Spatial and temporal variation in density and thallus morphology of Turbinaria ornata in Thailand

Turbinara ornata (Turner) J. Agardh, is a common brown alga, which occurs on tropical shores worldwide. We studied the effects of wave action and seasonal variation on T. ornata populations at Koh Pling, Sirinart Marine National Park, Thailand. Density, length of thallus, length of blade, number of blades, number of reproductive organs, and dry weights were investigated. The algae were collected bimonthly during August 2003–May 2004, at three different areas of wave exposure: sheltered, semi-exposed, and exposed. There were variations in all factors at sites and seasons (P < 0.05). We found that T. ornata populations were denser on the semi-exposed shore and their biological characteristics reached their peaks during October 2003. The highest density of T. ornata was 27 ± 10 fronds/m² (mean ± S.E.). While the average frond length, for example, was 24 ± 1.5 cm, 4 times greater than the minimum; and the number of blades on the thallus were 329 ± 47 blades, 15 times greater than the minimum. Surprisingly, the population disappeared at the beginning of May 2004, and returned in July 2004. In this work, we attempt to explain the differences in various characteristics of T. ornata in relation to the degree of wave exposure, nutrient concentration and other physical factors. We also discuss how our results may provide some insight into the current rapid expansion of T. ornata populations.