Abstract
Seasonal occurrence, diel vertical migration (DVM), biomass (dry weight, carbon and nitrogen contents), growth and behavior of the two phytal-dwelling harpacticoid copepods, Ambunguipes rufocincta and Eudactylops spectabilis, were investigated using field samplings and laboratory experiments. The field samplings were conducted at a subtidal station (St. M; ca. 6.5 m depth) in Tanabe Bay, Japan from March 1999 to January 2000. The results from the field revealed that the two species performed DVM between the water column and macroalgal beds of Colpomenia sin- uosa (brown algae), and the seasonal occurrence of the two species at St. M were almost identical to that of C. sinuosa, which bloomed only between December and May. The carbon/nitrogen ratios of A. rufocincta (5.00� 0.60) and E. spectabilis (3.95� 0.66) differed, probably due to the differences in their foods. Laboratory incubation showed that E. spectabilis needed both C. sinuosa and sediments as food for growth, whereas A. rufocincta that was fed only with the macroalgae was able to grow to maturity. Our results suggested that their DVM behaviors of both species were related to the dispersal of copepodids and adults, because 1) the nauplii grew on C. sinuosa, 2) their main food items were C. sinuosa and sediments, and 3) mating might not be the main purpose of the DVM since females with egg sacs emerged into the water column. Moreover, in later field investigations during summer, refuge populations of A. rufocincta were collected from the seagrass Halophila ovalis in an area shallower than St. M, indicating that A. rufocincta might sustain its population by moving to different habitats though the DVM behavior and changing food items from C. sinuosa to H. ovalis during summer. Therefore, at least for A. rufocincta, the DVM behavior might be indispensable in their life strat- egy for sustaining their population year round.
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