Reproductive biology, embryo and early larval morphology, and development rates of krill (Euphausia lamelligera and Euphausia distinguenda), endemic to the Eastern Tropical Pacific

Abstract

The reproductive biology and early life phases of tropical broadcast spawning krill are largely unknown worldwide. This investigation provides the first published data on the reproductive period, brood size, embryo and nauplius-to-metanauplius morphology, biometry, development, and hatching success rates of two of the smallest krill species known (Euphausia lamelligera, <11 mm and E. distinguenda, <14.5 mm total length), endemic to the Eastern Tropical Pacific. Embryos were obtained from gravid females collected on the Jalisco continental shelf (Mexico) every 2 wk from July 2011 to June 2012, and incubated under laboratory conditions. Both species spawned throughout the year (with higher brood sizes between Jan and Jun), showing similar mean interspecific brood sizes: E. lamelligera, 34 eggs female −1 (range: 4−95) and E. distinguenda, 36 eggs female −1 (range: 14−72). E. distinguenda spawned larger eggs (chorion 0.700, embryo 0.329 mean diameters, perivitelline space [PVS] 0.185 mm) than E. lamelligera (chorion 0.405, embryo 0.291, PVS 0.057 mm). Both species had high hatching success (> 66%) with the shortest hatching times (9 to 14 h) known so far for any species of the Order Euphausiacea. E. distinguenda was significantly larger than E. lamelligera at each early larval stage. A pseudometanauplius stage (molting between nauplius and metanauplius stages), previously thought to be an exclusive stage of sac-spawning species, was observed for both broadcast spawning species. Our results support the hypothesis that both species exhibit a continuous but seasonally variant spawning reproductive strategy associated with female body size and seasonal coastal upwelling dynamics, and show brood sizes within the low range of variability known for temperate krill species.

Embryo and early larval stages of the Humboldt Current krill Euphausia mucronata (Crustacea: Euphausiacea)

“…, ; Ambriz‐Arreola et al. ). However, the incubated females of E. mucronata were from only one sampling station and sampling date; therefore, considerably more research must be done to identify and distinguish eggs of E. mucronata from those of the other 12 broadcast‐spawning species that inhabit the HCS (Riquelme‐Bugueño et al.…”

“…, ; Ambriz‐Arreola et al. ). Embryos of E. mucronata showed a high degree of variability in chorion and embryo diameters, as well as in PVS sizes (Table ), which was likely due to the low number of individuals incubated in our study and the genetic and nutritional status of the females collected.…”

“…This was likely due to their relatively rapid development, which decreased the probability of observing them (the MC, blastula, and gastrula stages were not observed) (Gómez‐Gutiérrez , ; Ambriz‐Arreola et al. ). However, the biometry of those embryonic stages is well known from other krill species of the genus Euphausia and can be interpolated from biometric measurements of SC and eLB stages observed in embryos of E. mucronata .…”

“…), and Euphausia lamelligera Hansen 1911 and Euphausia distinguenda Hansen 1911 (Ambriz‐Arreola et al. ). Examples of description of embryonic and early larvae development of sac‐spawning species are Nematoscelis difficilis Hansen 1911 (Komaki ; Gómez‐Gutiérrez ) and Nyctiphanes simplex Hansen 1911 (Gómez‐Gutiérrez & Robinson ; Montuy‐Gómez et al.…”

“…; Ambriz‐Arreola et al. ) and the larval pseudo‐metanauplius to furcilia stages of 63 species (73%) have been measured and reported, but the early larval stages (nauplius and metanauplius) of only 34 species are known (~40%) (Brinton et al. ; Ambriz‐Arreola et al.…”