Fungal parasitism in a copepod population: the effects of Aphanomyces on the population dynamics of Boeckella dilatata Sars

Growth parameters of a Boeckella dilatata (Copepoda: Calanoida)population in Lake Hayes over 16 months were calculated in thepresence and absence of a fungus, Aphanomyces sp. (Phycomycetes:Saprolegniaceae) which kills the eggs and increases mortalityof the females. Parasitism was highest during winter and thefollowing summer when birth rates were depressed by up to 14.3%.When the incidence of Aphanomyces is high, parasitism couldbe important in regulating the growth of a copepod population.     

Relationships between fecal pellet production and feeding in the calanoid copepod Boeckella

The number, size (mm³ pellet ^–1) and total volume of fecalpellets produced (mm³ h^–1) by Boeckella titicacae increasedwith concentration of Chlorella and natural seston in threedifferent lakewaters from Bahia de Puno and Lago Grande of LakeTiticaca and nearby Laguna Arapa. The three lakewaters differedin the size and number of fecal pellets produced at seston concentrations>0.5 mg dry wt l^–1. However, the total volume of fecalpellets egested varied little. Large-sized food (>10 µg)resulted in larger pellets but smaller total fecal production.Food concentration had parallel effects on the production offeces and on feeding rates. Both fecal production and feedingincreased linearly with food concentration with saturation between5 and 7.5 x 10⁵ Chlorella ml^–1 (3.7–5.6 mg dry wtl^–1). Varied responses in fecal production when fed differentsize fractions of lake seston suggest Boeckella has a complexand flexible feeding behavior. Feeding preferences of B.titicacaeand B.occidentalis (Ivlev index) for two seston size fractionsare generally reflected by fecal production.     

Omnivory and predation impact of the calanoid copepod Boeckella poppei in a maritime Antarctic lake

The copepod Boeckella poppei is a major species in high latitude lakes of the Southern Hemisphere. In such lakes the reduced diversity of metazoans contrasts with a rich microbial assemblage, making these systems amenable to the study of predation controls on the microbial food web. However, the diet of B. poppei is subject to conflicting reports, with little information on feeding rates. We incubated this species in water from Sombre Lake, a much-studied maritime Antarctic Lake on the South Orkney Islands, in order to quantify its feeding rates and potential impact on the microbial assemblage. Overall, clearance rates were similar across 4 experiments spanning November 1999–March 2000, but increased with prey size over the range of 2.7–18 μm equivalent spherical diameter (esd). B. poppei fed omnivorously, although small phototrophic flagellates comprised the bulk of the diet because of their overwhelming dominance in the incubation water. Larger motile preys—heterotrophic ciliates of ~18 μm esd—were cleared fastest (mean 555 ml mg⁻¹ dry mass day⁻¹) and at equivalent rates to those found for freshwater and marine copepods of similar size and at similar temperatures. Estimated predation impact on the microbial food web varied with the abundance of copepods; these were ~30-fold greater in March than in December. In March even the relatively abundant B. poppei (1.7 adults l⁻¹) had a negligible impact on nanoflagellates, due to the low clearance rate on these small cells. However, in March, B. poppei adults were estimated to clear 24% of the lake water of ciliates daily. Given the generation time of ciliates (1.6 days measured in a previous summer study), and the fact that other larval stages of B. poppei were not assessed, this species has the potential to control this part of the microbial assemblage in Sombre Lake.     

The productivity and carbon budget of a natural population of Daphnia lumholtzi Sars

D. lumholtzi in Lake Samsonvale, Queensland, Australia, is a small species (max. size approx. 7 µgC) that occurs in low abundance (max. abundance 6400 m^–3), with an average daily biomass of 3.32 mgC m^–3. Its annual rates of carbon assimilation, production and respiration, are 166, 110, and 56 mgC m^–3 y^–1 respectively. Annual biomass turnover (annual production/average daily biomass) is 33 and production efficiency is 50–66%. The population may consume 1.65–2.20 mgC m^–3 daily, equivalent to about 1% of the average daily standing crop of phytoplankton. Clutch size is small, 2 eggs, but represents 30–80% of a female's weight. A female may only produce 8–10 offspring in a full lifespan, nevertheless egg production may account for 56% of total production. The population shows autumn and spring peaks in abundance, and is believed to oversummer (4 months) as ephippia.     

A seasonal carbon budget for a laminarian population in a Scottish sea-loch

Employing in situ SCUBA methods a seasonal carbon budget has been established for aLaminaria saccharina population in a Scottish sea-loch. Concurrent studies of photosynthesis, secretion rates, reserve fluctuations and frond growth were undertaken. Net annual production is in excess of 120 g C m^–2 yr^–1. Over 13% of gross carbon input is released as extracellular secretions (over 30% in autumn) and 40–50% is lost by distal decay, entering detrital food chains. The large concentrations of laminarin, synthesised in summer months, are nearly all lost in autumn-winter distal tissue loss and therefore not available for early spring growth.     

Ontogenetic changes in copepod behaviour: an ambush cyclopoid predator and a calanoid prey

The behaviour of the predatorMesocyclops thermocyclopoides andprey Eodiaptomus japonicus was observed in their several developmentalstages. Late copepodid M.thermocychpoides preyed on late naupliarand early copepodid E.japonicus. M.thermocyclopoides showedambush behaviour, and was not detected by E.japonicus beforeattack. Detection frequency by M.thermocyclopoides increasedas development of E.japonicus advanced. However, late copepodidsof E.japonicus were avoided by juvenile and adult female M.thermocyclopoides,and were probably recognized as mates by adult males. Neithertemperature nor the presence of other food affected the predator-preybehaviour Present address: Department of Biology, Faculty of Education,Kanazawa University, Marunouchi, Kanazawa, 920 Japan     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Multiscale patchiness of the calanoid copepod Temora longicornis in a turbulent coastal sea

We present evidence that intermittent variability in zooplanktonabundance can be characterized in terms of multifractals. A3-min-resolution time series of abundance in the calanoid copepodTemora longicornis, taken from a fixed mooring in the coastalwaters of the Eastern English Channel for 66 h, provided thedata for our analysis. The multifractal nature of the distributionof T. longicornis abundance appears to be very different fromthose of purely passive scalars (i.e. temperature and salinity),and also from phytoplankton biomass over a similar range ofscales in similar environments. Finally, we show that the multifractaldistribution of T. longicornis can be wholly described by threebasic parameters in the framework of universal multifractals,opening up very large perspectives for future modeling of pelagicecosystem structures and functions.     

Seasonal variability in the individual carbon content of the calanoid copepod Acartia bifilosa from the northern Baltic Sea

The seasonal variation in the carbon content of the calanoid copepod Acartia bifilosa was studied in the northern Baltic Sea. Monthly length-weight relationships were followed from November 1990 to October 1991 by analysing the organic carbon content of individuals, using a high temperature combustion method. The monthly length (L) on carbon (C) regressions of copepodites were best described by power functions (C = aL^b), where 75% to 88% of the variation could be explained by length. Nauplii length explained less of their carbon content (63–71 %). The carbon content per length was highest in summer when the nutritional situation was good and temperature at its highest. However, the carbon-length regressions differed significantly between months, except in winter, when two subsequent months had similar regressions. The results pointed out the importance of seasonal variation as well as the risk of making errors if biomass estimates based on length on carbon regressions are used. Carbon analysis should, if possible, be done on every sample or should at least be tested as to whether the regressions are consistent with the study material before estimations are calculated.     

The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 10⁵ cells mL^?1 (about 10 mg C L^?1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L^?1). 2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated. 3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle. 4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time. 5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch^?1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch^?1, produced 5.6 clutches and lived 37 days on average. 6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs. 7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.     

The ecology of the calanoid copepod Eurytemora affinis in salt marsh tide pools

We describe selected aspects of the ecology of the copepod Eurytemora affinis in tide pools of an inland salt marsh near L'Isle-Verte, Québec along the southern shore of the St. Lawrence estuary. E. affinis performed daily horizontal migrations moving from the centers of pools to the banks and into dense algae. Male E. affinis were mainly found in the center of the pools during twilight (21 : 00 hrs) and in dense algae in daylight (12: 00 hrs) whereas most females and copepodites were found near the banks at all three sampling periods. Although these daily movements among sites may have minimized predation by diurnally foraging sticklebacks (Pisces: Gasterosteidae), other explanations for the movements can not be excluded. We also quantified the effects of fish predation upon the population structure of E. affinis. Densities of all stages (nauplius, copepodite, adult) were significantly lower in pools with fish than in pools without fish. Female E. affinis were significantly smaller (mean length) in pools with fish than in pools without fish, indicating that the sticklebacks selectively ate larger females. Male-biased sex ratios were found in both types of pools, which excluded the possibility that biased ratios in this species are caused by selective predation upon the females.     

Spatial and temporal variations in calanoid copepod distribution in the Straits of Malacca

The distribution and abundance of planktonic calanoid copepods were studied from samples collected at 13–20 stations during four oceanographic cruises (pre- and post- monsoons, and during northeast (NE) and southwest (SW) monsoons) performed between 1998 and 2000 in the Straits of Malacca. Space and time variations of calanoid copepods were described using univariate (number of species, diversity indices, abundance) as well as multivariate (MDS, ANOSIM, SIMPER) techniques from the Plymouth Routines in Multivariate Ecological Research (PRIMER) package. There were significant differences in abundance between the cruises. k-Dominance curves also revealed significant differences in the relative species abundance distributions among the monsoon periods, and a decrease in diversity from northern to southern parts of the Straits during each cruise. Multi-dimensional scaling revealed four groups of abundances with differences in species composition. Evidence from analysis of similarity (ANOSIM) suggested that the differences in communities among monsoon periods were significant, although spatial differences among samples in geographic locations in the northern, central and southern parts of the Straits were insignificant. These differences resulted from an overall change in the balance of relative abundance of few dominant species, rather from changes of many species. Similarity percentage analyses (SIMPER) indicated that the major species contributing to the average dissimilarity between monsoons varied temporally.     

Effects of food quality on individual growth and development in the freshwater copepod Boeckella triarticulata

To quantify the demographic effects of food quality, and specificallyof the ‘poorquality’ cyanobecterium Anabaena flos-aquae,we reared individual Boeckella triarticulata (Copepoda, Calanoida)on two diets (monospecific Cryptomom sp. versus mixed Cryptomonas-Anabanmadiets) and quantified individual growth and developmental trajectoriesby examining exuviae produced at each molt, from hatching tomaturity. Size at molting was less variable among individuals,within and between diets, than age. Food quality had significanteffects on male sizes at molting and on stage-specific dailygrowth rates of both sexes; these effects were strongest duringlate naupliar and all copepodite stages Tke med Cryptomonas-Anabaenadiet significantly slowed development, particularly of copepoditestages. As a consequence of these effects, individuals raisedon the mixed diet were smaller and older at maturity. Withina given diet, individual differences explained much, if notmost, of the variation exhibited in growth and development.By following growth and development of a large number of individualsthroughout their Life cycles, we show that individual femalesproduce variable offspring, indicative of a bet-hedging life-historystrategy, and that B.triarticulata (like other calanoids) cangrow, develop and survive on diets that include ‘poorquality’ cyanobacteria. ¹Present address: Department of Biological Sciences, Universityof Rhode Island, Kingston, RI 02881, USA     

Diet changes in the carbon and nitrogen content of the copepod Metridia lucens

Diel changes in the near-surface (0–50 m) abundance, prosomelength, and carbon and nitrogen content of the copepod Metridialucens were measured in Deep Cove, Doubtful Sound, New Zealand(45°27'S, 167°9'E) between 3 and 6 September 1996. Metridialucens showed maximal abundance a night, suggesting a patternof normal diel vertical migration (DVM). The change in abundancesuggested that the descent of the population occurred –1h prior to dawn and the ascent –1 h after dusk. However,a proportion of the population remained near the surface duringthe day. Although there was no diel pattern in the prosome lengthof M.lucens collected near the surface, there was a marked dielcycle in the measured carbon and nitrogen contents, with maximalvalues being measured towards the end of the night prior tothe downward migration. We suggest that this diet cycle in themeasured elemental content was caused by DVM occurring morestrongly in those animals which had a better body condition,i.e. a higher elemental content per unit length.     

Phytoplankton and zooplankton population dynamics and production of a recently formed African reservoir

The study provides a 2.5 year record of Rhenosterkop Dam (KwaNdebele, South Africa) plankton population dynamics and production in relation to physical and chemical changes which occurred during the trophic depression and stabilization phases of the reservoir. The mean volume of the reservoir was 4% of full storage capacity. Water temperatures ranged from 14 °C to 27 °C. Due to inorganic suspensoids, the euphotic zone averaged 2.6 m. An anaerobic zone developed each summer. The nitrogen, soluble reactive phosphorus (SRP) and silica concentrations did not displaya seasonal pattern, but the latter two nutrients declined over the study. The dominant phytoplankton group was the cryptophytes while the zooplankton population was dominated by crustaceans. Chlorophyll a concentrations ranged from 1.1 to 27 mg m^–3 and were positively correlated to silica and SRP concentrations and inversely with NH₄-N concentrations. Primary production ranged from 22.6 to 375 mgC m^–2 h^–1; changes in A_max were positively correlated to silica and SRP concentrations. Total zooplankton dry weight biomass varied from <0.5 to >4 mg l^–1. Annual zooplankton (secondary) production was 8 to 15 gC m^–3 a^–1; both primary and secondary production were greatest in the first 12 months of study and remained at low levels for the remainder, similar to the trends for silica and SRP. The data indicate that the reservoir shifted from eutrophic to mesotrophic during the study, typical of events in new reservoirs, and that changes in the plankton populations were largely the result of changing nutrient concentrations.     

Diurnal depth-wise and seasonal changes of physico-chemical factors in Sathiar reservoir

The various physico-chemical factors such as rainfall, depth, water spread, temperature, dissolved oxygen, pH, redox potential, alkalinity, total phosphorus, nitrate, kjeldahl nitrogen and dissolved organic matter were studied both diurnally and seasonally and depth-wise for the period from April 1977 to March 1978. Consideration of physico-chemical factors indicates that they are inter-related. The main characteristics of Sathiar clearly indicate that it is highly eutrophic.     

The swimming behavior of the freshwater calanoid copepods Limnocalanus macrurus Sars, Senecella calanoides Juday and Epischura lacustris Forbes

The swimming behavior of the freshwater calanoid copepods Epischuralacustris, Senecella calanoides, and Limnocalanus macrurus wasexamined using a videotape analysis technique. E. lacustrisand S. calanoides alternate between periods of slow glidingand passive sinking. L. macrurus does not exhibit sinking behavior;its swimming activity consists of slow and steady gliding interruptedoccasionally by jumps. All three copepods exhibit behavioralresponses when exposed to prey organisms, as expressed by anincrease in the duration of sinking for E. lacustris and S.calanoides, a decrease in sinking speed for S. calanoides, anda less circuitous swimming path for L. macrurus. These behavioralchanges may allow the copepods to allocate more time for preydetection, to be less detectable by potential prey and to reducethe frequency of path re-crossing. The results demonstrate therelationship between the swimming and feeding behavior of calanoidcopepods and are consistent with previous findings that copepodshave the ability to modify their foraging behavior in responseto changes in food conditions.     

The spatial population structure of a harpacticoid copepod community in spring

The spatial population patterns of an assemblage of meiobenthic harpacticoid copepod species were analysed for two sets of samples resulting from a systematic survey of an intertidal, estuarine, sandy beach in spring. The fauna was characterised by mesopsammic species, the 6 most abundant of which showed a great degree of interassociation, such that they could not be considered to distribute themselves independently. Populations of each of the 6 species were overdispersed, such that a negative binomial distribution adequately fitted all population samples. Spatial segregation of closely related species was indicated during the late spring sample, so leading to a patchy population distribution. It is proposed that during early spring, during periods of extreme disturbance in the seasonal r-selecting environment, the species populations do not interact, but that during periods of less extreme perturbation an interactive community evolves.     

Biomass and production of Argyrodiaptomus furcatus,a tropical calanoid copepod in Broa Reservoir,southern Brazil

The biomass and the production of Argyrodiaptomus furcatus (Sars), the most abundant copepod in Broa Reservoir (São Carlos, São Paulo State), were estimated, determining in the laboratory the development time and the quantity of organic carbon and establishing the relationship between these two parameters. The daily production was calculated from P = B(1- e^gt) and the annual production was obtained by integrating daily production against time. The maximum production of Argyrodiaptomus furcatus in the reservoir depends on the region considered and on the period of the year. The maximum production was 45.15 mg C m^–3d^–1 in March, 1976 at station II, region of macrophytes and 6.74 mg C m^–3d^–1 at station IV, near the dam. The mean production for the year is 6.26 mg C m^–3d^–1 at station II and 1.43 mg C m^–3d^–1 at station IV.     

Temperature and population density determine reservoir regions of seasonal persistence in highland malaria

A better understanding of malaria persistence in highly seasonal environments such as highlands and desert fringes requires identifying the factors behind the spatial reservoir of the pathogen in the low season. In these ‘unstable’ malaria regions, such reservoirs play a critical role by allowing persistence during the low transmission season and therefore, between seasonal outbreaks. In the highlands of East Africa, the most populated epidemic regions in Africa, temperature is expected to be intimately connected to where in space the disease is able to persist because of pronounced altitudinal gradients. Here, we explore other environmental and demographic factors that may contribute to malaria''s highland reservoir. We use an extensive spatio-temporal dataset of confirmed monthly Plasmodium falciparum cases from 1995 to 2005 that finely resolves space in an Ethiopian highland. With a Bayesian approach for parameter estimation and a generalized linear mixed model that includes a spatially structured random effect, we demonstrate that population density is important to disease persistence during the low transmission season. This population effect is not accounted for in typical models for the transmission dynamics of the disease, but is consistent in part with a more complex functional form of the force of infection proposed by theory for vector-borne infections, only during the low season as we discuss. As malaria risk usually decreases in more urban environments with increased human densities, the opposite counterintuitive finding identifies novel control targets during the low transmission season in African highlands.