The reproductive potential of copepods in brackish water

The reproductive potential of 3 harpacticoid and 1 cyclopoid copepods, measured by the intrinsic rate of natural increase, was calculated from field data. Calculated values are much smaller than those obtained from laboratory experiments. The difference between species is small and cannot account for differences in occurrence.     

Aspects of water column primary productivity in the Chukchi Sea during summer

Measurements of primary productivity, chlorophyll a, incident solar radiation, phosphate-P, silicate-Si, nitrate-N, nitrite-N, ammonium-N, temperature and salinity were made in the Marginal Ice Zone of the Chukchi Sea in summer 1974. Low to moderate levels of primary productivity (0.07 to 0.97 g C m^-2 half-day^-1) were observed; primary productivity exceeded 3 g C m^-2 half-day^-1 at two stations. Surface primary productivity was nitrogen-limited at most stations. Mean chlorophyll a concentration in the photic zone varied from 0.4 to 17.8 mg m^-3. Higher concentrations and significant subsurface accumulation of chlorophyll a, reaching 40 mg m^-3, were observed in July at stations near the ice-edge than those in open water. No chlorophyll maximum was noted in September, when values ranged from 0.4 to 2.2 mg m^-3. It is postulated that the contribution of sea-ice algae to the total chlorophyll content can be substantial, but that the stay of these cells in the water column may not be long. Non-linear regression estimates from solar radiation and chlorophyll-specific primary productivity data showed a maximal photosynthetic rate of 18 mg C mg chlorophyll a ^-1 half-day^-1, an optimal light intensity of 54 langleys half-day^-1, and markedly reduced primary productivity at moderately higher light intensities. These features indicate that phytoplankton was shade-adapted.     

Heterotrophic flagellates from the water column in Shark Bay, Western Australia

The diversity of heterotrophic flagellates in the water column at Denham, in Shark Bay, Western Australia, was examined in April 1995 by observations of living cells in freshly collected samples, and in enrichment cultures. Observations were also made of cells on whole-mount preparations, using light and electron microscopy. A total of 41 species are described, drawn from the apusomonads, cercomonads, choanoflagellates, cryptomonads, euglenids, heteroloboseids, stramenopiles and groups of uncertain taxonomic affinities (Protista incertae sedis). A new species, Percolomonas denhami, is described and assigned to the Heterolobosea. Three-quarters of the species seen have not previously been reported from southern sub-tropical regions. The biogeography of the species seen in Western Australia is discussed with reference to studies in other localities. It appears that many heterotrophic flagellates have a cosmopolitan distribution. Received: 11 June 1996 / Accepted: 13 December 1996     

Diurnal rhythm of the bioluminescent field in the ocean epipelagic zone

Characteristics of the diurnal rhythm of the bioluminescence field are analyzed on the basis of experimental data obtained in the region around Kamchatka peninsula (50°31′N; 163°50′E). The feasibility of reconstructing the nocturnal structure of the bioluminescence field by measurements made at other times of the day has been demonstrated. Diurnal rhythm parameters for the bioluminescent field of several other studied areas of the ocean have been defined. The temporal parameters feature linear latitudinal dependence. At the equator the boundaries of morning and evening transition periods are 05:06 to 07:30 and 17:48 to 19:54 hrs, respectively. In the Barents Sea in spring these boundaries are 02:42 to 04:06 and 19:48 to 21:12 hrs. Boundary times of diurnal rhythm do not deviate from the linear regression by more than 10%. Received: 21 August 1998 / Accepted 4 March 1999     

Reproductive toxicity of metals in calanoid copepods

This study investigated the effect of exposure route on metal accumulation, tissue distribution, and toxicity in the marine copepods Acartia hudsonica and A. tonsa. Sublethal toxicity was measured as decreases in egg production, hatching rate, ovarian development and protein (yolk) content of the egg. When algal food, exposed to Hg at 1 nM or Cd at 5 nM resulting in cells containing 34 and 64 nmol metal g^-1 dry weight, respectively, was ingested over a 4-h period by copepods, the total copepod body burden increased nine-fold for Hg and two-fold for Cd over background concentrations, and egg production decreased by 50%. Sublethal concentrations of metals were >2 orders of magnitude lower than LC₅₀ concentrations. Hatching rate, ovarian development and egg protein content all decreased following trophic exposure to metals, implying that the process of yolk accumulation (vitellogenesis) was affected. Exposure to dissolved Cd had no effect, but dissolved Hg at concentrations as low as 0.25 nM did affect egg production. Different toxic effects following different exposure routes were related to different metal distributions in the copepods: exposure to dissolved metal resulted in metal deposition in the exoskeleton, whereas exposure to dietary metal resulted in metal deposition in internal tissues. These findings indicate that enrichment of metal concentrations in internal tissues, which occurs primarily after exposure to dietary metal, affects vitellogenesis. The reproduction rate decreases by about 75% at metal concentrations only moderately higher than levels in coastal waters. Toxicity tests involving aquatic animals need to consider effects following uptake by different pathways, including the trophic transfer of metals.     

Morphogenesis of opal teeth in calanoid copepods

Opal teeth of calanoid copepods develop early in the premolt phase of the molt cycle. They form in the apolysis space beneath the old tooth row on the mandibular gnathobase. We examined stages of tooth formation inNeocalanus spp. andCalanus pacificus. Apolysis occurs early in the distal gnathobase, then several epidermal cell types participate sequentially in formation of new teeth. Fibrous molds in the shapes of the new teeth are extruded onto the epidermal surface, then additional materials, probably proteinaceous, are secreted into them. Tooth molds next are linked to a gland in the proximal part of the gnathobase by ducts of an unusual type, lamellar-walled ducts. Silicification follows, apparently using highly osmiophilic material supplied by the proximal gland. Opal is laid down at the outer periphery of the mold then thickens toward the attachment of the mold to newly formed chitin at its base. During apolysis the epidermal cells move proximally without breaking ducts that connect small dermal glands with pores in the sides of the opal teeth. The molds for the new teeth form surrounding these ducts, and new pores result. The glands are like the ciliary exocrine glands seen in other Crustacea, with the duct deriving from fusion of the axonemes of a cilium. Presumably the glands secrete a substance into food newly broken by the teeth. This could be a toxin or a digestive enzyme.     

Diel vertical migration and feeding of copepods at an oceanic site near South Georgia

Twelve Longhurst Hardy Plankton Recorder (LHPR) profiles were taken over a 16 h period in January 1990, in order to study feeding of four copepod species at an Antarctic oceanic site near South Georgia. Vertical distributions of their life stages, as well as those of dominant competitors and predators, are described in relation to the feeding cycles of Calanoides acutus CV, Calanus simillimus CV, Calanus propinquus CV and Rhincalanus gigas CIII, CV and CVI. Comparisons with vertical ring-net catches, which were used for concomitant gutevacuation experiments, demonstrated the suitability of the LHPR for these fine-scale studies. Planktonic predators, with the exception of the diel migrant Themisto gaudichaudii, resided deeper than the herbivores. During the day and around midnight, when feeding rates were low, species and stages reached their maximum vertical separation. At these times, new generation copepodites of the four species lived progressively deeper and the overwintered generation (i.e., R. gigas Stages CIV, CV, CVI) were progressively shallower. During the afternoon or evening (depending on species), all stages older than CII, as well as Euphausia frigida and T. gaudichaudii, migrated upwards, to amass in the surface mixed layer. Feeding was restricted to darkness, although R. gigas commenced several hours before dusk. In detail their migration and feeding differed widely, with combinations of unimodal and apparent bimodal cycles. As a whole, the results suggest that (1) feeding could occur during sinking as well as during upward migrations, (2) upward migrations were not always associated with feeding increases, and (3) individuals appeared to descend after filling their guts.     

Photopigment and spectral sensitivity in the bioluminescent fish Porichthys notatus

Digitonin extracts from retinas of the marine fish Porichthys notatus, from California and Puget Sound (USA), contain a single photopigment with maximum absorbance at 498 nm. In the presence of hydroxylamine the final product of bleaching absorbs maximally at 367 nm, indicating that the photopigment is based on retinal. Spectral sensitivity measurements performed on intact eyes and eye-cup preparations in darkadapted and selectively light-adapted states yield curves which suggest that the retina of P. notatus contains at least 3 different types of receptors. In the darkadapted state, the spectral sensitivity curve has a broad peak, with a maximum between 480 and 500 nm. In the blue and red light-adapted states, in addition to depressing the sensitivity, the shape of the sensitivity curve also changes. Under these conditions new peaks appear which suggest the presence of at least two different types of cones, with sensitivity maxima in the blue and the green regions of the spectrum, respectively. Comparison of the spectral sensitivity curves with the in vivo bioluminescence emission spectrum of the fish gives an especially good correspondence and suggests that the fish is able to perceive the bioluminescence of its own species.     

Temporal and spatial variation in bacterial production in the water column over a coral reef

Production and doubling times of the bacterial populations in the water around and over the reefs at Lizard Island, Great Barrier Reef were measured during summer and winter, 1982 and 1983. Bacterial productivity, determined from the rate of tritiated thymidine incorporation into DNA, was high over the reef flats and a Thalassia hemprichii sand flat (28 to 58 g Cl^-1 d^-1). Bacterial growth rates increased during the day and fell at night over the reef flats and seagrass bed. Growth rates were slower over the reef front and in open water. Doubling times ranged from about 2 d in the open water to about 3 h over the reef flat in summer. As numbers did not increase, grazing was probably intense on the reef flats. Growth rates were much slower in winter. The main source of organic nutrient used by the bacteria was probably mucus released following photosynthesis in the corals. The cyanobacterium Synechococcus sp. was sometimes very numerous, especially in summer when 2×10⁸ cells l^-1 were recorded in one water mass. The number of bacteria was also very high in summer, with values ranging from 1×10⁹ to 2.5×10⁹l^-1.     

Dimorphism and possible sex change in copepods of the family Calanidae

Adult females of 14 of 25 species of the family Calanidae were found to be dimorphic with respect to the number of aesthetases on the first antenna. The trithek morph, in which most antennal segments bear a complement of one aesthetasc and two setae, appears to be the typical female phenotype. The quadrithek morph is less common and, as in males, odd-numbered segments 2b, 3, 5, 7 and 9 carry quadritheks, i.e., two aesthetascs as well as two setae. Segment 21 in the quadrithek female bears an aesthetasc that is absent in the trithek female. Male antennal segments are distinguished from those of trithek and quadrithek females by pronounced morphological differences in aesthetasc shape and size as well as fusion of one or more pairs of antennal segments. The quadrithek morph usually comprised only a small proportion (<10%) of a local population. Quadrithek morphs were found in tropical and subtropical genera (Cosmocalanus and Nannocalanus), broadly ranging genera (Calanoides), as well as in cool-water lineages (Calanus s.s., Calanus s.l. cristatus, C. s.l. plumchrus, C. s.l. propinquus and C. s.l. tonsus). Maximum frequencies of quadrithek morphs (10 to 12%) in Calanus pacificus californicus occurred during the upwelling season from late winter into spring. No indication of sexual or antennal dimorphism was found in CV C. pacificus californicus sexed by examination of gonad and gonaduct. The quadrithek dimorph appears to be the product of sex change by the larger-sized late-juvenile potential male. The evolutionary and ecological significance of this presumptive hypothesis is that the larger-sized potential male reaching adulthood one or more weeks before maturation of genotypic females may increase its reproductive output by sex change in the course of the final molt to mature as a functional female. Given the sex-change hypothesis, morphogenesis of secondary sexual structures would appear to be controlled by androgenic-like secretions from the genital tract, as has been shown in malacostrocans.     

Microdistribution of marine copepods in a small inlet

The pattern of microdistribution of 4 species of marine copepods in a small inlet was investigated, based on water samples of 20 l collected successively with a plankton pump. The distribution of each species in a limited area seemed to be related to the hydrographic conditions to some extent; on the other hand, a pattern of non-random and contagions distributions was also clearly indicated. The aggregation of organisms has considerable ecological significance in measurement of the zooplankton production in the sea and the feeding of fish larvae.     

A morphological approach for relating decapod crustacean cephalothorax shape with distribution in the water column

Cephalothorax profiles for individuals of 18 decapod crustacean species were obtained from pictures of specimens captured using various experimental bottom trawls in the Mediterranean basin, at depths ranging from 200 to 4000 m in 2000 and 2002. Profiles were compared using the shape (outline) of the entire cephalothorax (including and excluding the rostrum). Principal component analysis (PCA) of the profiles, rostrum included, yielded two large species groupings related to rostrum size, species having a long rostrum being clustered on the positive portion of the first axis and species having a short rostrum being clustered on the negative portion of this same axis (the F1 axis explained 72.17% of the total variance). The PCA separated pelagic and endobenthic animals (with short rostrums) from nektobenthic animals (with long rostrums). Only the two deepest-dwelling species (dwelling at depths below 2000 m) were distanced from their respective groups. The pelagic shrimp Acanthephyra pelagica was clearly grouped with the nektobenthic species despite being reported to have a pelagic habitat. The nektobenthic deep-sea species Nematocarcinus exilis has a relatively medium-size rostrum and was placed among the pelagic–endobenthic species. The endobenthic and pelagic groups remained stable even when rostral morphometrics were excluded from the PCA analysis. The hypothesis that predation and diet are the fundamental determining factors for all habitats throughout most of the lifetimes of individuals and hence that species will evolve specialised phenotypes to adapt to local environmental conditions is considered in the discussion.Communicated by O. Kinne, Oldendorf/Luhe     

Grazing in juvenile stages of some estuarine calanoid copepods

The grazing of juvenile Eurytemora affinis, Acartia tonsa and A. clausi from the Chesapeake Bay (USA) was investigated using natural particle distributions and freshly caught copepods, live-sorted into stages. Data were analyzed in 110 size channels using an electronic particle counter, and filtering rates (FR) were estimated based on total particle removal (mean FR), and that for each size channel (giving maximum FR). Mean and maximum filtering rates increased from NVI (Nauplius Stage VI) through CVI (Copepodid Stage VI). Both rates plotted against weight satisfied a log fit best for A. tonsa, and a linear fit best for E. affinis. Results for A. tonsa were quite variable, apparently due to differences in temperature between experiments. Particle selection was investigated from the shape of the filtering rate curve over particle size. We define selective feeding by a FR curve which is higher in some size categories, and non-selective feeding by a flat FR curve. The general pattern was one of selective feeding in all copepodid stages of the three calanoid copepods investigated. E. affinis tended to track biomass peaks while Acartia spp.'s feeding was more variable, including feeding in size ranges of greatest particle concentration, on larger particles, and in other size categories as well. Experiments with nauplii tended to yield flat FR curves, and it may be that selective grazing appears with, or is greatly accentuated by, metamorphosis from NVI to CI (Copepodid Stage I).University of Maryland, Center for Environmental and Estuarine Studies Contribution No. 762.     

Community structure and vertical distribution of cyclopoid copepods in the Red Sea

The species abundance, vertical distribution and diurnal vertical migration of cyclopoid copepods was analyzed in the central Red Sea in October–November 1980. Samples were taken to a depth of 450 m with a multiple opening — closing plankton net with 0.1-mm mesh-size. Selected important species were allocated to five different groups according to their depth distributions during daytime. The greatest number of species (9) was found in the lower epipelagic zone (40 to 100 m), below the strong seasonal thermocline. The lowest number of species (1) occurred in the upper part of the upper mesopelagic zone (100 to 250 m), which is characterized by a strong dissolved oxygen gradient. Five species had a bimodal vertical distribution, with dual peak abundances in the epipelagic and upper mesopelagic zones. Distinct differences in distribution patterns were noted between sexes and/or developmental stages. The vertical range of diurnally migrating species was small, usually less than 50 to 100 m. Characteristic diurnal changes in the vertical succession of dominant species occur within the epipelagic zone (0 to 100 m). Species-specific vertical distribution patterns are compared with published data from other areas. A conspicuous difference in the proportion of carcasses was noted between species: small species (<0.5 mm in length) had a much higher proportion of carcasses, usually between 20 and 40% of the total standing stock, than larger ones (<5%). The potential causes of this phenomenon, which may be due to (1) methodological bias, (2) a lower sinking velocity of small carcasses, or (3) a higher mortality rate of small species, are discussed.     

What is the sex ratio of harpacticoid copepods in the deep sea?

The sex ratios of deep-sea harpacticoids have been thought to be greatly skewed toward females. The representation of males is notably more equitable (approximately 1:2) at three deep-sea sites (San Diego Trough: 32°52.4N, 117°45.5W, 1 050 m, January 1987; Porcupine Seabight: 51°36.85N, 12°57.30W, 1 369 m, August 1984; northwest Atlantic, 40°27N, 62°20W, 4 820 m, July 1982, June 1983). This ratio conceals extensive variation at the species level. For some species, males are unknown. For other species, males are more numerous than females. Sampling bias against males can occur and may explain the more extreme reports of male rareness in the literature.     

Grazing by adult estuarine calanoid copepods of the Chesapeake Bay

Grazing by adult female Eurytemora affinis, Acartia tonsa and A. clausi on natural distributions of particles from the Chesapeake Bay has been investigated. During the course of a year's sampling, a wide variety of particle size-biomass distributions were observed as seasonal shifts in detritus, and over 150 algal species occurred. These distributions were grouped into 5 basic types in the analyses of feeding. All three species demonstrated similar capabilities for feeding over a broad range of particle size with selection (higher filtering rates) on larger particles and on biomass peaks. Feeding on multiple-peak distributions resulted in strong selection or tracking of each biomass peak with reduced filtering rates between peaks. Evidence is presented which suggests that the copepods first feed on large particles and then successively switch to biomass peaks of the smaller size categories. Comparisons of the feeding behavior of Eurytemora affinis and the Acartia species showing that the Acartia species have greater capabilities for taking large particles may be associated with modifications of their mouth parts for raptorial feeding. The results suggest considerable flexibility in copepod feeding behavior which cannot be explained solely by the mechanism of a fixed sieve.     

Lunar influence on distribution of a calanoid copepod in the water column of a shallow,temperate estuary

Moonlight had a significant influence on the distribution of the copepodPseudodiaptomus hessei in the water column. Copepod samples were taken between March 1986 and March 1987 in the Sundays River estuary. South Africa. Late copepodid stages and adults showed vertical differences in abundance on moonlit nights, with more animals in bottom waters, but not on dark nights. Numbers of adults present in the water column were markedly lower on full moon nights compared with new moon nights. The strongest decrease in abundance was displayed by ovigerous females. These observed distribution patterns support published predation hypotheses.     

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.     

Species-specific differences in lipid composition and omnivory indices in Arctic copepods collected in deep water during autumn (North Water Polynya)

To discern species-specific patterns in omnivory indices in copepods from the North Water Polynya, lipid classes and fatty acids were determined in Calanus hyperboreus Krøyer copepodite stage 5 (CV), C. glacialis Jaschnov (CV) and Metridia longa Lubbock (females) sampled below the mixed layer during autumn 1999. Generally, M. longa contained higher proportions of triacylglycerols, polar lipids and 18:1(n-9) than the other species. M. longa also had lower relative amounts of wax esters (WE), polyunsaturated fatty acids (PUFA), 20:1(n-9), 22:1(n-11), and lower absolute (g lipid copepod^-1) and relative (% lipid) lipid levels. Unsaturation coefficients (UC; ratio of polyunsaturated to total WE) were usually lowest in M. longa. These differences probably relate to a lesser dependence on phytoplankton in M. longa, and hence more ingestion of PUFA-poor prey. Moreover, levels of the carnivory index 18:1(n-9)/18:1(n-7) were highest in M. longa. Our data support the widespread contention that M. longa is more omnivorous than C. hyperboreus and C. glacialis. Proportions of bacterial fatty acids [odd-numbered and/or branched (OBFA); 18:1(n-7)] and PUFA/SFA (SFA: saturated fatty acids) ratios were largely unrelated to feeding strategy. Relationships between relative and absolute amounts of 16:1(n-7) and 18:1(n-7) in copepods suggest that the latter fatty acid is formed in vivo by chain elongation of the former. However, elevated levels of 18:1(n-7) and OBFA in M. longa at stations dominated by the microbial loop imply that these indices can be used to track ingestion of PUFA-poor protozoans when diatoms are scarce.Communicated by J.P. Grassle, New Brunswick