Marine Flora and Fauna of Hong Kong and Southern China IV

The distribution of ahermatypic corals at Cape d'Aguilar, Hong Kong

The Marine Flora and Fauna ofHong Kong and Southern China IV (ed. B. Morton). Proceedings of the Eighth International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 2-20 April 1995. Hong Kong: Hong Kong University Press, 1997. THE DISTRIBUTION OF AHERMATYPIC CORALS AT CAPE D'AGUILAR, HONG KONG T. H. Clark The Swire Institute of Marine Science, The University of Hong Kong, Cape d'Aguilar, Shek 0, Hong Kong ABSTRACT A survey of the ahermatypic, typically non-scleractinian, corals within the Cape d'Aguilar Marine Reserve, Hong Kong, identified 15 species of Gorgonoidea belonging to four genera and including Echinogorgia complexa, a new record for Hong Kong, two species of Antipatharia from one family (Antipathidae), three species of Dendrophyllia from one family (Dendrophylliidae) and two species of A1cyonoidea from one family (A1cyoniidae) and including Eleutherobia indica, a further new record for Hong Kong. The commonest species in the marine reserve area is the gorgonian Euplexaura curvata. In general, there was an increase in the abundance and diversity of the corals with increasing depth and with hard substratum availability. INTRODUCTION Ahermatypic corals include representatives of the Gorgonoidea and A1cyonoidea (Cnidaria: Octocorallia), Antipatharia and Dendrophyllia (Hexacorallia). Being ahermatypic and not, therefore, requiring light for zooxanthellae photosynthesis, they are not confined to shallow, tropical, reefs and are more widely distributed than their hermatypic counterparts (Veron 1993). Octocorals are common and conspicuous on almost all coral reefs (Lasker and Coffroth 1983) with representatives of the Gorgonoidea having a cosmopolitan distribution, from polar to tropical seas and throughout the range of depths studied (Zou and Scott 1980). A1cyonoideans are one of the major sessile invertebrates of Indo-Pacific reefs (Cary 1931; Crossland 1938; Dai 1991). Despite this global distribution, information on these corals is comparatively rare and studies of their communities in Hong Kong waters are restricted to the works of Zou and Zhou (1984) for the Antipatharia, Stimpson (1855) and Verrill (1865a,b) for the Gorgonoidea (9 species) and Zou and Scott (1980) who investigated the local distribution of 26 species of Gorgonoidea. Most of these species were recorded from the northeastern quadrant of Hong Kong, probably because of a combination of rocky 220 T.H. CLARK substratum, greater depth and higher, less variable, salinities (Zou and Scott 1980). Hong Kong's western waters are influenced by the Pearl River which lowers salinities overall. In this study, data are presented on the distribution and abundance of ahermatypic corals, primarily gorgonoideans, around the Cape d'Aguilar Marine Reserve, Hong Kong. The focus of the study is an 18 hectare area of coastal water at the southeastern tip of Hong Kong Island. Here, there is a wave-exposed shore which shelves steeply to a maximum depth of -22 m C.D.. Two rocky outcrops also drop off steeply to a boulder slope starting at about -6 to 8 m C.D. on the outer, exposed, edges of the reserve. At the end of this rocky peninsula, the island of Kau Pei Chau creates, in its lee, a small, sheltered, shallow bay (Lobster and Telecom Bays), which slopes gently from a boulder shore to a mixed boulder and sandy substratum at approximately 8 m. This then gives way to a sandy sea bed down to about 15 m (Fig 1). Such a diverse array of habitats supports a hermatypic scleractinian coral community, currently being studied, and an array of ahermatypic corals which is the subject of this paper. MATERIALS AND METHODS A survey of the ahermatypic corals of the Cape d'Aguilar Marine Reserve (220 12' N, 1140 15' E), was carried out in April 1995, using SCUBA. A total of 55 line transects were set out, each being split into 70 m lengths and extending in a north-south direction to the boundary of the reserve (Fig. 1) The transects were spaced evenly at distances of 40 m. The numbers and positions of ahermatypic corals observed in a band 1 m wide to either side of the transect were recorded. Samples of corals were collected and their positions labeled on a master chart to allow for species identification in the laboratory. Depth was also recorded at 5 m intervals along the transects, using diving gauges. Depth readings were later corrected to Chart Datum. The tissues of the collected gorgonians and antipatharians were dissolved in KOH to obtain spicules. These were washed, dried and examined using a Scanning Electron Microscope (Stereoscan 420). Species identifications were based on reference...