Study Of Benthic Food Web Dynamics In The Manila Clam (Ruditapes Philippinarum) Mariculture Waters

Benthos and their potential food sources, including POM （particulate organicmatter）, phytoplankton and SOM （sediment organic matter） were sampled in July andNovember2011, February and May2012at six sites were sampled in the Ruditapesphilippinarum mariculture waters in the Jiaozhou Bay. By analyses of δ¹³C and δ¹⁵Nvalues of the benthic food web components, food web information about trophicrelationships and relative trophic level were revealed.The δ¹³C and δ¹⁵N values of POM, phytoplankton and SOM had significanttemporal and spatial variance. The δ¹⁵N value of POM showed a similar seasonalchanging trend with phytoplankton, which was: spring>summer>autumn>winter. Thechanging trend of δ¹⁵N value of SOM showed a different trend:winter>spring>autumn>summer. A total of75species were analysised for stableisotope values, including meiofauna （free-living marine nematode and benthiccopepods） and macrobenthos （Crustacea,27species; Polychaeta,26species; Bivalvia,5species; Gastropoda,9species; Echinodermata,2species; Nemertinea,1species;Platyhelminthes,1species; Gobiidae,1species; Cephalopoda,1species）. The δ¹³Cvalue ranged from-24.93‰（benthic copepods） to-9.37‰（Ophiodromusangutifrons）, while δ¹⁵N value varied from3.33‰（Corophium sp.） to18.75‰（Octopus variabilis）.The results of trophic relationships were revealed. SOM was major food sourcefor benthic copepods, while the feeding strategy of nematodes was more complicated.POM and phytoplankton were important food sources for the benthic filter feederssuch as bivalves, while bivalves also filtered other food sources such as algae detritusand microphytobenthos. The food sources of Crustacea were more diverse. Crabswere mainly carnivorous or omnivores. Shrimps were carnivorous and amphipodswere deposit feeders or omnivores. Polychaetes were carnivorous, omnivores or deposit feeders while the deposit feeders may feed on SOM selectively. Gastropodswere carnivorous/scavengers or omnivores. Nemerteans were carnivorous. Brittle starand Protankyra bidenata were deposit feeders.The relative trophic level could be revealed by δ¹⁵N values. The relative trophiclevels were different in four seasons and overlaped existed among different functionalgroups. The food web of the Ruditapes philippinarum mariculture waters consisted of3trophic levels at least. Corophium sp., Cumacea and Brittle star occupied the bottomof the food web. Copepoda, Amphipoda and Anthuridea were in the intermediatetrophic level. Gastropoda, Decapoda, Nemertea, Protankyra bidenata and Bivalviawere at the top of the food web.Manila clams （Ruditapes philippinarum） were divided into different groupsaccording to shell length, shell width and shell height. The results showed that thestable isotope values were similar among different sizes of the clams，whichindicated that they filter the same food sources.