Zooplankton community attributes in an oligo-mesotrophic reservoir: A comparative study of two sampling strategies

Abstract Studies of the limnetic zooplankton in Brazilian freshwater have been done using several sampling strategies which are frequently associated to personal preferences, system constraints and objectives of the studies. It is known that a better sampling technique exists for each group of investigated zooplankton. So, the challenge is to provide a good sampling method for all groups at once. Regarding this theme we are contributing by pointing out the merits and demerits of two collecting methods of zooplankton widely used in many studies in Brazilian reservoirs to clarify the information about communities’ structure in past published and non-published biological data and also find a more useful sampler for future studies. Two simultaneous strategies were used with a 68μm-plankton net: filtration of water collected at sub-surface by bucket and vertical hauls throughout the euphotic zone. A total of 133 taxa was found with both strategies. Rotifers (69 taxa) comprised the group with the highest richness, followed by protozoans (31 taxa), cladocerans (30 taxa) and copepods (5 taxa). Paired t-tests showed significant difference for richness despite none for density in whole period. Spatially, sampling strategies differed in abundance and composition of zooplankton at most sites sampled (except for L1- shallowest site and L4 – deepest site). Temporally, both samplers showed the highest mean abundances at thermal stratification period. In general, the extent of spatial data collected throughout the vertical gradient provided better estimations in the limnetic area for the attributes analyzed: zooplankton density, richness, specific diversity, equitability and cumulative richness. Zooplankton sampling by vertical hauls through the euphotic zone was more efficient, but in order to obtain integrated data and according to the collector’s curve it might be useful to adopt both methodologies.

摘要 针对巴西淡水湖沼带浮游动物的相关研究，当前多采用多种采样策略，而策略的选择往往受研究者个人偏好、实验系统局限及研究目标影响。已有研究表明，针对不同类群的浮游动物，存在更适配的采样技术。因此，当前的核心挑战在于能否开发出一套可同时适用于所有浮游动物类群的高效采样方法。围绕这一研究主题，本研究对巴西水库研究中广泛使用的两种浮游动物采集方法的优缺点进行了系统评析，旨在厘清已发表及未发表的生物学数据中关于浮游动物群落结构的相关信息，并为后续研究筛选出更实用的采样工具。本研究采用68μm浮游生物网开展两种同步采样策略：一是利用采水器采集表层以下水体并过滤，二是在真光层范围内进行垂直拖网采样。两种采样策略共采集到133个分类单元，其中轮虫类（69个分类单元）的物种丰富度最高，依次为原生动物（31个分类单元）、枝角类（30个分类单元）以及桡足类（5个分类单元）。配对t检验结果显示，在整个观测周期内，两种采样方式的浮游动物密度无显著差异，但物种丰富度则存在显著差异。空间维度上，多数采样点的浮游动物丰度及群落组成在两种采样策略下存在显著差异，仅最浅采样点L1与最深采样点L4除外。时间维度上，两种采样方式所得的浮游动物平均丰度均在水体热分层时期达到峰值。总体而言，基于垂直梯度采集的空间数据，可对湖沼带的浮游动物密度、物种丰富度、物种多样性、群落均匀度及累积丰富度等分析指标做出更精准的估算。通过真光层垂直拖网开展的浮游动物采样效率更高，但若需获取完整的整合性数据，结合种积曲线分析结果，同时采用两种采样方法会更为适宜。