Reproductive and developmental characteristics of three mesopelagic Paraeuchaeta species (Copepoda: Calanoida) in the Oyashio region, western subarctic Pacific Ocean
2002
Yamaguchi, A. (Hokkaido Univ., Sapporo (Japan)) | Ikeda, T.
Reproductive parameters (egg diameter, brood size) and developmental changes in prosome length (PL), wet weight (WW), dry weight (DW), ash-free dry weight (AFDW) of the three dominant Paraeuchaeta species (P. elongata, P. birostrata, P. nibrd) in the meso- and bathypelagic zone of the Oyashio region were investigated. Among the three copepods, P. elongata were characterized by carrying smaller-sized eggs and larger brood size (mean: 26.2 eggs/female) as compared with P. birostrata and P. rubra which had larger-sized eggs but smaller brood sizes (mean : 7.3-8.5 eggs/female). All relationships between PL and WW, DW, AFDW for copepodid stages of the three species fitted an allometric equation (Y = a / X sup b ) very well (r**2=0.91-0.99), and the exponent b values varied species-specifically (3.16-3.25 for P. elongata, 2.88-2.93 for P. birostrata, 2.50-2.93 for P. rubra). Between-stage increments for copepodid stages of the three species were identical in terms of PL (10-50%), but those expressed by WW, DW, and AFDW showed a marked increment peak (300-400%) during mid-copepodid stages in P. elongata only (<200% in P. birostrata and P. rubra). Within the species, molt increment in body mass decreased with increasing depth. Through all developmental stages (eggs, nauplii, and copepodids) patterns of change in water contents and organic matter in the body were similar among the three species; the lower water content yet higher organic matter during early developmental stages reflecting the their large accumulation of lipids in the body, and its progressive utilization. The present results are compared with those of other euchaetid copepods in the other regions and discussed in light of possible depth-related food availability in the meso- and bathypelagic realm.
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