Temporal patterns of larval settlement and survivorship of two broadcast-spawning acroporid corals

Acroporid corals are the main reef-building corals that provide three-dimensional habitats for other reef organisms, but are decreasing on many reefs worldwide due to natural and anthropogenic disturbances. In this study, temporal patterns of larval settlement and survivorship of two broadcast-spawning acroporid coral species, Acropora muricata and A. valida, were examined through laboratory rearing experiments to better understand the potential for larval dispersal of this important coral group. Many larvae were attached (but not metamorphosed) to settlement tiles on the first examination 3–4 days after spawning (AS). The first permanent larval settlement (i.e. metamorphosed and permanently settled juvenile polyps) occurred at 5–6 days AS, and most larval settlement (85–97% of total) occurred within 9–10 days AS. Larval survivorship decreased substantially to around 50% by the first week of the experiment and to approximately 10% by the second to third week. The rates of larval attachment, settlement, and the initial drop in survivorship of larvae suggest that effective dispersal of some acroporid species may largely be completed within the first few weeks AS

Extended breeding seasons and asynchronous spawning among equatorial reef corals in Kenya

Patterns of sexual reproduction in scleractinian reef corals have been widely studied, and vary both systematically and biogeographically. Extensive sampling and repeated monitoring of 401 marked colonies of 20 Acropora spp. over 2 yr on equatorial lagoon reefs in Kenya (4°S) demonstrated an overall asynchronous spawning pattern extending over a 7 mo period (Mangubhai & Harrison 2008a; Mar Ecol Prog Ser 360:85–96). Spawning occurred during all lunar phases, and during both rising and maximum sea surface temperatures. Although some degree of multispecies spawning occurs on Kenyan reefs, most coral species exhibited relatively asynchronous and extended spawning over 2 to 5 mo with some level of temporal reproductive isolation among species. These data support previous hypotheses of more protracted breeding seasons and a breakdown in spawning synchrony nearer the equator, and contrast markedly with the mass spawning of corals on the Great Barrier Reef and some Western Australian reefs. Baird & Guest (2009, this volume) question this conclusion based on their redefinition of the term ‘mass spawning’, which they define to encompass lesser multispecies spawning events. They assert that Mangubhai & Harrison (2008a) (1) categorically state that mass spawning does not occur in equatorial regions, and (2) do not cite recent studies that document spawning in synchrony by numerous species in equatorial assemblages; both of these assertions are incorrect. The conclusions in Mangubhai & Harrison (2008a) are valid, and clearly demonstrate an unusually extended and asynchronous spawning pattern among many corals on equatorial reefs in Kenya

Effects of elevated temperature on larval settlement and post-settlement survival in scleractinian corals, Acropora solitaryensis and Favites chinensis

We examined the effects of elevated temperature under different exposure periods on larval settlement and post-settlement survival in scleractinian corals, Acropora solitaryensis and Favites chinensis. In the first experiment with the subtropical coral, A. solitaryensis, the numbers of larvae settling and those dead were examined daily for 5 days at 20, 23 (ambient), 26 and 29°C conditions. Larval settlement of A. solitaryensis was initially greater at higher temperature conditions, but the peak in number of settled larvae shifted from 29 to 26°C by day 5, due to ca. 90% post-settlement mortality at 29°C condition. In order to determine the effects under short-term exposure, larvae of F. chinensis were exposed to 27 (ambient), 31 or 34°C only for one hour in the second experiment. The number of larvae settling for 24 h after the exposure and their survivorship over subsequent week was monitored in the ambient temperature condition. Larvae of F. chinensis exhibited greater settlement at higher temperature treatments and constantly low post-settlement mortalities (\u3c ca. 17%) in all temperature treatments, resulting in the highest number of settled larvae at 34°C treatment. These results suggested two different effects of elevated temperature on the early stages of recruitment process of scleractinian corals; (1) the positive effect on larval settlement and (2) the negative effect on post-settlement survival under prolonged exposure

Embryonic and larval development of the host sea anemones Entacmaea quadricolor and Heteractis crispa

Little information is available on the sexual reproductive biology of anemones that provide essential habitat for anemonefish. Here we provide the first information on the surface ultrastructural and morphological changes during development of the embryos and planula larvae of Entacmaea quadricolor and Heteractis crispa, using light and scanning electron microscopy. Newly spawned eggs of E. quadricolor and H. crispa averaged 794 µm and 589 µm diameter, respectively, and were covered by many spires of microvilli that were evenly distributed over the egg surface, except for a single bare patch. Eggs of both species contained abundant zooxanthellae when spawned, indicating vertical transmission of symbionts. Fertilization was external, and the resulting embryos displayed superficial cleavage. As development continued, individual blastomeres became readily distinguishable and a round-to-ovoid blastula was formed, which flattened with further divisions. The edges of the blastula thickened, creating a concave-convex dish-shaped gastrula. The outer margins of the gastrula appeared to roll inward, leading to the formation of an oral pore and a ciliated planula larva. Larval motility and directional movement were first observed 36 h after spawning. E. quadricolor larval survival remained high during the first 4 d after spawning, then decreased rapidly

Asynchronous coral spawning patterns on equatorial reefs in Kenya

This study examined patterns of reef coral reproduction on lagoonal reefs adjacent to Mombasa in Kenya, at a latitude of 4°S. A total of 401 colonies comprising 20 Acropora species was marked and repeatedly sampled between 2003 and 2005 to determine patterns of reproduction at the individual and population level. Spawning was inferred from the disappearance of mature oocytes and spermaries from sequential samples. In comparison to other regions, the overall pattern of coral reproduction in Kenya is one of asynchrony; Acropora species release gametes over a 7 mo period (October to April), with some level of ‘temporal reproductive isolation’ occurring between species in relation to the lunar month and lunar phase when the main spawning occurred. Extended gametogenic cycles were recorded in A. tenuis, A. valida and Acropora sp. 1, and quiescent non-reproductive periods between cycles were either very short or absent. Spawning occurred during both rising and maximum sea surface temperatures, during both neap and spring tides, and across all lunar periods. The findings from Kenyan reefs support the hypothesis of protracted breeding seasons and a breakdown of spawning synchrony nearer the equator. It is hypothesised that the high fecundities recorded in coral species in Kenya compared to other regions may allow individual reef coral populations to stagger their reproduction over 2 to 5 mo without incurring a significant reduction in fertilisation rates

Broadcast spawning of two species of sea anemone, Entacmaea

As the sea anemones, Entacmaea quadricolor and Heteractis crispa, provide essential habitat for obligate symbiotic anemonefish, knowledge of their reproductive biology is crucial to their effective management and conservation. This paper provides the first detailed information on the spawning times, behaviour and mode of gamete release for these host anemone species. Anemones were collected from subtropical reefs in the Solitary Islands Marine Park, eastern Australia, and monitored in outdoor flow-through seawater tanks from 2003 to 2005. Sexually reproductive anemones were either male or female, releasing their gametes into the water column for external fertilisation and development. Spawning of both sexes was predominately synchronous and was restricted to a few nights each year during the austral summer and autumn. Males generally began to release gametes prior to females, suggesting that sperm or some associated product may trigger the females to spawn. Sperm were commonly released in milky white streams or clouds, whereas eggs were released singly or in large masses. Reproductive seasonality and synchrony of gamete release suggests that spawning in both species is coordinated by similar responses of individuals to a range of environmental factors such as seawater temperature, photoperiod and lunar cycles. Incorporating knowledge of the sexual reproductive biology of host sea anemones into management and conservation programs could help ensure the viability of their populations and their resident anemonefish