Yuzuru Ikeda

Geographical variations in carbon and nitrogen stable isotope ratios in squid

The magnitude of geographical variations of stable isotope ratios of carbon and nitrogen was examined in ten squid species captured in seven areas of the worlds oceans. The average of all 139 squid was −17.4±1.4‰ for δ 13 C and 11.6±1.6‰ for δ 15 N. The δ 13 C of squid showed a clear-cut negative correlation with the latitude of the sampling locations, reflecting the well-known latitudinal characteristics of phytoplankton δ 13 C, while squid δ, 15 N did not correlate with the latitude significantly. The δ 15 N reflected the regional characteristics of nitrogen metabolism such as denitrification and N 2 fixation, and it was conspicuous in the intraspecific variation in Sthenoteuthis oualaniensis ranging from 10.0±1.5‰ off Japan to 16.3±0.6‰ off Peru in the Pacific Ocean. Significant isotopic variations were also found in the local area among the five species off Japan in the Pacific Ocean and among the three species in the Japan Sea. Attention must be paid to the isotopic variations of primary producers as well as those of squid in examining the trophic positions of squid.

Concentration of statolith trace elements in the jumbo flying squid during El Niño and non-El Niño years in the eastern Pacific

Statoliths of the jumbo flying squid Dosidicus gigas (Cephalopoda: Ommastrephidae) in the eastern Pacific in 1995, 1996 (non-El Nino years) and 1997 (El Nino year) were analysed to observe whether unusual temperature increases due to El Nino was recorded in the concentration of trace elements. In addition to calcium (the major element), trace elements of manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and strontium (Sr) were detected. Strontium concentration in the calcified tissue of some aquatic animals changes with environmental variables. However, yearly comparisons revealed that Sr concentration did not significantly differ between the El Nino year and non-El Nino years. Instead, the Sr concentration differed with squid habitats. Strontium concentration in statoliths of D. gigas from Peruvian waters (high salinity) was significantly higher than those from Costa Rican waters (low salinity) regardless of El Nino.

RELATIONSHIP BETWEEN STATOLITHS AND ENVIRONMENTAL VARIABLES IN CEPHALOPOD

The hard tissues of cephalopod, namely statoliths were analyzed with PIXE for the Japanese common squid Todarodes pacificus of the Sea of Japan origin in order to examine the relationship between the amount of trace elements in statoliths and environmental temperature of the squid habitat. Calcium, iron, zinc. copper and strontium were detected in the statoliths. Negative relationship was observed between Sr concentration in statoliths and environmental temperature. On the contrary to Sr, Fe and Zn concentration in statoliths related positively with environmental temperature. These observations revealed that the statoliths would be a useful thermometer for reconstructing the environmental temperature of cephalopod habitat as seen in the hard tissues of other marine organisms.

COMPARISON ON TRACE ELEMENTS IN SQUID STATOLITHS OF DIFFERENT SPECIES' ORIGIN: AS AVAILABLE KEY FOR TAXONOMIC AND PHYLOGENETIC STUDY

Trace elements in squid statoliths were analyzed by PIXE for the following fourteen species in five families of different habitat origin: Ommastrephidae, Ommastrephes bartrami, Dosidicus gigas, Sthenoteuthis oualaniensis; Gonatidae, Gonatopsis makko, G. borealis, Berryteuthis magister; Loliginidae, Loligo bleekeri, L. duvaucelii, L. chinensis, L. edulis and Sepioteuthis lessoniana; Sepiidae, Sepia aculeata and Sepiella inermis; Sepiolidae, Rossia pacifica, Manganese, iron, copper, zinc and strontium were detected from statoliths of all species examined. Among these trace elements, Sr is the highest in concentration. Variation of statoliths Sr concentration reflects taxonomic position and the habitat of specimens. In Ommastrephids and Gonatids, that have oceanic habitat, statoliths Sr concentration is relatively high whereas that of Loliginids and Sepiids, that have coastal habitat, is comparatively low. This fact supports our previous report on this subject. R. pacifica exceptionally shows high statoliths Sr concentration although this species inhabits in coastal water.

PIXE ANALYSIS OF TRACE ELEMENTS IN SQUID STATOLITHS: COMPARISON BETWEEN OMMASTREPHIDAE AND LOLIGINIDAE

Trace elements in the squid statoliths were analyzed by PIXE for following seven species distributing at offshore and inshore waters: Family Ommastrephidae, Ommastrephes bartrami, Todarodes pacificus; family Loliginidae, Loligo bleekeri, L. duvaucelii, L. chinensis, L. edulis and Sepioteuthis lessoniana. Statoliths of all seven species contained manganese, iron, capper, zinc and relatively high amount of strontium. Statoliths Sr concentration, an possible index for thermal history of the animal’s habitat, were the highest in O. bartrami that spends their entire life time at pelagic water, and secondly highest in T. pacificus living at the pelagic as well as the coastal waters. On the other hand, statoliths Sr concentration was relatively low in the five species of Loliginidae living at coastal waters, with following order: L. edulis >S. lessoniana >L. duvaucelii >L. bleekeri >L. chinensis. These observations may indicate that quantity of the statoliths trace elements are species specific in squids, thus would be a possible “key” to reconsidering about taxonomy and distribution in squid.

PRELIMINARY REPORT ON THE PIXE ANALYSIS OF THE SQUID STATOLITHS

Micro trace elements in the squid statolith, a calcareous stone which acts as a balancer and hearing, was analyzed with Particle Induced X-ray Emission (PIXE) for the Japanese common squid for the first time. Calcium is the main component of the squid statoliths, which means that squid statolith is the pure calcified structure similar to the fish otolith. Beside Ca, Sr was detected with strong dosage, and some other elements as Mn, Fe, Cu, Zn and As were also detected. Possible assumption of intake of microelemts to the statoliths and the suitability of PIXE for statoliths analysis are discussed.

TRACE ELEMENTS IN CEPHALOPOD CALCIFIED TISSUE: CUTTLEBONE AS A POSSIBLE TRACER FOR LIFE HISTORICAL EVENTS OF CUTTLEFISH

Trace elements in a cuttlebone, a buoyant calcified tissue developing simultaneously with the individual growth, of an adult giant cuttlefish originating from the water of Ishigaki Island were measured by PIXE to examine the ontogenetic change of the element concentration. Beside calcium (major element), iron, zinc, manganese, copper, bromine and relatively large amounts of strontium were detected in the cuttlebone. Strontium concentration varied with position along the cuttlebone: it was high near the spine (the portion that deposited at the paralarval stage), then showed some variations at the middle portion of the cuttlebone (the portion that deposited from young stage to sub-adult stage) and became the highest near the locus (the portion that deposited near the catch date, i.e., adult stage). This variation was compared to migration of this species between inshore and offshore waters.