Latitudinal variation in growth of Crangon crangon (L.): Does counter-gradient growth compensation occur?
Length growth in relation to water temperature was studied for Crangon crangon (L.) from two populations at the northern and southern edges of its distributional range to determine whether counter-gradient growth compensation occurs. In crustaceans, growth rate depends on the time between moulting events (intermoult period) and the size increase at moult (moult increment). In this study, the period between moults was shorter at higher temperature, ranging respectively from about 11 days at 25 °C to 27 days at 10 °C at southern edge, and from 10 to 24 days at the same temperatures at the northern edge. Moult increment showed a large variability, from 1.5 to 2.7 mm with no clear trend with temperature at the northern edge; and decreasing from about 2.7 mm at 10 °C to about 1.5 mm at 25 °C at the southern edge. As a result, the temperature effect on the overall growth rate differed between shrimps from the north and those from the south, suggesting counter-gradient growth compensation. At the northern edge, mean growth increased from about 0.12 mm d - 1 at 10 °C to about 0.23 mm d - 1 at 25 °C, while at the southern edge, growth was lower, about 0.08 mm d - 1 at 10 °C and increased to about 0.16 mm d - 1 at 25 °C. Maximum observed growth rates of shrimps from the north were also higher and ranged from 0.17 mm d - 1 at 10 °C to 0.89 mm d - 1 at 25 °C, while shrimps from the south grew at a maximum of 0.08 to 0.75 mm d - 1 respectively at 15 and 20 °C. Sex and size differences were also found, with males growing slower than females and at a decreasing growth rate with increasing size. Implications for the brown shrimp's life cycle are discussed.