ECOLOGY OF PARATHEMISTO LIBELLULA AND P. PACIFICA (AMPHIPODA: HYPERIIDEA) IN ALASKAN COASTAL WATERS

• Main Author: Wing, Bruce L.
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 1976
• Subjects: Bering Sea; Chukchi Sea; Strong Peak; Chukchi; Alaska; Copepods
• Online Access: https://digitalcommons.uri.edu/oa_diss/1409; https://doi.org/10.23860/diss-wing-bruce-1976; https://digitalcommons.uri.edu/context/oa_diss/article/2424/viewcontent/diss_wing_bruce_1976.pdf

The planktonic amphipods Parathemisto libellula and P. pacifica coexist in coastal waters from southeastern Alaska (56° N) to the south-eastern Chukchi Sea (70° N). Observations on distribution, reproductive cycles, diets, metabolism, and starvation tolerance contribute to understanding this case of congeneric coexistence. Samples were collected monthly from September 1969 to October 1970 in southeastern Alaska, from May to September 1969 in the southeastern Bering Sea, and in September-October 1970 in the southeastern Chukchi Sea. Respiratory metabolism and starvation tolerance were studied in winter-caught amphipods from southeastern Alaska. Both species consistently occurred above 300 min southeastern Alaska. In the southeastern Bering Sea, their distributions were separate. With P. libellula restricted to an area where summer bottom temperatures were less than 8.0° C. The P. pacifica found in the Chukchi Sea were probably expatriates from the Bering Sea. In southeastern Alaska, P. libellula has a 1-year life cycle. Broods are released in early May. Juveniles initially live in the surface 50 m, but by late June (at a size of 10 mm) they migrate vertically. By late October they have a daytime depth of 200-300 m. Males mature in late winter at 19-21 mm and females at 21-25 mm. In southeastern Alaska, P. pacifica reproduces throughout the year with a strong peak in early May. Juveniles initially live in the surface 50 m. Adults and subadults migrate vertically to a daytime depth of 100-200 m. Summer growth is rapid, and maturity is attained in 6-8 weeks at a size of 4. 5-6. 5 mm. Generation time lengthens in winter to 8-12 weeks, and size at maturity increases to 6-0-7.0 mm. Diets of the two amphipods pods are similar. About half the food items were calanoid copepods, and 30% were compound-eyed crustaceans (primarily euphausiids and amphipods). Parathemisto pacifica were more cannibalistic than P. libellula. The temperature coefficient (Q10) for respiratory metabolism of P. libellula is 3-5 at temperatures below ...