In situ and laboratory assessment of heart rate in a Mediterranean limpet using a noninvasive technique

Heart rate of the Mediterranean limpet Patella caerulea L. was investigated on the natural shore and in the laboratory by using a technique based on i nfrared phototransducers. Field recording occurred in the Gulf of Trieste ( northern Adriatic) during March and lune 1997. A consistent dependence of h eart rate on temperature was observed in limpets both when submerged and wh en exposed to air in the two periods, but thermal acclimation was evident. During spontaneous activity at high tide, heart rate increased 1.5-1.7 time s the values observed during resting in water at corresponding temperatures . The dependence of heart rate on temperature (10 degrees 16 degrees, and 2 2 degrees C) and size (wet weight <1.25 and >1.30 g) in submerged limpets f rom different populations (northern Adriatic and Tyrrhenian) was tested in the laboratory by adopting a factorial design. The results showed a marked effect of temperature, body weight, and their interaction, independent from the site of origin. Smaller limpets showed a linear increase of heart rate in the whole range of temperature tests, while in the larger ones the incr ease between 10 degrees and 16 degrees C was greater than between 16 degree s and 22 degrees C. Heart rate decreased with increasing body size at contr ol (16 degrees C) and high (22 degrees C) temperature, while at lower tempe rature (10 degrees C) no effect of body size was evident. When removed from their home scar, limpets increased heart rate to about 1.5 times the refer ence value. Finally, correlation of oxygen consumption with heart rate of s ubmerged limpets maintained at a different temperature (10 degrees-22 degre es C) was statistically significant.