Organismal and Community Metabolism and Their Drivers in Coral Reefs

The two most important and fundamental processes describing coral reef ecosystem functioning are photosynthesis (primary production) and calcification. They determine energy flow, carbon cycling, and habitat provision (calcium carbonate structures) in reefs. In corals, as well as in other photosynthesizing calcifiers (e.g., crustose coralline red algae), photosynthesis and calcification are related to each other (e.g., higher calcification during the day then at night). However, considerable differences in their responsiveness to changing environmental conditions are evident as well. Numerous manipulation experiments have shown how the metabolism of corals is affected and/or able to adjust to changes of single and multiple environmental conditions, including stressful conditions that exceed naturally experienced conditions. However, much less is known about temporal and spatial dynamics of coral (and coral reef community) metabolism in-situ where multiple abiotic and biotic environmental factors, as well as species interactions, affect metabolic rates. Furthermore, the role of heterotrophy in coral energy and carbon budgets is poorly understood. The MABEE lab addresses research questions that relate to the temporal and spatial dynamics of reef organism and reef community metabolism under in-situ or near-natural conditions. The strong seasonal environmental fluctuations in Bermuda and the long-standing ocean time series, the Bermuda Atlantic Time-Series Study (BATS) provide an ideal framework to study the capacity for metabolic adjustments in corals and other photosynthesizing reef organisms. This knowledge forms an important basis for further studies that aim to understand how reefs and their functional processes may change under progressing global change.

 

In-situ community metabolism

A common limitation of in-situ community measurements is that they are logistically challenging. Sawall, Eric Hochberg, and Nick Bates were awarded the BIOS Cawthorn Innovation Fund (2018 – 2019; $150k) to advance the rather new “gradient flux” (GF) approach for reef metabolism measurements. This approach makes use of the benthic boundary layer overlying the benthic community, and of the gradient of molecules that are taken up or released by the community’s metabolic activity (e.g., O₂, carbonates, and bicarbonates – total alkalinity; picture 1.1). The major advancements of this approach compared to common respirometry approaches are (i) independence of local topography and water depth, (ii) high temporal resolution of metabolic rates (<1h), and (iii) autonomous data collection for >1 week. We recently started a reef metabolism time series providing unique insight into short-term vs long-term variability in reef metabolism and its drivers. This time series is embedded in BIOS educational programs (summer CRE courses & REU program) and is conducted in collaboration with Matthew Long at WHOI.

As part of the Cawthorn award two remote access water samplers (RAS-500, McLane, USA; picture 1.2 & 1.3) were purchased that are also available for other (non-related) projects.

Students involved in the project:

• Kelly Koehler (undergraduate, North Carolina State Univ, USA, 2021)

 

Organism metabolism, energy budgets, and nutrient fluxes

All living organisms and their environment are in constant exchange of components, including O₂, CO₂, inorganic nutrients, and a range of inorganic and organic carbon compounds. To understand (i) the flow of energy, carbon and nutrients through organisms, (ii) how the environment affects organism energy and carbon budgets, and (iii) the relative importance of different taxa contributing to reef community processes, we conduct incubation experiments in the lab, in outdoor mesocosms and in-situ. For in-situ experiments, we recently constructed an innovative fully automated in-situ incubation chamber setup (BIO-RESORT; value ~$100k), together with engineers at GEOMAR Helmholtz Center for Ocean Research, Kiel, Germany. The BIO-RESORT allows continuous measurements of metabolic rates in 6 units simultaneously for up to one week at a time (picture 1.9). Next to photosynthesis and respiration rate measurements (with O₂ sensors), custom-built automated water samplers connected to each incubation chamber allow determining rates of, for example, calcification and nutrient uptake/release. The BIO-RESORT is an advanced version of the “Coral Hotel” constructed by GEOMAR and previously deployed in the Red Sea (picture 1.6). As part of the recent Cawthorn Innovation Fund (Sawall and Tim Noyes; 2020-2021 $150k), the BIO-RESORT is currently being tested (picture 1.9). A more detailed description of its unique features and capabilities of the BIO-RESORT can be expected beginning of 2022.

Further research efforts are currently directed towards improving our understanding of diurnal dynamics of the coral energy gain and reserves using a combination of methods including oxygen evolution measurements, PAM fluorometery, stable oxygen isotope tracing and biochemical analysis of energy reserves (Cawthorn Innovation Fund 2020-2021). In particular, improving measurements of gross photosynthesis (GP) and daytime respiration are focus of this research, which will significantly improve our understanding of energy and carbon flow through organisms and ecosystems. Furthermore, the MABEE lab is exploring new approaches to improve coral heterotrophy quantification in collaboration with BIOS plankton scientist Leocadio Blanco-Bercial. (In-situ) coral heterotrophy and its contribution to the coral’s energy budget and nutrition is a so far poorly explored, although its significance may increase under climate change driven environmental stress.

A new collaborative NSF-project is currently underway that aims to understand the (potential) impact of mesoscale eddies on coral growth. This project, conducted in collaboration with BIOS scientist Damian Grundle and scientist Nathalie Goodkin from the American Museum of Natural History, combines in-situ investigations and historical analysis of eddy impacts on coastal carbon chemistry and coral calcification.

Students involved in metabolism projects:

• In-situ incubations (BIO-RESORT): Emie Woodburn (B.Sc., Univ. of Victoria, Canada, 2021)
• Gross photosynthesis and daytime respiration – diurnal and seasonal pattern: Benjamin Shirey (B.Sc., Eckerd College, USA, 2021), Chloe Root (undergraduate, Eckerd College, USA, 2021), Hanne Borstlap (undergraduate, Princeton University, USA, 2021), Roderick Bakker (bachelor thesis, Univ. of Leiden, Netherlands, 2021), Natalia Padillo-Anthemides (undergraduate, Florida International University,USA, 2020), Nicole Adams (undergraduate, Univ. of California – San Diego, USA, 2020), Charlie Schneider (undergraduate, Colorado College, USA, 2019).
• Temperature effects on coral metabolism (20-28°C): - Kathryn McLaughlin (undergraduate, Princeton Univ., USA, 2020), Anna Nicosia (undergraduate, Lehigh Univ., USA, 2019)
• Coral heterotrophy: Sem Docekal (undergraduate, Van Hall Larenstein Univ., Netherlands, 2021), Alexis Savard-Drouin (undergraduate, Dalhousie University, Canada, 2020)

 

NASA COral Reef Airborne Laboratory (CORAL) & light-use-efficiencies (LUEs)

When Sawall assumed a research position at BIOS in June 2016, she participated in the NASA Coral Reef Airborne Laboratory (CORAL) mission (2015-2019) led by BIOS senior scientist Eric Hochberg. The mission of CORAL was to investigate coral reef conditions, namely benthic community structure, primary production, and calcification via remote sensing, which would ultimately allow for reef monitoring on a global scale. Here, Sawall assessed community-scale light use efficiencies (LUEs) of different reef photosynthesizers using outdoor fumes (picture 1.4 in slideshow at top of page). These LUEs are defined as the daily gross photosynthetic rates (or calcification rate) per daily absorbed light, and are required to derive primary production of reefs from airborne hyperspectral imagery (Sawall et al. 2018). The ultimate goal of this work is to be able to model LUE based on community type and environmental condition, similar to what is already done for remote sensing of productivity in terrestrial ecosystems (e.g., satellite-based MODIS-GP).

Students involved in the CORAL LUE-flume experiments:

• Allison Doolittle (undergraduate, Los Angeles Harbor College, USA, 2019)
• David Flesher (Honors thesis, Arizona State Univ., USA, 2018)
• Ashley Miller (M.Sc. thesis, Univ. of Bremen, Germany, 2017)
• Kelly Chimpen Mac Leod (undergraduate, Towson Un, USA, 2017

Students involved in LUE-related side projects:

• Zoe Pearson (M. Sc. Thesis, of Southampton, UK, 2017)