The composition and distribution of the particulate matter in the Strait of Magellan (Chile) during the 1991 and 1995 Italian campaigns

During 1991 and 1995, the Italian National Program for Antarctic Research carried out two oceanographic campaigns in the framework of the International (Strait of) Magellan Project. In this paper, we describe the distribution, biochemical composition, and mineralogical characteristics of particulate matter and the characteristics of the water masses defining microbasins in the Strait of Magellan. The data analyses highlighted differences in quality and quantity of the suspended matter and its organic component in the basins that make up the Strait and the Pacific Ocean. The westernmost basin is subject to an eastward flow from the Pacific Ocean, and continental runoff in the surface layers, which are consequently rich in organic matter with a high C:N ratio. The central basin, Isla Carlos III–Segunda Angostura, is characterized by the mixing of Sub-Antarctic Pacific waters, continental runoff, and glacio-fluvial waters: The basin has the lowest particulate matter concentration, but at Paso Ancho showed high concentrations of organic matter with a lower C:N ratio. The easternmost basin, Segunda Angostura-Atlantic entrance, is characterized by the mixing of the water column due to strong Atlantic tides and showed high concentration of particulate matter with a high detritic component. Generally, the organic matter concentrations showed significant differences during the cruises, being higher in 1991. Using the multivariate discriminant factor analysis to determine whether statistically significant differences existed between defined sampling areas, we determined that temperature, particulate organic carbon, and total particulate matter were the variables most important for the difference between areas.     

Species diversity, spatial distribution, and assemblages of zooplankton within the Strait of Magellan in austral summer

The main aim of this work was to identify zooplankton assemblages by means of statistical testing and associate them with hydrographic properties of the Strait of Magellan and its microbasins. Zooplankton samples were collected by the R/V Cariboo in late austral summer 1991. Nineteen stations were sampled by BIONESS from the surface layer to 900 m depth, along the main longitudinal axis of the Strait of Magellan. There was a marked regional-scale pattern in zooplankton species diversity and richness, related to the hydrographical features of the Strait and its sub-basins. Six groups of samples were identified by cluster analysis in terms of zooplankton structure, and related to sea-water properties of temperature, salinity, and Chl a (Sperman’s correlation coefficient). Plankton assemblages of the Strait of Magellan seem closely linked to the remote sub-Antarctic and adjacent ocean biota, but populations may have independent evolutionary lines and population dynamics.     

Tintinnid distributions in the Strait of Magellan (Chile)

In the Strait of Magellan and in the adjacent Pacific and Atlantic Ocean shelf tintinnids were studied during three oceanographic cruises (November 1989, March–April 1991, and April 1995). Total tintinnid abundances were higher in the first cruise and dramatically decreased in the other two late summer cruises. As a general rule, abundances were higher at the surface and in the Atlantic sector. A total of 47 tintinnid species were found. There was not a single species, which could be identified as indicator of a specific water mass. For each cruise, cluster analysis applied on a species/samples matrix identified station sets characterized by a specific tintinnid association. Angosturas entrance was characterized by agglutinated lorica tintinnids, typical of the Atlantic waters, while the Pacific sector by hyaline species. In Punta Arenas basin, a peculiar tintinnid community was clearly identified, although water masses derived from the mixing process between the Pacific and Atlantic waters. Overall, tintinnid communities maintained the structure typical of the water mass despite advection and/or mixing. The main result of this study was to demonstrate that the structure of the tintinnid species association could be used as indicator of the origin of water masses.     

Roles of sulfate adsorption and base cation supply in controlling the chemical response of streams of western Virginia to reduced acid deposition

Micro-organisms are vital for the functioning of all food webs and are the major drivers of the global biogeochemical cycles. The microbial community compositions and physicochemical conditions of the different water masses in the North Sea, a biologically productive sea on the northwestern European continental shelf, were studied during two summer cruises, in order to provide detailed baseline data for this region and examine its microbial biogeography. For each cruise the stations were clustered according to their physicochemical characteristics and their microbial community composition. The largest cluster, which covered most of the central and northern North Sea, consisted of stations that were characterized by a thermally stratified water column and had low chlorophyll a autofluorescence and generally low microbial abundances. The second main cluster contained stations that were dominated by picoeukaryotes and showed the influence of influxes of North Atlantic water via the English Channel and south of the Shetland Islands. The third main cluster was formed by stations that were dominated by cyanobacteria and nanoeukaryotes in the reduced salinity Norwegian Coastal and Skagerrak waters, while the fourth cluster represented the German Bight, a region with strong riverine input, high nutrient concentrations, and consequently high heterotrophic bacterial and viral abundances. Despite the complex and dynamic hydrographic nature of the North Sea, the consistent distinctions in microbiology between these different hydrographic regions during both cruises illustrate the strong links between the microbial community and its environment, as well as the possibility to use microorganisms for long-term monitoring of environmental change.     

Primary production processes and photosynthetic performance of a unique periantarctic ecosystem: the Strait of Magellan

During the late austral summer and early autumn 1995 (March–April), an oceanographic cruise was conducted along the Strait of Magellan in order to study the photosynthetic performance of phytoplankton assemblages. The high correlations between the pico–nano fractions and both the total biomass concentrations (Chla) and primary production rates emphasized the role of these fractions in driving the primary production processes. Repeated P versus E experiments were conducted in the most productive area of the Strait, Paso Ancho, in order to assess the influence of the tidal currents on phytoplankton photosynthetic performance. These data were compared to those available from a previous cruise (February–March, 1991) carried out along the Strait. In the Pacific–Andean sector, the primary production processes were highly controlled by wind, land forcing, and irradiance availability. In the Paso Ancho, the observed highest photosynthetic capacity P_\textm^\textB P_{\text{m}}^{\text{B}} (up to 6.5 mgC mgChla ⁻¹ h⁻¹) and the high primary production rates may due to the continuous mixing of the water column forced by the strong tidal currents within the photic layer. The non-limiting, macro-nutrient concentrations in the Strait indicate that the available irradiance and the depth of mixed layer are the main driving factors of the primary production processes. The photosynthetic performance of the phytoplankton assemblages renders the Strait a unique ecosystem, which is more similar to those of the mid-latitudes than to those of the periantarctic areas.     

Spatial and temporal variability of the benthic assemblages associated to the holdfasts of the kelp <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> in the Straits of Magellan,Chile

Macrocystis pyrifera (L.) C. Agardh is a characteristic macroalga in the Magellan region covering almost 30% of the shallow coastal waters. The focus of this study was to analyse the spatial and seasonal patterns in macrofauna communities associated to the holdfasts of Macrocystis pyrifera at two study sites in the Straits of Magellan, South Chile. In total, 114 species from 10 major taxa were isolated from the holdfasts. MDS clearly separated the holdfast fauna collected in different seasons, with autumn and winter collections being richer in terms of species richness and abundance as compared to the spring and summer situation. MDS also clearly separated the holdfast associated faunas of the two study sites, Bahía Laredo and Fuerte Bulnes. The community structure and species composition of the associated macro-invertebrates and vertebrates appeared rather heterogeneous, probably due to the extremely heterogeneous environmental conditions along the entire coastline of the Subantarctic Magellan region.     

MORPHOMETRICS AND BREEDING BIOLOGY OF THE WHITECHINNED PETREL PROCELLARIA AEQUINOCTIALIS AT SUB-ANTARCTIC MARION ISLAND

Berruti, A., Cooper, J. & Newton, I.P. 1995. Morphometrics and breeding biology of the Whitechinned Petrel Procellaria aequinoctialis at sub-Antarctic Marion Island. Ostrich 66: 74–80.

Aspects of adult morphometrics and the breeding biology of the summer-breeding Whitechinned Petrel at sub-Antarctic Marion Island, southern Indian Ocean, are given, based on a study conducted in 1980/91, along with additional observations on breeding success made in 1990191. It is concluded that Whitechinned Petrels at Marion Island are similarly sized and breed in a similar manner to other studied populations of the nominate race. The eradication of cats at Marion Island in 1991 should now lead to a slow population recovery.     

Differences of the protozoan biomass and grazing during spring and summer in the Indian sector of the Southern Ocean

The dynamics of protozoa were investigated during two cruises in the Indian sector of the Southern Ocean: the early spring ANTARES 3 cruise (28 September to 8 November 1995) and the late summer ANTARES 2 cruise (6 February to 8 March 1994). Biomass and feeding activity of protozoa were measured as well as the biomass of their potential prey – bacteria and phototrophic flagellates – along the 62°E meridian. The sampling grid extended from the Polar Frontal region to the Coastal and Continental Shelf Zone in late summer and to the ice edge in spring, crossing the Antarctic Divergence. Protozoan biomass, although low in absolute terms, contributed 30% and 20% to the total microbial biomass (bacteria, phytoplankton and protozoa) in early spring and late summer, respectively. Nanoprotozoa dominated the total protozoan biomass. The geographical and seasonal distribution of protozoan biomass was correlated with that of phototrophic flagellates. However, bacterial and phototrophic flagellate biomass were inversely correlated. Phototrophic flagellates dominated in the Sea Ice Zone whereas bacteria were predominant at the end of summer in the Polar Frontal region and Coastal and Continental Shelf Zone. Furthermore, bacteria were the most important component of the microbial community (57% of the total microbial biomass) in late summer. Phototrophic flagellates were ingested by both nano-and microprotozoa. In contrast, bacteria were only ingested by nanoprotozoa. Protozoa controlled up to 90% of the daily bacterial production over the period examined. The spring daily protozoan ingestion controlled more than 100% of daily phototrophic flagellate production. This control was less strong at the end of summer when protozoan grazing controlled 42% of the daily phototrophic flagellate production. Accepted: 30 October 1999     

The microarthropods of sub-Antarctic Prince Edward Island: a quantitative assessment

The biodiversity in the sub-Antarctic region is threatened by climatic change and biological invasions, which makes the understanding of distributions of biotas on sub-Antarctic islands essential. Although the distribution patterns of vascular plants and insects on sub-Antarctic islands are well documented, this is not always the case for microarthropods. This study provides the first quantitative assessment of the distribution and abundance of microarthropods on Prince Edward Island (PEI), one of two islands in the Prince Edward Island group. Microarthropod community structure differed significantly between PEI and nearby Marion Island, with only two invasive alien species found on PEI compared with Marion Island. Furthermore, species richness, abundance and community structure differed significantly between habitat types on both islands. This study emphasizes the importance of quarantine measures when visiting PEI to maintain its status as one of the more pristine islands in the sub-Antarctic region.     

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.

     

Short-term changes in zooplankton community in Paso Ancho basin (Strait of Magellan): functional trophic structure and diel vertical migration

Knowledge on community structure oriented to describe energy flow during late summer season in Paso Ancho basin (Strait of Magellan) is scarce and particularly affected by vertical diel migration (VDM). The main aim of this work is to identify the VDM patterns of selected species and functional feeding groups of mesozooplankton, collected by the electronic multinet BIONESS in 1995. Detailed studies were carried out on keystone components of the community: 7 species of copepods (Ctenocalanus citer, Drepanopus forcipatus, Metridia lucens, Clausocalanus brevipes, Scolecithricella minor, Paraeuchaeta antarctica, Calanus simillimus), one ostracod (Discoconchoecia elegans), one chaetognath (Sagitta tasmanica), one euphausiid (Euphausia vallentini), and two polychaetes (Pelagobia longicirrata, Tomopteris planktonis). Unexpected deviations from the classic pattern reported in literature were uncovered. The shallow layer mesozooplankton at night, although dominated by exclusively or preferentially herbivores, particularly by E. vallentini, was not represented by several species known as herbivores that remained in the deep layer throughout the day cycle. The deep-layer zooplankton throughout the day cycle was well represented by carnivores, detritivores, and omnivores. It is suggested that during low-chlorophyll summer conditions, the composition of functional groups and diet, and VDM patterns changed to take advantage of sinking phytoplankton and picoplankton in deep layers. Pelagic-benthic coupling would be strengthened due to animals that suppressed their vertical daily rise to the shallow layer at nights but remained in the deep layers to feed on a rain of particulate organic matter and other non-migrant zooplankton.     

Isopod assemblages in the Straits of Magellan: structural and functional aspects

Isopod crustaceans were found to constitute a substantial fraction of the zoobenthos collected in the course of a survey carried on in the Straits of Magellan during austral summer 1991. Twenty-four species and 637 individuals were found. The highest abundance and diversity within the taxocoene were recorded from the eastern areas of the straits. An analysis of population and trophic characteristics was conducted, in particular on a conspicuous sample from a site dominated by a mollusc thanatocoenosis. At this site, parameters such as size range of individuals and number of ovigerous females were estimated as indicative of a well-established population. Trophic structure was dominated by functional plant- and plant detritus-feeders. Cryptic requirements and trophic habits of most species appeared to be satisfied under conditions of enhanced habitat complexity and/or spatial patchiness. It is hypothesized that spatial heterogeneity acts on isopod distribution at different scales. The role of hydrodynamism is briefly discussed. Received: 14 August 1996/Accepted: 9 March 1997     

Brittle stars from Southern Ocean (Echinodermata: Ophiuroidea)

The present biogeographic study on the ophiuroid fauna from the Southern Ocean (SO) contains an updated checklist, based on a compilation of all the published information provided for the Antarctic and sub-Antarctic regions as well as the information available in SCAR-MarBIN database. Faunal composition and geographical and bathymetric distribution are included. So far, 219 species have been recorded, of which 126 are endemic to the SO, 76 are exclusive to Antarctic waters, and 30 are exclusive to sub-Antarctic waters. This study corroborated the circumpolar and eurybathic character of the ophiuroid fauna of the SO, but some differences are discussed when considering shelf and deep-sea fauna in the whole SO, or in the Antarctic and sub-Antarctic regions separately. The biogeographic affinities of 17 areas considered in the SO are revised, based on a presence/absence datamatrix of the 219 species. This similarity analysis shows three main groups, two of them including sub-Antarctic areas and one for Antarctic areas. The faunal movement patterns between the main geographical connections have been based on historical site records of each species. These movements have a level of faunal exchange that exceeds that of other Antarctic benthic groups. Such movements are mainly from Antarctic and sub-Antarctic regions to the subtropical waters of South America, and from New Zealand and southern Australian waters to sub-Antarctic areas. In this context, the origin of the ophiuroid Antarctic fauna is discussed.     

Tasmanomysis oculata n.g. n.sp. from Tasmanian waters (Crustacea: Mysidacea: Mysini)

Tasmanomysis oculata n.g. n.sp. belonging to the Tribe Mysini is described from the coastal waters of southern Tasmania. This new genus superficially resembles the monospecific genus Arthromysis Colosi,1924 known only from the Straits of Magellan. The form of the pleopods in the male together with the segmentation of the thoracic legs and shape of the telson clearly distinguish the two genera.     

Spatial and temporal variations in calanoid copepod distribution in the Straits of Malacca

The distribution and abundance of planktonic calanoid copepods were studied from samples collected at 13–20 stations during four oceanographic cruises (pre- and post- monsoons, and during northeast (NE) and southwest (SW) monsoons) performed between 1998 and 2000 in the Straits of Malacca. Space and time variations of calanoid copepods were described using univariate (number of species, diversity indices, abundance) as well as multivariate (MDS, ANOSIM, SIMPER) techniques from the Plymouth Routines in Multivariate Ecological Research (PRIMER) package. There were significant differences in abundance between the cruises. k-Dominance curves also revealed significant differences in the relative species abundance distributions among the monsoon periods, and a decrease in diversity from northern to southern parts of the Straits during each cruise. Multi-dimensional scaling revealed four groups of abundances with differences in species composition. Evidence from analysis of similarity (ANOSIM) suggested that the differences in communities among monsoon periods were significant, although spatial differences among samples in geographic locations in the northern, central and southern parts of the Straits were insignificant. These differences resulted from an overall change in the balance of relative abundance of few dominant species, rather from changes of many species. Similarity percentage analyses (SIMPER) indicated that the major species contributing to the average dissimilarity between monsoons varied temporally.     

Predictive modeling of mixed microbial populations in food products: evaluation of two-species models

Predictive microbiology is an emerging research domain in which biological and mathematical knowledge is combined to develop models for the prediction of microbial proliferation in foods. To provide accurate predictions, models must incorporate essential factors controlling microbial growth. Current models often take into account environmental conditions such as temperature, pH and water activity. One factor which has not been included in many models is the influence of a background microflora, which brings along microbial interactions. The present research explores the potential of autonomous continuous-time/two-species models to describe mixed population growth in foods. A set of four basic requirements, which a model should satisfy to be of use for this particular application, is specified. Further, a number of models originating from research fields outside predictive microbiology, but all dealing with interacting species, are evaluated with respect to the formulated model requirements by means of both graphical and analytical techniques. The analysis reveals that of the investigated models, the classical Lotka-Volterra model for two species in competition and several extensions of this model fulfill three of the four requirements. However, none of the models is in agreement with all requirements. Moreover, from the analytical approach, it is clear that the development of a model satisfying all requirements, within a framework of two autonomous differential equations, is not straightforward. Therefore, a novel prototype model structure, extending the Lotka-Volterra model with two differential equations describing two additional state variables, is proposed to describe mixed microbial populations in foods.     

Feeding habits and diet overlap of marine fish larvae from the peri-Antarctic Magellan region

The Magellan region is a unique peri-Antarctic ecosystem due to its geographical position. However, the knowledge about the distribution and feeding ecology of fish larvae is scarce. Since this area is characterized by low phytoplankton biomass, we hypothesize that marine fish larvae display different foraging tactics in order to reduce diet overlap. During austral spring 2009–2010, two oceanographic cruises were carried out along southern Patagonia (50–56°S). Larval fish distribution and feeding of the two most widely distributed species were studied, the smelt Bathylagichthys parini (Bathylagidae) and black southern cod Patagonotothen tessellata (Nototheniidae). Larvae of B. parini showed a lower increase in the mouth gape at size, primarily feeding during daytime (higher feeding incidence during the day) mostly on nonmotile prey (invertebrate and copepod eggs, appendicularian fecal pellets, diatoms). They showed no increase in feeding success (number, total volume of prey per gut and prey width) with increasing larval size, and the niche breadth was independent of larval size. Larvae of P. tessellata showed a large mouth gape at size, which may partially explain the predation on motile prey like large calanoid copepods (C. simillimus) and copepodites. They are nocturnal feeders (higher feeding incidence during night) and are exclusively carnivorous, feeding on larger prey as the larvae grow. Nonetheless, niche breadth was independent of larval size. Diet overlap was important only in individuals with smaller mouth gape (<890 μm) and diminished as larvae (and correspondingly their jaw) grow. In conclusion, in the peri-Antarctic Magellan region, fish larvae of two species display different foraging tactics, reducing their trophic overlap throughout their development.     

Diazotrophic microbial community of coastal microbial mats of the southern North Sea

The diazotrophic community in microbial mats growing along the shore of the North Sea barrier island Schiermonnikoog (The Netherlands) was studied using microscopy, lipid biomarkers, stable carbon (δ(13) C(TOC) ) and nitrogen (δ(15) N) isotopes as well as by constructing and analyzing 16S rRNA gene libraries. Depending on their position on the littoral gradient, two types of mats were identified, which showed distinct differences regarding the structure, development and composition of the microbial community. Intertidal microbial mats showed a low species diversity with filamentous non-heterocystous Cyanobacteria providing the main mat structure. In contrast, supratidal microbial mats showed a distinct vertical zonation and a high degree of species diversity. Morphotypes of non-heterocystous Cyanobacteria were recognized as the main structural component in these mats. In addition, unicellular Cyanobacteria were frequently observed, whereas filamentous heterocystous Cyanobacteria occurred only in low numbers. Besides the apparent visual dominance of cyanobacterial morphotpyes, 16S rRNA gene libraries indicated that both microbial mat types also included members of the Proteobacteria and the Cytophaga-Flavobacterium-Bacteroides group as well as diatoms. Bulk δ(15) N isotopes of the microbial mats ranged from +6.1‰ in the lower intertidal to -1.2‰ in the supratidal zone, indicating a shift from predominantly nitrate utilization to nitrogen fixation along the littoral gradient. This conclusion was supported by the presence of heterocyst glycolipids, representing lipid biomarkers for nitrogen-fixing heterocystous Cyanobacteria, in supratidal but not in intertidal microbial mats. The availability of combined nitrogen species might thus be a key factor in controlling and regulating the distribution of the diazotrophic microbial community of Schiermonnikoog.     

Development and laboratory-scale testing of a fully automated online flow cytometer for drinking water analysis

Accurate and sensitive online detection tools would benefit both fundamental research and practical applications in aquatic microbiology. Here, we describe the development and testing of an online flow cytometer (FCM), with a specific use foreseen in the field of drinking water microbiology. The system incorporated fully automated sampling and fluorescent labeling of bacterial nucleic acids with analysis at 5-min intervals for periods in excess of 24 h. The laboratory scale testing showed sensitive detection (< 5% error) of bacteria over a broad concentration range (1 × 10(3) -1 × 10(6) cells mL(-1) ) and particularly the ability to track both gradual changes and dramatic events in water samples. The system was tested with bacterial pure cultures as well as indigenous microbial communities from natural water samples. Moreover, we demonstrated the possibility of using either a single fluorescent dye (e.g., SYBR Green I) or a combination of two dyes (SYBR Green I and Propidium Iodide), thus broadening the application possibilities of the system. The online FCM approach described herein has considerable potential for routine and continuous monitoring of drinking water, optimization of specific drinking water processes such as biofiltration or disinfection, as well as aquatic microbiology research in general.