Argentinean Waters Research Articles

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Bycatch of the piked dogfish Squalus acanthias Linné, 1758 (Chondrichthyes, Squalidae) in semi-pelagic longline fisheries at the Patagonian Shelf

The piked dogfish Squalus acanthias is part of the bycatch of several South American longline fisheries, although in Argentina, it was only reported in the bycatch of benthic and demersal fisheries operating bottom nets. This communication represents the first record of S. acanthias bycatch in a commercial semi-pelagic longline fishery within Argentinean waters. In October-November 2005, 185 piked dogfish were captured (122 females and 63 males). The es- timated mean catch rate was 0.37 sharks/1000 hooks (544,320 hooks deployed). Nearly half of the captured females and over 50% of captured males were morphometrically mature. The piked dogfish bycatch could have been influenced by the use of the Argentine shortfin squid Illex argentinus as bait; this squid is part of the shark's natural diet. Although S. acanthias is abundant in the region, we believe that the bycatch species could be more vulnerable than the targeted ones since the signs indicating a declining population of non-target species in commercial catches and collapses in bycatch populations go unnoticed.

Molecular systematics and patterns of morphological evolution in the Centropagidae (Copepoda: Calanoida) of Argentina

Recent studies have shown the value of complementing standard taxonomy with genetic analyses to reveal cryptic diversity and to aid in the understanding of patterns of evolution. We surveyed variation in the COI mitochondrial gene in members of the three genera of centropagid copepods from the inland waters in Argentina. In general, we found a close association between molecular and morphological systematics in this group. Similar to findings for marine calanoids, genetic distances within Boeckella species were modest ( 11%). Parabroteas is currently monotypic, although we detected cryptic genetic diversity, with two lineages showing 5.5% divergence. In contrast, Karukinka was not a valid genus, apparently representing an interesting and atavistic offshoot of B. poppei, a result reinforcing the value of considering both morphological and molecular evidence. Moreover, we used combined genetic and morphological information, analysed with maximum likelihood methods, to evaluate the common assumption that evolution tends to proceed via the loss of structures in crustaceans. Although analysis of other taxa and character types is required to evaluate fully the reduction hypothesis, our results suggest that structures may be gained readily as well as lost. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 279–292.

Seabird mortality at trawler warp cables and a proposed mitigation measure: A case of study in Golfo San Jorge, Patagonia, Argentina

We studied the interaction between seabirds and warp cables in the high-seas Argentine hake Merluccius hubbsi trawl fishery operating in Golfo San Jorge, Argentina, and tested the efficacy of a simple mitigation measure designed to reduce mortality at warp cables. Observations were made onboard hake trawlers during the height of the fishing season, between December 2004 and April 2005. Thirteen seabird species used food made available by fishing operations. The most frequent and abundant seabirds (% occurrence, mean maximum number per haul) were the Kelp gull Larus dominicanus (98.1%, 348.5) and the Black-browed albatross Thalassarche melanophrys (96.1%, 132.2). Contacts with warp cables were recorded for six species in 81.4% of hauls, with a mean number of contacts per haul of 14.4 ± 23.8 (range = 0–127). A total of 53 individuals were killed due to interactions with nets and cables, resulting in a total cable mortality rate of 0.14 birds/haul. Considering the fishery’s fishing effort, the estimated total number of birds killed during the study was 2703 (CV = 0.8), of which 306 (CV = 0.9) were killed due to contacts with warp cables (255 Kelp gulls and 51 Black-browed albatross). The tested device consisted of a plastic cone attached to each warp cable. In hauls with mitigation device, the number of contacts was reduced by 89% and no seabirds were killed. Mean distances between seabirds and cables were significantly larger in hauls with than without mitigation device (2.6 vs 0.9 m). The proposed device could be easily applied in this and other trawl fisheries operating in Argentine waters. Increased effort should be placed in implementing mitigation measures and the monitoring of cable related mortality associated to high-seas trawlers operating in the Argentine Continental Shelf.

Mugil curema in Argentinean waters: Combined morphological and molecular approach

A previously unidentified mullet species ( Mugil sp.) from Mar Chiquita lagoon, Argentina, was compared with two candidate species Mugil curema and M. cephalus using 12 truss landmarks and three mitochondrial DNA genes (12S rRNA, cytochrome b and COI). Both procedures confirmed that the Argentinean fish were white mullet M. curema. Morphological comparisons clearly segregated M. curema from M. cephalus samples in PCA plot. Similarly, Argentinean haplotypes at each gene overlapped with M. curema reference samples while M. cephalus haplotypes remained distinct. These combined data provide a valuable baseline for further investigations on the geographic distribution of this commercially important species group.

Food habits, selectivity, and foraging modes of the school shark Galeorhinus galeus

The foraging ecology of the school shark Galeorhinus galeus was studied in Anegada Bay, Argentina, during the seasonal occurrence of this species in Argentinean waters (October to April) from 1998 to 2001. Of the 408 individuals examined, 168 (41.2%) had food remains in their stomachs. The proportion of individuals with food remains was negatively correlated with total length. In general, the diet was composed mainly of teleosts (98.5% IRI (index of relative impor- tance)), with invertebrates and chondrichthyans as minor prey. The diet varied ontogenetically and seasonally. Juveniles and adults differed in their consumption of invertebrates, with juveniles prey- ing more on benthic invertebrates, mainly the octopus Octopus tehuelchus, and adults on squid. From December to February, adults preyed mainly on benthic teleosts (almost exclusively the Atlantic midshipman Porichthys porosissimus), while from March to April the consumption of squid increased. A comparison of numbers of prey in stomachs with abundance of prey in the environment in March and April showed that, in these months, juveniles selected invertebrates and demersal teleosts and avoided pelagic teleosts and chondricthyan prey, and adults selected squid and avoided pelagic teleosts. This indicates that, during this period, G. galeus is not an opportunistic predator. The mean size of prey increased with increasing shark length, but even large sharks consumed small prey. All shark sizes consumed prey fragments that were significantly larger than other prey con- sumed whole. This indicates that G. galeus is able to overcome gape limitation by mutilating prey, and that the ontogenetic diet shift was not due to a change in the ability to seize prey.

Mid-Holocene serpulid build-ups in an estuarine environment (Buenos Aires Province, Argentina)

A bed with several serpulid build-ups is described from a Holocene outcrop at Quequén Grande River, Argentina. The tubes were dated at 6360 ± 80 years BP. The morphology and size parameters of the serpulids were compared to different species of serpulids from the literature and tubes of Ficopomatus enigmaticus, Hydroides dianthus and Hydroides plateni from Argentinean waters. In spite of the fact that today only F. enigmaticus constructs build-ups in Argentine brackish environments, the fossil tubes could not be assigned to this species, but instead, they show close similarities to those of the two species of Hydroides. The sequence is interpreted as having originated from a brackish environment. At present, neither the endemic H. plateni nor any other species of Hydroides construct build-ups in brackish waters of southern South America. This suggests, that suitable environments to construct aggregates were more widespread than today or that the invasion of F. enigmaticus replaced Hydroides; alternatively various causes may have acted jointly.

Population structure of nuclear and mitochondrial DNA variation among South American Burmeister’s porpoises (Phocoena spinipinnis)

Little is known about the biology of Burmeister’s porpoises (Phocoena spinipinnis), a small cetacean species endemic to South American waters. Information on stock structure, however, is urgently needed, as the species suffers from considerable mortality due to local fishery activities throughout its distribution range. Using mitochondrial control region sequences and 11 species-specific microsatellite loci, we assessed the genetic differentiation among 118 stranded, incidentally or directly-caught Burmeister’s porpoises from different localities in Peruvian, Chilean, and Argentine waters. F-statistics and Bayesian clustering analyses indicate a major population differentiation along the South American Pacific coast, separating Peruvian from both Chilean and Argentine individuals. Interestingly, this population boundary is consistent with the population structure found in another sympatrically-occurring cetacean species: the dusky dolphin (Lagenorhynchus obscurus). Given that vulnerability to local depletion for South American coastal porpoises and dolphins is probably highest in the Peruvian population (due to high exploitation levels and recurrent El Nino events), the genetic data reported here considerably strengthen the need for conservation efforts focused on regulation of catches in local waters. Moreover, we discuss possible genetic differentiation among Burmeister’s porpoises (i) from the Atlantic and Pacific Ocean and (ii) from different Peruvian harbors. Finally, cross-species amplifications suggest that our newly-developed microsatellite markers will be useful in population genetic studies in the five other extant porpoise species.

Bycatch of the pelagic ray <i>Dasyatis violacea</i> in Uruguayan longline fisheries and aspects of distribution in the southwestern Atlantic

The presence of the pelagic ray Dasyatis violacea (Bonaparte, 1832) in Uruguayan waters has been monitored since April 1998, the beginning of the National Observer Programme on board the Uruguayan tuna fleet (PNOFA). These are the first records of these species for the South Atlantic off Uruguay. Its distribution within the area is analysed, based on 13 trips made from April 1998 to September 2001 from 26 to 37°S. Five hundred and twenty five specimens were caught during this period. The presence of the species appears to be closely associated with the highest values of surface water temperature, with CPUE being relatively low below 20°C. The southern border of its distribution is around 36°S. Dasyatis violacea is part of a well-defined warm water fauna that reaches Uruguayan and northern Argentinean waters following warm subtropical waters. The incidental capture of D. violacea in the area reaches significant levels; the species is always discarded. We suggest that this bycatch is important and should be monitored from a conservation point of view.

Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (Lagenorhynchus obscurus)

Using nine nuclear species-specific microsatellite loci and two mitochondrial gene fragments (cytochrome b and control region), we investigated the processes that have shaped the geographical distribution of genetic diversity exhibited by contemporary dusky dolphin (Lagenorhynchus obscurus) populations. A total of 221 individuals from four locations (Peru, Argentina, southern Africa, and New Zealand) were assayed, covering most of the species' distribution range. Although our analyses identify a general demographic decline in the Peruvian dusky dolphin stock (recently affected by high natural and human-induced mortality levels), comparison between the different molecular markers hint at an ancient bottleneck that predates recent El Niño oscillations and human exploitation. Moreover, we find evidence of a difference in dispersal behaviour of dusky dolphins along the South American coast and across the Atlantic. While data in Peruvian and Argentine waters are best explained by male-specific gene flow between these two populations, our analyses suggest that dusky dolphins from Argentina and southern Africa recently separated from an ancestral Atlantic population and, since then, diverged without considerable gene flow. The inclusion of a few New Zealand samples further confirms the low levels of genetic differentiation among most dusky dolphin populations. Only the Peruvian dusky dolphin stock is highly differentiated, especially at mitochondrial loci, suggesting that major fluctuations in its population size have led to an increased rate of genetic drift.

Viable but nonculturable Vibrio cholerae O1 in the aquatic environment of Argentina.

In Argentina, as in other countries of Latin America, cholera has occurred in an epidemic pattern. Vibrio cholerae O1 is native to the aquatic environment, and it occurs in both culturable and viable but nonculturable (VNC) forms, the latter during interepidemic periods. This is the first report of the presence of VNC V. cholerae O1 in the estuarine and marine waters of the Rio de la Plata and the Argentine shelf of the Atlantic Ocean, respectively. Employing immunofluorescence and PCR methods, we were able to detect reservoirs of V. cholerae O1 carrying the virulence-associated genes ctxA and tcpA. The VNC forms of V. cholerae O1 were identified in samples of water, phytoplankton, and zooplankton; the latter organisms were mainly the copepods Acartia tonsa, Diaptomus sp., Paracalanus crassirostris, and Paracalanus parvus. We found that under favorable conditions, the VNC form of V. cholerae can revert to the pathogenic, transmissible state. We concluded that V. cholerae O1 is a resident of Argentinean waters, as has been shown to be the case in other geographic regions of the world.

Consumption of marine mammals by broadnose sevengill shark Notorynchus cepedianus in the northern and central Patagonian shelf

The study of food habits of the broadnose sevengill shark (Notorynchus cepedianus) based on the observation of the stomach contents of 22 individuals, revealed the importance of marine mammals as part of the shark's diet. The analysis showed that marine mammals represent at least 30% of the total consumed biomass by broadnose sevengill sharks. The frequency of occurrence was estimated to be 35%. The three pinnipeds with local distribution and at least two species of cetaceans were consumed. Although consumption of marine mammal was high, there was no evidence of direct attack on living preys by N. cepedianus, in Argentine waters.

Zooplankton assemblages and hydrography in the spawning area of anchovy (Engraulis anchoita) off Río de la Plata estuary (Argentina - Uruguay)

The massive spawning of anchovy (Engraulis anchoita) in Argentine waters takes place in spring in the coastal sector off the Buenos Aires Province, with the highest concentrations of spawners occurring in front of the Río de la Plata mouth. In October 1995, the size structure, composition and abundance of the zooplankton community was analyzed and related to the hydrography and the abundance of anchovy eggs. Oceanographic conditions were different from the recorded means for the season. A higher proportion of the colder and more saline shelf waters were present in the coastal area and strong haloclines were not observed. High values of plankton biomass were observed in the estuarine frontal area and in the weakly stratified waters of the median shelf. The cluster analysis of the stations gave rise to the formation of coastal (CA), transitional (TA) and shelf (SA) faunistic areas. Mesozooplankton smaller than 1 mm total length (TL) dominated the whole area. The copepods, Paracalanus spp. and Oithona similis, and the cladocerans, Evadne nordmanni and Podon spp., constituted the bulk of this mesozooplankton fraction. Oithona similis was the dominant species in the SA. The copepod, Acartia tonsa (1–2 mm TL), was extremely abundant in the estuarine front (more than 17 600 individuals m–3) followed by appendicularians, members of Pseudocalanidae, anchovy eggs and decapod larvae. Species of Calanidae (Calanoides carinatus and Calanus simillimus), the amphipod hyperiid, Themisto gaudichaudii, and the euphausiid, Euphausia lucens, largely dominated the macrozooplankton (>2 mm TL) in the TA and SA. In the CA, significant positive correlations between the abundance of small copepods (size ranges <1 and 1–2 mm) and anchovy eggs were found. Trophic implications of these findings for first-feeding anchovy larvae were discussed. The adequacy of the TA and SA as feeding ground for adults of anchovy was evaluated.

The Association between Medusa Lychnorhiza lucerna (Scyphomedusae, Rhizostomeae) and Decapod Libinia spinosa (Brachyura, Majidae) Recorded for the First Time in Neritic Waters of Argentina

The paper discusses the first record of the association between the medusa Lychnoriza lucerna Haeckel, 1880 and the decapod Libinia spinosa Milne-Edwards, 1934 in neritic waters of Argentina. Our results allow us to conclude that the symbiotic relation between these two species is a common phenomenon. The crab L. spinosa is located in the subgenital pockets of L. lucerna such that one-half of its cephalothorax is exposed to the outside. The crabs feed at the expense of the medusa, ingesting some portion of its food. A few specimens of the crab have been found, mostly females; the only male was of a somewhat larger size.

Toxicity tests to assess pollutants removal during wastewater treatment and the quality of receiving waters in Argentina.

In Argentina, legislation to control adverse impacts of effluent discharges and the quality of receiving waters is scant and relies mainly on the physicochemical characteristics of the effluents and receiving waters. Objectives of this study were to use standardized acute toxicity tests to assess treatment of petrochemical industry effluents and the toxicity of various treated industrial effluents in the Buenos Aires metropolitan area and their receiving waters. Tests for the first objective used Daphnia magna and Ceriodaphnia dubia; those for the second used D. magna, Spirillum volutans, and Scenedesmus spinosus. Chemical analyses demonstrated that the removal of aromatic hydrocarbon compounds (benzene, toluene, ethylbenzene, xylene, styrene, and naphthalene) from the petrochemical effluents ranged between 77 and 93%, but toxicity removal was significantly lower: untreated effluents were very toxic and treated effluents were very toxic to toxic [acute toxicity units (TUa) > 3]. Physicochemical parameters measured according to current Argentinian regulations indicated that industrial effluents (e.g., from textile and paper industries) were within established guidelines, but 25% of the samples were moderately to highly toxic (TUa > 1.33). However, for the receiving waters, toxicity tests were moderate to very toxic. The results show the need of including tests for toxicity of discharged effluents, and their effects on receiving waters of Argentina, especially for regulatory purposes.

Proposed life cycle of Ascarophis marina (Nematoda: Cystidicolidae) in Argentine waters.

The life history of Ascarophis marina in Argentina is proposed on the basis of morphometric features of larval and adult specimens, as well as of trophic relationships among invertebrate and vertebrate hosts in the same geographic area. Adult and larval specimens of A. marina were found in the alimentary tract of the teleost fishes Parona signata (Carangidae) and Urophycis brasiliensis (Gadidae). Third-stage larvae ocurred in the shrimps Peisos petrunkevitchi (Sergestidae) and Artemesia longinaris (Penaeidae).

Description of an Architeuthis from Argentine waters

A specimen of the giant squid Architeuthis sp., caught by a trawler on the Patagonian inner shelf (46°30′S–66°00′W) in April 1995, is described. The squid was a mature female of 1 625 mm mantle length with 321 growth lines in the statoliths. Internal and external anatomy and morphometric characters were studied as far as possible, given the very damaged condition of the animal.

Cytogenetic study of two species of needlefish (Belonidae) from Argentina

The chromosomes of the two species of needlefish, Potamorraphis cf. eigenmanni and Strongylura microps, from fresh waters of Argentina were analyzed using C‐banding and silver staining and their karyotypes were described for the first time. The former species possessed 2n‐54 and karyotype composed of three pairs metacentric to submetacentric chromosomes and 24 pairs of subtelo to telocentric chromosomes. The NORs were situated on the end of the shorter arms of one middle‐sized bi‐armed pair of chromosomes. The later species possessed 2n=50 and karyotype composed exclusively of subtelo to telocentric chromosomes gradually decreasing in size. The NORs were situated inter‐stitially on the third pair of chromosomes. One or two supernumerary chromosomes were observed in one individual of the sample. Present data indicate greater cytotaxonomic diversity among species of needlefish which might be associated with their colonization of fresh waters.

Occurrence of Merogony ofAggregataFrenzel 1885 (Apicomplexa) inPleoticus muelleriandArtemesia longinaris(Crustacea: Natantia) from Patagonian Waters (Argentina)

The aim of this paper is to describe the merogonic phases of the coccidianAggregatasp. in the natantiansPleoticus muelleriandArtemesia longinarisfrom Argentina. Ninety-seven specimens ofP. muelleri(from San Jorge Gulf) and 49 ofA. longinaris(from Rawson) were examined for intestinal parasites. Intestines were processed under standard histological conditions. The distribution of the octopuses (where gamogony and sporogony ofAggregataspp. take place) in the area considered and the importance of finding these protistans in crustaceans other than brachyurans are also explored. High prevalence values for both hosts indicate that shrimps are the primary hosts for these parasites in Argentinean waters.

Echinobothrium notoguidoi n. sp. (Cestoda: Diphyllidea) from Mustelus schmitti (Chondrichthyes: Carcharhiniformes) in the Argentine Sea

A new cestode, Echinobothrium notoguidoi n. sp., is described from the spiral intestine of the shark Mustelus schmitti, from coastal waters off Mar del Plata, Argentina. This species is distinguished from all others in the genus by a rostellar armature consisting of 2 apical groups of 31 large hooks each, arranged in 2 rows (16 anterior, 15 posterior) with 13 hooklets per side, a wide corona of 8-11 rows of spines posterior to the rostellum, 8 rows of 24-26 spines on the cephalic peduncle, and 11-15 testes per proglottid. The new species most closely resembles 2 congeners that also parasitize sharks, Echinobothrium musteli and Echinobothrium scoliodoni, on the basis of the armature of the rostellum and cephalic peduncle and the presence of a corona of small spines. Echinobothrium notoguidoi can be differentiated from E. musteli by the number of hooklets (3) and testes (22), and from E. scoliodoni by the number of large hooks (10-13), spines on the cephalic peduncle (> 100), and segments (40-50). Echinobothrium notoguidoi is clearly distinguished from Echinobothrium pigmentatum described previously from Zapteryx brevirostris in Argentine waters by the following combination of characters: corona of hooks lacking, possession of fewer apical hooks (20), hooklets in a continuous row instead of separate groups, fewer spines in the cephalic peduncle (9-13 per row), and fewer testes (5-7) per proglottid.