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Journal of Sea Research 70 (2012) 32–41 Contents lists available at SciVerse ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares Thermal tolerance and potential impacts of climate change on coastal and estuarine organisms Diana Madeira a,⁎, Luís Narciso b, Henrique N. Cabral a, Catarina Vinagre a a Universidade de Lisboa, Faculdade de Ciências, Centro de Oceanografia, Campo Grande, 1749-016 Lisboa, Portugal b Universidade de Lisboa, Faculdade de Ciências, Centro de Oceanografia, Laboratório Marítimo da Guia, Avenida Nossa Senhora do Cabo, 939, 2750-374 Cascais, Portugal article info abstract Article history: The study of thermal tolerance is the first step to understanding species vulnerability to climate warming. Received 8 December 2011 This work aimed to determine the upper thermal limits of various fish and crustaceans in a temperate Received in revised form 24 February 2012 estuarine ecosystem and an adjacent coastal area. Species were ranked in terms of thermal tolerance and Accepted 3 March 2012 intraspecific variability was evaluated. The method used was the Critical Thermal Maximum (CTMax). The Available online 16 March 2012 CTMax was found to be higher for species typically found in thermally unstable environments, e.g. intertidal, supratidal, southern distributed species and species that make reproduction migrations because they are Keywords: Global Change exposed to extreme temperatures. Subtidal, demersal and northern distributed species showed lower Critical Thermal Maximum CTMax values because they live in colder environments. Species from different taxa living in similar habitats Temperate Species have similar CTMax values which suggests that they have evolved similar stress response mechanisms. This Tropical Species study showed that the most vulnerable organisms to sea warming were those that occur in thermally Intraspecific Variability unstable environments because despite their high CTMax values, they live closer to their thermal limits and have limited acclimation plasticity. Among the demersal species studied, two sea-breams (Diplodus bellottii and Diplodus vulgaris) are potentially threatened by sea warming because their CTMax values are not far from the mean water temperature and they are already under thermal stress during current heat waves. © 2012 Elsevier B.V. All rights reserved. 1. Introduction al., 1995). Temperature is a heterogeneous variable both in time and space (Re et al., 2005), structuring marine community assemblages Temperature is one of the most important factors affecting and ecosystems at the ultimate level (Glynn, 1988). organisms because it impacts the kinetic energy of molecules and Aquatic ectotherms do not physiologically regulate their body biochemical reactions. Hence, the animal's physiology and behavior temperature; their body temperature follows the environmental (e.g. Fry, 1971; Mora and Ospina, 2001; Somero, 1969) might be temperature. Due to water properties such as high heat conductivity, altered. Consequently, fitness and performance may be affected by water absorbs a lot of heat leading to a temperature increase. Consid- the thermal regime and other physical and chemical variables ering global warming scenarios, the increase in temperature may operating in the habitat. Dynamic fluctuations of these abiotic make aquatic ectotherms as vulnerable organisms to thermal stress. variables can interfere and dominate the life history, demographics Additionally, there is still a considerable lack of knowledge about and competition between species (Christian et al., 1983; Huey, their thermal limits, especially for temperate species, pelagic and 1991; Huey and Berrigan, 2001; Munday et al., 2008; Porter, schooling fish and even for some crustacean species that are widely 1989) explaining a diversity of adaptations among organisms distributed and easy to handle (Freitas et al., 2010). Therefore, further (Lutterschmidt and Hutchison, 1997a). Individual parameters such tolerance studies are needed. The tolerance window for each species as growth rate, longevity, excretion rate, food intake and basic metab- is described as a favorable range of temperature or performance olism as well as population parameters such as mortality, reproduc- breadth. It includes an optimal zone and a suboptimal zone. Above tive rate, recruitment and population size/distribution all depend on or below that range, performance is negatively affected and the temperature (e.g. Brey, 1995; Kröncke et al., 1998; Perry et al., species cannot survive unless it is for a limited period of time. 2005; Pörtner et al., 2008; Shaw and Bercaw, 1962; Southward et Moreover, ectotherms are only able to carry out behavioral thermo- regulation (Neill and Magnuson, 1974; Neill et al., 1972; Rozin and Mayer, 1961) which can imply habitat selection based on the habitat's thermal characteristics. Therefore, according to climate change ⁎ Corresponding author. Tel.: +351 21 750 08 26; fax: +351 21 750 02 07. fi E-mail addresses: [email protected] (D. Madeira), [email protected] scenarios, it is reasonable to expect inter and intraspeci c competi- (L. Narciso), [email protected] (H.N. Cabral), [email protected] (C. Vinagre). tion to occur if the thermal microhabitat is scarce. 1385-1101/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.seares.2012.03.002 D. Madeira et al. / Journal of Sea Research 70 (2012) 32–41 33 Facing current concerns about climate change scenarios, the in terms of temperature tolerance and hypotheses about the potential knowledge of thermal tolerance is the first step to understanding impacts of climate warming on the species studied were put forward. how vulnerable species are. However, not only there is a great diver- Another target of this work was to evaluate and compare intraspecific sity of responses but also global warming tends to vary regionally variability of the CTMax in order to discuss the species' potential to (Rivadeneira and Fernández, 2005) so there is a need to do regional adapt to ongoing global climate changes. Also, it was investigated and population studies (McFarlane et al., 2000). Most literature has which species live closer to their upper thermal limits and com- focused on tropical regions perhaps not only because models suggest parisons with tropical species were made. that impacts will be severe in the tropics (Tewksbury et al., 2008) but also because predictions for temperate regions are the hardest to 2. Materials and methods make due to the diversity of life history patterns, complexity of tro- fi phic relations, habitat variability and over- shing (IPCC, 1997; 2.1. Temperature data Roessig et al., 2004). Impacts of climate warming should be greatest on thermal special- 2.1.1. Atmospheric and water temperature for the intertidal zone ists that have limited acclimation potentials (Hoegh-Guldberg et al., Atmospheric temperature data for the intertidal zone was obtained 2007) and those that live in aseasonal environments (Tewksbury et from the MOHID database (open acess at www.mohid.com). In this da- al., 2008). The thermal limits of an organism are set genetically but in tabase, field data from the meteorological station of Laboratório evolutionary terms the rate at which temperature is increasing might Marítimo da Guia (38°41′42.91″ N; 9°27′08.52″ W — under 3400 m not allow the organisms to adapt genetically (Cuculescu et al., 1998). from the sampling site) was available. Temperature was recorded Thereby, the ecosystems that have evolved in stable conditions for a every half an hour during the day and night. For the purpose of this long time e.g. cold environments or tropical habitats are especially at study data from January 2010 to December 2010 were used. A detailed risk. Additionally, some tropical species are said to live close to their graph was drawn for July 2010, concerning only temperatures between upper thermal limits (Jokiel and Coles, 1977; Sharp et al., 1997) 7 am (sunrise) and 9 pm (sunset). although other authors present contradictory evidence (Mora and Ospina, 2001). It has also been suggested that warm-adapted species 2.1.2. Estuarine temperatures of the intertidal/supratidal zone may be particularly at risk since they Estuarine water temperatures were obtained from the Centro de live closer to their upper thermal limit and have limited acclimation Oceanografia database. Mean values from 1978, 1979, 1980, 1995, capacity (Hopkin et al., 2006; Somero, 2010). Despite the fact that 1996, 1997, 2001, 2002, 2005 and 2006 were used to calculate and they are more thermally tolerant there is a high probability that plot the general mean±SD temperature for each month in the maximum habitat temperatures surpass their upper thermal limit Tagus estuary. (Somero, 2010) because they live in a hot and unstable environment with wide daily and seasonal thermal amplitudes. Therefore, environmental variation has large ecological and 2.1.3. Coastal temperatures evolutionary consequences. It exerts a strong selective pressure leading Coastal water temperatures were obtained from the Centro de fi to the development of specific strategies which may be related not Oceanogra a database, Levitus and Boyer (1994) and Mohid database. only to reproductive strategies, growth and maturation but also to Thermal images of the Portuguese coast from the Mohid database were physiological and cellular mechanisms to deal with stressful conditions. obtained every 10 days throughout 2010. Environmental variability also sets life history patterns,