Seasonal growth, molt, and egg production rates of Nyctiphanes simplex (Crustacea: Euphausiacea) juveniles and adults in the Gulf of California

Abstract

Seasonal distribution of biomass and somatic growth, molt, and egg production rates of Nyctiphanes simplex were estimated in the Gulf of California

First measurements of euphausiid growth rates in the northern Humboldt Current (23ºS)

“…Pooling all the males and females data from our experiment, mean GI was -0.83% (± 4.46 SD) and mean DGR was -0.02 mm d -1 (± 0.11 SD). All our measurements were comparable to those reported in other studies on krill growth rates (Shaw et al 2010, Gómez-Gutiérrez et al 2012. No significant differences of TL, GI and DGR were found between E. mucronata males and females (ANOVA, P > 0.05).…”

“…Hosie & Ritz (1989) also observed shrinkage in Nyctiphanes australis, with >70% of incubated individuals experimenting decreased body size, apparently because of poor food quality or lack of feeding in nature. Negative DGR has been attributed to krill populations under unfavorable environmental conditions, such as unusually high temperature (Marinovic & Mangel 1999) and limited food availability (Virtue et al 2010, Gómez-Gutiérrez et al 2012, or as an overwinter strategy (Ikeda & Dixon 1982, Daly 2004. However, experimental evidence suggests that negative growth is commonly observed in krill during their life cycle and occurring in any season of the year in polar (Tarling et al 2006), temperate (Marinovic & Mangel 1999, Shaw et al 2010, and subtropical ecosystems (Gómez-Gutiérrez et al 2012).…”

“…The jars were kept in darkness in a cold room at 11-12°C, which was the sea surface temperature recorded in situ with a portable temperature sensor (SevenGo, Mettler Toledo). Incubations lasted 48 h to avoid laboratory artifacts with food deprivation (Shaw et al 2006(Shaw et al , 2010Gómez-Gutiérrez et al 2012) and each incubated euphausiid was checked for molting at 12 h intervals. Males were identified by examining the presence of spermatophores or the petasma located in the first pair of abdominal appendages and females were identified by observing their thelycum or presence of spermatophores attached on their thelycum (Brinton et al 2000).…”

“…However, experimental evidence suggests that shrinking in krill occur throughout the year round in polar (Nicol 2000, Tarling et al 2006, temperate (Pinchuck & Hopcroft 2007, Feinberg et al 2007, Shaw et al 2010, Pond et al 2012, Riquelme-Bugueño et al 2016, and subtropical krill species (Gómez-Gutiérrez et al 2012). These studies, among others, provide evidence that: 1) growth in krill is not necessarily limited by food but in occasions caused by anomalous changes in temperatures (Marinovic & Mangel 1999), 2) growth is highly variable at intraspecific and interspecific levels and body growth rates in females is negative correlated with brood size and interbrood periods (Feinberg et al 2007), and 3) positive, zero and negative growth should occur in any krill species because this physiological process have been observed in species from distinct biogeographic affinities (Atkinson et al 2006, Tarling et al 2006, Shaw et al 2010, Gómez-Gutiérrez et al 2012, Pond et al 2012.…”

Histophagous ciliate Pseudocollinia brintoni and bacterial assemblage interaction with krill Nyctiphanes simplex. II. Host responses

“…brintoni infection causes a sharp decrease in total fatty acid concentrations and the proportion of fatty acids during the infection, mostly decreasing the docosahexaenoic:eicosapentaenoic (DHA:EPA) ratio. Rapid depletion of long-chain fatty acids is not likely to be associated with gonad development because the endopa rasitoid ciliate life span is shorter (< 3.5 d) than the Nyctiphanes simplex ovarian cycle (7−15 d; Gómez-Gutiérrez et al 2010b, 2012b, and infected females cannot spawn, being made sterile before their death. It may not be adaptive to infect lowbiomass larvae, juveniles, or immature adults because it does not provide enough energy to complete the Pseudocollinia life cycle.…”