July 18th 2018 Wrigley Institute for Environmental Studies We’re just now wrapping up our first of four expeditions to Catalina Island’s rhodolith beds, and boy do we have a lot of data to process! In total, we’ve sampled five beds for fish, invertebrates, benthic cover (including cores) and set up 30 CBITs! We’ve talked about what we’re doing out here, and how it’s done, but the story won’t be complete until the data are analyzed. As ecologists, we try to balance field work with “office” work. While we’re often daunted by the enormity of trying to sample an entire ecosystem, the magic really happens when we analyze our data. But more on that later! Clearly, we’ve spent a lot of time underwater on this trip, maximizing our sampling effort and taking advantage of the incredible conditions. At first glance, the rhodolith beds look pretty plain and simple. But as we’ve shown, they’re a lot more dynamic than they appear. If you spend enough time in the ocean you’ll see some amazing organisms, and the rhodolith beds are no exception. From competitive macroalgae to charismatic vertebrates, check out some of the best biota the beds have to offer!
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“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! 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.
Our days are long. But the water is warm, the visibility is great and everyone is excited to continue exploring! Getting ready for field work is no easy feat, especially when you kick of a 10-day expedition at 4 o’clock in the morning. But that’s just what the Edwards Lab, accompanied by Dr. Ju-Hyoung Kim from Korea, did in the pre-dawn humidity on July 10th. After doing our final checks to make sure all of our equipment was properly stowed, we piled into the lab’s suburban, 21ft dive boat in tow, and headed from San Diego to San Pedro. At around 6:30am we met up with Dr. Diana Steller and another graduate student from Moss Landing Marine Labs (MLML) at the Southern California Marine Institute. There we loaded our gear onto USC’s Miss Christy, the small mainland-Catalina ferry, and prepared to cross the water to Catalina Island. During the summers of 2016 and 2017 the Edwards Lab, along with the Konar Lab from the University of Alaska Fairbanks, studied productivity in kelp forests along the Aleutian Archipelago. This time we’re doing a similar study in another kind of algal-dominated community: rhodolith beds. Rhodoliths (rhodo meaning “rose”, but in this case “red algae” and lith meaning “rock”) are rock-like “balls” of coralline red algae that can form massive beds on soft sediments in clear water. These little “tumble weeds of the sea”, as PhD candidate Scott Gabara calls them, can support a rich diversity of marine organisms in nearshore environments (Gabara 2018). While kelp forests dominate temperate waters on rocky reefs, rhodolith beds thrive in sandy habitats, especially in protected sandy coves. Which, as it turns out, is an excellent place to establish a mooring field for boats. These moorings, where boats tie up overnight, are anchored to the ocean floor (known as the benthos) by heavy chains and massive concrete blocks. Scientists have known for a long time that these mooring chains can crush rhodoliths, turning the once vibrant beds into coralline rubble patches. Scott, who did his Masters on rhodolith beds with Dr. Steller, aka Di, at MLML, showed that benthic diversity is significantly greater inside the beds than outside.
Which brings us to the purpose of this first of four expeditions to Catalina Island. In conjunction with Dr. Steller and several graduate students from MLML, the Edwards Lab plans on repeating our Collapsible Benthic Incubation Tent (CBIT) experiments inside and outside of rhodolith beds so we can finally understand just how productive these rolling red communities are. Di will be leading SCUBA surveys for diversity, and overall rhodolith community structure, while Ju-Hyoung will be conducting incubation experiments in the lab on individual rhodoliths, and the marine organisms that make their home among the algae. Our base of operations is USC’s Wrigley Institute for Environmental Studies, located adjacent to Two Harbors on the west end of Catalina. We’ve got two boats, the 21ft Stillwater Cove, and the 12ft inflatable Kenner (last seen in the Aleutians), 10 scientists and 10 days to learn as much as we can about rhodolith beds, the communities they support, and the consequences of their loss. Be sure to follow along for more rhodolith-related action! |
AuthorPike Spector is currently a Research Operations Specialist with Channel Islands National Marine Sanctuary Archives
August 2022
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