Chlorophyll-a concentrations in phytoplankton fractions in waters of the Black Sea

Comparison of daily and diel variability of chlorophyll-a concentration at three long-term stations in meso- and eutrophic regions indicates that their values are similar. Daily patterns of deviation in chlorophyll concentration in small and large phytoplankton fraction from average daily values are presented. In conformity with a hypothesis of daily removal rhythms correlated with changes in diel light-dark periods, it was concluded that the mesotrophic region during the dark period is characterized by predominance of grazing on large phytoplankton in the upper layers and accumulation of detritus from cell fragments in the lower layer, while during the light period smaller phytoplankton predominantly grazed. The eutrophic region is characterized by predominance of grazing on small phytoplankton fraction in the upper layers during the dark period and settling out of fecal pellets containing chlorophyll into deeper depths; but during the light period, large phytoplankton predominantly grazed throughout the whole water layer.对中营养化与富营养化区域内3个长期观测站的叶绿素a（chlorophyll-a）浓度日变化与昼夜（diel）变化进行对比分析，结果显示两类区域的叶绿素a浓度数值相近。本文还呈现了小型与大型浮游植物组分的叶绿素浓度相较于日均值的日偏差模式。结合与昼夜明暗周期变化相关的每日移除节律假说，研究得出：中营养化区域在黑暗时段的特征为上层水体中大型浮游植物被优先摄食，下层水体则积累细胞碎片形成的碎屑；而在光照时段，小型浮游植物成为主要摄食对象。富营养化区域则表现为：黑暗时段上层水体中小型浮游植物组分被优先摄食，含叶绿素的粪球粒沉降至更深水域；而光照时段，全水层均以大型浮游植物为主要摄食对象。