莱州湾拟哲水蚤Paracalanus sp.发育期丰度组成和个体大小季节变化

拟哲水蚤是莱州湾桡足类中周年出现的优势种；是上层鱼类幼鱼早期开口饵料的重要贡献者；掌握其种群动态分布特点；有利于了解湾内生物环境状况、次级生产力生产水平。基于2011年5月至20 12年4月采集的浮游生物资料的分析结果显示；莱州湾拟哲水蚤的发育期丰度组成和个体大小均表现了明显的季节变化。调查季节中；4-6月以成体居多；其他季节以桡足幼体CⅢ-CⅤ较多；其中10-11月和3月主要由后期桡足幼体CⅣ和CⅤ期构成。成体中以雌体为主导；雌/雄比介于1.46~9.62；该比值在3-4月最低；10-11月最高。拟哲水蚤各期桡足幼体和成体个体大小以4-5月最大、8月最小；并与水温表现出明显的负相关。拟哲水蚤桡足幼体和成体的总生物量月变化与丰度变化相同；即以8月值最高；3-5月值最低；月均值为2.69 mg/m3（以碳计）；日生产力估算值为0.74 mg/（m3·d）（以碳计）。由上述结果；推测莱州湾拟哲水蚤的种群结构周年变化主要可分3个阶段；4-6月是莱州湾拟哲水蚤开始繁殖期；7-8月为种群数量快速增长期；9月之后为种群增长相对停滞期。

Seasonal stage-specific abundance compositions and body size distributions of Paracalanus sp. (Copepoda: Calanoida) in Laizhou Bay, Bohai Sea

Paracalanus sp., which has been identified as Paracalanus parvus by previous reports in the northern part of China seas, is a very common small copepod in Laizhou Bay, Bohai Sea. The species is characterized ecologically by a high level of secondary productivity and a suitable food resource for early larvae of fishes in the bay. To explore the population dynamic in Laizhou Bay, copepodites and adult data of Paracalanus sp. were collected and analyzed from 147 samples over the annual surveys from May 2011 to April 2012 (excluding December 2011 and January and February 2012, because of the presence of sea ice). The results showed Paracalanus sp. occurred continuously in the plankton throughout the year, with an enormous peak in August. Its stage-specific population structure and body size fluctuated greatly during the study period. During the surveyed seasons, copepodites stages CⅢ, CⅣ and CⅤ contributed most percentages in total population abundance except that from April to June when the adults became dominant. Of the copepodite stages, CⅣ and CⅤ accounted for the largest proportion of the total population abundance from October to March. In the adult, pronounced dominance of females over males was found throughout the year. The female to male ratios ranged from 1.46 to 9.62, with the lowest value in March and April and highest in October and November. The body size of Paracalanus sp. changed seasonally, being the largest in April or May, and the smallest in August. Mean body size of each developmental stage was inversely related to temperature at the time of sampling by regression statistic. The biomass of Paracalanus sp. showed marked seasonal variations largely in parallel with numerical abundance. Its monthly mean value was 2.69 mg/m3. The species production rate was estimated with 0.74 mg/(m3·d) based on the reported experienced equation. From above results, the annual population dynamic of Paracalanus sp. could be divided into three main phases, starting breeding phase from April to June, rapid population growth phase from July to August, and relative population growth stagnation phase just after September.