Polar coralline algal CaCO₃-production rates correspond to intensity and duration of the solar radiation

Abstract. In this study we present a comparative quantification of CaCO₃ production rates by rhodolith-forming coralline red algal communities situated in high polar latitudes and assess which environmental parameters control these production rates. The present rhodoliths act as ecosystem engineers, and their carbonate skeletons provide an important ecological niche to a variety of benthic organisms. The settings are distributed along the coasts of the Svalbard archipelago, being Floskjeret (78°18' N) in Isfjorden, Krossfjorden (79°08' N) at the eastern coast of Haakon VII Land, Mosselbukta (79°53' N) at the eastern coast of Mosselhalvøya, and Nordkappbukta (80°31' N) at the northern coast of Nordaustlandet. All sites feature Arctic climate and strong seasonality.

The algal CaCO₃ production rates were calculated from fuchsine-stained, presumably annual growth increments exhibited by the rhodoliths and range from 100.9 g (CaCO₃) m⁻² yr⁻¹ at Nordkappbukta to 200.3 g (CaCO₃) m⁻² yr⁻¹ at Floskjeret. The rates correlate to various environmental parameters with geographical latitude being the most significant (negative correlation, R² = 0.95, p = 0.0070), followed by the duration of the polar night (negative correlation, R² = 0.93, p = 0.0220), the duration of the sea ice cover (negative correlation, R² = 0.87, p = 0.0657), and the annual mean temperature (positive correlation, R² = 0.48, p = 0.0301).

This points out sufficient light incidence to be the main control of the growth of the examined coralline red algal rhodolith communities, while temperature is less important. Thus, the ongoing global change with its rising temperatures will most likely result in impaired conditions for the algae, because the concomitant increased global runoff will decrease water transparency and hence light incidence at the four offshore sites. Regarding the aforementioned role of the rhodoliths as ecosystem engineers, the impact on the associated organisms will presumably also be negative.