Cephalopod hatchling growth: the effects of initial size and seasonal temperatures

Abstract Temperature is known to have a strong influence on cephalopod growth during the early exponential growth phase. Most captive growth studies have used constant temperature regimes and assumed that populations are composed of identically sized individuals at hatching, overlooking the effects of seasonal temperature variation and individual hatch ling size heterogeneity. This study investigated the relative roles of initial hatchling size and simulated natural seasonal temperature regimes on the growth of 64 captive Octopus pallidus over a 4-month period. Initial weights were recorded, and daily food con sumption and fortnightly growth monitored. Two temperature treatments were applied replicating local seasonal water temperatures: spring/summer (14-18°C) and summer/autumn (18-14°C). Overall octopuses in the spring/summer treatment grew at a rate of 1.42% bwd -1 (% body weight per day) compared to 1.72% bwd -1 in the summer/autumn treatment. Initial size influenced growth rate in the summer/autumn treat ment with smaller octopuses (<0.25 g) growing faster at 1.82% bwd -1 compared to larger octopuses at 1.68% bwd -1 . This was opposite to individuals in the spring/ summer treatment where smaller octopuses grew slower at 1.29% bwd -1 compared to larger octopuses a

Ammonoid Intraspecific Variability

Because ammonoids have never been observed swimming, there is no alternative to seeking indirect indications of the locomotory abilities of ammonoids. This approach is based on actualistic comparisons with the closest relatives of ammonoids, the Coleoidea and the Nautilida, and on the geometrical and physical properties of the shell. Anatomical comparison yields information on the locomotor muscular systems and organs as well as possible modes of propulsion while the shape and physics of ammonoid shells provide information on buoyancy, shell orientation, drag, added mass, cost of transportation and thus on limits of acceleration and swimming speed. On these grounds, we conclude that ammonoid swimming is comparable to that of Recent nautilids and sepiids in terms of speed and energy consumption, although some ammonoids might have been slower swimmers than nautilids