16:30 〜 16:45
[AOS17-05] Geographical variation of Sr/Ca in skipjack tuna (Katsuwonus peamis) collected from Northwestern Pacific Ocean
キーワード：カツオ、微量元素、北西太平洋、生態学、Sr/Ca
The trace element level of skipjack tuna (Katsuwonus pelamis, n=219) collected from various region of North Western Pacific Ocean (NPOW) was measured to analyze controlling factor of trace elements. The latitudinal migration of this species is useful to assess geographical difference from tropical equatorial region to Kuroshi-Oyashio transition region. Through the analysis of relative standard deviation, body size dependence, seasonal variation, regional variation, and elemental correlation, we could characterize homeostatic power of each element, and classified regional variation trend. There were several unique findings from this approach : (i) despite different biochemical function, major essential trace metals, e.g., Mn, Fe, Co, Cu, Zn, Mo, and Se, were mutually correlated, (ii) Zn shows poor correlation to the other essential metals, (iii) strong body size dependence is observed for Hg, Ca, Sr, Mo. (iv) simple mass balance model is useful to estimate muscular Hg level combining metabolic and behavioral data by archival tag, (v) the ratio of Sr/Ca plausibly reflect fine bone in muscle tissue shows strong linear correlation except for near equatorial ocean showing lower shift. Among these, the geographical variation of Sr/Ca in the bone of migratory fish has not been reported, thereby clarifying underlining mechanism is important.
The mean Sr/Ca of eight regions of NWPO is as following: 3.1 ± 0.4 (south of Kamchatka Peninsula, n=19), 3.8 ± 1.0 (off-Sanriku, n=25), 3.7 ± 0.8 (off-Izu, n=18), 3.5 ± 0.6 (off-Kochi, n=75), 4.1 ± 0.2 (near Guam, n=9), 3.3 ± 0.6 (East China Sea, n=55), 3.2 ± 0.6 (Japan sea, n=9), 7.5 ± 1.5 (equatorial region, n=8). The Sr/Ca in equatorial region is significantly higher than the other regions (p < 0.01). In the seawater, the level of these elements is constant with Sr/Ca ratio being 8.4 to 8.6 mmol/mol (Villiers ,1999). Considering reported distribution coefficient of Sr into Ca [Kd = (Sr/Ca)solid/(Sr/Ca)solution] which is insensitive to the pH is 0.27, expected Sr/Ca in bone equilibrated with seawater is 2.16 (Fujino, 1975). This indicated that Sr/Ca in bone of skipjack tuna is hard to explain by precipitation from seawater, particularly equatorial region. Unlike otholith, bone material likely affected by dietary intake. Dominant calcifying planktonic organism is coccolithophorid and foraminifera. The former forms calcite with Sr/Ca being 2.0 to 2.4 mmol/mol (Stoll and Schrag, 2000), while latter form aragonite with the mode value of Sr/Ca being 15 mmol/mol (Graham et al., 1982). Hence, preferential feeding of aragonite is a possible mechanism of high Sr/Ca in equatorial region. The other possible Sr rich diet is acantharea (radiorarean protozoa) which has the unique SrSO4 shell. This species mainly inhabit from mid-latitudes to the tropical, and it is known that their abundance increases relatively in oligotrophic waters. Although further approach is needed to distinguish these contribution, biomonitoring of migratory species can be useful tool of regional ecological structure in ocean.
The mean Sr/Ca of eight regions of NWPO is as following: 3.1 ± 0.4 (south of Kamchatka Peninsula, n=19), 3.8 ± 1.0 (off-Sanriku, n=25), 3.7 ± 0.8 (off-Izu, n=18), 3.5 ± 0.6 (off-Kochi, n=75), 4.1 ± 0.2 (near Guam, n=9), 3.3 ± 0.6 (East China Sea, n=55), 3.2 ± 0.6 (Japan sea, n=9), 7.5 ± 1.5 (equatorial region, n=8). The Sr/Ca in equatorial region is significantly higher than the other regions (p < 0.01). In the seawater, the level of these elements is constant with Sr/Ca ratio being 8.4 to 8.6 mmol/mol (Villiers ,1999). Considering reported distribution coefficient of Sr into Ca [Kd = (Sr/Ca)solid/(Sr/Ca)solution] which is insensitive to the pH is 0.27, expected Sr/Ca in bone equilibrated with seawater is 2.16 (Fujino, 1975). This indicated that Sr/Ca in bone of skipjack tuna is hard to explain by precipitation from seawater, particularly equatorial region. Unlike otholith, bone material likely affected by dietary intake. Dominant calcifying planktonic organism is coccolithophorid and foraminifera. The former forms calcite with Sr/Ca being 2.0 to 2.4 mmol/mol (Stoll and Schrag, 2000), while latter form aragonite with the mode value of Sr/Ca being 15 mmol/mol (Graham et al., 1982). Hence, preferential feeding of aragonite is a possible mechanism of high Sr/Ca in equatorial region. The other possible Sr rich diet is acantharea (radiorarean protozoa) which has the unique SrSO4 shell. This species mainly inhabit from mid-latitudes to the tropical, and it is known that their abundance increases relatively in oligotrophic waters. Although further approach is needed to distinguish these contribution, biomonitoring of migratory species can be useful tool of regional ecological structure in ocean.