Table colonies of faviids were the dominant coral types 1. Thirty-six specimens are lodged at MTQ with at the dive sites within the Harbour, except at ten specimens being portions of specimens Weed Reef where corals were sparse and the lodged at NTM. For specimens lodged in both substratum very silty. From East Point to Lee museums, both registration numbers are listed Point, the water was somewhat clearer and the in the Results section and the collection details substratum less muddy, compared with more listed in Table 1, corresponding to the NTM southerly study sites within the Harbour. Large registration number. colonies of Porites, Symphyllia and Galaxea (to 4 m diameter) were seen at the dive sites at Lee 382 Hard corals of the Darwin region VERNON ISLANDS •N BEAGLE GULF 12" 15' .... ~ Old Man Rock 15 Fig. 1. Collection sites. 383 J. Wolstenholme, Z.D. Dinesen and P. Alderslade Table 1: Registration details of specimens recorded in this paper. Registration number Habitat Collectors' Identification' NTM C3084-3085 Subtidal PA PA NTMC5409 Reefflat PA PA NTM C5423-5424 NTM C6000-6071 Reef flat PA,ZD,PH ZD NTM C6073-6l83 NTM C6244-6252 NTM C6948-6949 NTM C6072 Subtidal PA ZD NTM C6945 Subtidal PA BH NTM C7795-7808 Subtidal JW JW NTM C78l9-7959 NTM C7809 Reef Flat PA,SH JW NTMC78ll NTM C78l4-78l7 NTMCl1973 Reef Flat PA PA QM G specimens Subtidal JW JW 'PA: P. Alderslade, ZD: Z. Dinesen, BH: B. Hoeksema, PH: P. Homer, SH: S. Homer, JW: J. Wolstenholme. Point, Old Man Rock and Nightcliff. The high recorded subtidally (87 species) than intertidally est diversity of coral species for Darwin Har (79 species) (Table 2). The genus contributing bour appeared to be at the latter two sites, with most to these differences is Montipora, with two smaller colonies of most other families being species occurring in the intertidal zone and an present between the large colonies. East Point additional eight species occurring subtidally. A differed from all other dive sites in having less total of 53 species was recorded intertidally and suspended sediment in the water column and subtidally. Species from most families were re less sediment coating the substratum. No large corded in both zones. However, the families colonies were present at East Point, with Milleporidae (Millepora sp.), Astrocoeniidae Turbinaria being the most common genus grow (Stylocoeniella guentheri) and Agariciidae ing amongst many colonies of the sea whip (Pachyseris speciosa) were only found in the lunceella fragilis. Arborescent and corymbose intertidal zone and were only represented by species of Acropora were the most common one species each. These species may also be corals at the North West Vernon Island site. present subtidally but were either absent or rare This site was also silty, with the substratum at the sites surveyed in this project.