Study On Feeding Ecology Of Dominate Gobiid Fishes In Jiaozhou Bay

The feeding ecology of dominate gobiid fishes in Jiaozhou Bay was studied basedon the data from four seasonal bottom trawl surveys in Jiaozhou Bay from February toNovember2011. The food composition, food competition, spatial and temporalvariation of feeding habit were analyzed.The food composition, spatial and trophic niche width, trophic–spatial nicheoverlap for eight dominate gobiid fishes (Amblychaeturichthys hexanema,Acentrogobius pflaumii, Ctenotrypauchen microcephalus, Chaeturichthys stigmatias,Odontamblyopus lacepedii, Synechogobius ommaturus, Tridentiger barbatus, andTridentiger trigonocephalus) in Jiaozhou Bay were studied using the Shannon-Wienerindex and Pianka overlap index. The trophic–spatial niche overlap was calculated todescribe the relationship between feeding competition and spatial distribution of thesegobiid fishes. Results showed that all of the eight gobiid fishes could be classified asbenthic carnivorous predators. S. ommaturus fed mainly upon shrimps, polychaetes andfish. A. hexanema fed mainly upon bivalvia, copepoda and cumacea. The main preyitem of C. stigmatias was ophiuroidea. While the other five gobiid fishes fed mainlyupon some small benthic crustaceans such as copepods, amphipods and cumacea. Inautumn, the highest spatial niche overlap value (0.76) was shown between A. hexanemaand C. stigmatias; the A. pflaumii and A. hexanema had the highest trophic nicheoverlap value (0.70), and the A. hexanema and C. stigmatias had the highesttrophic-spatial niche overlap value (0.0843). In winter, A. hexanema and Tridentigerbarbatus had the highest trophic niche overlap value (0.64) while O. lacepedii and T.barbatus had the highest spatial niche overlap value (0.91); A. hexanema and T.barbatushad the highest trophic–spatial niche overlap value (0.3648). In the period of resoucesscarcity or the activity area expansion of fishes, the fishes with high trophic-spatial niche overlap were more likely to cause competition. So A. hexanema and C. stigmatiasin autumn might result in intensive food competition. The competitions among othergobiid fishes were reduced by partition of trophic and spatial niches.The feeding ecology of A. hexanema was studied by stomach content analysis. Theresults indicated that prey items of A. hexanema included more than40species, amongwhich Alpheus japonicas, Philine kinglippini and Leptochela gracilis were the dominantprey species. The diet composition of A. hexanema varied significantly among seasons,with gastropods, fish, decapods and microcrustacean being the most important preyitems in spring, summer, autumn and winter, respectively. This phenomenon mightmainly relate to seasonal variations in the species and biomass of preys in Jiaozhou Bay.With the increase of predator size, prey species of A. hexanema varied from copepod toP. kinglippini, Raphidopus ciliates and A. japonicas which were larger in sizes. Thecanonical correspondence analysis (CCA) showed that temperature and salinity werethe most important variables followed by predator size and pH.Stable isotope analysis was also use to study the food composition and ontogeneticshift of A. hexanema, and to compare the difference of these two methods. The resultindicted that the mean trophic level of A. hexanema in Jiaozhou Bay was3.69,calculated by the15N signatures. Small crustaceans dominated contributions the diet toof A. hexanema, followed by mollusca, crabs and shrimp. The importance of each preywas different with the result of stomach content analysis. With the increase of predatorsize, the main item varied from small crustaceans and organic detritus to larger preyitems such as mollusca, crabs and shrimp. This phenomenon is same to the stomachcontent analysis. Stomach content analysis can identified identify the prey itemsaccurate，and the short-term feeding habit can easily be studied by this method.However, it need volume of work and difficult to measure some items that rapidlydigested in the stomach. The stable isotope results may indicate more representativetrophic relationships between the predator and prey items, and the result is steady andhardly affected by seasons, temperature, and the sampling factors. It also canquantitative analysis the organic detritus, bacterium which were difficult identified by the stomach content analysis. However, the stable isotope analysis can’t confirm theprey items of predator. It is also not very effective in the study of seasonal variationeven the diurnal change of feeding habit. Each of these two methods has advantage anddisadvantage. It is suggested that the combination of these two methods would moreeffective in the furture study on the feeding ecology.