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Distribution of chlorophyll and phytoplankton in Xiapu, Fujian

Phytoplankton is the primary productivity of the ocean, increasing their biomass through accumulating organic matter synthesized by photosynthesis. Chlorophyll a and pheophytin will all bring important influence on the recognition of biological optical information for phytoplankton. So it’s necessary to analyse distribution of chlorophyll and phytoplankton. In this study, the concentration distributions of chlorophyll a and pheophytin in Xiapu were obtained. As a result, the overall trend of concentrations showed summer > spring> autumn > winter . This was mainly because of the difference of seawater temperature. The distribution of chlorophyll and phytoplankton varied with time. And they share a similar trend, indicating that chlorophyll content directly affects phytoplankton content.


Introduction
Marine phytoplankton is the primary productivity of the ocean, increasing their biomass through accumulating organic matter synthesized by photosynthesis. The growth of marine phytoplankton is inhibited, and one of the main reasons is that photosynthesis is affected by other factors [1].Chlorophyll a is the main pigment for photosynthesis of phytoplankton. As a basic parameter of marine ecology, concentration of chlorophyll a is an important indicator for whether the photosynthesis of phytoplankton is normal or not [2]. The high concentration of pheophytin will change the absorption characteristics of phytoplankton, which will bring important influence on the recognition of biological optical information in water [3].Temperature, light and zooplankton predation might also modulate the phytoplankton biomass in local regions [4] This paper analyzed distribution of chlorophyll and phytoplankton in Xiapu, Fujian Province. It will help understand the potential effect factors for chlorophyll and phytoplankton.

2.
Materials and method The study area is located in Xiapu county, Ningde city, Fujian Province. It is located about 15km southeast of Xiapu county, and about 59km as the crow flies from Ningde city (southwest of the factory). There were 48 large observation stations, 2 fixed point continuous observation stations (Station 5 and Station 6). The location of the study area and the survey stations were shown in figure 1.

Sample collection for chlorophyll a and pheophytin
Sea water samples for concentration analysis of chlorophyll a were collected at corresponding levels with spherical cover HQM-1 plexiglass sampler.100cm3 water samples were filtered by Whatman GF/F glass fiber membrane under negative pressure, and the filter membrane containing photosynthetic plankton was immediately frozen and stored until analysis. Samples were collected every 3 hours at the observation stations day and night in continuous observation stations (Station 5 and Station 6). Concentration of chlorophyll a was analyzed and determined by extractive fluorescence method with 90% acetone extract. The contents of chlorophyll a and pheophytin were determined by Turner Designs Fluorometer and Model 10 for the extracted samples. The collection, storage, transportation, pretreatment, analysis, determination and calculation of samples were all carried out in strict accordance with the requirements of the Code of Marine investigation.

Sample collection for phytoplankton
500mL sea water samples from 0.5m to the surface were collected with plexiglass water sampler for quantitative analysis in the large-area observation stations. Shallow water type III plankton net with flow meter was used for vertical trawling from bottom to surface to collect once for species composition analysis. Water samples of 0.5m layers were collected every 3 hours at the observation stations day and night in continuous observation stations (Station 5 and Station 6). The samples were fixed with neutral formaldehyde. The samples were concentrated and observed, identified and counted under a nissan Nikon microscope.

Horizontal distribution of chlorophyll a and pheophytin in summer in the large-area observation station
Specific survey statistics of chlorophyll a and pheophytin in the study area were shown in Fig.2. The increase of sea water temperature in summer promoted the growth and reproduction of photosynthetic plankton. The concentration of chlorophyll a in sea area was 0.990~27.488 mg/m3, with an average value of 10.149 mg/m3. The concentration of pheophytin was 0.640~16.360 mg/m3, with an average value of 4.184 mg/m3. The concentrations of chlorophyll a was higher than those of pheophytin.

Comparison for concentrations in different seasons
Comparison for concentrations in different seasons were shown in Table 1. Overall trend of the concentrations showed summer > spring> autumn > winter. This was mainly because in summer the increase of seawater temperature promoted the growth and reproduction of photosynthetic plankton, and the whole sea area was in the range of relatively high chlorophyll concentration. While the seawater temperature is low in winter, and the chlorophyll content is relatively low.

Concentrations of chlorophyll a and pheophytin variation with time in continuous survey stations
In summer, the surface chlorophyll a and pheophytin concentration at each moment of No. 5 continuous station was shown in Fig. 3  The blue line represents chlorophyll a while the red one represents pheophytin
During the continuous observation day and night, the abundance of phytoplankton was higher in the afternoon to evening due to the strong photosynthesis during the day. At night, photosynthesis is weakened and phytoplankton abundance is low. It can be seen that photoperiod is the main factor affecting the diurnal variation of phytoplankton abundance. The trend of phytoplankton was similar with that of chlorophyll, indicating that chlorophyll content directly affects phytoplankton content.

Conclusions
The concentration distributions of chlorophyll a and pheophytin were obtained. The overall trend of concentrations showed summer > spring> autumn > winter. This was mainly because of the difference of seawater temperature. The distribution of chlorophyll and phytoplankton varied with time. And they share a similar trend, indicating that chlorophyll content directly affects phytoplankton content.