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Seagrass fishes perform key ecological roles and are a critical component of many of the world’s fisheries. A sound understanding of seagrass fish communities, based on robust methods, is therefore integral for their successful environmental management and conservation. Here we quantitatively compare taxa and size class of seagrass fish assemblages collected using; baited and unbaited remote underwater video (BRUV, URUV), diver operated video (DOV), underwater visual census (UVC) and trawling. We assess comparisons of these methods in terms of biodiversity indicators and power to detect change. All five methods were deployed in coastal embayments dominated by Posidonia spp. and within three marine parks along the south-western coast of Western Australia. Fish assemblages recorded using the different methods separated into two distinct groups; those dominated by smaller and less motile species, that are typically present beneath the canopy among seagrass leaves; and those dominated by larger, faster swimming species present above the seagrass canopy. Trawling provided the most effective method for assessing species within the canopy, including those of conservation concern. Conversely, BRUV followed by URUV recorded the greatest number of individuals, successfully detecting the larger supra-canopy and highly motile species typically omitted by trawling. Both trawl and BRUV methods had a higher power to detect change in species richness of seagrass fishes compared to other methods, even though each method recorded different components of the fish assemblage. Fish assemblages recorded using UVC detected both inter and supra-canopy species, but fish abundances recorded by this method were low compared to trawl and BRUV surveys, resulting in reduced power to detect change in richness. DOV was a comparatively less effective method, recording few fish, as well as low richness and diversity values. The combination of trawling and stationary video techniques, particularly BRUV, provided a two-method combination able to holistically measure commonly used indicators of fish assemblage composition in seagrass habitat. These results demonstrate that careful consideration of the methodology is essential when assessing ichthyofauna in seagrass habitat, particularly when only a single method can be employed. As the extent of methodological influence on recording fish assemblages also varied among the three survey areas, geographical differences in the structure of fish and seagrass communities should be considered when selecting an appropriate sampling method.

Constant optogenetic stimulation targeting both pyramidal cells and inhibitory interneurons has recently been shown to elicit propagating waves of gamma-band (40-80 Hz) oscillations in the local field potential of non-human primate motor cortex. The oscillations emerge with non-zero frequency and small amplitude-the hallmark of a type II excitable medium-yet they also propagate far beyond the stimulation site in the manner of a type I excitable medium. How can neural tissue exhibit both type I and type II excitability? We investigated the apparent contradiction by modeling the cortex as a Wilson-Cowan neural field in which optogenetic stimulation was represented by an external current source. In the absence of any external current, the model operated as a type I excitable medium that supported propagating waves of gamma oscillations similar to those observed in vivo. Applying an external current to the population of inhibitory neurons transformed the model into a type II excitable medium. The findings suggest that cortical tissue normally operates as a type I excitable medium but it is locally transformed into a type II medium by optogenetic stimulation which predominantly targets inhibitory neurons. The proposed mechanism accounts for the graded emergence of gamma oscillations at the stimulation site while retaining propagating waves of gamma oscillations in the non-stimulated tissue. It also predicts that gamma waves can be emitted on every second cycle of a 100 Hz oscillation. That prediction was subsequently confirmed by re-analysis of the neurophysiological data. The model thus offers a theoretical account of how optogenetic stimulation alters the excitability of cortical neural fields.

We present a model for flicker phosphenes, the spontaneous appearance of geometric patterns in the visual field when a subject is exposed to diffuse flickering light. We suggest that the phenomenon results from interaction of cortical lateral inhibition with resonant periodic stimuli. We find that the best temporal frequency for eliciting phosphenes is a multiple of intrinsic (damped) oscillatory rhythms in the cortex. We show how both the quantitative and qualitative aspects of the patterns change with frequency of stimulation and provide an explanation for these differences. We use Floquet theory combined with the theory of pattern formation to derive the parameter regimes where the phosphenes occur. We use symmetric bifurcation theory to show why low frequency flicker should produce hexagonal patterns while high frequency produces pinwheels, targets, and spirals.