Parasite infections (Trematoda, Digenea) of Sagitta friderici (Chaetognatha) from the southwestern Atlantic Ocean: prevalence and distribution

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.     

Parasitism (Trematoda,Digenea) in medusae from the southwestern Atlantic Ocean: medusa hosts,parasite prevalences,and ecological implications

Digenean are important endoparasites of fish with complex life cycles; some genera include medusae as secondary hosts. Their transmission to fish occurs when fish prey on these jelly hosts. Fish predation on jellyfish is a widespread phenomenon, even though predation by fish on jellyfish has not been determined through parasitism yet. We hypothesized that medusae with high prevalences of digeneans could be important for their transmission to fish. A total of 48,900 specimens of 50 medusa species were analyzed; 2,181 harbored digeneans. Opechona sp. and Monascus filiformis were the most frequent and abundant parasites with the widest range of hosts. Hemiuridae gen. sp. and Bacciger sp. were found in few specimens of some medusa species. Prevalences were unevenly distributed in the region. Three groups with high prevalence values were identified mainly related to frontal areas: Río de la Plata, Bahía Blanca, and North Patagonian tidal front. Eucheilota ventricularis, Clytia hemisphaerica, Proboscidactyla mutabilis, Liriope tetraphylla, and Aequoerea spp. were the medusae that contributed the most as secondary hosts to M. filiformis and Opechona sp. The high prevalences found in these medusae suggest that may be a fundamental part of the life cycles of both parasites in these areas.     

A biological survey of St. Paul's Rocks in the equatorial Atlantic Ocean

In May 1971, an ornithological census was taken, and samples of soil and marine invertebrates collected, on St. Paul's Rocks-an isolated group of small islands in the equatorial Atlantic Ocean. Fish were caught nearby. Crabs (Grapsus grapsus) were abundant on the Rocks and rock pools contained anthozoa, polychaetes, Crustacea and gastropods–a marine invertebrate fauna apparently closely related to that of Brazil. Specimens of four species of fish were obtained including one of Holocentrum sanctipauli , a species endemic to the Rocks.
Protozoa, nematodes, bdelloid rotifers and cuticles of cryptostigmatid mites were found in the soil; most of the species identified were microbial feeders with a cosmopolitan distribution. The only terrestrial flora observed were green and blue-green algae and a nematode-predacious fungus, continuous sea-spray upon the Rocks preventing the growth of higher plants. Breeding populations of brown boobies and black and brown noddies were observed and counted. The presence of all life-cycle stages of the booby suggested that its breeding is aseasonal.     

Blooms of single bacterial species in a coastal lagoon of the southwestern Atlantic Ocean

We investigated seasonal differences in community structure and activity (leucine incorporation) of the planktonic bacterial assemblage in the freshwater and brackish-water zones of a shallow coastal lagoon of the southwestern Atlantic Ocean. Alphaproteobacteria formed the dominant microbial group in both zones throughout the sampling period. After an intrusion of marine water, members of the SAR11 lineage became abundant in the brackish-water zone. These bacteria were apparently distributed over the lagoon during the following months until they constituted almost 30% of all prokaryotic cells at both sampling sites. At the first sampling date (March 2003) a single alphaproteobacterial species unrelated to SAR11, Sphingomonas echinoides, dominated the microbial assemblages in both zones of the lagoon concomitantly with a bloom of filamentous cyanobacteria. Pronounced maxima of leucine incorporation were observed once in each zone of the lagoon. In the freshwater zone, this highly active microbial assemblage was a mix of the typical bacteria lineages expected in aquatic systems. By contrast, a single bacterial genotype with >99% similarity to the facultative pathogen gammaproteobacterial species Stenotrophomonas maltophilia formed >90% of the bacterial assemblage (>10(7) cell ml(-1)) in the brackish-water zone at the time point of highest bacterial leucine incorporation. Moreover, these bacteria were equally dominant, albeit less active, in the freshwater zone. Thus, the pelagic zone of the studied lagoon harbored repeated short-term blooms of single bacterial species. This finding may have consequences for environmental protection.     

The soluble fluorescence in the open sea: Distribution and ecological significance in the equatorial Atlantic Ocean

The red fluorescence of filtered sea water has been measured on 216 samples in the 0–150 m layer of the equatorial Atlantic Ocean.Soluble fluorescence is maximum where chlorophyll a and in vivo fluorescence are maximum, but the percentage of soluble fluorescence, (soluble fluorescence/in vivo fluorescence) × 100, is minimum at these levels; in recently upwelled waters of the equatorial divergence, the percentage of soluble fluorescence is equal to 10 in the 0–20 m layer and regularly increases to 60 or more at 100–150 m; in the nitrate depleted mixed layer of a convergence it averages 30, decreases to 15 in the thermocline maximum of chlorophyll a, and again reaches 60 in deep waters.A significant positive correlation has been found between the percentage of soluble fluorescence and the amount of phaeophytin, and soluble fluorescence in the open sea is thought to be the result of the degradation and release of chloroplastic products by aged or grazed phytoplankton populations. Low values (< 20) of the percentage soluble fluorescence indicate the presence of healthy phytoplankton cells, whereas high values (> 30) are evidence of unfavourable growth conditions (e.g., limiting nutrients or darkness) or high grazing pressure.The simultaneous measurement of in vivo fluorescence and soluble fluorescence is a method of obtaining valuable information rapidly on the physiological state of the phytoplankton population in the water column.     

Coccolithophores in the equatorial Atlantic Ocean: response to seasonal and Late Quaternary surface water variability

The present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial Atlantic. Data from a range of different samples, from the plankton, surface sediments as well as sediment cores are shown and compared with each other.In general, the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns. Cell densities reached a maximum of up to 300×10³ coccospheres/l in the upwelling area of the equatorial Atlantic. Here, Emiliania huxleyi is the dominant species with relatively high cell numbers, whereas Umbellosphaera irregularis and Umbellosphaera tenuis are characteristic for oligotrophic surface waters. Although they are observed in high relative abundances, these species only occur in low absolute numbers. The lower photic zone is dominated by high abundances and considerable cell numbers of Florisphaera profunda.The geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses. However, abundances of the oligotrophic species Umbellosphaera irregularis and Umbellosphaera tenuis are strongly diminished, causing an increase in relative abundance of the lower photic zone taxa Florisphaera profunda and Gladiolithus flabellatus.During the past 140,000 years the surface water circulation of the equatorial Atlantic has changed drastically, as can be seen from changes in the coccolithophore species composition, absolute coccolith numbers, as well as coccolith accumulation rates. Significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial Atlantic during the last glacial interval (oxygen isotope stages 2–4), which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site. In the western equatorial Atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods, which probably is caused by a deepening of the thermocline.     

Hermaphroditism in the lantern sharkEtmopterus unicolor (Squalidae,chondrichthyes)

Of the 70 specimens of the lantern shark,Etmopterus unicolor, collected in Suruga Bay and adjacent waters 22.9% were abnormal hermaphrodites, 30.0% normal males, and 47.1% normal females. Fifteen hermaphrodites had female reproductive organs composed of normal ovaries, oviducts, nidamentai glands and uteri as well as claspers. The clasper lengths of these hermaphrodites increased rapidly after the sharks reached 510 mm TL, the length about equal to the size at maturity for normal females. The ovary and uterus of abnormal females became mature at a total length greater than 500 mm, whereas the size at maturity was about 500 mm TL for normal females compared to 460 mm TL for normal males. In one specimen, the left gonad contained both ovarian and testicular tissues, the bulk of which was testicular.     

Discovery of Poromitra macrophthalma (Melamphaidae) in the Atlantic Ocean

Journal of Ichthyology - The occurrence of big-eyed rhinofish Poromitra macrophthalma in the central part of the Atlantic Ocean is reported for the first time. This species was previously known...     

Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean

Schejter, L. and Mantelatto, F.L. 2011. Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92 : 141–149. The available literature on zoanthid–hermit crab associations deals only with records of this phenomenon, providing no detailed information. We describe, for the first time, the shell‐like colonies of Epizoanthus paguricola associated with the hermit crab Sympagurus dimorphus from benthic samples taken in the Argentine Sea, between 85 and 131 m depth, and provide information about morphometric relationships between the hermits and the zoanthids. In total, 260 specimens (137 males and 123 females) of S. dimorphus were collected, 240 (92.3%) of which were living in symbiosis with E. paguricola. The remaining 20 (7.7%) were living inside gastropod shells. As the initial structure of the pseudoshell, 12 different gastropod species were found (all were almost totally covered with colonies of E. paguricola). The hermit crab lives in the spiral cavity inside the soft colony, which seemed to be slightly different depending on the initial gastropod. Aperture pseudoshell morphology did not seem to be related to the sex of the hermit crab host, although males showed larger apertures for a given colony size. This fact is probably related to a larger size of male’s cheliped (sexual dimorphic character) used like a gastropod operculum and that may serve as a template for the growing of the aperture pseudoshell edge. The number of epizoanthid polyps per colony increased in relation to the weight of the colony and to the size of the hermit crab. A process of selection of the initial shell was evident, because species of Naticidae were not the most common gastropods in this benthic community, but were those most used by hermit crabs (>60%). The puzzling association between hermit crab, shell and zoanthid presumably occurs during the hermit juvenile phase, when the crab occupies a small shell, and a zoanthid larva settles on it. Given the close relationship between S. dimorphus and E. paguricola found in this region, we support the idea that due to the low availability of adequate gastropod shells for hermit life cycle, this association allows the establishment and the continuity of the hermit crab population in the studied area.     

Abundance of thraustochytrids and bacteria in the equatorial Indian Ocean, in relation to transparent exopolymeric particles (TEPs)

Thraustochytrid protists are often abundant in coastal waters. However, their population dynamics and substrate preferences in the oceanic water column are poorly understood. We studied the abundance and distribution of thraustochytrids, bacteria and TEPs in the equatorial Indian Ocean waters during September 2003, October 2004 and September 2006. Thraustochytrids and bacteria were abundant, suggesting high biological productivity of the region. Thraustochytrids were positively related to bacteria during October 2004 but not at other times, suggesting overlapping or varying substrate preferences at different times. Thraustochytrid and bacteria were positively related to TEPs only in a few stations during October 2004, but were mostly positively related to TEPs generated from in situ water in a roller table experiment. TEPs from natural samples during October 2004 had a much greater affinity to the lectin Concanavalin A than to Limulin compared with those in September 2006 and from the roller tank experiments. The chemical composition of TEPs might explain their relationship with thraustochytrids. Thraustochytrids averaged a higher biomass than bacteria in two of the three cruises, but were less frequent and more patchily distributed compared with bacteria.     

Two new species of chimaeroid fishes from the southwestern Pacific Ocean (Holocephali, Chimaeridae)

 Two new species of chimaeroid fishes from the family Chimaeridae are described on the basis of morphological characters. The carpenter's chimaera is a large-bodied species of Chimaera distinguished from its congeners by massive head with blunt snout; firm, nondeciduous skin; purplish color; preopercular and oral lateral line canals branching together; and pelvic claspers that are divided for the distal one third of length, purple at the base with white fleshy tips. The pale ghost shark is a species of Hydrolagus distinguished from its congeners by a dorsal fin spine that reaches to the origin of the second dorsal fin when depressed; elongate second dorsal fin not indented along its length; preopercular and oral lateral line canals sharing a common branch; long, stout caudal filament; and pale silvery-gray coloration fading to white ventrally. The pale ghost shark has long been recognized as a new species from New Zealand, and formal taxonomic recognition of this species will prove important for fishery management. Received: October 15, 2001 / Revised: May 1, 2002 / Accepted: May 29, 2002 Acknowledgments I am grateful to Peter Last, Alastair Graham (CSIRO, Dept. of Marine Research), Clive Roberts, Andrew Stewart (NMNZ, Wellington), and Mark McGrouther and Doug Hoese (AMS, Sydney), for their hospitality and support of this research. This work was funded by grants from the National Science Foundation (NSF DEB-9510735) and the National Geographic Society (no. 5414–95), and also funded in part by the New Zealand Foundation for Scientific Research and Technology, Biosystematics of NZ EEZ Fishes Project, contract MNZ603, C. Roberts, program leader.     

Feral Brown rats, Rattus norvegicus, in South Georgia (South Atlantic Ocean)

Brown rats were introduced to the sub-antarctic island of South Georgia probably around 1800. They are now widespread and abundant, particularly on the north coast. The population is divided into discrete units by the rugged topography of the island, particularly the many glaciers. Rats are found mostly in dense stands of coastal tussock grass which provides both shelter and food. They dig burrows in the tussock stools and make nest chambers in the leaf canopy. Tussock, which is rich in carbohydrate, forms the main part of their diet throughout the year. Perimylopid beetles are regularly eaten, and the rats forage on the sea-shore. Carrion is eaten where available and the rats prey on ground-nesting birds. Breeding is probably seasonal, as litters were found only from December to February. The rats have adapted successfully to the rigorous South Georgia climate, but are dependent on tussock grass for their survival. They have made rather little impact on the vegetation. Dove prions, diving petrels and some large petrels are preyed on but breeding colonies of these birds can coexist with rats. The Antarctic pipit rarely if ever nests in rat-infested areas. No management procedures would be possible.     

Distribution of adult and juvenile Acantharia (Protozoa Sarcodina) in the Atlantic Ocean

The distribution of Acantharia (both adult and juvenile forms)has been studied in 34 different areas (33 in the Atlantic Oceanand one in the Mediterranean Sea). A low percentage of adultAcantharia was observed in the areas of high latitude, whilean abundance was observed in the zones between the tropics andEquator. Juvenile forms always appear in very low percentagesand no particular reproduction areas are identifiable. Withregard to their vertical distribution one can observe a gradualincrease from the surface down to 300 m; after this depth, Acanthariadecrease while in deeper waters they are scarcely represented.The distribution of juvenile forms is very irregular, but thehighest average value can be found in very deep waters (between500 and 900 m). Moreover a different daily distribution wasobserved in the percentage of Acantharia in most of the superficiallayers: percentages were higher in the daytime hours than inthe nocturnal ones, considering seasonal changes, Spring wasfound to be the period of greatest abundance both of adult andjuvenile forms, while the lowest percentage was observed duringSummer.     

Bloom of Emiliania huxleyi (Prymnesiophyceae) in the western South Atlantic Ocean

A monospecific bloom of the coccolithophorid Emiliania huxleyi(Lohmann) Hay & Mohler (Prymnesiophyceae) was detected offRio de La Plata at 36°S and 54°W in November 1989. Thecell densities observed were up to 6x10⁵ cells I^–1. Thisis the first record of a bloom of E.huxleyi in the area.     

Genetic Structure of Capelin (Mallotus villosus) in the Northwest Atlantic Ocean

Capelin (Mallotus villosus) is a commercially exploited, key forage-fish species found in the boreal waters of the North Pacific and North Atlantic Oceans. We examined the population structure of capelin throughout their range in the Canadian northwest Atlantic Ocean using genetic-based methods. Capelin collected at ten beach and five demersal spawning locations over the period 2002 through 2008 (N = 3,433 fish) were genotyped using six polymorphic microsatellite loci. Temporally distinct samples were identified at three beach spawning locations: Chance Cove, Little Lawn and Straitsview, Newfoundland. Four capelin stocks are assumed for fisheries management in the northwest Atlantic Ocean based on meristics, morphometrics, tag returns, and seasonal distribution patterns. Our results suggested groupings that were somewhat different than the assumed structure, and indicate at least seven genetically defined populations arising from two ancestral populations. The spatial mosaic of capelin from each of the two basal cluster groups explains much of the observed geographic variability amongst neighbouring samples. The genetic-defined populations were resolved at Jost’s D _est ≥ 0.01 and were composed of fish collected 1) in the Gulf of St. Lawrence, 2) along the south and east coasts of Newfoundland, 3) along coastal northern Newfoundland and southern Labrador, 4) along coastal northern Labrador, 5) near the Saguenay River, and at two nearshore demersal spawning sites, 6) one at Grebes Nest off Bellevue Beach on the east coast of Newfoundland, and 7) one off the coast of Labrador at Domino Run. Moreover, the offshore demersal spawners on the Scotian Shelf and Southeast Shoal appeared to be related to the inshore demersal spawners at Grebes Nest and in Domino Run and to beach spawners from the Gulf of St. Lawrence.     

Egg capsules, eggs and embryos of the southwestern Atlantic gastropod Coronium coronatum (Gastropoda: Muricidae)

The egg capsules, eggs and embryos of the muricid gastropodCoronium coronatum are described for the first time. Capsulesare sessile, bulliform, semi-circular, with a plug in the dorsalcenter. Sutures split the capsule into two asymmetrical halves.Recently laid capsules showed the presence of 3639 (n = 2) uncleavednurse eggs with a diameter of 180–210 µm (mean= 197.4 ± 8.9). The number of early embryos was 9–11.The size of the embryos was 320 x 320 to 820–880 µm.Nine pre-hatching embryos of 3.94 mm (n = 8, SD = 0.32)were found inside the older capsule. SEM illustrations of embryosand radulae are provided. Comparison of shell and radula ofembryos with the protoconch and radulae of adults of C. coronatumrevealed that the capsule belongs to this species. (Received 18 March 2006; accepted 10 October 2006)