The Effects Of Secondary Metabolites Produced By Diatoms On Copepod Reproduction In Jiaozhou Bay

In recent years, many studies have shown that: diatoms, considered as the main food source for copepods, induced inhibitory effects on reproduction, growth and development of copepods. Two respects were put forward for the inhibitory effects caused by diatom: (1) Some essential nutrients which were necessary for copepods reproduction perhaps were insufficient in diatom cell. Evidences indicated that the nutrients are directly correlated with the egg production. A large number of experiments on nutrient deficiencies were carried out, and the results showed that the substance is fatty acids, especially polyunsaturated fatty acids (PUFA). (2) Diatom cells release some toxic or deleterious substances that could inhibit copepods from reproduction. Recent studies have shown that the substance may be some aldehydes. However, there are few studies about whether diatoms in Jiaozhou Bay could produce aldehydes and induce inhibitory effects on reproduction of copepods.Jiaozhou Bay is a typical marine area which has high productivity, as a major primary producer in the marine area, diatoms predominate in marine phytoplankton, either in phytoplankton species or quantity account. Similarly, as the dominant species of zooplankton in Jiaozhou Bay, copepod lies in the center of the food chain, which is not only the main ingester of diatoms, but also the main food source for fish. It is possible of diatoms in high concentration inhibiting the reproduction of copepods in this sea area, where is the ideal sites to study on diatoms - copepod interaction. Further development of the studies that secondary metabolites of diatoms on the impact of copepods is significant to improve food web theory of marine ecology, while the studies can provide important theoretical support for the reasonable protection and development of the fisheries resources in the marine area.We conducted some laboratory experiments and field experiments, studying interactions of different diatom species (Skeletonema costatum, Chaetoceros didymus) and copepod species (Calanus sinicus) sampled from Jiaozhou Bay, compared with Prorocentrum micans. At the same time, aldehydes produced by phytoplankton were detected with HS-SPME/GC-MS analysis method. The results showed that, compared with Prorocentrum micans, Skeletonema costatum and Chaetoceros didymus induced negative effects on female survival, egg production and egg hatching of Calanus sinicus. 6 kinds of aldehydes were detected in Skeletonema costatum (trans-2-hexenal, heptaldehyde, trans-2-heptenal, trans-2,4-heptadienal, trans-2-decenal and trans-2,4-decadienal) and 5 kinds of aldehydes in Chaetoceros didymus (trans-2-hexenal, heptaldehyde, trans-2-heptenal, trans-2,4-heptadienal and trans-2,4-decadienal), while only 2 kinds were detected in Prorocentrum micans (trans-2-hexenal, trans-2-heptenal). Either some specific or total aldehydes, the contents in Skeletonema costatum and Chaetoceros didymus were significantly higher than that in Prorocentrum micans, indicating that the aldehydes produced by Skeletonema costatum and Chaetoceros didymus caused potential negative effects on the reproduction of Calanus sinicus.The conclusion on the component and content of aldehydes in the same kinds of algae is not the same to the overseas research in this paper, and some aldehydes are not seen in previous reports, which may mean that the same kinds of algae in different culture conditions could produce different aldehydes. In view of this, aldehydes component and content of 4 algae (Skeletonema costatum, Chaetoceros didymus, Prorocentrum micans, and Scrippsiella trochoidea) isolated from Jiaozhou Bay at different culture phases are measured and analyzed. The results show that the total content of aldehydes in Skeletonema costatum, Prorocentrum micans, and Scrippsiella trochoidea are gradually decreased from 4 culture phases—adaptive phase, logarithmic phase, quiescent phase and decline phase, while the total content of aldehydes in Chaetoceros didymus of logarithmic phase is higher than adaptive phase, and the total content of aldehydes in quiescent phase and decline phase tend to equal and are lower than adaptive phase. On the whole, the total content of aldehydes in the 4 algae of adaptive phase and logarithmic phase are higher than quiescent phase and decline phase.From our experiments, we conclude that, as the dominant species of diatoms in Jiaozhou Bay, Skeletonema costatum and Chaetoceros didymus do produce a large number of unsaturated aldehydes and induce negative effects on copepod. Finally, a field experiment of the reproduction of Calanus sinicus in different regions of Jiaozhou Bay was studied, the results showed that diatoms of high concentrations induced negative effects on Calanus sinicus in high chl a concentration area.