@misc{oai:ir.soken.ac.jp:00000824,
 author = {高橋, 邦夫 and タカハシ, クニオ and TAKAHASHI, Kunio},
 month = {2016-02-17},
 note = {The dominant Antarctic herbivorous copepod Calanoides acutus accumulates large quantities of lipids as an energy reserve during the productive season, and migrates to deeper waters to enter a state of diapause during winter month. Lipid storage is a major adaptation to the extreme seasonality of phytoplankton growth in the polar regions. Therefore, storage lipid is an important factor affecting their biological activity. However, there have only been sporadic studies on copepod lipid storage and life cycles in Antarctic waters. Taking the opportunity of multi-ship observations in the Indian sector of the Antarctic Ocean, the objectives in the present study were to examine both the preserved samples by a net sampling, and physiological characteristics of C. acutus over the whole summer, and to develop hypotheses of the species life cycle strategy. This is the first time that such time serial observations over the whole summer, combined with a comprehensive approach to the species life cycle from both preserved samples and physiological characteristics have been conducted.<br />　　　Copepods were collected on RSV Aurora Australis in November 2001, Hakuho Maru in January 2002 and RV Tangaroa in February 2002 along a transect on 140°E between 61 and 66.25°S using a twin NORPAC standard net. Closed 2-l jars served as cod ends to avoid damage to the specimens.<br /> 　　　Until recently it had been accepted that the life span of Calanoides acutus was one-year, and the overwintering stages are predominantly copepodite V （CV） stage. They molt to adulthood and mature at depth, and fertilized females ascend to the surface waters for spawning. However, from the observation of this study, CV stages were dominant in the surface in November ranging from 10 to 40％ of the total population. In previous studies, the development rate of C. acutus was reported to be around 15 to 30 days per copepodite stage. Therefore, CV stages at the surface in November had not developed from eggs in that spring, but had overwintered, and had not been able to mature at depth prior to ascending to the surface. Therefore, they belong to a second-year group.<br />　　　In addition, from the results of the dry weight and lipid weight, the dry weight of Calanoides acutus CV in January was double that of those of November, while the lipid weight did not change dramatically （34 and 40％）. Thus, CV stages after overwintering had preferred to store lipid as energy reserves, and maintained high lipid contents during summer months, with surplus energy probably used for growth. There was also high variation in the amount of lipid storage between individuals in February. The existence of CV stages in February that had developed from eggs in that spring was reasonable based on the previous reports of development rate of C. acutus （15 to 30 days/copepodite stage）. It is difficult to consider that CV stages with high lipid contents in November and January had used storage lipid at the surface prior to previous the winter. Therefore, they are probably new generation developed from eggs in the current spring.<br />　　　In this way, as a result of evaluation from both preserved samples and physiological characteristics, Calanoides acutus could probably have a life cycle of more than two years. A first-year group of lipid-poor individuals developed from eggs in the current spring co-existed in autumn with a second-year group, lipid-rich individuals with high lipid contents, evident in November, that had already overwintered once as a CV stage.<br />　　　The phytoplankton bloom at the sea-ice edge is often discussed as a factor affecting distribution, growth and reproduction of copepods inhabiting seasonal ice zone. The spatial variability of stage composition in November was also observed in this study associated with ice-edge retreat. Spring reproduction of Calanoides acutus in the seasonal ice zone coupled with primary production associated with the ice-edge, allowed suitable growth from eggs to early copepodite stage. In this study, only CV stage and adult female were found at the southern（continent） part of the transect in November, and young CI to CIII stages that had developed from eggs in that spring, were found towards the north. Therefore, the spawning period was late in the southern end, due to the time lag of the retreating ice-edge and phytoplankton bloom development in this study site. The results of stage composition in January confirmed that the timing of the life cycle of C. acutus was late in the southern region due to the time lag in spawning.<br />　　　Copepods in the southern end of the transect, experienced a short growth period due to the time lag of the retreat of sea-ice. They had a relatively high lipid weight, high weight of wax ester, high proportion of long-chain fatty acids （20 and 22）, a lipid-dominated metabolism and a low efficiency of lipid storage. On the other hand, relatively low lipid weight, low weight of wax ester, high proportion of short-chain fatty acids （16 and 18）, a protein-dominated metabolism and a high efficiency of lipid storage were observed in CV stage at the northern end with a long growth period. These results suggested that Calanoides acutus CV stage in southern regions had completed preparation to overwinter as first-year CV stages compared to those of the northern regions. The proportion of the second-year CV stage in the south in February was higher than in the proportions north. Thus, in the southern end, individuals with insufficient time to grow to lipid-rich CV stage in their first summer could probably adopt the two year life cycle strategy and overwinter. In other words, sea-ice is one of the controlling factors affecting the growth period, and determining the life span of Calanoides acutus., 総研大甲第762号},
 title = {Life cycle strategy of herbivorous copepod Calanoides acutus (Crustacea, Calanoida) in the Antarctic Ocean},
 year = {}
}