Effects of the fish anesthetic, clove oil (eugenol), on coral health and growth

Ecological research within coral reefs often requires the use of anesthetics to immobilize organisms. It is therefore important to consider the effect of these chemicals on the surrounding flora and fauna, particularly to the corals themselves. We quantified the effects of clove oil, a commonly used fish anesthetic, on the growth and occurrence of bleaching in three species of corals: Acropora striata, Pocillopora verrucosa, and Porites australiensis. We compared coral responses to five treatments: a gradient of four clove oil concentrations (0-28%) in seawater, and one concentration of clove oil (14%) in ethanol. Each week, we assessed the presence of bleaching, and then applied the treatment. We measured growth over the duration of the 6-week experiment using the buoyant weight technique. Growth and bleaching showed a dose response to clove oil exposure, and the use of ethanol as a solvent had an additional deleterious effect, as also suggested by observed changes in concentrations of eugenol following field application. Overall, growth was reduced by 37.6% at the highest concentration (28% clove oil in seawater) relative to the control (0% clove oil). The reduction in growth was nearly as great (35.3% of the control) at half the concentration of clove oil (14%) when dissolved in ethanol. These results suggest the repeated use of clove oil (even without a solvent) can deleteriously affect corals.     

A novel approach to measuring subtidal habitat complexity

Habitat complexity plays an important role in determining benthic community structure. A diverse range of methods for its measurement have been adopted but none are convenient for use underwater where access time is at a premium. We describe a novel, calibrated, tool for rapidly measuring scale-dependent habitat complexity developed, primarily, for use underwater. This tool is based on a distance-wheel with interchangeable wheels of different sizes to allow a scale-dependent measure of distance. This technique was calibrated against a profile of known complexity, at relevant scales, and then trialed on the Loch Linnhe Artificial Reef, a replicated artificial substratum offering two different scale-dependent habitat complexities. The distance-wheel was cost-effective, simple to fabricate and enabled the rapid and straightforward measurement of perceived distance over the step-length range of 133-1020 mm.     

Photosynthetic performance of transplanted ecotypes ofEcklonia cava(Laminariales, Phaeophyta)

Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m^–2s^–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P _max) at 10–29 °C and the light-saturation index (I _k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P _maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m^–2s^–1. However, at lower light intensities of 12.5–50 mol photon m^–2s^–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation.     

Sexual reproduction of Acropora reef corals at Moorea, French Polynesia

Little information is available on reproductive processes among corals in isolated central Pacific reef regions, including French Polynesia. This study examined the timing and mode of sexual reproduction for Acropora reef corals at Moorea. Spawning was observed and/or inferred in 110 Acropora colonies, representing 12 species, following full moon periods in September through November 2002. Gamete release was observed and inferred in four species of Acropora between 9 and 13 nights after the full moon (nAFM) in September 2002. Twelve Acropora spp. spawned gametes between 5 and 10 nAFM in October 2002, with six species spawning 7 nAFM and four species spawning 9 nAFM. In November 2002, spawning of egg and sperm bundles was observed and inferred in 27 colonies of Acropora austera, 6 nAFM. These are the first detailed records of spawning by Acropora corals in French Polynesia.