Phytoplankton Community Structure And Its Response To The Environmental Factors In The Semi-closed Coastal Area

In order to provide a better understanding of phytoplankton structure and theirrelationship with environmental parameters in typical semi-closed coastal areas,observations were carried out to estimate the phytoplankton structure and nutrients ina survey from April2011to December2012in the Zhanqiao waters. The results are:1. A total of98species in43genera of diatom were identified, non-diatomspecies (>15μm) were included in total phytoplankton as one group but withoutfurther identification. The mean cell density of diatom and chlorophyll aconcentration (from April to October) were175.42±460.31cell/ml and11.70±5.94mg/m~3in2011. And that of diatom and chlorophyll a value (from August to December)were499.17±2076.94cell/ml and9.27±4.9mg/m~3in2012. Dominant diatomsincluded Skeletonema costatum, Navicula spp. and Chaetoceros spp. during the wholesurvey. The dominant index (Y) of them were0.224、0.459and0.113, respectively.Besides, there were seasonal dominant species like Nitzschia closterium, Guinardiadelicatula, Pseudo-nitzschia pungens, Chaetoceros curvisetus, Chaetoceros teres,which predominated alternately or co-dominated together. The cell abundance ofdiatom varied in an irregular semiannual cycle with a lower peak in the period fromJanuary to April and a higher peak from July to September. The contributions ofdiatom to the total abundance were up to90%when the peaks occurred, while in theother periods contributions were generally below50%and the lowest could reach to1.9%. The average of H’(Shannon-Weiner index) is2.36, which was higher than thatin the Jiaozhou Bay (about0.70) and lower than that in the oligotrophic coastal water(about3.23).2. Annual average values of DIN, DIP and DSi were14.79μmol/l,0.627μmol/land8.177μmol/l, respectively. According to the nutrient concentrations and ratios and using the criteria of Justic et al.(1995), only3nutrient observations, possessing1.13%in all264observations, suggested nutrient limitation occurring, whichindicated the target area was eutrophic relatively. Pearson and PCA analysis showedthat water temperature and nutrient were important influencing factors onphytoplankton, but their significances were depended on seasons. In spring, nutrientwas a stronger factor than that of temperature, nutrient concentrations and ratios werehighly correlated with diatom abundance. In summer, DSi was significant negativecorrelation (P<0.05) with the diatom abundance in2011, suggesting a stronginfluence from land freshwater, but in2012no such significant correlations wereobserved. In autumn, temperature and nutrient were co-factors on phytoplankton withsimilar significances, only in2012the influence of nutrient was a little bit stronger. Inwinter, no significant relations between nutrient and abundance were observed, whichwas very different from other seasons, suggested special ecological responses ofphytoplankton in a low temperature environment.