The Effects Of Hypoxia On The Marine Organisms In Large-scale Algal Bloom Area

With the development of world economy, the marine eutrophication and HABs (HarmfulAlgal Blooms) became more and more serious day by day, and hypoxia also aggravated at thesame time. Hypoxia has had great impacts on the survival and reproduction of marine organismseven to the ecosystem structure. Thus, acute and chronic experiments were carried out about therelationship between HABs microalgae and hypoxia and the effects of hypoxia on marineorganisms.Results were as follows:The depression of A.catenella, P.donghaiense, and S.costatum was simulated. Thedissolved oxygen(DO), algal density and ammonia nitrogen over time in darkness of threespecies of HAB algae were investigated. The results showed that the three algae all caused thedecrease of DO, and the DO depletion of A.catenella (7400cells/mL,55ug/mL) was biggest andfastest. The lowest DO (3mg/L) appeared in the bottom in4days. The DO depletion ofP.donghaiense(79000cells/mL,55ug/mL) in the same biomass was obviously lower and slowerthan A.catenella but higher and faster than S.costatum, The lowest DO(4mg/L) appeared in thebottom in5days. DO depletion of S.costatum (275000cells/mL,55ug/mL) was few in earlydays, but DO of bottom quickly decreased and layered16days later. Algal density of A.catenellawould quickly decrease in darkness, and completely subsided and broken in5days,P.donghaiense would completely subsided and broken in11days, but there were still someentire cells in the bottom of S.costatum at24days. The three species algae were all releasedammonia nitrogen in darkness and the ammonia nitrogen concentrations were all layered, thatwas the surface>the middle>the bottom, and nearly had a linear increase. The biggest ammonianitrogen concentration of A.catenella was0.97mg/L-N, P.donghaiense was0.51mg/L-N andS.costatum was only0.18mg/L-N. There were some relationships between large-scale HABsand hypoxia, and dinoflagellate HABs was more likely to cause hypoxia than diatom HABs, andthe damage was more serious.The96hoursmortality rates of Calanus sinicus, Brachionus plicatilis, Artemiasalina larva,Chlamys Farreri, Mytilus edulis and Pseudosciaena polyactis in different concentration of DOwere investigated. The oxygen consumption rates of Chlamys Farreri, Mytilus edulis and Pseudosciaena polyactis and the effects of different concentration of DO on spawning andhatching of Calanus sinicus and Artemiasalina were investigated. The results showed that whenDO declined to2mg/mL Pseudosciaena polyactis and Calanus sinicus all died in4hours,Chlamys Farreri all died in30hours, but Brachionus plicatilis, Artemiasalina and Mytilus edulishad no death in96hours. The resistance to low oxygen of several organisms is Pseudosciaenapolyactis<Calanus sinicus<Chlamys Farreri<Brachionus plicatilis, Artemiasalina, Mytilusedulis. The oxygen consumption rates had great differences in several organisms. The maximumoxygen consumption rates of Mytilus edulis was0.00295ug/g·h and Pseudosciaena polyactiswas only0.222mg/g·h. The oxygen consumption rate was negatively related with the resistanceto low oxygen, that was Pseudosciaena polyactis> Chlamys Farreri> Mytilus edulis. Hypoxiawas significantly inhibited the spawning rate of Calanus sinicu and influenced the hatching rateof Calanus sinicus and Artemiasalina. Consequently, hypoxia inhibited both survival andreproduction of marine organisms. The resistance and adaptation to hypoxia of different specieswas great different, zooplankton like Calanus sinicus was sensitive to hypoxia. Long timehypoxia would change the structure and function of ecosystem.The96hours mortality rates,30days growth, spawning and enzymatic activity of Neomysisawatschensis in different DO were investigated. The results showed that hypoxic tolerance ofNeomysis awatschensis larva was greater than adult. When DO was3mg/L, Neomysisawatschensis would all died in70hours but larva was all survival in96hours. When DO was5mg/L, the growth of Neomysis awatschensis had been affected, the body length, wet weight,protein content and fatty acid content were1.4%,15.7%,1.1%and32.6%lesser than thenormoxic group’s(8.5mg/L) and the fatty acid had a marked decrease. Hypoxia obviouslyinhibited the reproduction of Neomysis awatschensis. The first releasing was prolonged for3-7days compared with the nomoxic group and the total releasing days was shortened. The totalnumbers of juveniles produced were only7%,27%and65%of the nomoxic group’s When DOwas4mg/L,5mg/L and6mg/L. The activity of protective enzyme (catalase, total superoxidedismutase) obviously increased in the mild low oxygen environment (4-6mg/L), but the activityof protective enzyme decreased in very low oxygen environment (2mg/L). The changes of lactic dehydrogenase were similar with protective enzyme. The activity of lipase and trypsin increasedwith the decreasing of DO. These all indicated that Neomysis awatschensis would adapt lowoxygen environment through changing the enzyme activity but when DO was too low, theautoregulation was broken, then the enzyme activity would changed. After all hypoxia wouldcause death, inhibit the reproduction, change the enzymatic activity and reduce the nutritionalvalue.of Neomysis awatschensis. And then caused adverse effects to the organisms of highertrophic levels, and even changed the structure and function of marine ecological system.Above all, the depression of abundance red tide algae would consume the DO of water andcaused hypoxia. Dinoflagellate HABs was more likely cause hypoxia than diatom HABs, and thedamage was more serious. Hypoxia would inhibit the survive, growth, reproduction andenzymatic activity of marine organisms. The resistance and adaptation to hypoxia of differentspecies was great different, and long time hypoxia may change the structure and function ofecosystem.