Ova production by hydromedusae from the NE Pacific

Abstract

Gonads of hydromedusae had a dry wt of ∼18° of wet wt, with carbon and nitrogen compos ition equalling ∼40 and 10° of dry wt, respectively. These values are ∼4 times higher than for whole specimens. Gonads of mature medusae represented 2–15° of total wet wt (10–50° of total dry wt). For Phialidium gregarium (the most numerous hydromedusa in surface waters of Saanich Inlet, BC), gonads varied in size seasonally and were largest in May when food was most abundant and when daily rations were maximum. Diameters of ova ranged from 70 to 200 μm; estimated dry wts equalled 0.03–0.8 μg and estimated carbon weights were 0.01–0.3 μg. Medusae released up to > 10 000 ova/female/day. This rep resented 0.1–4° of total dry wt/day (1–16° of carbon). Egg production was dependent on nutritional state and on female biomass; ova size, on the other hand, was independent of female biomass both within and among species. For the hydromedusae in Saanich Inlet, carbon flux of ova was estimated to equal only about 50° of metabolic carbon losses because reproductive individuals represented only a small part of the total hydromedusa population.