No abstract

Broadcast spawning of gametes with planktonic development of larvae is the most common reproductive mode in tropical corals, and is generally thought to optimize the dispersal potential of larvae. To this end, many previous studies of coral larval dispersal have focused on the maximum time larvae can remain competent to settle and consequently how far they might disperse. However, dispersal ability of broadcastspawned coral larvae will be linked, at least in part, to the minimum time to settlement competency as well as the length of the planktonic period -although estimates of minimum time to competency remain largely anecdotal, with few rigorous studies of the pre-competent period. To determine the minimum time to larval settlement in two species of broadcast-spawning coral (Platygyra daedalea and Goniastrea favulus), we monitored larval settlement rates in aquaria every 6 h from the time larvae commenced swimming (i.e. were ciliated, fully developed larvae) for a period of approximately 10 days. For P. daedalea, peak settlement occurred between 60 and 66 h following fertilization (2.5 and 2.75 days), which is markedly earlier than the 4-to 6-day time period commonly cited as the minimum time before broadcast-spawned coral larvae are competent to settle. Surprisingly, it was also clear from our experimental results that settlement in P. daedalea occurred as a distinct pulse during the 60-to 66-h period, rather than continuously throughout the study period. G. favulus larvae also appear to be able to settle quickly (from 54 h following fertilization). We argue, on the basis of these short competency times and apparently rapid settlement, that dispersal in broadcast-spawning coral larvae may not be as great as has previously been assumed.

Ant~pathes fiordensis is a black coral species endermc to the south western reglon of New Zealand Restncted larval dlspersal has been demonstrated to occur In A fiordens~s although the exact scale of larval dlspersal is unknown Thls study examlnes the fine-scale (<50 m) pattern of relatedness between black coral colonles at 3 sltes in Doubtful Sound Fiordland to mfer dspersal &stance and gain a better understanding of patch size in this species At each of the 3 sites the position of all black coral colonles was mapped and allozyme electrophoresis was used to determine the 10-locus genotype of each colony Two statlstlcal methods were used to examine the association between colony genotype and dlstance at each of the 3 plots, spatlal autocorrelatlon of ~n&vidual loci and Mantels Test which exanunes the relatlonshlp between multi locus genotypes At 1 of the 3 sites (Trlcky Cove) there was a signif~cant positive association among colonles separated by < 5 m for 4 of the 6 loci tested Sinularly Mdntel s Test showed a signdlcant positive correlation between genetic distance and Euclidean distance at the Tricky Cove site (r = 0 2 p = 0 007) These results suggest dlspersal of black coral larvae 1s highly philopatnc and that larvae settle very close to parent colonles However at the other 2 sites there was no spatial associabon detected among genotypes indicating either that gametes or larvae are more widely dspersed at these 2 sites (>50 m) or that other ecological and evolutionary factors are operating that have influenced the observed genetic structure of the populations Genetic stu&es suggest that gene flow in A f~ordensis populations ~1 1 1 b e restncted and that patch size In this species may b e relatively small These findlngs w l l have Important mlplications for the conservation and management of the rare and unique shallow water populations of black corals In New Zealand s flords

Scleractinian corals are notoriously variable and the high degrees of morphological variation displayed by some species, particularly in response to environmental influences, confound our understanding of species boundaries. In order to fully understand the ranges of variation and the influence of habitat on colonies within the genus Platygyra, levels of intra-and interspecific morphological variation were quantified and colony morphology was examined relative to environmental gradients. Measurements of 9 skeletal characters of colonies of Platygyra were analysed by multivariate analysis of variance and canonical discriminant analysis to examine morphological species boundaries. While the taxonomic literature suggests the existence of 5 morphological species of Platygyra, results from this study suggest there may be 7 present on the Great Barrier Reef, Australia. A comparison of skeletal characters of 2 species, F? daedalea and F? pini, across 4 different habitats indicates that the environment does not influence skeletal characteristics in these species. Similarly, a detailed survey of distribution patterns of Platygyra spp. indicates that all species occur sympatrically across 6 reef habitats and that colony morphology does not change predictably along environmental gradients. The absence of any association between morphology and habitat in Platygyra suggests environment has little influence on morphology in these species. Numerical techniques are likely to be useful for defining species boundaries in highly variable groups of corals and similarly for understanding ranges of intraspecific morphological variation.