Short communication Critical thermal maxima of common rocky intertidal fish and shrimps — A preliminary assessment Catarina Vinagre a, ⁎, Marta Dias a , Joana Roma a , Ana Silva b , Diana Madeira c , Mário S. Diniz c a Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal b Departamento Engenharia Civil, Arquitectura e Georecursos, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal c Requimte, Departamento de Química, Centro De Química Fina e Biotecnologia, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal abstract article info Article history: Received 31 January 2013 Received in revised form 25 February 2013 Accepted 31 March 2013 Available online 11 April 2013 Keywords: Global change Climate warming Thermal tolerance Thermal niche Sentinel species CTMax Rocky shore ecosystems are considered sentinels of climate warming because they are in close contact with the atmosphere and their shallow waters present low thermal inertia. Concerns on the vulnerability of rocky shore species subject to climate warming make the investigation of their thermal tolerance an urgent topic. The aim of this study was to determine the upper thermal limits of species that are common in tidal pools of rocky shore ecosystems of the Northeast Atlantic. The method used was the Critical Thermal Maximum (CTMax), which allowed the ranking of species in terms of their upper thermal limits as follows: Coryphoblennius galerita (32.0 °C), Palaemon serratus (33.0 °C), Gobius paganellus (33.1 °C), Palaemon elegans (33.4 °C), Lipophrys pholis (33.9 °C) and Paralipophrys trigloides (35.0 °C). Intraspecific variability was always lower than 2%. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Understanding the impact of global warming on biodiversity and pop- ulation stability is one of the most important challenges faced by mankind (Schwenk et al., 2009). One of the ecosystems where climate warming is expected to strike first is the rocky intertidal zone (Helmuth et al., 2006). Rocky intertidal habitats exist at the margins between the terrestrial and the marine realms so they are not only subject to the changes in water temperature, but also the aerial climatic regime. Tidal pools in the rocky shore are home to diverse biological com- munities. However, they have a small water volume, which means that these environments, unlike other aquatic environments, have low thermal inertia. This way, tidal pools will be one of the aquatic environ- ments hardest hit by temperature rise and have the potential to serve as early warning systems for the impacts of climate change. Vulnerability towards a rise in temperature will depend mainly on an organism's thermal tolerance and its upper thermal limits, both of which remain unknown for most species. An experimental approach to thermal tolerance is needed as a first step in the understanding of the present and future effects of climate warming. The critical thermal maximum (CTMax) is considered the most reli- able parameter to conduct macrophysiological comparative studies in ectotherms (Cowles and Bogert, 1944; Lutterschmidt and Hutchison, 1997) and most suitable to explore upper tolerances across different taxa (Deutsch et al., 2008; Huey et al., 2009; Somero, 2010). The present study aims to determine the CTMax of species that are common in tidal pools of rocky shore ecosystems of the Northeast Atlantic and for which information on thermal limits is lacking. Four fish species, Coryphoblennius galerita, Gobius paganellus, Lipophrys pholis and Paralipophrys trigloides and two shrimp species, Palaemon serratus, Palaemon elegans, were tested. Intraspecific variability was also estimated. 2. Materials and methods 2.1. Specimen collection and acclimation conditions Specimens were collected in the Portuguese West coast (38°71′ N; 9°48′ W) in a rocky exposed shore, in September of 2012. Individuals were collected using hand nets in six representative tidal pools. Tem- perature in the tidal pools at the time of capture was 20 °C. This temper- ature was chosen for the acclimation of the specimens to the laboratory conditions. Tidal pools were surveyed monthly for 2 years (2011–2012) to determine their temperature fluctuations throughout the year. Tem- perature was measured with a multi-parameter probe. The pools' mean area was 12.7 m 2 and mean depth was 41 cm. After capture, organisms were transported to the laboratory and housed in a re-circulating system and aquaria with a capacity of 70 l, with aerated sea water, a constant temperature of 20 °C and salinity of 35‰. The water dissolved O 2 level varied between 95% and 100%. Journal of Sea Research 81 (2013) 10–12 ⁎ Corresponding author. Tel.: +351 21 750 08 26; fax: +351 21 750 02 07. E-mail address: cmvinagre@fc.ul.pt (C. Vinagre). 1385-1101/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seares.2013.03.011 Contents lists available at SciVerse ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares