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Corals require efficient heat and mass transfer with the overlying water column to support key biological processes, such as nutrient uptake and mitigation of thermal stress. Transfer rates are primarily determined by flow conditions, coral morphology and the physics of the resulting fluid -structure interaction, yet the relationship among these parameters is poorly understood especially for wave-dominated coral habitats. To investigate the interactive effects of these factors on fluxes of heat and mass, we measure hydrodynamic characteristics in situ over three distinct surface morphologies of massive stony corals in a Panamanian reef. Additionally, we implement a numerical model of flow and thermal transport for both current and wave conditions past a natural coral surface, as well as past three simplified coral morphologies with varying ratios of surface roughness spacing-to-height. We find oscillatory flow enhances rates of heat and mass transfer by 1.2-2.0Â compared with unidirectional flow. Additionally, increases in Reynolds number and in surface roughness ratio produce up to a 3.3Â and a 2.0Â enhancement, respectively. However, as waves begin to dominate the flow regime relative to unidirectional currents, the underlying physical mechanisms mediating transfer rates shift from predominantly turbulence-driven to greater control by inertial accelerations, resulting in larger heat and mass transfer for small surface roughness ratios. We show that for rough corals in wave-dominated flows, novel trade-off dynamics for heat and mass transfer exist between broadly spaced roughness that enhances turbulence production versus narrowly spaced roughness that produces greater surface area. These findings have important implications for differential survivorship during heatinduced coral bleaching, particularly as thermal stress events become increasingly common with global climate change. rsif.royalsocietypublishing.org J. R. Soc. Interface 15: 20180448 rsif.royalsocietypublishing.org J. R. Soc. Interface 15: 20180448

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Coral reefs all over the Indo-Pacific suffer from substantial damage caused by the crown-of-thorns seastar Acanthaster planci, a voracious predator that moves on and between reefs to seek out its coral prey. Chemoreception is thought to guide A. planci. As vision was recently introduced as another sense involved in seastar navigation, we investigated the potential role of vision for navigation in A. planci. We estimated the spatial resolution and visual field of the compound eye using histological sections and morphometric measurements. Field experiments in a semi-controlled environment revealed that vision in A. planci aids in finding reef structures at a distance of at least 5 m, whereas chemoreception seems to be effective only at very short distances. Hence, vision outweighs chemoreception at intermediate distances. A. planci might use vision to navigate between reef structures and to locate coral prey, therefore improving foraging efficiency, especially when multidirectional currents and omnipresent chemical cues on the reef hamper chemoreception.

Keywords:Acanthaster planci (Linnaeus 1758) Echinodermata Gonad index Magnetic resonance imaging Non-invasive Pyloric cecum index Starfish (Echinodermata: Asteroidea) are present in most benthic ocean habitats and play an important ecological role as keystone species or by dominating through sheer individual numbers. In order to assess nutritional and reproductive states in ecological studies on asteroids, invasive techniques to calculate organ indices are conventionally used. We present a non-invasive method that enables imaging and morphometric measurements in starfish in vivo. We used a clinical 1.5 T magnetic resonance imaging (MRI) scanner to produce sectional images of three starfish species and employed these image stacks to generate 3D models of the pyloric ceca, gonads and the endoskeleton. In comparison to pre-clinical MRI scanners, that provide higher resolutions, clinical MRI is not limited to small objects, but allows the investigation of larger samples such as the starfish used in the present study. Volume data from MRI-based 3D reconstructions were compared to conventional invasive measurement techniques as well as high resolution MRI scans and were tested for inter-observer effects. Here we show that MRI is a suitable method for precise imaging and volumetric measurements in fixed and living marine specimens. Compared to other methods, it allows not only the production of time series data on single individuals as well as populations, but also non-destructive analyses of valuable specimens, such as museum material.