Egg production and hatching success in the calanoid copepods Calanus helgolandicus and Calanus finmarchicus in the North Sea from March to September 2001

Spatial and seasonal egg production rates (E_r) and egg hatchingsuccess in the copepods Calanus finmarchicus and Calanus helgolandicuswere measured in the North Sea from March to September. Foodavailability was monitored by chlorophyll and protist concentrationsand three size fractions of seston fatty acids. Seasonal andspatial distribution and production differed between the species.Calanus finmarchicus was found only offshore of the 50-m isobath,with decreasing E_r (37–28 eggs female^–1 day^–1)from March to July. Calanus helgolandicus had two abundancepeaks, in spring and autumn, with a low in May during whichtime the highest E_r were observed (38 eggs female^–1 day^–1).At other times, E_r in C. helgolandicus remained lower than inC. finmarchicus (     

Egg production of the marine,planktonic copepod,Calanus pacificus Brodsky: Laboratory observations

When acclimated to a continuous, superabundant food supply and constant temperature, Calanus pacificus Brodsky females produce eggs at a weight-specific rate ranging from 0.13 · day^?1 at 8°C to 0.21 · day^?1 at 15°C. Maximum weight-specific egg production rates do not change with seasonal changes in female body size. The relationship between egg production rate and food concentration is hyperbolic, with threshold and critical concentrations that are high relative to other species for which data are available. Food concentration and temperature influence spawning frequency (i.e., the time required for oocytes to mature) much more than the number of eggs in a single spawning event (i.e., clutch size). Clutch size is significantly related to female body size.     

Egg development and hatching success in alpine chironomids

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Seasonal fluctuations in fecundity and hatching success in the planktonic copepod Centropages typicus

A mismatch of {small tilde}2–3 months was observed betweenreproductive rates and population abundances in the planktoniccopepod Centropages typicus, with the highest production atrelatively low female abundance and low production at high abundance,during the course of a 2 year study in 1989 and 1990 in neriticwaters of the Gulf of Naples. During this period, egg mortalitywas at times severe, with values as high as 59% in February1989. The seasonal trend in percentage hatching success didnot match seasonal fluctuations in breeding intensity, and wasnot correlated with variations in environmental variables suchas temperature and chlorophyll a. The results of experimentsusing the fluorescent dye Hoechst 33342 showed that unhatchedeggs had been fertilized and that in most cases developmenthad proceeded to an advanced stage before death of the embryo.The causes of high egg mortality are uncertain, but here wegive evidence, for the first time, that egg mortality may notonly be due to infertility caused by failure to remate.     

Effect of essential dietary fatty acids on egg production and hatching success of the marine copepod Temora longicornis

The calanoid copepod Temora longicornis and its food (seston of size < 200 μm) was sampled during three successive seasons (2002-04) in the Trondheimsfjord, Central Norway. Egg production (24 h) and hatching success (72 h) was determined by incubation experiments, and the essential fatty acid (EFA) content of their in situ food was analysed. The dominant EFA in the seston were DHA (22:6n-3) and EPA (20:5n-3), whereas ARA (20:4n-6) were present in low quantities. Egg production and hatching success was relatively low during early spring and late autumn (~ 10 eggs female^- 1 day^- 1 and ~ 30%), and relatively high during summer. Spring phytoplankton, dominated by diatoms, contained low amounts of DHA. Dinoflagellates, small flagellates, and ciliates dominated during summer, when a high content of DHA was recorded.The rate of egg production of T. longicornis did not show any relationship with food concentration (r² = 0.003), but was positively correlated to temperature, although not statistically significantly (r² = 0.48, p = 0.05). The quantitative and percent DHA contents of the food was significantly related to the rate of egg production (r² = 0.96 and 0.95, respectively, p < 0.001), but no such relationship were observed for the quantitative or percent content of EPA and ARA in the seston. The egg production of T. longicornis during May-August was 43-47 eggs female^- 1 day^- 1, with dietary DHA contents higher than 7-8 mg DHA g^- 1 DW. Also the hatching success of T. longicornis was positively correlated to the quantitative content of DHA in the diet (r² = 0.88), but hatching was also inversely related to the percentage ARA (r² = 0.84). The maximum hatching success was found when the ARA content was < 0.15% of total fatty acids and the DHA:ARA ratio was > 50. The conclusion that DHA most strongly affected egg production whereas ARA affected hatching, fit well with earlier findings for fish. Our results do not exclude that toxic aldehydes interact with reproduction of calanoid copepods when diatoms are present, but we observed a consistent pattern where dietary DHA and ARA alone explained a majority of the variability in egg production and hatching of T. longicornis.     

Egg production, growth and development of the cyclopoid copepod Oithona similis

Egg production, growth and development rates of Oithona similiswere measured in the laboratory as a function of food concentrationand composition. On an optimum diet, development is isochronaland growth is near exponential. The maximum juvenile growthrate at 15C (0.2 day^–1) is similar to juvenile growthin calanoid copepods. The maximum weight-specific egg productionrate (0.1 day^–1), on the other hand, is substantiallyless than in free-spawning calanoids, but similar to that inegg-carrying calanoids. In the Kattegat, Oithona spp. egg productionis strongly limited by food during summer and controlled bytemperature during winter. The seasonal signal in fecundityand population biomass is much weaker than in the co-occurringfree-spawning calanoid genera, where fecundity and populationbiomass undergo dramatic seasonal viaration. ¹Present address: Instituto Nacional de Investigacin y DesarrolloPesquero, INIDEP, CC 175, Playa Grande, Mar del Plata, Argentina     

Egg production and growth rates of Calanus euxinus (Copepoda) in the Black Sea

Egg production rates (EPRs) of Calanus euxinus were measuredin the Black Sea during October 2000 and May 2001. EPRs weregenerally low, on average 1.7 eggs female^–1 day^–1in October 2000 and 3.9 eggs female^–1 day^–1 in May2001. The relationships between EPRs and gonad maturity, depth-integratedchlorophyll a (Chl a) and mean surface layer temperature wereexamined. The EPRs were not related to depth-integrated Chla, but were negatively correlated with temperature. EPRs werestrongly related to the proportion of mature females. Growthrates of C. euxinus were derived from the EPRs. The mean growthrate was 0.011 day^–1 in October 2000 and 0.03 day^–1in May 2001. Growth rates were not significantly correlatedwith Chl a concentrations, but were negatively related to femaleweight and temperature.     

Zooplankton feeding ecology: does a diet of Phaeocystis support good copepod grazing, survival, egg production and egg hatching success?

The bloom-forming alga Phaeocystis is ingested by a varietyof zooplankton grazers, but is thought to be a poor source offood. We examined copepod grazing on solitary Phaeocystis cellsby adult females of Temora stylifera, and survival, fecal pelletproduction, egg production and egg hatching success in Calanushelgolandicus and T. stylifera over periods of 15 consecutivedays. Phaeocystis cell concentrations were high (1.2–3.6x 10⁴ cells ml^–1 for C. helgolandicus and 2.5–7.9x 10⁴ cells ml^–1 for T. stylifera), but within the rangeof maxima recorded for natural blooms. Both copepods survivedwell and continuously produced fecal pellets (indicating continuousgrazing) on a diet of Phaeocystis. However, egg production ratesfor both copepods were low, even though hatching success ofthe few eggs produced was high. Clearance rates for T. styliferawere higher than for most previous measurements of other copepodsfeeding on Phaeocystis solitary cells at lower cell concentrations.We conclude that even though copepods feed well upon Phaeocystis,resulting poor fecundity on this diet may inhibit copepod populationincreases during blooms, thereby contributing to the perpetuationof blooms. However, the high egg hatching success on this dietargues against Phaeocystis containing chemical compounds thatact as mitotic inhibitors reducing copepod egg viability, suchas those found in some other phytoplankters.     

Egg production rates of the neritic marine copepod Acartia tumida Willey in the Aleutian Archipelago

Acartia tumida, a neritic copepod of the northern North Pacific Ocean and Bering Sea, is an unusually large member of its genus, adult females measuring 2.0–2.4 mm in total length. In the summers of 1986 and 1987 we investigated egg production of A. tumida in nearshore habitats of several islands in the Aleutian Island chain. A. tumida was found within protected embayments, where it could reach adult densities as high as 1000m^–3. Highest egg production rates were measured at Amchitka Island (up to 86 eggs copepod^–1 d^–1 at 6°C), where the phytoplankton was dominated by chain-forming Thalassiosira spp. In situ egg production rates at Amchitka were more than twice as high as maximum rates measured with cultured T. weissflogii, a single cell diatom, or during blooms of chain-forming Chaetoceros spp. at Adak and Kiska Islands. Approximately 12–24 h was necessary for recent feeding to be reflected in egg production. At high food concentrations 75% of spawning occurred at night and in discrete clutches, a pattern not observed at a lower food concentration.     

Effect of food composition on egg production and hatching success rate of two copepod species (Calanoides carinatus and Rhincalanus nasutus) in the Benguela upwelling system

We have analysed the daily egg production (EPR) and hatchingsuccess rates of the calanoid copepods Calanoides carinatusand Rhincalanus nasutus as a function of nano- and microplanktonconcentration and composition in the northern Benguela upwellingsystem off Namibia. Food concentration explained 55% (R. nasutus)to 62% (C. carinatus) of the EPR variability. We found no relationbetween the residuals of the food concentration–EPR regressionand the percentage of the different taxonomic components ofthe nano- and microplankton. Nor was there a relation with theproportion of the diatom Skeletonema costatum that dominatedthe major blooms or with the number of nano- and microplanktonspecies. We conclude that food quality differences could notbe attributed to the relative composition of microplanktonicparticles of the different groups (i.e. taxonomic composition).     

Population genetic patterns of the copepod Calanus sinicus in the northwest Pacific

Mixing zones between aquatic ecosystems are known diversity hot spots, but so far no study evaluated the effect of mixing waters on bacterial metabolism. Samplings were performed in four of the major Amazonian rivers, and aquatic bacterial production (BP) was measured both before the confluences and in the mixing zones downstream of the confluences. BP in mixing zones was higher than before the confluence in 75% of cases, representing an increase ranging from 31% to more than 1,000% of BP. In most of these cases, the confluence zone was formed by aquatic ecosystems that differed in the water type (environmental conditions and limiting nutrients to BP). The proportional contribution of the water from each source in the mixture had no impact on the outcome of BP in the mixtures, while BP in the mixtures peaked after 12 h of mixing, indicating that the increase in BP can continue downstream from the confluence zone. Overall, the results presented here do not contradict the low aquatic bacterial metabolism suggested for most Amazonian waters, but show that this general pattern may be sprinkled with hot spot areas of high bacterial metabolism in the confluence of aquatic ecosystems.     

Omnivory in the calanoid copepod Temora longicornis: feeding, egg production and egg hatching rates

We measured in laboratory experiments the ingestion, egg production and egg hatching rates of female Temora longicornis as a function of diet. The diets consisted of a diatom (Thalassiosira weissflogii), an autotrophic dinoflagellate (Heterocapsa triquetra), and a bacterivorous ciliate (Uronema sp.) given as sole foods, or combinations of these single-food items: diatom+dinoflagellate, diatom+ciliate, dinoflagellate+ciliate, and diatom+ciliate+dinoflagellate. For the three single-item diets, the functional response was similar; i.e., ingestion rate increased linearly with food concentration (food range: ∼25 to ∼600 μg C l⁻¹). When all diets were considered, maximum daily carbon ration (∼70% of body weight) was independent of food type. However, the maximum daily egg production rate (12% of body carbon) was obtained with the diatom diet. For all diets, both ingestion and egg production rates increased with food concentration. Ingestion and egg production rates were affected differently by the interaction of food concentration and food type: at low food concentrations, ingestion rates were highest on diets containing the diatom. At high food concentrations, egg production rates were highest on the two phytoplankter diets and their combination. The presence of the ciliate in the diet did not enhance ingestion rate or egg production. Mixed-food diets did not enhance egg production relative to single-food diets. Hence, dietary diversity did not appear to be particularly advantageous for reproduction. Carbon-specific egg production efficiency (EPE; egg production/ingestion) was independent of food concentration and type, and equaled 9%. Egg hatching success was low (mean<30%) and independent of food concentration and type, and egg production rates. Our results are consistent with previous observations that egg production in T. longicornis is enhanced during diatom blooms. However, the relatively low EPE and egg hatching success suggest that reproduction and recruitment in this study were severely constrained by the biochemical composition of the diet, or the physiological condition of the females towards the end of their season of growth in Long Island Sound.     

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

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

Genetic similarity and hatching success in birds

The ecological correlates of fitness costs of genetic similarity in free-living, large populations of organisms are poorly understood. Using a dataset of genetic similarity as reflected by band-sharing coefficients of minisatellites, we show that bird species with higher genetic similarity experience elevated hatching failure of eggs, increasing by a factor of six across 99 species. Island distributions and cooperative breeding systems in particular were associated with elevated genetic similarity. These findings provide comparative evidence of detrimental fitness consequences of high genetic similarity across a wide range of species, and help to identify ecological factors potentially associated with increased risk of extinction.     

Egg variability and hatching success in the Cape petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Eggs of the Cape petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica, exhibited high variability in volume between females (up to 48%), while for each individual female, both volume and shape of eggs were highly correlated over two seasons. Both female size and body-condition at laying were unrelated to egg-volume in the 'good'season 1991, but larger females produced larger eggs in the 'bad'season 1990, when eggs were smaller on average. In 1991, females in better body-condition, but not larger, started laying earlier. In spite of synchronized laying (75% of eggs laid within five days), egg-volume decreased with laying date. Egg-volume differed significantly between the two years, which could not be explained by changes in the breeding population or timing of breeding. The laying of relatively small eggs and low overall breeding success in 1990 most probably reflected changes in food availability. Overall hatchability was 88% and did not differ significantly between disturbed and control colonies in 1991. Larger and more rounded eggs showed better hatching success, but hatchability was related more to egg-volume whereas hatching rate was related more to egg-shape. As the majority of egg losses were attributable to predation, the hatching rate was influenced by parental performance relatively more than by hatchability. Hence the relationship between hatching rate and egg-shape probably reflects improvement in hatching success with female age/experience, whereas the relationship between egg-size and hatchability suggests effect of egg-size independently of parental traits.     

Light primes the escape response of the calanoid copepod, Calanus finmarchicus

The timing and magnitude of an escape reaction is often the determining factor governing a copepod's success at avoiding predation. Copepods initiate rapid and directed escapes in response to fluid signals created by predators; however little is known about how copepods modulate their behavior in response to additional sensory input. This study investigates the effect of light level on the escape behavior of Calanus finmarchicus. A siphon flow was used to generate a consistent fluid signal and the behavioral threshold and magnitude of the escape response was quantified in the dark and in the light. The results show that C. finmarchicus initiated their escape reaction further from the siphon and traveled with greater speed in the light than in the dark. However, no difference was found in the escape distance. These results suggest that copepods use information derived from multiple sensory inputs to modulate the sensitivity and strength of the escape in response to an increase risk of predation. Population and IBM models that predict optimal vertical distributions of copepods in response to visual predators need to consider changes in the copepod's behavioral thresholds when predicting predation risk within the water column.     

Egg and faecal pellet production rates of the marine copepod Metridia gerlachei northwest of the Antarctic Peninsula

Egg and faecal pellet production rates, and their functional response to food and temperature, were measured for the Antarctic copepod Metridia gerlachei during January 1996. The study area comprised the Gerlache and Bransfield Straits and Drake Passage. The highest rates of “in situ” egg and faecal pellet production were observed in Gerlache stations, coinciding with chlorophyll a concentrations approaching food saturation levels. In the Bransfield and Drake stations, with very low chlorophyll concentrations, the rates of egg production were either very low, or no eggs were produced. Egg production rates, although well correlated with “in situ” chlorophyll values, appeared to be independent of food concentration on a short time-scale (24-h incubations), while the production of faecal pellets was closely related to food abundance in the same experiments. In general, the rates of egg production were low, even at food saturation, with a very high individual variability. Although in the majority of Gerlache stations about 50% of total chlorophyll a corresponded to the phytoplankton size-fraction >10 μm, M. gerlachei feeds preferentially on the <10-μm fraction. Temperature had no clear effects on egg production rate but had a significant effect on pellet production rates, with maximum values at 2.5°C. These features appear to agree with the reproductive strategy attributed to the species, based on a relatively low rate of egg production extended over a long reproductive period. Received: 18 November 1996 / Accepted: 24 March 1997     

Egg incubation time and hatching success in tench Tinca tinca (L.) related to the procedure of egg stickiness elimination

The experiment showed different results after a short (2 min) enzyme alcalase Merck EC 3.4.21.14 (5.0 ml L^?1 concentration) treatment of tench eggs in contrast to the traditional methods of eliminating egg stickiness involving milk solution (50 g L^?1) treatment for 70 min followed by the addition of a talc suspension (33 g L^?1) for 10 min or treatment by fine clay suspension (20 g L^?1) for 60 min or talc suspension (33 g L^?1) for 80 min. The alcalase enzyme treatment resulted in decreased egg stickiness compared with the conventional milk/clay/talc treatments, indicated by lower duration of egg incubation and higher hatching rates (anova for hatching rate, P < 0.0084). The highest hatching rate (93.2%) was achieved using the enzyme; the lowest (31.3%) was using a talc suspension (control hatching rate was 86.2%). Duration of egg incubation at degree‐days (D°) after enzyme treatment (58.6 D°) was about 4–5 h shorter than the classical method using milk solution and talc suspension (63–65 D°). Prolongation in the latter classical method may also be explained by a hardening of the egg envelopes.     

Egg production of the copepod Acartia tonsa: The influence of hypoxia and food concentration

Low dissolved oxygen conditions, or hypoxia, occur in estuaries and impact more than just the obvious commercially important species. Copepods are an important link in the food web, and the influence of hypoxia upon them is relatively unstudied. Using the copepod Acartia tonsa, a study of the impact of hypoxia on egg production was conducted. A. tonsa had reduced egg production at low dissolved oxygen concentrations (DO), with the lowest egg production occurring at 0.53-ml/l O₂ concentration. Another experiment was conducted to determine if, by increasing food concentration, the affect of hypoxia could be mitigated. The results indicate that increased food did not offset the impact that hypoxia had on egg production of A. tonsa. These results suggest that as A. tonsa experiences hypoxia in the wild, population numbers will decrease. Thus, if hypoxic conditions increase in scope and duration, declines in copepod abundance may lead to a decline in the abundance of species that depend on them as food. These species may be of commercial importance (e.g., fish, crabs, and oysters).