Lagoons and coastal marine zones are very productive and useful ecosystems, but they are threatened by the effects of global change and anthropogenic pressures. These effects have a negative impact on the zooplankton, weakening its function of phytoplankton consumer, leading to uncontrolled proliferation of microalgae in case of eutrophication. In this study we test the hypothesis that tidal exchanges with the sea can counteract these deleterious effect, by renewing the zooplankton community and by enhancing its top-down control of phytoplankton through selective retention of zooplankton grazers. Our study focused on the southern region of the Gulf of Gabes and the Boughrara lagoon which presents the highest tidal range in the Mediterranean. During two field campaigns (October 2016 and April 2017) we have analyzed zooplankton descriptive (taxonomic composition, abundance; biomass) and functional (ingestion rate, grazing pressure) variables and environmental variables during time series at a fixed station during ebb-flood sequences and at 8 stations along a sea-lagoon transect and during different tidal amplitude periods. Multivariate analyses of both environmental parameters and zooplankton taxa showed the existence of three distinct zones along the sea-lagoon transect, but also the influence of tidal circulation and water mixing on the renewal of the zooplankton community up to the innermost zones of the lagoon. Time series gave clear patterns for the input/output of marine/lagoon species and show a net import for different taxa and for the total zooplankton abundance and biomass (mean flood/ebb ratio = 2.2 for the total abundance and 2.4 for the biomass), leading to differential retention of zooplankton in the lagoon and to an increase in the potential grazing pressure on phytoplankton (mean flood/ebb ratio = 2.8). We also estimated that the grazing pressure in the lagoon was twice higher during the periods of high tidal amplitudes (at or close to spring tide) compared to periods with low amplitude (neap tides), clearly showing that the retention of zooplankton significantly increases the grazing impact on phytoplankton. These results highlight the importance of the tidal forcing for maintaining the good status of the zooplankton structure and function in strongly anthropized coastal and lagoon ecosystems.

泻湖和沿海海洋区是非常有成效和有用的生态系统，但它们受到全球变化和人为压力的威胁。这些影响对浮游动物有负面影响，削弱了浮游植物消费者的功能，在富营养化的情况下导致微藻不受控制地增殖。在这项研究中，我们测试了这样的假设，即通过更新浮游动物群落并通过选择性保留浮游生物放牧者来增强其对浮游植物的自上而下的控制，与海潮交换可以抵消这些有害影响。我们的研究集中在加贝斯湾的南部地区和布劳拉拉泻湖，这些地区呈现出地中海最高的潮差。在两次野外活动期间（2016年10月和2017年4月），我们分析了固定站退潮序列中浮游动物的描述性（分类学组成，丰度;生物量）和功能性（摄入率，放牧压力）变量和环境变量以及环境变量。在沿泻湖样带的8个站点，以及不同的潮汐振幅周期。对环境参数和浮游生物类群的多变量分析显示，沿泻湖样带存在三个不同的区域，而且潮汐环流和水的混合对浮游动物群落的更新直至泻湖最内层区域的影响。时间序列为海洋/泻湖物种的输入/输出提供了清晰的模式，并显示了不同分类单元和浮游动物总丰度和生物量的净进口（总洪水/退潮比= 2.2总生物量和2.4生物量），导致浮游动物在泻湖中的滞留差异，并导致浮游植物的潜在放牧压力增加（平均洪水/退潮比= 2.8）。我们还估计，在高潮幅（春季潮或接近春季潮）期间，泻湖的放牧压力是低潮时期（潮汐）的两倍，这清楚地表明浮游动物的滞留显着增加了放牧。对浮游植物的影响。