Natural antifouling defences of tropical sea stars

Guenther, Jana (2007) Natural antifouling defences of tropical sea stars. PhD thesis, James Cook University.

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Abstract

Qualitative evidence suggests that sea stars have remarkably clean epidermal surfaces. To quantify surface-associated micro- and macroorganisms, field surveys were conducted in northern Queensland, Australia, during the wet and dry seasons. Mean bacterial abundances on 7 sea star species were approximately 104 to 105 cells cm-2 during both seasons. There were no consistent trends in bacterial abundances with season, species and aboral positions on sea star arms. Low numbers of parasitic and commensal macroorganisms were found on 6 sea star species, and no common generalist macrofouling organisms, such as algae, barnacles, serpulid polychaetes, bryozoans and ascidians, were discovered on any specimens. Sea stars therefore offered an excellent model to investigate the mechanisms driving fouling-resistant surfaces. Subsequently, 5 sea star species belonging to the order Valvatida were chosen for this study to investigate mechanical, physical and chemical fouling deterrence: Acanthaster planci (Family Acanthasteridae), Linckia laevigata and Fromia indica (both Family Ophidiasteridae), Cryptasterina pentagona (Family Asterinidae) and Archaster typicus (Family Archasteridae).

It has been proposed that mechanical antifouling defence mechanisms of sea stars are linked with pedicellariae, which are pincer-like appendages made of calcareous ossicles. In this study, the role of pedicellariae of the sea star A. planci in fouling control was investigated. The morphology and distribution of its pedicellariae were measured to determine if larvae or propagules of fouling organisms could settle between pedicellariae without being in their physical range. The elementary and straight pedicellariae of A. planci had a mean length of 0.7 mm and a mean distance of 2.6 mm. The total number of pedicellariae was proportional to the estimated surface area of A. planci. To determine how pedicellariae respond to tactile stimulation, pedicellariae were stimulated by touching either inner, outer or basal sites of pedicellariae with a hypodermic needle. Pedicellariae closed rapidly on touch and closed for significantly longer when touched at their inner sites (8.9 s) than outer (6.7 s) and basal (7.9 s) sites. Settling larvae were simulated by dropping silica beads (size: 50.2 μm, 181.5 μm, 255.7 μm and 510.7 μm, density: 2.5 g ml-1) and zirconium/silica beads (size: 191.2 μm and 507.6 μm, density: 3.7 g ml-1) over the pedicellariae. The percentage of responding pedicellariae increased proportionally with increasing size of the silica beads. However, the percentage also increased when zirconium/silica beads of similar size but higher density were used, demonstrating that the mass, not size, of the beads was the main driving factor for the closure of pedicellariae. Pedicellariae were also stimulated by placing larvae of the bryozoan Bugula neritina (250 μm)

Item ID: 3223
Item Type: Thesis (PhD)
Keywords: sea stars, Valvatida, north Queensland, fouling-resistant surfaces, antifouling defence mechanisms, Pedicellariae, morphology, distribution, tactile stimulation, wettability, surface microtopography, paxillae, settlement, surface chemistry, hexadecanoic acid, cholesterol, lathosterol
Date Deposited: 14 Jul 2009 04:34
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
06 BIOLOGICAL SCIENCES > 0606 Physiology > 060601 Animal Physiology - Biophysics @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
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