Egg production in the copepod Acartia tonsa was evaluated using different densities of the microalgae Thalassiosira weissflogii, Chaetoceros muelleri and Isochrysis galbana. Male and female were kept under controlled conditions (salinity 30, 20 • C, photoperiod 12L:12D), acclimated to the experimental conditions and left over a period of 24 h to allow copulation. Algal densities tested were equivalent in biovolume and corresponded to 0, 2.5, 5, 10, 20, 40 and 60.10 3 cells.mL −1 of T. weissflogii. Ten acclimated female were separated, transferred to glass bottles and exposed for further 24 h to the corresponding experimental medium. After this period, the eggs were fixed and counted. Copepod egg production reached a threshold value when T. weissflogii, C. muelleri and I. galbana were supplied at 10.10 3 , 140.10 3 and 640.10 3 cells.mL −1 , respectively. Mean egg production corresponded to 28.0 ± 0.5, 20.1 ± 1.0 and 22.0 ± 3.5 eggs.female −1 .day −1 , respectively. Copepods fed T. weissflogii showed the highest mean egg production while those fed I. galbana reached a maximum egg production when the algae were supplied at a density two-to fourfold higher, considering the biovolume of T. weissflogii and C. muelleri. These differences are explained considering the different sizes of the microalgae used to feed the copepods.

ABSTRACT. Temporal variation of the zooplankton from Tramandaí Beach, RS, southern Brazil, with emphasis on Copepoda. The temporal variability of density, species composition, biomass and diversity of the surf zone zooplankton from Tramandaí Beach, RS, Brazil, was studied between August 2005 and August 2006. Samples were taken forthnightly using a zooplankton net of 150 cm total length, 50 cm mouth diameter and 300 µm nylon mesh size. Data on clorofila-a, wind direction, longshore current, salinity, air and water temperature were taken as well. Copepoda presented the highest species diversity, being Temora turbinata (Dana, 1849) the species with higher relative abundance and frequency of occurrence. Other Copepoda species were also numerically important, such as Acartia tonsa (Dana, 1849), Subeucalanus pileatus (Glesbrecht, 1888) and Ctenocalanus vanus (Glesbrecht, 1888). The Mysidacea Metamysidopsis elongata atlantica (Bascescu, 1968) presented frequency of 58.33% and relative abundance of 44%. The peak of mesozooplanktonic biomass (96 mg.m -³) was recorded in September/2005, corresponding to the maximum density value presented for this species (3,535 org.m -³). Information about zooplankton of this region is scarce and the results of this study will provide a base for the knowledge about the biological processes occurring in the surf zone of Tramandaí Beach.

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Sampling was seasonally performed in the Patos Lagoon estuary (Rio Grande, RS, Southern Brazil) to estimate zooplankton biomass and production comparing values obtained using an enzymatic (chitobiase) method and the traditional mathematical models based on growth. Comparison of data obtained from zooplankton samples collected with 90 and 200-μm mesh nets showed that net selectivity influences the estimation of zooplankton biomass and production. Furthermore, it showed differential results for dominance of taxa and proportions of developmental stages in samples. Differences among samples collected at the different sites in the same season were observed using either the mathematical models or the enzymatic method. The two different approaches were also able to detect the seasonal variation in production. In a broad view, data obtained using the chitobiase method showed a similar pattern of zooplankton production compared to those obtained with the traditional mathematical models based on growth. However, values estimated using the enzymatic method were systematically higher than those obtained with the mathematical models. Maximum total production values were estimated as 12.5, 9.2 and 7.9 mg C m − 3 day − 1 for the "chitobiase method", "Huntley model", and "Hirst model", respectively. Considering all sampling sites and seasons, the magnitude of this difference corresponded to 1.95 and 2.49 mg C m − 3 day − 1 for the "Huntley model" and the "Hirst model", respectively. These findings indicate the reliability of the enzymatic method in estimating crustacean production also in estuarine environments of changing salinity, as previously demonstrated for marine waters. In addition, the use of this method is more practical and comparatively less time-consuming and cheaper than the use of the mathematical models based on growth.

In this study the acute and sub-lethal effects caused by the Water Soluble Fraction (WSF) of a light crude oil were assessed for the first time on the planktonic copepod Acartia tonsa. Chromatographic analysis was also performed to quantify the levels of hydrocarbons (total, aliphatic and polyaromatic hydrocarbons) to which copepods were exposed to. Male and female individuals were exposed to hydrocarbon concentrations varying from 12 to 196 µg.L-1 (Total hydrocarbons). The LC 50 was 69.5 (24 hours) and 48.0 µg.L-1 (48 hours) for females and 84.8 (24 hours) and 70.1 µg.L-1 (48 hours) for males. Sub-lethal effects were also evaluated by exposing females to the equivalent of LC 10. Females showed significant reduction in egg and fecal pellet production, and also a delay in the eggs hatching time. Thus, the toxic effects of WSF of oil may be crucial for the specie population maintenance, possibly influencing the equilibrium of marine ecosystems.

Although tropical oceans are generally assumed to have low zooplankton biomass throughout the year, high copepod abundance coupled with fast growth rates can result in a significant amount of crustacean zooplankton production. Here, we use the crustacean moulting enzyme chitobiase to obtain routine estimates of community-level crustacean productivity over a 3-mo period in Guanabara Bay, Rio de Janeiro, Brazil. Chitobiase-based daily production to biomass ratios (P/B) and production rates were compared to values derived from more traditional global predictive models. We examined the abiotic and biotic factors most strongly influencing copepod biomass, daily P/B, and production rates. Mean copepod biomass was 24.0 mg C m −3 over the sampling period, while daily P/B ranged between 0.15 and 1.20. Copepod biomass was negatively related to dissolved oxygen and tidal amplitude, characteristic of the highly eutrophic waters from the inner bay. Mean crustacean productivity over our sampling period was 22.0 mg C m −3 d −1 , varying more over monthly timescales compared to weekly or daily variations. No relationship was found between production rates and biomass, suggesting that biomass, alone, does not explain productivity in Guanabara Bay. Chitobiase-based daily P/B and crustacean production rates were almost always higher than production estimates from global models. Results from this study highlight the need for accurate estimates of crustacean production rates in order to fully understand trophic relationships given that biomass, alone, did not explain the short-term variability in crustacean production. Ultimately, this study reveals that small, fast-growing copepods can contribute just as much, if not more, energy to higher trophic levels in eutrophic tropical estuaries compared to temperate regions.