Autecology of an intertidal Alaskan harpacticoid copepod Apolethon sp.

The life history and ecology of a harpacticoid copepod, Apolethon sp., were investigated for one year in the intertidal zone of a subarctic bay in southeastern Alaska. Core samples were collected biweekly at the 0 m tidal level from March, 1992 through March, 1993; zonation and vertical distribution were determined from additional samples. Large seasonal variations in density of Apolethon sp. parallelled that of the total harpacticoid community, with highest densities (124.3±12.5 10 cm^–2; mean ± standard error) in March and lowest densities in May and October (7.6±4.5). The sex ratio of Apolethon sp. varied directly with population density, varying from <0.1 to 1.2 (male:female) during the study period. The species was restricted to a relatively narrow vertical band within the intertidal zone, having its greatest density at – 1 m and being rare above + 1 m tidal height. Adult Apolethon sp. bear conspicuous ovoid mucin structures located laterally on the genital double-somite. The mucin structures are unique to the species; several putative functions are discussed.     

Bioassay evidence for the transmission of WSSV by the harpacticoid copepod Nitocra sp

White Spot Syndrome Virus (WSSV) is now one of the most devastating and virulent viral agents threatening the penaeid shrimp culture industry and has been responsible for serious economic losses for shrimp farms worldwide. One remarkable characteristic of WSSV is its wide reservoir range, which contributes to its wide geographical distribution. Among epizootiological surveys, there is substantial evidence for WSSV-positive copepods found in shrimp farming ponds. Therefore, copepods are suspected to be the vector of WSSV. In the present study, nested-PCR analysis showed positive results in the harpacticoid copepod Nitocra sp. exposed to WSSV by virus-phytoplankton adhesion route. Oral route and intramuscular injection were used to test the pathogenicity of WSSV isolated from the WSSV-positive Nitocra sp. For the oral route of infection, Marsupenaeus japonicus postlarvae were fed with WSSV-positive copepods. The shrimp postlarvae in the infected treatment became WSSV-positive and occurred 52.50+/-5.00% mortality which was significant higher (P <0.05) than that in the control treatment (20.00+/-0.00%) when postlarvae were fed with WSSV free copepods. In the intramuscular injection challenge, M. japonicus juveniles were injected with the copepods inoculum extracted from the WSSV-positive Nitocra sp., and showed 72.50+/-9.57% mortality which was also significant higher (P <0.05) than that in the control treatment (22.50+/-5.00%) when juveniles were received mock injection of a tissue homogenate prepared from WSSV-negative Nitocra sp. Based on these laboratory challenge studies, it was confirmed that the copepods can serve as a vector in WSSV transmission.     

Syrticola mediterraneus n. sp., a harpacticoid copepod from the Bay of Calvi,Corsica

Syrticola mediterraneus n. sp. belonging to the family Cylindropsyllidae Sars (sensu Lang, 1948) is described from the Bay of Calvi (Corsica). The species is closely related to (?) Notopontia galapagoensis Mielke, 1982 and Syrticola flandricus Willems & Claeys, 1982. The former species is now transferred to the genus Syrticola as Syrticola galapagoensis n. comb.     

Reproductive behaviour in the harpacticoid copepod Tigriopus fulvus

The results of several experiments on reproductive behaviour of Tigriopus fulvus, indicate that females release a sex pheromone promoting sexual recognition and attraction in males. This compound has been verified to be not only species-specific, but also slightly modified in specimens belonging to different geographical populations. The compound possesses a mass of between 100 and 1000 daltons. A male can invest from one to 15 days in the precopulatory phase; delayed fertilization causes a strong reduction in the average number of offspring produced by parental specimens belonging to the oldest agegroups, but does not have any effect on the sex ratio.     

The morphology of a harpacticoid copepod gut: A review and synthesis

The digestive tract of a harpacticoid copepod, Tigriopus californicus (Baker), was studied by using techniques of light and electron microscopy. Four cell types could be distinguished: type 1, an embryonic cell which will replace cells worn away or lost during secretion; type 2, a cell which synthesizes and secretes proteins and also plays a role in lipid absorption; and types 3 and 4, two cell types which absorb lipids. From the abundance of each cell type, the length of microvilli, the development of basal plasma membrane (PM), and luminal projections, the following conclusions were made. (1) The midgut caecum absorbs digested nutrients. (2) The anterior midgut absorbs nutrients and more importantly functions in merocrine and exocrine secretion. The presence of concretions in cell types 2 and 3 in the anterior midgut suggests that these tissues contribute in excretion, and in water and/or ion regulation. (3) The posterior midgut absorbs nutrients and contributes some holocrine secretion.     

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.     

Heritability of sex tendency in a harpacticoid copepod,Tigriopus californicus

Abstract.— Systems with genetic variation for the primary sex ratio are important for testing sex-ratio theory and for understanding how this variation is maintained. Evidence is presented for heritable variation of the primary sex ratio in the harpacticoid copepod Tigriopus californicus. Variation in the primary sex ratio among families cannot be accounted for by Mendelian segregation of sex chromosomes. The covariance in sex phenotype between full-sibling clutches and between mothers and offspring suggests that this variation has a polygenic basis. Averaged over four replicates, the full-sibling heritability of sex tendency is 0.13 ± 0.040; and the mother-offspring heritability of sex tendency is 0.31 ± 0.216. Genetic correlations in the sex phenotype across two temperature treatments indicate large genotype-by-temperature interactions. Future experiments need to distinguish between zygotic, parental, or cytoplasmic mechanisms of sex determination in T. californicus.     

The response of a harpacticoid copepod community to sediment disturbance in a semi-enclosed lagoon

The harpacticoid fauna of a sandy sediment in the Sluice Dock of Ostend, Belgium, was dominated by a single species, Canuella perplexa, that attained an average annual density of over 400 ind. 10 cm^–2 in 1976 and 1977, whereas other species had a total mean density of less than 10 ind. 10 cm^–2. In the summer of 1979 a dystrophic crisis with abundant growth of Ulva occurred and in March 1980 the lagoon was drained. After refilling of the lagoon, the sediment was immediately colonized by good swimming harpacticoids, that attained densities of 200 ind. 10 cm^–2. Three months after refilling Canuella perplexa reappeared and the system returned to its original state within one month.     

Ontogeny of the thymus in an antarctic teleost,Harpagifer sp. (Notothenioidei: Perciformes)

Summary The development of the thymus was examined in different stages of Harpagifer sp. from Signy Island (South Orkney Islands; 60°43S, 45°38W). The thymus was typical, both in position and structural development, of that observed in warmer-water teleosts. The infiltration of the thymic epithelia was not observed until 4 weeks post-hatch. Full development of the lymphoid organs was not achieved until the juvenile stage. Although an increased infiltration of the thymus, by sub-epithelial connective tissues and epithelial mucous cells, occurred in the juvenile and adult stages, there was no evidence of an advanced stage of thymic regression or involution in the adult Harpagifer. Thus a suppressive influence of the low temperature environment, on the onset and degree of thymic development and involution, was indicated in this species.The signy Island population of Harpagifer has been given the species name H. antarcticus (Prof. J.C. Hureau; personal communication)     

The effect of sediment characteristics on the distribution of two subtidal harpacticoid copepod species

Abundances of two harpacticoid copepod species, Enhydrosoma littorale Wells and Zausodes c.f. arenicolus Wilson, were significantly higher in one of two adjacent subtidal, soft-bottom habitats in St. George Sound, Florida (29°54′N : 84°37′48′′W). For Enhydrosoma littorale, a laboratory-preference experiment indicated that sediment-related factors caused the observed distribution. In a series of preference experiments, differences between the sediments of the two habitats in granulometry and organic matter were shown not to account for the preference. Rather, the preference results from differences in the microbes attached to the sediment particles in the two areas. In contrast, Zausodes c.f. arenicolus did nol prefer sediments from its area of high field abundance in laboratory preference experiments, indicating that factors external to the sediment i.e. hydrographic conditions or biological interactions, were responsible for this species' distribution.     

The harpacticoid copepod Tisbe holothuriae is resistant to the insidious effects of polyunsaturated aldehyde-producing diatoms

Numerous species of diatoms liberate oxylipins including polyunsaturated aldehydes (PUAs) in response to cellular damage such as may occur during grazing. PUAs are cyto- and genotoxic and negatively disrupt reproductive processes in copepods, their principal grazers, although experimental evidence would suggest that the grazer response may be species specific. The reproduction of the benthic harpacticoid copepod Tisbe holothuriae was compared over two generations. Copepods were reared using four diet treatments: PUA-producing diatom strains Skeletonema marinoi (Adriatic Sea Isolate FE6) and Melosira nummuloides (CCAP 1048/6); and non-PUA-producing diatom strains Phaeodactylum tricornutum (CCAP 1052/A) and S. marinoi (Seasalter (Walney) Ltd). Life tables were generated for each treatment using measured reproductive parameters and the net reproductive rate (R₀) calculated. No significant differences were observed between the individual reproductive parameters of T. holothuriae fed PUA-producing diatoms compared to those fed non-PUA-producing diatoms although diets of P. tricornutum resulted in some decreases in individual reproductive parameters in the second generation. There were no significant differences in the R₀ values between the four tested diets. These observations indicate that T. holothuriae exhibits a tolerance of known PUA-producing diatom diets that has not been similarly demonstrated in pelagic calanoid copepods. Harpacticoid copepods may have a greater capacity to detoxify diatom oxylipins than their planktonic calanoid counterparts.     

Selective attraction and reproductive performance of a harpacticoid copepod in a response to biofilms

The relationship between monobacterial films and the preference of harpacticoid copepods for such films was investigated using still water multiple-choice assays with natural biofilm and sterile conditions as controls. Adult Schizopera sp. were most attracted by a heterogeneous natural biofilm, followed by monospecies-biofilms of Rhodovulum sp., Vibrio proteolyticus, and Flexibacter sp. The preferred bacterial films stemmed from different phylogenetic and physiological groups. The results indicated that the harpacticoid Schizopera sp. was effectively and differentially attracted by bacterial films. Since bacteria constitute a substantial portion of the organic carbon available at the sea bottom as nutritive sources for harpacticoid copepods, we subsequently examined the influence of 9 bacterial strains and a natural biofilm as a nutrient source on the growth and reproductive performance of ontogenetic stages (nauplii and copepodids) of Schizopera sp. The food value of bacterial strains was assayed in terms of life table data that provided growth parameters. All variables were affected by the type of food offered. A diet on Rhodovulum sp. resulted in optimal growth performance of nauplii and copepodids demonstrating that bacteria can be used as a sole diet to support postembryonic development. The present study is the first to link behavioral preferences to bacterial biofilms with life history parameters when cultivating harpacticoid copepods on the same bacterial strains as the only diet. This study revealed a discrepancy between the biofilm favored (natural biofilm) and the one leading to maximal reproductive performance (monobacterial film of Rhodovulum sp. MB253) as indicated by major life table data as net reproductive rate (R_o), mean generation time (T_m), and capacity for increase (r_c).     

Decoupling of molecular and morphological evolution in deep lineages of a meiobenthic harpacticoid copepod

Molecular and biochemical genetic analyses have revealed that many marine invertebrate taxa, including some well-studied and presumably cosmopolitan species, are actually complexes of sibling species. When morphological differences are slight and estimated divergence times are old, data suggest either unusually high rates of sequence evolution or long-term morphological stasis. Here, five gene regions (mitochondrial cytochrome oxidase subunit I and large-subunit ribosomal 16S rDNA and nuclear ITS1, 5.8S rDNA, and ITS2) were analyzed in four geographic samples of the meiobenthic harpacticoid copepod Cletocamptus deitersi. Molecular sequences revealed four extremely differentiated molecular lineages with unalignable nuclear intergenic spacers and mitochondrial uncorrected divergences reaching 25% (cytochrome oxidase) and 36% (16S rDNA). These levels of divergence are greater than those reported previously for congeneric species in diverse invertebrate taxa, including crustaceans. The nominally intraspecific divergence matches or exceeds the corresponding divergence from a known congener (Cletocamptus helobius). A molecular clock applied to the cytochrome oxidase subunit I data suggests that these lineages split in the Miocene, consistent with the fossil record of a North American Cletocamptus from the same period. Morphological differences among the major lineages are subtle but congruent with the patterns of genetic differentiation. Our conclusion, based on concordant patterns of variation in two mitochondrial and three nuclear gene regions, as well as morphological observations, is that C. deitersi in North America is composed of at least four separate species by the genealogical concordance, phylogenetic, and morphological-species criteria. Alternative explanations for the deep phylogenetic nodes and apparent morphological stasis, including high rates of sequence evolution, balancing selection, and genetic signatures of historical events, are considered unlikely.     

Planococcus soli sp. nov., isolated from antarctic soil

Antonie van Leeuwenhoek - A novel bacterial strain, designated C23T, was isolated from a soil sample obtained from King George Island, Antarctica. Phenotypic, phylogenetic, chemotaxonomic and...     

The colonial cyanobacterium Trichodesmium as a physical and nutritional substrate for the harpacticoid copepod Macrosetella gracilis

The pelagic harpacticoid copepod Macrosetella gracilis usesthe colonial cyanobacterium Trichodesmium not only as a physicalsubstrate for juvenile development, but also as a food source.By associating itself with a buoyant colonial cyanobacterium,M.gracilis has developed a successful mode of life for existencein the plankton. Further evidence of M.gracills' dependenceon Trichodesmium as a physical substrate is demonstrated bypreviously undescribed microscopic observations of a gravidM.gracilis female attaching eggs to a Trichodesmium colony.Shipboard experiments investigating the ingestion and assimilationof Trichodesmium carbon (C) were conducted in September 1991and January/February 1992 in waters of the Bahamas and the Caribbean,respectively. Macrosetella gracilis not only ingested, but rapidlyincorporated, cyanobacterial organic matter into its own cellularmaterial. Utilization of ingested Trichodesmium by M.graciliswas investigated by assessing the metabolic partitioning andincorporation of ¹⁴C-labelled Trichodesmium into copepod lipids,proteins, polysaccharides and low-molecular-weight (LMW) compoundsusing sequential biochemical fractionation techniques. Despitevariations in grazing rates between the two sites and times(September 1991,0.017 µg C^* µg^–1 C h^–1;January 1992, 0.134 µg C ^* µg^–1 C h^–1,the partitioning of incorporated C into the different biochemicalfractions was relatively consistent. There was rapid assimilationof ingested C into the LMW ({small tilde}60%) and polysaccharidefractions ({small tilde}30%) in the first few hours, with asubsequent increase in the percent C incorporated into protein.On average, {small tilde}21% of the Trichodesmium C ingestedby M.gracilis was assimilated. Therefore, M.gracilis is an importantsecondary link in the food web of oligotrophic waters whereTrichodesmium is abundant.     

The biology and morphology of the marine harpacticoid copepod Heteropsyllus nunni Coull, during encystment diapause

Heteropsyllus nunni Coull, a meiobenthic harpacticoid copepod is the marine crustacean to undergo a state of diapause within a cyst. A 12 month field study indicated H. nunni adults reached peak population densities in winter, with nauplii maturing in the spring, becoming adults by April or May.At the last stage of development, a mature but unmated adult, they begin to prepare for encystment diapause. The copepods remain within their cyst in a state of diapause for 3–4 months during the summer only. Studies on the effects of temperature and photoperiod suggested that these two environmental cues are not crucial for induction or termination of diapause. Low temperature delayed development and time to encystment, while high temperatures accelerated development, making the time to encystment shorter. There were males than females in the cysts in laboratory experiments. Upon excystment, the copepods mate, and females begin egg production within one week. Adults that have excysted and mated die after a few weeks of active reproductive effort. Nauplii go on to mature and begin the univoltine diapause/reproductive cycle.The copepods prepare for dormancy in two ways: they begin to produce and store two types of secretory products to be used in cyst construction; then they produce large quantities of lipid to be used as a nutrient supply throughout diapause. Histochemistry of the cyst-building material indicated the lower urosome is full of two chemically different products. Dorsally, there is a storage sac of proteinaceous material. The ventral sac of secretory product is a mucopolysaccharide. The copepod builds the spherical cysts in a matrix of small and large sand grains. The cysts fit tightly around the ventral portion of the animal in the its flexed position: however, there is a large space between the cyst and the sides of the copepod.Biochemical analysis of the cyst showed it is composed of an amino acid complex similar to collagenous material. Scanning electron microscopy revealed a complex of large cuticular pores located in the lower urosome and caudal rami. There are specific pores for secretion of the two cyst-building products.     

Predator-limited population growth of the copepod Pseudocalanus sp.

The impact of predators on population growth of Pseudocalanussp. was investigated in Dabob Bay, Washington. Mortality ofPseudocalanus sp. was determined from stage-specific survivorship,from seasonal changes in mortality rates of adult males andfemales and from incidence of injuries to adult copepods. Theprincipal predators of adult Pseudocalanus were identified asthe predatory copepod Euchaeta elongata, the omnivorous euphausiidEuphausia pacifica and the chaetognath Sagirta elegans. Predatorattack rates - and prey mortality rates - are highly density-dependentand thus sensitive to prey dispersion in the water column, particularlyto layering in the vertical plane. Predation rates by the threeprincipal predators exceeded 100% of the recruitment rate toadult Pseudocalanus sp. beginning in early summer, thus restrictingpopulation growth. Planktivorous fish predation (by adult three-spinestickleback, Gasterosteus aculeatus, and juvenile chum salmon,Oncorhynchus keta) on Pseudocalanus sp. adults was estimatedto be two orders of magnitude lower than consumption rates bypredatory zooplankton, at a deep water station in July. Analysisof seasonal changes in prey ingested by Sagitta elegans revealedthat Pseudocalanus sp. was the major prey item of S. elegansin April (61.0% of prey) and in June (67.0% of prey), thereafterdeclining seasonally in importance. Predation by S. elegansvaried seasonally with changes in chaetognath stage structure,vertical distribution and diapause, not size structure alone.Although chaetognath recruitment and population growth appearto be directly coupled to the abundance of Pseudocalanus sp.,predation by S. elegans has little reciprocal impact on Pseudocalanussp. population growth; hence asymmetries may occur in the interaction of planktonic prey and predators.     

A harpacticoid copepod Microsetella spp. from sub-Arctic coastal waters and its sensitivity towards the polyaromatic hydrocarbon pyrene

Species of the harpacticoid copepod genus Microsetella are commonly reported to occur in Arctic and sub-Arctic coastal waters, but nothing has yet been reported on their sensitivity towards toxic substances. Effects of the polyaromatic hydrocarbon pyrene on Microsetella spp. from Western Greenland were investigated by looking at survival of females, feeding status, and nucleic acid content after a 96-h exposure. Less than 10% survived at 100 nM exposure concentration, and a 50% reduced survival was also evident at 0.1 and 10 nM. The RNA:DNA ratio was significantly higher, 2.1 ng/individual, at the lowest concentration of 0.01 nM compared to 0.9 ng/individual in the control, which indicates increased metabolic activities. A reduced DNA content in higher exposure concentrations of 1–100 nM suggests inhibition of egg development. Gut content was significantly declining with increasing exposure concentrations with only 2% of exposed females displaying full guts at 100 nM pyrene. Together with reduced feeding activity, effects at the population level can be anticipated, but would have to be confirmed in future experiments. The data suggests a higher sensitivity of Microsetella spp. compared to other Arctic copepods, which implies more severe effects from oil on the pelagic food web in the areas and periods where Microsetella spp. dominates Arctic plankton food webs.     

Adhesion of bacteria and diatoms to the exoskeleton of the harpacticoid copepod Tigriopus fulvus in culture: electron and epifluorescent microscope study.

In the marine environment associations between picoplankton and copepods are very important not only for the lifestyle of these animals, but also for marine ecosystems and human health. In the present study we investigated the biofouling of Tigriopus fulvus in culture and possible effects of this colonization by means of scanning electron microscopy and epifluorescence microscopy. These investigations show that T. fulvus is heavily and not uniformly colonized by bacteria and algae.