Heterotrophy of Oceanic Particulate Organic Matter Elevates Net Ecosystem Calcification

Abstract

Coral reef calcification is expected to decline due to climate change stressors such as ocean acidification and warming. Projections of future coral reef health are based on our understanding of the environmental drivers that affect calcification and dissolution. One such driver that may impact coral reef health is heterotrophy of oceanic‐sourced particulate organic matter, but its link to calcification has not been directly investigated in the field. In this study, we estimated net ecosystem calcification and oceanic particulate organic carbon (POCoc) uptake across the Kāne'ohe Bay barrier reef in Hawai'i. We show that higher rates of POCoc uptake correspond to greater net ecosystem calcification rates, even under low aragonite saturation states (Ωar). Hence, reductions in offshore productivity may negatively impact coral reefs by decreasing the food supply required to sustain calcification. Alternatively, coral reefs that receive ample inputs of POCoc may maintain higher calcification rates, despite a global decline in Ωar.

Autonomous Ion-Sensitive Field Effect Transistor-Based Total Alkalinity and pH Measurements on a Barrier Reef of Ka̅ne’ohe Bay

“…From the daily A T amplitude measured with this sensor, the NEC is estimated to range from 10.3 to 17.3 mmol CaCO 3 m –2 h –1 , which agrees well with prior studies at the CRIMP-2 site and fits well within the range of other strongly calcifying ecosystems. Although the NEC estimated from the pH– A T sensor is slightly greater than the range of 7.3–13.8 mmol CaCO 3 m –2 h –1 reported by Shamberger et al and 4.2–12.8 mmol CaCO 3 m –2 h –1 by Courtney et al, it is less than the rates of up to 24.62 mmol CaCO 3 m –2 h –1 reported by Kealoha et al when flow was faster. Of course, the experiment presented here was not designed to assess NEC and assumes many of the same conditions of flow and initial A T as Shamberger et al., but the estimate does demonstrate the value of having simultaneous rapid measurements of pH and A T on a coral reef mooring.…”

Oceanic productivity and high-frequency temperature variability—not human habitation—supports calcifier abundance on central Pacific coral reefs

“…In this study, higher coral and CCA cover was observed in more productive waters. Increasing evidence shows reef calcifiers (including corals and calcifying algae) are capable of capitalizing on higher productivity in oligotrophic waters-be it overall or in episodic pulses from deep-water upwelling or terrestrial subsidies-to increase their nutrition and enhance net calcification (Teichberg et al, 2013;Benkwitt et al, 2019;Kealoha et al, 2019;Radice et al, 2019). For mixotrophic corals, species-specific trophic strategies such as heterotrophic feeding can assist some taxa to meet nutritional needs under sustained ocean warming (Hughes et al, 2018;Radice et al, 2019).…”

Impacts of remotely sensed environmental drivers on coral outplant survival

“…In oligotrophic oceanic regions, approximately 40% of POC has been associated with bacteria alone (Cho & Azam 1990), where coral disease is positively correlated with POC concentrations (Haapkylä et al 2011). On the other hand, POC levels can also indicate productivity (Fan et al 2018) and some heterotrophic coral colonies which actively consume POC can increase their calcification rates under increased POC levels (Kealoha et al 2019).…”