A zero-dimensional model for phytoplanktonicproduction in turbid, macro-tidal, well-mixed estuaries is proposed. It is based on the description of light-dependentalgal growth, phytoplankton respiration and mortality. The model is forced by simple time-functions for solar irradiance, water depth and light penetration. The extinction coefficientis directly related to the dynamics of suspended particulate matter. Model results show that the description of phyto-plankton growth must operate at a time resolution sufficientlyhigh to describe the interference between solarly and tidallydriven physical forcing functions. They also demonstrate that in shallow to moderately deep systems, simulations using averaged, instead of time-varying, forcing functions lead to significant errors in the estimation of phytoplankton productivity. The highest errors are observed when the temporalpattern of light penetration, linked to the tidal cycle of solidssettling and resuspension, is neglected. The model has alsobeen applied using realistic forcing functions typical of two locations in the Scheldt estuary. Model results are consistentwith the typical phytoplankton decay observed along the lon-gitudinal, seaward axis in the tidal river and oligohaline part of this estuary.
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Representatives of Ligophorus Euzet et Suriano, 1977 were found on the gills of Mugil liza Valenciennes caught in southern Brazil. They were identified as Ligophorus uruguayense Failla Siquier et Ostrowski de Núñez, 2009 and Ligophorus saladensis Marcotegui et Martorelli, 2009, even though specific identification proved to be difficult due to inconsistencies in some diagnostic features reported for these two species. Therefore, a combined morphological and molecular approach was used to critically review the validity of these species, by means of phase contrast and confocal fluorescence microscopical examination of sclerotised hard parts, and assessing the genetic divergence between L. saladensis, L. uruguayense and their congeners using rDNA sequences. The main morphological differences between the two species relate to the shape of the accessory piece of the penis and the median process of the ventral bar. The accessory piece in L. uruguayense is shorter than in L. saladensis, has a cylindrical, convex upper lobe and straight lower lobe (vs with the distal tip of the lower lobe turning away from the upper lobe in the latter species). The ventral bar has a V-shaped anterior median part in L. uruguayense (vs U-shaped in L. saladensis). The two species are suggested to be part of a species complex together with L. mediterraneus Sarabeev, Balbuena et Euzet, 2005. We recommend to generalise such comparative assessment of species of Ligophorus for a reliable picture of the diversity and diversification mechanisms within the genus, and to make full use of its potential as an additional marker for mullet taxonomy and systematics.
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