Progress in Oceanography 174 (2019) 37–43 Contents lists available at ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean The Antarctic fish Harpagifer antarcticus under current temperatures and salinities and future scenarios of climate change T ⁎ Jorge M. Navarroa,b, , Kurt Paschkeb,c, Alejandro Ortiza,b, Luis Vargas-Chacoffa,b, Luis Miguel Pardoa,b, Nelson Valdiviaa,b a Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Valdivia, Chile b Centro Fondap de Investigación de Altas Latitudes (Fondap IDEAL), Universidad Austral de Chile, Valdivia, Chile c Instituto de Acuicultura, Universidad Austral de Chile, Puerto Montt, Chile ARTICLE INFO ABSTRACT Keywords: Antarctic coasts are highly vulnerable environments where temperature have remained very constant along Warming millions of years. These unique environmental conditions have generated a large number of stenoic species that Salinity decrease could be highly sensitive to future scenarios of climate change. We investigated the separate and interactive Harpagifer effects of increasing seawater temperature and decreasing salinity on the physiological performance of the Physiology notothenioid fish, Harpagifer antarcticus. Adult individuals were exposed to an orthogonal combination of five Antarctic temperatures (2, 5, 8, 11, 14 °C) and three salinities (23, 28, 33 psu) for a 10-day period. A drastic increment in Magellan Region fi Climate change mortality was observed with seawater warming; the pattern in response to lower salinity was less clear. No sh died at the two lowest temperatures (2 and 5 °C); however, mortality increased significantly at the two highest temperatures across the salinity treatments (33.3% at 11 °C; 93.3% at 14 °C). No data were obtained at 14 °C that could be included in the physiological analyses. Ingestion and absorption rates were significantly affected by temperature and salinity, but not by the interaction of the two. Finally, we observed a negative effect of tem- perature but not of salinity or the interaction of both on the scope for growth of H. antarcticus. These results suggest that this species could cope with a moderate temperature increase (5 °C) in the Antarctic. However, the higher metabolic rates observed at 8 and 11 °C are associated with conditions beyond the natural thermal window of this species, representing a disadvantage in the face of climate change. Therefore, and even in the hypothetical case that H. antarcticus were able to disperse to sub-Antarctic areas such as the Magellan Region, current and projected scenarios of seawater temperatures might be unsuitable for the development of effective populations of this species. The results confirm the stenothermal nature of H. antarcticus, considering its high vulnerability to environmental changes and its limited ability to cope with the more severe global warming models projected for the Antarctic and Magellan regions for the end of the century (mainly temperature). 1. Introduction makes them potentially vulnerable to warming scenarios. The Antarctic Peninsula has been described as one of the environ- Antarctic coasts are highly vulnerable environments and sensitive to ments most affected by climate change in the world, which can disrupt climate changes and the environmental conditions (e.g., seawater local interactions and, thus, ecosystem functioning and stability (Duffy temperature, dissolved oxygen) there have remained very constant et al., 2017). Changes in temperature and salinity in the Southern along millions of years. Ectotherms living in these unique environ- Ocean have been described as a prominent signal of climate change. On mental conditions have generated a large number of stenoic species that average, surface seawater of the Western Antarctic Peninsula has could be highly sensitive to environmental changes such as those ex- warmed nearly 1 °C in the last half century, and salinity has experienced pected by the end of the century (Ficke et al., 2007; IPCC, 2014). It strong changes, especially in coastal surface waters, due to melting should be noted that coastal Antarctic communities are characterized Antarctic sea ice (Szafranski and Lipski, 1982; Meredith and King, by high endemism (Hogg et al., 2011; Griffiths and Waller, 2016) and 2005; Turner et al., 2005; Haumann et al., 2016). Currently, tempera- that the limited ability to move to colder latitudes as the ocean warms, tures up to 3 °C have already been reported for shallow benthic ⁎ Corresponding author at: Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Valdivia, Chile. E-mail address: [email protected] (J.M. Navarro). https://doi.org/10.1016/j.pocean.2018.09.001 Available online 06 September 2018 0079-6611/ © 2018 Elsevier Ltd. All rights reserved. J.M. Navarro et al. Progress in Oceanography 174 (2019) 37–43 environments in the Antarctic Peninsula (Cárdenas et al., 2018). De- Sub-Antarctic communities. spite these rapid abiotic changes, the responses of Antarctic organisms and consumer-resource interactions to ocean warming and reduced 2. Materials and methods salinity remain unclear. The ability of an organism to face changes in temperature and 2.1. Collection site and experimental design salinity is related to its level of tolerance. Stenoic organisms have low tolerance and can only survive in a narrow thermal range. Therein, Adult Harpagifer antarcticus (n = 75) were caught by turning over their aerobic performance is maximal and covers all physiological costs. rocks in the lower intertidal zone off the South Shetland Islands, Fildes When the organism is exposed to either extreme of the temperature Bay, King George Island (62° 11′ S, 58° 59′ W). Fish were maintained for range, its capacity for aerobic performance is reduced (Pejus tempera- one week at 2 °C, 33 psu, under a natural photoperiod (period to re- tures; Pörtner, 2002). Beyond those critical temperatures, the mi- cover from the stress of collection, in situ environmental conditions tochondrial demand for oxygen cannot be met. were preserved), and fed ad libitum with their natural diet. For this, Stenohaline organisms also have a rather narrow range of tolerance amphipods, Gondogeneia antarctica (length = 6.8 ± 0.67 mm, dry for salinity, and survival decreases above and below the optimal range weight = 0.91 ± 0.06 mg), were collected every two days. (Kinne, 1964). In terms of the relationship between temperature and After the recovery period, the fish were placed in individual aquaria salinity, a reduction in salinity can heighten the sensitivity of an or- (one fish per aquarium; 5-L volume) and exposed to different combi- ganism, reducing its thermal tolerance range as well as its capacity to nations of temperature (2, 5, 8, 11, 14 °C) and salinity (23, 28, 33 psu) respond to certain levels of environmental change (Kinne, 1970). for 10 days (n = 5 aquaria per combination). The control group corre- Temperature is one of the most important environmental variables sponded to the specimens exposed to 2 °C and 33 psu and the other for ectotherms as it controls all biochemical reactions within the body combinations of temperature/salinity to experimental conditions that tissues (Hochachka and Somero, 2002). Because many marine organ- simulated current environmental conditions of the Magellan region and isms live close to their thermal compensatory capacity (Somero, 2002), possible future scenarios of climate change for Antarctica and they are highly affected (i.e., behavioral and physiological responses) Magallanes. Seawater was changed every other day (regardless of by environmental temperatures that fluctuate beyond their species- temperature) and maintained within a range of variation of ± 0.5 °C. specific optimum, with effects extending to survival and ecological in- teractions (Pörtner, 2006; Godbold and Solan, 2013; Sandblom et al., 2.2. Fish mortality, ingestion, and absorption rates 2014). Thus, physiological plasticity has been described as one of the main factors influencing survival in ectothermic organisms, and the All aquaria were monitored daily, and dead fish were removed each capacity to acclimate has been recognized as a key process for coping day. The number of dead individuals was pooled for a period of 10 days (or not) with climate change drivers (Calosi et al., 2008; Peck et al., and expressed as accumulated mortality for each treatment combina- 2010). tion. The coastal ichthyofauna of Antarctica is highly endemic and Ingestion rates of H. antarcticus were determined every two days. dominated by fish belonging to the suborder Notothenioids Twenty new amphipods were supplied to each aquarium every day and (Andriashev, 1987). The physiological characteristics of this group of consumed preys were determined by collecting all uneaten amphipods. fish are related to its isolation as well as the physical characteristics of To evaluate the daily ingested ration, regressions between total length the environment (Clarke, 1983): stable low temperatures, high salinity, (anterior margin of head to telson) of 80 individuals of each prey and seasonal changes in the ice sheet. The model species for the present (L = cm) versus dry tissue weight (W = mg) were carried out using the study was the Antarctic notothenioid fish, Harpagifer antarcticus. This allometric equation W = aLb. Ingestion rates (mg·h-1) were converted to stenothermic species (Brodeur et al., 2003) inhabits shallow waters energy units using the conversion factors 1 g dry tissue weight of the (0–20 m) from the Antarctic