Molting and mortality depend on age and stage in naupliar Calanus pacificus: triplication for development time of field cohorts

Abstract

Molting success and survivorship increased during naupliar development in the marine calanoid copepod Calanus pacificus studied in the laboratory. However, both rates decreased with age within each instar Simulations of the development of different naupliar stage I11 (NIII) age-groups suggest that mortality can shorten estimated cohort development times below the minimum possible in individual nauplii. The magnitude of this reduction depends strongly on differences in initial mortality rate among instars. The suggestion that copepod generation times in the field are independent of food availability can be reconciled with the well-established relationship between stage durations and food concentration if a distinction is made between individual and cohort development rates. Individual development rates decrease at low food levels, but with the death of a sufficiently large fraction of slowdeveloping individuals, cohort development rates may remain maximal.

Medium-term exposure of the North Atlantic copepod <i>Calanus finmarchicus</i> (Gunnerus, 1770) to CO<sub>2</sub>-acidified seawater: effects on survival and development

“…By comparison, stage distribution was not significantly affected by long-term exposure to 2300 ppm CO 2 in a multiple generation study on A. tsuensis (Kurihara and Ishimatsu 2008). Retardation in the development may have consequences for the survival since a delayed development can lead to animals staying in more vulnerable stages for longer periods (Lopez, 1996). The reduction in development rate observed for C. finmarchicus in the present study could be related to extra energetic costs associated with the induction of compensatory mechanisms in an effort to maintain a normal internal environment.…”

Growth of marine planktonic copepods: Global rates and patterns in relation to chlorophyll a, temperature, and body weight

“…Development rates in the field at 15ЊC are on average 88% of those at food saturation; the fact that this is closer to food saturation than the juvenile growth rates leads us to suggest that development rates overrepresent faster growing individuals. This may be a result of greater survival of fast-growing individuals (Lopez 1991) and/or simply a consequence of bias in how we measure development (Carlotti and Nival 1991;Hirst and Sheader 1997).…”

“…At the level of an individual juvenile, not only does food limitation act to reduce growth, but under severe limitation it may also control whether individuals survive or not. Juveniles that do not gain a sufficient quantity of weight between molts (i.e., within a relatively strictly predetermined period) do not survive (Lopez 1991; see concepts in Carlotti and Sciandra 1989). By contrast, adults need sufficient ration to meet metabolic demands or they can live off food reserves, but they do not need to produce eggs to survive.…”

“…Although in some instances no correlations between growth/ fecundity of copepods and Chl a concentration have been found, significant positive relationships have been reported in a diverse range of species and environments. These significant relationships include polar (Hirche and Bohrer 1987;Lopez et al 1993;Shreeve et al 2002), temperate (Durbin et al 1983;Kiørboe and Nielsen 1994), and tropical waters (Hopcroft and Roff 1998a;Hopcroft et al 1998), and from shallow estuaries/lagoons (Landry 1978;Ambler 1986;Beckman and Peterson 1986) to upwelling (Peterson and Bellantoni 1987;Hutchings et al 1995;Richardson and Verheye 1998) and oligotrophic open ocean regions (Calbet and Agustí 1999). Chl a is a general indicator of the trophic condition of an ecosystem, albeit an imperfect index of the food used in growth and fecundity.…”

“…Postembryonic development times can be biased toward the fastest growing (least food limited) animals as a result of methodological bias (Carlotti and Nival 1991;Hirst and Sheader 1997). Additionally, slower growing more food-limited individuals may never make it to adulthood (Lopez 1991) and so are not included in a measurement reliant only upon those individuals that do. Development times have to some extent biased our appreciation of the role food control plays in the natural environment.…”