[Show abstract][Hide abstract] ABSTRACT: The distribution pattern, frequency and density (ind./1000 m) of different mesozooplankton species from the South Georgia Islands, South Orkney Islands and the Weddell-Scotia Confluence were analyzed using data obtained in 1994. The maximum densities of the species found were: Eukrohnia hamata (5330), Sagitta gazellae (1052), Clione limacina antarctica (450), Spongiobranchaea australis (375), Clio sulcata (100), Limacina helicina (4076 x 103), Limacina retroversa (71 x 104), Pelagobia longicirrata (29170), Rhynchonereella bongraini (117), Tomopteris carpenterii (26), Tomopteris planktonis (498), Tomopteris septentrionales (498) and Salpa thompsoni (189). Species density and frequency decreased from South Georgia to the South Orkney Islands, recording intermediate values at the Weddell-Scotia Confluence. Species density in the South Orkney area seemed to be limited by variations in temperature and salinity. The southern area around South Georgia showed the highest density of species, probably due to the influence of the Southern Front of the Antarctic Circumpolar Current. The presence of species characteristic of sub-Antarctic waters such as L. retroversa in the Confluence area could be related to the southward movements of eddies that originate in the Polar Front.
Brazilian Journal of Oceanography 12/2010; 58(4):287-298. · 0.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During a 1-year study period between March 2000 and 2001, 195 (6%) out of 3236 Sagitta friderici were found to be parasitized by metacercariae of digenean species and metacestodes. Parasites belonged to Derogenes sp., Ectenurus virgulus, Monascus filiformis, Lepocreadiidae, Parahemiurus merus and tetraphyllidean metacestodes. Among the chaetognaths parasitized, 178 (91%) harboured one parasite, and the remaining 17 (9%) showed two or three parasites of the same or two different species. The highest prevalences for most of the species occurred in autumn–winter (April–August), except for E. virgulus, which had maximum values in summer (December–January). Species richness varied during the year, reaching a peak in May and June 2000 with six species. The metacercariae of Lepocreadiidae were present in autumn, winter and summer at all maturity stages of S. friderici, with higher prevalence values for stages 0 and I, whereas the rest of the digeneans were absent in stage 0, with higher prevalences for the more advanced maturity stages II and III. The different types of metacercariae did not seem to induce castration in the host. Copepods (Corycaeus amazonicus) were observed attached to the body of chaetognaths or partially digested in their gut. No nematodes, internal parasitic copepods or polychaetes were found.
Journal of Plankton Research 02/2008; · 2.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The following chaetognaths were found in the Atlantic Ocean between 34 to 40 degrees S and 52 degrees 20' to 62 degrees 00' W: Sagitta friderici, S. tasmanica, S. minima, S. gazellae, and S. enflata (in order of abundance). Of these, only S. friderici was parasitised by unencysted metacercariae of the families Derogenidae (Derogenes sp.), Hemiuridae (Ectenurus sp.) and Fellodistomidae (Monascus filiformis), and encysted metacercariae of Lepocreadiidae. The percentage of infection for each sampling station varied from 0.033 to 0.001 in August and from 0.02 to 0.001 in October 1996, with the highest values occurring at stations closer to the coast. The intensity of infection (worms per host) varied from 1 to 3 for Ectenurus sp. and was 1 for Derogenes sp., Monascus filiformis and Lepocreadiidae. Unencysted metacercariae were found in mature developmental stages of chaetognaths, whereas encysted ones occurred mainly in juveniles. The size and length of the ovaries of parasitised and unparasitised chaetognaths did not differ significantly. This is the first report of encysted Lepocreadiidae metacercariae and a progenetic metacercaria of Ectenurus sp. in Chaetognatha from the SW Atlantic Ocean.
Diseases of Aquatic Organisms 09/2006; 71(3):225-32. · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The planktonic chaetognaths from the Brazil-Malvinas (Falkland) confluence, extending between 36º 30' - 50º 5' S and 60º 33' - 41º 7' W, were studied. Ten species were found: Eukrohnia hamata (Möbius, 1875) (Eukrohniidae), Pterosagitta draco (Krohn, 1853) (Pterosagittidae), Sagitta enflata Grassi, 1881, Sagitta gazellae Ritter-Zahony, 1909, Sagitta hexaptera d´Orbigny, 1834, Sagitta lyra Krohn, 1853, Sagitta minima Grassi, 1881, Sagitta planctonis Steinhaus, 1896, Sagitta serratodentata Krohn, 1853, and Sagitta tasmanica Thomson, 1947 (Sagittidae). Sagitta gazellae was the most abundant species followed by E. hamata, S. tasmanica and S. serratodentata. The association analysis among the different species, salinity and temperature revealed two groups of species, one related to higher salinities and warmer waters (P. draco, S. hexaptera and S. serratodentata) and the other to lower salinities and colder waters (E. hamata, S. gazellae and S. tasmanica). The fact that P. draco and S. hexaptera, formerly defined as warm-water species, appeared further south than previously reported might be related to the existence of warm core eddies up to 46º S in September and October 1988.
Iheringia Série Zoologia 01/2004; 94(4). · 0.42 Impact Factor