Effects of Low Ph and Low Salinity Induced by Meltwater Inflow on The
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Journal of Marine Science and Engineering Article Effects of Low pH and Low Salinity Induced by Meltwater Inflow on the Behavior and Physical Condition of the Antarctic Limpet, Nacella concinna Eunchong Sin 1, In-Young Ahn 1, Seojeong Park 2,3 and Taewon Kim 2,3,* 1 Division of Polar Ocean Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 21990, Korea; [email protected] (E.S.); [email protected] (I.-Y.A.) 2 Department of Ocean Sciences, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Korea; [email protected] 3 Program in Biomedical Science and Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Korea * Correspondence: [email protected]; Tel.: +82-32-860-7714 Received: 30 July 2020; Accepted: 16 October 2020; Published: 20 October 2020 Abstract: Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, to two different pH (8.00 and 7.55) and salinity (34.0 and 27.0 psu) levels and measured their righting ability after being flipped over, mortality, condition factor, and shell dissolution. During the 35-day exposure, there was no significant difference in behavior and mortality between different treatments. However, the condition factor was negatively affected by low salinity. Both low pH and low salinity negatively influenced shell formation by decreasing the aragonite saturation state (Warg) and enhancing shell dissolution. Our results suggest that, though limpets can tolerate short-term low pH and salinity conditions, intrusions of meltwater accompanied by the glacial retreat may act as a serious threat to the population of N. concinna. Keywords: ocean acidification; glacial retreat; meltwater; Nacella concinna; Marian Cove; shell dissolution 1. Introduction Increasing atmospheric CO2 has induced ocean acidification with 0.1 unit reduction of pH over the last 200 years [1]. According to the climate change scenario RCP8.5 of 5th IPCC assessment, the global average surface pH is estimated to decline 0.3–0.32 by 2100 [2]. Moreover, the aragonite saturation state of the Southern Ocean is expected to become undersaturated by the year 2030, and no later than 2038, due to low seawater temperature of Southern Ocean [1,3,4]. In addition, aragonite undersaturation events are predicted to spread rapidly, affecting more than 70% of the Southern Ocean surface water this century [5]. Accordingly, marine calcifying organisms will have difficulty in maintaining calcium carbonate skeleton or shells. In addition to the increased atmospheric CO2, glacial meltwater input due to shrinking ice sheets likely aggravates the acidification [6]. The fresh meltwater has a lower Total Alkalinity (TA) and concentration of Dissolved Inorganic Carbon (DIC) compared to seawater that contribute to carbonate undersaturation [7]. Therefore, the meltwater inflow could additionally reduce the pH in seawater. It was reported that freshwater dilution has facilitated low calcium carbonate saturation states in both the Amundsen Sea and Ross Sea [8]. The Western Antarctic Peninsula (WAP) is one of the regions on the earth where warming and glacial melting are proceeding quickly [9,10]. Recent studies revealed that the substantial reduction of marine-terminating glaciers in the WAP in recent years is the result of coastal-trapped waves and ocean J. Mar. Sci. Eng. 2020, 8, 822; doi:10.3390/jmse8100822 www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2020, 8, x FOR PEER REVIEW 2 of 14 J. Mar. Sci. Eng. 2020, 8, 822 2 of 14 The Western Antarctic Peninsula (WAP) is one of the regions on the earth where warming and currents,glacial which melting induce are proceeding the warm quickly seawater [9,10]. inflow Recent [11, 12studies]. There revealed are few that studies the substantial that determine reduction the effect of marine-terminating glaciers in the WAP in recent years is the result of coastal-trapped waves and of meltwater inflow on Southern Ocean acidification on marine organisms. However, carbonate ion ocean currents, which induce the warm seawater inflow [11,12]. There are few studies that determine undersaturationthe effect of meltwater was found inflow to be on a directSouthern consequence Ocean acidification of the recent on marine extensive organisms. melting However, of sea ice in the Canadacarbonate Basin; ion undersaturation this phenomenon was found could to be aff aect direct both consequence the planktonic of the andrecent benthic extensive ecosystems melting [6]. In theof WAP,sea ice because in the Canada of the complex Basin; this coastline phenomenon and fast could glacial affect retreat, both the studyplanktonic of the and response benthic of the ecosystemecosystems to ocean [6]. In acidificationthe WAP, because and fresheningof the complex should coastline be addressed and fast glacial as an retreat, important the study issue. of the responseMarian of Cove, the ecosystem a small glacialto ocean fjord acidification (~4.5 km and long freshening and ~1.5 should km be wide) addressed is located as an inimportant King George Island,issue. the biggest island of the South Shetland Islands, which belongs to the WAP (Figure1). In Marian Cove, theMarian glacier Cove, has rapidlya small glacial retreated fjord around (~4.5 km 1.9 long km fromand ~1.5 1956 km to wide) 2017 [is13 located]. The glacierin King retreatGeorge occurs duringIsland, most the of biggest the summer island of months the South and Shetland is being Islands, accompanied which belongs by massive to the intrusionWAP (Figure of turbid1). In melt Marian Cove, the glacier has rapidly retreated around 1.9 km from 1956 to 2017 [13]. The glacier water [14]. Freshwater streams and ponds are also developed from the surrounding snow field in retreat occurs during most of the summer months and is being accompanied by massive intrusion of summer,turbid and melt a water substantial [14]. Freshwater amount streams of fresh and water ponds is introducedare also developed into the from cove. the surrounding The meltwater snow stream andfield pond in watersummer, of and Baton a substantial Peninsula amount and Weaver of fresh Peninsula, water is introduced between into which the cove. Marian The Covemeltwater is located, has relativelystream and lower pond pHwater ranges of Baton (meltwater: Peninsula <and4.38, We pondaver Peninsula, water: <5.00), between because which King Marian George CoveIsland is is a volcaniclocated, island has relatively [15]. As lower a result, pH ranges the surface (meltwater: water <4.38, in Marian pond water: Cove <5.00), has a because distinct King salinity George gradient alongIsland the distanceis a volcanic from island the glacier[15]. As duringa result,the the australsurface summerwater in Marian months Cove [16 ].has In a addition, distinct salinity the pH and salinitygradient of the along seawater the distance of Marian from the Cove glacier fluctuates during the depending austral summer on the months unexpected [16]. In weatheraddition, andthe tidal conditionspH and insalinity the austral of the seawater summer of (Supplementary Marian Cove fluctuates Materials depending Figure on S1). the This unexpected suggests weather that local and ocean acidificationtidal conditions has been in the driven austral rapidly summer by (Supplementary the meltwater Materials inflow from Figure both S1). the This tidewater suggests glacierthat local and the ocean acidification has been driven rapidly by the meltwater inflow from both the tidewater glacier snow fields, although their relative contribution was not quantified. and the snow fields, although their relative contribution was not quantified. (a) (c) e ov ANTARCTICA C ian ar M Sampling Barton Peninsula 59˚W 58˚W (b) site King Sejong 62˚S 62˚S Station King George Island 0 1km 62˚15’S 0 10km 58˚W 62˚15’S FigureFigure 1. Study 1. Study area: area: (a ()a) the the location location of King King George George Island Island (red (red square), square), (b) the (b) location the location of Marian of Marian CoveCove (red (red square), square), and and (c ()c the) the sampling sampling site (circle). (circle). TheThe retreat retreat of of marine-terminating marine-terminating glaciers, particularly particularly thos thosee grounded grounded on the on sea the floor sea floor (tidewater glaciers), has a profound influence on the nearshore coastal environment and inhabitants (tidewater glaciers), has a profound influence on the nearshore coastal environment and inhabitants [17]. [17]. Antarctic benthic communities can be significantly impacted by a series of physical processes Antarcticfollowing benthic glacier communities retreat, occurring can be significantlymostly during impacted the summer by a seasons series of (e.g., physical ice scouring, processes water following glaciercolumn retreat, stratification, occurring and mostly nearshore during turbidity) the [14,18–20]. summer seasonsNot only (e.g.,physical ice impacts, scouring, but also water large column stratification,variations in and the nearshore water chemistry, turbidity) can occur [14,18 because–20]. Not of meltwater only physical inflow impacts, (e.g., pH, but salinity, also large aragonite variations in thesaturation, water chemistry, metal level, can melting occur becausecirculation, of meltwaterDIC, and TA inflow changes) (e.g., [21–23]. pH, salinity, The Antarctic aragonite marine saturation, metal level, melting circulation, DIC, and TA changes) [21–23]. The Antarctic marine organisms inhabiting this area, particularly benthic fauna, are most likely vulnerable to climate changes, as they have low physiological flexibility, low growth rate, deferred maturity, and a constraining adaptation to short-term environmental changes [24–26]. Even pH and salinity are related, and these stressors J. Mar. Sci. Eng. 2020, 8, 822 3 of 14 possibly occur at the same time due to the inflow of meltwater from glaciers and snow, in the polar research field, there are few studies that investigated the negative effect of the combined stressors of low pH and low salinity on Antarctic marine animals [7,27].