Reproduction in cultured versus wild coral colonies: fertilization, larval oxygen consumption, and survival.

In the late 1990s, the once prolific populations of the coral Acropora intermedia surrounding Okinawa, Japan, dramatically declined because of thermal stress, bleaching caused by heat stress, and consequent mortality. Before the bleaching event, 72 fragments (about 15 cm in length) were collected and transferred to the Okinawa Churami Aquarium. Through growth and repeated fragmentation, these original fragments developed into about 100 colonies that spawned from 1999 to 2009. In this study, we compared gametogenesis, fertilization, survival, and O(2) consumption in cultured and wild colonies of A. intermedia and their offspring. Cultured A. intermedia had larger oocytes and higher fertilization and survival rates than samples from wild colonies. O(2) consumption of cultured embryos was similar to that of wild embryos. These results suggest that cultured A. intermedia and their offspring are as viable as wild colonies. Aquaria can play a role in the conservation of endangered corals, and their cultured colonies could be used to re-establish devastated species on the Okinawa reefs.

Gene flow of Acanthaster planci (L.) in relation to ocean currents revealed by microsatellite analysis.

Population outbreaks of the coral-eating starfish, Acanthaster planci, are hypothesized to spread to many localities in the Indo-Pacific Ocean through dispersal of planktonic larvae. To elucidate the gene flow of A. planci across the Indo-Pacific in relation to ocean currents and to test the larval dispersal hypothesis, the genetic structure among 23 samples over the Indo-Pacific was analysed using seven highly polymorphic microsatellite loci. The F-statistics and genetic admixture analysis detected genetically distinct groups in accordance with ocean current systems, that is, the Southeast African group (Kenya and Mayotte), the Northwestern Pacific group (the Philippines and Japan), Palau, the North Central Pacific group (Majuro and Pohnpei), the Great Barrier Reef, Fiji, and French Polynesia, with a large genetic break between the Indian and Pacific Oceans. A pattern of significant isolation by distance was observed among all samples (P = 0.001, r = 0.88, n = 253, Mantel test), indicating restricted gene flow among the samples in accordance with geographical distances. The data also indicated strong gene flow within the Southeast African, Northwestern Pacific, and Great Barrier Reef groups. These results suggest that the western boundary currents have strong influence on gene flow of this species and may trigger secondary outbreaks.

Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence.

The cause(s) of primary outbreaks of the coral-eating crown-of-thorns starfish (Acanthaster planci) are still subject to scientific controversy. The possibility of primary outbreaks being linked to terrestrial runoff has been postulated a number of times, suggesting that enhanced nutrient supply is critical for enhanced A. planci larval development. This paper examines the evidence for such a cause, focussing particularly on the Great Barrier Reef (GBR). Nutrient discharges from rivers have increased at least four-fold in the central GBR over the last century, and concentrations of large phyto-plankton (>2 microm) of the inshore central GBR shelf in the wet season when A. planci larvae develop, is double that of other places and times. Larval development, growth and survival increase almost ten-fold with doubled concentrations of large phyto-plankton. This and other lines of evidence suggest that frequent A. planci outbreaks on the GBR may indeed be a result of increased nutrient delivery from the land.