浮游动物摄食在赤潮生消过程中的作用

The effects of zooplankton grazing on the development of red tides

浮游动物摄食在赤潮生消过程中起相当重要的作用。由于摄食过程的复杂性和生物物种与个体行为存在的多样性 ,使得赤潮过程中浮游动物的摄食研究具有相当难度。从浮游动物的摄食类型和习性、浮游动物摄食率测定、浮游动物选择性摄食对赤潮群落演替发展方向、浮游动物摄食在有毒微藻赤潮中的作用、浮游动物摄食在中国赤潮研究中的关键科学问题等几个方面探讨了浮游动物摄食对赤潮生物种群动力学的影响 。

Red tides have become a major environmental issue in China. A national fundamental and key project in China called “The ecological and oceanographical occurring mechanism of harmful algae blooms in the coastal seas of China (CEOHAB)” started in 2001. Zooplankton grazing is a key process during red tide events, and its study is a component of this project. This paper analyzes and reviews the zooplankton grazing strategies and food type, measurement methods for grazing rates and pressure, grazing effects on red tide community development and its pathway, selective grazing of zooplankton, the relationship between zooplankton grazing and harmful algae, and the key objectives in studying the effects of grazing on harmful algae blooms in China. Red tide communities are a subset of phytoplankton community, so all the behavior of red tide should obey the rules of phytoplankton population dynamics. The most obvious role of grazing is the removal of cells from the phytoplankton community. Different phytoplankton cell types will, however, be grazed at different rates by zooplankton and these differences will impact on phytoplankton community development and its pathway. Three types of zooplankton grazing strategies are discussed in the paper: Type A, the grazing rate gets increasingly higher as phytoplankton concentration approaches zero; in this case, the zooplankton would tend to exploit the phytoplankton to extinction, and its grazing will have limited effects on controlling red tide occurrences. Type B, the grazing rate is at its maximum until the phytoplankton concentration is very high; in this case, the zooplankton would, at low phytoplankton concentrations, exert a constant mortality rate, which, if less than the growth rate of phytoplankton community would allow the phytoplankton population to grow despite being grazed. Such grazing will affect the red tides to some extent, and would contribute to preventing the occurrence of red tides. Type C, the zooplankton reduce the grazing effort as phytoplankton become very scarce; the grazing rate will increase with phytoplankton concentration increasing until an optimum grazing rate is reached and then decrease with the increasing phytoplankton concentration. Such grazing will most efficiently control the red tides. These different grazing strategies of dominant zooplankton clearly can have distinctive effects on the occurrence dynamics of red tides in China Coastal Waters. The cell size of red tide organism will also affect the grazing behaviour during red tide events. The very small zooplankton, such as microzooplankton, are likely to be most efficient at utilizing very small cell-sized phytoplankton, whereas large zooplankton are likely to utilize large cell-sized phytoplankton. Several methods for measurement of zooplankton grazing are discussed in the paper, the most important grazing effect on red tide is considered to be change of phytoplankton species succession, so the direct counting method and dilution method are discussed in detail. Although interactions between toxic phytoplankton and their grazers are complex, variable and situation-specific, specific issues are discussed in this paper: the phytoplankton toxins as a grazing deterrent; the types of deleterious effects of toxic phytoplankton upon zooplankton; selective grazing of toxic phytoplankton; and the effect of zooplankton grazing on development and persistence of toxic phytoplankton blooms. Zooplankton grazing studies in China are also reviewed in the paper, and several key objectives are proposed for studies of zooplankton grazing effects on development of red tides. (1)What type of grazing strategies of dominant zooplankton influence the occurrence frequency of red tides in China? (2) The population dynamics of dominant zooplankton and key species of red tide organism, and their relationships. (3) The pathways phytoplankton community development during red tides affected by zooplankton grazing. (4) Application of some new concepts and methods for studying of zooplankton grazing in red tide research.