We speak for the rhodoliths

A core sample, one of eight, taken from a rhodolith bed. We see healthy rhodoliths on top of anoxic sand. Image courtesy of D. Steller

“We speak for the rhodoliths”. But first we need to learn their language. Of the 10 scientists on this expedition, only three of us (project PIs Dr.’s Matthew Edwards and Diana Steller, and PhD candidate Scott Gabara) have worked in rhodolith beds before. That means that the rest of us have a lot of learning to do. And quickly! After a few “shake-out” days, we finally have our sampling protocol dialed in: subtidal surveys, collapsible benthic incubation tents (CBITs), and lab based incubations. Dr. Steller is leading the survey dives, while Dr. Edwards and the Edwards Lab is in charge of the CBITs. We’re incredibly fortunate to have Dr. Ju-Hyoung (who joined us in the Aleutians) working tirelessly in the lab running seemingly endless incubations.

​Most of the divers rotate through the survey dives; it takes six or so divers at least three dives to effectively survey a rhodolith bed. Each dive team, consisting of at least two divers, is responsible for a piece of the survey puzzle. For example, a dive team might be running fish transects, which consist of four surveys for fish inside and outside of the rhodolith bed (i.e. over an adjacent sandy bottom). During this time, another team is conducting four transects for invertebrate cover, uniform point contacts (UPC), and quadrats for percent cover. We also take eight cores inside the rhodolith bed. These cores help us understand the size frequency distribution of individual rhodoliths, and what the sandy bottom looks like under the rhodoliths. That’s a lot of work just to understand who is in and around a rhodolith bed! 

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​We’re coupling these surveys with our CBIT incubations. Just the like larger “chambers” we used in the Aleutians, these “chamberitos” allow us to estimate in situ productivity and respiration. That is, what exactly goes on in a community dictated by these coralline algae. The rhodoliths themselves make up the community we’re studying, but the individuals produce and consume oxygen just like any other photosynthetic being. We want to know what net productivity (photosynthesis minus respiration) looks during over a daily cycle. Our CBITs are secured to the benthos via heavy chain and contain a fixed volume of sea water. Inside this CBIT the community goes on producing and consuming oxygen without being disturbed by the experiment. The flexible design allows for the transfer of water motion, and the polycarbonate panels allow undistorted sunlight in without trapping it like a green house. We leave an oxygen and temperature sensor along with a sunlight sensor inside the CBIT to record daily changes.

It’s all well and good to study the components of the community, but our metrics of community composition and Net Community Productivity (NCP) aren’t complete without a detailed understanding of individual contributions to NCP. Enter our productivity expert, Ju-Hyoung. He flew all the way from South Korea to help us understand what individual organisms, including rhodoliths, are capable of from a physiological perspective. All day long Ju-Hyoung is measuring how much oxygen heterotrophs (organisms that only consume oxygen, like humans) consume, and how much oxygen autotrophs (organisms like plants) produce and consume in a rhodolith bed.
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Our days are long. But the water is warm, the visibility is great and everyone is excited to continue exploring! ​