Muxagata, E., Amaral, W. J. A., and Barbosa, C. N. 2012. Acartia tonsa production in the Patos Lagoon estuary, Brazil. – ICES Journal of Marine Science, 69: 475–482. Acartid copepods are abundant in estuaries, harbours, and semi-enclosed waters. A monitoring programme with the objective of evaluating copepod production, particularly that of Acartia tonsa, the dominant taxon in the Patos Lagoon estuary, was implemented. Zooplankton samples are collected monthly from two fixed locations with bongo nets 30 cm in diameter with nets of 90 and 200 μm mesh. Over a full year, 33 quantitative samples were analysed; copepods represented 40% of the organisms collected with the 90-μm mesh. Adults and copepodites of A. tonsa accounted for ∼19% of the total copepod fauna at both locations. Daily production rates of A. tonsa were calculated as 0.40 mg C m−3 d−1 for the inner estuary and 3.65 mg C m−3 d−1 in the channel. The value of 1 333 mg C m−3 year−1 calculated for A. tonsa at the channel station is very high relative to the situation in other estuaries, indicating that the estuary has a high production of copepods.
In this study the effects of different salinities and algal diets on number of eggs produced by the copepods Pseudodiaptomus richardi and Notodiaptomus incompositus, were evaluated under controlled laboratory conditions. For P. richardi the development time from newly hatched nauplii to adults was compared for the three salinities under saturating food conditions. This species showed to be very tolerant to a wide range of salinities presenting the same growth rate from nauplii to adults when reared at salinities (S) 5, 15 and 30. The survivorship was 40,51 ± 7,6% in average, with a maximum of 49% at S = 15. The mean development time was 16 days (20°C), with no differences (ANOVA, p > 0,05) among the three salinities tested. The egg production values where in average higher (p < 0,05) for females reared at tested salinity since nauplii stages, when compared to acclimated females captured from the natural environment. The copepod N. incompositus showed oligohaline characteristics since adults of this species presented total mortality at S = 15. The survivorship increased with the decrease of salinity, being 20% at S = 10 and 79% at S = 1. There was no clutch production of N. incompositus at S = 10, whereas it was very low at salinities 5 and 1. Regarding the diets tested there was no significant differences (ANOVA, p > 0.05) among the algae evaluated (Isochrysis galbana, Thalassiosira weissflogii, Chaetoceros muelleri and mixed diet). However the number of eggs produced found for P. richardi were in average twelve times higher than those observed for N. incompositus. The results of this study indicate that P. richardi is a very tolerant species, being well adapted for the constant fluctuating conditions of salinity and food composition usually found in estuaries and coastal areas.
Litopenaeus vannamei is the most cultivated shrimp species in Brazil, being fed basically on high protein formulated diets. However, some studies have shown that the natural zooplankton found in shrimp ponds can be part of the diet of this crustacean. In this study, the zooplankton composition, density and biomass were evaluated for two shrimp ponds from a shrimp farm in the Patos Lagoon estuary, in southern Brazil (32°00'S, 51°59'W) between 11/09/2005 and 01/20/2006. The two ponds were sampled over three consecutive months using a zooplankton net of 150 cm total length, 30 cm mouth diameter and 140 µm nylon mesh size. All the zooplankton samples were preserved in formaldehyde solution at a final concentration of 4% and transported to the laboratory, where the composition, density and biomass (wet and dry weight) were assessed. Copepoda and Cladocera were the most frequent groups, while the most abundant species were Acartia tonsa, Pseudodiaptomus richardi and Moina micrura, species commonly found in the Patos Lagoon Estuary. The density values obtained in the ponds were higher than those usually found in the estuary during periods of maximum production, reaching 278 org.L-1 in 11/18/2005 (pond 1), and 277 org.L-1 in 12/08/2005 (pond 2), suggesting that the zooplankton grow well in the shrimp ponds. Zooplankton biomass in the ponds was also relatively high, ranging from 0.15 to 13.28 g.m-3 of wet weight and 0.01 to 2.72 g.m-3 of dry weight, following the same tendency of density. These results clearly indicate that the natural zooplankton occurring in the shrimp ponds represents a potential food source for the shrimp larvae and juveniles during the first months of culture.
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