Effects of <i>Exopalaemon modestus</i> on nutrient levels and plankton communities in spring and Summer subtropical lakes and reservoirs: A microcosm experiment

Abstract

秀丽白虾（Exopalaemon modestus）是我国大型淡水湖库的重要经济渔获对象，也是水体中浮游动物的捕食者之一.以往的研究从渔业的角度揭示了秀丽白虾的生物学特征与食性，但少有研究探讨秀丽白虾这一无脊椎动物捕食者对春、夏季浮游生物群落的影响.本研究设计了一个单因素户外微宇宙实验，比较了春季-初夏（4—6月）时期，有无秀丽白虾条件下水体氮、磷浓度以及浮游生物生物量和群落结构的变化.结果表明：1）秀丽白虾的存在显著降低了春季水体总氮（TN）浓度，增加了水体总磷（TP）浓度，降低了水体TN：TP比值；2）秀丽白虾的捕食减少了大型枝角类Daphnia pulex和浮游动物总生物量，D.pulex在浮游动物群落中的优势度被轮虫取代，浮游动物群落趋于小型化；3）秀丽白虾显著增加了春季水体叶绿素a浓度，但对浮游植物群落结构的影响不明显.研究表明在大型湖库中，秀丽白虾等无脊椎动物捕食者可能是影响浮游生物群落变化的因素之一，在春季浮游生物研究中应予以关注.;Shrimp (Exopalaemon modestus) is one of the most important aquatic products and zooplankton predators in large freshwater lakes and reservoirs in subtropical China. Previous studies have revealed the biological characteristics and diets of E. modestus, while few studies studied the influences of this invertebrate predator on plankton dynamics in spring-summer. Here, we designed an outdoor microcosm experiment to compare the difference of nutrient levels and plankton communities under contrast shrimp scenarios (shrimp absent/present). The results showed that:1) E. modestus significantly reduced total nitrogen (TN) concentrations, while increased total phosphorus (TP) concentrations and thereby caused a decline in TN:TP ratios in spring. 2) The predation of E. modestus in spring significantly reduced the biomass of large-sized cladoceran-Daphnia pulex and the total zooplankton biomass. Meanwhile, D. pulex dominance in the zooplankton community was replaced by rotifers when E. modestus were present, which caused a decline in zooplankton size; 3) E. modestus significantly elevated chlorophyll-a concentrations, while no significant effect of E. modestus on phytoplankton community structure was observed. Our study suggests that in large lake and reservoir ecosystems, invertebrate predators such as E. modestus may affect plankton succession. Thus, more attention should be paid to spring plankton studies.