Synchronization in the molting and spawning activity of northern krill (Meganyctiphanes norvegica) and its effect on recruitment

Abstract

The molting, spawning, and recruitment of northern krill (Meganyctiphanes norvegica) were analyzed over an annual cycle (1999)(2000) in the Clyde Sea (west coast of Scotland). Results supported the hypothesis of a functional relationship between egg production and molt development for the duration of the reproductive season (March to August), with one reproductive cycle being made up of two molt cycles. Females remained in reproductive condition throughout the reproductive season, and the timing of their spawning and molting was synchronized at the population level throughout this period. A semiempirical model predicted that the krill population produced an egg pulse every 20 to 26 d (depending on temperature), and three cohorts were evident in net samples taken later in the year. The likely date on which the first cohort was spawned was around 26 d after the main phytoplankton bloom, suggesting that the bloom triggered egg development in all adult females. Such a synchronized spawning period was observed directly in adult females 26 d after a bloom in March 2000. A total of three cohorts over the 6-month reproductive season is less than the maximum of seven that would be possible if spawning occurred at a periodicity of between 20 and 26 d, suggesting that larval recruitment was not always successful. Analysis showed that successful recruitment was only achieved when chlorophyll a levels were adequate during both the period of egg maturation in the ovary and the subsequent development of larvae, especially the furcilia stages.

On the timing of moulting processes in reproductively active Northern krill Meganyctiphanes norvegica

“…A multi opening and closing net with environmental sensing system (MOCNESS, 1 m 2 net opening, 2 mm mesh, Wiebe et al 1985) was deployed over the course of the day and night during each of the campaigns. Further details on the sampling protocols can be found in Tarling and Cuzin-Roudy (2003). In the present study, we pooled all of the net catches within a campaign to obtain an estimate of the relative frequency of moulting individuals every other month over an annual cycle (June, August, October, December 1999 andJanuary, March, May 2000).…”

“…Moreover, there is a close coordination with vertical migration behaviour, in that moulting occurs in the deep and spawning in the top layer of the water column (Tarling et al 1999). Mass moulting and spawning peaks have been observed, indicating that these processes can be synchronised (Hamner et al 1983;Buchholz 1985;Tarling and Cuzin-Roudy 2003). Local plankton blooms may act as a cue for initiating investment in ovarian tissue and so may entrain moult and spawn cycles for the rest of the productive season (Tarling and Cuzin-Roudy 2003).…”

Life in the sea of plenty: Seasonal and regional comparison of physiological performance of Euphausia hanseni in the northern Benguela upwelling system

“…Studies on E. superba indicated that food availability affects moult frequency (Buchholz and Buchholz, 1989) and that higher temperatures decrease the intermoult period (Buchholz, 2003). Since Table 5 Distribution (%) of moult phases of E. hanseni at different sampling stations (RPt, RPt-N and Kun-S) during austral winter 2010. favourable trophic conditions promote synchronized moult activities (Buchholz et al, 1996) and reproduction (Tarling and Cuzin-Roudy, 2003), high moult or reproductive activity may be considered indicative of favourable food conditions prior to sampling. Accordingly, it is assumed that animals at station RPt-N were exposed to unfavourable environmental conditions, e.g., trapped in nutrient-poor eddies with low productivity (Gruber et al, 2011), leading to reduced oxygen consumption and lower O:N ratios.…”

“…Thus, a "waiting" stage, where females bear fully developed oocytes yet wait to spawn, may allow them to respond quickly to improving trophic conditions and could well evolve in poly-pulsed systems with perennial upwelling events. Ideally, vitellogenesis should only occur when trophic conditions are optimal in order to promote strong non-feeding stages of larvae, due to the optimal development and condition of eggs (Tarling and Cuzin-Roudy, 2003). The quality and quantity of food influence growth rates in feeding stages of krill larvae and accordingly, the onset of upwelling would be a critical period for this developmental stage (Siegel, 2000).…”

“…Accordingly, euphausiids adapt their reproductive cycles to local feeding conditions (Tarling and Cuzin-Roudy, 2003); both egg production and length of the reproductive period are controlled by temperature and trophic conditions (Cuzin-Roudy and Buchholz, 1999). Furthermore, the recruitment success of krill species depends both on adequate condition of the females prior to spawning and favourable trophic conditions during larval development (Tarling and Cuzin-Roudy, 2003).…”