Fertilisation and larval development in an Antarctic bivalve, Laternula elliptica, under reduced pH and elevated temperatures

Elevated temperatures associated with ocean warming and acidification can influence development and, ultimately, success of larval molluscs. The effect of projected oceanic changes on fertilisation and larval development in an Antarctic bivalve, Laternula elliptica, was investigated through successive larval stages at ambient temperature and pH conditions (-1.6°C and pH 7.98) and conditions representative of projections through to 2100 (-0.5°C to +0.4°C and pH 7.80 to pH 7.65). Where significant effects were detected, increased temperature had a consistently positive influence on larval development, regardless of pH level, while effects of reduced pH varied with larval stage and incubation temperature. Fertilisation was high and largely independent of stressors, with no loss of gamete viability. Mortality was unaffected at all development stages under experimental conditions. Elevated temperatures reduced occurrences of abnormalities in D-larvae and accelerated larval development through late veliger and D-larval stages, with D-larvae occurring 5 d sooner at 0.4°C compared to ambient temperature. Reduced pH did not affect occurrences of abnormalities in larvae, but it slowed the development of calcifying stages. More work is required to investigate the effects of developmental delays of the magnitude seen here in order to better determine the ecological relevance of these changes on longer term larval and juvenile success

High resolution microscopy reveals significant impacts of ocean acidification and warming on larval shell development in Laternula elliptica.

Environmental stressors impact marine larval growth rates, quality and sizes. Larvae of the Antarctic bivalve, Laternula elliptica, were raised to the D-larvae stage under temperature and pH conditions representing ambient and end of century projections (-1.6°C to +0.4°C and pH 7.98 to 7.65). Previous observations using light microscopy suggested pH had no influence on larval abnormalities in this species. Detailed analysis of the shell using SEM showed that reduced pH is in fact a major stressor during development for this species, producing D-larvae with abnormal shapes, deformed shell edges and irregular hinges, cracked shell surfaces and even uncalcified larvae. Additionally, reduced pH increased pitting and cracking on shell surfaces. Thus, apparently normal larvae may be compromised at the ultrastructural level and these larvae would be in poor condition at settlement, reducing juvenile recruitment and overall survival. Elevated temperatures increased prodissoconch II sizes. However, the overall impacts on larval shell quality and integrity with concurrent ocean acidification would likely overshadow any beneficial results from warmer temperatures, limiting populations of this prevalent Antarctic species

Effects of reduced pH and elevated temperatures on shell sizes.

<p>a) Shell height and b) shell length on prodissoconch I (PI) and c) on growth of prodissoconch II. Letters indicate significance as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0175706#pone.0175706.g002" target="_blank">Fig 2</a>. The temperature/pH combination of 0.4°C/7.80 was not used. NS = no significant differences between treatments, n = 3. Error bars are standard error.</p

SEM images of D-larvae from various experimental treatments.

<p>(a) normally developed D-larva from the control treatment (pH 7.98 and -1.6°C, x370), and (b-e) damaged and/or malformed larvae from reduced pH (7.65) treatments at various temperatures (d: -1.6°C, x430, b: -0.5°C, x450, c and e: 0.4°C, x400), (f) extremely malformed (left) and uncalcified (right) larvae from pH 7.65, -1.6°C (x450). PI: prodissoconch I; PII: prodissoconch II. All scale bars are 50 μm.</p

Seawater conditions for all experimental treatments.

<p>Seawater conditions for all experimental treatments.</p

SEM image (x370) of the shell of a <i>L</i>. <i>elliptica</i> D-shape larva.

<p>Showing prodissoconch I (PI), the boundary (B) between PI and prodissoconch II (PII) and the narrow band of PII. H and L indicate measurements of shell height and length, respectively, of PI. Scale bar as indicated.</p

Summary table of 2-way ANOVA.

<p>Summary table of 2-way ANOVA.</p