| From May 2008 to June 2010, the studies were conducted with field experiments using artificial reefs of different materials, surface structure and surface orientations to survey the development and succession process of biofilm community in sea cuccumber culture ponds of Homey Group in Rongcheng, Shandong. Annual succession and seasonal variation of epilithic biofilm on artificial reefs were also studied. Artificial interventional measurement by soaking ocement substrate with nutrient solution was employed to explore culture technology of the biofilm, trying to speed up the colonization and development of biofilm, and to improve the speed of biofilm maturation. In order to evaluate the influence of nutrient solution soaking for artificial substrate on the pond environment and biofilm ingredients, nutrient flux on surface of artificial soaking cement reefs and biogenic element of C, N, P in biofilm were analyzed, which may provide references for sea cucumber pond culture with artificial reefs in our country.1. Succession and seasonal variation of epilithic biofilms on artificial reefs in sea cucumber culture pondTwo experiments, using artificial test panels, were conducted in sea cucumber Apostichopus japonicus culture waters to survey the succession and seasonal variation of epilithic biofilms. A total of 67+ species were identified in biofilms of the succession test panels, and 46+ species were recorded in biofilms of the seasonal test panels. In both experiments, communities of epilithic biofilms were dominated by diatoms, green algae and the annelid Spirorbis sp. Dominant diatoms of the initial colonization were Cocconeis sp., Amphora spp. and Nitzschia closterium in June, which were succeeded by species of Navicula, Cocconeis and Nitzschia (July to September), and then by Licmophora abbreviata, Nitzschia closterium and Synedra spp. in the following months. Diatom bloom in autumn and filamentous green algae burst in summer were also observed. Ecological indices well annotated the succession and the seasonal change of epilithic communities. Fast growth of biofilms were observed in summer and autumn, whereas the biomass of summer biofilms was largely contributed by filamentous green algae. Present results show that components of epilithic biofilms are mostly optimal foods of A. japonicus, suggesting that biofilms on artificial reefs may contribute important nutrition source for sea cucumbers during the growth seasons of A. japonicus.2. Colonization and succession of biofilms on artificial reefs of different material in sea cucumber culture pondThe commonly used artificial reefs of stone (ST), cement (CM), tile (TL) and PVC (PVC) in sea cucumber farming were employed to studied the occurrence and succession process of periphytic organisms in order to provide basis for substrate selection in culture. The results show that, absolute dominance of diatom in biofilms on the four substrates was observed (30 taxa totally), Nitzschia, Navicula and Synedra were the most commonly found genera, the first two appeared in the entire period of the experiment, while the latter was frequently seen after three weeks, the most species were identified on CM substrate, and the least species appeared on PVC substrate. Changes in the total number of diatoms exhibited character of CM> ST> TL> PVC, and the dominant species of Spirorbis sp. attached more on the surface of ST and TL substrates. Biofilm grew significantly with time variation, namely dry weight (DW) and ash free dry weight (AFDW) biomass of biofilm increased with time, and grew fastest on CM followed by ST, and slowest on PVC. The change of chlorophyll a and biomass indicated similar trend, but in later period of experiments (after 8 weeks), chla content on CM and ST were less than the other two substrates, which indicating onset of diatom communities declination and the faster succession rate of algal communities than PVC and TL. In the first two weeks, primary production of biofilm on CM was higher than that on other substrates, after three weeks, the highest production was found in biofilm on ST, and respiration and biomass dry weight change was always consistent.3. Colonization and succession of biofilms on artificial reefs of different surface roughness in sea cucumber culture pondThe commonly used stone artificial reefs in sea cucumber farming were employed to studied the occurrence and succession process of periphytic organisms on three different roughness surfaces of smooth surface (SS), moderate rough surface (MS) and rough surface (RS) in order to provide reference for artificial reef selection, design and delivery in culture. The results show that, 29+ taxa of algae were found on the three surfaces totally with the most dominant taxa of diatoms (24+ taxa totally), species of the genera Nitzschia, Synedra, Tabularia and Licmophora occured more frequently, the former three genera appeared during the whole experiment, the latter dominated only after six weeks. The number of microalgae species on MS surface was a little more than RS and SS. The dominant species on the three kinds of surface were of little difference, and all had a similar succession process. RS surface was attached by the largest density of microalgae, and Spirorbis sp. was found more on MS surface. Shannon-Wiener diversity index (H’), evenness index (J) and dominance index (D) of microalgae communities on three surface varied similarly, and the variation trend of the first two indices was consistent with the highest value at the third week and the lowest one at the sixth week, while dominance index (D) was in the opposite trend. Cluster analysis based on microalgae community Bray-Curtis similarity index shows that incubation time was the main factor influencing the community structure. Community succession process can be divided into four stages of the 1st week, the 2nd to the 4th week, the 6th to 8th week and the last 12th week, similarities between RS and MS were mostly higher than that between SS and RS or MS in the initial 6 week. Growth rate in terms of dry weight biomass for biofilm on RS was faster initially, and biofilm on SS grew faster later. Variation trends of chlorophyll a and AFDW in biofilm of all the three kinds of roughness were basically the same. Primary production of the biofilm increased with the development of biofilms while affected by the weather with no significant difference (P> 0.05) among the three surface.4. Colonization and succession of biofilms on stone artificial reefs of different orientation sides in sea cucumber culture pondIn order to provide reference for artificial reefs selection, design and delivery in culture, the commonly used stone artificial reefs in sea cucumber farming were employed to studied the occurrence and succession process of periphytic organisms on surfaces with four different orientation of sun facing facade (FS), back shady facade (BS), down horizontal surface (DS), up horizontal surface (US). The results show that, a total of 30 taxa of algae were found on the four surfaces with the most dominant taxa of diatoms (25 taxa totally), species of the genera Nitzschia, Synedra, Tabularia and Licmophora occured more frequently, the former three genera appeared during the whole experiment, the latter dominated only after six weeks. The number of microalgae species on US surface was significant more while DS surface was less than that on other surfaces (P< 0.05). The number of species over the surface increased with incubation time. Although the dominant species on the surfaces varied with orientation, all the four had a similar succession process of Nitzschia longissimaâ†'Euglena sp.â†'Nitzschia closteriumâ†'Synedra spp. or Tabularia fasciculataâ†'Licmophora spp. Total number of microalgae showed features of US> BS> FS> DS, US is significantly higher than BS and FS (P< 0.05), and Spirorbis sp. was found more on DS and BS surface. Variation trends of Shannon-Wiener diversity index (H’), evenness index (J) and dominance index (D) of microalgae communities among three surfaces of FS, BS and US varied similarly while it was completely different for DS. According to result of the cluster analysis based on microalgae community Bray-Curtis similarity index, the samples could be divided into five groups at the similarity of 62.8%. For the factors affecting community structure, incubation time was found the main followed by surface orientation and DS had low similarity with other surfaces. Dry weight (DW) of biofilm on US surface was always significantly higher than (due to pond sedimentation) other surfaces which was of no significant difference in the early stage and higher value of BS (rapid growth of algae) and DS (more attached Spirorbis sp.) were found later. Ash free dry weight (AFDW) on FS was a slightly higher initially and showed the trend of BS> FS> DS later. Chlorophyll a on FS was a little higher initially followed by a higher value on BS later, the value was higher on US surface in early stage and was significantly lower than that on BS side, DS was always significantly lower than the other surfaces (P< 0.05).5. Cultivation technology of biofilms on artificial reefs in sea cucumber culture pondCement substrates soaked with different concentrations of inorganic, organic and mixed nutrient solution were employed in pond field experiment to study algae composition, biomass, primary production of biofilm. Culture technology, process and effect of biofilm were analyzed. The results show that, the nutrient soaking could accelerate succession speed of algal community on substrate, the cell number of algae on nutrient soaked substrate increased and was significantly more than the control group, especially for the dominant species. Algae community in biofilm experienced the succession process of Cylindrotheca closteriwmâ†'Nitzschia marginulataâ†'Spore of Ulva sp.â†'Navicula corymbosaâ†'Ulva sp.â†' Synedra spp. Filamentous green algae first appeared in substrate soaked in high concentration nutrient. There was highly significant difference (P< 0.01) among algal biomass of each treatment, which indicated the rising growth rate of biofilm with increasing nutrient concentrations, and inorganic nutrient of high concentration and mixed nutrient group performed the most obvious effect of promoting followed by organic nutrient solution. Scarce algae in biofilm and hence negative net primary production were found in the 1st week, so biofilm was estimated to be dominated by heterotrophic organisms such as bacteria. Diatom growth and primary production reached the peak in the 3rd week and started to fall in the 4th week. Thus, artificial biofilm culture techniques could promote the colonization and development of biofilm, accelerate the succession speed of biofilm community, increase its biomass and primary production, and thereby enhance the contribution rate of the biofilm to the feed of sea cucumber.6. Preliminary analysis of nutrient flux on surface of artificial treated reefs and biogenic element in biofilmsCement substrates soaked in organic, inorganic and mixed nutrient solution were deliveried in sea cucumber culture pond, pond field experiment was adopted to study oxygen O2, nitrogen N, phosphorus P fluxes between water and reef surface in the 1st,2nd,3rd,4th and 6th week after reef immersion, total carbon TC, total nitrogen TN and total phosphorus TP in biofilm of the 4th and 6th week were analyzed as well. The results showed that, O2 flux between biofilm-water interface increased with the culture time, and the release flux at the same sampling week were significantly higher than the absorption one (P< 0.05), namely a net release of O2 flux through the interface. Substrates soaked in inorganic (group C) and mixed (group D) nutrient solution can significantly increase its interface O2 flux. Nitrogen of each group soaked in nutrient solution released faster in the initial 1-2 weeks, NO3- flux was higher than NH4+ flux, D group had a higher flux of NO2-, and all groups showed more absorption flux later. P released slowly and till 4th-6th week. Substrates soaked in inorganic (group C) and mixed (group D) nutrient solution can significantly increase its interface N, P flux. Nutrient solution soaking treatment to substrate had a significant impact on major biogenic elements C, N, P content in biofilm. TC, TN and TP content in biofilm of inorganic nutrient solution (group C) was significantly higher than other groups, and C:N and N:P of group C was significantly lower than the other groups (P< 0.05). After preliminary evaluation, soaking with inorganic nurient solution (group C) is expected to get better results in sea cucumber culture. |
PDF Full Text Request