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Ecological and physiological studies of euphausiids in the Oyashio region, western subarctic Pacific

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Please use this identifier to cite or link to this item:http://doi.org/10.14943/doctoral.k9079

Title: Ecological and physiological studies of euphausiids in the Oyashio region, western subarctic Pacific
Other Titles: 西部北太平洋親潮域におけるオキアミ類の生理・生態学的研究
Authors: Kim, Hye Seon1 Browse this author
Authors(alt): 金, 惠仙1
Issue Date: 26-Mar-2009
Abstract: (1) The present study was made to fill the gap of our knowledge about biological (early larval morphology), ecological (abundance, biomass, life cycle) and physiological characteristics (oxygen consumption, ammonia excretion, chemical composition of the body) of dominant euphausiids (Euphausia pacifica, Thysanoessa inspinata and T. longipes) in the Oyashio region as a basis to evaluate their trophic importance in the pelagic ecosystem of this region. (2) Brood size and egg hatchability of Thysanoessa inspinata and T. longipes were 76-142 eggs and 81-99%, and 136 eggs and 65%, respectively. In terms of morphology, eggs, Nauplius I, II and Metanauplius larvae of T. inspinata and T. longipes raised in the laboratory showed no marked differences between the two, excepting for the general sizes (T. inspinata < T. longipes). (3) Analysis of time series Bongo net samples (0-1000 m) over 2 years (August 2002 through August 2004) revealed that Euphausia pacifica was the most abundant (1,120 individuals m^[-2], or 832 mg C m^[-2]), followed by Thysanoessa inspinata (163 individuals m^[-2], or 144 mg C m^[-2]) and T. longipes (73 individuals m^[-2], or 75 mg C m^[-2]). E. pacifica spawn twice in a year (April - May and August), T. inspinata year-round (peak season: March - May), and T. longipes in spring (March - May). The maximum size of males and females found were 21 mm and 24 mm, respectively, for E. pacifica, 18 mm and 23 mm, respectively, for T. inspinata, and 27 mm and 31 mm, respectively, for T. longipes. The life spans of E. pacifica, T. inspinata and T. longipes were estimated to be 17-26 months, 17-19 months and 29-31 months, respectively. (4) During phytoplankton bloom season (9 March - 29 April 2007) where water temperatures ranged from 1.1 to 6.1℃ and chlorophyll a from 0.02 to 6.3 mg m^[-3], the abundance fluctuated from 41 to 1,040 individuals m^[-2] for Euphausia pacifica and from 50 to 186 individuals m^[-2] for Thysanoessa inspinata. Population of both species was composed of one large modal group (14-18 mm TL for E. pacifica, 17-18 mm TL for T. inspinata) often accompanied with one small modal group (<11 mm TL for both euphausiids). Tracing the progressive increase in the mean sizes of the large modal group, growth rates were estimated to be 0.082 mm day^[-1] for E. pacifica and 0.022 mm day^[-1] for T. inspinata. The difference in the growth rates between the two euphausiids is interpreted as species-specific differences in the allocation of energy ingested into reproduction and somatic growth. (5) Respiration and ammonia excretion rates were determined on Euphausia pacifica and Thysanoessa inspinata in March, April and December 2007 at in situ temperature (3.8-10.6℃). Respiration rate (R: μl O2 indiv.^[-1] h^[-1]) and excretion rate (E: μg NH4-N indiv.^[-1] h^[-1]) were expressed as a function of body dry mass (DM: mg): R = 1.440DM^0.788 and E = 0.006DM^1.273 for E. pacifica; R = 1.852DM^0.729 and E = 0.046DM^0.829 for T. inspinata (all in p < 0.01). The rates standardized to a body size of 1 mg DM (AMR) and at 10℃, the differences due to sex and season were not significant. In terms of respiration to ammonia excretion ratio (O : N ratio, by atoms), E. pacifica exhibited higher ratio (88) than T. inspinata (46), suggesting that the proportion of protein in metabolites was relatively less in the former than the latter. (6) Body chemical composition (water, ash, C, N) of Euphausia pacifica and Thysanoessa inspinata were analyzed in March, April and December 2007. The ranges of water content (% of WM), ash (% of DM), C (% of DM) and N (% of DM) were 76.0-77.7, 9.5-12.8, 32.8-36.3 and 9.2-9.5, respectively, for E. pacifica, and 75.4-78.2, 9.7-11.5, 35.2-37.1 and 9.5-10.0, respectively, for T. inspinata. C : N ratios were 3.6-3.9 for E. pacifica and 3.7 for T. inspinata. Differences in the composition due to species, sampling season and sex were not significant (p > 0.05). (7) Daily ingestion (I) by Euphausia pacifica and Thysanoessa inspinata populations in the Oyashio region during phytoplankton bloom (7-29 April 2007) was estimated as the sum of daily metabolism (R) and daily growth (G) assuming an assimilation efficiency to be 0.9 [I = (R+ G)/ 0.9]. R was calculated by combining data of size (BL) structure, BL-DM relationship and R-DM relationship and G was tracing the increment in modal BL and BL-DM relationship. Resultant R and G were expressed by C unit. Over the 22 days, daily I thus estimated ranged from 5.9 to 131.9 mg C m^[-2] day^[-1] for E. pacifica and from 7.7 to 25.1 mg C m^[-2] day^[-1] for T. inspinata, total of which attributed to 1.5-25.2% of primary production (mean 5.8%). (8) Daily ammonia-N regeneration by Euphausia pacifica and Thysanoessa inspinata populations was calculated during phytoplankton bloom (7-29 April 2007) by combining data of size (BL) structure, BL-DM relationship and E-DM relationship. Over the 22 days, daily N regeneration ranged from 0.10 to 2.32 mg N m^[-2] day^[-1] for E. pacifica and from 0.38 to 1.24 mg N m^[-2] day^[-1] for T. inspinata, total of which attributed to 0.33-2.94% of primary production (mean 0.84%). (9) Physiological and ecological characteristics of the euphausiids (Euphausia pacifica and Thysanoessa inspinata) in the Oyashio region are highlighted from the comparison with Neocalanus copepods in the same Oyashio region. Both euphausiids and Neocalanus copepods are similar in terms of primary herbivores, euphausiids are different from Neocalanus in that higher metabolic rates enabling active forage, less depending energy reserve and utilizing phytoplankton bloom for rapid somatic growth/reproduction (not lipid accumulation). In contrast, Neocalanus copepods are characterized by less active swimming (lower metabolic rates), large capacity of energy storage in the form of lipids, energy saving life history trait (diapauses) yet strong dependence on phytoplankton bloom for large accumulation of lipids in the body.
Conffering University: 北海道大学
Degree Report Number: 甲第9079号
Degree Level: 博士
Degree Discipline: 水産科学
Type: theses (doctoral)
URI: http://hdl.handle.net/2115/38346
Appears in Collections:学位論文 (Theses) > 博士 (水産科学)

Submitter: 金 惠仙

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