Composition,abundance and distribution of holoplanktonic polychaetes within the Strait of Magellan (southern America) in austral summer

This study enlarge the knowledge on species composition, distribution and community structure of pelagic polychaetes on the basis of finely stratified spatial sampling representing austral summer conditions in the Strait of Magellan. Zooplankton samples were collected in late austral summer 1995. A total of 56,489 pelagic polychaete specimens were collected. Eight holopelagic polychaete taxa were recorded in addition to Spionidae and Terebellidae larvae and reproductive stolons of Autolytinae. Pelagobia longicirrata (Lopadorhynchidae) was the most abundant species, representing about 96 % (54,092 specimens, 184.6 ind. 100 m^?3) of all individuals, followed by Tomopteris planktonis (Tomopteridae) at 3 % (1,725 specimens, 5.9 ind. 100 m^?3). The longest measured individuals belonged to T. planktonis, which also showed the largest size range, whereas the smallest individuals belonged to P. longicirrata. Spatial distribution of polychaetes in terms of abundance was not related to bottom depth, but rather the number of taxa was lower in the central part of the Strait. P. longicirrata and T. planktonis were negatively related to chlorophyll a. In addition, the first was negatively related to temperature instead the second was positively affected by salinity. Polychaetes were widely distributed in both epi- and mesopelagic realms, whereas they were almost absent above 80 m depth. Both of the most abundant species were concentrated in the deepest layers sampled (below 100 m) throughout day and night hours without showing any specific migratory behavior.     

Distribution,abundance and diversity of macrozoobenthos in Aiba Reservoir,Iwo, Nigeria

Spatial and seasonal variation in macrozoobenthic composition, abundance and diversity in Aiba Reservoir were investigated bimonthy between June 2004 and April 2005 using a van Veen grab. A depauperate fauna of nine taxa was recorded. Generally, larger numbers of taxa were recorded during the dry season than in the wet season. Melanoides tuberculata and chironomid larvae dominated the macrozoobenthos and showed wide spatial distribution. Diversity and evenness were lower during the wet season than in the dry season, when densities of the major species were low. Melanoides tuberculata and chironomid larvae were recorded from maximum depths of 3.9 m and 2.6 m, respectively. Both taxa were also recorded from all substrate texture types, regardless of the amount of macrophyte material present. The benthic fauna is characterised as being poor in terms of density, taxonomic richness and diversity     

An analysis of temporal variability in abundance, diversity and growth rates within the coastal ichthyoplankton assemblage of South Georgia (sub-Antarctic)

The study of spatial and temporal distribution and diversity of ichthyoplankton (fish eggs and larvae) can provide fisheries-independent information on the population dynamics and recruitment processes of marine fish species. Ichthyoplankton studies in the Southern Ocean have to date been largely constrained to the summer months. We analysed ichthyoplankton data collected from a year round, long term (2002–2008), plankton trawl sampling programme in a large fjord system (Cumberland Bay) at South Georgia, sub-Antarctic (54.25°S, 36.5°W) to assess temporal changes in larval fish diversity and abundance. Larvae of 22 species, representing nine families, were identified although three, Krefftichthys anderssoni (Myctophidae), Lepidonotothen nudifrons/Trematomus hansoni (Nototheniidae) and Champsocephalus gunnari (Channichthyidae), dominated abundance in all years. Significant seasonal and interannual differences in the larval fish assemblage were revealed by multivariate analyses. Estimates of larval growth are provided for five abundant species. Considerable inter-specific differences in relative larval growth rate were recorded but interannual variability within species was small. However, in the commercially important C. gunnari, multiple larval cohorts, representing a protracted spawning season, were observed to grow at different rates, and this may be related to temperature and/or food availability. A comparison with historical growth data from South Georgia suggests there has been little change in growth rate for the main species over the last three decades.     

Trophic structure of shallow-water benthic communities in the sub-Antarctic Strait of Magellan

Trophic structure is among the most fundamental characteristics of an ecosystem since it is a useful way to determine the main energy flow at the ecosystem level. In the Magellan Strait, the local spatial heterogeneity at the shallow-waters ecosystems may have a great variety of potential food sources; however, knowledge about their biological communities and their structure is still unclear. We examined the trophic structure of shallow-water-mixed bottom communities at two sites in the sub-Antarctic Magellan Strait based on carbon (δ ¹³C) and nitrogen (δ ¹⁵N) stable isotope ratios. The benthic communities were composed of 46 species from 20 major taxa at Bahía Laredo (BL) and 55 species from 18 major taxa at Punta Santa Ana (PSA). Benthic macroalgae and organic matter associated with sediment are the major primary food sources at both sites. Although both sites are quite similar in their food sources and in their vertical trophic structure (≥three trophic levels), the food web structure varied distinctly. Functionally, predators and grazers dominated both communities, but top predators were shorebirds, carnivore anemones and predatory nemerteans at BL, and sea stars, shorebirds, crabs and fishes at PSA. The distinct differences in the trophic structure at BL and PSA highlight the important variability of δ ¹⁵N at the base of the benthic food web, the role of local environmental conditions and community dynamics in structuring shallow-water communities.

     

Phytoclimatic segregation of sub-Antarctic Nothofagus woodland types in Tierra del Fuego,southern South America

Background: Climatic variables determining the most suitable sites for the woodlands of Tierra del Fuego are not yet as well understood as those related to their geographical range.

Aim: The aim of this paper is to provide some insights into the relationships between climatic niche and current distribution of three Nothofagus species in Tierra del Fuego.

Methods: We have identified the climatic variables responsible for the most suitable sites for three sub-Antarctic Nothofagus woodland types within their climatic ranges by calculating suitability indices, using the CLIMPAIR niche-based phytoclimatic model.

Results: The distribution range of the major Nothofagus woodlands is mainly driven by variables related to water stress, whereas phytoclimatic suitability is mainly driven by thermal variables related to warm summer temperatures for Nothofagus betuloides and N. pumilio and to winter cold for N. antarctica that are also mainly responsible for the peculiarity of the Fueguian climate.

Conclusions: These findings introduce a new perspective in the study of the Nothofagus ecology, based on the climatic traits responsible for the high-suitability locations instead of the traditional focus on the overall geographical distribution.     

Seasonal, altitudinal and host plant-related variation in the abundance of aphids (Insecta, Hemiptera) on sub-Antarctic Marion Island

Although aphids are the most species-rich group of invasive alien insects across the Southern Ocean Islands, their biology on the islands is poorly known. In this study, host plant-related, seasonal and altitudinal variation in the abundance of the three aphid species (Macrosiphum euphorbiae, Myzus ascalonicus, Rhopalosiphum padi) found on sub-Antarctic Marion Island is examined. Myzus ascalonicus is the most abundant of the species, reaching densities of c. 2,400 individuals per 1,200 cm² on the indigenous Acaena magellanica (Rosaceae) and 479 individuals per 1,200 cm² on the indigenous Cotula plumosa (Asteraceae), with lower numbers at elevations up to 300 m and a pronounced seasonal peak in December-February. Macrosiphum euphorbiae occurs on the same plant species in densities of between c. 11 individuals per 1,200 cm² on C. plumosa and c. 200 individuals per 1,200 cm² on A. magellanica, and with a pronounced summer peak in December. In both species, small numbers of winged forms are found (c. 1–5%), although they are permanently parthenogenetic on the island. Rhopalosiphum padi is also permanently parthenogenetic on the island and likewise shows a December peak in abundance. The current data suggest that low ambient temperatures, which are close to the lower development threshold of R. padi, and other temperate aphid species, limit development in winter, thus leading to a decline in abundance.     

Subsistence productivity and hunting effort in native South America

The question of why people work more or less at various activities is an old one in anthropology and recently has surfaced in studies of native South American societies. Growing out of debates about protein scarcity, arguments have arisen over the reasons why people spend time on hunting and fishing. Some authors suggest that labor allocation and other societal features can be explained with reference to absolute minimum requirements for specific nutrients (e.g., protein). This study presents data from four native Central Brazilian societies on the time spent at various subsistence tasks and the productivity of those tasks. The evidence suggests that decisions to allocate labor to hunting and fishing are influenced more by the overall possibilities for production in an area than by the availability of animal proteins alone. Satisfaction of calorie requirements appears to take precedence over satisfaction of protein requirements. In those societies in which gardening is highly productive, people can spend more time on hunting and fishing and improve the overall quality of their diet.     

The bacterioplankton of Lake Taihu,China: abundance,biomass, and production

Abundance, biomass and production of pelagic bacteria were examined over one year at monthly sampling intervals across a trophic profile in Meiliang Bay, Lake Taihu. With the lowest density in the open lake, the bacterial abundance showed a clear trend in relation to trophic status. The carbon content per cell was higher in autumn and winter, and the opposite was true for bacterial biomass. Bacterial ³[H]-TdR and ¹⁴[C]-Leu incorporation rates, cell production, turnover times and carbon production varied during the annual cycle at different sites. The ratio of bacterial production to primary production was high, independently of the method used, indicates that the microbial food web in Lake Taihu is an important component of the total food web of the lake and dominated by external inputs. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users     

Distribution patterns in the biomass of macrozoobenthic communities in Admiralty Bay (King George Island, South Shetlands, Antarctic)

The distribution patterns of macrozoobenthic communities as shown by the biomass of the higher taxa were investigated in Admiralty Bay. Material was collected at depths ranging from 4 to 500 m (102 quantitative samples), representing the full depth range of this basin and including areas characterized by the different levels of glacial influence. Five community groups were distinguished by multivariate analysis (clustering, MDS) based on the Bray--Curtis similarity index. In the Ezcurra Inlet, the area characterized by intensive glacial processes resulting in a high sedimentation rate, the distribution of biomass was not depth related, but was associated with the intensity of glacial disturbance along the axis of the fjord. The innermost part of this fjord, which receives strong outflows from glaciers, had a low biomass value (2.9 g/0.1 m²) and was dominated by polychaetes. The middle part of the fjord which is not so heavily disturbed had higher biomass values (46.1 g/0.1 m²) due to the dominance of bivalves. A clear depth gradient of biomass distribution was observed in bottom areas located far from glaciers, in the central basin of the bay, with three zones within the depth ranges 4–30, 40–380, and 400–500 m. The highest mean biomass values (92.5 g/0.1 m²) were found in the middle sublittoral (40–380 m) dominated by ascidians. In the shallow and deep assemblages, the biomass was lower (33.8 g/0.1 and 30.9 g/0.1 m² respectively), most probably associated with the ice disturbance in the shallows and lower food supply in the deepest part of the shelf.     

Diversity and Distribution of Hantaviruses in South America

Hantaviruses are important contributors to disease burden in the New World, yet many aspects of their distribution and dynamics remain uncharacterized. To examine the patterns and processes that influence the diversity and geographic distribution of hantaviruses in South America, we performed genetic and phylogeographic analyses of all available South American hantavirus sequences. We sequenced multiple novel and previously described viruses (Anajatuba, Laguna Negra-like, two genotypes of Castelo dos Sonhos, and two genotypes of Rio Mamore) from Brazilian Oligoryzomys rodents and hantavirus pulmonary syndrome cases and identified a previously uncharacterized species of Oligoryzomys associated with a new genotype of Rio Mamore virus. Our analysis indicates that the majority of South American hantaviruses fall into three phylogenetic clades, corresponding to Andes and Andes-like viruses, Laguna Negra and Laguna Negra-like viruses, and Rio Mamore and Rio Mamore-like viruses. In addition, the dynamics and distribution of these viruses appear to be shaped by both the geographic proximity and phylogenetic relatedness of their rodent hosts. The current system of nomenclature used in the hantavirus community is a significant impediment to understanding the ecology and evolutionary history of hantaviruses; here, we suggest strict adherence to a modified taxonomic system, with species and strain designations resembling the numerical system of the enterovirus genus.     

Physical and biotic factors limiting the distribution and abundance of littoral molluscs on Macquarje Island (sub-Antarctic)

A number of factors have been examined for their influence on the limits of upper distribution and abundance of six species of adult molluscs in the rocky littoral zone of Macquarie Island. The molluscs were Amphineura: Plaxiphora aurata (Spalowsky), Hemiarthrum setulosum Dall; Gastropoda: Patinigera macquariensis (Finlay), Cantharidus (Plumbelenchus) coruscans (Hedley), Laevilittorina caliginosa (Gould), Kerguelenella lateralis (Smith), and the factors included habitat, temperature, desiccation, salinity, food, predation, and reproduction. Macquarie Island is mid-way between the southern temperate zone and the Antarctic and has an equable, oceanic climate. Because of differences in both geography and environmental stability, the results allow important comparisons to be made with those on the effects of factors limiting the distribution of littoral molluscs elsewhere. The effects of physical factors are similar to those examined in other regions as shown by tolerance to temperature, desiccation, and salinity. Habitat and zonal sequence of species are related to tolerances with the notable exception of the heat resistance of chitons which, when compared with that of gastropods, is greater than their distribution would suggest. In the field, the temperatures and desiccation of the animal bodies and the surrounding salinities do not reach critical lethal levels but the debilitating effects in combination with other adverse factors can be lethal — in particular, a combination of high temperatures and predation. Biotic factors have considerable influence on the distribution and abundance of the species and this may reflect the comparative stability of the physical environment. The aspects of the biotic factors which are important in this regard include morphology, mobility, food preferences, the presence of the large kelp Durvillea antarctica (Chamisso) Hariot, predation by birds and by isopods on enfeebled animals, and a brooding mode of reproduction. In all species, no single factor limits the upper distribution and factors vary in their importance for each species. Synergistic effects of factors are limiting and the effective combinations differ for each species. This stresses the danger of placing too much emphasis on results from studies of a single factor.     

2007年10月南海北部浮游纤毛虫的丰度和生物量

报道2007年10月南海北部海域(21°25.47′N 17°24.95′N,109°28.86′E 113°13.01′E)纤毛虫丰度和生物量的水平分布及砂壳纤毛虫的种丰富度。包括了13个断面的82个站位,Rosette采水器采水,水深低于15 m的站位采0,5 m和10 m;小于30 m站位,采0,10 m和底层;大于30 m的站位,采0,10,30 m和底层。纤毛虫丰度为0 5757 ind./L,平均(848±776)ind./L。无壳纤毛虫占绝对优势,其丰度占纤毛虫总丰度的比例平均为(91.9±9)%;纤毛虫生物量为0 12.09μg C/L,平均是(1.2±1.54)μg C/L,无壳纤毛虫的生物量平均为(0.94±1.27)μg C/L,占纤毛虫总生物量的78.6%。共发现砂壳纤毛虫16个属,49种,拟铃虫最多,具有一定的季节性。纤毛虫水体(40 m到表层)丰度为6.4×1069.1×107ind./m2,平均是(3.6×106±1.4×106)ind./m2;水体生物量3.6 195.8 mg C/m2,平均(48.1±33.7)mg C/m2。纤毛虫多分布于近岸浅水区(高温低盐,高Chl a),最大丰度要高于我国其他海区,不是Chl a最高的地方纤毛虫的丰度也最大,纤毛虫丰度最大时Chl a偏低。     

Distribution and abundance of blackflies (Diptera: Simuliidae) in relation to impoundments in the Buffalo River, eastern Cape, South Africa

1. The abundance of blackfly species along the length (140 km) of the multiply impounded Buffalo River, eastern Cape, South Africa, was studied between 1986 and 1988. 2. Twenty-three species of blackflies were recorded, most of which (95%) were usually found 5–10 km from the source. 3. Impoundments favoured five lower-reach (pest) blackfly species at the expense of two upper-reach (non-pest) species. Impoundments have therefore shifted the distribution of blackfly species ‘upstream’, and have increased the distribution of pest blackflies. 4. The smallest impoundment, situated in the Upper Foothill Stony Run Zone, had the greatest effect on blackfly distribution. 5. There was no typical filter-feeding guild below impoundments. Possible reasons for this included the discharge of toxic algae from impoundments, the lack of compensatory releases, the sudden drying of impoundment tailwaters and the paucity of natural lakes in southern Africa which precludes a pre-adapted ‘outlet’ fauna.     

The distribution and abundance of white-chinned petrels (Procellaria aequinoctialis) breeding at the sub-Antarctic Prince Edward Islands

The white-chinned petrel (Procellaria aequinoctialis) is the seabird most often killed on longlines in the Southern Ocean and is listed as vulnerable to extinction. We estimated the population breeding at the Prince Edward Islands, the last breeding site for the nominate subspecies that lacks a recent population estimate. White-chinned petrel burrows are largely confined to deep, muddy soils, usually on slopes below 200?m, but locally up to 420?m. After correcting for count bias, Marion Island has an estimated 29,900 nests (95?% CI 27,700–32,400). Burrow occupancy rates at the start of the incubation period were 65?% during one-off surveys, but repeat surveys found that at least 73?% of burrows were occupied and 87?% of burrows showed signs of occupancy. This suggests that there were roughly 24,000 occupied nests on Marion Island (95?% CI 20,000–28,000). A more cursory survey on Prince Edward Island yielded 14,700 burrows, suggesting that there are 9,000–15,000 occupied nests. The nominate subspecies of white-chinned petrel occupies approximately 974,200 nests (95?% CI 678,000–1,286,000), with the Prince Edward Islands, the third most important breeding site, after South Georgia and Kerguelen. Assuming that populations breeding at islands in the Atlantic and Indian Oceans winter in different regions, the impact of fishery bycatch is likely to have had a greater impact on the Indian Ocean population. The Marion Island survey provides a baseline against which future population changes can be assessed.     

Planktonic ciliates in the northwestern Indian Ocean: their abundance and biomass in waters of contrasting productivity

The abundance and biomass of planktonic ciliates in the northwesternIndian Ocean ranged from 31 l^–1 and 0.1 µg C l^–1in oligotrophic open-ocean waters to 823 l^–1 and 1.2 µgC l^–1 in more productive waters of the equator, northernArabian Sea and Gulf of Oman. ³Present address: British Antarctic Survey, High Cross, MadingleyRoad, Cambridge, CB3 OET, UK     

Lamniform Shark Teeth from the Late Cretaceous of Southernmost South America (Santa Cruz Province,Argentina)

Here we report multiple lamniform shark teeth recovered from fluvial sediments in the (Campanian-Maastrichtian) Cerro Fortaleza Formation, Santa Cruz Province, Argentina. This small tooth assemblage is compared to various lamniform sharks possessing similar dental morphologies, including Archaeolamna, Cretalamna, Dwardius, Dallasiella, and Cretodus. Although the teeth share numerous morphological features with the genus Archaeolamna, including a developed neck that maintains a relatively consistent width along the base of the crown, the small sample size and incomplete nature of these specimens precludes definitive taxonomic assignment. Regardless, the discovery of selachian teeth unique from those previously described for the region broadens the known diversity of Late Cretaceous South American sharks. Additionally, the discovery of the teeth in fluvial sandstone may indicate a euryhaline paleobiology in the lamniform taxon or taxa represented by this tooth assemblage.