Abstract
Two periods are clearly distinguished within the last two decades (1997–2017) by several quantitative parameters of the plankton community in the northern shelf zone of the Okhotsk Sea: the period of high productivity in the 1997–2005 with the biomass of 1000–1200 mg/m3 and the period of medium productivity in the 2006–2017 with the biomass of 550–580 mg/m3. The sharp drop of the biomass had occurred in just one year because of decreasing of the large-sized zooplankton abundance (euphausiids, mysids, hyperiids, and pteropods) that formed the bulk of the food base for commercial species of nekton. After the drop, the plankton biomass had stabilized again. The similar decreasing was observed earlier, in 1998, as the result of several warm years, but in those times the zooplankton abundance restored its maximal values in 2 years. Correlations of the large-sized zooplankton dynamics with the thermal parameters, as the cold subsurface layer temperature and the maximum and mean values of the ice cover are considered. Generally, the period of high productivity was distinguished by cold environments, and they were warmer in the period of medium productivity.
Highlights
Two periods are clearly distinguished within the last two decades (1997–2017) by several quantitative parameters of the plankton community in the northern shelf zone of the Okhotsk Sea: the period of high productivity in the 1997–2005 with the biomass of 1000–1200 mg/m3 and the period of medium productivity in the 2006–2017 with the biomass of 550–580 mg/m3
The sharp drop of the biomass had occurred in just one year because of decreasing of the large-sized zooplankton abundance that formed the bulk of the food base for commercial species of nekton
The similar decreasing was observed earlier, in 1998, as the result of several warm years, but in those times the zooplankton abundance restored its maximal values in 2 years
Summary
В зимне-весенний период 1997–2017 гг. в северной шельфово-сваловой зоне Охотского моря (районы 1–10а) в планктонном сообществе эпипелагиали по ряду количественных показателей четко выделяются два периода: «высокопродуктивный» 1997–2005 гг. с биомассой крупной фракции 1000–1200 мг/м3 и «среднепродуктивный» 2006–2017 гг. с биомассой 550–580 мг/м3. Групп крупной фракции, составляющих основу кормовой базы промысловых видов нектона, и на этом уровне она остается уже 12 лет. Привлекает внимание совпадение динамики биомассы крупной фракции и ее основных групп с динамикой термических составляющих моря — типами лет по холодному промежуточному слою, максимальной и среднегодовой ледовитостью, количеством свободной ото льда воды. Two periods are clearly distinguished within the last two decades (1997–2017) by several quantitative parameters of the plankton community in the northern shelf zone of the Okhotsk Sea: the period of high productivity in the 1997–2005 with the biomass of 1000–1200 mg/m3 and the period of medium productivity in the 2006–2017 with the biomass of 550–580 mg/m3. В этот период важна оценка качественных и количественных показателей состояния перезимовавшего планктонного сообщества, в первую очередь как кормовой базы минтая, сельди и лососей. По мере выполнения очередных съемок появляются новые материалы, их анализ показывает тенденции в развитии планктонного сообщества, от которого зависит состояние кормовой базы многих промысловых объектов в этот и последующие сезоны
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