Every winter, for 10 years, divers descended into kelp forest plots throughout the South Coast of California. Armed with knives and sometimes saws, they meticulously removed bunches of kelp from the canopy in imitation of the strong waves accompanying winter storms.
In some plots, divers returned to the forests with greater frequency, removing bunches of kelp with every season.
Meanwhile, other plots were left to their own devices, the canopy denuded only with the arrival of uncommonly powerful winter storms.
In doing so, the divers set the stage for a decade-long research experiment, recently published in Ecology Letters. The question: How does a kelp forest respond to the repeated loss of the canopy? Even broader than that, though, was another question: How does a torrent of disturbances affect the underlying behavior of a forest — any forest — and how might the forest adapt?
“We hope that the processes that we are uncovering here are relevant to, you know, a broad array of ecosystems, but it’s just an easier question to address in kelp forests than other systems,” said Dan Reed, a research biologist and the deputy director of the Marine Science Institute.
“The kelp forest is a really amenable system to work in to ask questions that relate to disturbance in the canopy and how that affects, you know, other primary producers and consumers in the forest.”
Reed first began working on this project with his collaborators while leading the Santa Barbara Coastal Long-Term Ecological Research project, initially having designed the experiment in 2008. This program is one out of a network of sites that the National Science Foundation funds to conduct long-term research, a necessity when one wants to monitor ecological processes that occur on a multiyear or even decadal scale.
The experiment itself, made up of sites from Carpinteria to Point Conception and extending out to Santa Cruz Island, has operated and been monitored since 2000. Initially, the experiment was devoted to monitoring watersheds and the interactions between the land and the ocean.
However, when this topic of focus was cut back, Reed and his collaborators began looking increasingly into kelp forests.
Noticing the similarities between kelp and terrestrial forests, the researchers were particularly interested in how the different layers of vegetation that are dispersed vertically throughout the canopy of the forest would adapt to the loss of the canopy.
“This particular paper focused on the extent to which primary production in the system would respond to this canopy being torn out every year. For instance, the understory algae that live beneath the kelp are typically shaded by the kelp,” Reed said.
“Would they then be allowed to grow at a level that would capture all the light and basically compensate for all the production that is lost by the giant kelp?”
According to Reed, this is particularly relevant because of how a changing climate is anticipated to alter the frequency of severe storms that impact California.
Climate projections show that as the area warms, rain events will be less frequent. However, the rain events that do manage to barrel through the Santa Barbara coast will more often be severe, bringing with them large waves which are capable of tearing up kelp canopies.
The researchers were able to monitor relatively large plots of varying kelp environments that ranged in their abundance of kelp and understory algae. With this, they had a snapshot of the broader kelp forest ecosystem and its nuances.
With repeated disturbances, the researchers found that the difference between the experimental and the control plots, those which had kelp removed periodically and those which were left alone, respectively, continued to grow. Understory productivity from algae was still rising to compensate for the loss of the canopy and after several years had not managed to reach the productivity of the more intact kelp canopy.
This stuck out to Reed.
“I actually thought that in a couple of years, things would kind of level out and we’d come to a new sort of equilibrium. I was surprised to see our data show that, in fact, the effects were continuing to increase, as long as they did. After 10 years, we still did not see a leveling out,” Reed said.
“To me, that was surprising. And it also speaks to the value of long-term studies, right? You really do need to look at systems — even a system like ours that is really dynamic and really fast growing — over a relatively long period of time.”