Annual Abundance Variations And Spatial Distributions Of Dominant Copepods In The Laizhou Bay, China

Annual abundance distributions and variations of four dominant copepod speciesParacalanus parvus, Centropages dorsispinatus, Centropages abdominalis and Calanussinicus，in the Laizhou Bay of the Bohai Sea were studied based on the year-roundzooplankton samples from May2011to April2012. Zooplankton individuals werecollected vertically from2m above bottom to the surface water by conic net with meshsize160μm. The spatial-temporal patterns of the copepods were depicted in the bay aswell as the their relationship with environmental factors by applying the relevantmodules in software PRIME6. In addition, populations structure of small copepod P.parvus were characterized, e.g. stage-specific abundance, body length and theirrelationships with environmental factors. Main results were listed as followed:1. P. parvus and C.sinicus were observed continuously throughout the investigatedperiod, while C. dorsispinatus and C. abdominalis were concentrated from June toNovember and from August to October respectively. The year-round changing patternsof the four copepods abundance presented single peak in different special seasons. Themost abundant season for C. abdominalis and C.sinicus were May, while those for P.parvus and C. dorsispinatus were August and September respectively. Of the studiedcopepods, P. parvus contributed the most percentages to the total abundance in summerand autumn, but it was replaced by C. abdominalis in spring.2. Three geographic cluster groups were recognized based on P. parvus abndancedistribution. They distributed separately i) out of the Laizhou Bay and just near thecentral Bohai Sea; ii) near the runoff inlet in the west of the bay; iii) in the transitionarea of the two groups above. P. parvus preferred to have its density in the transitiongroup rather than in the group outside the runoff inlet. For C. dorsispinatus, two groupscould be divided; one was the west group with higher abundance and the other was theeast one with lower abundance. Regarding to the other two species, C. abdominalispresented a decreasing trend from the mouth to the top of the bay, while C.sinicus concentrated in northeast of the bay all round the year except in November when itshigh abundance located in western bay contrarily.3. According to the results of BIOENV analysis, of all environmental factors, thesurface water temperature and pH of one month earlier could be the best combinationfor the P. parvus seasonal distributions, while the seawater salinity and depth had moreeffects on the spatial distributions of the species. From the significant correlationsanalysis between seawater pH and Huanghe River runoff, we deduce that runoff of onemonth earlier might be one possible indirect factor which affects the temporal variationsof the P. parvus. The surface water temperature of one month and two months earliercould be the best combination for the C. dorsispinatus seasonal distributions, while theseawater salinity and depth had more effects on the spatial distributions of this species.The correlations between seasonal distributions of abundance of C. abdominalis andenvironmental factors was not significant, it’s also suitable for C.sinicus. The spatialdistributions of C. abdominalis and C.sinicus had significant relationship with seawatersalinity, depth and surface water temperature; we deduce that Huanghe River runoffmight be one possible indirect factor which affects the seasonal variations of C.sinicusabundance.4. Stage-specific compositions of P. parvus variated monthly.The percentagecontributed by adult to the total population abundance remained high during April toJune, but the value decreased greatly after those seasons. Copepodite larva becamedominant from July to November. The body length of P. parvus presented a generaltrend that it was decreasing with surface water temperature rising.5. Of the studied environmental factors, the surface water temperatures in thecurrent month and one month earlier had positive correlations to the stage-specificabundance of P. parvus most significantly; the surface water salinity and DO of twomonths earlier had also significant effects on most stage-specific abundance. Bodylengths of copepodid were related closely to the surface water temperature in the currentmonth, however, those of adult related closely to the surface water temperature of onemonth earlier. Huanghe River runoff for the month and two months earlier might affectthe body length of P. parvus.