Life cycle of <Emphasis Type="Italic">Oithona</Emphasis> <Emphasis Type="Italic">similis</Emphasis> (Copepoda: Cyclopoida) in Kola Bay (Barents Sea)

The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population density of O. similis ranged from 110 to 9,630 ind m⁻³ and averaged 1,020 ± 336 ind m⁻³. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature, while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female⁻¹ day⁻¹ and 0.0011 ± 0.003 day⁻¹, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m⁻³ day⁻¹ (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive parameters appeared to be controlled by hydrological factors and food conditions.     

The effects of temperature and salinity on egg production and hatching success of Baltic Acartia tonsa (Copepoda: Calanoida): a laboratory investigation

The functional response of the aspects of reproductive success of a southwestern Baltic population of Acartia tonsa (Copepoda: Calanoida) was quantified in the laboratory using wide ranges in temperatures and salinities. Specifically, daily egg production (EP, # female⁻¹ day⁻¹) was determined for 4 or 5 days at 18 different temperatures between 5 and 34°C and the time course and success of hatching were evaluated at 10 different temperatures between 5 and 23°C. The effect of salinity (0 to 34 psu) on egg hatching success was also examined. The highest mean rates of EP were observed between 22 and 23°C (46.8–50.9 eggs female⁻¹ day⁻¹). When studied at 18 psu, hatching success of eggs increased with increasing temperature and was highest (92.2%) at 23°C. No hatching was observed for eggs incubated at low temperatures (≤12°C) that were produced by females acclimated to temperatures ≤10°C indicating a possible thermal threshold between 10.0 and 13.0°C below which only the production of diapause (or low quality) eggs exists in this population. When tested at 18°C, the hatching success of eggs incubated at 15 different salinities increased asymptotically with increasing salinity and was maximal (81.4–84.5%) between 17 and 25 psu. The high reproductive success observed over wide ranges in temperatures and salinities in this Baltic population demonstrates one of the mechanisms responsible for the cosmopolitan distribution of this species within productive, estuarine and marine habitats.     

Seasonal reproductive biology of the egg-carrying calanoid copepod Pseudodiaptomus marinus in a eutrophic inlet of the Inland Sea of Japan

In situ egg production of the egg-carrying calanoid copepod Pseudodiaptomus marinus was investigated in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan, at 3- to 5-d intervals for a year. This species reproduced throughout the year, and the adults showed a large abundance peak in June/July and a small peak in September/October. Females usually outnumbered males, comprising 61.4% of the annual mean. The composition of ovigerous females varied from 7.9 to 100%, with an annual mean of 55.7%. Adult prosome length was consistently large throughout winter and spring, and decreased with increasing temperature in summer and fall. Egg diameter varied from 98 to 121 μm, and was negatively correlated to temperature. The seasonal variation in clutch size (range: 15.1 to 38.2 eggs) was bicyclical, with peaks in May and December. The egg production rate of breeding females was low in January to March (mean: 2.3 eggs female⁻¹ d⁻¹), while it was constantly high from mid-May to early October (mean: 12.1 eggs female⁻¹ d⁻¹). The specific egg production rate for the breeding females was highly correlated to temperature; it increased linearly from 0.03 d⁻¹ at 9 °C to 0.27 d⁻¹ at 26 °C. Compared to other co-occurring copepods, the reproductive rate of P. marinus was lowest, which is one of the reasons why this species never dominates in this inlet. Received: 11 November 1996 / Accepted: 7 December 1996     

Egg production of Calanus finmarchicus : effect of temperature, food and season

The use of the egg production rate of herbivorous copepods as an important parameter for understanding population dynamics and as an index of secondary production requires knowledge of the regulatory mechanisms involved and of the response to changes in food concentrations and temperature. Furthermore, the effects of season and generation on egg production have to be studied. In this context data are presented for Calanus finmarchicus from the northern North Atlantic. Prefed and prestarved females were exposed to different concentrations of the diatom Thalassiosira antarctica over 1 to 2 wk at 0 or 5 °C, and egg deposition was controlled daily. Egg production increased with higher food concentrations, but much less when prestarved. The effect of temperatures between −1.5 and 8 °C on egg production was studied in females maintained at optimum feeding conditions. Egg production rate increased exponentially over the whole temperature range by a factor of 5.2, from 14.2 to 73.4 eggs female⁻¹ d⁻¹, and carbon-specific egg production by 4, from 2.1 to 8.5% body C d⁻¹. The response to starvation was also temperature dependent. In both the temperature and feeding experiments egg production rate was regulated mainly by changes of the spawning interval, while changes of clutch size were independent of experimental conditions. Different responses to optimum feeding conditions were observed in females collected in monthly intervals on three occasions between March and May. The March females deposited more clutches than the April and May females. In May, >50% of the females did not spawn at all. Maximum egg production rates were never >25% of the rate expected at 5 °C, indicating endogenous control of egg production in addition to food and temperature effects. Received: 4 August 1996 / Accepted: 11 September 1996     

The effects of temperature and salinity on reproductive success of <Emphasis Type="Italic">Temora longicornis</Emphasis> in the Baltic Sea: a copepod coping with a tough situation

At specific locations within the Baltic Sea, thermoclines and haloclines can create rapid spatial and temporal changes in temperature (T) and salinity (S) exceeding 10°C and 9 psu with seasonal ranges in temperature exceeding 20°C. These wide ranges in abiotic factors affect the distribution and abundance of Baltic Sea copepods via species-specific, physiological-based impacts on vital rates. In this laboratory study, we characterized the influence of T and S on aspects of reproductive success and naupliar survival of a southwestern Baltic population of Temora longicornis (Copepoda: Calanoida). First, using ad libitum feeding conditions, we measured egg production (EP, no. of eggs female⁻¹ day⁻¹) at 12 different temperatures between 2.5 and 24°C, observing the highest mean EP at 16.9°C (12 eggs female⁻¹ day⁻¹). Next, the effect of S on EP and hatching success (HS, %) was quantified at 12°C for cohorts that had been acclimated to either 8, 14, 20 or 26 psu and tested at each of five salinities (8, 14, 20, 26 and 32 psu). The mean EP was highest for (and maximum EP similar among) 14, 20 and 26 psu cohorts when tested at their acclimation salinity whereas EP was lower at other salinities. For adults reared at 8 psu, a commonly encountered salinity in Baltic surface waters, EP was relatively low at all test salinities—a pattern indicative of osmotic stress. When incubated at 12°C and 15 different salinities between 0 and 34 psu, HS increased asymptotically with increasing S and was maximal (82.6–84.3%) between 24 and 26 psu. However, HS did depend upon the adult acclimation salinity. Finally, the 48-h survival of nauplii hatched and reared at 14 psu at one of six different temperatures (10, 12, 14, 16, 18 and 20°C) was measured after exposure to a novel salinity (either 7 or 20 psu). Upon exposure to 7 psu, 48-h naupliar mortality increased with increasing temperature, ranging from 26.7% at 10°C to 63.2% at 20°C. In contrast, after exposure to 20 psu, mortality was relatively low at all temperatures (1.7% at 10°C and ≤26.7% for all other temperatures). An intra-specific comparison of EP for three different T. longicornis populations revealed markedly different temperature optima and clearly demonstrated the negative impact of brackish (Baltic) salinities. Our results provide estimates of reproductive success and early survival of T. longicornis to the wide ranges of temperatures and salinities that will aid ongoing biophysical modeling examining climate impacts on this species within the Baltic Sea.     

Life cycle of <Emphasis Type="Italic">Pseudocalanus acuspes</Emphasis> Giesbrecht (Copepoda,Calanoida) in the Central Baltic Sea: II. Reproduction,growth and secondary production

The population dynamics of Pseudocalanus acuspes in the Central Baltic Sea were studied from March 2002 to May 2003 on a monthly basis. All stages were present year round with a stage shift from nauplii to older copepodite stages over the course of the year. Biomass, estimated from prosome length, peaked between May and September with maximum recorded values of 594 and 855 mg C m⁻² in May 2002 and 2003, respectively. Differences in biomass between stations up to a factor of 20 were observed especially in April/May and October. Mean egg production rate (EPR) showed a seasonal course and was highest in April 2002 and 2003 with 3.6 and 2.1 eggs f⁻¹ day⁻¹, respectively, corresponding to a mean weight-specific egg production rate (SEPR) of 0.13 and 0.04. Egg production seems to be limited by food from May on. Stage durations determined from moulting experiments turned out to be extremely long. Maximum growth rates based on stage durations of 15–25 days at 4°C in May and July 2003 amounted for 0.03–0.05 day⁻¹ in CI-CIV. Comparing these rates with rates derived from temperature–development relationships for P. acuspes from the literature resulted in five times higher growth rates for the latter case. Secondary production reached values up to 9.1 mg C m⁻² day⁻¹ (method for continuously reproducing populations) and 10.5 mg C m⁻² day⁻¹ (increment summation).     

Zooplankton growth rates: the influence of female size and resources on egg production of tropical marine copepods

Egg production was measured in 17 species of copepods from the genera Acartia, Calanopia, Centropages, Clausocalanus, Corycaeus, Eucheata, Euterpina, Oithona, Oncaea, Paracalanus, Parvocalanus, Temora and Undinula in Jamaican waters. At the high local temperatures (∼28 °C), mean egg production ranged from 3.2 to 88 eggs female^–1 d^–1, and instantaneous female growth (g, as egg production) ranged from 0.04 to 0.87 d^–1. Female growth was positively related to ambient chlorophyll concentration (r ² = 0.44) and negatively to female body size (r ² = 0.29). Together these two variables explained 60% of the variation in growth. When quadratic terms for chlorophyll and a term for interaction of body size and chlorophyll were introduced, 82% of the variance in growth rate was explained. Egg production rates represent an extension of the resource and size-dependent relationship established for copepodites. In smaller species (<3.5 μg), egg production was comparable to prior copepodite somatic growth; in larger species (>3.5 μg), egg production is compromised at lower resource concentrations than copepodite somatic growth. Thus, it appears that egg production in tropical copepods may be frequently limited by resources in a size-dependent manner. Under conditions where growth is resource limited, we caution against the application of egg production rates for the calculation of total copepod production. Received: 30 May 1997 / Accepted: 13 May 1998     

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod <Emphasis Type="Italic">Rapana</Emphasis><Emphasis Type="Italic">venosa</Emphasis> (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female⁻¹ week⁻¹. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

High reproduction of <Emphasis Type="Italic">Calanus finmarchicus</Emphasis> during a diatom-dominated spring bloom

Feeding, egg production, hatching success and early naupliar development of Calanus finmarchicus were measured in three north Norwegian fjords during a spring bloom dominated by diatoms and the haptophyte Phaeocystis pouchetii. Majority of the copepod diet consisted of diatoms, mainly Thalassiosira spp. and Chaetoceros spp., with clearance rates up to 10 ml ind⁻¹ h⁻¹ for individual algae species/groups. Egg production rates were high, ranging from ca 40 up to 90 eggs f⁻¹ d⁻¹, with a hatching success of 70–85%, and fast naupliar development through the first non-feeding stages. There was no correlation between the egg or nauplii production and diatom abundance, but the hatching success was slightly negatively correlated with diatom biomass. However, the overall high reproductive rates suggested that the main food items were not harmful for C. finmarchicus reproduction in the area, although direct chemical measurements were not conducted. The high population egg production (>1,20,000 eggs m⁻² d⁻¹) indicated that a large part of the annual reproduction took place during the investigation, which stresses the importance of diatom-dominated spring phytoplankton bloom for population recruitment of C. finmarchicus in these northern ecosystems.     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. IV. Pseudodiaptomus marinus, the egg-carrying calanoid

Population dynamics and production of the egg-carrying calanoid copepod Pseudodiaptomus marinus were studied for a year in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was perennial, with a large numerical peak in June and small peaks in September/October and November/December. During the study period, at least 11 generations could be detected. For each generation, the stage-specific survival from egg to Copepodite Stage (C) V was determined; it was very high during early life stages (egg to NIII), and gradually decreased beyond. On average, 94% of eggs recruited into NIII, which is strongly contrasted with very high (>ca. 90%) mortality during the corresponding stages for free-spawning copepods, i.e. Acartia omorii, Centropages abdominalis and Paracalans sp. This demonstrates that the egg-carrying strategy has a great advantage to reduce mortality in egg stage. The biomass of this species showed marked seasonal variations largely in parallel with numerical abundance. The instantaneous somatic growth rate increased linearly with temperature. The population production rate was estimated as the sum of somatic growth of larval stages and egg production of adult females; the annual integration was 51.0 mg C m⁻³ yr⁻¹ or 0.38 g C m⁻² yr⁻¹. Received: 11 November 1996 / Accepted: 7 December 1996     

Calanoid resting eggs in the Baltic Sea: implications for the population dynamics of Acartia bifilosa (Copepoda)

Resting eggs of Acartia spp. (presumably A. bifilosa Giesbr.) at densities between 65 and 125 eggs cm^-2 were found in sediment off the southern coast of Finland and represent the first observations of dormant calanoid eggs in the Baltic Sea. The highest egg densities were found at sediment depths between 4 and 8 cm. The hatching percentage varied between 0 and 90% in the different sediment layers and at different experimental temperatures (13, 16 and 19°C). Some nauplii emerged from the eggs extracted from sediment layers 9 to 10 cm beneath the surface layer and other nauplii emerged from eggs after 82 d of dark storage at 3°C. Light was not needed to trigger hatching; the nauplii were able to hatch in darkness when the eggs were resuspended in filtered seawater. Indirect evidence suggests that the marked spring peak of Acartia spp. nauplii seen in a monitoring data from the years 1973 to 1984 was derived from benthic eggs and not from spawning. The possible mechanisms for induction of hatching and the adaptive benefits of resting egg production for A. bifilosa are discussed.     

Production of tropical copepods in Kingston Harbour, Jamaica: the importance of small species

The copepod community observed during an 18-month period at the mouth of eutrophic Kingston Harbour, Jamaica, was dominated by small species of Parvocalanus, Temora, Oithona, and Corycaeus. Mean copepod biomass was 22.1 mg AFDW m⁻³ (331 mg m⁻²). Annual production was 1679 kJ m⁻², partitioned as 174 kJ m⁻² naupliar, 936 kJ m⁻² copepodite, 475 kJ m⁻² egg and 93 kJ m⁻² exuvial production. All nauplii, most copepodites and many adults, equivalent to half of the biomass and production, were missed by a standard 200-μm plankton net, emphasizing the importance of nauplii and small species in secondary production estimates. The evidence suggests that growth rates and production are generally not food limited, and we speculate that size-selective predation shapes the structure of the harbour community. Biomass and production are higher than previous estimates for tropical coastal waters, but comparable to other eutrophic tropical embayments and many productive temperate ecosystems. Far from being regions of low productivity, tropical zooplankton communities may have significant production and deserve greater research attention than they currently receive. Received: 19 September 1997 / Accepted: 21 October 1997     

Early reproduction and development of dominant calanoid copepods in the sea ice zone of the Barents Sea—need for a change of paradigms?

Reproduction and growth of the dominant copepods Calanus finmarchicus, C. glacialis, C. hyperboreus and Pseudocalanus minutus were studied on transects across the sea ice zone of the northern Barents Sea in May and June 1997. C. glacialis and C. finmarchicus were numerically dominant and also the largest component of the biomass. C. hyperboreus was rather rare. Moderate levels of phytoplankton and eventually high concentrations of ice algae supported maximum egg production rates of 53.6 and 48.5 eggs female^–1 day^–1 of C. glacialis in May and June, respectively. Results of incubation experiments were supported by a tremendous abundance of C. glacialis eggs in the water column ranging from 7×10³ to 4.4×10⁴ m^–2 in May and from 9.8×10³ to a maximum of 9.7×10⁴ m^–2 in June. In contrast, C. finmarchicus spawned only in the vicinity of the ice edge, at a maximum rate of 30 eggs female^–1 day^–1. Egg sacs of P. minutus were often observed in the preserved samples, but contained only few eggs, which may be due to loss during sampling. The presence of considerable concentrations of young stages in May and June indicated successful recruitment of C. glacialis and P. minutus. Back calculation using published stage duration estimates indicates March/April as the begin of the reproductive and growth period for these species under the first-year ice of the Barents Sea. Hence, secondary production in the study area starts at the same time as in open water regions and polynyas in the northern North Atlantic. Although the role of ice algae in the nutrition of copepods was not clarified here, the significant relationship between phytoplankton chlorophyll and egg production of C. glacialis suggests that high reproductive activity has already been achieved at moderate food concentrations.Communicated by O. Kinne, Oldendorf/Luhe     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg⁻¹, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC₅₀s ranged from 32.9 μg l⁻¹ (Zoeae 2) to 10.7 μg l⁻¹ (Mysis 3), and from 3.9 μg l⁻¹ (Zoeae 3) to 2.0 μg l⁻¹ (Mysis 3), respectively; 48 and 96 h  LC₅₀s in postlarvae (PL) at the same salinity ranged from 1.8 μg l⁻¹ (PL1) to 0.6 μg l⁻¹ (PL5), and from 0.3 μg l⁻¹ (PL7) to 0.4 μg l⁻¹ (PL15). In juveniles, 96 h LC₅₀s were 0.8 μg l⁻¹ in seawater and 1.5 μg l⁻¹ in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC₅₀. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion. Received: 7 October 1996 / Accepted: 13 November 1996     

Diet and egg production of the copepod Acartia tonsa in Florida Bay. II. Role of the nutritional environment

 As part of an ongoing study of changes in the trophic pathways of Florida Bay's pelagic ecosystem, the nutritional environment (seston protein, lipid and carbohydrate levels), diet (taxon-specific microplankton ingestion rates) and egg production rate of the important planktonic copepod Acartia tonsa were measured off Rankin and Duck Keys in July and September 1997 and in January, March and May 1998. Rankin Key has been the site of extensive sea grass mortality and persistent ultraplankton blooms since 1987. Duck Key has experienced neither of these perturbations. Protist (auto-plus heterotroph) biomass was approximately twice as high off Rankin as off Duck Key. Diatoms, dinoflagellates and heterotrophic protists dominated the food environment off Rankin Key, while cells <5 μm diam often predominated off Duck Key. Protein and carbohydrate concentrations were higher off Rankin Key than Duck Key, while average lipid levels were usually low at both stations. Ingestion rates at both stations frequently approached temperature- and food-dependent maxima for the species, exceeding 100% of estimated body C d⁻¹ on 3 of 5 occasions off Rankin Key. Egg production rates, however, were consistently low (Rankin: 3 to 16 eggs copepod⁻¹ d⁻¹; Duck: 1 to 12 eggs copepod⁻¹ d⁻¹), and gross egg production efficiencies (100% × egg production C/ingested C) averaged <10%. At Duck Key, egg production rate varied with temperature and food concentration, while off Rankin Key, egg production was strongly correlated with seston protein content. The efficiency with which lipids (which were scarce in the seston) were transferred from the diet to the eggs increased exponentially with decreasing seston lipid content. Egg production efficiencies based on protein, however, were independent of seston protein content and never exceeded 10%. Received: 23 December 1998 / Accepted: 23 March 2000     

Reproductive biology of deep-water calanoid copepods from the Arctic Ocean

Reproductive modes and egg production were studied in 15 species of meso- and bathypelagic copepods from nine Calanoida families in the Arctic Ocean. During shipboard incubation, females of seven species released eggs freely into the water and females of three species produced membrane-bound egg sacs. One species, Aetideopsis rostrata, produced a mass of eggs looking like an egg sac, but the “sac” lacked a membrane and disintegrated within 2 h. Females of four additional species were encountered with membrane-bound egg sacs in the preserved samples. In most families, only one reproductive mode, either egg-carrying (the Euchaetidae, Augaptilidae), or broadcast spawning (the Heterorhabdidae, Spinocalanidae, Scolecitrichidae, Tharybidae, Bathypontiidae) was observed. In contrast, different genera of the Aetideidae family demonstrated different reproductive modes, with broadcast spawning predominant in the benthopelagic species, and both broadcast spawning and egg-brooding in the planktonic species. Clutch size and egg diameter varied widely between species in both broadcast spawners and egg-brooders. In broadcast spawners, the clutch size varied from 1 to 95 eggs female⁻¹, while the average egg diameter ranged from 152 to 440 μm. The clutch size for egg brooders varied between 3 and 82, while average egg diameter varied from 258 to 732 μm. Deep-water broadcast spawners produced much larger eggs compared to surface-dwelling broadcast spawning species. This larger egg size may result in a reduction, or elimination, of feeding during naupliar stages, thereby improving the survival potential of deep-water species.     

Are monoalgal diets inferior to plurialgal diets to maximize cultivation of the calanoid copepod Temora stylifera?

Temora stylifera adult copepods were fed with four different monoalgal diets and six combinations of the same cultures for 15 days. Fecundity, hatching success, number of cannibalized embryos, fecal pellet production, adult mortality and naupliar recruitment were compared, in order to find the best diet for this species. Phytoplankton species tested were Prorocentrum minimum (PRO); Isochrysis galbana (ISO); Tetraselmis suecica (TETRA) and Rhodomonas baltica (RHO) which were supplied alone or in different combinations and at various concentrations ranging from a minimum of 1 mg C L⁻¹ day⁻¹ to a maximum of 66 mg C L⁻¹ day⁻¹. Of the ten diets tested, ISO was the worst and was unable to sustain egg production and adult survival possibly because adults were unable to ingest this alga due to its small size. TETRA was also a poor food since it negatively impacted egg production and adult survival, as well as egg hatching success, possibly due to the lack of essential compounds necessary for optimal embryogenesis. RHO and PRO were the best foods inducing highest egg production, hatching success and naupliar recruitment. Even if mean egg production rates were similar to those obtained with some mixed diets, carbon intake concentrations with mixed diets were from 3 to 33 and from 6.6 to 66 times higher than with RHO and PRO given alone, respectively. Mixed diets of ISO and PRO, especially when supplied at higher concentrations (66 mg C L⁻¹ day⁻¹), had a negative effect on egg hatching success and adult survival, with a corresponding reduction in naupliar recruitment. On the other hand, mixed diets of TETRA and PRO promoted high naupliar recruitment but values were similar to PRO offered alone. Our results indicate that a good monoalgal diet such as RHO and PRO can be as effective as a mixed diet to sustain the mass cultivation of T. stylifera.     

Egg production by the subtropical copepod Undinula vulgaris

Egg production by Undinula vulgaris, collected off Kaneohe Bay, Hawaii, was measured under field and laboratory conditions on 16 occasions from June to December 1991. In situ rates ranged from 0 to 15.7 eggs female^-1 d^-1, with a mean of 6.4 eggs female^-1 d^-1, 2.1% female body carbon d^-1. Maximum in situ production was 53 eggs female^-1 d^-1, 17.2% C d^-1. Average egg production (Y, eggs female^-1 d^-1) was related to the concentration of particulate carbon (X, g C l^-1) by the Ivlev function, Y=13.9[1-e^{-0.0097 (x-10)}], with R ²=0.96. Individuals with the same feeding history produced more eggs at lower temperatures in the laboratory. Egg production was not significantly correlated with dry weight, and no noticeable temporal trend was found. Despite the elevated habitat temperatures (26 to 27°C) of this subtropical copepod, maximum fecundity of U. vulgaris was comparable to, but average rates were lower than, egg production rates of similarly-sized, temperate and borcal species of the genus Calanus. Our results caution against broad extrapolations of the temperature-growth relationship for temperate coastal copepods to species from poorly studied, oligotrophic regions of the oceans.Contribution No. 3257 from the School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA     

Population biology of Dyopedos monacanthus (Crustacea: Amphipoda) on estuarine soft-bottoms: importance of extended parental care and pelagic movements

The suspension-feeding amphipod Dyopedos monacanthus (Metzger, 1875) is a common epibenthic amphipod that lives on self-constructed “mud whips” (built from filamentous algae, detritus and sediment particles) in estuaries of the northern North Atlantic Ocean. The population biology of D. monacanthus at a shallow subtidal site in the Damariscotta River Estuary (Maine, USA) was examined between July 1995 and July 1997. The resident population at the study site was dominated by adult females during most months of the year. High percentages of subadults were found in late summer/early fall. Often, between 10 and 20% of the adult females were paired with males, and the percentage of ovigerous females varied between 40 and 100%, indicating continuous reproduction. The percentage of parental females varied between 40 and 80% during most months, but dropped to levels below 20% during summer/early fall. The average size of amphipods on their own mud whips was ∼4 mm during the summer/early fall, after which it increased continuously to >7.0 mm in March or April, and then dropped again. In March and April, the average number of eggs and juveniles female⁻¹ was ∼100 eggs and 55 juveniles, while during the summer/early fall the average number of eggs female⁻¹ was <20 and that of juveniles female⁻¹ was <10. Many juveniles grew to large sizes (>1.4 mm) on their mothers' whips in winter/early spring but not in the summer/fall. The average number of amphipods at the study site was low in late summer/early fall (<50 individuals m⁻²), increased steadily during the winter, and reached peak densities of >3000 individuals m⁻² in April 1996 (>1600 individuals m⁻² in May 1997), after which densities decreased again. The decrease of the D.␣monacanthus population at the study site coincided with a strong increase of amphipods found pelagic in the water column. This behavioural shift occurred when temperatures increased and benthic predators became more abundant and active on shallow soft-bottoms, suggesting that D. monacanthus at the study site is strongly affected by predation. The effects are direct (by predation on amphipods) and indirect (by reducing duration of extended parental care and enhancing pelagic movements). Both extended parental care and pelagic movements are important behavioural traits of D.␣monacanthus (and other marine amphipods), and significantly affect its population dynamics. Received: 18 January 1998 / Accepted: 27 May 1998