Response Of Intertidal Benthic Foraminifera To Temperature And Salinity

Intertidal benthic foraminifera are the important component of microbenthos with high biomass and play an important role in the material circulation and energy flow of benthic microbial food web.Simultaneously,it is a very important carrier in palaeoenvironment and paleoclimate reconstruction of marine studies due to its variety,wide distribution,small size,short life cycle,sensitive responses to environmental changes,and excellent preservation potential in sediment.In this paper,we studied the benthic foraminifera from the intertidal zone of Qingdao Bay with combined research techniques of field study and laboratory culture experiment.Our purpose of this study was to explore the responses of intertidal benthic foraminifera to important environmental factors,temperature and salinity.The main four parts of this study were listed as follows.1.Effects of temperature and salinity on the growth and survive of Ammonia aomoriensisLiving specimens of Ammonia aomoriensis which was common and dominant in the Qingdao intertidal flat were cultured under a fully crossed experiment involving three temperatures(6,12 and 18°C)and four salinities(20,25,30,35 psu)for 28 days.144 specimens in total and 12 specimens for each treatment were cultured individually.We assessed the response of survival,growth and morphological change of A.aomoriensis to temperature and salinity changes by recording the survive,major/minor axis length,and chamber numbers of each specimens respectively every two days.The results showed that the survive of A.aomoriensis responding to temperature obviously,and death occurred earlier and more at 6°C.No significant relationship was observed between survive and salinity.Growth was positively correlated to the temperature while not significantly correlated with salinity.At 18°C which was optimum for A.aomoriensis in this research,every chamber growth took about 3.5–7 days.The growth rates of major or minor axis length were about 0.7–1.3or 1.2–1.9 ?m/day.In addition,A.aomoriensis became more rounded when temperature increasing,so we speculated that the length/width ratio could be used as an indicator of temperature.Interaction between temperature and salinity was significant in the growth of major axis for A.aomoriensis,but not significant in the growth of minor axis and length/width ratio.Compared to salinity,our study indicated that temperature has more significant effects on the survival,growth and morphological change of A.aomoriensis.2.Laboratorial cultured-based impacts of temperature on intertidal foraminiferal communitiesBenthic foraminiferal communities from Qingdao intertidal sediments were cultured at five temperatures(6,12,18,24,and 30°C)under a laboratorial microcosmic condition.The culturing experiment was last for 100 days and four replicates were set up in each temperature treatment.The responses of foraminiferal community parameters(abundance,species richness,Margalef index,Shannon-Wiener diversity,and Pielou's evenness)and species composition to temperature were studied.In total,6771 live(stained)specimens of benthic foraminifera were obtained.Foraminiferal community abundance after culture varied from 75 to 131 individuals/g dry sediment,occurring at 6°C and 18°C,respectively.With rising temperature,most the community parameters increased until 18°C or 24°C but declined when temperature continuously increase.The proportion of live foraminifera in total assemblages decreased significantly with temperature increasing.In addition,species composition was also significantly altered.Temperature has a significantly positive effect on the proportion of porcelaneous taxa,while negative on hyaline type.The dominant species(including Ammonia aomoriensis,A.tepida,and A.beccarii)showed different optimum temperature limits,i.e.,A.aomoriensis showed a broader temperature tolerance and a preferring of lower temperature(6–12°C),while A.tepida preferred higher temperature(18–30°C),and A.beccarii had an intermediate range(12–18°C).Results of morphometric study indicated that the major and minor axes of A.beccarii were significantly increased in higher temperature.In addition,the length/width ratio of three dominant species were significantly reduced and the abnormal rates enhanced with increasing temperature.Our study indicated that temperature rising could significantly alter the community structure and chamber morphology of intertidal foraminifera.3.Responses of intertidal benthic foraminiferal assemblages to salinity changes in a laboratory culture experimentBenthic foraminifera communities from Qingdao intertidal sediments were cultured at six salinity gradients(17,22,27,32,37,and 42 psu)with four replicates under laboratorial microcosmic conditions for 100 days.In total,10324(7471 live and1853 dead)foraminiferal specimens belonging to 24 species were obtained and analyzed respectively.Salinity showed significant effects on foraminiferal community diversity parameters(including species number,Margalef index,Shannon-Wiener index,and Fisher's alpha),but not on abundance.The foraminiferal community diversity showed a maximum at 32 psu which was consistent with field condition and declined obviously with salinity increasing or decreasing from that.In this study,we found an euryhaline foraminiferal assemblage dominant by salinity-tolerant Ammonia aomoriensis,Cribrononion gnythosuturatum,and A.tepida.The abundance and proportion of these three dominant species did not show significant decline when salinity altered.Especially for A.aomoriensis,the proportion showed an obvious increase in brackish or hypersaline waters.Simultaneously,salinity has a significant positive effect on the proportion of Quinqueloculina seminula,while negative on hyaline taxa.Test size of 10,173 foraminiferal specimens were measured.Significant negative correlations were found between the test size of foraminiferal community and salinity.And more abnormal specimens appeared in foraminiferal assemblages when salinity altered from field conditions.Our study indicated that when salinity altered from normal conditions,species diversity decreased with the decline of salinitysensitive population,and foraminiferal assemblages kept high abundance because salinity-tolerant species would fill the unoccupied ecological niche.The growth of foraminifera reduced in hypersaline waters.This work revealed the high adaptability of benthic foraminiferal assemblages to the various and changeable intertidal environment.4.Seasonal variations of benthic foraminifera in a Qingdao intertidal zone and correlations with temperature,salinity and p HBenthic foraminifera in a Qingdao intertidal zone were investigated thirteen times monthly from January 2017 to January 2018.We analyzed of seasonal variations of abundance,diversity,species composition and test abnormality of foraminiferal assemblages.The results showed that the abundance,community parameters,species composition and test abnormal rate of the intertidal benthic foraminifera community in Qingdao Bay showed obvious seasonal changes,which were related to the seasonal changes of temperature,salinity and p H,and the effects of temperature were higher than salinity and p H.The benthic foraminifera community in this region showed higher diversity when surrounding was characterized lower temperature,salinity and p H.When temperature,salinity and p H increasing,the diversity of foraminifera reduced but foraminiferal abundance increased simultaneously.Because the opportunistic species,represented by Quinqueloculina seminula and Ammonia aomoriensis,would grow and multiply rapidly.We also found the obvious different response of foraminifera with different shell types and different dominant species to environmental changes.The porcelaneous taxa represented by Quinqueloculina seminula and the agglutinated taxa represented by Triloculina inflata preferred high temperature conditions,while most hyaline benthic dominant species were less sensitive to changes in temperature and salinity.Cribrononion gnythosuturatum,a common foraminiferal species in the Chinese seas,has shown remarkable adaptability of dramatic seasonal changes of environment factors,such as temperature and salinity.And it has shown higher abundance and proportion in the Qingdao intertidal flats compared with that of five years ago.Combined with the above four parts,the results show that changes in temperature and salinity have significant effects on foraminifera community diversity,species composition and shell morphology.An increase in temperature within a certain range will promote the growth of foraminifera individuals,increase the diversity and abundance of foraminifera communities,and enhance the hyaline group.When temperature increasing,foraminiferal tests tend to become larger and round,and more test become deformities.When the salinity increased or decreased from the field seawater salinity value,the community diversity decreased significantly,the shell deformity rate increased,and the abundance did not change significantly.As the salinity increases,the foraminifera shell tends to become smaller.The preference of different foraminiferal species for temperature and salinity is obviously different.Opportunity species have excellent adaptability to extreme conditions: Quinqueloculina seminula prefers high-temperature and high-salt conditions,Ammonia tepida prefers hightemperature and adapts euryhaline conditions,Ammonia aomoriensis and Cribrononion gnythosuturatum show excellent adaptability to changes of temperate and salinity in a wide range.When the temperature or salinity changes,these opportunistic foraminiferal species will grow and multiply rapidly,occupying the vacated ecological niche.Thus,the foraminifera community abundance maintains high.This is also the reason why the foraminifera community in the intertidal zone of Qingdao Bay has changed significantly compared with the results of field study several years ago.