Grad fellow investigates community response of macroalgae

For beachgoers, boaters and fishermen, seaweed brings to mind nothing more than unsightly, tangled blobs that can ruin a coastal outing or expensive equipment.

Gordon Ober, Ph.D., University of Rhode Island, looks beyond the stinky mess and sees a community where sea life and ocean health hang in a complex balance of ecological relationships.

“These species have the ability to grow fast and can outgrow many other marine species,” Ober explains.“Opportunistic algae can shade out and smother eelgrass, a very important species in coastal systems, as well as outcompete other seaweeds.”

If these algal species flourish unchecked, faster than whatever eats them, their proliferation can be harmful, says Ober, now in a postdoctoral position at Claremont McKenna College, where he is researching how intertidal creatures, mostly barnacles, are affected by extreme temperatures at low tide, and exploring how different temperatures influence physiology.

Ober earned his B.S. in Ecology and Evolutionary Biology from the University of Connecticut and then spent about two years as a research assistant in human genetics at Yale University. He arrived at URI in 2011 for his Ph.D. and set out to investigate the impact of multiple environmental stressors — ocean acidification (a byproduct of increased carbon dioxide, CO2) and nutrient loading — on the growth of macroalgae, working in the lab of Carol Thornber, interim dean of research, College of the Environment and Life Sciences.

Early on, Ober secured a 2012-13 graduate fellowship from Rhode Island NSF EPSCoR, support he defines as critical in helping establish his project. The EPSCoR funding for relevant and important research topics is significant, but the draw for applicants is significantly smaller than for comparable national fellowships, according to Ober. That improves the chances to gain support, which, in turn, attracts more opportunities. Ober calls the EPSCoR fellowship his “ticket in,” paving the way for funding from other sources.

“Getting one grant or fellowship almost always opens the floodgate for future success, where reviewers look kindly on applicants who have past success,” says Ober. “The funding through EPSCoR was foundational in allowing me to build my experimental design, but it also helped me obtain other grants and fellowships, including prestigious and competitive fellowships.”

The acidification impact

Ober says he was drawn to the question of how macroalgae respond to ocean acidification, when CO2 in the atmosphere is absorbed by the ocean, coupled with excess nutrients, a key resource for macroalgae, deposited in the water by runoff from urban and agricultural land.

“Ocean acidification is a hot topic, but most of the research was based on things like corals and bivalves — clams, oysters, etc.,” notes Ober. “I saw a lack of research on macroalgae and marine communities in respect to acidification and decided that was the route I wanted to pursue. I saw a question that needed answers in a field I was interested in, experienced in, and passionate about.”

Specifically, he investigated two species, Fucus vesiculosus, a long-living, slow-growing perennial, and Ulva spp., which is short-lived, fast-growing, and opportunistic. Both species, on opposite ends of the spectrum, play different roles in the ecosystem, Ober told those gathered to hear his thesis defense in July. To test competition between the two, he ran three experiments for 21 days, each species alone and together, looking at growth rates with and without high levels of nutrients and CO2.

Under normal conditions, Ober found both Fucus and Ulva both grew at a 3 percent daily rate. But under high CO2 and high nutrient levels, Ulva seized the advantage, taking up more nitrogen than Fucus and growing three times faster. Ober also explored what happened when he added snails (Littornia littorea) to the mix, to see whether the grazers might alter their consumption and offset algal growth.

All things being equal, this particular snail eats both species of macroalgae and can be found in abundance — up to 200 per meter-sized square, which means that what and how much the Littornia littorea eat carries consequences. Ober tracked the snail feeding rate, feeding preference, and respiration rate.

Whereas nitrogen levels did not change the feeding pattern, Ober says, heightened CO2 levels dropped consumption by about half and snails switched from a mixed diet of both Fucus and Ulva to almost exclusively Ulva. The snails also breathed, moved and ate less.

Curious about the consumption shift, Ober ran an artificial food trial. He exposed the seaweed to the same environmental conditions, and froze and ground it to a paste to remove toughness, figuring that if toughness was the driving factor, the artificial food would be consumed equally across treatments. If instead nutritional quality was the driving factor, then the artificial food consumption would mirror the shift. Ober’s results turned up no change, indicating Fucus proved too tough for the snails to eat under stressful conditions.

Consequently, grazers can mitigate algal growth, but only if — as Ober’s experiment showed — the indirect effects outweigh the direct physiological effects on grazers; if the grazers are too stressed to eat, they won’t keep pace with the algal growth.

One thing leads to another

Ober also investigated how communities of algal turf, found in coral reef ecosystems, responded to ocean acidification. His experiment exposed the turf algae to ambient, medium and high CO2 for 41 days, finding no statistical difference under ambient and medium levels. High CO2 levels, however, told another story.

“When you ramp up the CO2, that’s when the communities really start to take off,” explains Ober. “But, what about the community breakdown? How much is there of one in relation to the others?”

He found as the CO2 increased, the prevalence of Rhodophyta (red algae) dropped, making room for Phaeophyta (brown algae), Chlorophyta (green algae), and Cyanobacteria (blue-green bacteria) to grow. The take-home message, says Ober, is that under ocean acidification, turf algae success comes at the expense of coral reefs.

“Opportunistic macroalgae species are going to thrive under future acidification conditions,” Ober says of his research findings. “Novel interactions of CO2 and nutrients highlight the additive impact on growth of opportunistic species, and the success of these species comes at the expense of other important organisms that create space and habitat.”

He concludes: “It is necessary to study climate change in the context of communities and food webs. We need to take into account how dynamic these systems are.”

In addition to his findings, Ober says the research process provided an unparalleled opportunity to develop as scientist, allowing him to gain perspective, patience and self-sufficiency. Designing an experiment that worked took time and perseverance; he ran into moments when he felt as though he had tried everything only to run into more roadblocks.

He concedes that it is easy to feel discouraged, but he altered his approach as necessary and eventually got his experimental design to work. Even though there are undergraduate students to assist and advisors to guide, graduate students learn to navigate and push themselves, Ober says:

“Scientists fail, a lot. But being a good scientist isn’t about running successful experiments, it’s about dealing with failures and hurdles that occur day after day, and coming back with the same passion and energy despite low success rates.

“This is one of the reasons why grad school provides professional development. Regardless of our post-grad school path, we need to know how to be self-sufficient as well as when to rely on others.”

Story and photos by Amy Dunkle