Strait Of Magellan Research Articles

Macromoluscos intermareales de sustratos rocosos de la playa Buque Quemado, Estrecho de Magallanes, sur de Chile

The Strait of Magellan is a complex natural channel that connects the Pacific and Atlantic Oceans. Due to the weather and oceanographic characteristics of th...

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 \( P_{\text{m}}^{\text{B}} \) (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.

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.

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.

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.

Vagrant Antarctic fur seals, Arctocephalus gazella, in southern Chile

The Antarctic fur seal, Arctocephalus gazella, in the eastern South Pacific Ocean, first reported on Hoste Island, Cape Horn in 1973, and then on the Juan Fernandez Archipelago in 1982 and 1983, was recorded again in October and December 2009 on the southern coast of Chile. Three different individuals were seen simultaneously on a single day at Punta Dungenes, Magellan Strait, and a fourth individual was sighted at the northeastern coast of Almirantazgo Sound, Tierra del Fuego. These records represent the first sightings of live Arctocephalus gazella in southern Chile. Although it is difficult to establish both their origin and rationale for dispersion outside of their distribution range, the substantial breeding population recovery in South Georgia and food shortages during the breeding and post-breeding season are suggested as possible explanations.

Estrategias de subsistencia de cazadores recolectores de Isla Dawson (Estrecho de Magallames) durante la segunda mitad del Holoceno: primeras aproximaciones

El desarrollo de una prospeccion arqueologica en la costa de isla Dawson e isla Wickham, ubicadas en una posicion estrategica entre las diferentes vias de comunicacion que conectan la porcion central del estrecho de Magallanes con el archipielago fueguino, registro 27 yacimientos que corresponden a antiguos campamentos de cazadores-recolectores marinos que habitaron la zona. La realizacion de excavaciones de sondeo en seis de estos sitios permitio recuperar un interesante conjunto de restos arqueofaunisticos. A partir del analisis de estos conjuntos, describimos las principales caracteristicas observadas y ofrecemos un primer panorama referido a la subsistencia de los grupos que habitaron esta zona del archipielago fueguino.

Genetic divergence over small geographic scales and conservation implications for Commerson's dolphins (Cephalorhynchus commersonii) in southern Argentina

Cephalorhynchus commersonii is distributed in the nearshore coastal waters of South America, and thus is particularly vulnerable to bycatch in coastal nets and trawls. Our study documents genetic structure in presumed Commerson's dolphin subpopulations along the southern Argentina coastline, from the Ría Deseado in the north to Ría Gallegos in the south, and focuses on the potential for depletion in the apparently more heavily impacted Ría Gallegos area. Only two control region (423 bp) haplotypes were shared among all these locations (out of 11 identified), and striking differences in haplotype frequencies between areas are apparent. AMOVA analysis, using mitochondrial sequence data, indicates significant population subdivision (overall FST= 0.21, P < 0.001) between Ría Deseado (n= 8), Bahía San Julián (n= 11), Ría Gallegos (n= 31), and a small sample of dolphins from the captive colony at San Diego Seaworld (n= 7) derived from animals originally captured in the Strait of Magellan. Comparisons based on haplotypic distances indicated relatively strong differences between regions (ΦST= 0.30, P < 0.001). This research provides the first indication of reduced gene flow and genetic differentiation within local subpopulations of Commerson's dolphins, along a relatively small stretch of coastline.

Response to “Whales Might Also Be an Important Component in Patagonian Fjord Ecosystems”

Comment to: Hucke-Gaete, R. 2011. Whales might also be an important component in Patagonian fjord ecosystems: Comment to Iriarte et al. AMBIO 40(1). (This issue). Our contribution (Iriarte et al. 2010) focused on a more general vision, engulfing almost all Patagonian fjord and channel systems under the umbrella of “ecosystem services” (ES). Ecosystem services offer a promising means for aligning conservation, production and socio-economic goals, while simultaneously increasing human welfare and protecting biodiversity, engaging a wider range of places, people, policies, and financing resources. This approach allowed us to integrate organisms of all size spectra (from bacteria to whales) and all types of systems (from the headwaters of the forested watersheds downstream to the related pelagic and benthic coastal marine ecosystems). Furthermore, we gave particular emphasis in the assessment of selected ES, including water quality, carbon sinking and sequestration, the production of pelagic fisheries, and the impact of top predators in the Patagonian fjords. This conceptual model described some ES selected (e.g. water availability and regulation, nutrient cycle, food production, climate regulation) as functions of ecosystem processes (e.g. water reserve and flux, nutrient availability and recycling, carbon flux as energy, climate processes modulating biological processes) and forested watershed-fjord dynamics, human disturbances and climate change. Thus, these ES could be used in the design of comprehensive management recommendations. Hucke-Gaete (2011) points out an interesting aspect, particularly in terms of carbon export (Pershing et al. 2010) and its impact on the tertiary level of consumers in oceanic upwelling trophic webs (Alava 2009), of the role of whales, when present, in semi-enclosed systems. Although not yet quantified, the role of whales in pelagic food webs associated with semi-enclosed Patagonian systems should be highly relevant in areas with enhanced water exchange between the adjacent coastal region and wide-open, relatively deep, semi-enclosed areas (i.e. Corcovado Gulf; Straits of Magellan). Abundant whales have often been observed in these systems, which seem to be important feeding and nursing grounds, during the productive season (austral spring and summer) (Hucke-Gaete et al. 2004). In addition, whales constitute a major mechanism for recycling iron through feeding on krill and the production of unconsolidated iron-rich faeces. The faecal iron content (145.9 mg kg−1) has been reported to be 10 million times higher than in the surrounding Antarctic waters (Nicol et al. 2010). Thus, whales might contribute significantly to maintaining the sustained high primary production (PP) levels found in the area. Ideally, we would be able to calculate this contribution (expressed as maximum recycled iron in mg) by using an actual estimate of PP (this can be extrapolated from Iriarte et al. (2007) and Gonzalez et al. (2010) and the number of whales per 1000 km−2, considering the total carbon (in tons) that each of these large cetaceans are able to consume. Unfortunately, these calculations cannot be made given the current lack of relevant data. Another fertilization mechanism not mentioned by Hucke-Gaete is the mixing effect exerted by whales in semi-enclosed systems. If vertically migrating organisms such as krill can affect the physical structure of the upper ocean through turbulent mixing associated with their diurnal vertical migrations (Kunze et al. 2006; Kajita and Dabri 2009), whales could be expected to have a similar effect, disrupting the physical structure during swimming. The effects of whales and vertically migrating animals on ocean chemistry and physical structures may affect the whole system in different ways and on different spatial/temporal scales. Among others, certain euphausiid species (i.e. Euphausia vallentini) and blue whales (Balaenoptera musculus) seem to be key components in maintaining high levels of PP during the productive season, thereby stabilizing the food web structure in some Patagonia fjord systems.

The importance and distinctiveness of small-sized phytoplankton in the Magellan Straits

The distribution of summer phytoplankton across the Straits of Magellan (SOM) was studied with the aims of tracing differences among the distinct subregions of the area and contributing to the knowledge of its biodiversity. Samples collected at 25 stations were observed and counted in light microscopy. Selected samples were observed with transmission electron microscopy. The main unifying feature of the phytoplankton in the SOM was the high abundance and numerical dominance of small-sized (<10 μm) eukaryotic species, among which coccoid cells of <3 μm size were predominant (56.2 ± 30.6 of the total phytoplankton abundance). They mostly belonged to the prasinophyte Pycnococcus provasolii, which was abundant (0.8–6,834 cells × 103 ml−1) at all stations with the exception of those in proximity to the Atlantic entrances, where it was not recorded. Small-sized (<3 and 3–5 μm) diatoms (Minidiscus trioculatus, Lennoxia faveolata and other undetermined centric species) attained high densities (<3,757 cells 103 ml−1) especially at stations of the Patagonian sectors, whereas microplanktonic diatoms were only found at the two entrances of the Straits. Dinoflagellates were constituted mainly by >10 μm forms in the Andean subregion and <10 μm naked species in the Patagonian subregion, contributing up to 75.9 and 41.8% of the total carbon in these two areas, respectively. In the Patagonian subregion, flagellates mainly constituted by <5 μm forms and by cryptomonads <10 μm comprised up to 53.9% of the total biomass. Several species identified in this study have never been reported in other investigations in the SOM, while others, including Pycnococcus provasolii and Lennoxia faveolata, have rarely been recorded elsewhere. Overall, the summer phytoplankton of the Straits does not resemble that of any other region of the world’s seas. Although some of the predominant species might have been overlooked elsewhere, their abundance and relative importance apparently constitute a distinctive feature of the SOM.

Diversity and spatial distribution patterns of polychaete assemblages in the Paso Ancho, Straits of Magellan Chile

The polychaete fauna of the Paso Ancho Basin in the Straits of Magellan was studied by means of three different sampling gears: a multibox corer, an Agassiz trawl, and a Rauschert dredge. A total of 1743 polychaete specimens belonging to 166 species from 36 families were collected at 10 stations. Significant differences were found between the catches of the three gears in terms of species numbers. The multibox corer brought up 63% of all species caught, especially macroinfauna polychaetes, the Rauschert dredge caught 16%, mostly small-bodied macroepifauna species and the Agassiz Trawl brought up 6% of the total species, largely mega-epifauna polychaetes. Only 15% of the total species occurred in more than one of the gears and only one species was found parallel in all three gears thus indicating that the combination of these gears allowed a better description of the polychaete communities than possible by just one of the gears. Using the Abundance-based Coverage Estimator and combining all species from the three different gears led to an asymptotic value of the species accumulation curve of 223 species for the Paso Ancho. Non-metric multidimensional scaling based on presence/absence data distinguished between shallow (<120 m) and deep (>120 m) polychaete assemblages. The shallow assemblage showed higher species richness values than the deep assemblage, and the taxonomical composition, too, differed considerably between both assemblages.

A morphological and phylogenetic study of Glaphyrosiphon gen. nov. (Halymeniaceae, Rhodophyta) based on Grateloupia intestinalis with descriptions of two new species: Glaphyrosiphon lindaueri from New Zealand and Glaphyrosiphon chilensis from Chile

Hommersand M.H., Leister G.L., RamÍrez M.E., Gabrielson P.W. and Nelson W.A. 2010. A morphological and phylogenetic study of Glaphyrosiphon gen. nov. (Halymeniaceae, Rhodophyta) based on Grateloupia intestinalis with descriptions of two new species: Glaphyrosiphon lindaueri from New Zealand and Glaphyrosiphon chilensis from Chile. Phycologia 49: 554–573. DOI: 10.2216/09-106.1A new genus, Glaphyrosiphon Hommersand & Leister gen. nov., is proposed to contain the generitype Glaphyrosiphon intestinalis (Harvey) Leister & W.A. Nelson comb. nov., a species known in New Zealand under the name Grateloupia intestinalis (Hooker. f. & Harvey) Setchell ex P.G. Parkinson, and two additional species: Glaphyrosiphon lindaueri W.A. Nelson & P.W. Gabrielson sp. nov. from the northern part of New Zealand and Glaphyrosiphon chilensis M.E. Ramírez, Leister, and P.W. Gabrielson sp. nov. in the southern part of Chile from Valdivia (Región de Los Ríos), to Punta Arenas in the Strait of Magellan (Región de Magallanes). Thalli are borne singly or in clusters from a small discoid holdfast and consist of simple or one- to three-times-branched slippery tubes that are copiously filled with mucilage. The medulla consists of a one- to several-layered network inside the cortex composed of stellate cells that interconnect by short to long extensions linked by pit connections. Primary rhizoidal filaments are absent. Spermatangia are superficial on terminal cortical cells. Carpogonial and auxiliary-cell ampullae are formed separately and link by unsegmented tubular connecting filaments, as in other Halymeniaceae. The auxiliary-cell ampulla consists of a basal cell and four unilaterally branched filaments in which the auxiliary cell is the basal cell of one of the four filaments. The auxiliary cell and inner ampullar filaments unite forming a fusion cell. Ampullar filaments connect terminally to inner cortical cells and laterally with one another by short filaments and pit connections that form an involucral network surrounding the gonimolobes. Tetrasporangia are cruciately divided and borne laterally on filaments produced secondarily from surface cortical cells. Sequence analyses of the rbcL gene place Glaphyrosiphon sister to Polyopes in the Halymeniaceae. The two New Zealand species consist of southern and northern clades separated by 1.2% to 1.7% base-pair distances in rbcL analyses and a Chilean species that forms a single clade separated from the New Zealand clades by 3.9% to 4.4% base-pair distances. Records of Grateloupia intestinalis from Tasmania have not been studied.

The possible causes of the tragedy of "Port Famine" in the Strait of Magellan

The attempts to colonize the Strait of Magellan soon followed the discovery of this route. PeDro Sarmiento de Gamboa, a Spanish sailor, established human settlements to fortify those lands and control the transit of vessels, especially those of English corsairs, which devastated Chilean and Peruvian coasts. During the summer of 1584, approximately 500 soldiers, artisans, priests, women and children established two villages called "Nombre de Jesús" and "Rey Don Felipe". From the beginning, these settlers had leadership and communication problems and difficulties to obtain food. After three winters only 17 to 18 people survived according to the testimony of one of the survivors, that was rescued by an English sailor named Cavendish, which renamed the village "Rey Don Felipe" as "Port Famine". When he observed the scenes of abandonment and death, he supposed that the settlers died due to lack of food. Other factors that facilitated the desolation were hypothermia, execution, anthropophagy and lesions caused by natives. There is also a possibility that intoxication by red tide (harmful algal bloom) could explain in part the finding of unburied corpses in the strait beaches.

La increíble empresa de Sarmiento de Gamboa y su triste fin: Posibles causas de la tragedia en el Estrecho de Magallanes en el siglo XVI

The attempts to colonize the Strait of Magellan soon followed the discovery of this route. PeDro Sarmiento de Gamboa, a Spanish sailor, established human settlements to fortify those lands and control the transit of vessels, especially those of English corsairs, which devastated Chilean and Peruvian coasts. During the summer of 1584, approximately 500 soldiers, artisans, priests, women and children established two villages called "Nombre de Jesús" and "Rey Don Felipe". From the beginning, these settlers had leadership and communication problems and difficulties to obtain food. After three winters only 17 to 18 people survived according to the testimony of one of the survivors, that was rescued by an English sailor named Cavendish, which renamed the village "Rey Don Felipe" as "Port Famine". When he observed the scenes of abandonment and death, he supposed that the settlers died due to lack of food. Other factors that facilitated the desolation were hypothermia, execution, anthropophagy and lesions caused by natives. There is also a possibility that intoxication by red tide (harmful algal bloom) could explain in part the finding of unburied corpses in the strait beaches.

Bryozoan assemblages on hard substrata: species abundance distribution and competition for space

Bryozoans are colonial invertebrates that often dominate epibenthic assemblages on the lower surfaces of hard substrata. Competition among neighbouring organisms is usually a critical process regulating biodiversity, and hard substrata have proved to be a suitable model habitat to analyse spatial interactions. We explored the relationships among abundance, species richness, diversity, competitive ability, coverage, available surface, depth and substratum size in an assemblage of bryozoans encrusting pebbles and cobbles in a bank off the eastern mouth of the Strait of Magellan. We also tested whether overgrowth competition can be regarded as hierarchical, and whether the species abundance distribution shows a mode of rare species and a decreasing frequency of increasingly abundant species. Abundance, species richness, diversity and overgrowth competition were highest on the largest substrata. Smaller pebbles tended to be encrusted by the commonest bryozoans, while the rarest species were mainly found on relatively larger clasts. A high proportion of the lower surfaces of most substrata was available for growth. Diversity values of relatively shallow stations were lower than expected under Caswell’s neutral model. Interspecific competition was hierarchical, but the abundance of colonies was not related to the competitive ability of each species. The species abundance distribution was bimodal, with a main mode of rare species and a second one partly composed of relatively abundant bryozoans with poor competitive abilities. This study shows that even in an encrusting assemblage where competition is hierarchical, the weakest competitors persist and the dominant species are far from being capable of monopolizing space.

Latitudinal patterns of export production recorded in surface sediments of the Chilean Patagonian fjords (41–55°S) as a response to water column productivity

The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ 13C org) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ∼44°S), Northern Patagonia (44° to ∼47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m −2 d −1) and Northern Patagonia (1667 and 2616 mg C m −2 d −1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m −2 d −1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (Si OPAL ∼1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ 13C org and C/N ratios; the more depleted ( δ 13C org −26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.

Infestation of Lithodes santolla (Decapoda: Lithodidae) by Pseudione tuberculata (Isopoda: Bopyridae) in San Jorge Gulf, Southwestern Atlantic Ocean

The bopyrid isopod Pseudione tuberculata infests decapod crustacean species of the family Lithodidae. It has previously been found in Neolithodes diomedeae from Chile, in Lithodes santolla and Paralomis granulosa from the Beagle Channel and in L. santolla from the Magellan Strait. A case was detected in 1980 in San Jorge Gulf and since then no bopyrid has been found in any of the 12,300 specimens of Lithodes santolla studied from commercial captures. In the present study we collected and analysed 648 juveniles of Lithodes santolla measuring between 8.38 and 49.04 mm carapace length (CL) from shallow waters in the central area of San Jorge Gulf. Sixteen females of Pseudione tuberculata along with 12 attached males were recorded. Additionally, six exuviae showed branchial swelling but no parasites were found. An infestation of the right branchial chamber was observed only once. Ten bopyrid females were mature and six were immature. Prevalence was very low and closely related to the age and the habitat of young king crabs in open coastal waters. The infestation occurs during the first months following postlarval settlement, and the parasite reaches sexual maturity within the next year, before host juveniles leave the coastal waters. So, the entire life span of the bopyrid could occur in coastal waters.

Systematics and phylogeny of Cristacoxidae (Copepoda, Harpacticoida): a review

Both sexes of a new species of Noodtorthopsyllus Lang, 1965 (Harpacticoida, Cristacoxidae) from a sandy beach in São Paulo State (Brazil) are described using light and scanning electron microscopy. Noodtorthopsyllus tageae sp. nov. displays a mosaic of characters drawn from both Noodtorthopsyllus and Cristacoxa Huys, 1990, blurring the boundaries between both genera. Consequently, Cristacoxa, the type genus of the nominal family-group taxon Cristacoxidae Huys, 1990, is relegated to a junior subjective synonym of Noodtorthopsyllus, and its type species is transferred to the latter as N. petkovskii (Huys, 1990) comb. nov. A new genus Acuticoxa is proposed to accommodate A. ubatubaensis sp. nov. (type species), collected on the northern continental shelf of São Paulo State, and A. biarticulata sp. nov., previously identified as Laophontisochra sp., from the Northern Magellan Straits. Amended diagnoses are provided for Noodtorthopsyllus and Laophontisochra. Autapomorphies supporting the monophyly of the Cristacoxidae are re-evaluated, including new data on P3 endopod sexual dimorphism and caudal ramus development. It is concluded that a recently published hypothesis of a deeply rooted split of the family into two highly divergent lineages cannot be supported. Consequently, both Laophontisochra and Acuticoxa gen. nov. are removed from the Cristacoxidae and tentatively assigned to the Nannopodidae (ex Huntemanniidae), forming a clade with three other genera displaying coxal modifications on leg 1 (Rosacletodes Wells, 1985; Huntemannia Poppe, 1884; and an as yet undescribed genus from Brazil). Based on the sexual dimorphism of the P4 endopod, we propose to transfer Metahuntemannia Smirnov, 1946 and Pottekia Huys, 2009 from the Nannopodidae to the Canthocamptidae (subfamily Hemimesochrinae) where they are probably most closely related to Psammocamptus Mielke, 1975; Bathycamptus Huys &amp; Thistle, 1989; Perucamptus Huys &amp; Thistle, 1989; and Isthmiocaris George &amp; Schminke, 2003. An identification key to the genera of the Nannopodidae is presented.

Nitrate to silicate ratio variability and the composition of micro-phytoplankton blooms in the inner-fjord of Seno Ballena (Strait of Magellan, 54°S)

The along-fjord variability of nitrate and dissolved silicate was studied in a silled fjord, Seno Ballena, in the Strait of Magellan during flood and ebb tidal phases in December 2007. The spatial and temporal variability of both nitrate and dissolved silicate were consistent with the dynamics of a tidal intrusion front previously described for this fjord by Valle-Levinson et al. (2006). During flood, maximum nitrate values were found seaward and close to the sill due to the upwelling of dense, nutrient-rich water by means of Bernoulli aspiration. Conversely, a sharp drop in surface nitrate landward of the sill was consistent with the sinking of saltier, nitrate-rich, dissolved silicate-poor upwelled waters under relatively less dense, nitrate-poor, dissolved silicate-rich surface waters after flowing landward over the shallow sill. The waters flooding over the sill were particularly enriched in nitrate but poor in dissolved silicate, ( NO 3 − :Si(OH) 4 ratio ∼5). The ratio tended to decrease landward of the sill, particularly during the ebb tide ( NO 3 − :Si(OH) 4 ratio <2), but the absolute Si(OH) 4 concentration values were still very low, normally ranging between 2 and 3 μM Si(OH) 4. Consistent with the low availability of dissolved silicate (DSi), only dinoflagellates (in the micro-phytoplankton size range) bloomed in nitrate-enriched (10 μM NO 3 − ) waters at the base of a shallow halocline. Thus, it is likely that the variability of surface water nutrients and DSi in Seno Ballena results mainly from the interplay among tidally forced fertilization (the aspiration of subpycnocline water with a high NO 3 − :Si(OH) 4 ratio), the input of continental waters (low NO 3 − :Si(OH) 4 ratio), and local productivity. The combination of these factors explains the micro-phytoplankton composition observed landward of the sill on this and previous expeditions to the study area.