Stable isotopes analysis to understand the feeding habits of mesopelagic fish larvae near the Kuroshio off southern Kyushu, Japan Weiping Mei, Yu Umezawa
W Mei
Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan,
[email protected]
1. Introduction
3. Stable isotope (SI) analysis
Most mesopelagic fishes vertically migrate every day, often following to similar migrations of their main food, zooplankton. Therefore feeding habits of mesopelagic fishes vary depending on the species and developmental stages, and are an important link between primary consumers and top predators in marine ecosystems1).
Sample processing: ① Sorting → ② Vacuum freeze-drying → ③ Delipidization → ④ Drying → ⑤ Weighting → ⑥Acidification → ⑦ Drying→ ⑧ Wrapping → ⑨ EA/IRMS analysis (δ13C
M.asperum larva
Ostracoda
Growing
N.tripes juvenile
Calocalanidae Diaphus kuroshio juvenile
Sapphirinidae
N.tripes larva
Candaciidae V.nimbaria juvenile
E.japonicus larva
Growing
Oncaeidae Paracalanidae Oithonidae Scomber larva & juvenile
V.nimbaria larva
Copepoda
Oikopleura
Zooplankton
Fig.1 Schematic diagram showing the feeding habits of the main species in Kuroshio-Oyashio region (by National Research Institute of Fisheries Science, Fisheries Research Agency, Japan)
In the Kuroshio region at the eastern ECS, 6 mesopelagic fish species (i.e. V.nimbaria, S.gracilis, Diaphus slender type, N.japonicas, M.asperum and L.ochotensis (hereafter Vn, Sg, Ds, Nj, Ma and Lo, respectively) were dominant (C. Sassa, unpublished data). The other abundant organisms having similar size to fish larvae, Sagittoidea and 2 zooplankton (Eucalinadae & Calanoida) were also analyzed as potential species competing with fish larvae, as well as their potential food sources, particulate organic matter (POM).
4.
δ13C
and
Area 1
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Gear: 0.33 mm Norpac net (LNP) Layer: 0-150m (vertically towing)
RV Yoko-maru (499 ton)
Kyushu
Area 1 Area 2
Area 4
Area 3
(a)
Eucalinadae-13C V.nimbaria-13C S.gracilis-13C Diaphus slender-13C L.ochotensis-13C Calanoida-13C M.asperum-13C N.japonicus-13C
25 20 15 10 5 Squared Euclidean distance
0
ARG larvae might compete for potential food sources with MYC larvae. STO larvae seemed to be similar feeding habits with zooplankton (Sagittoidea & Eucalinadae). Diaphus slender -15N
(b)
Calanoida-15N M.asperum-15N Eucalinadae-15N
S.gracilis-15N N.japonicus-15N
8
8
6 4 -23
6
-22
-21
-20
-19
-18
Area 3
4 -17 -23
10
8
8
6
6
-22
-21
-20
Sagittoidea-15N
25 -22
-21
-19
-18
4 -17 -23
M.asperum Diaphus slender N.japonicus
-20
-19
-18
-17
Area 4
12
10
δ15N
L.ochotensis-15N
20
15
10
5
0
Squared Euclidean distance Fig.4 Dendrogram of δ13C (a) and δ15N (b) using Ward linkage.
Higher overlapping of trophic niche was found between STO, MYC communities and two zooplankton, except for ARG and Sagittoidea. -22
-21
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δ13C L.ochotensis S.gracilis V.nimbaria
Sagittoidea Eucalinadae Calanoida
δ13C and δ15N values of each fish larvae species seemed to be separately categorized in the same category of the order: Stomiiformes (STO, include Vn and Sg), Myctophiformes (MYC, include Ds, Nj and Ma), and Argentiniformes (ARG, only include Lo). Acknowledgement. We sincerely thank Dr. C. Sassa (Seikai National Fisheries Research Institute, Fisheries Research Agency, Japan) for providing the larvae samples and many advices for the identification. References
Fig.2 Map of Kuroshio region showing the sampling stations in February 2014.
Sagittoidea-13C
V.nimbaria-15N
Fig.3 δ13C and δ15N distributions of fish larvae and zooplankton near Kuroshio off southern Kyushu, Japan.
Date: February 15-19, 2014
(STO: Vn & Sg); (MYC: Ds, Nj & Ma); (ARG: Lo).
10
Legend
Kyushu, Japan
Hierarchical cluster analysis was carried out on the average individual isotopic contents in each area by Ward’s methods, using squared Euclidean distances as a measure of similarity2).
Area 2
δ13C
Area: Kuroshio region off southern
East China Sea
compositions
12
10
4 -23
2. Sample collection
δ15N
Since δ15N of L.ochotensis larvae (ca. 9 per mil) were 2 or 3 ‰ higher than those of the other fish larvae, we concluded that L.ochotensis larvae are primarily zooplanktivorous. The other 5 fish larvae species were considered to be herbivorous or omnivorous, because they had a similarδ15N values (ca. 6-7 per mil) to that of zooplankton (ca. 5-8 per mil).
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The aim of this study is to understand the feeding habits of the dominant mesopelagic fish larvae through stable isotope analyses (δ13C and δ15N) near the Kuroshio off southern Kyushu, Japan.
δ15N):
SI analysis , -Whole frozen individual of fish larva (ca. 0.02-0.8 mg dry-wt) was used. -All samples were defatted and acidified before the analysis to remove lipids and inorganic carbon. -Isotope Ratio Mass Spectrometer (Delta V Advantage) with an Elemental Analyzer. -δ13C , δ15N = [Rsample/Rstandard-1]×1000, while R=13C/12C or 15N/14N.
δ15N
Euphausiacea
5. Cluster analysis
1) M Olivar, A Bernal, B Moli, et al. (2012) Deep-Sea Research I, 62: 53-69. 2) M Vega, R Pardo, E Barrado, et al. (1998) Water Research, 32: 3581-3592.
6. Conclusions l No significant difference in spatial distributions of fish larval isotopic compositions was observed near Kuroshio off Kyushu, Japan in Feb. 2014. l Based on SI (δ13C and δ15N) analysis, feeding habits of 6 mesopelagic dominant fish larvae species seemed to be separately categorized in the same category of the order: Stomiiformes (STO, include Vn and Sg), Myctophiformes (MYC, include Ds, Nj and Ma), and Argentiniformes (ARG, only include Lo). l Higher overlapping of trophic niche and potential food competition were found in fish larvae species that belong to the same order. l Larval L.ochotensis is considered to be zooplanktivorous, while the other 5 larval fish species are herbivorous or omnivorous.
