Age effect on the antioxidant activity of Daphnia magna (Anomopoda: Daphniidae): does younger mean more sensitivity?

It has been accepted that for most species newborns and senescent organisms are more sensitive than other ages to environmental stressors. Nevertheless, it must be considered that there are several biochemical and physiological compensatory processes which are not expressed with the same magnitude during the whole life cycle. With this aim, Daphnia magna individuals of different age were exposed to hexavalent chromium, Cr (VI), at two different sublethal concentrations (0.032 and 0.0064 mg l(-1)), and the activity of some antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione peroxidase (GPx) were evaluated during most of the life cycle of this cladoceran. The antioxidant enzymatic activity showed an inverse relationship with respect to age. The activity of CAT, GR and GPx were increased in the two treated groups, at all life stages tested. On the other hand, the activity of SOD decreased in the same groups. Both, increase and decrease in the antioxidant enzymatic activities, showed significant differences with respect to the control group, being higher for the 0.032 mg l(-1) group. The Cr (VI) LC50 was also estimated for these age groups, finding statistical differences among them. Even though adults exhibited higher responses, these enzymatic activity changes should not be interpreted as higher sensitivity, since the daphnids acute chromium toxicity followed a different pattern, with increasing LC50 values according to age.     

Spatial–temporal pattern of bluefin tuna (Thunnus thynnus L. 1758) gonad maturation across the Mediterranean Sea

Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that this species is divided into a western and an eastern stock, which spawn in the Gulf of Mexico and the Mediterranean Sea, respectively. To learn more about the reproductive behavior of the eastern BFT stock, we tracked gonadal development in adult fish that were sampled between April and July during three consecutive years (2003–2005). Sampling campaigns were carried out using common fishing methods at selected locations within the Mediterranean Sea, namely Levantine Sea, Malta, and Balearic Islands. An additional sampling point, Barbate, was situated northwest of the Straits of Gibraltar along the Atlantic coast. Morphometric parameters such as the total body mass (M _B) and the weights of the gonads (M _G) were recorded, and the respective gonadosomatic index (GSI) values were calculated. The data collected revealed two important trends: (1) GSI values are higher in fish caught in the eastern rather than the western locations across the Mediterranean Sea, and (2) the GSI reaches maximum values between late May and early June in Levantine Sea (eastern Mediterranean Sea), and only 2 and 4 weeks later in the central (Malta) and western (Balearic Islands) locations, respectively. The advanced gonadal development in BFT correlates well with higher sea surface temperatures. Our findings also distinguish the northern Levantine Sea BFT population (mean M _B 78.41 ± 4.13 kg), and the Barbate BFT population with the greatest M _B (all fish sampled > 100 kg). These data reflect a situation in which the eastern Mediterranean basin may function as a habitat for young BFT, until they gain a larger M _B and are able to move to the Atlantic Ocean. However, the existence of genetically discrete BFT populations in the Mediterranean Sea cannot be ruled out.     

Spatio-temporal variations in the diet and stable isotope composition of the Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 of the continental shelf of southeastern Brazil

The feeding ecology of Merluccius hubbsi was investigated in 2 regions of SE Brazil. The major food sources for the hakes were fish, crustaceans, and squid. In the upwelling system of Cabo Frio, the diet was very similar in the summers of 2001/2002 and spring 2002; fish were the most important prey followed by crustaceans. In Ubatuba, euphausiids were an important prey during the winter 2001 (100 m), while in the summer 2002, fish and amphipods predominated in the diet in the shallower site (40 m) and squid in the deeper site (100 m). The hakes showed temporal differences in stable isotope signatures in both regions, while C:N ratios varied only in Cabo Frio. δ¹⁵N and δ¹³C (bulk and corrected for lipid content) increased with fish length, which seems to be related to the increasing importance of fish and decreasing importance of euphausiids and amphipods in the diet of larger hakes. The mean trophic level of 3.7 for M. hubbsi was estimated using δ¹⁵N of bivalves as baseline and the fractionation of 3.4‰ between trophic levels.     

Critical thermal maxima and upper lethal temperatures for the calanoid copepods Acartia tonsa and A. clausi

Determination of the critical thermal maxima and upper lethal temperatures for Acartia tonsa Dana and A. clausi Giesbrecht revealed the relative temperature tolerance of the two species. A. tonsa exhibited a wider range of acclimation temperatures compared to A. clausi. The response of A. tonsa is related to its ubiquity in Atlantic Ocean estuaries (temperate and tropical), and its capacity to live in temperate waters throughout most of the year. Differences between upper lethal temperatures and critical thermal maxima were very narrow for A. tonsa from tropical and subtropical areas. This suggests that, in warm climates, this copepod lives close to its upper lethal temperature limits.Based in part on a dissertation submitted in partial fulfillment for the Ph.D. degree at the University of Rhode Island.     

Molecular prey identification in wild Octopus vulgaris paralarvae

The trophic ecology of Octopus vulgaris paralarvae collected in 2008 off the Ría de Vigo, NW Spain (42° 12.80′ N–9° 00.00′ W), was approached by both morphological and molecular methods. External digestion of prey and posterior suction of the liquefied contents by wild O. vulgaris paralarvae made the morphological identification of gut contents impossible. Thus, a PCR-based method using group-specific primers was selected to identify prey consumed by O. vulgaris paralarvae in the pelagic realm. The mitochondrial ribosomal 16S gene region was chosen for designing group-specific primers, which targeted a broad range of crustaceans and fishes but avoided the amplification of predator DNA. These primers successfully amplified DNA of prey by using a semi-nested PCR-based approach and posterior cloning. Homology search and phylogenetic analysis were then conducted with the 20 different operational taxonomic units obtained to identify the putative organisms ingested. The phylogenetic analysis clustered ingested prey into 12 families of crustaceans (11 belonging to the order Decapoda and 1 to the order Euphausiacea) and two families of fishes (Gobiidae and Carangidae). According to the Czekanowski’s Index (CI), the trophic niche breadth of O. vulgaris paralarvae is low (CI = 0.13), which means that these paralarvae are specialist predators at least during the first weeks of their life cycle. It is the first time that natural prey has been identified in O. vulgaris paralarvae collected from the wild, and such knowledge may be critical to increasing the survival of O. vulgaris hatchlings in captivity, a goal that has been actively pursued since the 1960s by aquaculture researchers.