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Context. Longspined sea urchins (Centrostephanus rodgersii) form extensive urchin barrens in south-eastern Australia, threatening biodiversity and lucrative fishery stocks. Although large urchins are readily visible on reefs, small or 'undersized' urchins have often been considered non-emergent, cryptic, and largely inaccessible to predators, meaning smaller predators are considered not to contribute to top-down urchin control. Aims. Here,we aimto investigate variation in nocturnalmovement across urchin size classes and discuss the associated ecological implications. Methods. Using timelapse footage we measured timing of movement, distance covered, and displacement of different sized sea urchins in various habitats. Key results. Small urchins emerge from cryptic habitats and are active overnight on open reef areas. At dusk, smaller urchins emerge later than larger urchins, whereas at dawn, movement of all size classes of urchins decline at a similar rate. Conclusions. The nocturnal emergence and movement of small urchins on open reef spaces makes them accessible to nocturnal predators, such as the southern rock lobster (Jasus edwardsii). Implications. This time- space overlap of predator and prey implies that rock lobsters (including small lobsters) may be inflicting higher predatory pressure than previously considered on undersized sea urchins. [ABSTRACT FROM AUTHOR]

Context. Settlement and metamorphosis are key processes influencing the natural recruitment and aquaculture production of aquatic organisms. Recruitment requirements in limpets (Patellogastropoda) are mostly unknown, because of the lack of reliable settlement inducers. Aims. This study tested the reliability of different cues as settlement inducers for competent larvae of the economically valuable Patella aspera. Methods. Natural crustose coralline algae (CCA) and biofilms of the benthic diatom Navicula salinicola were tested as positive controls. The following four pharmacological agents were tested as chemical inducers in a wide range of concentrations: gamma-aminobutyric acid (GABA), acetylcholine (ACH), 3-isobutyl-1-methylxanthine (IBMX) and potassium chloride (KCl). Settlers were identified by the velum loss and teleoconch development. Key results. CCA were strong settlement cues in all the assays. Contrary to previous hypotheses, GABA was a weak inducer with a peak effect at 10-5 M. Neither the diatom biofilms nor the other pharmacological agents (ACH, IBMX and KCl) promoted the settlement response. All pharmacological agents at high concentrations influenced larval behaviour. Conclusions. CCA were reliable positive controls and settlement inducers for the production of post-larvae. With regard to pharmacological agents, P. aspera showed restrictive settlement requirements that should be considered for ecological and aquaculture studies in other limpet species. Implications. This method allows the study of the settlement biology of limpets. It provides a positive control and integrates animal monitoring and comparative response to other cues. [ABSTRACT FROM AUTHOR]