Effect of temperature on statolith growth of the European squid Loligo vulgaris during early life (original) (raw)

Over the past decade, statolith interpretation has resulted in a major advance in our knowledge of squid population-dynamics, but the way in which environmental conditions aect the statolith increment-deposition ratio remains virtually unknown. The object of the present study was to determine the eect of temperature on this process, using tetracycline marks to validate statolith growth in Loligo vulgaris Lamarck, 1798 under rearing conditions equivalent to severe winter (11°C) and summer (19°C) temperature regimes. Tetracycline marking was performed every 10 d (at 10, 20, 30, 40, 50 and 60 d of age). The newly hatched squid paralarvae were slightly smaller in summer than those hatched in winter. Survival rates were similar in both cultures, but growth rates (wet mass) of summer squids were double those in winter. At hatching, statoliths were already longer in the summer squids, and growth rates were 2% d )1 as opposed to 0.9% d )1 for winter statoliths. For the dorsal dome area of the statolith, where more increment counts were made, statolith growth was of 3.25 lm d )1 in summer, and daily increment deposition was con®rmed in 87% of the statoliths. The slow growth of statoliths at winter temperatures yielded a mean growth of 1.1 lm d )1 ± insucient to discern the increments using light microscopy. Subsequent SEM observation enabled only 21% of the winter statoliths to be read; these also indicated a deposition rate of one increment d )1 . Since the life span of L. vulgaris is '1 yr, squids will experience at least one winter during their life cycle, and this might be visible on the statolith.