Deep-sea Adaptation And Ecological Stoichiometry Of Zooplankton

The purpose and meaning of this research are:to study the adaptive characteristics of zooplankton in deep and shallow layers in the western tropical Pacific ocean.This is conducive to a better understanding of the ecological habit of zooplankton in the deep sea and providing background information to the future research of their ecological response.This research also focuses on the elemental composition?C:P,C:N,and N:P?of the main zooplankton taxa in the western tropical Pacific ocean and their variation with body size,trophic level,and prey elemental composition.This could provide the data about marine ecosystem on ecological stoichiometry and is helpful in the application of this theory to ecology processes.At the same time,based on differences of the elemental compositions of zooplankton and their diet,the potential nutrient limitations of zooplankton were evaluated.Representative species of different zooplankton taxa were selected and cultured under different nutrient conditions to observe the effects of nutrent limitations on zooplankton.This could supply basic data about the prediction and explanation of the effects of nutrient changes on zooplankton community succession.The main results were listed as follows.The deep sea was considered as one of the most rigorous environments with limited food resources.In contrast,zooplankton and their food supply were abundant in the shallow layer.In this study,different adaptive characteristics of zooplankton taxa in the deep and shallow layers were explored from three aspects of feeding types,trophic niche partition among taxa and growth performance.Our results showed that wider range of?¹⁵N and?¹³C values were detected in deep-layer taxa,indicating various feeding types.This was crucial for zooplankton in deep-sea ecosystems to make full use of limited resources?e.g.marine snow and fecal pellets?.Lower trophic-niche overlap among taxa was revealed in the shallow layer,indicating higher level of trophic niche partition.This was a fundamental mechanism minimizing the inter-taxa competition and sustaining the co-existence of zooplankton in the shallow layer.From the perspective of ecological stoichiometry,in the deep layer,most taxonomic groups exhibited higher values of C:P and N:P ratios than the taxa with similar taxonomic status in shallow layer,suggesting lower maximal growth rate.Lower growth rates potentially reduced the consumption of limited resources in the deep layer,and higher growth rates facilitated the rapid exploitation of abundant resources and flourish of zooplankton in the shallow layer.The elemental composition?C:P,C:N,and N:P?of the main zooplankton taxa?19 taxa?,and their variation with body size,trophic level,and prey elemental composition were detected in this region?near 11°N,139°E?.The results indicated that the zooplankton elemental composition was taxa specific.The C:P and N:P ratios of the non-gelatinous zooplankton changed inversely with their equivalent spherical diameter?ESD?and were inversely linearly proportional to the trophic levels.Non-gelatinous zooplankton had a weak homeostat for C:P ratios,while their C:N ratios remained relatively constant.RDA analysis showed that zooplankton elemental composition was more closely related to their prey elemental composition than the ESD and trophic level.A mismatch between zooplankton stoichiometric demand and their prey stoichiometric supply might cause the zooplankton to suffer from nutrient limitations.The results of this study showed that non-gelatinous taxa suffered potential N and P-limitation?P-limitation was stronger?,and a weak potential co-limitation of N and P.In contrast,the gelatinous zooplankton did not experience a potential P limitation.These potential nutrient limitation differences across taxonomic groups could provide valuable insights into the driving forces of community succession in the western tropical Pacific Ocean.Some comments and discussions were added about the effects of nutrent limitations on zooplankton.Nutrient imbalance-a mismatch in nutrient ratios between the available food supply and the demands of consumers-has the potential to be transported up food chains,exposing higher trophic-level organisms to nutrient limitations.We estimated the tolerance of jellyfish ephyrae?Aurelia sp.1?and fish larvae?Paralichthys olivaceus?to nutrient limitations and analyzed their growth,survival,and elemental homoeostasis.We found that nutrient limitations had stronger negative effects on the fish larvae than jellyfish ephyrae.The reason for this phenomenon may be that the different body structures of jellyfish and fish lead to different elemental demand,which in turn make them have different toleraces to nutrient limitations.Additionally,as primary consumer,rotifers?Brachionus plicatilis?exhibited the lowest amino acids content but the highest fatty acids content in the P-limited treatment.And the growth and survival of P.olivaceus larvae could be negatively affected by the reduction of amino acid contents?but not fatty acids?in its nutrient-limited food.Thus,the content of amino acids could be a good indicator of food quality under nutrient limitation.