Reproductive traits and population dynamics of benthic invertebrates indicate episodic recruitment patterns across an Arctic polar front

Abstract

Climate-induced changes in the ocean and sea ice environment of the Arctic are beginning to generate major and rapid changes in Arctic ecosystems, but the effects of directional forcing on the persistence and distribution of species remain poorly understood. Here, we examine the reproductive traits and population dynamics of the bivalve Astarte crenata and sea star Ctenodiscus crispatus across a north-south transect that intersects the polar front in the Barents Sea. Both species present large oocytes indicative of short pelagic or direct development that do not differ in size-frequency between 74.5 and 81.3º latitude. However, despite gametogenic maturity, we found low frequencies of certain size classes within populations that may indicate periodic recruitment failure. We suggest that recruitment of A. crenata could occur periodically when conditions are favorable, while populations of C. crispatus are characterized by episodic recruitment failures. Pyloric caeca indices in C. crispatus show that food uptake is greatest at, and north of, the polar front, providing credence to the view that interannual variations in the quantity and quality of primary production and its flux to the seafloor, linked to the variable extent and thickness of sea ice, are likely to be strong determinants of physiological fitness. Our findings provide evidence that the distribution and long-term survival of species is not only a simple function of adaptive capacity to specific environmental changes, but will also be contingent on the frequency and occurrence of years where environmental conditions support reproduction and settlement.

Keywords: functional biogeography; gametogenesis; interannual variability; life history; reproductive plasticity.

FIGURE 1

Transverse histology sections of Astarte crenata from the Barents Sea. (a) Composite image from a 25.36‐mm shell length individual from station B16 showing gonadal alveoli and digestive diverticula; (b) oocyte development in a 21.90‐mm shell length individual from station B16; (c) high density of oocytes in a 30.1‐mm shell length individual; (d) gelatinous mucous layer surrounding mature previtellogenic oocytes. dg, digestive diverticula; ga, gonadal alveoli; arrows indicate pedunculated oocytes

FIGURE 2

Astarte crenata oocyte size–frequency histograms. (a) oocyte size–frequency from station B13, south of the polar front; (b)oocyte size–frequency from station B16, north of the polar front

FIGURE 3

Ctenodiscus crispatus oocyte size–frequency histograms. (a) oocyte size–frequency from station B13, south of the polar front; (b) oocyte size–frequency from station B14, approximate location of the polar front; (c) oocyte size–frequency from station B16, north of the polar front

FIGURE 4

Histology sections of the dissected gonad from Ctenodiscus crispatus from the Barents Sea. (a) Small oocytes developing around large vitellogenic oocytes; (b) composite image showing an overview of a complete section of gonad showing narrow finger‐like structure and oocytes of different developmental stage; (c) vitellogenic oocyte showing signs of atresia and cell wall deterioration

FIGURE 5

Gonad and pyloric caeca index of Ctenodiscus crispatus from the Barents Sea. (a) Gonad index of C. crispatus based on wet mass of dissected gonad; (b) pyloric caeca index of C. crispatus based on wet mass of dissected pyloric caeca

FIGURE 6

Shell length–size–frequencies of Astarte crenata in the Barents Sea. (a) Shell length–size–frequency at station B13, south of the polar front; (b) shell length–size–frequency at station B16, north of the polar front; (c) Gaussian kernal density estimate of the shell length–frequency distributions at stations B13 and B16

FIGURE 7

Arm length–size–frequencies of Ctenodiscus crispatus from stations across a south–north transect in the Barents Sea. (a) Arm length–frequency from station B13, south of the polar front; (b) arm length–frequency from station B14, approximate location of the polar front; (c) arm length–frequency from station B16, north of the polar front; (d) Gaussian kernal density estimate of the shell length–frequency distributions at stations B13 and B16