Effects of mesozooplankton removal and ammonium addition on planktonic trophic structure during a bloom of the Texas 'brown tide': a mesocosm study
Effects of mesozooplankton removal and ammonium addition on planktonic trophic structure during a bloom of the Texas 'brown tide': a mesocosm study
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DOI：
10.1093/plankt/25.2.215
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发表时间：
2003-02-01
影响因子：
2.1
通讯作者：
Villareal, TA
中科院分区：
文献类型：
--
作者：
Buskey, EJ;Deyoe, H;Villareal, TA
在20世纪90年代的大部分时间里，德克萨斯州的拉古纳马德雷一直存在着被称为德克萨斯州“褐潮”的拉古纳水母的水华。拉古纳马德雷的优势中型动物- lagunensis，在水华期间，几乎没有其他合适大小的浮游植物细胞可供摄食。我们推测，这些桡足类增加了对微型浮游动物的摄食，从而减少了微型浮游动物对A. lagunensis和有助于持久的这种开花。1999年夏季进行了一次围隔生态系统实验，以检验这一假设。12个玻璃纤维围栏型中型生态系统被部署在现场16天，每个封闭类似于1.2米（3）的拉古纳马德雷水和1.1米（2）的天然底栖生物。从6个中生态系统中取出浮游动物，每4天用153妈妈网眼浸网;其他6个中生态系统以相同的方式处理，除了网的内容物返回到中生态系统。对于每种浮游动物处理，一半的围隔生态系统在4天的时间间隔内给予类似于40 mum的NH 4，另一半没有接受任何添加。实验开始时，这些围隔中的浮游植物种群以A. lagunensis和蓝细菌Synechococcus spp. A.生长速率lagunensis在没有铵添加的围隔中较高，没有提供氮限制的证据。在去除浮游动物的围隔生态系统中，松细针蜱的种群数量减少了约50%，纤毛虫的种群数量显著增加。纤毛虫种群数量的增加对A.然而，lagunensis种群动态没有提供任何证据来支持以下假设，即减少微型浮游动物种群的营养级联导致了褐潮水华的持续。与此相反，聚球藻的种群表现出“自上而下”和“自下而上”的控制证据，他们生长更快的营养补充围隔和更低的人口密度增加的纤毛虫食草动物的围隔。
A bloom of the alga Aureoumbra lagunensis, known as the Texas 'brown tide', persisted in the Laguna Madre of Texas for most of the 1990s. The dominant mesozooplankter in Laguna Madre, Acartia tonsa, does not feed on A. lagunensis, and during blooms there are few other suitably sized phytoplankton cells available to feed on. We hypothesized that these copepods increased their feeding on microzooplankton, thereby reducing grazing pressure by microzooplankton on A. lagunensis and contributing to the persistence of this bloom. A mesocosm experiment was carried out to test this hypothesis during the summer of 1999. Twelve fiberglass corral-type mesocosms were deployed in the field for 16 days, each enclosing similar to1.2 m(3) of Laguna Madre water and 1.1 m(2) of natural benthos. Mesozooplankton were removed from six mesocosms with a 153 mum mesh dip net every 4 days; the other six mesocosms were treated in the same way, except that the contents of the net were returned to the mesocosm. For each zooplankton treatment, half of the mesocosms were dosed with similar to40 mum NH4 at 4 day intervals, and half received no additions. Phytoplankton populations in these mesocosms at the start of the experiment were dominated by A. lagunensis and the cyanobacterium Synechococcus spp. Growth rates of A. lagunensis were higher in mesocosms without ammonium additions, providing no evidence for nitrogen limitation. Acartia tonsa populations were reduced by similar to50% in the zooplankton removal mesocosms, and ciliate populations were significantly higher. The increase in ciliate population had no significant impact on A. lagunensis population dynamics, however, providing no evidence to support the hypothesis that a trophic cascade reducing microzooplankton populations contributed to the persistence of the brown-tide bloom. In contrast, populations of Synechococcus sp. showed evidence of both 'top-down' and 'bottom-up' control; they grew faster in nutrient addition mesocosms and had lower populations in mesocosms with increased densities of ciliate grazers.