Spatial and temporal distribution of mesozooplankton in the Gulf of Aqaba and the northern Red Sea in February/March 1999

The distribution pattern, taxonomic composition and communitystructure of mesozooplankton was studied along a transect with10 positions between the Gulf of Aqaba and the northern RedSea. Five positions were resampled two or three times duringa cruise of RV ‘Meteor’ in February/March 1999.In spite of clear differences in the density stratificationbetween the Gulf of Aqaba and the northern Red Sea, the mesozooplanktoncomposition was very similar: Copepods were by far the mostabundant taxon, contributing 76–95% to the total community.The remainder was composed largely of ostracods, chaetognaths,appendicularians and molluscs. The mesozooplankton of the deeplymixed stations was homogeneously distributed, at all other stationsthe bulk of the mesozooplankton (>70%) was concentrated inthe mixed surface layer with peaks of calanoids, cyclopoidsand appendicularians in the vicinity of the chlorophyll a (Chla) maximum layer. Ostracods and poecilostomatoids dominatedthe layers below. Standing stocks within the total water column(550–1200 m) varied between 93 and 431 x 10³ individualsm^–2 for copepods and 5–76 x 10³ individuals m^–2for other mesozooplankton with highest numbers in the northernGulf of Aqaba, where vertical mixing was deep (400–500m) and Chl a and mesozooplankton distributions homogeneous throughoutthe water column. Towards the south, the mixed depth decreasedfrom 300 m in the central Gulf of Aqaba to 50 m in the Red Sea.Cluster analysis separated three distinct groups of stations,compounding the observed differences between the northern Gulfof Aqaba (Position I) and the other positions. The analysisalso revealed temporal differences between the February andMarch sections of the cruise, indicating the winter–springtransition. The stations sampled in March are characterisedby a higher total abundance and by a higher percentage of appendiculariansand ostracods than the stations sampled in February     

Temporal and spatial changes in body size and reproductive state of Nannocalanus minor (Copepoda) females across and along the Gulf Stream

The temporal and spatial trends of cephalothorax length andreproductive state of adult females of the cosmopolitan copepodspecies Nannocalanus minor are described across the Gulf Streamnear Cape Hatteras. NC. Consistent regional differences anda cross-stream gradient in size were found, with the largestanimals in the Slope Water, animals of intermediate size inthe Gulf Stream and the smallest animals in the Sargasso Sea.Distinct seasonal patterns in size were observed within eachcross-stream region (Slope Water, Gulf Stream and Sargasso Sea)and these patterns followed seasonal changes in environmentalconditions (temperature and sea surface pigment concentration).Body sizes of the Slope Water animals were inversely and linearlyrelated to temperature with no clear relationship to sea surfacepigment concentration, while body sizes of the Sargasso Seaanimals were correlated with pigment concentration (asymptotic,non-linear relationship) with no relationship to temperature.The lack of consistent regional and seasonal trends in reproductivestate suggested that continuous reproduction was a life historytrait for adults of this species. The potential effect of short-term,episodic events on the size distribution and reproductive stateof this species was investigated across and along a Gulf Streammeander during the BIOSYNOP project in 1988. Upwelling of nutrientsmay occur on the trailing flank of a meander, with enhancedprimary and, possibly, secondary production occurring downstreamin the leading flank of the meander. No specific meander effectwas observed for body size. More individuals were reproducingdownstream of the upwelling region, suggesting a response tothe enhanced primary production characteristic of the upwellingregion.     

Gulf Stream warm core rings: phytoplankton in two fall rings of different ages

Warm core ring (WCR) 82-H was sampled in September–October(1982) as a Gulf Stream meander pinched off and became a ring.It is compared with the 3-month-old WCR 81-D, visited September–October(1981). Although the rings have different histories, their phytoplanktonassemblages share some characteristics. Using cluster analysesbased on quantitative group counts, a station from one ringoccasionally clusters most closely with a station from the otherring, showing a similar balance of organisms. The younger ringat the time of sampling, WCR 82-H, had lower diversity, fewershelf species, and greater consistency between stations, exceptfor a high level of Oscillatoria in the meander before the ringpinched off. Interaction with slope water was seen principallyat the ring margin. WCR 81-D, on the other hand, showed a greatdeal of structure, and immediate dilutions with slope waterand the Gulf Stream were apparent, with higher diversity beforeand a week after such interactions. The upper water column ofwarm core rings, although showing evidence of physical mixing,can exhibit stratification of species, even after a storm.     

Phytohydrography,Gulf Stream rings,and herbivore habitat contrasts

The Gulf Stream constitutes a major ecological discontinuity separating two distinct phytohydrographic provinces: the Slope Water and the Northern Sargasso Sea. Differences between phytoplankton assemblages are maximal above well-established seasonal thermoclines. Due to systematic differences in the composition, quantity, distribution, and variability of their phytoplankton assemblages, the upper euphotic zones of the Slope Water and the Northern Sargasso Sea represent very different herbivore habitats. Although the Northern Sargasso Sea has been thought to be a relatively monotonous biogeographic province, within its geographic boundaries Gulf Stream cold core rings constitute largescale floral non-homogeneities. The rings observed differed markedly in species composition from both the Slope Water and the Northern Sargasso Sea. Although species groups isolated by correspondence analysis were not strictly confined to one or another phytohydrographic province they represented ecotypes differing in their apparent ‘responsiveness’ to variation in nutrient concentration.     

Entry of migrating American eel leptocephali into the Gulf Stream system

Abundance, size and depth distributions of American eel(Anguilla rostrata) leptocephali collected in four transects across the Florida Current between the Straits of Florida and Cape Hatteras, North Carolina, were examined in order to assess the relative importance of two migration routes into the Gulf Stream system. A nine-fold increase in the abundance and an increase in the mean length of leptocephali collected in the Florida Current north of the Straits of Florida indicate that most leptocephali enter the Gulf Stream system directly from the Sargasso Sea rather than by a more southern route through the Bahama Islands. Leptocephali were concentrated in the upper 140 m at night and upper 350 m during the day. Wide vertical ranges in daytime collections precluded more refined estimation of vertical distribution. The collection of eight small leptocephali (11 to 17 mm total length) in the western Caribbean Sea is discussed in relation to the origin of leptocephali taken in the Straits of Florida.     

Distinct protistan assemblages characterize the euphotic zone and deep sea (2500 m) of the western North Atlantic (Sargasso Sea and Gulf Stream)

Protistan diversity was characterized at three locations in the western North Atlantic (Sargasso Sea and Gulf Stream) by sequencing 18S rRNA genes in samples from euphotic (< or = 125 m) and bathypelagic depths (2500 m). A total of 923 partial-length protistan sequences were analysed, revealing 324 distinct operational taxonomic units (OTUs) determined by an automated OTU-calling program set to 95% sequence similarity. Most OTUs were comprised of only one or two sequences suggesting a large but rare pool of protistan diversity. Many OTUs from both depth strata were associated with recently described novel alveolate and stramenopile lineages while many OTUs from the bathypelagic were affiliated with Acantharea, Polycystinea and Euglenozoa and were not observed in euphotic zone libraries. Protistan assemblages from the euphotic zone and the deep sea were largely composed of distinct OTUs; only 28 of the 324 protistan OTUs were detected in both shallow and deep sea clone libraries. The diversity of protistan assemblages in the deep sea was distinctly lower than the diversity of euphotic zone assemblages. Protistan assemblages from the Gulf Stream were the most diverse for either depth strata. Overall, protistan assemblages from different stations but comparable depths were more similar than the assemblages from different depths at the same station. These data suggest that particular groups of protistan OTUs formed distinct 'shallow' and 'deep-sea' assemblages across widely spaced oceanic locales.     

Spawning ofConger oceanicus andConger triporiceps (Congridae) in the Sargasso Sea and subsequent distribution of leptocephali

Synopsis Distribution of leptocephali ofConger in the Western North Atlantic Ocean was studied using specimens from our collections, specimens from other collections, and various existing collection records. The presence of leptocephali ofConger oceanicus andConger triporiceps < 30 mm long over deep water in the southwestern Sargasso Sea in autumn and winter implies a protracted spawning period there. The subtropical convergence zone, meandering east-west across the Sargasso Sea, is probably the northern limit of spawning of both species. Spawning may also occur close to the Bahamas and Antilles.C. triporiceps may spawn also in the Caribbean Sea judging by the capture of small leptocephali in the western Caribbean and of the more southerly continental distribution of its juveniles. The claim of Johannes Schmidt in 1931 that the EuropeanC. conger spawns across the North Atlantic into the western Sargasso Sea is probably incorrect, because leptocephali ofConger are rare in the eastern Sargasso Sea and becauseC. triporiceps, with myomere numbers overlapping those ofC. conger, was recently described in the western North Atlantic. With increasing size, leptocephali ofC. oceanicus and a portion ofC. triporiceps spread westward and northward in the Florida Current and Gulf Stream, but larger leptocephali especially ofC. triporiceps are found also in the Caribbean and Gulf of Mexico. Spawning ofC. oceanicus in the Sargasso Sea indicates that adults cross the Florida Current-Gulf Stream, and successful leptocephali cross the current in the opposite direction to colonize juvenile habitat on the continental shelf, a migratory pattern similar to that of the American eelAnguilla rostrata (Anguillidae).     

Patterns of sarcodine feeding in epipelagic oceanic plankton

The range of in situ prey composition was determined in marineplanktonic acantharia, foraminifera and radiolana collectedby divers, and quantitatively compared with the prey available,as determined by surface plankton hauls on cruises in the FloridaCurrent, Gulf Stream and Sargasso Sea. A relatively large percentageof the sarcodines (60% of acantharia, 48% of foraminifera and46% of radiolana) had no detectable prey Of those which hadfed on identifiable prey, there was considerable overlap betweensarcodine species m the types of prey captured. Nevertheless,some partitioning of food resources was evident Foraminiferaconsumed greater numbers of diatoms and copepods than otherprey types, radiolana consumed more tintinnids and mollusc larvae,and acantharia consumed mostly tintinnids. Copepods and theirnauplii dominated the biomass consumed for all three groups,though mollusc larvae were significant for both acantharia andradiolana. The results of parameteric univariate statisticalanalyses earned out on each major predator group and multivariateanalysis on a species-by-speaes basis confirmed that there wasevidence for some partitioning of prey resources among the majorsarcodine predators. The partitioning appeared to follow primarilymorphological rather than taxonomic criteria, however, and mayhave been at least partially a mechanical effect.     

Bioluminescence of sound-scattering layers in the Gulf of Maine

Submersible-based investigations of bioluminescence were conductedin sound-scattering layers (SSLs) in the Gulf of Maine, usingintensified video and dual-beam acoustic methods. Stimulatedbioluminescence in the SSLs was high (3–41 µW sr^–1m^–3 while spontaneous bioluminescence was not detected.The average intensity of individual bioluminescent sources inthe SSLs was 30–200 times greater than the intensity oflight emitters outside the SSLs. The two brightest sources ofbioluminescence were identified as the euphausiid, Meganyctiphanesnorvegica and the cydippid ctenophore, Euplokamis sp. Meganyctiphanesnorvegica formed a SSL within 50 m of the bottom during theday and migrated to the uppermost 30 m of the water column atnight, forming a near-surface SSL. Euplokamis sp., which producedexceptionally intense and long-lasting bioluminescent secretions,occurred within the near-bottom SSL in concentrations up to7 m^–3. Our findings indicate that traditional methodsof identifying the primary light emitters in a region, basedon light measurements from net- or pump-captured organisms,may have underestimated the significant in situ bioluminescencepotential of euphausiids and gelatinous zooplankton. ³ Present address: NOAA/NURP/R-OR2, Silver Spring, MD 20910,USA     

Patterns of planktonic foraminiferal abundance and diversity in surface sediments of the western North Atlantic

Seventy-two core tops and grab samples from the western North Atlantic were analyzed to determine what aspects of planktonic foraminiferal abundance and diversity are most closely related to ocean circulation. Some species appear to be reliable indicators of the Gulf Stream, a warm surface current. Both Globorotalia menardii and Globigerinoides sacculifer have their highest abundances under the main trend of the Gulf Stream. Globorotalia inflata reaches high abundances in the cold slope water north of the Gulf Stream but its distribution is not as continuous as the Gulf Stream indicators.Contoured values of species diversity, the Shannon diversity index, and species equitability also reflect surface circulation. A plot of species diversity (number of species) shows a poorly defined region of high diversity beneath the major trend of the Gulf Stream. Use of the Shannon diversity index enhances and clarifies this region of high diversity. A map of species equitability shows a broad belt of low species dominance (high equitability) beneath the Gulf Stream. North of the Gulf Stream, a tongue of high dominance (low equitability) corresponds to the increased relative abundance of Globorotalia inflata.High diversity of planktonic foraminifera in bottom sediments characterizes the warm shifting surface currents of the Gulf Stream; low diversity is typical of slope and Sargasso Sea waters. Low equitability (high species dominance) indicates either cold currents or gyre center waters. Maps of foraminiferal diversity and equitability for other intervals of geologic time may be useful in tracing the evolution of ocean circulation.     

Oligotrophic waters of the Northwest Atlantic support taxonomically diverse diatom communities that are distinct from coastal waters

Diatoms are important components of the marine food web and one of the most species-rich groups of phytoplankton. The diversity and composition of diatoms in eutrophic nearshore habitats have been well documented due to the outsized influence of diatoms on coastal ecosystem functioning. In contrast, patterns of both diatom diversity and community composition in offshore oligotrophic regions where diatom biomass is low have been poorly resolved. To compare the diatom diversity and community composition in oligotrophic and eutrophic waters, diatom communities were sampled along a 1,250 km transect from the oligotrophic Sargasso Sea to the coastal waters of the northeast US shelf. Diatom community composition was determined by amplifying and sequencing the 18S rDNA V4 region. Of the 301 amplicon sequence variants (ASVs) identified along the transect, the majority (70%) were sampled exclusively from oligotrophic waters of the Gulf Stream and Sargasso Sea and included the genera Bacteriastrum, Haslea, Hemiaulus, Pseudo-nitzschia, and Nitzschia. Diatom ASV richness did not vary along the transect, indicating that the oligotrophic Sargasso Sea and Gulf Stream are occupied by a diverse diatom community. Although ASV richness was similar between oligotrophic and coastal waters, diatom community composition in these regions differed significantly and was correlated with temperature and phosphate, two environmental variables known to influence diatom metabolism and geographic distribution. In sum, oligotrophic waters of the western North Atlantic harbor diverse diatom assemblages that are distinct from coastal regions, and these open ocean diatoms warrant additional study, as they may play critical roles in oligotrophic ecosystems.     

Temporal and spatial distribution of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in the St Lawrence, Canada

The occurrence of the potentially ichthyotoxic dinoflagellateGyrodinium aureolum Hulburt is reported for the first time inthe Lower Estuary and Gulf of St Lawrence. Taxonomic identificationusing an iramunochemical tagging method suggests a close taxonomicproximity between the species found in the St Lawrence and G.aureolumpresent in European waters. In 1993, G.aureolum was observedalong the entire coast of Quebec and in offshore waters of theGulf of St Lawrence. At the coastal stations, G.aureolum showedlarge week-to-week variations, but higher densities were observedduring late August and early September. Bloom concentrations(10⁶ cells 1^–1) were only observed in the GaspéCurrent at Mont-Louis, on the north coast of the Gaspd peninsula.In the central part of the Gulf, G.aureolum was concentratedin the upper 5 m of the stations directly influenced by thefreshwater run-off of the St Lawrence Estuary. Results fromprincipal component analysis indicate that G.aureolum favorsenvironments with high nitrogen recycling activity.     

The Distribution and Ecology of Ariosoma Balearicum (Congridae) Leptocephali in the Western North Atlantic

A total of 4589 leptocephali of the congrid eel, Ariosoma balearicum, were examined from 17 cruises in the western North Atlantic Ocean. Myomere counts made on 915 of these indicated there were two ranges of number of myomeres that appear to be associated with separate spawning populations. Those with the higher range (high count: 128–137) were consistently 70–100mm in length in the Sargasso Sea from February to April and 20–80mm in length in the northern Sargasso Sea and Gulf Stream from September to October. Those with the lower range (low count: 120–130) were rare in the northern and eastern Sargasso Sea where they had consistently greater lengths than high count leptocephali and were most abundant in the Florida Current and Providence Channel. The geographic distributions of size and myomere ranges in relation to hydrography provide strong support for the hypothesis that high count eels found along the South Atlantic Bight (SAB) migrate across the Florida Current to spawn in the northwest Sargasso Sea. This migratory pattern is similar to those of Anguilla rostrata and Conger oceanicus, which use the southern Sargasso Sea for development as larvae. However, the distribution of high count leptocephali suggests that they use the entire Sargasso Sea gyre as a development area as larvae before crossing the Florida Current and recruiting to the SAB. The low count eels inhabiting the Bahamas appear to spawn near the banks and their abundance in the Providence Channel and southwest Sargasso Sea suggests most are retained close to the Bahamas. These two distinct styles of spawning, distribution and recruitment of larvae are hypothesized to be related to the different hydrographic regimes of the two juvenile habitats and the resulting constraints on growth and recruitment of larvae. Vertebral and myomere counts reported from other areas suggest there are distinct populations in other regions of the North Atlantic Ocean.     

Diurnal variations in photosynthetic rates: comparisons of ultraphytoplankton with a larger phytoplankton size fraction

We compared the composition and photosynthetic activity of twosize fractions of phytoplankton during a cruise from the Gulfof Maine to the Sargasso Sea in August 1983. At every station,and at every depth, ultraplankton (defined here as cells passingthrough 3 µm pores in filters) made a major contributionto both the standing crop of chlorophyll and the rate of primaryproduction. Ultraphytoplankton assemblages were dominated byphycoerythrin-rich cyanobacteria. Overall, the ultraplanktoncontribution to total primary production was greatest at lowphoton fluxes: (i) at the beginning and end of the photoperiod;(ii) with increasing depth in the euphotic zone; and (iii) whendaily irradiance was low. The composition of ultraphytoplanktonvaried with depth. Surface (2 m) ultraphytoplankton assemblageswere almost exclusively composed of phycoerythrin-rich cyanobacteriawith smaller (0.2–0.8 µm) cyanobacteria predominating.Below the surface mixed-layer, the proportion of larger (0.8–30 µm) to smaller cyanobacteria increased and the eukaryoticcomponent of the ultraphytoplankton often became important.At two Sargasso Sea stations, the greatest numbers of cyanobacteriawere below the mixed layer at the 1% light level, while themaximum numbers of eukaryotic ultraphytoplankters occurred deeperstill, at the 0.5% light level, coincident with the chlorophyllmaximum. At the bottom of the euphotic layer in the SargassoSea. eukaryotes numerically dominated the ultraphytoplanktonand made a major contribution to the chlorophyll maximum.     

Bioluminescence of the solitary spumellarian radiolarian, Thaiassicolla nucleate (Huxley)

Bioluminescence of the solitary spumellanan radiolanan, Thaiassicollanucltata(Huxley), was investigated with photon-counting radiometryand intensified videography Light emission originated from numerousmicrosouices distributed throughout the extracapsulum and propagatedat a rate of 0 5 cm s^–1. The central capsule was not asource of bioluminescence A single brief mechanical stimulusproduced a flash with a simple waveform, mean duration of 5s,and maximum photon flux of 7 x 10⁸ photons s^–1. Totalmechanically stimulable luminescence was 5x10⁹ photons per organism.Maintained mechanical stimulation caused summation of lightemission that persisted for 18 s at a stirring speed of 2000r.p.m. Lower rates of stimulation increased the period overwhich luminescence was expressed. The response to electricalpulses involved minimal excitation during stimulation, a flashwas produced only after the cessation of stimulation and includedadditional flashes superimposed on the decay of luminescenceThe night-time vertical distribution of T nudeata during May1987 in the northern Sargasso Sea had a subsurface maximum ata depth of 45 m.     

Distribution of chiorophylls and phaeopigments in the Northwestern Atlantic Ocean

During a cruise in the Northwestern Atlantic the distributionsof chlorophylls and phaeopigments were investigated in relationto mesoscale features by high-performance liquid chromatography.Samples were collected from hydrographic Stations and from twoContinuous underway sampling systems fished simultaneously atthe surface (2 m) and at deeper (30–90 m) depths. Highestpigment concentrations were associated with the transitionalzones between Slope Water, the Gulf Stream and Northern SargassoSea. Chlorophyll b occurred in 47% of the samples analyzed andthe dominant chlorophyll a degradation product was phaeophorbidea. Chlorophyllide a was usually found at low concentrationsand phaeophytin a levels were undetectable. Concentrations ofthe various chlorophylls and their degradation products wereused to infer Changes in taxonomic composition, phytoplanktonbiomass and zooplankton grazing pressure across several frontalzones.     

Diel reproduction and vertical distributions of the marine cladocerans, Evadne tergestina and Penilia avirostris, in contrasting coastal environments

Evadne tergestina and Penilia avirostris were sampled duringseveral diel cycles in the well-mixed, turbid Inland Sea ofJapan and the more stratified, less turbid Gulf of Mexico shelf.Parthenogenetic female Evadne contained embryos with pigmentedeyes only at night, and apparently released neonates near dawnor in the morning. There was no significant diel vertical migrationin the Gulf of Mexico, and a ‘reverse’ migrationin the Inland Sea. Female Penilia could contain mature embryosat any time, but were most likely to do so at night. Peniliadid not migrate dielly, and in the Gulf of Mexico was concentratedin a nepheloid layer near the bottom.     

Biomass and size structure of the scyphomedusa Aurelia aurita in the northwestern Black Sea during spring and summer

The abundance, biomass and size structure of the scyphomedusa,Aurelia aurita, was measured during two research cruises tothe northwestern Black Sea (July–August 1995 and April–May1997). Average biomass of Aurelia was relatively constant (132–179g wwt m^–2) throughout the investigation period and similarto previous years. Abundance and biomass at individual stationsappeared to be unrelated to temperature and salinity when thelatter exceeded ~13. Biomass was low at coastal stations inthe plume of the Danube where depth was <20 m and salinitydropped to <11. The spring cruise (April–May) coincidedwith, or just followed the peak of strobilation. The summercruise (July–August) took place near the beginning ofplanulae larvae release. The population size structure was dominatedby small individuals in spring, while large medusae prevailedmainly in late summer. Aurelia was, on average, larger at deepwater stations during summer, suggesting that per capita foodsupply was higher further offshore. The individual body massincreased from spring through summer. Accordingly, the volume(wet wt) to length (bell diameter) relation changed significantly.If all medusae measured throughout the seasons were pooled,volume (V, in cm³) was related to length (L, in cm) accordingto V = 0.08 L^2.71, which is similar to measurements conductedin other coastal areas. In contrast to the common conjecture,we did not find inverse relations between biomasses of Aureliaand the combjelly Mnemiopsis leidyi. Preliminary feeding experimentsindicate that Aurelia may feed upon small Mnemiopsis. The significanceof indirect trophic relations and direct feeding interactionsamong the gelatinous zooplankton in the Black Sea has importantconsequences for the energy flow along the food web and, therefore,needs further study.     

Physiological responses of Sargasso Sea picoplankton to nanomolar nitrate perturbations

A study was conducted in July 1989 at three stations in thenorthern Sargasso Sea, where picoplankton (<1 µm)provided approximately half of the standing crop of chlorophyll.Temporal changes in the position of the nitracline at a singlelocation indicated that the vertical supply of nitrate was notat ‘steady-state’ and phytoplankton distributionstracked the nitracline. Our main experimental objective wasto examine the short-term effects of ecologically significantnitrate perturbations (+20 and +100 nM) on the physiologyof <1 µm communities growing at low (nanomolar)ambient nitrate concentrations. A chemiluminescent nitrate methodwas used to measure the time course (up to 4 h) of nitratedisappearance at in situ irradiance, in parallel with measurementsof photosynthetic ¹⁴CO₂ assimilation. Picoplankton growing at<60 nM nitrate rapidly responded to nanomolar nitratesupplements with luxury consumption and enhanced photosynthesisin proportion to their ambient nitrate environment. Light-saturatedSynechococcus populations from the most nitrate-depleted waters(13 nM) had doubled their cellular rate of photosynthesisafter 4 h, in response to a 20 nM nitrate pulse.     

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.