Impact of climate change on coastal versus estuarine nursery areas: cellular and whole-animal indicators in juvenile seabass Dicentrarchus labrax

The effects of thermal conditions of coastal and estuarine nurseries, both in the present and in the near future, on juvenile fish were compared. The response of the European seabass Dicentrarchus labrax was investigated through a long-term experiment in captivity, where 0-group juveniles were exposed to temperatures that reflect the average summer temperature that they encounter in coastal (18 degrees C) and estuarine nurseries (24 degrees C), and also the temperature that they endure inside estuaries during heat waves (28 degrees C). The combined expression of 2 heat shock proteins (Hsc/Hsp70) in white muscle was assessed throughout a long-term experiment (30 d). Growth and condition were determined at the end of the experiment. Hsc/Hsp70 levels were constant throughout the first 15 d at 18 degrees C, and then decreased steeply. At 24 and 28 degrees C, Hsc/Hsp70 levels increased considerably after 15 d, particularly at 28 degrees C, and decreased at the end of the experiment. Daily growth was 0.20 mm d(-1) at 18 degrees C, it increased to 0.34 mm d(-1) at 24 degrees C, and was lowest at 28 degrees C, at 0.16 mm d(-1). Condition, assessed by Fulton's K, was 0.95 at 18 degrees C, 1.00 at 24 degrees C and 0.83 at 28 degrees C. The Hsc/Hsp70 increase at 24 and 28 degrees C is an indication that molecular reparation processes were underway. The peak growth and condition values registered at 24 degrees C suggest that estuarine average summer temperatures are more beneficial for this species' juveniles than coastal temperatures. Acclimation was observed at 24 degrees C, yet growth rates and condition values indicate that prolonged heat waves (28 degrees C) may result in lower fitness.