Temporal variability in copepod fecundity during two different spring bloom periods in coastal waters off Plymouth (SW England)

The temporal variation in egg production of the planktonic copepodsCalanus helgolandicus, Temora longicornis and Pseudocalanuselongatus was studied during two different spring bloom periodsin 1989 and 1990 by weekly sampling at two permanent stationsin coastal waters off Plymouth (SW England). Copepod egg productionwas estimated in situ by incubating individual adult femalesin filtered seawater for 24 h (72 h until hatching for P.elongatus)at the field surface temperature. The relationship between copepodegg production rates and: (i) chlorophyll a concentration (totaland >10 µm size fraction), (ii) temperature and (iii)initial copepod gut pigment content was investigated. The springbloom periods were very different in both years, with the occurrenceof a Phaeocystis sp. bloom in 1990, which negatively affectedthe feeding and fecundity of copepods. Egg production ratesin spring 1989 were significantly correlated with chlorophylla concentration (particularly with the >10 µm fraction),field temperature and copepod gut pigment contents. In spring1990, egg production rates were also correlated with copepodgut pigment contents, but no significant correlations were obtainedwith temperature or with chlorophyll a concentration, as a consequenceof the lower egg production rates obtained during the Phaeocystissp. dominance period. These results show that food availabilityis the factor which mainly affects the fecundity of neriticcopepods in short time periods.     

Egg production by Acartia tonsa in Long Island Sound

The egg production of adult Acartia tonsa females in Long IslandSound, NY, during and after the fall bloom, was measured inshort-term (8 h) incubations in natural seawater, and estimatedfrom the egg-ratio method, using preserved samples of eggs andfemales. Egg production, as estimated from the in cubation technique,closely tracked changes in chlorophyll concentration with time.The fecundity estimates from the egg-ratio method were significantlylower than from the incubation method in September but werenot significantly different in October. We suggest that a comparisonof the egg production rates using these two techniques may bea useful way of gaining some insight into the extent of eggpredation in the field. We attribute differences between eggratio and incubation fecundities in September to ctenophorepredation.     

A laboratory study of the effect of non-phytoplankton diets on the reproduction of Calanus helgolandicus

The effect of five non-phytoplankton and one phytoplankton dietson reproduction is described for the copepod Calanus helgolandicusand compared to field fecundity estimates. A fecundity increasefollowed ingestion of larvae of the sea urchin Sphaerechinusgranularis (LSU) and the oyster Crassostrea gigas (OYS) by copepodfemales, whereas a decrease followed ingestion of eggs of thecopepods Acartia and Temora spp. (COP), as a function of proteinconcentration in diets. With larvae of the sea urchin Paracentrotuslividus (SSU) and the dinoflagellate Prorocentrum minimum (PM;standard phytoplankton diet), fecundity was identical. Althoughprotein concentrations differed greatly from one food treatmentto the other, mean fecundity values were rather low. For unknownreasons, and despite their very high protein concentrationsin comparison to in situ, none of these diets could improvefemale fecundity or reach maximum egg production rates reportedin C.helgolandicus. Hatching rates were >80%, stable andsimilar with both PM and COP diets. With SSU, LSU and OYS diets,egg viability was lower than in situ and with PM, showing astrong and mild decrease with time with LSU and SSU, respectively.Ingestion of zygotes of the brown alga Fucus spiralis (ZYG)led to the death of females. These results suggest that denseblooms of zygotes of macroalgae and invertebrate embryos andlarvae, occurring in the continental shelf as part of copepoddiets, could have different effects on the demographic responseof C.helgolandicus.     

Egg size and reproductive allocation in eusocial thrips

Reproductive allocation, in terms of fecundity and egg size,has been given little consideration in eusocial societies. Tobegin to address this, absolute and body size–adjustedegg volumes were compared, along with fecundity, between thefoundress and her subfertile soldier offspring in the eusocial,gall-inducing thrips, Kladothrips hamiltoni, Kladothrips waterhousei,and Kladothrips habrus, and a congeneric, Kladothrips morrisi,with fully fecund soldiers. Soldiers produced significantlylarger eggs than the foundress in all species except K. morrisi,where egg volumes did not differ. After accounting for bodysize, soldiers produced significantly smaller eggs than thefoundress in K. morrisi and marginally so in K. waterhousei,but egg sizes did not differ in K. hamiltoni and K. habrus.When egg size and fecundity data are combined, K. morrisi soldiersinvest less in reproduction than the foundress, and in conjunctionwith other life-history features the species can be consideredeusocial. Maximum likelihood analyses reveal relatively lowreproductive allocation skew in the ancestral lineages and highskew in the derived lineages, but the trend is not significantwhen fecundity and egg size are considered separately. Gallsize covaried negatively with soldier-to-foundress relativebody size–adjusted egg size and reproductive allocationand marginally so with fecundity, suggesting that gall sizeis a determinant of egg size and fecundity trade-offs in eusocialthrips and providing the strongest support to date that gallsize has featured in the social evolution of this clade. Thisstudy highlights that data on fecundity alone may be insufficientfor assessing reproductive division of labor.     

Seasonal reproductive biology of Centropages tenuiremis (copepoda) in Xiamen waters, People's Republic of China

The egg production rate (EPR) and the effects of environmentalvariations on diapause induction in the copepod Centropagestenuiremis in Xiamen waters were studied in 2002 and 2003. TheEPR ranged from 7.33 ± 8.14 (on 18 February 2003) to91.08 ± 20.61 (on 6 June 2003) eggs female^–1day^–1(mean ± 95% confidence limits), and displayed a significantseasonal pattern. Before the period of maximum egg production,EPR increased with seawater temperature and chlorophyll a concentration;but after the maximum, no significant relationship was foundbetween EPR and chlorophyll a concentration, and there was anegative linear relationship between EPR and temperature. Seawatertemperature and photoperiod, respectively, played a primaryrole in the switch to diapause egg production by the femalesas shown by single-factor probit analysis. However, the differencein effect between the two factors was demonstrated by binarylogistic multivariate analysis. These results suggest that thiscopepod rapidly increases subitaneous EPR by taking full advantageof conditions in favorable seasons (winter and spring). SubitaneousEPR decreases and there is a switch to the production of diapauseeggs that survive in the bottom sediments during unfavorableseasons (summer and autumn) in Xiamen waters.     

Reproductive strategies of sub-Antarctic lithodid crabs vary with habitat depth

We present the first fecundity and egg size data for three species of lithodid crab from Antarctic waters south of the Polar Front, caught in the fisheries operating around the island of South Georgia. In all species, fecundity was observed to increase with body size, but reproductive allocation was found to differ significantly between species. The highest relative fecundity (eggs^−g body weight) and smallest egg size was found in Paralomis spinosissima, which is found in shallower waters, whereas the lowest relative fecundity values and largest eggs were recorded in the deeper living species, Neolithodes diomedeae. Evidence is presented that closely related sympatric species may employ quite different reproductive strategies that suit their depth distribution whilst indicating the overriding evolutionary adaptation of reproductive traits to temperature and food availability.     

Food type induces different reproductive responses in the copepod Centropages typicus

Egg production and hatching success were determined for individualCentropages typicus fed two diatoms (Thalassiosira rotula andPhaeodactylum tricomutum) and two dinoflagellates (Prorocen-trumminimum and Gonyaulaxpolyedrd). Both reproductive responseswere strongly affected by food type. Females incubated withoutmales produced eggs with all diets, but fecundity was twiceas high with the larger T. rotula and G.polyedra cells. In contrast,hatching success was 2–3 times higher with the dinoflagellatediets. The presence of males did not enhance egg productionrates. Males also did not improve hatching success when thediet consisted of the diatom T.rotula. However, egg viabilitywas higher for couples fed the dinoflagellate G.polyedra, indicatingthat egg viability was possibly being controlled by both rematingand food type. Egg viability was artificially lowered by exposingnewly spawned eggs to high concentrations (10⁴–10⁹ pgC) of extracts from T.rotula, whereas the development of eggsproceeded normally at all concentrations of extracts from P.minimum.Blockage of egg development was not due to anoxia, but to thepresence of intracellular, deleterious chemical compounds indiatoms, suggesting that bottom-up prey control mechanisms underlieseasonal fluctuations in C.typicus populations at sea.     

Seasonal and fine-scale spatial variations in egg production and triacylglycerol content of the copepod Acartia tonsa in a river-dominated estuary and its coastal plume

We measured egg production rates of the estuarine calanoid copepodAcartia tonsa in Mobile Bay, an estuary in the northern Gulfof Mexico. Two stations were sampled approximately monthly,one at the mouth of the bay and the other just beyond the mouthin the salinity front between bay and coastal waters. Over thewhole year, temperature was the most important environmentalvariable controlling egg production. Rates increased with temperatureup to 30°C and 140 eggs female^–1 day^–1. We foundno evidence of food limitation. There was no correlation betweenegg production and phytoplankton abundance, nor increased eggproduction in response to supplements of phytoplankton addedto natural food, suggesting that non-phytoplankton food wasimportant in the diet. At the highest egg production rates,the amount of the storage lipid triacylglycerol (TAG) in adultfemales was greatly diminished, to <50 ng female^–1.This suggests that lipids in the diet can be very tightly coupledto egg production. Both egg production and TAG content of femalesshowed significant variability on spatial scales of 3–15km, especially in relation to the salinity front separat ingwater outwelling from the bay from open coastal water. For organismsthat are using copepods and their eggs as food, this variabilitywould result in a heterogeneous food environment, both in termsof the abundance of food and its nutritional content.     

ADAPTATIONS FOR COLD WATER SPAWNING IN LOLIGINID SQUID: LOLIGO GAHI IN FALKLAND WATERS

Inshore spawning sites of the cold water squid Loligo gahiwere found in the waters of East Falkland (Southwest Atlantic),where there is a major fishery based on this species. Egg massesoccurred in algal beds, often at the outer (seaward) edge, with ambientwater temperatures of 6.5-90C and salinity 33.75- 33.58. They wereattached to the stipes of the kelp algae Lessonia spp. and Macrocystispyrifera from 0.5 m to 2.5 m off the bottom at 8-20 m depths.The overall density of egg masses was low. The egg mass is abundle of elongated gelatinous translucent capsules with eachcapsule firmly attached to the kelp stipe at its basal end.The capsules are mainly 50-60 mm in length and contain an averageof 70 fertilized eggs. Sampled egg masses consisted of 4-161 capsulesand from 138 to 11,487 eggs. Large egg masses (. 50 capsules) wereapparently formed by several females at different times, as embryosin different capsules were at various stages of development.Eggs laid in winter are significantly larger than those laidin summer. In comparison with tropical and temperate Loligo spp.L. gahi have short egg capsules containing a small number of eggs,but the eggs (2.2-2.5 mm diameter) and hatchlings (3.1-3.4 mm mantlelength) are large. These are probable adaptations for cold waterspawning and development. (Received 30 March 2000; accepted 5 June 2000)     

Naupliar growth versus egg production in the calanoid copepod Centropages typicus

Growth rates of the copepod Centropages typicus were assessedduring May 1998 in the Alboran Sea. The goal of the work wasto compare field growth rates of juvenile (artificial cohortmethod) and adult copepods (female egg production rates) underan extensive range of natural conditions. The results showedthat adult and juvenile growth rates were similar in some stations,while in others no such relationship was apparent. In contrastto the common belief that juvenile growth may be saturated undernatural conditions whereas adults may be food-limited, in mostof our study, adult growth rates were greater than juveniles.We discuss these results in the light of food availability atthe surveyed stations. In summary, the assumption that copepodgrowth rates estimated through egg production rates of adultsare equivalent to juvenile growth is not always valid.     

Latitudinal variation in fecundity among Arctic charr populations in eastern North America

Variation in fecundity was examined from 32 populations of Arctic charr Salvelinus alpinus in eastern North America covering a range of 37° latitude and extending from Maine, U.S.A., to northern Ellesmere Island in the Canadian Arctic. Populations were classed as dwarf, normal or anadromous and covered a suite of different habitat and climatic regimes. Fecundity varied with fork length ( L _F), with L _F adjusted fecundity differing significantly among populations within each of the morphotypes implying that fecundity was a continuously responsive trait influenced by local environmental factors. Latitudinal variation in fecundity was also evident among morphotypes when the simultaneous effects of both latitude and L _F were controlled. There was a significant trade‐off between fecundity and egg size in two of five populations of anadromous Arctic charr, but no evidence in limited data from either normal or dwarf populations. In contrast with some other studies of fecundity in salmonids, there was no evidence for a latitudinal cline in egg size.     

Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results. 2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood. 3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity. 4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based. 5. Ovaries of host‐deprived females contained fewer eggs at death (at ～29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition. 6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.     

Major changes in fecundity and the effect on population egg production for three species of north-west Atlantic flatfishes

Temporal and spatial variability in fecundity was investigated for three species of north-west Atlantic flatfishes: American plaice Hippoglossoides platessoides , yellowtail flounder Limanda ferruginea and witch flounder Glyptocephalus cynoglossus . Significant log₁₀ linear relationships existed between fecundity and total length ( L _T) for all three species and for all combinations of area (NAFO regulatory areas) and year. Fecundity differed between areas for yellowtail flounder and witch flounder and changed significantly for all three species since the last reported fecundity studies in the region 30–40 years ago. Three populations experienced decreases in fecundity (3LNO American plaice and yellowtail flounder, 3Ps witch flounder), one experienced an increase (3NO witch flounder) and one did not change (3L witch flounder). Significant yearly variability in fecundity at length and relative fecundity existed for all three species within the 6 year sampling period (1993–1998). Estimates of population egg production based on new and historic fecundity data revealed that using the old, invariant fecundity and L _T relationship resulted in overestimation of total annual egg production by up to 24% for 3LNO American plaice and as high as 41% for 3LNO yellowtail flounder. These results clearly demonstrate the variable nature of fecundity for flatfishes in Newfoundland waters and suggest that the use of an invariant fecundity and L _T relationship may result in inaccurate estimates of stock reproductive potential.     

Sexual selection for large male size in a polyandrous butterfly: the effect of body size on male versus female reproductive success in Pieris napi

Sexual selection theory predicts that the larger sex shouldbe that for which fitness increases at the faster rate withsize. In butterflies, as in most invertebrates, females areusually the larger sex, but previous comparative analysis hasshown that relative male size increases with female polyandryamong butterflies. In agreement with this pattern, males arelarger than females in the strongly polyandrous green-veinedwhite butterfly, Pieris napi L., and in this article we assessthe size dependence of reproductive success in both sexes. Inan experiment where virgin males and females were released inthe field, we found no strong association between size and malemating success. However, laboratory experiments showed thatthere was a strong correlation between size and the ejaculatethat the male delivered to the female at mating and that largeejaculates delayed female remating for a longer time comparedto small ejaculates. Moreover, female P. napi utilize male-derivednutrients received at mating to increase their fecundity. Hence,large males sire more offspring both by way of donating morenutrients to female egg production and by way of delaying femaleremating (given that the last male to mate with the female willfather most of the offspring). Laboratory experiments showedthat the association between size and fecundity was low, ornonexistent, among P. napi females allowed to mate only once.However, weak size dependence was found for polyandrous females.We hypothesize that size dependence of female fecundity maybe especially weak among polyandrous butterflies because a fundamentalsource of variation in fecundity relates to their ability tofind nutrient giving males, an ability which may be unrelatedto female size. According to this hypothesis there is a causalassociation between weak size dependence of female fecundityand polyandry, and a strong size dependence of male reproductivesuccess that may underlie the comparative pattern of positivecorrelation between relative male size and polyandry.     

THE RELATIONSHIP OF BODY SIZE AND GROWTH TO EGG PRODUCTION IN THE HERMAPHRODITIC FRESHWATER SNAIL, HELISOMA TRIVOLVIS

Among several other factors, body size has been found to influenceegg production in several species of hermaphroditic snail. Wetested whether this relationship between body size and egg productionexists in Helisoma trivolvis, a freshwater hermaphroditic species.We isolated 50 H. trivolvis from a laboratory population, measuredshell diameter, and monitored egg production for seven weeks.We found a positive relationship between body size and totalnumber of eggs produced, as well as body size and number ofeggs per egg mass. When body size and egg production are linked,it should be adaptive for larger individuals to act as femalesand smaller individuals as males. Since body size is relatedto female fecundity in this species, the relative size of snailsshould determine, at least in part, which individual acts asmale and which as female during copulation. However, the relationshipbetween body size and egg production is not nearly as strongas it is in other snail genera. Other factors such as age, genotypeand previous experience may be important in determining egg-layingcapacity and therefore gender choice in this species. In addition,we found a negative relationship between growth during thisperiod and egg production. This relationship has been foundin other pulmonates, and is evidence of resource allocationtradeoffs. (Received 3 August 2004; accepted 2 August 2005)     

Secondary production of Calanus helgolandicus in the Western English Channel

The objective of this study was to investigate the production of Calanus helgolandicus off Plymouth, Western English Channel, from April to August 1998 comparing a range of different methods. The abundance of all developmental stages from NI to adult was determined. Body carbon and nitrogen and length were measured on individual NVI to adults. Female egg production was also monitored. All developmental stages were generally represented but four main periods of recruitment were determined. Two periods of low egg production were observed on the 13th and on the 27th of July: (i) the first was due to the arrival of newly moulted or not yet fertilised females in the population and (ii) the second low period was possibly due to the senescence of the females. Finally, the total production of C. helgolandicus was estimated using four different methods: the weight increment, the egg production, Huntley and Lopez and Hirst and Lampitt methods. Depending on the methods used, the production accumulated over the period from May 14 to August 10 ranged between 12 and 45 mg C m⁻³.     

Trade-off between egg mass and egg number in brown trout

Individual egg mass and fecundity increased with somatic mass in first time and repeat spawning wild anadromous and freshwater resident brown trout Salmo trutta . The egg mass was larger for similar-sized trout in south (58° N) than mid Norway (63° N), whereas fecundity was higher in mid- than in south Norway, making total gonadal investment similar in the two areas. Repeat spawners had heavier eggs than similar-sized first time spawners. The egg mass of residents was c. 10% larger than that of similar-sized first time spawning anadromous trout. Common garden experiments with offspring of wild anadromous trout showed no significant correlation between egg and somatic mass in first time spawners in two of the three populations studied. In the third population, a slight positive correlation was found. Similar results were found for repeat spawners. In the three populations, fecundity increased significantly with somatic mass in both first time and repeat spawners. Wild and hatchery-reared trout showed negative correlation between egg mass and fecundity when the effect of body size was excluded, indicating a trade-off between the two parameters. In wild trout, this was caused by variation among populations, whereas in hatchery fish, within population variation was observed in egg mass over fecundity. Furthermore, the egg mass of first time and repeat spawners were positively correlated, when adjusted for fish size. Size-specific gonadal investment was significantly higher in wild anadromous than resident trout. There was no significant difference in gonadal investment between first time and repeat spawners in wild anadromous trout. However, in the hatchery-reared trout, gonadal investment was significantly higher at repeat than first time maturation. The hatchery trout did not spawn naturally, but were artificially stripped. Among populations, a part of the variation in egg mass and fecundity is phenotypically plastic, a part appears genetically determined.     

Size-fractionated primary production studies in the vicinity of the Subtropical Front and an adjacent warm-core eddy south of Africa in austral winter

Results are presented of size-fractionated primary productionstudies conducted in the vicinity of the Subtropical Front (STF),an adjacent warm-core eddy, and in Sub-antarctic waters duringthe third South African Antarctic Marine Ecosystem Study (SAAMESIII) in austral winter (June/July) 1993. Throughout the investigation,total chlorophyll (Chl a) biomass and production were dominatedby small nano- and picophytoplankton. No distinct patterns intotal Chl a were evident. At stations (n = 7) occupied in thevicinity of the STF, total integrated biomass values rangedfrom 31 to 53 mg Chl a m^–2. In the vicinity of the eddy,integrated biomass at the eddy edge (n = 3) ranged from 24 to54 mg Chl a m^–2 and from 32 to 43 mg Chl a m^–2 inthe eddy (n = 2). At the station occupied in the Sub-antarcticwaters, total integrated biomass was 43 mg Chl a m^–2.Total daily integrated production was highest at stations occupiedin the vicinity of the STF and at the eddy edge. Here, totalintegrated production ranged from 150 to 423 mg C m^–2day^–1 and from 244 to 326mg C m^–2 day^–1, respectively.In the eddy centre, total integrated production varied between134 and 156 mg C m^–2 day^–1. At the station occupiedin the Sub-antarctic waters, the lowest integrated production(141 mg C m^–2 day^–1) during the entire survey wasrecorded. Availability of macronutrients did not appear to limittotal production. However, the low silicate concentrations duringthe survey may account for the predominance of small nano- andpicophytoplankton. Differences in production rates between theeddy edge and eddy core were related to water column stability.In contrast, at stations occupied in the vicinity of the STF,the control of phytoplankton production appears to be relatedto several processes, including water column stability and,possibly, iron availability.     

Measuring the precision of estimates of total egg production based on plankton surveys

Methods are given to measure the effects of spatial and temporaldifferences in egg production on the precision of estimatesof total seasonal egg production derived from ichythyoplanktonsurveys. The techniques are applied to the results of largescale plankton surveys conducted in 1977 and 1979 off the northeasternUSA. For the three species analyzed (Atlantic mackerel, Scomberscombrus; silver hake, Merluccius bilinearis and yellowtailflounder, Limanda ferruginea). the surveys produced estimatesof total egg production having an average coefficient of variationequal to 31%. Estimates of spawning stock size based on theegg production estimates compared favorably with other independentassessments of stock size. ^*MARMAP Contribution MED/NEFC 83–39.     

A simulation of the distribution of Acartia clausi during Oregon Upwelling, August 1973

The distribution of the estuarine copepod Acartia clausi incoastal waters off Oregon during an upwelling period in August1973 is simulated. A time dependent, two dimensional (x, z,t) model relates maximum offshore extent of the copepod's fourlife stages (egg, nauplius, copepodite, and adult) to intensityof the wind stress driving the upwelling circulation, stagedevelopment time, and mortality. Realistic solutions are obtainedby using actual intermittent wind forcing recorded by an anemometerat Newport. Offshore transport is overestimated when the circulationmodel is driven by theoretical continuous winds, suggestingzooplankton may be washed out of coastal upwelling zones (e.g.off Northwest Africa) which undergo periods of prolonged upwelling. With an accurate model of offshore transport and stage developmenttime, the mismatch between predicted and observed distributionsmay be used to estimate field mortality of the various stages.