Food Source Of Sea Urchin Mesocentrotus Nudus And Its Potential Predator's Predation Strategies

Sea urchins are the key species in the algal-bed ecosystem,which plays an important role as the ecosystem engineer,especially its population quantity in maintaining the balance of the algal-bed ecosystem.The composition of sea urchins' food sources and their predators are important factors that control the changes of sea urchin population.In this thesis,the Mesocentrotus nudus with high economic value in northern China coast was taken as the research object.And the composition of the food sources of the M.nudus in the natural sea area was studied to understand its food source and predator composition by field survey,laboratory simulation experiments,and stable isotope technique,respectively.The results of this study will help to elucidate the influencing factors of the population change of M.nudus.This will not only deepen the understanding of the regulatory role of sea urchins in the algal-bed ecosystem,but also provide theoretical basis and data support for the protection and rational development of M.nudus population resources.The main findings are as follows.(1)The potential food source of M.nudus in natural waters and its contribution to the predatorsBased on the current situation survey combined with stable isotope technology,the study showed that the M.nudus in the waters of Long Island belonged to the primary consumers of the second trophic level in the food chain,and there were differences in the feeding of various potential food sources.Among them,Chrysymenia wrightii contributed the highest potential food source rate of 9.42% to M.nudus.It was followed by carrageenan Chondrus ocellatus,Sargassum thunbergia,and phytoplankton accounting for6.56%,6.15%,and 6.07%,respectively.Besides,the contribution rates of particulate organic matter(POM)and sediment organic matter(SOM)to the potential food source of M.nudus were only 4.07%,and 3.50% respectively.The trophic level of zoobenthos in the waters of Long Island ranges from 2.00 to 4.39.The potential food contribution rate of M.nudus to various predators is low,which is related to the fact that Echinococcus urchins have large body size and thick spines restricting the predators' feeding.(2)The selection of potential predator and predation strategy of M.nudus.Eight decapod species from 29 common macrobenthic species were observed with the capability of preying on juvenile individuals of the M.nudus through simulated experimental observation.Of which,six species were firstly reported as its potential predators,including Gaetice depressus,Hemigrapsus sanguineus,Portunus trituberculatus,Romaleon gibbosulum,Hyastenus ducator and Diogenes edwardsii.Another two species,Pugettia quadridens and Charybdis japonica,their predation ability and strategy on M.nudus were further determined.The above eight species showed different predation rate on three sized M.nudus individuals.The small-size individuals could be captured by 8 predators,of which,the C.japonica showed the highest predation rate of 4.66 ± 0.47 ind./24 h.The predation rates of G.depressus and D.edwardsii were the lowest,0.67±0.47 ind./24 h,and 0.67±0.62 ind./24 h,respectively.The medium-sized sea urchins could only be preyed on by four species,including R.gibbosulum,P.quadridens,P.trituberculatus and C.japonica,with the predation rate ranging from 0.50 to 2.00 ind./24 h.Whereas,the large-size individuals could not be captured by all the predators.It was also found that the shells and spines of the sea urchin compel predators to adopt similar strategies by removing the spines or turning over the sea urchins firstly,and then attacking its weak parts of the mouth or anus.However,there were always some differences in details due to the morphological structure of different predators,such as the robust of cheliped.(3)The predation selection of C.japonica to the three sized sea urchins individualsThe predator C.japonica and three different sized sea urchin individuals were selected to test if the predations selection exist.It was found that the C.japonica showed randomness in its predation behavior for three sizes of sea urchins,and it would preferentially attack the closest prey.However,there are significant differences in the success rate of predation for different sizes of sea urchins.Among them,the success rate of predation for small-sized sea urchins is the highest,and the predation of large-sized sea urchins is not possible.