Horizontal and vertical distributions of siphonophores in relation to oceanographic conditions in Chilean Patagonian fjords

Siphonophores collected in Chilean Patagonian fjords, between the Gulf of Penas and the Trinidad Channel in 2008 were analysed. A total of 12 species were recorded, of which Muggiaea bargmannae, Lensia subtilis, Praya dubia and Sphaeronectes fragilis were identified for the first time in this sector of the Patagonian fjords. M. bargmannae represents a new record for the southeastern Pacific. The most abundant species were Muggiaea atlantica (78.6%), Lensia conoidea (8.7%) and Dimophyes arctica (8.5%). M. atlantica, the dominant species, showed high densities in both oceanic and interior waters. L. conoidea and D. arctica, on the other hand, were principally collected in interior waters. M. atlantica was collected in less saline (<30), more oxygenated (6-7 mL L–1) shallow strata (0-50 m), while L. conoidea and D. arctica were collected below 50 m depth in more saline (30-33) and less oxygenated (4-6 mL L–1) waters. The eudoxids of these species followed the same horizontal and vertical distribution patterns as their polygastric stages. These results confirm the success of M. atlantica in the colonization of all the southern fjords and document an increase with respect to the results obtained for the same geographical area in the spring of 1996. They also allowed us to infer that salinity and dissolved oxygen vertical gradients play an important role in determining the depth distribution patterns of these species.


INTRODUCTION
A steady increase in gelatinous predator populations in marine ecosystems has been observed in recent years, and this has promoted studies on gelatinous macroplankton due to their significance in determining marine ecosystem structure (Mills 2001, Brodeur et al. 2002, Purcell et al. 2007).Such predators include the siphonophores, a widespread and abundant group that are found in coastal and oceanic waters and play a critical ecological role as competitors and predators of other zooplankters, particularly micro-crustaceans and marine invertebrate and vertebrate larval stages (Mackie et al. 1987, Pugh 1999).Siphonophores have a polymorphic colony structure, with a life cycle allowing them to produce high quantities of the sexual stage (eudoxids in the Calycophorae), thus generating large population densities during some periods of the year, particularly in highly productive biological areas (Pugh 1999, Palma and Apablaza 2004, Thibault-Botha et al. 2004, Pavez et al. 2010).
Siphonophore communities have been studied in diverse geographical areas bathed by the Humboldt Current System in Chilean coastal waters, particularly in coastal areas of upwelling such as Antofagasta, Valparaíso and Concepción, where common species (e.g.Muggiaea atlantica and Sphaeronectes koellikeri) can reach high population densities during spring and summer (Palma 1994, Palma and Rosales 1995, Pagès et al. 2001, Palma and Apablaza 2004, Apablaza and Palma 2006, Pavez et al. 2010).M. atlantica also commonly inhabits Chilean Patagonian fjords and channels and is a dominant species in this southern region (Palma and Silva 2004, Villenas et al. 2009, Palma et al. 2007a, 2011).
The Chilean Patagonian fjords form one of the most extensive estuarine areas in the world, extending from the Reloncaví fjord (41°20'S) to Cape Horn (55°58'S) and including areas of complex geomorphology and oceanography.They are approximately 1600 km long and cover a total area of 240000 km 2 (Palma and Silva 2004).This ecosystem involves a two-layer estuarine circulation system: a surface layer (from the surface to 20-30 m depth) of Estuarine Water (EW) flowing towards the adjacent ocean, with low salinity due to freshwater discharge, high annual precipitation and coastal runoff; and a deeper layer (20-30 m to the bottom), which is more saline, colder and of higher density as a result of the inward flow of the Subantarctic Water (SAAW).A strong halocline develops between the two layers and, therefore, a pycnocline forms at 20-30 m depth, thus generating a highly stratified system (Silva and Calvete 2002).
The ecosystem of the interior waters, located between the Reloncaví Fjord and the Elefantes Gulf (46º30'S), has been intensively studied during the last two decades because of activities associated with marine transportation, tourism, fisheries and aquaculture (Buschmann et al. 2006, Silva andPalma 2008).Thus, numerous oceanographic and biological studies have been carried out in this zone (Silva and Palma 2008), including studies on siphonophores and jellyfish with results showing that the two-layer hydrographic struc-ture may affect not only the species composition but also the vertical distribution of the zooplankton in interior waters (Palma et al. 2007a, 2007b, 2011, Villenas et al. 2009, Bravo et al. 2011).
In contrast, the fjord ecosystem located between the Gulf of Penas (47°S) and Cape Horn has received little attention.In this vast area, the sector covering the Gulf of Penas and the Trinidad Channel (50°10'S) has been barely studied and published works on zooplankton are restricted to reports on siphonophores, chaetognaths, euphausiids and cladocerans (Palma et al. 1999, Rosenberg andPalma 2003), ichthyoplankton (Bustos et al. 2011) and decapod crustacean larvae (Mujica and Medina 2000).This southern area receives Subantarctic Water input from the adjacent Pacific, entering through the Gulf of Penas (0-150 m) to the north, the Ladrillero Gulf (0-50 m) in the centre and the Trinidad Gulf (0-70 m) to the south.These highly saline subantarctic waters merge with freshwater from rivers, such as the Baker (870 m 3 s -1 ) and Pascua (574 m 3 s -1 ) Rivers and melt water from the Southern Ice Field, thus forming EW flowing seawards in the upper 25-30 m depth stratum (Silva andCalvete 2002, Calvete andSobarzo 2011).
This work analyses the effect of water column stratification on the spatial distribution of the polygastric and eudoxid stages of siphonophores in the central Patagonian fjords of southern Chile (47°-50°10'S).

MATERIALS AND METHODS
A total of 40 oceanographic stations were occupied during the CIMAR 14 Fiordos cruise performed between 25 October and 24 November 2008, and these were distributed between the Gulf of Penas (47°S) and the Trinidad Channel (50°10'S) (Fig. 1).Only the sampling stations situated along two longitudinal transects were considered in the vertical distribution analysis.The oceanic transect (OT, 10 stations) comprised the Gulf of Penas and the Fallos, Ladrillero, Picton and Trinidad Channels, and included the stations with the highest adjacent oceanic water input.The estuarine transect (ET, 9 stations), on the other hand, involved the Gulf of Penas and the Messier, Paso del Indio and Wide Channels and the stations with the highest EW input (Fig. 1).
A CTDO Sea-Bird model SBE 25 was used at each station to record the oceanographic variables of temperature, salinity and dissolved oxygen content in the water column.Salinity and dissolved oxygen records were corrected using the results from instrumental (salinometer) and chemical (Winkler) analyses of discrete samples collected in the water column during the CTDO casting.
Zooplankton samples were obtained by oblique tows in three strata: surface (0-25 m at 40 stations), middle (25-50 m at 40 stations) and deep (50-200 m or 50 m-near bottom, depending on bottom depth at 28 stations), during day and night.The strata were selected considering the two-layer oceanographic structure characterizing the interior region of the fjords and channels (Silva and Calvete 2002).The sampling gear was a Tucker trawl net (1-m 2 mouth opening and 350-mm mesh aperture), which included a two-net system provided with a digital flowmeter in order to estimate the volume filtered by each net.Zooplankton samples were fixed immediately after collection and preserved in 5% formalin-seawater buffered with sodium borate.
A total of 108 vertically stratified samples were examined.The siphonophores were sorted from the original samples, and the nectophores (asexual polygastric stage) and eudoxids (sexual eudoxid stage) were identified and counted.The abundances of Calycophorae were estimated considering the highest number of anterior or posterior nectophores.Pyrostephos vanhoeffeni was the only species of the Physonectae collected, and its abundance was estimated by considering one individual to have 20 pairs of nectophores per colony (Totton 1965).The taxonomic identification of siphonophore species followed the works of Totton (1965) and Pugh (1999).Polygastric and eudoxid stages for the whole column were converted for every stage to density (ind 1000 m -3 ), using the volume of water filtered by the nets.Only the dominant species (>5% of the total of individuals) were considered when characterizing the horizontal and vertical distribution patterns.Vertical distributions, using the normalized data, were expressed according to the percentage of individuals in each stratum compared to the total number of individuals collected from the entire water column; and dif-ferences in the vertical distributions in depth strata at sampling stations were tested by a Kruskal-Wallis test.The relationship between the distribution patterns of siphonophore abundances and oceanographic physical and chemical features over the sampling stations were explored using a canonical correspondence analysis (CCA; Ter Braak and Verdonschot 1995).The level of significance was set at p<0.05.Initial analysis included abundance data for 11 dominant faunal and 4 environmental variables (depth strata, temperature, salinity and dissolved oxygen).The Monte Carlo permutation test (with 999 unrestricted permutations) was used to determine the significance of fauna-environment relationships.The CCA analysis was performed using XLStat software (version 2011.4.04, Addinsoft).

Hydrographic characteristics
The surface temperatures in the Baker Fjord (not shown) were almost uniform from its mouth to its head (~9°C); in the Eyre Fjord (not shown), however, they decreased from its mouth (~8°C) to its head (~7°C).The water column was almost homothermal (~8°C) below 50 m in both fjords, while the whole water column was almost homothermal in the oceanic and longitudinal transects.Surface temperatures for the interior channels were around 8°C-9°C and around 9°C-10°C for the external channels (Fig. 2A and D).The highest surface temperature values were observed in the Gulf of Penas, at the northern extreme of both longitudinal transects.The lowest surface temperature values in the ET were observed near the middle of Angostura Inglesa and in the OT, at the southernmost end of the Concepción Channel.Below 200 m the temperature of the deep layer was almost homothermal in every single micro basin (~8°C).
The surface salinity in the Baker and Eyre Fjords decreased from their mouths to their heads (28 to 2 and 26 to 24, respectively).Both fjords had a highly stratified low salinity (20-33) surface layer (~50 m), giving rise to strong haloclines above 50 m (Fig. 2B  and E).The water column below 50 m was almost homogeneous, with salinities around 33-34 in the Baker Fjord and 32-33 in the Eyre Fjord.In the ET transect, the lowest surface salinity values occurred near Angostura Inglesa (<24), Wide Channel (<20), in the OT transect and in the Fallos-Ladrillero channels (<26).A highly stratified low salinity (20-33) surface layer (~50 m) occurred in both transects, giving rise to strong haloclines.The depth of the bottom of the halocline generally coincided with the 32 salinity isopleth, which was at around 50 m depth.Below this highly stratified surface layer (i.e.>50 m), the water column was saltier (32-34) and almost homogeneous.
Dissolved oxygen concentration in the Baker and Eyre Fjords was almost homogeneous in the surface layer (~0-10 m) from mouth to head (~7 mL L -1 ).Below this well-oxygenated surface layer, dissolved oxygen decreased to around 3 mL L -1 in the Baker Fjord and to around 4 mL L -1 in the Eyre Fjord.In both longitudinal transects (Fig. 2C and F) the surface layer (~0-50 m) had a nearly homogeneous high dissolved oxygen content (>6 mL L -1 ).Below this layer, the dissolved oxygen decreased rapidly to 4 mL L -1 at around 100 m.In the deep layer of both transects the dissolved oxygen concentrations decreased below 3.5 mL L -1 in the northern micro basin and below 5 mL L -1 in the southern micro basin.

Specific composition
A total of 12 species of siphonophores (polygastric and eudoxid stages), 11 calycophorans and one physonect were identified.The total number of collected organisms, abundance ranges, average abundance, dominance and occurrence data are shown in   and 6).The dominant gelatinous species in terms of relative abundances were Muggiaea atlantica (78.6% of the total number of polygastric stages), Lensia conoidea (8.7%) and Dimophyes arctica (8.5%), while the remaining species were only found occasionally (Table 1).In decreasing order, the most commonly occurring species were M. atlantica (100% of stations), D. arctica (90% of stations) and L. conoidea (88% of stations).

Horizontal distribution
The abundances of siphonophores ranged between 35 and 39140 ind 1000 m -3 in the Picton and Messier channels (stations 87 and 22, respectively).M. atlantica occurred with a minimum abundance of 14 ind 1000 m -3 (station 14) in the Baker Channel, and a maximum of 38174 ind 1000 m -3 (station 22) in the Messier Channel (Fig. 3A).The highest densities were found in the Gulf of Penas (oceanic waters), the Messier Channel and the Eyre Fjord (interior waters).Intermediate densities were obtained in the oceanic channels (Fallos, Ladrillero, Picton and Trinidad) and the lowest density was found in the Baker Channel, where the salinity fluctuated between 5 and 33 in the upper 100 m.Lensia conoidea and Dimophyes arctica showed a very similar spatial distribution, with maxima in the Eyre Fjord and at some stations in the Messier and Trinidad channels (Fig. 3B-C).The most significant difference between the two species was found in the Gulf of Penas, where L. conoidea was almost absent, and D. arctica was collected at most stations, being concentrated at the mouth of the gulf.
The eudoxids of M. atlantica, L. conoidea and D. arctica were always more numerous than the polygastric stages.These eudoxids followed the same patterns of geographic distribution as the polygastric stages.Eudoxids of M. atlantica also exhibited abundance maxima in the Gulf of Penas and Messier Channel (Fig. 3D).Maximum concentrations of the eudoxids of L. conoidea were found in the Trinidad Channel and of D. arctica in this same channel and in the Eyre Fjord (Fig. 3E-F).It is worth mentioning that in the Gulf of Penas, where highly saline waters (ASAA) predominated, only M. atlantica eudoxids were abundant, with both L. conoidea and D. arctica being extremely rare.
The abundance of polygastric stages of M. atlantica (Table 2) exhibited significant differences between the two transects (p<0.05), with a higher dominance in the ET (90.7%) than in the OT (47.0%).This difference in abundance was also observed for rarer species,  2).Lensia conoidea and D. arctica also showed significant differences in abundance between the two transects (p<0.05);however, their maxima occurred in the OT, with dominance values of 32.5% and 16%, respectively-a trend also apparent in S. fragilis (Table 2).

Vertical distribution in OTs and ETs
The dominant species showed two kinds of vertical distribution patterns.Muggiaea atlantica was found throughout the water column, the highest densities always being found in the upper 50 m, except at station 2 in the Gulf of Penas, where the greatest numbers were found be- low 50 m (Fig. 4A-B).On the other hand, Lensia conoidea and Dimophyes arctica were more abundant at greater depths, below 50 m at most stations (Fig. 4C and F).There were non-significant differences between the vertical distributions of polygastric and eudoxid stages of M.
atlantica between the two transects (Kruskal-Wallis test, p>0.05,Table 3).In contrast, significant differences were obtained between the vertical distributions of polygastric and eudoxid stages for both L. conoidea and D. arctica in both transects (Kruskal-Wallis test, p<0.05,Table 3).

Relationships between siphonophores and oceanographic conditions
The relationships between siphonophore abundances and oceanographic variables are presented in a CCA triplot (Fig. 5).The Monte Carlo permutation test indicated significance in the ordination diagram (F ratio =2.83, p<0.001), in which the first two axes explained 98.9% of the total variance (83.8% in the first axis and 15.1% in the second axis).Axis one was positively correlated with depth strata and salinity, and negatively correlated with dissolved oxygen and temperature.This indicated an increase in salinity and depth strata from left to right in the diagram (Fig. 5), mainly evidenced at the deepest sampling stations (50-200 m).The species coupling with these environmental conditions in the deepest stratum were Muggiaea bargmannae, Lensia conoidea, L. meteori, L. subtilis, Pyrostephos vanhoeffeni, Sphaeronectes koellikeri and Dimophyes arctica (Fig. 5).On the other hand, the species associated with the shallower stratum, lower salin-ity and higher oxygen were Chelophyes appendiculata and Eudoxoides spiralis.At the centre of the diagram, Muggiaea atlantica is located as a dominant species which is not associated with any particular depth stratum, because it was found throughout the water column.The second axis explained a lower fraction of the total variance and was mainly negatively correlated with temperature, indicating an increase in this environmental variable in the shallower strata.

Hydrographic characteristics
During the CIMAR 14 Fiordos cruise, the temperature was nearly homogeneous over the whole water column along both longitudinal transects, which was not the case for salinity, leading to a highly stratified water column (Fig. 2B and E).Therefore, the vertical density structure is governed by the salinity distribution.The vertical distribution of salinity was character-Table 3. -Kruskal-Wallis test for differences in abundances of polygastric and eudoxid stages of the dominant species between the three depth strata in both the oceanic and estuarine transects.Significant values are indicated in bold (p<0.05).ized by two layers: a surface layer (0 to ~30-50 m), and a deeper layer (30-50 m to the bottom) including a strong vertical salinity gradient and therefore a pycnocline.The vertical stratification was less intense at both the northern and southern oceanic ends and more intense at the centre of the transects (Fig. 2B and E), where the freshwater input from continental rivers and glacial melting is greater (Silva andCalvete 2002, Sievers et al. 2002).The freshwater input in the ET and at the heads of Baker and Eyre fjords is greater, due to the input from continental rivers, rain and melting water.This explains the lower salinities (20-32) in the surface layer of the ET, compared with the low salinities (26-32) along the OT, which receives mainly rainwater input.Below the highly stratified surface layer, a marine, saltier (33-34) deep layer is present (~50 m to the bottom), and is less variable and almost homohaline (Fig. 2B and E).
The surface layers (0-50 m) of the Baker and Eyre Fjords and along both longitudinal transects were well oxygenated, generally above 6 mL L -1 (>90% saturation; Fig. 2C and F), due to photosynthetic processes (Aracena et al. 2011) and ocean-atmosphere oxygen exchange.Beneath the highly oxygenated surface layer, dissolved oxygen concentrations dropped below 4 mL L -1 (<50% saturation), presumably due to consumption caused by the degradation of autochthonous and allochthonous particulate organic matter coming from the surface layer and river discharge (Silva 2008).Similar low dissolved oxygen concentrations (3-4 mL L -1 ) have been recorded previously in the area (Silva and Calvete 2002).
Subantarctic Water (SAAW) from the adjacent Pacific Ocean penetrates into the region through the Gulf of Penas and Trinidad Strait, giving the marine characteristics to the deeper layers.As the SAAW spreads into the channels and fjords, it mixes with freshwater (FW) in different proportions (Sievers and Silva 2008).The water formed of salinities between 31 and 33 is known as Modified Subantarctic Water (MSAAW) or if fresher (2-31) it is known as Estuarine Water (EW).The EW remains in the surface layer and the MSAAW fills the subsurface and deeper layers of the interior fjords.

Siphonophore community composition and horizontal distribution
Results from spring 2008 were similar to those of spring 1996 (Palma et al. 1999), with 8 out of the 12 presently identified species overlapping (Table 4).The nine rare species that were recorded, representing 4.2% of the total number of siphonophores caught, were collected in estuarine interior waters and included some species found widely in oceanic waters, such as Eudoxoides spiralis, Chelophyes appendiculata, Lensia subtilis and Praya dubia (Totton 1965, Pugh 1999).However, it is supposed that the extreme oceanographic characteristics of these interior waters would be detrimental for the maintenance of reproducing populations.In general, all the identified species were epipelagic species, including some species abundant in Antarctic waters, such as Dimophyes arctica, Muggiaea bargmannae and Pyrostephos vanhoeffeni (Pagès et al. 1994, Pugh et al. 1997), and some species from warm and temperate oceanic waters (the remaining species), which may enter through the Gulf of Penas and the Ladrillero and Trinidad Channels.Their shallow sills (Ladrillero and Trinidad ~50 m, and Penas ~150 m) would prevent the entrance of mesopelagic species into interior waters.
M. bargmannae is a bipolar species mainly collected in boreal waters (Totton 1965, Pugh 1999).This finding represents the first record for Chilean waters, thus increasing the biodiversity of siphonophores known from the southeastern Pacific.The number of siphonophore species reported in the southern fjords ecosystem has therefore increased from the 14 previously recorded species (Palma and Silva 2004, Palma et al. 2007a, 2011, Villenas et al. 2009) to 17 species.However, the southern Chilean Patagonian fjords exhibit a lower diversity of siphonophores than the Humboldt Current System, where 54 species have been recorded (Palma 1977, 1994, Palma and Rosales 1995, Pagès et al. 2001, Palma and Apablaza 2004, Apablaza and Palma 2006, Pavez et al. 2010), and than the global ocean, where almost 190 species have been recorded (Pugh 1999, Boltovskoy et al. 2005).In any event, the low diversity detected in Chilean fjords and channels has also been reported for Norwegian fjords (Båmstedt 1988, Hosia andBåmstedt 2007).
The high abundance of Muggiaea atlantica was particularly noteworthy.It is a eurythermic and euryhaline species, widely distributed in both the adjacent oceanic SAAW and the interior MSAAW and EW throughout the study area.Both polygastric and eudoxid stages abundances were highest in the ET, particularly in the Wide Channel and Eyre Fjord (Table 2).We hypothesize that the high tolerance of M. atlantica to the temperature and salinity gradients favours its reproductive success in interior waters, where it is the dominant siphonophore species in the fjords of southern Chile (Pagès and Orejas 1999, Palma et al. 1999, 2007a, 2011, Palma and Aravena 2001, Villenas et al. 2009).M. atlantica is common in neritic zones and represents the predominant siphonophore along the coast of Chile, where it forms dense coastal aggregations in spring and summer (Palma 1977, 1994, Palma and Rosales 1995, Ulloa et al. 2000, Palma and Apablaza 2004, Apablaza and Palma 2006).M. atlantica occurs widely in coastal and shelf waters from warm and temperate regions in the Pacific, Atlantic and Indian Oceans, and the Mediterranean Sea (Alvariño 1971).It is also very frequent in areas of high productivity such as upwelling ecosystems like the Benguela Current (Pagès and Gili 1992) and the Humboldt Current (Palma and Rosales 1995, Palma and Silva 2004, Pavez et al. 2010).
Lensia conoidea and Dimophyes arctica occurred at much lower densities than M. atlantica, and their highest densities were found in the OT (Table 2), where SAAW waters were dominant.Only some polygastric stages of L. conoidea were collected in the Gulf of Penas and eudoxids were not found there at all (Fig. 3E).On the other hand, a larger abundance of the polygastric stages of D. arctica occurred, although eudoxids were extremely scarce.The spatial distribution of eudoxids for both species was shifted towards MSAAW and EW with lower temperatures (<6°C) and salinities (<30) (Silva and Calvete 2002), a situation even clearer in the Eyre Fjord, where the highest densities of eudoxids were found (Fig. 3F).
L. conoidea is common and abundant in the great oceans, particularly in the California and Benguela currents, and in the Mediterranean Sea (Alvariño 1971), spanning a broad depth distribution from the surface down to the bathypelagic zone (Pagès and Gili 1992).D. arctica is a cosmopolitan species with a bipolar distribution, inhabiting the great oceans as well as the Antarctic, Arctic, and Mediterranean Sea (Alvariño 1971).In boreal and austral latitudes it is more abundant in epipelagic waters than in tropical and temperate waters, where it is more common in meso-and bathypelagic waters (Pagès and Gili 1992).
It is interesting to note that the dominant siphonophores (M.atlantica, Lensia conoidea and Dimophyes arctica) found in these Patagonian fjords have also been found in fjords in the northern hemisphere, such as the Norwegian fjords Fanasfjord, Korsfjord and Hardangerfjord (Bakke and Sands 1977;Pagès et al. 1996).Though M. atlantica has been found sporadi-cally, it appeared in large numbers during the warmer than average year of 2002 in Fanafjord (Fossa et al. 2003), which had received high salinity waters from the Atlantic Ocean (Hosia andBamsted 2007, 2008).In the Korsfjord Fjord, an abundance of polygastric stages of both Lensia conoidea and Dimophyes arctica has been found throughout the year, with the maximum abundance being reached in spring (late May to early June) (Hosia and Bamsted 2008).

Vertical distribution
The presence of a strong pycnocline at around 50 m depth, separating the EW from the MSAAW, had an important effect on the vertical distribution of M. atlantica, concentrating the polygastric and eudoxid populations in the upper 50 m, where the more stable, oxygenated, low-salinity layer of the water column occurred (Fig. 4A-B).L. conoidea and D. arctica, on the other hand, for which the polygastric and eudoxid populations also coexisted, were distributed in deeper waters (below 50 m) where quasi-homogeneous conditions for temperature, salinity and dissolved oxygen occurred (Fig. 4C and F).The results of a Kruskal-Wallis test indicated that these species had a significantly different depth distribution, being deeper (>50 m) in both OTs and ETs (p<0.05;Table 3).The difference in the use of the water column suggests that M. atlantica has different ecological requirements to L. conoidea and D. arctica.The diel vertical distribution of this species could not be studied, because day and nighttime samplings were never performed at the same stations.
The vertical distribution pattern of some dominant siphonophore species (Lensia conoidea, Dimophyes arctica and Pyrostephos vanhoeffeni) was such that their presence and higher abundances were associated with the deeper (50-200 m) stratum: CCA plots showed a clear separation between the shallower (0-25 m and 25-50 m) and deeper strata.The CCA indicated that a relatively large proportion of amongsite variances in the abundance of these three species among the sampling stations were positively correlated with depth strata and salinity, and negatively with dissolved oxygen and temperature.This is an expected association, because as depth increases so does the salinity, and the temperature and dissolved oxygen concentration decrease (Fig. 2).The oceanographic conditions in the deeper stratum where three species were most abundant are characteristic of the MSAAW water masses.The CCA also demonstrated that M. atlantica, the most dominant species, was mainly associated with high dissolved oxygen and low salinity in surface layers.However, the low correlation also indicates that M. atlantica can be distributed throughout the water column (Palma et al. 2011).The canonical analysis also indicated that L. subtilis and M. bargmannae abundances were correlated with the deeper stratum with high salinity and low dissolved oxygen concentrations.E. spiralis and C. appendiculata were found in shallow and warm waters, probably associated with the influence of oceanic waters.Rare species such as L. meteori and S. koellikeri were correlated with the deeper stratum with higher salinity and temperatures.

Comparison between the results obtained in spring 1996 and 2008
Species richness in spring 1996 was 75% of that found in spring 2008 (see Palma et al. 1999), with Muggiaea bargmannae, Lensia subtilis, Praya dubia and Sphaeronectes fragilis being found for the first time in this area (9 and 12 species in 1996 and 2008, respectively).The average abundance per station for siphonophores was almost one order of magnitude higher in 2008 (Table 4).This trend was observed for most species, except for L. conoidea, whose average abundance per station was only 2-3 times higher in 2008.The most significant increases were observed in M. atlantica and D. arctica (Table 4).Moreover, D. arctica, which was a very rare species comprising less than 1% of the total number of siphonophores in spring 1996, comprised 7.7% of the total number of siphonophores in spring 2008, with a wide geographic distribution of both polygastric and eudoxid stages in the same area (Fig. 3C-F).
The results obtained in the spring of 1996 indicated that the community of siphonophores was mainly dominated by M. atlantica (67.51%) and L. conoidea (30.02%), while D. arctica (0.99%) was almost absent.However, in spring 2008, a high dominance of M. atlantica (80.37%) compared with L. conoidea (8.53%) and D. arctica (7.77%) was evident (Table 4).The large increase in the relative abundance of M. atlantica observed in different areas of the southern Chilean fjords ecosystem (Palma et al. 2007a, 2011, Villenas et al. 2009) confirms its high adaptability to areas of low water temperature and salinity, where the highest densities of its eudoxid phase were concentrated (Fig. 3D).In fact, in spring 1996 the highest densities were found in ocean channels (OT, Fallos and Ladrillero Channels), while in spring 2008 a peak of abundance was found in EWs with lower temperature and salinity (ET, Messier Channel and Eyre Fjord).This species has become the dominant species in the Chilean fjords ecosystem, where it has achieved considerable reproductive success.
This increase in abundance cannot be explained on the basis of inter-annual differences in the abiotic variables analysed, as temperature, salinity and dissolved oxygen concentration values recorded in spring 2008 were similar to those recorded in spring 1996 by Silva and Calvete (2002).The increase may be the result of the different sampling gear used.In November 1996, integrated oblique tows (0-200 m) were carried out using bongo nets (0.28-m 2 mouth opening and 350-mm mesh size),while in November 2008 the oblique tows were performed at three depth levels (0-200 m) using Tucker trawl nets with a much larger mouth opening (1 m 2 , 350-mm mesh size).The capture results were standardised according to the volumes filtered by each net (ind 1000 m -3 ) but, according to Pepin and Shears (1997), the large sample volume of the Tucker trawl relative to the bongo nets can result in significantly higher estimates of species diversity for fish eggs and larvae but not for crustaceans or medusae.Therefore, the differences may actually be due to a higher abundance of gelatinous organisms in interior waters, especially for M. atlantica, a situation also observed in other areas of the interior water region in southern Chile (Palma et al. 2007a, 2011, Villenas et al. 2009).

FINAL REMARKS
A total of 12 species were recorded, of which Muggiaea bargmannae, Lensia subtilis, Praya dubia and Sphaeronectes fragilis were identified for the first time in the central Patagonian fjords.M. bargmannae represents a new record for the southeastern Pacific.The most common and abundant species in Chilean Central Patagonian fjords were Muggiaea atlantica (78.6% of total), Lensia conoidea (8.7%) and Dimophyes arctica (8.5%).M. atlantica, the dominant species, was present at high relative abundances in EW (ET, 90.7%), while L. conoidea and D. arctica were principally collected in oceanic waters (OT, 32.5% and 16.0%, respectively) (Table 2).The eudoxids of these species followed the same horizontal distribution patterns as their polygastric stages.These distributions allowed us to hypothesize that salinity and dissolved oxygen vertical gradients play an important role in determining the depth distribution patterns of some of the siphonophore species.This is in agreement with results reported for many species of gelatinous zooplankton from the northern hemisphere, which are distributed in different water column strata of varying thickness, also reflecting the physical/chemical structure of the water column (i.e.Graham et al. 2001, Raskoff et al. 2005).

Fig. 2 .
Fig. 2. -Vertical distribution of temperature (A), salinity (B) and dissolved oxygen (C) in the longitudinal oceanic transect (OT) and temperature (D), salinity (E) and dissolved oxygen (F) in the longitudinal estuarine transect (ET) between Penas Gulf and Trinidad Channel in spring 2008.

Table 1
. The calycophorans Muggiaea bargmannae, Lensia subtilis, Praya dubia and Sphaeronectes fragilis are recorded for the first time in this central Chilean Patagonian area (47-50°S).The presence of four nectophores of M. bargmannae in the Picton Channel (Sta.88) represents the first record of this species in Chilean waters.L. subtilis and S. fragilis were collected from several stations; meanwhile, P. dubia was only represented by two stem groups collected in the Baker Fjord (stations 4

Table 1 .
-Summary of basic statistics for polygastric (po) and eudoxid or sexual (eu) stages of siphonophores.Total number of individuals, range of abundances, average per station, dominance and occurrence.Abundances are expressed as ind 1000 m -3 .Ne, nectophores; Sg, stem group.

Table 2 .
-Summary of basic statistics for polygastric stage abundances (ind 1000 m -3 ) between the oceanic and estuarine transects.Range of non-zero abundances, average abundance per station, dominance and occurrence.

Table 4 .
-Summary of basic statistics for polygastric stages of siphonophores between the springs of 1996 (CIMAR 2 Fiordos cruise) and 2008 (CIMAR 14 Fiordos cruise).Total number of individuals, range of abundances, average abundance per station, standard deviation (SD), dominance (D) and occurrence (O).Abundances are expressed as number of individuals per 1000 m -3 .Ne, nectophores.