In situ decrease in rhodolith growth associated with Arctic climate change

Area of Science:

• Marine Biology
• Climate Change Science
• Ecosystem Ecology

Background:

• Rhodoliths, built by crustose coralline algae (CCA), are vital ecosystem engineers in the Arctic photic zone, creating complex habitats.
• Unlike coral reefs, rhodoliths exhibit extremely slow growth rates (micrometers per year).
• Climate change impacts on CCA calcite skeletons are known, but long-term field growth data are scarce.

Purpose of the Study:

• To investigate the impact of rising ocean temperatures on Arctic rhodolith growth over decadal timescales.
• To quantify the relationship between temperature increase and rhodolith growth rates.
• To assess potential synergistic effects of climate change factors on rhodoliths.

Main Methods:

• Development and application of a temporally explicit model.
• Analysis of rhodolith growth data across different depths (11, 27, and 46m) in the Arctic.
• Statistical analysis of growth rates in relation to seawater temperature fluctuations over nearly 100 years.

Main Results:

• A significant negative correlation was found between rising summer seawater temperatures and rhodolith growth.
• Each 1°C increase in temperature reduced growth by a mean of 8.9 μm/year.
• Growth reduction was observed at 11m and 27m depths, but not significantly at 46m, which had a shorter data series.

Conclusions:

• Anthropogenic climate change, specifically rising ocean temperatures, is impairing Arctic rhodolith growth.
• Observed temperature increases may have surpassed the thermal optimum for these CCA, or other factors like ocean acidification and turbidity play a synergistic role.
• Reduced rhodolith growth contributes to habitat loss, impacting marine biodiversity and ecosystem function worldwide.