The distribution and abundance of euphausiid larvae and salps was studied from samples collected in 2002 and 2006 from Prydz Bay.Antarctica. Larvae of Thysanoessa macrura and Euphausia superba were mainly distributed in the north of the continental shelf.T.macrura was more abundant and had a relatively wider distribution.In 2006,with ice having retreated and higher seawater temperatures and chlorophyll a levels,E.superba and T.macrura occurred in higher abundances and at more mature developmental stages.Euphausia crystallorophias was mainly distributed in the neritic region.In 2002,with severe ice conditions in the neritic region,abundance of E.crystallorophias was only 95.6 ind·(1000 m)^(-3).In 2006 when a polynya existed,the abundance of E.crystallorophias reached 43966.6 ind·(1000 m)^(-3).The population mainly consisted of metanauplius(MN) and calyptopis I(CD.Salps,mostly Salpa thompsoni,had a low abundance in Prydz Bay.In 2002,S.thompsoni was only found at one station in the north of the bay with an abundance of 10 ind·(1000 m)^(-3).In 2006,S.thompsoni was found at three stations located near the continental slope and average abundance reached 146.7 ind·(1000 m)^(-3).Environmental factors,such as the timing of ice melt,polynya formation and food concentration appear to have a marked effect on the distribution and abundance of euphausiid larvae and salps.
This paper presents two comparisons or tests for a Lagrangian model of zooplankton dispersion:numerical schemes and time steps.Firstly,we compared three numerical schemes using idealized circulations.Results show that the precisions of the advanced Adams-Bashfold-Moulton(ABM) method and the Runge-Kutta(RK) method were in the same order and both were much higher than that of the Euler method.Furthermore,the advanced ABM method is more efficient than the RK method in computational memory requirements and time consumption.We therefore chose the advanced ABM method as the Lagrangian particle-tracking algorithm.Secondly,we performed a sensitivity test for time steps,using outputs of the hydrodynamic model,Symphonie.Results show that the time step choices depend on the fluid response time that is related to the spatial resolution of velocity fields.The method introduced by Oliveira et al.in 2002 is suitable for choosing time steps of Lagrangian particle-tracking models,at least when only considering advection.
To model Skeletonema costatum blooms and their relationship with environmental parameters in situ, a S. costatum-specific zero-dimensional box model based on the mechanistic model Eco3M was established using physiological features. The parameters were calibrated using experimental counterparts, and simulations were compared with published laboratory findings. The resulting normalized objective function (NOF) values are less than 1.0 (and in most cases less than 0.58) and the values for the slope y (between 0.656 7-1.127 4) and R2 (between 0.806 8-0.971) are close to 1.0 for most of the sub-figures. This indicates good agreement between simulated and measured data and suggests that the model reproduces the general characteristics of S. costatum growth and use of nutrients under different N- or P-limiting conditions. The model is appropriate for further applications and can be used to test more scenarios using other nutrients.
This study analyzed and compared variations of the sulcus and otolith outlines of three geographic stocks(Huanghe(Yellow)River estuary(HHE),Jiaozhou Bay(JZB),and Changjiang(Yangtze)River estuary(CJE))of white croaker Pennahia argentata in northern Chinese coastal waters.The sulcus and otolith outline analyses via elliptical Fourier transform(EFT,i.e.,outline analysis)achieved an overall classifi cation rate of 80.4%and 87.2%,respectively.Based on a combination of sulcus and otolith shape indices(SIs)and two derivative ratios,a moderate discriminatory effi ciency of 64.7%was obtained.The results indicate that sulcus outline analysis could be used alone to discriminate white croaker stocks,and that both sulcus and otolith outline analyses discriminated the fi sh stocks at a higher classifi cation rate than the shape indices.The sulcus outline analysis provided complementary information to the whole otolith outline analysis for stock discrimination.Both the sulcus and otolith outline analyses effi ciently discriminated between the most geographically separated CJE and HHE stocks,indicating that they could be considered discrete stocks for fi shery management.