Abiotic influences on embryo growth: statoliths as experimental tools in the squid early life history

Abstract

Statolith size and growth was used to determine the influence of abiotic factors on the growth of Loligo vulgaris and Sepioteuthis australis embryos. Recently spawned egg masses collected from the field were incubated in the laboratory under different levels of light intensity, photoperiod, or short periods of low salinity (30&). Double tetracycline staining was used to follow statolith growth. In L. vulgaris constant light conditions produced significantly slower growth in the embryonic statoliths and embryos held at summer photoperiod had slower statolith growth than those held at winter photoperiods. However once they hatched out there was no evidence that photoperiod affected statolith growth. After hatching, in all photoperiods statolith growth rates decreased in comparison with late embryonic rates. In S. australis embryos, differences between the high and medium light intensities for summer and intermediate photoperiods were found, suggesting that under summer incubation temperature, longer daylengths at medium light intensity favoured higher statolith growth for this species. In comparison to controls, slower statolith growth in S. australis embryos due to low salinity only occurred when exposed for 72 h. Comparison with previous studies indicates that temperature seems to be the main abiotic factor influencing statolith growth during early stages, however, interactions among all abiotic factors needs to be determined as well as the unknown influence of other isolated factors, e.g., oxygen concentration within the egg mass.

Environmental pH, O2 and Capsular Effects on the Geochemical Composition of Statoliths of Embryonic Squid Doryteuthis opalescens

“…These stages were indicated by the pigmentation of the ink sac (this occurs earlier in D. opalescens than in D. pealeii), the complete covering of the eyes by the cornea, but not a prominent Hoyle's Organ [37,68,69]. Cultures were maintained at constant temperature (11.3 °C ± 0.3 °C, SD), salinity (33.4 ± 0.2) and light levels using 15 W LED lights on a 12:12 h light:dark cycle to reduce these types of environmental effects on statolith development [21,40,72]. Salinity, temperature and seawater flow rate were constant among treatments.…”

“…After death, the statoliths can sometimes even be preserved in the fossil record [33,38,39]. Statolith aragonite crystal grows with a daily banding pattern, and growth is heavily influenced by the environment [33,34,38,40]. However, the squid statolith is not in direct contact with the environment, but rather with endolymph fluid within the statocyst [41].…”

Growth and reproduction of the squid Illex coindetii Verany, 1839 in the central Mediterranean Sea

“…Accurate assessment and effective management depend on population models that incorporate life history parameters, such as proportion of sexual maturity at size and growth rate. Statolith analysis has proved to be one of the best tools for squid age and growth estimation in wild populations (Jackson, 1994;Arkhipkin, 2005;Villanueva et al, 2007;. Growth studies based on direct age estimation or studies on relative investment between somatic and gonad growth are poor or still lacking in many oceanic regions and in the Mediterranean Sea (Sánchez, 1995;Arkhipkin et al, 2000;Arkhipkin & Roa-Ureta, 2005;Cavanna et al, 2008).…”

Impacts of seawater desalination on the giant Australian cuttlefish Sepia apama in the upper Spencer Gulf, South Australia

“…The decrease in mantle size as an effect of salinity has been noted previously and described as a malformation (Paulij et al 1990). Also, correlations with size of hatchlings and hatching success have been determined for cephalopod embryos grown in low salinities (Palmegiano and Dapote, 1983;Fàgundez and Robaina, 1992;Cinti et al, 2004;Sen, 2004;Sen, 2005;Villanueva et al, 2007); however this is the first study which indicates a decrease in weight and mantle length in salinities greater than 42‰. The yolk reserves of individual eggs are the only energy source for development of the embryo; the smaller the hatchling, the greater the physical constraints imposed on the functional morphology of organs responsible for swimming and food capture, therefore once hatched survivability may also be decreased (Boyle and Boletzky, 1996).…”

“…What has been found however is that salinity ranges for embryonic development and hatching success are species specific and higher salinities (28-38‰) appear to be optimal (Palmegiano and Dapote, 1983;Paulij et al, 1990;Cinti et al, 2004;Sen, 2005). Growth rates of cephalopods are also affected by salinity, where lower salinities increase statolith size (Villanueva et al, 2007), but also cause deformations of embryos (Paulij et al, 1990). At present there is no published information on the effects of high salinities (>42‰) especially those typical of desalination brine ($70-80‰) on the growth and survival of the cephalopod embryo or juvenile stage.…”