BULLETIN OF MARINE SCIENCE. 31(3): 558-573, 1981 ASPECTS OF SEXUAL REPRODUCTION AND LARVAL DEVELOPMENT IN THE SHALLOW WATER HERMATYPIC CORAL, GONIASTREA A USTRALENSIS (EDWARDS AND HAIME, 1857) Barbara L. Kojis and Norman J. Quinn ABSTRACT Sexual reproduction and larval development in Goniastrea australensis. a shallow water hermatypic coral. were studied from September 1977 to November 1980 on Heron Island reef. Australia. G. australensis is a simultaneous hermaphrodite with ovary and testis in- termingled on the same mesentery. Gonad development occurred synchronously within and between colonies. An annual spring spawning season of approximately 2 days was observed. Gametes were released between 1600-1800 h on neap low tides between the full and last quarter moon phases. Fertilization is probably external; eggs from a single polyp were re- leased in clumps held together by mucus and sperm were freely released. Egg clumps were negatively buoyant and sticky, adhering to objects when contact was made. Sperm and eggs were usually released simultaneously from the same polyp. Laboratory experiments indi- cated that self-fertilization was possible with apparently normal larval development and settlement. In aquaria ciliated larvae developed in approximately 2 days and settlement commenced 17 days after spawning. Reproduction began in colonies with an arithmetic mean radius of !.5-2.0 cm. aged 4+ years. While G. aU.I'tralen.l'i.\· did not planulate, the mode and timing of spawning and larval development substantiated Stimson's (1978) hypothesis that the mode of reproduction in hermatypic corals may be related to habitat. but not his prediction that corals characteristic of the reef flat would begin to sexually reproduce at an early age and planulate. It has been assumed from studies of sexual reproduction in hermatypic corals that they are viviparous and release planulae (Hyman, 1940; Wells, 1954). How- ever, it has been noted that the release of planulae has not been observed in most species of coral, including species in which gonads were present at some time during the studies (Connell, 1973; Stimson, 1978). The most comprehensive report of sexual reproduction in a non-planulating hermatypic coral was the study of Favia pallida (Marshall and Stephenson, 1933) (nomenclature of Faviidae is in accordance with Veron and Pichon, 1976). The presence of gonads in November and absence in December 1928 indicated a relatively brief spawning period, contrasting with the long, often year-round, period of larval release found in known planulating species, and suggested that gamete release and external fertilization may have occurred. Stimson (1978) synthesized information from his own and previous studies on the presence or absence of planula release and habitat distribution of corals and compared reproduction among corals in shallow and deep water. He hypothesized that the mode of reproduction in hermatypic corals is related to habitat and predicted that corals characteristic of the reef flat would begin to sexually repro- duce at an early age and characteristically planulate while deep water corals would have alternate modes of reproduction, probably seasonal gamete release. The sexual reproduction, larval development, distribution and abundance of Goniastrea australensis were studied on Heron Island, Australia, to augment the meager data on the life history of hermatypic corals and to test Stimson's hy- pothesis. G. australensis (Fig. 1) is a massive hermatypic coral widely distributed in the Western Pacific (Veron, 1974; Veron et al., 1977). It has been recorded as 558 KOJIS AND QUINN: SEXUAL REPRODUCTION IN GONIASTREA 559 Figure I. Reef flat colony of Gon;(lstre(l (lustra/ens;s on Heron Island reef. present in a variety of habitats from the reef flat to the deeper water of the reef slope (Veron et a\., 1977). On Heron and Wistari Reefs of the Capricorn Group, Great Barrier Reef (23°27'S, 1510155'E), G. australensis is largely restricted to major shallow water habitats: lagoon, inner and outer reef flat and crest. It is rarely found on the reef slope and then only in water less than 5 m deep. MATERIALS AND METHODS Gonads Reproduction was studied from September 1977 to November 1980 on the reef flat at Heron Island. Ten colonies (> 15 cm diameter) at each of three different sites (total 30 colonies) were individually tagged on the inner reef flat (Fig. 2). Sites were more than 200 m apart to allow determination of variation in the timing and mode of reproduction within the same general habitat. In addition, large untagged colonies from the outer reef flat, crest and lagoon were sampled to assess variation in the mode and timing of reproduction with habitat. Colonies were sampled monthly between September ]977 and November 1978 by removing samples of approximately 5 to 20 polyps with a hammer and chisel. Samples were fixed in 10% sea water formalin in the field and 24 h later transferred to a fresh solution of 10% formalin for storage. Preserved whole samples were decalcified in Gooding and Stewart's solution and initially treated as follows: (I) single polyps were embedded in "Tissue Prep," sectioned at a nominal thickness of 8 J.tm, stained either with Mayer's hematoxylin and eosin or Heidenhain's hematoxylin, and examined for the presence of gonads; (2) other polyps from the same samples were then dissected and observed using a binocular dissecting microscope. It was found that eggs (2-530 J.tm diameter) and sperm clusters could be seen in both calcified and decalcified polyps if the mesenteries were removed and gently squashed on a slide. Eggs and testes nearing maturity were visible in the field with the naked eye when the mesenteries were exposed. Five entire colonies with ripe gonads were repeatedly split and examined to determine whether gonad development was synchronized throughout a colony. Spawning Additional colonies from the reef flat were maintained in aquaria with unfiltered, running sea water and plankton netting filtering the run-off from the outlets. Colonies on the reef flat were periodically sampled to determine if they spawned at the same time. The convention of numbering days according to the lunar cycle has been adopted for comparative purposes (Atoda, 1947a; Stimson, 1978), i.e. new moon is lunar day I; first quarter, day 8; full moon, day 15: last quarter, day 22. 560 BULLETIN OF MARINE SCIENCE, VOL. 31, NO.3, \98\ --- REEF CREST./ ---'"' ..•• -- ... t N 500m IlIIIIJ Beachrock Figure 2. Map of sample and transect sites on Heron Island reef. Larval Settlement and Development To estimate the approximate time from spawning to development of mobile, ciliated larvae, all colonies were removed from aquaria the morning following spawning, leaving the spawn in the aquar- ia, In 1978, ciliated larvae were transferred to and maintained in 2-4 I clean plastic aquaria containing glass slides and pieces of dried coral rubble. Aquaria were ventilated to provide air and increase water movement; the latter may enhance larval settlement (Harrigan, 1972). As larvae adhered to the bottom and sides of aquaria, unfiltered sea water was changed twice a week by siphoning. Plastic film was placed over the tops of aquaria to reduce evaporation and keep the containers clean. In 1979, another laboratory trial was made to determine the interval between spawning and settle- ment and whether normal larvae developed from self-fertilized eggs. Fifty to 200 larvae from aquaria with single colonies (self-fertilized) and two or more colonies (possibly cross-fertilized) were held in covered 2-1large-mouth jars and provided with air for short intervals. Prior to placing larvae inside, aquaria were conditioned in sea water for several days. Once larvae had settled and metamorphosed, the polyps were fed by running unfiltered sea water into aquaria for several hours daily. The aquaria with polyps were cleaned periodically by removing algae and sediment with the fingertips. To compare rates of development, larvae were collected from the substrate surrounding colonies known to have spawned in the field and in aquaria respectively on the same day and were observed, using a dissecting microscope 16 and 40 h after spawning. Samples of larvae were collected, fixed in 3-4% gluteraldehyde in phosphate buffer or filtered sea water, stored in 0.1 M (pH 7.2) phosphate buffer and embedded in Spurr's medium. Semi-thin sections (3-5 ILm) were cut with an ultra-microtome and stained with 0.3% toluidine blue, a metachromatic stain which stains mucin an intense pink (Humason, 1972). Colony Size and Reproduction To determine the approximate size at the onset of reproduction, 101 colonies were measured and sampled. The arithmetic mean radius (x) of colonies in situ was found by measuring the height KOJIS AND QUINN: SEXUAL REPRODUCTION IN GONIASTREA 561 Table I. The arithmetic mean radius (x), standard deviation (SO), and coefficient of variation (CV%) for repeated size samples of 6 colonies of GOlliaslrea auslralellsis Colonies 6 x (cm) \.89 3.67 5.63 6.27 6.56 7.56 SO 0.07 0.15 0.29 0.]0 0.21 0.11 CV% 3.7 4.] 5.2 \.6 3.2 1.5 (distance from the point of attachment to the tip of the colony), length (greatest diameter at right angles to the height) and width (greatest diameter at right angles to both the height and length). Wooden calipers and ruler were used to measure coral colonies. The calipers prevented damage to coral skeletal projections. Hughes and Jackson (1980) found that partial colony mortality distorted the linear relationship between size and age among reef corals. Partial colony death commonly occurred in G. auslralellsis (personal observation). Thus the arithmetic mean radius (x) was used in preference to the geometric mean radius (Gm) (Loya, 1976b) because the Gm decreases in relation to X as differences in I, wand h measurements increase.