8. Biological effects of rising seawater temperature Biological effects

The increase in temperature associated with global climate change is expected to impact all physiological processes, survival, and many ecological interactions (Godbold and Solan, 2013). Because many marine live close to their thermal compensatory capacity (Somero, 2002).

Temperature is a key environmental factor that affects the physiology, behavior, and ecology of all organisms, particularly , and strongly modifies the effects of other stressors (Schulte 2007; Sokolova and Lannig 2008; Pörtner 2012), making it advisable to consider environmental temperature in all studies of the effects of multiple stressors in natural populations. Biological effects

In aquatic ectotherms, the upper limit of thermotolerance is set by the inability of the ventilatory and circulatory systems to deliver sufficient oxygen to cover the tissues’ demand for energy at high temperatures.

As a result, a progressive mismatch between the oxygen consumption of tissues and the delivery of oxygen develops at, and above, the critical temperatures leading to tissue hypoxemia and the onset of partial anaerobiosis, and it heralds transition into the pessimum range.

Ventilatory and circulatory system can’t supply adequate oxygen for tissues above upper limit of thermotolerance. Climate Change Has a Direct Influence on the Physiology and Development of Organisms

. Environmental temperatures affect metabolism, determining heat exchange with the environment . The larger the body size, the less surface area for heat dissipation (Because of body surface/volume ratio) . Average body size increases with decreasing mean annual temperature (in general, increasing latitude). It means that around equator and low latitudes animals are generally small. They can dissipate the heat more easily. At high latitudes (cold climates) animals are bigger. They don’t need to dissipate heat. . In both birds and , a smaller body size is more energetically efficient in a warm climate Heat and body size

Surface/volume ratio of the small mussel is higher than that of big mussel.

Large animals have difficulties to decraese body temperature by heat dissipation. Climate Change Has a Direct Influence on the Physiology and Development of Organisms

. The body temperature and metabolic rate of an are directly affected by environmental temperatures . Metabolic activity increases exponentially with temperature (especially in ecthotherms), so warming may have a greater proportional impact on warmer climate ectotherms . As temperature increases, the rate of metabolism increases and then rapidly declines at higher temperatures

Thermal performance curve: Relationship between environmental temperature and a physiological rate of an ectotherm expressed as a thermal performance curve

(grey line). The optimum temperature (Topt) specifies the temperature at maximum performance. The ecophysiological key characteristics critical thermal

minimum (CTmin) and maximum (CTmax) delimit an ’s thermal tolerance. Extreme temperatures and thermal tolerance

All organisms have a range of tolerable body temperature

 Homeothermic -narrow range () Maintain body temperature at relatively constant independent of mean environmental temperature Marine mammals are endothermic (whales, sea otter etc).

 Poikilothermic ectotherms – broad range Thermal conformity () Allow body temperature to fluctuate with environmental temperature Most marine species are ecthotermic (fish, marine invertebrates etc.)

Exceeding limit of thermal tolerance cause death Problems with high temperature

 Denaturization of (structural and enzymatic)  Thermal inactivation of enzymes faster than rates of activation

 Inadequate O2 supply to meet metabolic demands  Different temperature effects on iterdependent metabolic reactions  Membrane structure alterations  Increased evaporative water loss (terrestrial animals) Climate Change Has a Direct Influence on the Physiology and Development of Organisms

. Predicted increase in metabolism in the tropics was large (even though the temperature increase was small) because the environment was initially warm . Increased metabolic rate can lead to increased need for food and increased vulnerability to starvation if food resources do not increase . could lead to reduced energy allocation for reproduction Global changes in temperature and ectotherm metabolic rates since 1980

Arctic North temperate Tropical (b) (a) South temperate 50 2.0

40 C) ° 1.5 30

1.0

body body mass) 20 3/4 0.5 10

W W per g 0 

0 (

Change in metabolic in Change metabolic rate Change in temperature in Change temperature ( 10 0.5 1980 1990 2000 2010 1980 1990 2000 2010 Year Year

(a) Changes in mean temperature for Arctic, northern temperate, southern temperate and tropical regions. (b) Predicted absolute changes in mass normalized metabolic rates by geographic region. Mass-specific metabolic rates were calculated using parameters estimated for an average ectotherm (Data from Dillon et al. 2010.) Climate Change Has a Direct Influence on the Physiology and Development of Organisms

. Tropical ectotherms may be especially vulnerable to climate warming, even if predicted warming is small . Thermal tolerance limits are closely aligned with temperatures in an organism’s habitat . The upper thermal tolerance limits (temperature at which 50 percent mortality

occurs – LT50) are positively correlated with maximum temperature in the species’ microhabitat – adaptive variation Climate Change Has a Direct Influence on the Physiology and Development of Organisms

. Tropical species generally have a current maximum habitat temperature (MHT) closer to

their LT50

. For instance if maximum habitat temperature (MHT) is 28 °C, LT50 is about 30 °C

. Also have a relatively small ability to increase LT50 through acclimation Relationship between maximum habitat temperature and upper thermal tolerance limits

Relationship between maximum habitat temperature and upper thermal tolerance limits (Tmax) for 20 species of porcelain crabs of the genus Petrolisthes, from intertidal and subtidal habitats throughout the eastern Pacific (temperate: and Chile; tropical/subtropical: Panama and Northern Gulf of California). Each symbol represents a different crab species. Maximal habitat temperature is the maximum recorded water temperature at the geographic location and microhabitat used by the species. Tmax represents the LT50 (lethal temperature; the water temperature at which 50 percent of test crabs died). The line of equality (Dashed line: LT50 = MHT) allows estimation of risk of heat death under current habitat conditions. Species with current MHT near LT50 are highly susceptible to further increases in water temperature compared to species where MHTs are far below values of LT50. Stenotherm-eurytherm

 Tropical species are generally stenoterm; adapt within a narow range of temperature.

 Corals are also stenotherm. 1 °C increase of monthly avarage temperature caused coral bleaching and mortality in 1983, 1991 and 2016-2017.

 Some species are stenotherm: Some antarctic fish live between -2 and +4

 Euritherm (live within a wide range of temperature) are also sensitive to warming. For instance 1-2 °C increase in summer maximum seawater temperature can cause a mass mortality in an euritherm animal.

 An intertidel goby fish (longjaw mudsucker Gillichthys mirabilis) is an extreme eurythermic, can change body temperature between 5 and 37. Despite this high range of tolerance, 1-2 °C increase in summer maximum seawater temperature can kill this species.

 Taken together, both stenotherm and eurytherm are affected by warming. Coral bleaching due to seawater warming

 Bleaching occurs when algal symbionts (Symbiodinium spp.) in a coral host are killed by environmental stress, revealing the white underlying skeleton of the coral

 Since the 1980s, rising sea surface temperatures owing to global warming have triggered unprecedented mass bleaching of corals, including three pan-tropical events in 1998, 2010 and 2015/16

 Bleached corals are physiologically damaged, and prolonged bleaching often leads to high levels of coral mortality

 In 2016, the proportion of reefs experiencing extreme bleaching (>60% of corals bleached) was over four times higher compared to 1998 or 2002. Coral–algae symbiosis

coral polip symbiosis

Coral tentacle

Symbiodinium (zooxanthellae)

Coral- invertebrate animal, (anthozoa-cnidaria)

Symbiodinium-is a dinoflagellate (unicellular phosyntetic algae) Severe Coral bleaching in Great Barrier, in 2016

From air

Great Barrier is the world largest coral reef. Coral are damaged due to warming about 1 °C.

(Hughes et al., 2017 Nature) Physiology of thermal response

. There is evidence of the capability of marine organisms to acclimate the metabolic rate within certain range of temperature (thermal window) (Pörtner et al., 2005, Pörtner, 2008, 2010; Ezgeta-Balic et al., 2011). . However, at high temperatures, beyond the range of thermal tolerance of a species, a drastic decline occurs in oxygen consumption and an increase in the anaerobic metabolic pathways (Jansen et al., 2007) . Any temperature change outside the optimum range will increase the baseline energy demand of an ectothermic animal and reduce e.g. the growth performance of the organism (oxygen- and capacity-limited thermal tolerance (OCLTT; Pörtner, 2010). . Elevated seasonal temperatures led to a higher baseline energy demand (Guderley and Pörtner, 2010). This causes increased respiration and excretion rates. Estuarine and coastal waters are sensitive to warming

 Lower capacity of thermal buffering of the shallow waters and the thermal exchanges with the land and fresh waters also predispose estuarine and coastal zones to rapid warming and temperature extremes (Helmuth et al., 2002; Gilman et al., 2006).  Warming in a coastal area and in wetland rapidly increase seawater temperature in a coast or estuary.  For instance, warming in Alibeyköy and Kağıthane creeks can easily warm up water in Haliç  Warming in East Europe can increase fresh water temperature in Danube (Tuna) and then north–east Black Sea coast. Effects of Danube river on Black Sea coast Thermotolerance in mussel Mytilus galloprovincialis

 Temperature levels of 24-25°C have been identified, for this species, as an upper limit for normal physiological activities (Anestis et al., 2007, 2010).  This indicates that Mediterranean mussels already live close to their thermal acclimation limits (Anestis et al., 2007).  Total mortality of mussels has been observed in Fangar Bay, when seawater temperature reached 28°C for more than 10 days (Ramón et al., 2007).  In the northwestern Mediterranean Sea, mean maximum summer temperatures have increased by about 1°C between 2002 and 2010 relative to the 1980–2000 average (Marba and Duarte, 2010) and a rapid warming of 2.8 ± 1.1°C is expected by the end of the century (Jorda et al., 2012). Do you know Mediterraean? Distribution of black mussel Mytilus galloprovincialis in Turkish coasts

Black mussel Mytilus galloprovincialis lives in coasts (0-80 meters). It adapt in Black Sea, Sea of Marmara and Aegean Sea but not Levantine Sea coast of Turkey. One of the main reason of this is temperature (the others are: nutrient content, salinity etc.). Because summer temperature can reach 30-31 °C in Levantine Sea coast (Antalya, Mersin and Adana). They live near critical thermal maximum in South Aegean. So 1-2 °C anomaly can kill the mussel in this region. This Show that temperature rising can chanve species composition, abundance Mussel sampling in Turkish coast in 2012. and biodiversity.