Difference analysis of trace elements in statolith of Sthenoteuthis oualaniensis in South China Sea

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure the concentration of trace elements in the otolith of the South China Sea squid (Sthenoteuthis oualaniensis). The composition of trace elements in the otolith and the change of the ratio of trace elements to calcium (Ca) were analyzed. The differences and the relationship between the otolith and habitat were discussed. The results show that the main trace elements are Ca, Sr, Na, Fe, Ba and Mn. Analysis of variance (ANOVA) reveals no significant difference between populations and genders (P>0.05). There was significant difference in the ratio of trace elements to calcium among different regions of statolith (P<0.01) except for Fe/Ca. The Sr/Ca ratio was the highest in the nucleus and then decreased. There was no significant difference in Sr/Ca ratios among different spawning groups and geographical regions (P>0.05). There was a positive relationship between Sr/Ca and temperature, and a negative relationship with salinity at the larval stage. Sr/Ca can be used as a good temperature indicator. Na/Ca first increased and then decreased, highest at the dark zone. Na/Ca is significantly different among different spawning populations at the nuclear and post nuclear zones (P<0.01). Mn/Ca and Ba/Ca, which first decreased and then increased (lowest in the dark region), increased at the edge zone and peripheral zone. There was a positive relationship between Ba/Ca and salinity at adult stage, and Ba/Ca can be used as an indicator of vertical movement. Fe/Ca was significantly different among different spawning populations and geographic areas (P<0.01). It is shown that Na/Ca and Fe/Ca are suitable for distinguish of different groups of squid, and Sr/Ca and Ba/Ca can be used to estimate the habitat environment of squids in the South China Sea.