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Latin american journal of aquatic research

versión On-line ISSN 0718-560X

Lat. Am. J. Aquat. Res. vol.44 no.3 Valparaíso jul. 2016


Research Article


Abundance and spatial distribution of neustonic copepodits of Microsetella rosea (Harpacticoida: Ectinosomatidae) along the western Magellan coast, southern Chile

Abundancia y distribución espacial de copepoditos neustónicos de Microsetella rosea (Harpacticoida: Ectinosomatidae) en la costa occidental de Magallanes, Chile


Juan I. Cañete1, Carlos S. Gallardo2, Carlos Olave3, María S. Romero4, Tania Figueroa1 & Daniela Haro5

1Laboratorio de Oceanografía Biológica Austral (LOBA), Facultad Ciencias Universidad de Magallanes, Punta Arenas, Chile
Instituto Ciencias Marinas y Limnológicas, Facultad de Ciencias Universidad Austral de Chile, Valdivia, Chile
Centro Regional de Estudios, CEQUA, Punta Arenas, Chile
Departamento de Biología Marina, Facultad Ciencias del Mar Universidad Católica del Norte, Coquimbo, Chile
Laboratorio Ecología Molecular, Facultad Ciencias, Universidad de Chile, Santiago, Chile

Corresponding author: Juan I. Cañete (
Corresponding editor: Sergio Palma

ABSTRACT. The pelagic harpacticoid copepod Microsetella rosea inhabits the cold waters along the temperate southern coast of Chile, where its population biology and ecological role in the neuston are unknown. During a CIMAR 16 Fiordos cruise realized in the Magellan Region, 26 neustonic samples were collected to analyze the abundance, spatial distribution of copepodits and oceanographic conditions (temperature, salinity, and dissolved oxygen). M. rosea copepodits, the most abundant holoneustonic taxa (30% of total abundance), were present at all sampled stations and were 0.5 times more abundant than calanoids. These copepodits inhabited waters ranging between 6.5-8.5oC and salinity of 26-33, with maximum abundances (1,000-10,000 ind/5 min horizontal drag) at means of 7.2 ± 0.6°C and salinities of 30.7 ± 0.9. Froward Cape, Almirantazgo Sound, and Inútil Bay stations accounted for 65% of total M. rosea abundance, whereas Beagle Channel stations present the lowest abundances (<4%). The entire sampling area was as an oxygenated estuary (7.4 ± 0.4 mL L-1). Given the abundance and recurrence of M. rosea in the Magellanic neuston, future research should assess the ecological functions of this species. Finally,M. rosea could also be used as a biotracer for processes of aggregation in other estuarine neustonic communities of southern Chile.

Keywords: Microsetella rosea, Copepoda, neuston, subantarctic zooplankton, estuaries, oximax zone, southern Chile.

RESUMEN. El copépodo harpacticoide pelágico Microstella rosea habita las aguas frías a lo largo de la costa templada del sur de Chile, donde se desconoce su biología poblacional y rol ecológico en el neuston. Durante el crucero CIMAR 16 Fiordos realizado en la región de Magallanes, se recolectaron 26 muestras neustónicas para analizar la abundancia, distribución espacial de los copepodítos y condiciones oceanográficas (temperatura, salinidad y oxígeno disuelto). Los copepoditos de M. rosea, el taxa holoneustónico más abundante (30%), se encontraron en todas las estaciones analizadas y fueron 0,5 veces más abundantes que los copépodos calanoides. Los copepoditos habitaron aguas de 6.5-8.5oC, con salinidades de 26-33, con máximos de abundancia (1.00010.000 ind/5 min arrastre horizontal) con promedios de 7,2 ± 0,6°C y 30,7 ± 0,9 de salinidad. En las estaciones localizadas en Cabo Froward, Seno Almirantazgo y Bahía Inútil se colectó el 65% de la abundancia total de copepoditos; mientras que en las estaciones del Canal Beagle se registraron las menores abundancias (<4%). Toda el área de muestreo representa un estuario oxigenado (7,4 ± 0,4 mL L-1). Dada la abundancia y recurrencia de M. rosea en el neuston magallánico, se deberían efectuar futuras investigaciones para evaluar las funciones ecológicas de este copépodo. Finalmente, M. rosea podría ser utilizado como un biotrazador para procesos de agregación en otras comunidades estuarinas neustónicas del sur de Chile.

Palabras clave: Microsetella rosea, Copepoda, neuston, zooplancton subantárctico, estuarios, zonas Oximax, sur de Chile.



While harpacticoid copepods are primarily benthic crustaceans, a small proportion (<0.5%) of harpacticoid species inhabit the pelagic zone during their life cycle (Boxshall, 1979; Uye et al., 2002). These pelagic species, which include Microsetella spp. and Macrosetella spp., have relatively strong swimming abilities and unique structural features, such as an elongated worm-like body and long caudal setae that delay sinking velocity. These copepods also show a close resemblance to floating substrates (e.g., the colonial cyanobacterium Trichodesmium; Calef & Grice, 1966; Tokioka & Bieri, 1966; O'Neil, 1998), and suspended organic matter (Alldredge, 1972; Ohtsuka et al., 1993; Green & Dagg, 1997; Uye et al, 2002; Zaitsev, 2005).

Microsetella rosea is widely distributed in sub-antarctic waters (5-10°C), ranging from the southern end of South America to western Antarctica, in addition to inhabiting the warm, subtropical waters of the South China Sea, Mediterranean Sea, and Black Sea (Razouls et al., 2005-2014) ( Adult females can reach a dry weight of 0.02 mg and a length of 800 μm.

Compared to the vast information available on the population and production dynamics of marine planktonic calanoid copepods, there are relatively few studies that focus on marine and estuarine planktonic non-calanoid copepods, particularly for Microsetella species (Sabatini & Ki0rboe, 1994; Uye & Sano, 1998; Uye et al., 2002). One study focusing on a non-calanoid copepod was conducted by Uye et al. (2002). Specifically, these authors researched the population and production dynamics of Microsetella norvegica in the Sea of Japan and found that reproductive activities of this species occur in the early fall and that brooding sacs contain a maximum of 16 eggs/sac. In the Magellan Strait, typical pelagic calanoid and cyclopoid copepods have been previously studied (Marín & Antezana, 1985; Mazzocchi et al., 1995; Hamamé & Antezana, 1999; Marín & Delgado, 2001), and there are some references to pelagic harpacticoids (Aguirre et al., 2012). However, work on pelagic harpacticoid copepods is limited in regards to the waters of South America (Palma & Kaiser, 1993; Boltovskoy, 1999).

In addition to the lack of studies on non-calanoid species, there is also little available research regarding neustonic communities along the Chilean coast (Palma & Kaiser, 1993). In the neuston, especially in coastal waters, members of the Microsetella genus are numerically dominant and highly abundant (Anraku, 1975; Dugas & Koslow, 1984; Uye et al., 2002; Zaitsev, 2005). The community structure and biodiversity of the neuston, including copepodits of species such as M. rosea, are particularly relevant when considering the number of roles that neuston plays in the marine environment.

The neuston forms a boundary between the air and water that, although only of few centimeters thick (Hardy, 1991; Upstill-Goddard et al, 2003), covers 71% of the planet's surface. Moreover, in temperate zones the neuston plays an important trophic role as a food source for meso and macrozooplankton, in addition to being a key component in the production of marine snow and in the vertical transport of organic material from the ocean surface to greater depths (Conte et al, 1998; Hays et al, 2005; Zaitsev, 2005; Koski et al., 2007). The neuston is also important to the early and larval life cycle stages of a number of commercially valuable and/or ecologically significant species in Chile, particularly in regards to larval dispersion (Scheltema, 1986; Gallardo et al., 2012; Cañete et al., 2012a).

Nevertheless, the impact of latitudinal differences on the functions of the neuston in the fragmentation and transport of organic matter to greater depths is not fully understood (Zaitsev, 2005; Koski et al., 2007). Further information is also needed to enhance the understanding on how the neuston is influenced by environmental and oceanographic factors, such as temperature, solar radiation, marine pollution, water salinity and density, UV radiation, acidification, and climate change, among others (Hardy, 1991; Rodríguez et al., 2000; Zaitsev, 2005). Therefore, the goals of the present study were to: i) record the abundance and spatial distribution of M. rosea neustonic copepodits along the western coast of the Magellan region; ii) connect these ecological observations with oceanographic parameters (temperature, salinity, and dissolved oxygen) in order to define the conditions under which the M. rosea population develops; and iii) compare M. rosea abundances against those of other collected neustonic taxa, thus determining their biological contributions as biotracers for processes associated with the aggregation of Magellan neustonic communities.


Sampling was conducted onboard the RV Abate Molina as part of the CIMAR 16 Fiordos cruise during the austral spring of 2010 (October 11 to November 19). Twenty six stations were used for sampling. These stations were located along the western mouth of the Magellan Strait (Sta. 7-15) to Navarino Island in the Beagle Channel (Sta. 37-43). At stations close to Dawson Island, samples were primarily collected from the Almirantazgo Sound, Whiteside Channel, and Inútil Bay (Sta. 51-60). Additionally, the sampling area included stations near channels and islands with proximity to the Pacific Ocean (Sta. 27-35) (Fig. 1). Sampling was originally planned to include stations along the eastern margin of the Magellan Strait; however, rough weather conditions did not allowed sample collection (Sta. 1-6, not shown).


Figure 1. Geographical position of neuston sampling stations in the Magellan Region,
CIMAR 16 Fjords cruise (October-November 2010).


At each station, sampling was done with a neuston net (80 cm wide and 30 cm deep) with a 50 μm mesh size zooplankton net (Kršinić, 1998). The net was dragged along the surface at a speed of 0.77-1.03 m s-1. At stations 7-9, the net was dragged for 8 min, but given the high amount of plankton collected, this was reduced to 5 min for all subsequent sampling stations. According to the layer classification established by Hardy (2005), the sampled layers corresponded to the centilayer and surface layer (1-100 cm depth). Only one haul per station was collected. Samples were fixed with 5% neutralized formalin.

Vertical profile of oceanographic conditions for each stations were obtained by a rosette equipped with a Sea-Bird CTD deployed to different depths according to the bottom depth of each site (Data Report CIMAR 16 Fiordos cruise). Since the neuston is in the surface layer, data for temperature, salinity, and dissolved oxygen content were recorded as average of readings between 1 to 2 m depths.

Due to the lack of a flow-meter, abundance and biomass data were standardized to the number of individuals or biomass wet-weight (g) per 5 min drag. To determine biomass wet-weight, which included phytoneuston and zooneuston, samples were filtered on a 30 μm sieve. Mainly micro- to mesoneuston (20 μm-20 mm) (Hardy, 2005) samples were collected. Folsom fractioning was used to further divide the collected biomass into 1/8th subsamples, thereby facilitating the counting of neuston holoplankton and M. rosea copepodits.

The copepod stages of M. rosea were identified following Uye et al. (2002). Abundance data only considered the copepodit stages of the M. rosea lifecycle, while nauplius and adult stages were excluded. Additionally, the methodology described by Davies & Slotwinski (2012) was used to discriminate individuals of M. rosea from M. norvegica. Other zooplankton components were identified based on Palma & Kaiser (1993) and Boltovskoy (1999). Samples were stored at the Austral Biological Oceanography Laboratory (LOBA), Department of Sciences & Natural Resources, Faculty of Sciences, Universidad de Magallanes, Punta Arenas, Chile.

The Kruskal-Wallis test was used to detect different trends in M. rosea abundance and differences in trends between the sampled stations, which were grouped into four geographic zones located along the Magellan and Fuegian channels (Antezana, 1999). The relationship between M. rosea copepodit abundance and the oceanographic parameters of temperature, salinity, and dissolved oxygen content were tested using Spearman's Rank-Order Correlation Coefficient (rs) (Zar, 1999; Daniel, 2000).

Magellan plankton can be used to establish distributional trends of bio-physical interactions in estuarine ecosystems. In relation to this study, assessing only the thin neuston layer reduced the number of spatial components (x,y) and prevented constraints associated with vertical water stratification. Additionally, the spatial area of sampling was sufficiently large to cover mesoscale patterns (10-1000 km; Mann & Lazier, 1991; Garçon et al., 2001). Finally, the sampled area, a heterogeneous coastal system, represents a natural laboratory for studying the population dynamics and topographic mechanism that could to produce the aggregation or clumping of the plankton (Downing, 1991).

To classify the type of spatial distribution presented by M. rosea copepodits within the study area, a dispersal index (Id) was applied. This index is based on the variance to mean ratio (s2/͞x) and describes a trend of spatial distribution. If Id = 1.0, there is random distribution (s2 = x); if Id < 1, there is uniform or regular distribution (s2 < ͞x); and if Id > 1, there is clumped distribution (s2 > ͞x) (Ludwig & Reynolds, 1988; Hulbert, 1990).



The spatial variability of ocean temperature, salinity, and dissolved oxygen content were measured for the surface layer of the analyzed stations. Water temperature fluctuated between 6.16oC (St 52) and 8.42oC (St 56), with an average water temperature of 7.2 ± 0.6oC within the study area. The highest temperatures were detected in the Whiteside Channel and Inútil Bay, while the lowest temperatures were detected along the western side of the Magellan Strait and in Almirantazgo Sound, near the glacial discharge from the Darwin Ice Field.

Salinity was the most variable among all measured parameters. Salinities ranged from 26.4 (Sta. 10) to 32.78 (Sta. 15), with an average salinity of 30.7 ± 0.91. Based on the classification criteria proposed by Valdenegro & Silva (2003) for southern Chile, all samples in the study area were taken from estuarine (132) or modified subantarctic waters (32-33). Values corresponding to 32-33 were recorded for stations in the Magellan and Fuegian channels.

Dissolved oxygen content ranged from 6.65 mL L-1 (Sta. 15) to 8.27 mL L-1 (Sta. 55), with an average of 7.4 ± 0.4 mL L-1. The surface layer was oxygenated throughout the study area, with a maximum value recorded in a glacial area of the Almirantazgo Sound. According to Cañete et al. (2012b), the surveyed area can be classified as an oximax or normoxic condition (maximum oxygen zone; values > 2 mL O2 L-1).

Neuston biomass and abundance

The collected neuston biomass fluctuated by up to two orders of magnitude, ranging from 0.7 g 5 min-1 of horizontal drag (Mhd) (Sta. 39) to 31.89 g 5 Mhd (Sta. 52), with an average of 8.55 ± 7.33 g 5 Mhd (Fig. 2). Neuston biomass was highest in wind protected areas, such as in Froward Cape, Almirantazgo Sound, and Inútil Bay (average = 12.3 g 5 Mhd-1) and along the western arm of the Magellan Strait, between Capitán Aracena Island and the western mouth of Magellan Strait (average = 11.1 g 5 Mhd-1). The lowest neuston biomass measurements were recorded along the Beagle Channel (average = 5.5 g Mhd-1; Table 1).


Figure 2. Neustonic biomass (g 5 Mhd-1) and neustonic abundance (ind 5 Mhd-1) in
the western Magellan coast. Both measurements are expressed in log scale and include
phytoneuston and zooneuston together. The average and standard deviation of neustonic
biomass and abundance were 8.55 ± 7.33 g 5 Mhd-1 and 9,179 ± 10,281 ind 5 Mhd-1,
respectively. The function log (x+1) was applied to the original abundance data to obtain
only values >0 in the axis. Mhd: minutes of horizontal dragging.


Table 1. Total neustonic biomass and abundance and Microsetella rosea abundance collected
from four macrozones along the western margin of the Magellan Region during the CIMAR 16
Fjord cruice (Oct-Nov 2010). Average values ± standard deviation. Mhd: minutes of horizontal
drag. Significant differences (*) were detected between macrozones using the Kruskal-Wallis
test (F3, 25 = 8.63; P < 0.05).


The spatial pattern of neuston abundance followed a trend similar to that of biomass, with maximum abundances in the Almirantazgo Sound and Inútil Bay (average = 18,350 ind 5 Mhd-1), and minimum abundances in the Beagle Channel (average = 3,358 ind 5 Mhd-1). The average abundances of stations located along the western arm of the Magellan Strait and between the western side of Dawson Island and the Pacific Ocean varied between 7,172 and 7,337 ind 5 Mhd-1 (Table 1). Average neuston abundance for the entire study area was 9,179 ± 10,281 ind 5 Mhd-1, which is indicative of clumped distribution with a variation coefficient of 112% (Fig. 3).


Figure 3. Spatial distribution of Microsetella rosea copepodits collected along the western
margin of the Magellan coast. Abundances are expressed as ind 5 Mhd-1 (minutes of horizontal
dragging). The average and standard deviation of M. rosea copepodit abundances were
2,761 ± 4,278 ind 5 Mhd-1.


Abundance and spatial distribution of Microsetella rosea

Copepodits of M. rosea were collected at all studied stations (Fig. 3). However, there were evident differences between zones that indicated wide spatial variability along the western margin of the Magellan Region. Specifically, maximal abundance of M. rosea was recorded in the Almirantazgo Sound, Inútil Bay, the Paso Ancho zone, and Froward Cape (mid-Magellan Strait, average = 6307 ± 5993 ind 5 Mhd-1), while the lowest abundances were recorded at stations along the Beagle Channel and in open areas near Navarino Island (average = 362 ind 5 Mhd-1; Table 1).

M. rosea copepodits accounted for 30% of all recorded neustonic taxa (238,673 ind; Table 2). Almirantazgo Sound, Inútil Bay, the Paso Ancho zone, and Froward Cape accounted for 61.5% of total M. rosea abundance, while sites near the Beagle Channel accounted for <4%. The western margin of the Magellan Strait accounted for nearly 25% of total M. rosea abundance, and the zone west of Dawson Island accounted for 10% (Fig. 3). The abundance of M. rosea copepodits showed a geographic trend in terms of abundance, with significant differences found mostly between the Paso Ancho microbasin and the Beagle and Fuegian Channels (Antezana, 1999) (Table 1).


Table 2. Comparative analysis of neustonic zooplankton
collected along the western margin of the Magellan Region
during the CIMAR 16 Fjord cruise (Oct-Nov
2010). A: Total
abundance (%; n = 238.673 individuals). Larval type refers
to the number of different families or orders for polychaetes
and crustaceans, respectively. The total percentage of
abundances is less than 100% as some larval types were
unidentified or scarce.


The distribution pattern of M. rosea copepodits varied up to four orders of magnitude. Therefore, the spatial distribution pattern of copepodits along the western margin of Magellan Region was classified as clumped (Ludwig & Reynold, 1988; Hulbert, 1990; Downing, 1991) (Figs. 4a-4b). A similar trend was observed for total neuston abundance and biomass (Table 1).


Figure 4. Temperatures and salinities recorded for the neustonic layer
along the western Magellan coast. These data were used to determine
the oceanographic requirements of Microsetella rosea copepodits.
Abundances are expressed as ind 5 Mhd-1 (minutes of horizontal dragging).
The average temperature and salinity of the neustonic layer in the study
area were 7.2 ± 0.6°C and 30.7 ± 0.9, respectively.


Oceanographic conditions and habitat of Microsetella rosea copepodits

M. rosea copepodits were found inhabiting the neuston at ocean temperatures ranging between 6.5°C (Sta. 40) and 8.4°C (Sta. 56), but maximum abundance (1,000 to 10,000 ind 5 Mhd-1) was only detected at stations 7, 55, and 60, which presented surface temperatures between 6.79°C and 7.69°C. In turn, Spearman's Rank-Order Correlation Coefficient between surface temperature and M. rosea copepodit abundance produced a significant, negative trend between both parameters (rs = -0.36; P < 0.05; n = 26) (Table 1; Figs. 2-3). The average and standard deviation of M. rosea copepodit abundances was 2,761 ± 4,278 ind 5 Mhd-1.

Additionally, M. rosea copepodits were found in salinity levels between 26.4 (Sta. 10) and 32.777 (Sta. 15) (average = 30.7 ± 0.9), with the highest M. rosea copepodit abundances found in waters with salinity levels between 30.37 (Sta. 55) and 30.53 (Sta. 7). The relationship between salinity and the copepodit abundance produced a significant, positive trend between both parameters (rs = 0.22; P < 0.05; n = 26).

Finally, the area inhabited by M. rosea copepodits was classified as an oxygenated estuary (mean = 7.4 ± 0.4 ml O2 L-1) (Table 1). There was a significant, negative trend in the relationship between dissolved oxygen content and M. rosea copepodit abundance in Magellan waters (rs = -0.19; P < 0.05; n = 26).

Overall, the limited ranges of oceanographic variables at the stations where M. rosea was found indicate that this pelagic harpacticoid copepod is adapted to specific estuarine environmental conditions. This situation was evidenced along of the western margin of the Magellan Region and within the limits of the Magellan Strait, where much of the water is near Dawson Island or enclosed between the Paso Ancho microbasin and the Forward Cape Channel (Fig. 3).

Contribution of Microsetella rosea to the neuston

During the CIMAR 16 Fjords cruise, 238,673 ind were counted from the meroplankton and holoplankton taxa (41.3% and 51.0%, respectively; Table 2). Of the holoplankton, calanoide and harpacticoide copepods, including M. rosea, were the most abundant. The abundance of M. rosea copepodits was nearly twice that of calanoide copepods (Table 2). Additionally, an important percentage of juvenile appendicularians was collected (4.3%).

Among the collected meroplankton, the numerically dominant groups included mytilid larvae (21.12%), unidentified polychaete larvae (tentatively identified as a Polygordiid exolarvae; P. Ramey-Balci, com. pers. from the Polygordiidae family) (16.5%), and cyphonaute larvae (2.4%). Cypris of barnacle (0.6%) and pluteus of echinoderms (0.42%) were also detected (Table 2). Decapod crustacean larvae were scarce (<0.26%). A total of seven holo- and nine meroplankton taxa of the neuston could be used as biotracers in the western Magellan Region (Table 2).

In summary, holoplankton numerically dominated meroplankton in the neuston communities along the western margin of the Magellan Region during spring oceanographic conditions.


Presence of Microsetella rosea in western Magellan waters

Microsetella rosea was found inhabiting the surface waters of all studied stations along the western margin of the Magellan Region, Chile. This species was the most numerically dominant species of the identified copepods, in addition to being the most dominant taxa of the neuston. These findings have not been previously reported, possibly due to the use of large net meshes (generally >200 μm) (Mazzocchi et al., 1995; Antezana, 1999; Defren-Janson et al., 1999; Marín & Delgado, 2001; Biancalana et al., 2007; Guglielmo et al., 2014). M. rosea copepodits may only inhabit surface layers of the water column, which would be mostly missed by vertical tows (Kršinić & Grbeco, 2012). Additionally, population density of M. rosea in the neuston was greater than that of the detected calanoid pelagic copepods. Similar abundance magnitudes were found for M. norvegica in the Japan Sea (Uye et al., 2002), where M. norvegica biomass can reach up to 100 mg C m-3 in the fall. In contrast, copepodit and adult Microsetella spp. in the Adriatic Sea were less abundant than calanoid and cyclopoid (oncaeids, oithonids) copepods (Kršinić & Grbeco, 2012). Altogether, these findings represent opportunities to study mesoscale spatial variabilities of important biological phenomena arising from interactions between the physical processes, physiology, and behavior of estuarine neuston organisms (Garçón et al. , 2001) along southern Chile. Additionally, the typical morphological features of the M. rosea cope-podits could ease the identification and justify their use as biotracer.

Microsetella rosea copepodits as biotracer of brackish estuaries

Neuston spatial distribution can be influenced by diverse environmental and oceanographic factors, such as temperature, solar radiation, marine pollution, ocean salinity and density, UV radiation, acidification, and climate change (Zaitsev, 2005). Therefore, understanding the physiological requirements of the neuston, particularly in regards to salinity, is key to explaining the spatial distribution of Magellan estuarine taxa.

The observed spatial distribution of M. rosea appears to be regulated by changes in salinity, with greater abundances at salinities between 29 and 31 and lower numbers at salinities >31. Similar tendencies have been found for other members of the Microsetella genus. For example, M. norvergica inhabits areas near bay mouths rather than sites close to river mouths or other freshwater inputs (Yamazi, 1956). Likewise, Uye & Liang (1998) found low M. norvegica densities at salinities <30, which is further supported by Uye et al. (2002), who indicated that M. norvegica is a stenohaline species intolerant to large salinity variations.

The wide surface salinity variations (0-32) recorded for the Magellan Region (Valdenegro & Silva, 2003; Palma et al., 2014b), together with the limited salinity range (≈29-32) detected by the present study, suggest that M. rosea copepodits could be stenohaline organisms. Nevertheless, new experimental studies on the physiological responses to oceanographic and thermal parameters are needed to confirm.

Microsetella rosea copepodits as biotracer of neustonic aggregation

Abundant patches of small copepods could be influenced by a frontal zone (Zervoudaki et al., 2007). In the western Magellan, frontal zones are detected through the accumulation of ice, strings of detached macroalgae, such as of the kelp Macrocystis pyrifera; color changes in surface waters; and the accumulation of foam in the surface layer (Valle-Levinson et al., 2006). The high abundance of M. rosea copepodits (1,000-10,000 ind 5 Mhd-1) found at some stations of the present study, especially near Dawson Island, could be due to the presence of frontal zones, especially when considering the wide differences in abundances between stations or, as previously described, the deep sill in the Whiteside Channel (Palma et al., 2014b).

Analyses of other meteorological, oceanographic, and topographic variables are needed to fully explain the abundance and spatial distribution patterns of the Magellan neuston (Owen, 1989), knowledge which is relevant to determining the aggregation, dispersal, and transport of small plankton in this pelagic environment. The high concentration of neustonic biomass, and of M. rosea in particular, near Dawson Island, may be due to the island wake effect and a coast predominantly protected from spring winds (Mann & Lazier, 1991), and future neuston sampling programs should be established for this area. Further related to the importance of Dawson Island, temperature, salinity, and dissolved oxygen content data from the present study showed uniform spatial distributions, but total neuston biomass and abundance, as well as Microsetella abundance, showed a clumped spatial distribution around this island. These contrasting distributions between environmental factors and neuston communities indicate that around Dawson Island may dominate processes of planktonic aggregation.

Apart from depth, another aspect that could explain the spatial pattern of Microsetella copepodits is the spatial distribution of chlorophyll-a. Indeed, four stages of chlorophyll production have been detected along the western margin of the Magellan Strait (Hamamé & Antezana, 1999) in relation to salinity, temperature, and water column stratification. These stages are as follows: i) the Paso Ancho microbasin and Magdalena Sound area, with a shallow chlorophyll maximum (≈5 mg m-3 at 0-20 m) in a vertically homogeneous cold and brackish water column; ii) the Magdalena, Cockburn, and Brecknock Channels area, with relatively low chlorophyll concentrations (2-3 mg m-3 at 0-50 m), minor salinity stratification and a surface lens of warmer water directly influenced by the Pacific Ocean; iii) the Ballenero Channel and western arm of the Magellan Strait, with high chlorophyll concentration in the subsurface layer (>4 mg m-3) and a vertically stratified water column with two salinity layers and three temperature layers; and iv) the Beagle Channel area, with maximum subsurface chlorophyll concentrations (>4 mg m-3) extending to the ocean floor and vertically homogeneous salinity and temperature distribution. In the present study, maximum M. rosea abundance was recorded in the Paso Ancho microbasin-Magdalena Sound area, including in the zone of Froward Cape (Fig. 3), where there is a shallow chlorophyll maximum, a vertically homogeneous cold and brackish water column.

Another aspect that should be considered is the ability of M. rosea and other members of the same genus to preserve the normal behaviors of harpacticoid copepods that inhabit the benthos. Recently, Pacheco et al. (2013) detected two Microsetella species in subtidal soft bottom zones of northern Chile. These species emerge from the sediment into the water column, a process defined as diel migration. Therefore, it is possible that spatial variations in the Magellan abundance of the copepod M. rosea could be affected by sampling time (day/night), wide of channels and bathymetry. Indeed, the M. rosea neuston population in Magellan waters could be supplied by shallower waters through horizontal transport due to the deepest of each microbasin (Valdenegro & Silva, 2003; Palma et al., 2014b).

Applications of the Magellan neustonic studies

In the present study, no direct relationship between salinity and M. rosea abundance was observed, a situation possibly associated with low local variability in temperature and salinity. Cañete et al. (2013) demonstrated a positive and significant lineal relationship between neuston biomass and salinity (5-33 range) and abundance in southern Chile. Furthermore Johan et al. (2012) detected that the spatial distribution of copepods follows the salinity gradient in the tropical estuary of the Perai River, Malaysia. The neuston could be an important monitoring tool to track the flow of estuarine, brackish waters into the inner channels of southern Chile (Palma et al., 2014a).

The actual spatial pattern of the estuarine neuston communities from Magellan waters could be modified if global warming directly affects the rate of melting ice and rainy conditions along the southern Chilean coast, and specifically affect to stenohaline species such as M. rosea. Therefore, a permanent monitoring of subantarctic neustonic communities is highly recommended.


The authors would like to thank the Servicio Hidrográfico y Oceanográfico (SHOA), Chilean Navy, the financial support grant by CONA C16F 10-014, the assistance given by the crew of RV Abate Molina, and the Instituto de Fomento Pesquero, Chile (IFOP) for providing the facilities necessary for collecting neuston samples. We would also like to thank GAIA Antártica (MAG1203), Contract MINEDUC-UMAG, for assisting in the translation of the original manuscript. Special thanks are also given to the UMAG Research Grant N° PR-F2-01CRN-12, CIMAR 18 and CIMAR 20 Programs for providing partial funds supporting the publication of this study. We also thank Ms. Sc. Jaime Ojeda for collecting the neuston samples.



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Received: 18 August 2015;
Accepted: 5 May 2016


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