Comparative Transcriptome Analysis of Shell-Matrix-Protein Genes and Observation of the Shell Microstructure in the Deep-Sea Clam Calyptogena marissinica

The deep-sea clam Calyptogena marissinica is widely distributed in the Haima cold seep ecosystem on the northwes-tern slope of the South China Sea with low pH values,low temperature and high pressure.Limited information is available on the biomineralization of this species.In this research,we generated a comprehensive transcript dataset of C.marissinica’s mantle tissue,and a total of 19821 unigenes were assembled.Fourteen shell matrix proteins(SMP)-related genes were identified.The qPCR results showed that four out of six prismatic matrix genes(MSP2,MSP5,prisilkin-39,and shematrin),four out of the six nacreous matrix genes(perlucin,pif,pif97,and papilin),and two extrapallial fluid proteins(SPARC and calmodulin)were significantly expressed in the mantle.Both the nacreous and the prismatic layers are chrysanthemum-shaped,which are stacked on the top of each other to form a laminated nacreous structure.The alignment and phylogenetic analysis of MSP-5,Prisilkin-39,Perlucin,and Pif homologues showed that some amino acids of C.marissinica that differed from those detected in other molluscs may cause the different shape of the nacreous and prismatic layers,but do not lead to a change in the species’evolutionary status.These results indicated the conservation of the functions of SMP-related genes in C.marissinica,and the specific shape of the prismatic and nacreous layers of this deep-sea mollusc,which will contribute to the research on the molecular regulation mechanisms of biomineralization in C.marissinica and provide a new perspective to investigate biomineralization in deep-sea clams in general.

Transcriptome Analysis of Mantle Tissues Reveals Potential Shell-Matrix-Protein Genes in Gigantidas haimaensis

Haima cold seep ecosystem is on the northwestern slope of the South China Sea,which is characterised by high pressure,low temperature,hypoxia,and low pH value.The deep-sea mussel Gigantidas haimaensis is distributed in this ecosystem.Previous studies have focused on its adaptation to abiotic stress,biogeography,ecotoxicology,genomes,immunity and symbiosis,but knowledge on biomineralisation remains lacking.Herein,we generated a comprehensive transcript dataset from G.haimaensis mantle tissue,and 30255 unigenes were assembled.The top 20 most highly expressed genes are related to energy supply,such as mitochondrial genes,suggesting they may mediate the adaptability of this deep-sea mussel to the high pressure and hypoxia environment.Eleven shell matrix protein(SMP)-related genes were identified from the transcriptome data.Quantitative PCR analyses showed that five of ten acidic SMPs and nacreous-layer-matrix-protein genes(nacrein,perlucin,perlwapin,pif and mantle protein)were highly expressed in mantle tissue,while the expressions of other five genes(chitinase,SPARC,TRY,papilin and calmodulin)were low.Scanning electron microscopy showed that the shell was composed of a prismatic layer and a nacreous layer,and every nacreous layer was made of the whole pieces of aragonite that stacked on top of each other.These results indicated the conservation of the structure and functions of nacreous matrix genes in G.haimaensis.Moreover,the nacreous layer was made of whole pieces of aragonite that were not quadrilateral or polygonal pieces.Studying these genes will likely reveal the molecular mechanisms of biomineralisation in G.haimaensis and other deep-sea mussels.

Identification and Expression of the Conotoxin Homologous Genes in the Giant Triton Snail (Charonia tritonis)

Conotoxin(CTX)is a small peptide toxin,and plays crucial role in anesthetizes prey,preys and defends competitors.Charonia tritonis is the natural predator of the crown of thorns starfish(CoTS)and the protector of coral reefs.It plays an important role in the coral reef ecosystem.However,the types of toxins produced by tritons and the molecular mechanisms of toxin secretion of C.tritonis are unknown.In the present study,the four conotoxin homologous genes(CTXs)from C.tritonis were identified.Species and conotoxin superfamily phylogenetic tree indicated that CTX-1(CL2216.Contig2)and CTX-4(Unigene 58438_All)belong to the C superfamily,CTX-2(Unigene 66414_All)belong to the V superfamily,and CTX-3(Unigene 21408_All)belong to the B1 superfamily.CTXs were highly expressed in salivary gland,liver and digestive gland.The predation control experiment revealed that the expressions of CTXs were significantly different in salivary gland,liver and digestive gland.The results indicated that CTXs may participate in the process of C.tritonis predating CoTs,and provided a scientific basis for further studying the toxins secretion mechanism of C.tritonis.

Molecular quantification of copepod Acartia erythraea feeding on different algae preys

Quantitative evaluation of the copepod feeding process is critical for understanding the functioning of marine food webs, as this provides a major link between primary producers and higher trophic levels. In this study, a molecular protocol based on quantitative polymerase chain reaction(qPCR) targeting 18S rDNA was developed and used to investigate the feeding and digestion rates of the copepod Acartia erythraea in a laboratory experiment using microalgae Thalassiosira weissflogii, Prorocentrum shikokuense, and Alexandrium catenella as prey. Although offered an equal encounter rate based on biovolume, prey uptake varied substantially among the three algal species, with the ingestion rate(IR) and digestion rate(DR) of A. erythraea differing significantly(P <0.001) based on both cell counting and qPCR detection. Acartia erythraea showed the highest IR(2.79×10~4 cells/(ind.·h)) and DR(2.43×10~4 cells/(ind.·h)) on T. weissflogii, and the lowest amounts of ingested P. shikokuense were detected. The highest assimilation rate(~90.64%, IR/DR) was observed in copepods fed with P. shikokuense. The qPCR method used here can help determine the digestion rate and assimilation rate of copepods by detecting cells remaining in the gut hence providing the possibility to examine trophic links involving key species in the marine ecosystem. Our results indicate that A. erythraea has diet-specific feeding performance in different processes, and a quantitative assessment of copepod feeding is needed to accurately determine its functional role in the energy and matter uptake from marine food webs.

Genetic basis of embryo and juvenile physiological responses to salinity changes in freshwater pipefish (Hippichthys heptagonus)

DEAR EDITOR,Syngnathidae species commonly inhabit ocean environments.However,some have adapted to live exclusively in freshwater over long-term adaptive evolution but continue to retain physiological adaptations to saltwater environments.The genetic basis underlying the adaptive strategies and molecular regulation of freshwater syngnathids to freshwater and saltwater remains unclear.Here,we investigated the molecular characteristics and core gene expression in freshwater belly pipefish(Hippichthys heptagonus)embryos and juveniles through salinity stress experiments and transcriptome analysis.Results showed that embryonic exposure to salinity at a concentration of 30‰down-regulated cell cycle-associated genes vital to embryonic development.Retinol metabolism,neuroactive receptor interaction,and peroxisome proliferator-activated receptor signaling pathways were significantly enriched in up-regulated genes in the embryos.Notably,there was no significant change in the expression of ion transport and energy metabolism genes.Conversely,juvenile exposure to 30‰salinity up-regulated ion transport-related genes and significantly enriched immune-related signaling pathways,including lysosome,phagosome,autophagy,and mitophagy signaling pathways.Carbohydrate metabolism genes were also up-regulated,whereas oxidative phosphorylation genes were significantly down-regulated.These results suggest that brood pouch protection during the embryonic stage and salinity adaptation plasticity in juveniles may be strategic adaptations in freshwater pipefish.

The effects of four transplantation methods on five coral species at the Sanya Bay

Coral transplantation is considered as one of the major tools to increase coral abundance for degraded coral reefs.To investigate the effects of various methods and coral species in transplantation, coral fragments（n=902） of five coral species were transplanted by four methods at Luhuitou, the Sanya Bay, Hainan Province, China, where the reef has been over-exploited and is still threatened by human activities and natural disasters. Ten months after the transplant, the average survivorship of the transplanted corals was 45.5%. Methodologies had different effects on the transplanted corals, but none of them was efficacious for all coral species. Methodology could not change the decreasing trend for Montipora foliosa and Acropora hyacinthus, although it did slow down their decline. All transplants of A. hyacinthus and M. foliosa had high mortalities and significant decrease on survival area, while Porites andrewsi and Galaxea fascicularis had lower mortalities and partial mortalities. Only one method had significant effect on increasing survival area of G. fascicularis, same as P. andrewsi. Out of the five transplanted coral species, Pocillopora damicornis was the only species that had living tissue area increase in all applied methods, while the others had decreased live tissue area in one or more methods. The results of this study suggested that performing coral transplantation in a highly threatened area was not efficient unless the threats were diminished or erased. Moreover, proper species selection for coral transplantation is crucial, especially in a disturbed environment. Methodology, although having limited effects on improving results of coral transplantation, cannot compensate the maladjustment of vulnerable species to the stresses on the Luhuitou Reef. Coral transplantation on Luhuitou Reef should not be performed unless the stresses are under controlled,and corals with good tolerance to the environment should be considered first.

Long duplication of 18S ribosomal DNA in Cynoglossus lineolatus(Pleuronectiformes： Cynoglossidae)： novel molecular evidencefor unequal crossing over model

Although 18 S r DNA sequence is extremely conservative, the polymorphism still has been found in few species.In the present study, three types(Type A, B and C) of 18 S r DNA sequence coexisted in Cynoglossus lineolatus genome, suggesting a non-concerted evolution process, rather than a strictly concerted evolution fashion.Based on the differences of sequence variation, GC content, secondary structure and minimum free energy,Types A and B were speculated as the potential pseudogenes. Additionally, a fascinating finding was a 189-bp duplication of 18 S r DNA in Type A sequence. To our knowledge, this is the first report on such a long duplication in teleostean ribosomal DNA. Compared with several theories accounting for the formation of tandem repeats, the unequal crossing over model was thought to be the most likely mechanism to generate the189-bp duplication of 18 S r DNA. These results not only provide a novel molecular evidence for the unequal crossing over model, but also benefit for the further study on 18 S r DNA in fishes.

Environmental Drivers of Temporal and Spatial Fluctuations of Mesozooplankton Community in Daya Bay, Northern South China Sea

The response of zooplankton to the ecological environment in Daya Bay is unclear under the influence of both climate changes and anthropogenic activities on a seasonal to inter-annual scale.Based on monthly surveys and historical data,we found the zooplankton community had changed temporally and spatially.A total of 134 species was recorded during the study,and copepods dominated numerically in terms of diversity and abundance.Both copepods and cladocerans were the main contributors to zooplankton abundance.The community structure of zooplankton was temporally classified into the warm and cold groups,and spatially into the three groups located in the marine cage-culture area(MCCA),the outflow of nuclear power plants(ONPP)and unpolluted waters(UPW).The zooplankton was characterized by low biomass(dry weight),high diversity and abundance in the warm period in contrast to that in the cold period.Compared with the other two groups,the MCCA group of zooplankton showed high abundance,low diversity and biomass.Variations in dominant species were closely related to temperature,salinity and chlorophyll a concentration.Species diversity and dry weight decreased in comparison with 30 years ago,while zooplankton abundance increased.The seasonal variation in zooplankton was affected mainly by temperature that was controlled by monsoon,while the spatial difference in the community structure was probably due to eutrophication in the MCCA and thermal water discharge from ONPP.The zooplankton community is undergoing great changes with the tendency of miniaturization and gelatinization in recent 30 years in Daya Bay.

Temperature-Dependent Fatty Acid Composition Change of Phospholipid in Steelhead Trout (Oncorhynchus mykiss) Tissues

In this study, the changes of the fatty acid composition of phospholipid in different tissues(muscle, heart, brain and spleen) of steelhead trout(Oncorhynchus mykiss) were analyzed when the water temperature decreased gradually from 16 to 12℃℃, 8℃, 6℃, 4℃, 2 and 1℃℃. Three fish individuals each tank(average weight 70.32 g ± 9.12 g) were collected and used to analysis at each designed temperatures. At normal temperature(16℃), the fatty acid composition of phospholipid of muscle and heart was similar each other. The highest concentration of saturate fatty acids(SFA) was found in the phospholipid of spleen. The brain phospholipid contained higher oleic acid(18:1 n9) than the phospholipid of other tissues at 16℃. When the environmental temperature decreased, the concentration of unsaturated fatty acids of phospholipids in all tissues increased, and accordingly the ratio pf the unsaturated to saturated fatty acids(U/S) and unsaturation index(UI) increased, indicating that steelhead trout can compensate temperature-dependent changes in membrane fluidity by remodeling the fatty acid composition of phospholipids. The changes in the fatty acid composition of phospholipid were tissue-specific. At the early stages of the experiment(16 to 8℃℃), the fatty acid composition of phospholipid changed remarkably in muscle, heart, and spleen. When temperature decreased to less than 8℃, an obvious response of phospholipid fatty acid was observed in all tissues. The change of phospholipid composition of steelhead trout tissues may be affected by both cold stress and starvation when the temperature decreased to 2℃, and the change of phospholipid composition of muscle was very obvious.

Distribution of reactive aluminum under the influence of mesoscale eddies in the western South China Sea

To understand the distribution of aluminum （A1） under the influence of mesocale eddies in the western South China Sea （SCS）, sea level anomaly, geostrophic current, environmental parameters and reactive A1 were investigated in the western SCS in August 2013. The highest reactive A1 concentration （（180±64） nmol/L） was observed in the surface waters, indicating a substantial atmospheric input. Vertically, the reactive A1 decreased from the surface high concentration to the subsurface minima at the depth of chlorophyll a （Chl a） maxima and then increased again with depth at most of the stations. The average concentration of reactive A1 in the upper 100 m water column was significantly lower in the cyclonic eddy （（137±6） nmol/L） as compared with that in the non- eddy waters （（180±21） nmol/L）. By contrast, the average concentrations of Chl a and silicate in the upper 100 m water column were higher in the cyclonic eddy and lower in the anticyclonic eddy. There was a significant negative correlation between the average concentrations of reactive Al and Chl a in the upper 100 m water column. The vertical distribution of reactive AI and the negative correlation between reactive A1 and Chl a both suggest that the reactive A1 in the upper water column was significantly influenced by biological removal processes. Our results indicate that mesoscale eddies could regulate the distribution of reactive A1 by influencing the primary production and phytoplankton community structure in the western SCS.

Zooplankton in the Huangyan Atoll,South China Sea:A comparison of community structure between the lagoon and seaward reef slope

Relatively few studies have investigated the community structure of zooplankton in the atolls of the central South China Sea. Zooplankton were sampled at nine stations within the lagoon and four facing the seaward reef-slope in the Huangyan Atoll during May 2015. Lagoonal samples contained 48 zooplankton taxa( H' =2.25±0.95; J =0.70±0.23) with planktonic larvae, copepods, and euphausids contributing 95.63% of total abundance. Seaward oceanic samples contained 114 zooplankton(H ' =5.27±0.27; J =0.90±0.03) with copepods, siphonophores, chaetognaths, appendicularians, and planktonic larvae accounting for 93.66% of abundance. Lagoonal zooplankton abundance was lower than that on the seaward reef-slope. Zooplankton community dif fered significantly between the lagoon and reef-slope groups(R =0.708, P =0.001). The former was dominated by Macruran larvae, Brachyuran larvae, S tylocheiron carinatum, and Acartia spp., while the latter was predominately represented by O ikopleura longicauda, Chelophyes contorta and C opilia mirabilis. Chlorophyll a concentration was significantly higher in the lagoon than the reef slope regions( P <0.01), which may be due to the nutrient input from fishing vessels near the lagoon mouth. Zooplankton abundance was negatively correlated with chlorophyll a concentration(P <0.01). A clear dif ference was observed statistically in the species composition and abundance of zooplankton between the lagoon and the seaward slope at Huangyan Atoll, which suggests that it may be resulted from the influence by natural and anthropogenic interactions.

Global-Scale Diversity and Distribution Characteristics of Reef-Associated Symbiodiniaceae via the Cluster-Based Parsimony of Internal Transcribed Spacer 2 Sequences

Photosynthetic species belonging to Symbiodiniaceae play important ecological roles in coral reef ecosystems. Nine phylogenetically supported Symbiodiniaceae clades(each containing multiple genetically distinct molecular types) have been detected in reef-associated animals and in seawater or sediments near coral reef areas. Although major advances in research on Symbiodiniaceae diversity have been made, information on the global-scale diversity and distribution characteristics of Symbiodiniaceae clades/types is still limited or must be expanded because most studies on Symbiodiniaceae have mainly focused on a limited number of hosts associated with Symbiodiniaceae or coral reef areas. Here, the diversity and distribution characteristics of Symbiodiniaceae data derived from reef-associated animals and seawater or sediments near coral reef areas were analyzed using 3899 qualified Symbiodiniaceae internal transcribed spacer 2(ITS2) sequences retrieved from the GenBank database in May 2017. These sequences were annotated as Symbiodiniaceae ITS2 types via sequence alignment against database of Symbiodiniaceae ITS2 types. Results showed that photosynthetic Symbiodiniaceae ITS2 sequences could be annotated as 119 Symbiodiniaceae ITS2 types within nine clades(A–I), and Symbiodiniaceae ITS2 types mainly inhabited coral reefs between 30?N and 30?S. Symbiodiniaceae ITS2 types could be associated with multiple host taxa. Interestingly, these results implied that the distribution of Symbiodiniaceae ITS2 types was distinct in the Atlantic Ocean, the Red Sea, the Mediterranean Sea, and the Indo-Pacific Ocean. Although future field research should be performed to verify our results, this study provided a broad perspective of the diversity of Symbiodiniaceae clades/types on a global scale.

Roles of interleukins in antibacterial immune defense of the brood pouch in the lined seahorse Hippocampus erectus

Seahorse embryos are brooded in the enclosed nutrient-rich environment of the male brood pouch,which may be prone to bacterial infection.The immune responses of interleukin(IL)genes in the brood pouch have not been well studied.We identifi ed 13 interleukins in the lined seahorse Hippocampus erectus.Tissue-specifi c expression analysis revealed increased mRNA expression levels of il-1β,il-18,and il-8 in the brood pouch.When challenged with lipopolysaccharide or Vibrio parahaemolyticus,il-1βand il-18 were active as part of the acute and chronic infl ammatory responses,respectively.Importantly,il-8 may be involved in powerful antibacterial immune responses and may be induced by il-1βand il-18 via a process involving the nuclear factor-κB signaling pathway.These results suggest that il-1β,il-18,and il-8 may play key roles in the antibacterial immune defense of the brood pouch in male seahorses.

Fast acclimation of phytoplankton assemblies to acute salinity stress in the Jiulong River Estuary

Mixing of freshwater and seawater creates the well-known salinity gradients along the estuaries. In order to investigate how phytoplankton respond to the acute salinity changes, we exposed natural phytoplankton assemblies from the Jiulong River Estuary to differential saline field water while continuously monitoring their photosynthetic performances under both indoor-and outdoor-growth conditions. When the natural cell assemblies from salinity 30 field water were exposed to series low saline field water(salinity 25, 17, 13 and 7.5), the effective Photosystem II quantum yield(ΔF/Fm′) decreased sharply, e.g., to one-fifth of its initials after 5 min exposure to salinity 7.5 field water, and then increased fast during the following 40 min and almost completely recovered after 320 min. During such an exposure process, non-photochemical quenching(NPQ) sharply increased from 0 to 0.85 within 5 min, and then decreased to nearly 0 within the following 70 min. When these cells re-acclimated to salinity 7.5 field water were exposed to series high saline field water(salinity 13, 17, 25 and 30), a similar response pattern was observed, with the decreased ΔF/Fm′ accompanied with increased NPQ, and followed by the recovery-induced increase in ΔF/Fm′ and decrease in NPQ. A similar response pattern as ΔF/Fm′to the acute osmotic stress was also observed in the photosynthetic carbon fixation capacity according to radiocarbon(14C) incorporation. Our results indicate that estuarine phytoplankton assemblies could rapidly recover from the acute osmotic stress, implying a potential cause for their frequent blooms in coastal-estuarine waters where despite drastically varying salinity, available nutrients are abundant due to the land-derived runoffs or mixing-caused relaxations from sediments.

Analysis of novel immune-related genes and microsatellite markers in the transcriptome of Paphia undulata

Increasingly,exogenous stressors such as pathogen infections,variable water conditions,and pollution are resulting in high mortality of Paphia undulata,deleteriously affecting the quality of clam harvests.The foot is a burrowing organ in clams.Physical damage and constant contact with the external environment cause the foot to be highly sensitive to pathogen invasion and water condition variation.In the present study,the foot tissue transcriptome was analyzed to identify genes involved in immune and stress responses.The P.undulata transcriptome included 5 286 668 078 bp reads generated by Illumina Hiseq 2000 sequencing and were assembled into 1 785 226 contigs by de novo method.The contigs were clustered into 99 339 transcripts and further grouped into 60 201 unigenes.Of them,22 260 unigenes were successfully annotated using public databases.Twelve genes that were response to immune and stress were identified with abundant expression levels,including heat shock protein 70,cold shock protein,complement C3,cathepsin L,ubiquitin carboxyl-terminal hydrolase L5,and translationally controlled tumor protein.Furthermore,566 unigenes were found homologous to genes involved in the immune response systems of pathogen discrimination,signal transduction,and immune effector,such as lectins,toll-like receptors,complement pathway,toll-like receptor signaling pathway,heat shock proteins,antioxidant enzymes,lysozymes,and mucins,indicating that P.undulata could have a complete set of innate immune mechanisms.In addition,4 270 microsatellite markers(SSRs)were identified from 60 201 unigenes,of which trinucleotide repeats were most abundant and 16 SSRs were tested to be polymorphic.The present study provides a new insight into innate immunity and stress response mechanisms in P.undulata.

The role of Smad6 in immunity of the pearl oyster Pinctada fucata martensii

Inhibitory Smads(I-Smads),which belong to the Smad family and inhibit bone morphogenic protein 2(BMP2)signaling by a variety of mechanisms,can suppress innate immunity responses in vertebrates.However,there are no reports for the role of Smad6 in immunity in mollusks.In this study,we showed that Smad6 of the pearl oyster Pinctada fucata martensii was located in the Smad6 cluster of the phylogenetic tree;mRNA expression of Smad6 and Smad3 was up-regulated after lipopolysaccharide and polyinosinic:polycytidylic challenge;and transcript levels of Smad6 and Smad3 showed opposite patterns during wound healing.Under salinity stress,water inflow and outflow in the gills appear to be regulated by BMP2-Smads signals,and BMP2-Smads signaling may be closely related to the immune response.Our results indicate that Smad6 is involved in immunity,that it plays a positive role in the response to immune challenge and an inhibitory role during wound healing,and that Smad6 and Smad3 may work against each other.

Transcriptomic Analysis and Comparison of the Gene Expression Profiles in Fast- and Slow-Growing Pearl Oysters Pinctada fucata martensii

The pearl oyster Pinctada fucata martensii is an economically valuable shellfish that is cultured for seawater pearl pro-duction,which mainly depends on oyster growth.However,the growth mechanisms of the pearl oyster are still poorly understood.In this study,oysters were grouped with relative growth rate,including fast-growing(FG)group and slow-growing(SG)group.Oxford Nanopore Technologies(ONT)long-read sequencing was applied to investigate the molecular mechanisms involved in the growth of this species.Five alternative splicing(AS)types were analyzed in both FG and SG groups,which include alternative 3’splice site,alternative 5’splice site,exon skipping,intron retention,and mutually exclusive exon.Transcriptome analysis showed that four of five different AS events(excluding mutually exclusive exons)occurred more frequently in FG than in SG oysters,and the five main AS types exhibited different characteristics.The AS events that were detected may be involved in growth,and the difference in ex-pression of AS events between FG and SG oysters may be involved in the mechanism underlying the difference in growth.Fifty dif-ferentially expressed genes(DEGs)were identified between the FG and SG oysters.The results showed that 40 genes were signifi-cantly up-regulated in FG oysters,while 10 genes were significantly down-regulated in SG oyster.Several genes related to nutrient metabolism,shell formation,and immunity were more highly expressed in FG oysters than in SG oysters.In summary,FG oysters exhibited higher metabolic and biomineralization activities and had a more powerful immune system than SG oysters.These results provide insight into the growth of P.f.martensii that can be used to improve breeding programs.

Flexible feeding patterns of copepod Centropages tenuiremis in fluctuating conditions: a possible survival strategy to cope with disturbance

Centropages tenuiremis is a species with a wide distribution range in disturbed coastal waters.However,due to a lack of dietary information,it remains unclear as to how they maintain such dominance in fluctuating conditions.In this study,C.tenuiremis was collected from the Daya Bay Nuclear Power Plant both in inlet and outfall regions at 06:00,12:00 and 18:00 on April 27,2011 and their in situ diet was analyzed using a PCR protocol targeting 18S ribosomal genes.Thirty-four species of prey organisms were identified totally,including Dinophyta,Baciliariophyta,Viridiplantae,Rhizaria,Apicomplexa,Chordata,Mollusca,Arthropoda and Fungi,indicating an obvious omnivorous feeding habit of C.tenuiremis.Centropages tenuiremis obviously exhibited spatial and temporal variations in diet composition.More plant prey(land plants and phytoplankton)were consumed in the morning(~50%),while more animal prey(metazoans and protozoans)were ingested at midday and night(60%–70%).Furthermore,a more diverse diet was detected in the outfall region(10–11 taxa),where the temperatures were relatively higher and more fluctuating,than in the control region(5–10 taxa).This finding indicated that C.tenuiremis could potentially expand its food spectrum under stressful condition.Specifically,C.tenuiremis exhibited phytoplankton preference(58.62%–67.64%)in the outfall region with a lower omnivory index(0.27–0.35)than in the control region(0.51–0.95).However,phytoplankton density was lower than that in the control region,suggesting a possible herbivorous tendency of C.tenuiremis under elevated temperatures to balance the energy acquirement and feeding effort.The flexible food choices of C.tenuiremis observed here could effectively buffer environmental fluctuations and might be an important survival strategy in coastal ecosystems.

Dietary separation between co-occurring copepods in a food-limited tropical coral reef of the Sanya Bay

Food differentiation among coexistent species in the field is important strategy for copepods to acquire materials and maintain population stabilization.In situ diet analysis of co-occurring six copepod species in coral waters of the Sanya Bay was conducted using a PCR protocol based on 18 S ribosomal gene.Various prey organisms were uncovered,including dinoflagellate,diatom,green algae and plant,protozoa and metazoan.All these spatially coexisting six species showed different dietary diversity,with the food niche breadth(B)ranging from 1.00(Temora turbinate in morning)to 10.68(Calanopia elliptica in night).While food overlap between all these copepods were low,with the average value of the diet niche overlap index being approximately 0.09.Even temporally co-existing species sampled from the same time point fed on different groups of prey items with the food overlap index of 0.04 to 0.07 in midday and night but 0 in morning.As the most important dominant copepod in the Sanya Bay,Subeucalanus subcrassus seems to be capable to regulate its feeding,by exhibiting a rhythm of herbivorous feeding in midday and carnivorous feeding in morning and night,to better coordinate with other competitors for utilization of food resources.For most copepods,none of the prey items belonged to the dominant phytoplankton in the ambient water,indicating that copepod can better their survival by widening the choice of potential food resources in food limited environment.The dietary separation observed here might be important strategy for copepod to maintain population stabilization and thriving in the Sanya coastal waters.

Mechanisms of high-frequency dinoflagellate blooms of Scrippsiella trochoidea in Daya Bay,South China Sea

Harmful algal blooms(HABs),such as dinoflagellate blooms,have adverse eff ects on coastal water environments,causing seafood contamination and aquaculture economic losses.Based on historical HAB records data(1983-2017)and phytoplankton data(1982-2008),field investigation and laboratory experiments on frequently bloomed dinoflagellate species,we analyzed the possible mechanisms of high frequency dinoflagellate blooms in Daya Bay,South China Sea.The HAB records data show that the proportion of dinoflagellate blooms increased from 15% before 1994 to 77.27% after 2011.The bloom occurred mostly in summer(57.58%)in Yaling Bay(76.92%).The species inducing dinoflagellate blooms tended to be singular over time,with high proportion of Scrippsiella trochoidea(42.86%-88.88%).Laboratory experiment and field investigation of S.trochoidea bloom showed that this species grew rapidly at 30℃ and 32.1℃(r=0.47,P<0.05),respectively.Results indicate that temperature rise in Yaling Bay was aff ected by nearby nuclear plant effluent,which favored the S.trochoidea bloom.Coincidently,nearly 70% of S.trochoidea blooms occurred in about 7 days after local spring tide and strong wind(wind velocity>7 m/s),which disturbed the resting cysts in the sediment and bring them into surface layer.Taking into account of environmental parameters,algae source,and atmospheric conditions,the probable mechanism of S.trochoidea bloom could be explained.The cysts were resuspended by the spring tide or strong wind,germinated at the bottom layer,reproduced rapidly at higher temperature,and then aggregated in the inner bay(Yaling Bay),resulting the frequent S.trochoidea bloom.Considering the influences of global warming and human activities,it should be taken more attention that dinoflagellate blooms might increase along the coastal waters.