Studies On Community Structure Of Ichthyoplankton In Laizhou Bay

Laizhou Bay,a semi-closed bay located in the south of Bohai, goes into the sea along the coast of more than 10 rivers such as the Yellow River,Xiaoqing River.The diluted water of The Yellow River created the water environmental conditions such as rich estuary formed nutrients, suitable water temperature, low salinity water and so on,which makes Laizhou Bay become an important spawning grounds, feeding grounds and nursery field. In recent years, with increasing land-based sources of pollution, worsening eutrophication and frequent oil spill incidents, the habitat quality of Laizhou Bay has declined markedly, while long-term overfishing has changed in the structure of fisheries resources, therefore fishery resources has declined significantly. The composition of the species of ichthyoplankton and the number of it determines the supplementary group structure, which if of great significance. Through the 6 surveys during 2014--2015, this paper analyzes the seasonal variation of the species composition and the number of the ichthyoplankton. This paper also analyzes ichthyoplankton community structure with the consideration of the environmental factors,focusing more on the analysis of the community structure diversity and interannual changes of the ichthyoplankton during the spring of the year 2007--2015 in Laizhou Bay to acquire the dynamic changes of the species and quantity of ichthyoplankton,which accumulated material for the study of Laizhou Bay early supplementary groups to provide a basis for the protection and utilization of fish resources policy development.In this paper, the data of ichthyoplankton is provided by the Shandong Provincial Oceanic Fisheries Resources and Environment Research Resource Center, and the environmental data is provided by Shandong Province Institute of Marine Resources and Environment, Marine Environmental Monitoring Center.The sample collection of ichthyoplankton uses the horizontal trawl, dragging10 min each station at the speed of 2kn. The analysis shows that during the year of 2014- 2015,135275 eggs, 2456 larvae, 23 species are collected in four seasonal voyages.The species and quantity of ichthyoplankton collected in spring is higher than that in the other three seasons. The dominant species of ichthyoplankton changes obviously seasonally, the dominant species of spring eggs are Engraulis japonicus and Konosirus punctatus, that of summer eggs are Thryssa kammalensis and Sillago sihama; dominant species of larvae in spring is Liza haematocheilus, summer dominant species are Allanetta bleekeri and Konosirus punctatus, autumn dominant species is Protosalanx hyalocranius. The seasonal changes of fish eggs and larvae diverses significantly. Apart from winter, the abundance index(D), diversity index(H), evenness index(J) of fish eggs and larvae in spring is the smallest of the 3 left seasons, those in summer are the highest and next comes the autumn. The seasonal changing rate of eggs and fish larvae and juveniles changes along with the season changes, the changing rate of species from spring to summer is the smallest, that from autumn to winter and winter to next spring is 100%. The community structure of ichthyoplankton in spring and summer is similar but varies from that in autumn and winter. The results showed that the species composition and quantity changes of ichthyoplankton in four seasons are in line with changes in the law of fish spawning in the Laizhou Bay.By analyzing the correlation between the number of ichthyoplankton and environmental factors, the salinity influences significantly on the number of eggs, the temperature have more obvious effect on the larvae. The number of fish eggs was significantly associated with that of larvae, and has no relation with other factors;Aside from the number of fish eggs,the number of larvae was greatly correlated with inorganic nitrogen and dissolved oxygen(DO), nitrite activated phosphate(P < 0.05), and almost completely correlated with the ammonia nitrogen(NH4-N), and chlorophyll- a(P < 0.01). In the survey, the number of eggs has a significant positive correlation(r = 0.479, P = 0.479) with copepoda, and the number of larvae shows significant negative correlation with t copepoda(r =-0.510, P = 0.510).By analyzing the data of ichthyoplankton during the spring of 2007-2015 in Laizhou Bay,it shows that 42 species of fish eggs and larvae are researched,which includes 33 species of fish eggs and 21 species of fish larvae.The number of species of ichthyoplankton decreased and then increased as the years passing by. The number of ichthyoplankton changes is volatile, the number of eggs reached the lowest in 2013 while larvae didn’t appear, the number of eggs reached the highest in 2014, but the biological diversity index, evenness index were at the lowest level.The replacement of dominant species of ichthyoplankton is obvious, the dominant species of larvae in spring during 2007-2008 is Engraulis japonicus, that in 2009-2010,becomes the Gobioidae, that after 2011 remains the Liza haematocheilus. Significant difference was found in community structure of ichthyoplankton in Spring Laizhou Bay. CLUSTER analysis showed that the community structure of ichthyoplankton remains similar during 2007-2010, that in 2012 and 2014 are similar,that in 2011, 2013 and 2015 are similar. Results show that since 2007, the community structure of ichthyoplankton in Laizhou bay waters have changed obviously.