A new record of the non indigenous freshwater jellyfish Craspedacusta sowerbii Lankester , 1880 ( Cnidaria ) in Northern Patagonia ( 40 ° S , Chile )

A new record of the freshwater jellyfish Craspedacusta sowerbii in northern Chilean Patagonia is reported. The specimens were collected from Laguna Illahuapi, an oligotrophic shallow lake (15 m maximum depth) in early austral autumn, May 2013. This water body is located in the upper zone of the Rio Bueno basin, Province of Ranco, Region de los Ríos, Chile. The region is characterized by a great diversity of freshwater environments with minimal human pressure. This report confirms the presence of C. sowerbii in Chilean Patagonia and represents the southernmost range of distribution of this exotic medusa in South America. This study also contributes additional information on the limnological characterization of this water body.


Introduction
Craspedacusta sowerbii (Lankester, 1880) is a freshwater cnidarian native to the Yangtze valley in China (Kramp 1961).The life cycle of this organism is well known (De Vries 1992;Sasaki 1999;Lewis et al. 2012) including both benthic polyp and free-swimming medusa stages.Like many other freshwater organisms, C. sowerbii develops a resting stage under unfavorable environmental conditions, an adaptation conferring not only high potential of survival but also enhancing the capacity for dispersal.At present C. sowerbii is recognized as the most abundant and cosmopolitan freshwater cnidarian with a medusa stage (Dumont 1994;Jankowski et al. 2008;Fritz et al. 2009).During the last century C. sowerbii has invaded and successfully colonized practically all continents with the exception of Antarctica (Dumont 1994;Jankowski et al. 2008).Craspedacusta sowerbii exhibits an expansive ecological niche, being reported from streams, ponds, lakes, swamps and reservoirs (Boothroyd et al. 2002;Fritz et al. 2007;Lewis et al. 2012).Nevertheless, the medusa stage of this species seems to prefer temperate, stillwater, freshwater bodies of mesotrophic character (Jankowski 2001;Moreno Leon and Ortega-Rubio 2009;Jankowski et al. 2008) and water temperatures ranging from 12 to 33°C (Lewis et al. 2012).In these lentic aquatic ecosystems C. sowerbii medusa stage is basically planktivorous, and is capable of developing blooms, particularly during the warm seasons (Jakowski et al. 2005;Stefani et al. 2010;Gophen and Shealtiel 2012).Optimum growth temperature for sexually mature C. sowerbii medusae ranges from 19 to 25°C (McClary 1959;Pérez-Bote et al. 2006).The impact of this jellyfish on inland freshwater ecosystems is unclear and remains insufficiently studied (Oscoz et al. 2010).
There is a general consensus about human mediated introduction via the transplantation of fish and aquatic plants (Dumont 1994;Marsden and Hauser 2009).The northernmost limit of C. sowerbii in North America is reported from Canada at 46°N (McAlpine et. al. 2002), a biogeo-graphically different zone compared to the U.S. distribution (De Vries 1992).For Meso-America, only the recent study by Moreno-Leon and Ortega-Rubio (2009) confirmed the establishment in Mexico.In contrast, the first reports of C. sowerbii in South American inland waters (Panama, Brazil, Uruguay, Argentina and Chile) date back to 1925 (Ringuelet 1950).The first reports of C. sowerbii from Chile date to 1942, when Porter and Schmitt (1942) collected and described free living medusae in "Tranque (dam) Marga-Marga", located in the commune of Quilpué, province of Valparaíso, central Chile (32°S).In this same province, which hosts Chile's principal international seaport for containers and passenger ships, large stable populations of C. sowerbii were later documented from Peñuelas reservoir (Schmid-Araya and Zúñiga 1992).The latter study reported that the highest abundance of free living medusa in the eutrophic waters of this water body occurred during February, the warmest month of the austral summer.More recently, Figueroa and De Los Ríos (2010) reported the presence of C. sowerbii in the Araucania Region, from Laguna Carilafquen (38 °S).In Argentina, C. sowerbii has only three published reports.The earliest record from General San Martin reservoir, Mendoza (31°S) was in 1950 (Ringuelet 1950).Later reports include a pond close to the La Florida dam, province of San Luis (33°S) in 1979 (Richard 1990) and from the Rio Tercero reservoir, province of Cordoba (32°S) in 1980 (Boltovskoy and Battistoni 1981).Currently there are no governmental monitoring programs aimed at studying the emergence of aquatic non-indigenous species in Chile.The generally scarce information on aquatic biological invasions in the country is mainly due to restrictions in the Chilean environmental legislation, which only allows funding of this kind of research when the exotic taxon is declared a pest.Such was the case of Didymosphenia geminata, detected forming blooms in different watersheds from Patagonia (Reid et al. 2012).
The presence of C. sowerbii in Laguna Illahuapi, Region de los Ríos (40 °S), constitutes a new record of this exotic freshwater jellyfish in Patagonia and represents the southernmost known distribution of the organism for the American continent (Figure 1 and Appendix 1).

Methods
On 5 May 2013 (early austral autumn) we conducted a limnological characterization of Laguna Illahuapi (40°16'16''S, 72°18'00'', Figure 1 and 2), Province of Ranco, Region de los Ríos, Chile.This aquatic environment is located in a rural area very close to the large and deep (< 200 m) oligotrophic Lago Ranco (Campos et al. 1992).Laguna Illahuapi is located at 169 m a.s.l. and has a surface area of 14.1 ha, a maximum width of 365 m and a maximum length of 708 m.Tributaries are absent and water level fluctuates depending on precipitation.This lagoon is surrounded by a dense and diverse belt of submerged and emergent macrophytes, grading into forest cover dominated by Nothofagus dombeyi.The dominant submerged plants present in the littoral zone were Myriophyllum sp. and Potamogeton sp.
The sampling of this water body is part of a comparative study between large deep (>100 m) lakes and small shallower water bodies in North Patagonia (40-41°S) carried out by the Limnology and Aquatic Ecology laboratory from the Austral University, Valdivia, Chile.The sampling of Laguna Illahuapi was performed using a zodiac boat.An approximated bathymetric profile was constructed along the main longitudinal axis using echosounding (Garmin fishfinder 140) from the moving zodiac boat.A sampling station was established on the point of maximum depth (15.5 m), where limnological variables [dissolved oxygen (DO), temperature, conductivity, chlorophyll-a and pH] were measured every meter, from surface to a maximum depth of 14 m, using a YSI probe (model 6920 V2, USA).Water transparency was assessed using a Secchi disk (20 cm diameter).Based on the temperature profiles recorded in situ it was possible to assess where the thermocline was located.A single integrated epilimnetic water sample (Z mix = 6 m) was later constructed by collecting 2 L of water at regular intervals of 2 m using a 5 L UWITEC bottle and a plastic container of 10 L. Sub-volumes of the integrated epilimnetic water sample were dark stored in plastic containers at 4°C for chemical and phytoplankton analyses.Chemical analyses [Total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN), nitrate (NO 3 ), nitrite (NO 2 ) and the major ions (Na + , K + , Ca ++ , Mg ++ , SO 4 = , CaCO 3 , Cl -and SiO 2 )] were carried out according to standard methods (APHA 2005).Qualitative and quantitative zooplankton samples were collected by vertical hauls, from surface to 14 m depth, using a plankton net of 80 μm with flow meter (General Oceanics, USA).Samples were concentrated and narcotized with carbonated water prior to being fixed with buffered formalin solution at 4%. Phytoplankton was preserved in  plastic bottles with Lugol's iodine solution.Counting of cells was performed according to Utermöhl (1958).Zooplankton samples were analyzed under a compound microscope following the taxonomical guide for Chilean inland waters (Araya and Zúñiga 1985) and the taxonomic and systematic diagnoses for cnidarians described by Jankowsky (2001).

Limnological characterization of Laguna Illahuapi
Based on the study of physical, chemical and biological attributes (Figure 3 and Table 1), Laguna Illahuapi is characterized as a temperate warm monomictic shallow lake (15 m depth) with oligotrophic status.At the time of sampling it was thermally stratified with a surface water temperature of 15.4°C.The epilimnetic waters (0-7 m deep) of Laguna Illahuapi were well oxygenated, but exhibited hypoxic condition in the hypolimnetic strata (Figure 3).Typical of most freshwater ecosystems in Central South Chile, Laguna Illahuapi has low ionic strength, with a conductivity of 45 μScm -1 and circumneutral pH of 7.36.In contrast with the Araucanian lakes (sensu Thommason 1963), Laguna Illahuapi has low transparency (Secchi Depth 4.5 m, Table 1), probably due to humic substances that commonly confers yellowish-brown water color.The maximum chlorophyll-a concentration (Chl-a) was 2.33 μg L -1 using in situ fluorimetry.

Discussion
Laguna Illahuapi is characterized as oligotrophic (Carlson 1977), which is consistent with the phytoplankton functional group X2.The phytoplankton and zooplankton composition is similar to plankton communities from other temperate lentic inland water bodies where C. sowerbii has established large summertime populations (Stefani et al. 2010;Pérez-Bote et al. 2006).Medium and large sized cladocerans such as B. longirostris, C. dubia and D. pulex, and the rotifer P. dolichoptera, which dominated the zooplankton community in our study, have been described as a suitable prey for the medusa stage of C. sowerbii (Davis 1955;Dodson and Cooper 1983;Spadinger and Maier 1999).Together with the warm stratified surface water (commonly reaching 24°C in midsummer at 40°S), conditions might be considered optimal for jellyfish blooms in this and other North Patagonian shallow lakes.In order to test this hypothesis, more intensive summer surveys must be conducted.Furthermore, we suspect that the distribution of C. sowerbii could be extensive in Chilean Patagonia, given the presence of many other small shallow lakes with similar characteristics (MMA 2012), and potentially considered an empty niche throughout Southern Chile.In agreement with Dumont (1994), we believe that N-S inter-valley dispersion of drought-resistant resting stages of C. sowerbii in Southern Chile (Patagonia) could be mediated mostly by aerial dispersal of migrating birds along the Andes Mountain corridor.In the current scenario of global climate change, and in a strong agreement with Rosenzweig et al. (2007), we also believe that the expansion of this freshwater jellyfish towards higher latitudes (poleward) in Chilean and Argentinean territory (Patagonia) would also be favored.
Even though our sampling does not consider the polyp stage of C. sowerbii in sediments of littoral-sub littoral strata, the finding of the medusae stage with developed gonads (sexually mature specimens) in the pelagic habitat of Laguna Illahuapi is in itself evidence that this exotic cnidarian has successfully bypassed physical and climatic barriers and has established in Chilean aquatic environments at this latitude.According to Oscoz et al. (2010), the impact of this jellyfish on freshwater ecosystems is unclear.However, alien species invading freshwater systems can commonly lead to loss and degradation at all levels of biological organization (Vilà and Garcia-Berthou 2010), with cascading effects on entire ecosystems.In conclusion, this report constitutes new evidence of an expansion of this non-indigenous cnidarian towards southern latitudes in Chilean Patagonia.More limnological studies, including the analysis of both medusa and polyp stages (Duggan and Eastwood 2012), are required in order to assess the current and potential distributional range of C. sowerbii in North Patagonian lakes, as well as possible effects on the functioning of freshwater ecosystems.

Figure 1 .
Figure 1.A) Distribution records of Craspedacusta sowerbii Lankester, 1880 in South America, shown on Google map.Numbers correspond to sites in Appendix 1. B) Lago Ranco with the specific location of Laguna Illahuapi (n° 4) and C) Detailed image of Laguna Illahuapi.

Table 1 .
Chemical characteristics of the epilimetic water (Zmix= 6m) of Laguna Illahuapi measured in the early autumn, May 2013.

Table 2 .
List of phytoplankton species detected in Laguna Illahuapi.In parenthesis the relative percentage (biovolume) values are reported for those species contributing in more than 1 % to the total phytoplankton biomass.