Estimation of the underwater attenuation of light is important to ecosystem modellers, who require information on Photosynthetically Available Radiation (PAR), and on the euphotic depth for calculation of primary production. Characterisation of these processes can be achieved by determining the diffuse attenuation coefficient of PAR, KPAR. A review of bio-optical models of the spectral diffuse attenuation coefficient for downwelling irradiance, K-d, is presented and stresses the necessity for a better knowledge and parameterization of these coefficients. In the second part of this work, radiative transfer simulations were carried out to model K-dZ1\% the spectral diffuse attenuation of downwelling irradiance averaged over the euphotic depth Z(1\%) (depth where the downwelling irradiance is 1\% of its surface value). This model takes into account the effects of varying sun zenith angle and cloud cover and needs absorption and backscattering coefficients (the inherent optical properties, IOPs) as input. It provides average and maximum relative errors of 1\% and 5\% respectively, for sun zenith angles [0 degrees-50 degrees] and of 1.7\% and 12\% respectively at higher sun zenith angles. A relationship was established between K-dZ1\% at a single wavelength (590nm) and KPAR at Z(PAR1\%) (where PAR is 1\% of its value at the surface) which allows for a direct expression of KPAR(ZPAR1\%) in terms of inherent optical properties, sun angle and cloudiness. This model provides estimates of KPAR within 25\% (respectively 40\%) relative errors respectively with a mean relative error less than 7\% (respectively 9\%) for sun zenith angles ranging from 0 degrees to 50 degrees (respectively higher than 50 degrees). A similar method is applied to derive a model for the diffuse attenuation of photosynthetically usable radiation, KPURZPUR1\%, with similar performance.
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The life cycle, the phenology and the interannual variability of jellyfish (i.e. cnidaria medusozoa scyphozoa) are under study across the world as there is debate on their increasing occurrence under human pressure (overfishing, eutrophication, climate change) (Condon et al. 2012). Beside interference in human activities, jellyfish swarms affect the marine food web as these organisms feed on fish eggs and larvae, and compete for food with adult fish (Lynam et al. 2005, Pauly et al. 2009). Whether jellyfish nuisance can be mitigated remains unclear and depends on our understanding of the causes of outbreaks. Most North Sea jellyfish species have a sessile polyp stage as part of their life cycle, and therefore need solid substrate to fix. While A. aurita polyps are visible along the Belgian and Dutch coasts, the location of other species polyps (e.g. Cyanea, Chrysaora) remains largely unknown. Tracing back the origin of an observed jellyfish swarm in the North Sea could help identifying the potential location of polyps and the timing and temperature of strobilation. A Lagrangian particle tracking model parameterized for jellyfish in the English Channel and the southern North Sea is used in backtracking (15 days) and forecast (3 days; forced by UKMO forecast) modes to study the potential origin and fate of jellyfish swarms. A backtracking simulation was applied on a jellyfish swarm observed in 2013 in the Belgian coastal zone . It allowed identifying potential areas of origin for the outbreak, raising new scientific questions. A first sensitivity study illustrates the wind influence on the backtracking simulation.
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Recent research on early bats has shown that diversification began early in the Early Eocene. The diversity was the highest in Europe and India and composed of the families Onychonycteridae, Icaronycteridae, Archaeonycteridae, Palaeochiropterygidae, and Hassianycteridae. However, in Europe, the oldest species have all been described from Northern Europe with the exception of Archaeonycteris? praecursor from Silveirinha (MP7, Portugal). Here we present a new bat from La Borie (MP8+9, South France). It is the first early Eocene species from Southern Europe identified on a relatively complete dentition: about 40 isolated teeth and dentary fragments. The teeth are nyctalodont and characterized by: moderate sized canines; middle sized p4 with well-developed metaconid; wide m1-2 with very lingual hypoconulid and high entoconid; middle sized P4; M1-2 with deep ectoflexus, weak paraconule, weak to absent metaconule, centrocrista not joining the labial border; m3/M3 smaller than m1-2/M1-2. These characters indicate that this species belongs to the Archaeonycteridae and is close to Archaeonycteris. It differs from Archaeonycteris trigonodon from Messel (MP11, Germany), A. brailloni from Mutigny and Avenay (MP8+9, France), and Protonycteris gunnelli from Vastan (India) by being about 25 % smaller. It is similar in size to Archaeonycteris? praecursor, A? storchi from Vastan, and the new archaeonycterid from Meudon (MP7, France). It differs from A? storchi by smaller p4 and shallower dentary, and from the Meudon species by more lingual hypoconulid, higher entoconid, and longer postcristid. In fact, it is very similar to A? praecursor by the m2 with relatively high entoconid and long postcristid; the main difference being the hypoconulid that is a little more lingual. The latter character suggests a more advanced dilambdodonty than A? praecursor, which is in agreement with the ages of the two localities. Both species seem to belong to the same evolutionary lineage geographically restricted to Southern Europe.
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RBINS Staff Publications 2016
