Embayments and salt ponds along the coast of Massachusetts can host localized blooms of the toxic dinoflagellate Alexandrium fundyense. One such system, exhibiting a long history of toxicity and annual closures of shellfish beds, is the Nauset Marsh System (NMS) on Cape Cod. In order to measure net growth rates of natural A. fundyense populations in the NMS during spring 2012, incubation experiments were conducted on seawater samples from two salt ponds within the NMS (Salt Pond and Mill Pond). Seawater samples containing natural populations of grazers and A. fundyense were incubated at ambient temperatures. Concentrations of A. fundyense after incubations were compared to initial abundances to determine net increases from population growth, or decreases presumed to be primarily due to grazing losses. Abundances of both microzooplankton (ciliates, rotifers, copepod nauplii and heterotrophic dinoflagellates) and mesozooplankton (copepodites and adult copepods, marine cladocerans, and meroplankton) grazers were also determined. This study documented net growth rates that were highly variable throughout the bloom, calculated from weekly bloom cell counts from the start of sampling to bloom peak in both ponds (Mill Pond range = 0.12–0.46 d⁻¹; Salt Pond range = −0.02 to 0.44 d⁻¹). Microzooplankton grazers that were observed with ingested A. fundyense cells included polychaete larvae, rotifers, tintinnids, and heterotrophic dinoflagellates of the genera Polykrikos and Gymnodinium. Significant A. fundyense net growth was observed in two incubation experiments, and only a single experiment exhibited significant population losses. For the majority of experiments, due to high variability in data, net changes in A. fundyense abundance were not significant after the 24-h incubations. However, experimental net growth rates through bloom peak were not statistically distinguishable from estimated long-term average net growth rates of natural populations in each pond (Mill Pond = 0.27 d⁻¹ and Salt Pond = 0.20 d⁻¹), which led to peak bloom concentrations on the order of 10⁶ cells l⁻¹ in both ponds. Experimental net growth rates from the incubations underestimated the observed natural net growth rates at several time intervals prior to bloom peak, which may indicate that natural populations experienced additional sources of vegetative cells or periods of reduced losses that the 24-h incubation experiments did not capture, or that the experimental procedure introduced containment artifacts.

马萨诸塞州沿岸的海湾和盐池可能是有毒甲藻亚历山大藻的局部繁殖地。科德角的瑙塞特沼泽系统 (NMS) 就是这样一个系统，它具有悠久的毒性历史，每年都会关闭贝类养殖场。为了测量 2012 年春季 NMS 中自然A.fundyense种群的净增长率，对 NMS 内两个盐池（盐池和磨坊池）的海水样品进行了孵化实验。含有自然食草动物种群和A.fundyense 的海水样品在环境温度下孵育。将孵化后的A.fundyense浓度与初始丰度进行比较，以确定种群增长带来的净增加，或推测主要是由于放牧损失造成的减少。还测定了微型浮游动物（纤毛虫、轮虫、桡足类无节幼体和异养甲藻）和中型浮游动物（桡足类和成年桡足类、海洋枝角类和小型浮游生物）食草动物的丰度。这项研究记录了整个花期的净生长率变化很大，计算方法是从采样开始到两个池塘的花期高峰期间每周的花期细胞计数（工厂池塘范围 = 0.12–0.46 d ^-1 ；盐池范围 = -0.02 至0.44d- ¹ )。观察到摄入A.fundyense细胞的微型浮游动物包括多毛类幼虫、轮虫、丁丁类动物以及Polykrikos和Gymnodinium属的异养甲藻。显着A. 在两次孵化实验中观察到了 Fundyense 的净生长，并且只有一次实验表现出显着的种群损失。对于大多数实验来说，由于数据的高度可变性，24 小时孵育后A.fundyense丰度的净变化并不显着。然而，水华高峰期的实验净增长率与每个池塘自然种群估计的长期平均净增长率在统计上没有区别（磨坊池塘 = 0.27 d ^-1和盐池 = 0.20 d ^-1 ），这导致了高峰期两个池塘中的水华浓度约为 10 ^{6 个}细胞 l ^-1 。孵化的实验净增长率低估了在开花高峰之前的几个时间间隔观察到的自然净增长率，这可能表明自然群体经历了 24 小时孵化实验未捕获的额外营养细胞来源或损失减少时期，或者实验过程引入了遏制伪影。