The combined effects of temperature and food supply on Calanus sinicus in the southern Yellow Sea in summer

The effects of temperature and food availability on the lifehistory strategy of the planktonic copepod Calanus sinicus inthe southern Yellow Sea in summer were studied in this paper.The fifth copepodite stage (CV) dominates the population inthe central part of the southern Yellow Sea, where the YellowSea Cold Water Mass (YSCWM) occurs below the thermocline. Incubationexperiments were conducted on CV C. sinicus caught from theYSCWM to examine the effects of temperature and food availability.Temperature at the surface (27°C) is lethal to CVs regardlessof food availability. At the temperature in the middle of thethermocline (18°C), survival time of the specimens dependson food availability, being     

Life history strategies of Calanus sinicus in the southern Yellow Sea in summer

Ecological and physiological features of the planktonic copepodCalanus sinicus in the southern Yellow Sea in summer were studiedto reveal its life history strategy. From the coastal shallowwaters to the central part of the southern Yellow Sea, a shiftof the stage composition occurs from being dominated by theegg-nauplius stage to being dominated by the fifth copepodite(CV) stage. Most CVs reside in the Yellow Sea Cold Water Mass(YSCWM), where both temperature and food abundance are low.CVs in the YSCWM have longer body lengths, heavier body weightsand higher carbon contents than those outside the YSCWM. Onboardincubations show that the development of CVs in the YSCWM issuspended. Energy conservation, development suspension and lackof diel vertical migration (DVM) behavior suggest a diapausestatus for the CVs in the YSCWM, although vertical distributionpatterns indicate the CV individuals are not fully synchronousin physiology and development. This adaptive oversummering strategywould help C. sinicus to live through the warm and food-limitedsummer in the central part of the southern Yellow Sea; bothlow temperature and low food supply are necessary for CV tomaintain the resting state in the YSCWM. Calanus sinicus exhibitsdifferent life history strategies in different regions of thesouthern Yellow Sea in summer.     

Seasonal variation of reproduction rates and body size of Calanus sinicus in the Southern Yellow Sea, China

Annual variations of egg production rate (EPR) and clutch sizeof Calanus sinicus, as well as body size of females (prosomelength and dry weight), were investigated at a series of stationsin the Southern Yellow Sea by onboard incubation. Calanus sinicuswas spawning in all the 11 cruises investigated, and the annualvariation of EPR was bimodal. Monthly average EPR was highestfrom May to July, respectively, 5.97, 5.36 and 6.30 eggs female^–1d^–1, then decreased dramatically to only 1.37 eggs female^–1d^–1 in August and attained the lowest 1.07 eggs female^–1d^–1 in October. In November, average EPR increased againto 4.31 eggs female^–1 d^–1. Seasonal variation ofclutch size was similar to EPR, except that it decreased graduallyafter August rather than dramatically as did EPR. Prosome lengthof females was maximum in May and minimum in October, but dryweight was highest in November. Monthly average EPR correlatedbetter with prosome length than dry weight, while clutch sizewas rather determined by dry weight of females. It is suggestedthat egg production of C. sinicus was active during two discontinuousperiods when both surface and bottom temperature fell into itsfavorite range (i.e. 10–23°C), and different reproductivestrategies were adopted in these two reproductive peaks: otherthan the highest EPR, longer prosome length was also achievedby C. sinicus from May to July, while females in November developedshorter bodies but accumulated more energy for reproduction.     

Spatial distribution of Euphausia pacifica (Euphausiacea: Crustacea) in the Yellow Sea

Euphausia pacifica were collected in the Yellow Sea in summer(August, 1997) and winter (February, 1998), and their distributionwas investigated in terms of the developmental stages in relationto environmental factors (temperature, salinity and chlorophylla). In summer, the water column was highly stratified with athermocline between 10–30 m depth, whereas the water columnwas well mixed in winter. Seasonal variation in temperaturewas large, ranging between 6.3 and 28.8°C in summer and3.9 and 12.2°C in winter. Chlorophyll a concentration changedlittle seasonally but a high concentration was observed in coastalareas. Salinity in the two seasons varied little spatio-temporally.In the studied area and sampling period, E.pacifica was themost dominant euphausiid species (99.7 and 99.8% in summer andwinter, respectively), and comprised adults and juveniles (74.6%in summer and 41.9% in winter), furcilia (17.5 and 44.9%) andcalyptopis (7.9 and 13.1%). The spatial distribution of theE.pacifica population varied seasonally depending on developmentalstage and appeared to be related primarily to the seawater temperatureand secondly to the chlorophyll a concentration, but not tosalinity. In summer, adults were abundant in areas below 10°C,and furcilia and calyptopis above 9°C. In winter, adultswere confined to areas between 7 and 10°C, and furciliaand calyptopis, to areas between 6 and 8°C. Furcilia andcalyptopis were concentrated in the vicinity, or at the centerof chlorophyll a-rich water masses, whereas adults seemed toavoid those water masses.     

Reproductive biology of the planktonic copepod Paracalanus sp. in the Inland Sea of Japan

Egg production of the planktonic copepod Paracalanus sp. wasinvestigated both in the laboratory and in the Inland Sea ofJapan. Its spawning varied daily, but not always, being highestduring the night or around dawn. The egg size was correlatedpositively with female body size. Under food-satiated laboratoryconditions, the specific egg production rate increased exponentiallywith an increase of temperature from 5.0 to 17.5°C, beyondwhich the rate decreased. However, the egg production rate ofthe natural population did not decrease up to     

The China Coastal Current as a driving force for transporting Calanus sinicus (Copepoda: Calanoida) from its population centers to waters off Taiwan and Hong Kong during the winter northeast monsoon period

Calanus sinicus is a copepod with wide geographical distributionin the continental shelf waters of China. Its occurrence inoceans around Taiwan and Hong Kong is limited by temperatureto winter and spring. We present evidence to show that C. sinicusis carried into the coastal waters of Taiwan and Hong Kong frompopulation centers in the Yellow Sea and the East China Seaby the China Coastal Current during the northeast monsoon periodin winter.     

Effect of temperature and food concentration on post-embryonic development, egg production and adult body size of calanoid copepod Eurytemora affinis

Post-embryonic development time, egg production rate and adultbody size of calanoid copepod Eurytemora affinis from Lake Ohnuma,Japan, were determined under six temperature-food conditions(10³,5 x 10³, 10⁴ and 5 x 10⁴ cells ml^–1 at 15°C,5 x 10⁴ cells ml^–1 at 10and20°C) in the laboratory.The measured parameters varied with both temperature and foodconcentration. Development time from hatching to adult femalewas 9.2, 11.4 and 22.8 days at 20, 15 and 10°C respectively,at the highest food concentration. The males developed to adultat one to two days earlier than the females. An effect of foodshortage on development time occurred at the lowest food concentration.This development time was 24.8 days even at 15°C, beingtwice as long as that at the highest food concentration. Prosomelength of these food-limited females was approximately 75% ofwell-fed ones, which reduced by only 10% with increasing temperaturefrom 10 to 20°C. Clutch size (C, eggs clutch^–1) ofwell-fed individuals depended on prosome length of the adultfemale (L, mm), and was expressed as an equation: C = 65.2 L³⁸³. Clutch size of individuals reared at less than 10⁴ cellsml^–1, however, mostly laid below the estimated curve,especially at the lowest food concentration being only 10% ofthat at the highest food concentration. These results suggestthat food availability is a more important factor affectingpopulation growth of E.affinis in Lake Ohnuma than variationof temperature.     

LABORATORY OBSERVATIONS ON THE EARLY LIFE STAGES OF THE DIAMOND SQUID THYSANOTEUTHIS RHOMBUS

The early life stages of the diamond squid Thysanoteuthis rhombusfrom early embryogenesis to post-hatching (0–7 days old)were observed through laboratory incubation using egg massescollected in the southern Sea of Japan. The egg diameter andmantle length increased during embryonic development throughhatching. Mantle-length growth was linear over time, and thegrowth rate was significantly higher at 25°C than at 20°C.The inner yolk was located on the dorsal side of the mantlecavity and increased in volume through hatching. Immediatelyafter they hatched, the hatchlings remained on the bottom ofculture plates with their ventral sides facing up, but 2–3days after hatching they began to swim with their dorsal sidesfacing up. Feeding experiments were conducted, but none of thehatchlings fed. Statolith growth increments were shown to formdaily. Ontogenetic changes that occur from fertilization throughpost-hatching are discussed. (Received 8 June 2005; accepted 2 November 2005)     

Geographic distribution, seasonal life cycle, biomass and production of a planktonic copepod Calarms sinicus in the Inland Sea of Japan and its neighboring Pacific Ocean

The geographical distribution, seasonal life cycle, biomassand production of a copepod Calanus sinicus were investigatedin and around Kii Channel of the Inland Sea of Japan. The distributioncenter of the population was located in Kii Channel. The patternof the seasonal variation in abundance of copepodites and adultsdiffered geographically within the study area. In Kii Channel,for example, they were most abundant in June-July and leastabundant in October. Over the study area, the reproduction ofC.sinicus took place throughout the year, indicating the absenceof diapause phase. In adults, females usually outnumbered males.The prosome length of late copepodites and adults was inverselycorrelated with water temperature. The annual mean biomass washighest (4.87 mg C m^–3 or 231 mg C m^–2) in Kii Channel.The potential production rate of the population exhibited aseasonal variation more or less similar to that of the biomassand the annual potential production rate was 358 mg C m^–3year^–1 (14.1 g C m^–2 year^–1) in Kii Channel.Daily production and biomass (P/B) ratios in Kii Channel increasedfrom 0.11 at 11.8°C to 0.26 at 20°C.     

Laboratory studies on egg and faecal pellet production of Centropages typicus: effect of age, effect of temperature, individual variability

The rates of egg production of individually reared females ofCentropager typicus have been observed from the moulting C5-adultto death under constant conditions of food (10 000 cells ml^–1of Hymenomonas elongara) and temperature (15 and 20°C).Preliminaiy experiments showed that virgin females could produceunfecunded eggs, but that the distinctive spines of the eggsof C.typicus were only obtained after fecundation occurred.High and continuous egg production needs several matings, andthe following experiments were run with a couple. In all experiments,both males and females fed and produced faecal pellets. Thefemales show a high variability in spawning life periods, inspawning rhythms, in daily rates and, consequently, in cumulatednumbers of eggs spawned during their life. The highest dailyrates of egg production were obtained in the first half of thefemale's life, and were as high at 20°C as at 15°C.Nevertheless, the females survived longer at 15°C than at20°C, and finally produced 47.6% more eggs during theirwhole life at 15°C than at 20°C, which can be partiallydue to the difference in size (almost 10% bigger at 15°Cthan at 20°C). The production of faecal pellets occurredduring the whole of life and was more regular than egg production,with a maximum daily rate in the first part of life, and showeda decrease until death. The decline in daily egg productionwith age was parallel to the decrease in daily faecal pelletproduction. The daily production of faecal pellets was higherat 15°C than at 20°C. At 20°C, a good correlationwas observed between the total egg production per female andthe total faecal pellet production per female. The individual-basedegg production rates of our experiments have been compared withrates obtained in different conditions by several authors, andwere lower than in other published studies, probably due tothe food offered. We emphasize the difficulties of comparingresults which have been obtained for the entire life of thefemales with those based on daily egg production. The totalegg production of a female is an important parameter in regardto the population d because it fixes the maximal rate of losses(mortality plus dispersion) for which a population can continueto develop.     

Sex Determination and Sex Ratios in Crocodylus palustris

Incubation temperature determines sex in the mugger crocodile,Crocodylus palustris. Exclusively females are produced at constanttemperatures of 28.0°C through 31°C. At 32.5°C,only males are produced. Both sexes are produced in varyingproportions at 31.5, 32.0, and 33.0°C. Embryo survival isnot affected within this range, but developmental rate and totalincubation time are strongly temperature dependent. In naturalnests laid in breeding enclosures, cool incubation temperaturesproduced only females whereas males were produced only in warmnests. Clutch sex ratios were female or male biased. Yearlysex ratios (=percent male) varied from 0.05 to 0.58; overallsex ratio during six nesting seasons was 0.24 (1 male: 3 females).Sex ratio and incubation time vary with nest location and temperaturein a manner consistent with the constant temperature results.Incubation time decreases with increasing incubation temperature,and is an accurate predictor of sex ratio in the field and laboratory. To date, temperature-dependent sex determination (TSD) has beenreported in five species of Crocodylus and in three speciesof Alligatorinae; but the TSD patterns in these groups differ.The TSD pattern of C. palustris is similar to that of C. porosus.Nesting in C. palustris is synchronized with the seasonal availabilityof thermal regimes suitable for incubation. Resultant sex ratiosare a consequence of when and where eggs are laid. Early nestsare located in warm, sunny sites; in contrast, late season nestsare located in the shade. An egg transplant experiment demonstratedthat sex ratios could be altered by simple manipulations ofnest temperatures in the field. The adaptive significance ofTSD in crocodilians may relate to the influence of incubationtemperature on various hatchling attributes, particularly growth.     

Comparison of egg period, hatching rate, and first-instar nymphs among three species of stonefly

Egg period was compared among several temperature conditions (11°C, 16°C, 20°C, 23°C) in Sweltsa sp., Stavsolus japonicus, and Isoperla aizuana (Plecoptera). The shortest mean egg incubation period was 27.8 days at 20°C in Sweltsa sp., 118.1 days at 16°C in Stavsolus japonicus, and 162.0 days at 20°C in Isoperla aizuana on average. Egg hatching rate was also the highest at the water temperature that provided the shortest egg incubation period. Based on laboratory data, eggs of Sweltsa sp. were considered to be deposited in May and hatched in June in the field. Thus, they must have spent the summer as nymphs in the field. Eggs of Stavsolus japonicus and Isoperla aizuana were considered to be deposited in April to May and hatched in September to October in the field. Visible eyes of Stavsolus japonicus and Isoperla aizuana appeared in August. It is likely that the long egg period of Stavsolus japonicus and Isoperla aizuana reflects that these two species spend the summer as dormant eggs in the field.     

How incubation temperature influences the physiology and growth of embryonic lizards

Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures, being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic production cost of hatchling B. duperreyi (3.52 kJ · g⁻¹) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g⁻¹) than at 25 °C (3.47 kJ · g⁻¹). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling morphology. Accepted: 27 January 2000     

Feeding, excretion and egg production by individuals and populations of the marine, planktonic copepods, Acartia spp. and Centropages furcatus

Diel variations in vertical distribution, gut pigment content,ammonium excretion and egg production were investigated foradult females of Acartia erythraea and A.pacifica in the verticallymixed Inland Sea of Japan and Centropages furcatus in the stratified,neritic Gulf of Mexico. Gut pigment content and egg productionrate were maximal at night and ammonium excretion was maximalduring the daytime. Neither A.erythraea nor A.pacifica adultfemales showed an apparent diel migration, but the former werehighly concentrated in the surface layer during the afternoon.In contrast, C.furcatus adult females showed a clear diel migration,residing immediately above the bottom during the daytime andbeing concentrated between 10 and 25 m depth during the nighttime.Individual-based data on gut content and excretion and egg productionrates were combined with vertical-distribution data to calculatepopulation values. In the Inland Sea of Japan, the resultantpattern for Acartia spp. reflected the diel variation in physiologicalrates and even distribution of adult females, except for theafternoon, surface aggregation of A.erythraea. In the Gulf ofMexico, the pattern for C.furcatus reflected largely the dielvariation in each rate process and the heterogeneous distributionof adult females in the water column. Elevated nocturnal feedingactivity of these copepods may be due to an endogenous rhythm.The daytime maximum in ammonium excretion and night-time maximumin egg production rate indicated approximate half-day and daytime lags, respectively, after the intake of food until itsconversion into dissolved excreta and released eggs.     

Measuring production and viability of eggs in Calanus helgolandicus

The effect of several biotic and abiotic factors on the fecundityand hatching success of Calanus helgolandicus was tested duringshort- and long-term incubations. The results show that thevariations of the reproductive responses of C.helgolandicusare time dependent and rely on the type of factor tested. Whenstandardized over a 24 h incubation period, estimates ofin situproduction and egg viability can be obtained with good accuracy.     

Effects of temperature experienced during embryonic development on biomass and C and N composition at hatching in Palaemon serratus (Pennant, 1777)

In decapod crustaceans, the conditions experienced during embryonic development trigger phenotypic plasticity of the larvae at hatching. The objective of this study was to test the effects of temperature during embryonic development of Palaemon serratus on the phenotypic plasticity of hatching larvae. We incubated egg-bearing females from eggs laying to hatching at four temperatures (10, 15, 18 and 20°C). Weight, carbon and nitrogen contents were measured on newly laid eggs and on freshly hatched larvae. The duration of embryonic development was negatively correlated with incubation temperature. At 20°C, all females abandoned their eggs during development. Incubation temperature had no effect on the weight and the percentage of N of the larvae at hatching, while it did affect their percentage of C and their C/N ratio. Embryos incubated at 10°C seemed to produce larvae with fewer lipid reserves than those incubated at 15 and 18°C. They probably overconsumed their lipid reserves to compensate for the metabolic losses due to the low temperature. These results provide information on the link between maternal investment per egg and larval development in P. serratus.     

In situ egg production and hatching success of the marine copepod Pseudocalanus newmani in Funka Bay and adjacent waters off southwestern Hokkaido, Japan: associated to diatom bloom

. Clutch size and egg viability were examined for wild femalesof Pseudocalanus newmani collected from four different stationsinside and outside Funka Bay, southwestern Hokkaido, Japan,during pre-phytoplankton-bloom conditions in 1997, and froma single station outside the bay during the period from pre-to post-blooming seasons in 1998, to examine spatio-temporalvariability of the reproductive parameters and to detect deleteriouseffects of diatom blooms on in situ copepod reproduction. Clutchsize and hatching success in P.newmani were relatively similarat the four stations in 1997. The eggs almost always hatchedcompletely, but deformed nauplii occurred in 20–40% ofthe cases. The proportion of deformed nauplii gradually decreasedwhen the females were fed on non-diatom Pavlova sp. in the laboratory,suggesting that the occurrence of deformed nauplii was relatedto the quality of in situ food particles, including diatoms.Clutch size varied from 12 to 30 eggs female^–1 duringthe study period in 1998; more than 90% of the variation couldbe explained by the body size of the females which dependedon ambient water temperature. Hatching success also varied,from 15 to 80%, but was not related to either clutch size, femalebody size, water temperature or diatom biomass. These resultssuggest that not only egg production but also hatchability shouldbe measured routinely when estimating recruitment of the copepodinto the planktonic population, and show that neither clutchsize nor egg viability are directly affected by diatom biomass.Although we could not obtain clear evidence of in situ deleteriouseffects of diatoms on abnormal embryos and nauplii, this mightbe related to methodological problems and properties or characteristicsof prey–predator interactions. Also, deformities of copepodnauplii have not yet been observed for reasons other than feedingon diatoms.     

Effects of Temperature on the In vivo Assay of Nitrate Reductase in some C3 and C4Species

Nitrate reductase (NR) activity was measuredin vivo in differentcrop species at 25–60 °C. Highest NR activity wasobserved at 40 °C in pigeon pea, cowpea, sunflower, sesameand sorghum, 45 °C in maize and 50 °C in bajra. At higherincubation temperatures NR activity declined in all species.In mung bean the optimum incubation temperature varied withthe season. In the summer crop of mung beans, NR activity wasmaximum at 50 °C while in the rainy season crop 30 °Cwas the optimum incubation temperature. NR in sesame was relativelyheat-tolerant. The results indicate that 30 °C is not theoptimum incubation temperature for all crop species. Nitrate reductase, temperature, in vivo assay     

Delayed Egg Hatching and Semivoltinism in the Nearctic Stonefly Megarcys signata (Plecoptera: Perlodidae)

Delayed egg hatching can influence the survival of aquatic insects by reducing exposure to competitors, predators, parasites, or unfavorable environmental conditions. We examined egg development in a Colorado population of the stonefly, Megarcys signata (Plecoptera: Perlodidae), whose larvae inhabit high altitude streams in the Rocky Mountains of western North America. Five-thousand fertilized eggs were collected from 40 different females and incubated in the East River, Gunnison County, Colorado, until late fall, at which time unhatched eggs were transported to incubation chambers in Ithaca, New York. We used three different combinations of photoperiod and temperature (10L:14D, 4°C; 10L:14D, 8°C; 8L:16D, 8°C) in an attempt to induce hatching. Eggs in the treatments with temperatures elevated above normal winter temperatures in the East River (8°C) began developing after 6 months, whereas eggs in the treatment most closely simulating natural stream conditions (4°C) did not hatch after 10 months of incubation. Our data indicate that this population of Megarcys signata has an extended egg stage that persists for almost a year, and that it is semivoltine at these elevations of 2885 and 2895 meters.     

Analysis of the hatching site and migratory behaviour of the swordtip squid (Uroteuthis edulis) caught in the Japan Sea and Tsushima Strait in autumn estimated by statolith analysis

In contrast to the swordtip squid (Uroteuthis edulis) caught in the spring and summer, those caught in the autumn in the Japan Sea and the Tsushima Strait are characterized by thick bodies with large clubs, long tentacles and large suckers. In addition, most females and many males are immature. However, the reasons for these characteristics, as well as the hatching site and migratory behaviour, are not well known. The empirical water temperature of juveniles was estimated at ～17°C through strontium:calcium (Sr:Ca) ratios in statoliths and information on seawater temperature distribution. The ontogenetic variation in Sr:Ca ratios decreased from hatching to 60 days after hatching and then remained stable. The estimated water temperature was ～21°C after 60 days. Thus, individuals of the autumn-migrating group most likely hatch in the southern East China Sea in the winter and early spring and then move north-eastwards with currents and pass through the Tsushima Strait into the southern Japan Sea during or after July. However, the squid could be present in these waters without strong currents northeast of Tsushima Island, where thermoclines occur during summer, and become confined in limited layers until vertical mixing occurs in the autumn. The distribution of the squid would thereafter extend to fishing grounds in the southern and south-eastern Japan Sea and then to the Tsushima Strait. This migratory behaviour could be the cause of the observed characteristics because bottom seawater temperatures are much lower in the Japan Sea than in the East China Sea.