Maine’s kelp forests and the impact of environmental change

By, Camryn Sudimick, Maine EPSCoR Writing Intern

The Gulf of Maine (GoM) is warming rapidly, and ecosystems contained within, including Maine’s rocky reefs, are undergoing significant changes. The kelp forest habitats along Maine’s coast are transitioning to red algae turf reefs. These kelp forests stand from one to a few meters tall that fish and other organisms swim through, hide in, and gain nutrients from. When these forests disappear they are replaced by red algae which only stands a few centimeters tall.

Researchers at Bigelow Laboratory for Ocean Sciences with the NSF EPSCoR RII Track-1 Maine-eDNA project are trying to understand this transformation in the GoM. One of those researchers is Dara Yiu, a University of Maine Ph.D. candidate in Marine Biology advised by Bigelow Senior Research Scientist Doug Rasher and Associate Professor of Marine Mammal Science Kristina Cammen. Her research focuses on the ecological role of fish communities in these rocky reefs and how these communities are impacted by this habitat transition.

Explaining, Yiu said, “We know that these reef ecosystems are changing in the GoM, but we need to evaluate how much they are changing, and the impact of this change on both energy channels and ecological niches of reef communities.”

Essential to this is understanding the importance of Maine’s kelp forests on its animal communities. However, most existing research on kelp forests is based in the Eastern Pacific. The relationship between fish and kelp forests in the North Atlantic is far less studied. Kelp forests in the Eastern Pacific differ structurally from those in the North Atlantic, so we cannot assume that their ecological importance or roles in their communities are the same. Yiu explained, “We know from other kelp forest systems that kelp is really important for fish as habitat, but no one really knows if that’s true for kelp forests in the Gulf of Maine.”

Based at Bigelow Laboratory, Yiu is working to quantify the degree to which this habitat change is impacting Gulf of Maine reef fishes, to determine if the loss of kelp and change in reef habitat is affecting the structure of these fish communities or the ecological niches they occupy.

To quantify the change in the reef communities, Yiu assessed reef communities along the coast of Maine using visual surveys and environmental DNA (eDNA) metabarcoding to estimate fish species diversity. The visual surveys, conducted via scuba diving, identified a low species diversity, with cunner and pollock being the main species found across the coast and in both kelp forests and turf reefs. eDNA metabarcoding complemented these surveys by detecting unseen or rare species. This combined approach gives a more multifaceted representation of the fish present at these study sites. Comparing the fish species in kelp-dominated to that of turf-dominated reefs will demonstrate if these two distinct habitats host different fish communities, which can help us understand how this habitat transition impacts communities and species diversity.

The loss of kelp forests can impact fish communities by shaping the species that live there if the fish directly use kelp for habitat. But it may also indirectly impact the ecology and energy dynamics of reef fishes if fish depend on kelp forests for their food or energy. To assess the possible effects of the habitat change on the reef community ecology, Yiu collected fish and invertebrates from places with robust kelp forests in Downeast Maine, as well as from places like Casco Bay, that have turned into turf reefs. Currently, Yiu is working to analyze these samples in various ways, to understand fish prey communities, fish diets, the ecological niche spaces fish use, and the proportion of energy they are getting from the kelp compared to other sources.

Recently, Yiu worked with collaborators at the University of New Mexico Center for Stable Isotopes to use stable isotopes to help address these questions. As primary producers such as kelp and red algae take carbon dioxide out of the environment to fix it into their tissues, they use different ratios of carbon-13 to carbon-12 (carbon isotopes). These physiological differences leave a subtle chemical signature in the molecules in producer tissues. When a consumer eats a primary producer, they assimilate the molecules from it, so this carbon moves up through the food web. Therefore, isotopic signatures in animal tissues contain clues about the food they eat, the energy channels they use, and the ecological niches they occupy. The preliminary stable isotope data is suggesting that fishes in kelp forests and turf reefs occupy different ecological niches and use different sources of energy. In kelp forests, a large proportion of fishes’ energy looks like it is coming from kelp, but when kelp disappears, they change to use more energy from both phytoplankon and red algae. We are still working on analyzing fish diets and invertebrate communities to try to understand if these differences between habitats are due to their prey availability, prey selection, or the energy channels that their invertebrate prey species are using.

As the GoM continues to warm, understanding the implications for fish communities and their habitats becomes increasingly crucial. The loss of kelp forests could have far-reaching consequences, not only for the diversity of fish species but also for the fisheries dependent on these ecosystems. For instance, the transformation of kelp forests to turf reefs may have consequences for important commercial species, as their larval and juvenile stages depend on kelp forests as a refuge from predators. In addition to evaluating the ecological impacts of these changing reef communities, Yiu’s work can also help inform models that help predict how species distributions might shift in response to changing reef communities. This is crucial for anticipating and managing future ecological shifts in the face of climate change.

Throughout the past four years, Yiu has observed firsthand how this habitat change can shape food webs and influence fish communities. As Yiu stated, “Our preliminary data shows that the kelp forests are definitely changing the way that fish either interact with their environment, or each other, or their resources.” But there are still questions left to untangle. “There are lots of intricacies, and now I have a lot more questions” remarked Yiu.