Filter feeding by Oikopleura vanhoeffeni: grazing impact on suspended particles in cold ocean waters

Because of the abundance and size of Oikopleura vanhoeffeni its quantitative role as a suspension feeder in cold ocean waters needs to be defined. To minimize the effect of manipulation and containment, and to assess the effect of naturally occurring factors on clearance rate, I used an in situ latex microbead technique in Logy Bay, Newfoundland, from February 1985 to June 1986. Individual clearance rates ranged from 8–944 ml h^-1, increasing exponentially with increasing trunk length. Partial correlation and principal components analysis indicated that trunk length and the concentration of ingestible chlorophyll a accounted for a majority of the variation in clearance rate. At densities of 4–110 m^-3, O. vanhoeffeni populations removed from >1 to 13% of the standing stock of ingestible food particles each day. Grazing by near-surface populations was lowest during the spring diatom bloom (>1.4% of daily particle production removed per day), and was highest in June during the post-bloom crash (4 to 10% of daily production removed). Some populations in mid-depth waters had much higher population clearance rates (ca. 50% of daily production removed) because of a greater proportion of large animals. The median percentage daily ration (g Cxg C^-1xd^-1x100%) of 64% accounted for observed house production rates (1 to 2 d^-1, with each house=23% of body carbon).     

Plankton of the fladen ground during FLEX 76 III. Vertical distribution,population dynamics and production of Calanus finmarchicus (Crustacea: Copepoda)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR), the Longhurst Hardy Plankton Recorder (LHPR) and by our colleagues from other participating Institutes during the Fladen Ground Experiment (FLEX 76) were used to describe the vertical distribution and population dynamics of Calanus finmarchicus (Gunnerus) and to provide estimates of the production and carbon budget of the population from 19 March to 3 June, 1976. Total production of the 19 March to 3 June, 1976. Total production of the nauplii and copepodite stages (including adults), during the exponential growth phase in May, was estimated to be in the range of 0.49 to 0.91 g C m^-2 d^-1 or 29.0 to 55 g dry wt m^-2 (14.5 to 27.8 g C m^-2) for the three successive 10 d periods in May. Two gross growth efficiencies (K ₁) (20 and 34%), together with the lower value of C. finmarchicus production, were used to calculate the gross ingestion levels of algae as 2.45 and 1.44 g C m^-2 d^-1 (73.5 and 43.2 g C m^-2 over the May period). These ingestion levels, together with the algae ingested by other zooplankton species, are greater than the estimated total phytoplankton production of 45.9 g C m^-2 over the FLEX period. A number of factors are discussed which could explain the discrepancies between the production estimates. One suggestion is that the vertical distribution of the development stages of this herbivorous copepod and their diel and ontogenetic migration patterns enable it to efficiently exploit its food source. Data from the FLEX experiment indicated that the depletion of nutrients limited the size of the spring bloom, but that it was the grazing pressure exerted by C. finmarchicus which was responsible for the control and depletion of the phytoplankton in the spring of 1976 in the northern North Sea.JONSDAP Contribution No. 51     

Vertical distributions of Calanus finmarchicus and C. helgolandicus (Crustacea: Copepoda)

The vertical distributions of the spring populations of Calanus finmarchicus (Gunnerus) and C. helgolandicus Claus are described and compared. The differences we observed between the two species have probably confused the understanding of the vertical distribution and development of the populations of Calanus spp. in the shelf seas around the United Kingdom where the species occur together. The results imply that these two congeneric species have different behaviour patterns which minimise interspecific competition where the species have sympatric distributions. C. finmarchicus has its younger development stages overlying the older stages in the water column. In C. helgolandicus the converse is true; i. e., the majority of the populations of Stage I and II copepodites of the first spring generations are found below the thermocline. It is also suggested that the different behaviour patterns lead to different feeding regimes and strategies.JONSDAP Contribution No. 52     

Grazing rates of the copepods Calanus glacialis and C. finmarchicus in arctic waters of the Barents Sea

Natural feeding rates of Copepodite Stages IV and V, and adult female Calanus glacialis (Jaschnov) and Copepodite Stage V and adult female C. finmarchicus (Gunnerus) were estimated using fluorescence analysis of gut contents. Measurements were made on copepods sampled from arctic waters east of Svalbard (Barents Sea) during the spring phytoplankton increase, in the period from 27 May to 13 June, 1983. Observations on Copepodite Stages IV and V and adult female C. glacialis suggest that the gastric evacuation rate is independent of developmental stage, whereas C. finmarchicus Copepodite Stage V showed a lower gastric evacuation rate than adult females. Gut fullness displayed a low correlation with the ambient chlorophyll concentrations. Ingestion rates calculated for C. glacialis were 0.3, 2.3, and 11.0 g C h^-1 for Copepodite Stages IV and V and adult females, respectively. Copepodite Stage V and adult female C. finmarchicus ingested 0.9 and 1.1 g C h^-1 at a temperature of ca.-1.0°C. The maximum ingestion rate in terms of percent body carbon d^-1 was higher for adult female C. glacialis and C. finmarchicus than for the respective Copepodite Stage V's. The results are discussed both in relation to the physiological state of the species and to the environmental conditions.     

Oil exposure in a warmer Arctic: potential impacts on key zooplankton species

Oil exploration activities are rapidly increasing in Arctic marine areas with potentially higher risks of oil spills to the environment. Water temperatures in Arctic marine areas are simultaneously increasing as a result of global warming. Potential effects of a combination of increased water temperature and exposure to the PAH pyrene were investigated on fecal pellet and, egg production and hatching success of two copepod species, Calanus finmarchicus and Calanus glacialis, sampled in Disko Bay, Greenland on 23–25 April 2008. The two species were exposed daily to nominal pyrene concentrations of 0-0.01-0.1-1-10-100 nM at water temperatures of 0.5, 5 and 8°C for 9 and 7 days, respectively. Daily measurements of faecal pellet production, egg production and hatching showed different responses of the two species to the applied stressors. When temperature increased, low concentrations of pyrene caused a decrease in faecal pellet production by C. finmarchicus, whereas C. glacialis faecal pellet production showed no negative response to pyrene exposure when temperatures increased. Pyrene exposure decreased egg production of C. finmarchicus at all temperatures, but the species was more sensitive at 0.5 and 8°C. A lag period of 1 day before egg production began was prolonged with several days when warmer water was combined with pyrene exposure. Egg production by C. glacialis was only negatively affected by pyrene in a dose-dependent manner at 0.5°C. Hatching success in both species was not affected by pyrene, where increased water temperatures led to a higher hatching success. In conclusion, C. glacialis seemed to be the less sensitive of the two species to the stress combination of increased water temperature and pyrene exposure. As a consequence of the differential responses of the two species, their competition can be impaired with a consequent impact on energy transfer between trophic levels.     

Sinking rates of fecal pellets from gelatinous zooplankton (Salps,Pteropods, Doliolids)

Sinking rates were determined for fecal pellets produced by gelatinous zooplankton (salps, Salpa fusiformis and Pegea socia; pteropods, Corolla spectabilis; and doliolids, Dolioletta gegenbaurii) feeding in surface waters of the California Current. Pellets from the salps and pteropods sank at rates up to 2 700 and 1 800 m d^-1, respectively; such speeds exceed any yet recorded for zooplankton fecal pellets. Fecal pellets of salps were rich in organic material, with C:N ratios from 5.4 to 6.2, close to values for living plankton. The relation between volume and sinking rate indicates that salp and pteropod pellets are slightly less dense than those of pelagic Crustacea; moreover, pellet density varied between different collection dates, probably because of differences in composition. In contrast, doliolid pellets sank at rates up to 208 m d^-1, a rate much lower than would be expected from pellet size. Thus, density and sinking rates of pellets are much more variable in zooplankton than would be expected from studies of crustaceans alone. Moreover, the extraordinarily high sinking rates of fecal pellets of salps indicates that these tunicates may be disproportionately important in the flux of biogenic materials during periods when they form dense population blooms.     

Annual population development and production by Calanus finmarchicus, C. glacialis and C. hyperboreus in Disko Bay, western Greenland

The populations of the copepod species Calanus finmarchicus, C. glacialis and C. hyperboreus were investigated in Disko Bay during a 14-month period in 1996-1997. The three species were predominant in the copepod community. The biomass reached a maximum at the beginning of June (127 mg C m^-3). From the end of July until the end of April the following year, the biomass was <1-6 mg C m^-3. All three species showed seasonal ontogenetic migration. The spring ascent for all three species was just prior to or in association with the break-up of sea ice and the development of the spring bloom, whereas descent occurred over a larger time span during summer. The main overwintering stages were CV for C. finmarchicus, CIV and CV for C. glacialis and C. hyperboreus. Peak abundance of juvenile copepodites, representing the new generation, was in August for C. finmarchicus, in July for C. glacialis and in May/June for C. hyperboreus. From the timing of reproduction and the population development, the life cycles were deduced to be 1 year for C. finmarchicus and at least 2 years for C. glacialis and C. hyperboreus. Secondary production and potential grazing impact of the Calanus community were estimated by two methods based on specific egg-production rates and temperature-dependent production. The Calanus community was not able to control the primary producers during the spring bloom but probably did during post-bloom. The estimates also indicated that grazing on ciliates and heterotrophic dinoflagellates contributes as an essential food source in the post-bloom period.     

Effects of starvation,season, and diet on the free amino acid and protein content of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> females

Effects of food availability and season on the free amino acid (FAA) and total protein content of the copepod Calanus finmarchicus females were investigated in two mesocosm experiments on the Norwegian west coast in spring and autumn. Starved C. finmarchicus females showed no change in total FAA content, but the FAA pool composition changed drastically. During the first 10 days of starvation the protein content showed a moderate decline (<2 µg ind ^-1); however, during the following 21 days the total content was drastically reduced, from 63 to 9 µg ind ^-1. This supports the notion of a sequential catabolism of endogenous nutrients during starvation. In females at high food concentrations, the body protein content increased during spring, but decreased during autumn. The FAA pool composition of females differed between spring and autumn in 14 of the 18 FAA investigated. Reduced body protein content and increased proportion of essential free amino acid were observed during starvation. Similar changes were observed in females sampled at the end of the mesocosm experiments in the autumn. The results suggest that mature C. finmarchicus females are in a negative protein balance during autumn, despite high food concentrations, contributing to a lower fitness than in females maturing during the spring.     

Animal-sediment relations in Cape Cod Bay,Massachusetts II. Reworking by Molpadia oolitica (Holothuroidea)

Populations of Molpadia oolitica (Holothuroidea) were sampled over an area of 440 km² in Cape Cod Bay, Massachusetts, USA. This species occurs in silt-clay muds in densities of 2 to 6/m², and is limited to depths greater than 22 m where the highest annual temperature does not exceed 10°C. M. oolitica lives within the mud, with its anterior end located approximately 20 cm below the surface. This species ingests only fine-grained particles at depth in the sediment, and deposits uncompacted feces at the surface, producing a fecal mound around the anal opening. This reworking produces vertical sediment sorting, high sediment-water content, and topographic relief of the sea floor. The fecal cones of M. oolitica provide a relatively stable surface for settlement and growth of the suspension feeders Euchone incolor (polychaete), Aeginina longicornis (amphipod), and Thyasira gouldi (bivalve) Uncompacted feces, accumulated in depressions between the mounds, form an unstable substratum frequently resuspended by tidal flow. Suspension feeders are absent from intercone areas.Contribution No. 236 of the Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts, USA.     

Impacts of copepods on marine seston,and resulting effects on<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> RNA:DNA ratios in mesocosm experiments

We investigated the impact of copepods on the seston community in a mesocosm set-up, and assessed how the changes in food quantity, quality and size affected the condition of the grazers, by measuring the RNA:DNA ratios in different developmental stages of Calanus finmarchicus. Manipulated copepod densities did not affect the particulate carbon concentration in the mesocosms. On the other hand, chlorophyll a content increased with higher copepod densities, and increasing densities had a positive effect on seston food quality in the mesocosms, measured as C:N ratios and 3:6 fatty acid ratios. These food quality indicators were significantly correlated to the nutritional status of C. finmarchicus. In contrast to our expectations, these results suggest a lower copepod growth potential on higher quality food. However, in concordance with earlier studies, we found that when copepods were in high densities the large particles (>1000 µm³) decreased and that the smaller particles (<1000 µm³) increased in number. These patterns were closely linked to the condition of C. finmarchicus, which were of better condition (RNA:DNA ratios) with increasing biovolumes of large particles, and, conversely, lower RNA:DNA ratios with increasing biovolumes of smaller particles. Consequentially, the selective grazing by copepods stimulated increased biovolumes of smaller plankton, and this increase was responsible for the increased food quality, in terms of C:N and 3:6 ratios. Thus, we conclude that the decreasing growth potentials of C. finmarchicus were a result of a decrease of favourably sized food particles, induced by copepod grazing.Communicated by O. Kinne, Oldendorf/Luhe     

Biosynthesis of trimethylamine oxide in calanoid copepods. seasonal changes in trimethylamine monooxygenase activity

Live copepods, Calanus finmarchicus (Gunnerus) and C. hyperboreus (Krøyer), exposed to dissolved ¹⁴C-labeled trimethylamine (TMA) in seawater, oxidized TMA to trimethylamine oxide (TMAO), which accumulated in the organisms. The amount of TMAO synthesized was dependent on the time of exposure to TMA and the concentration of TMA in the seawater. It was inferred that copepods can produce TMAO by oxidation of TMA found in their plant food. Choline and methionine did not appear to be of importance as precursors of TMAO. There were large seasonal changes in TMA monooxygenase activity of both copepods. The activity was high in spring, and decreased through summer and autumn to a winter low in October to March. The changes in TMAO content of C. finmarchicus were, in comparison, small (this aspect was not tested for C. hyperboreus).     

Production and fate of copepod fecal pellets across the Southern Indian Ocean

The vertical distribution of copepods, fecal pellets and the fecal pellet production of copepods were measured at seven stations across the Southern Indian Ocean from productive areas off South Africa to oligotrophic waters off Northern Australia during October/November 2006. We quantified export of copepod fecal pellet from surface waters and how much was retained. Furthermore, the potential impact of Oncaea spp. and harpacticoid copepods on fecal pellets degradation was evaluated and found to be regional substantial. The highest copepod abundance and fecal pellet production was found in the western nutrient-rich stations close to South Africa and the lowest at the central oligotrophic stations. The in situ copepod fecal pellet production varied between 1 and 1,000 μg C m⁻³ day⁻¹. At all stations, the retention of fecal pellets in the upper 400 m of the water column was more than 99% and the vertical export of fecal pellets was low (<0.02 mg m⁻² day⁻¹).     

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

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

Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). I.<Emphasis Type="Italic"> Mysis mixta</Emphasis> (Mysidacea)

Seasonal population dynamics of Mysis mixta Lilljeborg were studied from December 1998 to November 2000 at a 240 m deep site in Conception Bay, Newfoundland. At this depth, temperature was <0°C and salinity between 32.0 and 34.0 psu year-round. The spring phytoplankton bloom began in early or late March and reached a maximum in late April to mid-May. M. mixta exhibited a highly synchronised life cycle, with spawning and mating occurring in October to November, embryos brooded for ~5 months, and juveniles released during spring bloom sedimentation in April and May. Females were semelparous and died at age 2.5 years, following release of juveniles in spring, whereas the majority of mature males died at age 2 years, following mating in November. The biennial life cycle of this population resulted in the presence of two cohorts in the hyperbenthos at any given time. Variation in density and biomass was low among cohorts but high within cohorts, the latter probably due to the high motility of mysids. Densities in 1999 and 2000 were 242±379 and 544±987 ind. per 100 m³ (mean±SD), respectively. Although growth rates were similar between years, rates measured from changes in dry mass differed both seasonally and among life-history stages (range from –4 to 7 mg month^–1). Annual secondary production was estimated at 29–73 mg C m^–2 in 1999 and 53–205 mg C m^–2 in 2000. The annual P/B ratios were 1.62 and 1.19 in 1999 and 2000, respectively.Communicated by J.P. Grassle, New Brunswick     

Geographical range and taxonomic divergence in North Atlantic Calanus (C. helgolandicus,C. finmarchicus and C. glacialis)

The known distribution of Calanus helgolandicus in the North Atlantic Drift is difficult to explain in the absence of a reproductively active population inhabiting continental waters off eastern North America. New evidece indicates that this population, overlooked in the past, does in fact exist. The species has been found in a study of zooplankton samples from a number of MARMAP (Marine Resource Monitoring, Assessment, and Prediction Program) cruises surveying ichthyoplankton between Cape Hatteras and the New York Bight. Sexual activity in these stocks of C. helgolandicus was indicated by the ripeness of ovaries, the frequency of males, the presence of sperm in the females' seminal receptacles and the appearance of a female bearing a Calanus spermatophore. The new records provide a likely origin for the presence of the species in the vicinity of the Labrador Grand Banks as well as further east in the North Atlantic Drift. C. finmarchicus, similarly sexually active, was found to be sympatric with C. helgolandicus in the MARMAP collections which were taken from a region contiguous with the southernmost, known distribution, of C. glacialis. The distribution of integumental organs (i.e., pore signature patterns) was examined in the three species to determine whether they would be taxonomically useful. Strikingly different patterns were found on the female urosome. Pore signature differences between the polar species C. glacialis and the temperate C. helgolandicus proved to be as pronounced as those between the boreal C. finmarchicus and its two neighboring species. The successively overlapping ranges and the distinctive differences in pore signature patterns suggest that divergence from the generic pattern of integumental organ distribution has been a product of selection against hybridizing among the three species. If this is in fact the case, the reproductive range of C. helgolandicus has overlapped with those of C. finmarchicus and C. glacialis for appreciable periods in the history of the three species.     

Respiration and nitrogen excretion of zooplankton. IV. The influence of starvation on the metabolism and the biochemical composition of some species

Changes in the respiration, ammonia excretion and biochemical composition were studied for three species of starving zooplankton (Calanus finmarchicus, Sagitta elegans, and Acartia clausi). Over the period of starvation, the respiration rate of all three species followed the same pattern of an initial decrease followed by a more or less constant level. A similar pattern was observed for the ammonia excretion rate of S. elegans and A. clausi, whereas C. finmarchicus excretion appeared to oscillate between high and low levels of protein catabolism. Study of the biochemical changes showed that C. finmarchicus consumed primarily lipids, and at times proteins, to meet its energy requirement whereas S. elegans and A. clausi primarily used protein. Variations in the elemental composition as well as the O:N ratio confirmed that C. finmarchicus alternated between periods of protein-dominant catabolism and lipid-dominant catabolism during starvation. No similar change in catabolism was observed in the two other species. The results are discussed in terms of physiological mechanisms of resistance to starvation and were used to calculate the energy budget of S. elegans and C. finmarchicus during the period of total starvation. The significance of such budgets is discussed and some of the sources of error examined.Bedford Institute of Oceanography Contribution.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Does the spawning of Calanus finmarchicus in high latitudes follow a reproducible pattern?

In the spring of 1989, an experimental study of the spawning behaviour of Calanus finmarchicus was carried out in Malangen, northern Norway. Here, a single cohort of females reproduce from mid-March to May, approximately coinciding with the wax and wane of the spring phytoplankton bloom. An evaluation of population characteristics such as the proportion of adults, sex ratio, as well as gonad maturation and daily productivity of the females clearly reveals three phases within the population's reproductive period. In between incline and decline, the highest spawning rates (on average >20 eggs female^-1 d^-1, equivalent to 5.7% body C d^-1) occur after the males have disappeared from the population and almost all females have mature gonads. During this period, the ratio of adults to copepodid Stage Vs changes from dominance of adults to that of CVs. Although first egg production was observed prior to the phytoplankton increase, it is suggested that the onset of the phytoplankton spring bloom in the first few days of April enhances the final maturation of ovaries in the females and therefore triggers the onset of the main spawning period. The clutch sizes (max. 95 eggs clutch^-1) vary with the age of the females, while the spawning frequencies depend on the available food quantities. The overlap of an estimated minimal 4 wk spawning period for the individuals leads to a main reproductive phase for the population of ca. 3 wk, during which time mean clutch sizes and spawning frequencies are maximal (highest average clutch size: 70 eggs female^-1 clutch^-1, 100 to 60% of the females spawning). This period ends before the end of the phytoplankton bloom. Calculated by stepwise interpolation and summation of the mean daily egg production in the population, an average female produced ca. 600 eggs during the spring bloom in Malangen 1989. We suggest that reproduction and population development of C. finmarchicus in spring follows a reproducible pattern for a given temperature regime and non-limiting food conditions. In the case of clearly identifiable cohorts, it seems possible to trace the state of reproduction by evaluating population parameters.     

Phenology and demography of a marine specialist herbivore: Placida dendritica (Gastropoda: Opisthobranchia) on the central coast of Oregon

The occurrence of small specialist herbivores in marine rocky intertidal communities has been largely ignored. From 1984 to 1989, the phenology and demography of the common oligophagous ascoglossan opisthobranch Placida dendritica A.& H. was documented at several sites along the central coast of Oregon, USA. P. dendritica was found on the low intertidal green algae Codium setchellii Gardn., C. fragile (Sur.) Har. and Bryopsis corticulans Setch. during spring and summer. Ascoglossan abundance on Codium spp. varied spatially and temporally. Peak density usually occurred in May or June. Maximum ascoglossan live mass was 4 to 6 mg on Codium spp. and 100 mg on B. corticulans. Larval recruitment of P. dendritica to algal hosts was continuous during spring and summer. Rapid recruitment (200 to 400 sea slugs thallus^-1mo^-1) of newly metamorphosed ascoglossans to C. setchellii in wave-protected areas suggests that high densities of competent larvae occurred in nearshore waters and/or that larvae were efficient at locating algal hosts. Ascoglossan growth was rapid, with less than one month elapsing from larval settlement to adult sexual maturity. Therefore, populations of P. dendritica were composed of many overlapping generations. Movement of adult ascoglossans among thalli of C. setchellii was rapid. Continuous larval settlement and adult movement enabled P. dendritica not only to locate and colonize its algal hosts quickly but also to maintain a persistent association with algal hosts during spring and summer.     

Pharmacokinetics of [14C]-atrazine in rhesus monkeys,single-dose intravenous and oral administration

This is the first study regarding the pharmacokinetics of [¹⁴C]-atrazine conducted with rhesus monkeys. The animals received one dose (0.25 mg) intravenously (IV) or three doses (1, 10, or 100 mg) orally. Plasma, urine, and feces were collected at defined times up to 7 days post-dosing. Sample radioactivity was measured to determine the mass equivalent. IV administered [¹⁴C]-atrazine disappeared rapidly from blood, with an elimination half-life of about 5.5 ± 1.1 h. The pharmacokinetic profiles of [¹⁴C]-atrazine following oral administration at the three dose levels show that kinetic parameters such as AUC and C _max are linearly correlated with the dose. Seven days after dosing, urinary and fecal excretion of [¹⁴C]-atrazine reached 99% of total administered dose in the IV group and 91–95% in the three oral dose groups. In the IV-administered monkeys, approximately 85% of the dose was excreted in urine and 12% in feces. In three oral dose groups, urinary and fecal radioactivity recoveries approximated 57% and 21%, 58% and 25%, and 53% and 35%, respectively. More than 50% of the total urinary excreted radioactivity was found within the first 24 h after dosing. In conclusion, the principal elimination of [¹⁴C]-atrazine, IV and orally administered, is via urine. The oral bioavailability was 60% or higher. There was a significant linear correlation between administered oral dose and plasma concentration. Overall oral dose accountability ranged from 91% to 95%. Data generated may be useful in the risk assessment of human exposure to environmental atrazine contamination.