Effect of ocean acidification and elevated temperature on growth of calcifying tubeworm shells (<i>Spirorbis spirorbis</i>): An <i>in-situ</i> benthocosm approach

Abstract

<p><strong>Abstract.</strong> The calcareous tubeworm <i>Spirorbis spirorbis</i> is a wide-spread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus <i>Fucus</i>). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO<sub>2</sub> increase. However, <i>Spirorbis</i> tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO<sub>2</sub> may influence <i>S. spirorbis</i> shell growth we carried out four seasonal experiments in the 'Kiel Outdoor Benthocosms' at elevated pCO<sub>2</sub> and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of <i>S. spirorbis</i> are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO<sub>2</sub> conditions. No influence of daily average CaCO<sub>3</sub> saturation state on the growth rates of <i>S. spirorbis</i>was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favored selective shell surface dissolution. The results suggest an overall resistance of <i>S. spirorbis</i> growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, <i>S. spirorbis</i> did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO<sub>2</sub>, the growth rates of juvenile <i>S. spirorbis</i> were higher under elevated temperature conditions. The results reveal that <i>S. spirorbis</i> may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.</p>

Ocean acidification affects calcareous tube growth in adult stage and reared offspring of serpulid polychaetes

“…However, to be buffered, the benefits during the day need to be great enough to offset the negative effects of respiration at night. In addition, the tube worm response can be driven by temperature (Campbell and Fourqurean, 2014;Ni et al, 2017). For example, S. spirorbis, in the laboratory, had reduced recruitment on a fucoid alga at extreme P CO2 (3150 µatm) but not at moderate levels (1200 µatm; Saderne and Wahl, 2013).…”

“…An in situ benthocosm study, using the same species, concluded that early life stages are promoted by moderately warm temperatures. However, high temperatures exacerbate tube dissolution and do not alter growth when water is undersaturated with respect to CaCO 3 (Ni et al, 2017) Table 3 for statistical results).…”