盐碱池塘细巧华哲水蚤对浮游植物的摄食生态研究

Feeding Ecology of Sinocalanus tenellus (Copepoda:Calanoida) Grazing on Phytoplankton in Saline-alkaline Ponds

利用常规显微镜直接计数法和叶绿素 a法研究了盐碱池塘细巧华哲水蚤 ( Sinocalanustenellus)对浮游藻类的原位摄食率及其影响因素。测得该水蚤对水柱浮游植物的滤水率为 1 .73～ 1 5 5 .1 6μl/ ( ind.· h) ,摄食率为 92～ 2 5 38cell/( ind.· h)或 0 .7～ 2 7.7ng C/ ( ind.· h)。两种方法测定的滤水率和摄食率基本相符 ( p>0 .5 ,t检验 )。该水蚤可有选择地滤食诸如小色球藻、光甲藻、绿裸藻 ,单生卵囊藻和小环藻等 ,其选择性指数分别为 0 .81、0 .75、0 .72、0 .6 1和 0 .35。不同光处理下细巧华哲水蚤的滤食率多数情况是无光时摄食率高。在本实验的条件下该水蚤在饥饿后的滤水率和摄食率与正常情况相比均显著降低 ( P<0 .0 1 ,t检验 )。

A direct counting method and present/absence method (observed chlorophyll-a content of nature pond phytoplankton with and without addition of copepods) were used to estimate in situ grazing capacity of a brackish copepod Sinocalanus tenellus grazing on phytoplankton in saline-alkaline ponds located in Zhaodian Fish Farm (Latitude 37°17′N, Longitude 117°55′E), Gaoqing County, Shandong Province from 4 May to 7 May,1998, aimed to provide the scientific evidence for understanding of the features of energy flow and substance cycling in saline alkaline ponds, and better performing of water management and studying of possibility of mass cultivation of the copepod used as food of shrimp and fish. To ensure a natural food composition, plankton organisms were obtained from pond water drawn from a depth of 0.5 m. The pond water was sieved through a 35μm mesh to remove most of zooplankton, and then were placed all jars. A part of the water was original water sample. Adult copepods were obtained by plankton net <64μm in mesh from pond #00, and were first adapted for 2 h to one or other food condition, and then 300～5000 individuals were placed in each experimental bottles 1 L in volume (light and dark). Suspensions without copepods served as controls. All jars were then placed in the pond at 0.5 m depth for 24 h. Density, biomass and chlorophyll a concentration of phytoplankton among of original, experimental and control series after 24h were measured. 4 experiments were conducted. During the experiment, salinity was 3, total alkalinity was 4.47 mmol/L, water temperature was 17～23℃, pH was 8.32～8.96. More over, the effects of starvation and food content on ingestion of S. tenellus were conducted followed the mentioned methods. The results showed that the clearance rate of S. tenellus is 1.73~155.16 μl/(ind. ·h), the grazing rate is 92~2538 cell/(ind.·h) or 0.7~27.7 ngC/(ind. ·h). The different of the grazing capacity could be due into the variation of water temperature and the density of phytoplankton in in situ pond #00. Both methods gave similar results (P>0.5, t-test). Most of grazing rates of S. tenellus in the present experiments were higher in dark groups (0L:24D) than that of the light groups (12L:12D). Compared to constant feeding experiments, the clearance rate and ingesting rate of S. tenellus after starvation were significantly decreased (P<0.01). The grazing rate and clearance rate of the copepod were increased with the increasing of the concentration of phytoplankton chlorophyll-a in the present experiment. It was obvious that the grazing capacity of S. tenellus could be significantly influenced by the food concentrations. Major phytoplankton species of pond #00 were Dactylococcopsis rhaphidioides, Phorimidium tenus, Chroococcus minor, Isochrysis galbana, Prymnesium parvum, Glenodinium gymnodinium, Navicula halophila, Cyclotella sp., Euglena viridis, Chlorella vulgaris, Oocystis solitaria, Kirchneriella contorta, Crucigenia lauterbornei and Scenedesmus acuminatus. The abundance and biomass of phytoplankton in experimental bottles were significantly impacted by the grazing of S. tenellus. There is Cyclidium sp. in the incubation water of experiment 1, and the density of which in original water and control groups were 6.48×10 5/L, however, it was not seen in all treatment groups. S. tenellus grazed most effectively on phytoflagellates such as C. mino, G. gymnodinium, E. viridis, O. solitaria and Cyclotella sp. ect. On the basis of numbers per liter, the selective feeding indices were 0.81,0.75,0.72 , 0.61 and 0.35, respectively. However, S. tenellus does not like to eat some of filament cyanobacteria such as D. rhaphidioides and P. tenus, the selective feeding indices were -0.89 and -0.62, respectively. Those evidences demonstrated that S. tenellus is a species of omnivorous copepod, which feeding priority on ciliates protozoa from the food composed of planktonic algae and ciliates protozoa. This is coincidence with results of field observation, i.e. not ingested well ciliates such