Reassessment of the life cycle of the pteropod Limacina helicina from a high resolution interannual time series in the temperate North Pacific

Abstract

Limacina helicina is the dominant pelagic gastropod mollusc species in temperate and polar ecosystems, where it contributes significantly to food webs and vertical flux. Currently, considerable uncertainty exists in the interpretation of L. helicina’s life cycle, hindering our understanding of its potential responses to environmental change. Here, we present size-frequency data on L. helicina collected from three consecutive years (2008–2010) in a North Pacific temperate fjord. Two methods of length-frequency analysis were used to infer the growth of L. helicina, i.e. linking successive means extracted from finite-mixture distributions, and using the ELEFAN software to fit seasonally oscillating versions of the von Bertalanffy growth equation to the available length-frequency data. Against a background of continuous low level spawning between spring and autumn, both approaches identified two sets of major cohorts, i.e. (i) spring cohorts (G1) spawned in March/April by (ii) overwintering cohorts (G). G overwintered with minimal to low growth, before undergoing rapid growth the following spring and completing the cycle by spawning the G1 generation and disappearing from the population by May/June. Our findings are discussed in the context of L. helicina response to climate change.

Determining how biotic and abiotic variables affect the shell condition and parameters of <i>Heliconoides inflatus</i> pteropods from a sediment trap in the Cariaco Basin

“…Pteropods are protandric hermaphrodites, meaning they transition from juveniles to mature males to females during ontogeny (Lalli and Wells, 1978). Their lifespans are thought to be between 0.5 and 2 years (Gannefors et al, 2005;Hunt et al, 2008;Kobayashi, 1974;Wang et al, 2017;Wells, 1976a). Isotopic studies have found that pteropods calcify between 50 and 650 m depth (Fabry and Deuser, 1992;Juranek et al, 2003;Keul et al, 2017), suggesting they are exposed to a wide range of water chemistries during their diurnal migration.…”

“…Although net catches have the advantage of sampling pteropod populations at the time of collection, they only represent a snapshot in time. Pteropods have patchy distributions (Bednaršek et al, 2012a;Thibodeau and Steinberg, 2018;Wang et al, 2017), and therefore pteropod yields in net samples are highly variable. Sediment traps use a large, upward-facing cone to collect the flux of organic and inorganic particles that sink through the water column into collection cups containing preservative.…”

“…6b), which suggests there are no cohorts. Another low-latitude study found that H. inflatus collected off the coast of Barbados reproduced throughout the year (Wells, 1976a), although H. inflatus from off Bermuda in the Sargasso Sea have been shown to spawn in the spring (Almogi-Labin et al, 1988). Both van der Spoel (1967) and Janssen (2004) have described variability in the shape and position of the aperture tooth in H. inflatus, which could be attributed to intraspecific or interspecific variations.…”

Assessing annual variability in the shell thickness of the pteropod <i>Heliconoides inflatus</i> in the Cariaco Basin using micro-CT scanning

“…Pteropods are protandric hermaphrodites, meaning they transition from juveniles, to mature males, to females during ontogeny (Lalli and Wells, 1978). Their lifespans are thought to be between 0.5 and 2 years (Gannefors et al, 2005;Hunt et al, 2008;Kobayashi, 1974;Wang et al, 2017;Wells, 1976a). Isotopic studies have found that pteropods calcify between 50 and 650 m depth (Fabry and Deuser, 1992;Juranek et al, 2003;Keul et al, 2017) suggesting that they are exposed to a wide range of water chemistries as they migrate through the water column diurnally.…”

“…Although net catches have the advantage of sampling pteropod populations at the time of collection, they only represent a snapshot in time. Pteropods have patchy distributions (Bednaršek et al, 2012a;Thibodeau and Steinberg, 2018;Wang et al, 2017), and therefore pteropod yields in net samples are highly variable. Sediment traps use a large, upward facing cone to collect the flux of organic and inorganic particles that sink though the water column into collection cups containing preservative.…”