AN INTRODUCTION TO OCEAN ACIDIFICATION AND TEMPERATURE CHANGES ON PHYSIOLOGICAL TRADE-OFF OF INTERTIDAL MARINE GASTROPODS Sedercor Melatunan and Shelly M. Pattipeiluhu

Sedercor Melatunan and Shelly M. Pattipeiluhu. Department of Aquatic Resource Management, Faculty of Fisheries and Marine Science, University of Pattimura Ambon, Campus Poka 97123 ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Due to an equilibration of partial pressure of CO 2 (pCO 2 ) in the atmosphere, 30% of its concentration has been absorbed by ocean and making it more acidic and generate potential global warming. Future changes of ocean pH and temperature are predicted to impact biodiversity of marine ecosystems, particularly those animals that rely on calcification process. Reduced pH will induce dissolution rates of calcium mineral particularly aragonites and calcites and that alter decalcification rates. The reduction of pH also disrupts acid base balance and metabolic rates that lead to metabolic depression whilst increase temperature affects organisms' thermo-tolerance capacity. Even though decreased metabolic rates were associated with metabolic depression, a strategy to match oxygen demand and availability, however prolong exposure to these stressors have affected growth, survival and reproduction rates. In addition, increase CO 2 and temperature have also magnitude end-product metabolites such as succinic and lactic acids and reduced energy nucleotides (adenosine 5triphosphate, adenosine diphosphate and adenosine monophosphate) in the cells, indicating an increased reliance on anaerobic metabolism. Furthermore, anthropogenic alteration of CO 2 and temperature may also lead to plastic responses, a fundamental mechanism of many marine gastropods to cope environmental variability. Shells of marine gastropod were also more globular in order to defend desiccation rates, a primary threat to most intertidal organisms to elevated temperature particularly those that lack of mobilization aggregates (sessile). Although level of impacts may also vary from species to species as well as populations, however, physiologically, the result always came at cost.

…………………………………………………………………………………………………….... Introduction:-
Ocean acidification (OA) is the result of an ongoing process caused by an excessive increase of carbon dioxide (CO 2 ) into the world's oceans Wickett 2003, Kleypas et al. 2006). This chemical change to seawater is driven by increased levels of atmospheric CO 2 . For the past 650,000 years and prior to the Industrial Revolution, the concentration of atmospheric CO 2   In general, the increase of CO 2 concentration in the atmosphere is caused by an imbalance of CO 2 exchange (input and output), for example, through the burning of fossil fuels, land-use changes and the industrial production of cement (Orr et al. 2005). Although CO 2 is also absorbed by terrestrial plants (Metaphytes), more than 40% of atmospheric CO 2 enters the oceans (Falkowski et al. 2000). There are several pathways in the carbon cycle which are particularly important for this process. Figure for the global carbon cycle (Fig.2) shows that there is a net flux of CO 2 into the oceans of 1.7 x 10 15 g C y -1 .   As well as altering the pH of the oceans, increased CO 2 has been suggested to be responsible for a 55% increase in radiative forcing (change in net solar radiance between different layers of the atmosphere in unit Wm -2 ) (Jenkinson et al. 1991) and subsequent increases in air temperatures (McMullen 2009). Increased radiative forcing ultimately alters the incoming and outgoing energy balance between the Earth and its atmospheric system. When radiative forcing is positive, the Earth's surface tends to warm (IPCC 2007). In 2005 the mean value of radiative forcing was +1.6 indicating a rate of warming of +1.   Jenkinson et al. (1991) also proposed that increased air temperatures would increase emissions of CO 2 gas from soils, through an increase in the turnover of organic matter (Jenkinson et al. 1991). Warming caused by increased atmospheric CO 2 levels will also increase ocean temperatures (Kleypas et al. 2006, Allison et al. 2008). At present, seawater temperature has warmed by approximately 0.7 ºC compared with the pre-industrial era (Kleypas et al. 2006) and is predicted to rise by a further 2 ºC by 2050 (Huesemann 2006, Guldberg et al. 2007).
Jacobson (2005) developed a model with uncertainty input parameters that predicted an increase of CO 2 to 375 ppmv there would be an increase in temperature of 3 ºC. However this model has been corrected by Sokolov et al. (2009) with certainty input parameters (e.g. world volcanic eruptions and gross domestic product (DGP) growth) which predicts that sea surface temperature (SST) will increase between 3.5 and 7.4 ºC with a median increase of 5.1 ºC by 2100 (Fig. 4b).  . Decreases in carbonate ions will decrease the precipitation of CaCO 3 and the carbonate saturation state calculated as:

Impact of Ocean Acidification and Temperature on Calcifying Organisms:-
In which the solution of saturation state of [Ca 2+ ] and [CO 3 2-] is calculated as: where k ′ sp is the stoichiometric solubility product for a particular mineral phase of CaCO 3 (i.e. calcite, aragonite, or high-magnesium calcite) (Kleypas et al. 1999 Reduced calcium carbonate saturation can make the process of calcification more difficult (Sigler et al. 2008). Also with a carbonate saturation state less than 1 (Ω < 1) CaCO 3 will start to dissolve, whereas at a value greater than 1 (Ω > 1) CaCO 3 will spontaneously precipitate. Calcium carbonate is represented in seawater in two forms Coccolithophores exhibited a reduction in the mineral content of their shells by about 10 -30% when exposed to low pH condition (Muller et al. 2010) and reduced calcification rates by 66% when exposed to a CO 2 level three times that of pre-industrial levels (Zondervan et al. 2001). Coralline algae also showed an increased dissolution rate in seawater enriched by CO 2 (pH 7.7) (Martin et al. 2008). The destruction of the protective outer shell layer (periostracum) in gastropods has also been found to occur in the top shell Osilinus turbinata exposed to pH 7.2 and in the black foot limpet Pattela caerulea exposed to pH 7.4 in the 1253 volcanic CO 2 vents (Hall-Spencer et al. 2008). Pacific Oyster (Crassostrea gigas) and edible mussel (Mytilus edulis) also reduced calcification between 10 and 25% after incubation in a mesocosm for a month under CO 2 levels ranging between 700 to 2000 ppmv (Gazeau et al. 2007). It has also been found that reef building organisms reduce calcification between 11-46% (Langdon 2002). However, calcification rate can also increase under extreme CO 2 conditions as demonstrated in the mussel M. edulis in the Kiel Fjord (Thomsen et al. 2010).
Effects of OA on traits other than calcified structures have also been found in calcifying organisms. Larvae of the mussel M. californianus showed lower tissue growth when it was exposed to CO 2 of 900 ppmv for 8 d (Gaylord et al. 2011). The brittle star Amphiura filiformis showed muscle degeneration after being exposed to pH 6.8 in 40 d (Wood et al. 2008). Even more exposure to pH 7.7 after 8 d caused 50% mortality of a brittle star larvae Ophiothrix fragilis and after 25 d caused 100% mortality (Dupont et al. 2008). However, adult individuals of the velvet swimming crab Necora puber reached 100% mortality within 4 -5 d when expose to 6040 ppm CO 2 (pH 7.1) as a result of the ability to compensate for the changes in haemolymph pH ), contrasting with adult N. puber that can survive 30 d expose to pH 6.69 or 21500 ppmv CO 2 (Small et al. 2010). An indirect effect of OA on the common periwinkle Littorina littorea was also reported by Bibby et al (2007); when exposed to low pH conditions (pH 6.6 for 15 d) this species had its ability to exhibit induced shell defences (shell thickness) disrupted.
As well there being clear evidence that OA affects calcifying organisms, temperature has also been shown to affect the process of calcification in marine organisms and can cause dramatic changes in shell plasticity. For example, Trussell and Smith (2000) demonstrated that shell thickness of the snail Littorina obtusata was positively correlated with temperature. The phenotypic variation of shell morphology in different temperatures may be related to the chemical properties of the different calcium carbonate shell materials (aragonite and calcite). For example decreased calcium carbonate availability at low temperatures is caused by increased solubility that makes shell deposition more difficult (Graus 1974, Vermeij 1978, Trussell and Etter 2001, Melatunan et al. 2013). Irie and Fischer (2009) also reported that temperature influenced shell size in the cowry Monetaria annulus, with this species demonstrating a reduced size during warm season compared with the cold season. In contrast, shell thickness in Cypraea annulus increased linearly with increasing temperature (Irie 2006), and in the marine mussel M. edulis (Nielsen 1988) increased temperature resulted in increased shell size (length).
Given that increased temperature enhances calcium carbonate precipitation (Kleypas et al. 1999) the physiological mechanism for reduced calcification rates at low temperatures may be linked to reduced metabolic rates and energy production (Whiteley and Faulkner 2005). In addition, increase temperature can also create systemic hypoxia, leading to an increase in ventilation rate and reduce energy production (Pörtner 2001). An overall, increase in temperature may disrupt energy production and a concomitant increases in pCO 2 would lead to the disruption in oxygen transport proteins (Seibel and Walsh 2003), which in turn would disrupt calcification.

Impact of Ocean Acidification and Temperature on Ecosystems:-
As well as affecting single organisms, it is now clear that OA (and temperature) can have significant effects at higher ecological levels. For example, OA has serious negative effects on several fundamental biogeochemical and ecosystem processes including key elemental cycles and biodiversity (Widdicombe and Spicer 2008, Blackford 2010) and nutrient fluxes (Widdicombe and Needham 2007). These processes included decalcification of planktonic organisms, carbon and nutrient assimilation, primary production and acid-base balance, all of which potentially affect the composition, size structure and successional processes of ecosystems and may lead to a modification of energy flow and resources (Blackford 2010). Although Blackford and Gilbert (2007) suggested that the alteration of ecological function by OA is still unclear with the potential for populations acclimating to altered ocean carbonate chemistry, Hall-Spencer et al. (2008) have showed that a shallow water benthic community in the vicinity of natural CO 2 seepage might change due to the vulnerability of important groups of organisms, with no evidence for adaptation. For example increased levels of pCO 2 in seawater leads to hypercapnia that causes metabolic rate depression in Sipunculus nudus Pörtner 1996, Pörtner et al. 1998) and brings about 31% metabolic rate reduction in jumbo squid, Dosidicus gigas (Rosa and Seibel 2008) and 23% reduced in L. littorea (Melatunan et al. 2011). Increased CO 2 levels has also been shown to decrease aerobic scope (Metzger et al. 2007, Walther et al. 2010, increase induced acidosis in extracellular fluid (Burnett 1997, Miles et al. 2006, Pane and Barry 2007). Metabolic acidosis can also reduce protein synthesis, increase respiratory stress and induce metabolic depression (Seibel and Walsh 2002) which may be lethal to organisms unable to compensate for haemolymph acidosis (Burnett 1997). Such lethal effects of high pCO 2 were shown in Necora puber exposed to highest levels of hypercapnia at 6040 ppm (pH 6. , that would allow them to cope with local environmental conditions such as thermal stress. Such metabolic and energetic shifts are likely to have associated energetic costs. For example, the alteration of metabolism under anaerobic scope leads to a reduction in energy production and mitochondrial density (Pörtner 2002). Under such conditions, time-limited, passive survival is supported by increased synthesis of heat shock proteins (Hsp) as a cellular defence mechanism (Feder and Hofmann 1999) although prolonged exposure is likely to cause lethal effects (Gehring and Wehner 1995). Increased temperature has also been shown to affect metabolic rates and energy metabolism of marine gastropods (Sokolova and Pörtner 2001, Melatunan et al. 2011), cause cardiac failure and reduce thermal windows (Stillman 2003, Tomanek and Helmut 2002, Denny et al. 2006). Pörtner (2001Pörtner ( , 2002 and Frederich and Pörtner (2000) demonstrated that increasing temperature caused increased ventilation and heart rates of aerobic capacity. Progressive increases in temperature may cause excessive oxygen demand and decrease aerobic capacity (Pörtner 2001). In addition, temperature can also affect biochemical reactions for physiological homeostasis (Hochachka and Somero 1973, Prosser and Nelson 1981, Hoffman and Dionne 1983. Initially, organisms could adjust to such temperature extremes by shifting their thermal tolerance or narrowing thermal windows via the adjustment of mitochondrial densities (Pörtner 2002). However, Pörtner (2002) also suggested that the crucial process in shifting thermal tolerance is that the organisms should face unidirectional (higher or lower) thermal conditions which may disrupt molecular function. As an alternative to coping with extreme temperature conditions, animals may also shift metabolic scope under anaerobic conditions or shift to hypometabolic physiology (Storey and Storey 2004). This mechanism requires shifting metabolic pathways and biochemical mechanisms for regulatory reversible transition to and from anaerobic physiology Storey 2004, Hochachka andSomero 2005). Pörtner and Farrell (2008) suggested that under the optimum temperature conditions (T opt ), aerobic performance was high but an increase or decrease in temperature beyond this optimum (T pej ) will lead to lowering aerobic performance. Further progress on to the critical temperature (T crit ) will lead to a loss in aerobic scope and a transition to an anaerobic mode of mitochondrial metabolism (Fig. 5).
1255 In this stage a progressive insufficiency of cellular energy levels occurs. At more extreme temperatures (T den ), only time limited passive survival is supported by anaerobic metabolism or the protection of molecular functions by heat shock proteins and antioxidative defense (Pörtner 2002, Pörtner andFarrell 2008). Pörtner and Knust (2007) have also suggested that increased temperature causes a mismatch between the demand for oxygen and the capacity of oxygen supply to tissues. Such a constraint could affect higher functions such as muscular activity, behavior, growth, and reproduction, ultimately leading to changes in species biogeography (abundance, occupancy, position of range edges and size of the geographical range of distribution).
It is highly likely that marine organisms will be subject to the combined effects of ocean acidification and temperature and recent studies have addressed these combined effects on physiological function in various organisms for example in jumbo squid Dosidicus gigas (Rosa and Seibel 2008), in the decapod Metapenaeus joyneri (Dissnayake and Ishimatsu 2011) and in brittle star Ophiura ophiura (Wood et al. 2010). Rosa and Seibel (2008) found that metabolic rate of jumbo squid D. gigas was depressed by 31% and activity levels by 45% under combined high CO 2 and temperature. Dissanayake and Ishimatsu (2011) demonstrated that in the decapod M. joyneri, reduced aerobic scope and swimming ability was reduced by 30% under high CO 2 (1000 ppm = pH 6.9) and temperature (20 ºC). Even though Wood et al. (2010) found increased in brittle star O. ophiura under interaction of high CO 2 and temperature, there was an apparent trade off with increased arm degeneration. Also, increased metabolic rates in oysters C. gigas exposed to high CO 2 and temperature (25 ºC) was associated with high accumulations of metabolic-end products (Lanning et al. 2010). Finally, Donohue et al. (2012) also found synergistic effects of OA and temperature on metabolic activity and heat tolerance in the intertidal crab Porcellana platycheles. These parameters were positively affected by temperature but exoskeleton calcification was negatively affected by high CO 2 of 2707 ppm. Clearly, more studies are needed if we are to understand more fully the synergistic effects of ocean acidification and warming on marine organisms.  . Morphological variations in various taxa of calcified marine organisms were also found, for example, in the shallow water gastropod (Graus 1974), cowry the Cypraea annulus (Irie 2006), and in the zebra coral Oulastrea crispata (Chen et al. 2011). In general they found that morphological variations of these organisms were mainly caused by a change in CaCO 3 saturation state linked to temperature, however, causative factor such as salinity should also be considered.

Geographical variation in the impacts of Ocean Acidification and Climate
Chemical effects of OA linked to carbonate saturation state (Ω) are likely to be linked to local seawater temperature regimes as the solubility of carbonate is temperature-dependent (Hill et al. 1999). Since the availability of carbonate depends on the saturation state of aragonite and calcite, which is temperature-dependent (see  (1987) showed that the precipitation of aragonite increased rapidly with temperature. Aragonite precipitated four times faster than calcite at 25 and 37 °C respectively, whilst at 5 °C precipitation of aragonite decreased relative to calcite. This trend has also been shown in the ratio of calcite and aragonite in the shell of mussel M. edulis, which increased with decreasing water temperature along latitudinal gradient (Lowenstam 1954, Dodd 1963. Variation in biogenic calcification across latitudinal gradients also occurs with most calcified organisms in northern latitudes tending to be thinner shelled due to low temperature (Kuklinski and Taylor  Carter (1980) revealed that such mineralogical differences may have functional consequences as calcite is softer and less strong than aragonite.
Increased dissolution rates may also vary along latitudinal gradients. For example Findlay et al. (2010a and b) showed that a population of the barnacle S. balanoides living at the northern range limit for this species was more sensitive to high CO 2 conditions, suggesting that the potential risk of climate change is likely to be greater in populations living at higher latitudes. Latitudinal gradients in pH, [CO 3 2-] and Ω ara and Ω calc have been suggested to exist in both the Northern and Southern hemisphere (Orr et al 2005).