Co-produced ecological monitoring of kelp ecosystems for adaptive management in a multiple- use marine protected area

The coast of southern Chile is a place where the ocean meets the land in a rugged, living tapestry. Here, vast forests of brown seaweed, known as kelp, cling to the rocky seabed, creating underwater cities that shelter countless fish, crabs, and snails. These ecosystems are not just biological wonders; they are the foundation of local livelihoods. For generations, artisanal fishers and Indigenous Mapuche-Huilliche communities have harvested these seaweeds and the creatures that live among them, relying on the sea for food and income. But this relationship is delicate. The seaweed forests face pressure from storms, changing ocean temperatures, and the very people who depend on them. When too much is taken, or when the environment shifts too quickly, the forests can thin out, taking their sheltering creatures with them. The challenge for scientists and communities alike is to find a way to watch these ecosystems closely enough to know when they are struggling, without stopping the people who need them to survive. This requires a new kind of watching, one that blends the precise measurements of science with the deep, daily knowledge of the people who live on the water.

In the Lafken Mapu Lahual Multiple-Use Marine and Coastal Protected Area, a stretch of ocean and coastline in the Los Lagos Region, researchers set out to build exactly this kind of partnership. The area is a designated protected zone, but it is also a place where fishing and harvesting are allowed, creating a complex social-ecological system where conservation and use must coexist. For years, the management of this area had been hampered by a lack of clear data and a disconnect between the scientists studying the ocean and the fishers working it. To fix this, a team led by Pablo M. Rojas and Sandra Saavedra developed a monitoring framework that was co-created from the ground up. Instead of scientists designing a plan and then asking fishers to follow it, they brought thirty-five stakeholders together—including fishers, Indigenous representatives, government officials, and researchers—to design the monitoring system together. They used a structured approach to link human activities, the health of the seaweed, and potential management actions, ensuring that the questions being asked were relevant to both the science and the community.

The team began by mapping the seaweed meadows across three distinct sectors of the protected area, from the north to the south. They worked alongside local fishers, who used their knowledge of the coastline to guide the research vessel through the waters. In the field, they measured the size and density of the seaweed, counting how many individual plants were in a given area and measuring the diameter of the holdfasts—the root-like structures that anchor the seaweed to the rocks. They also collected samples of the tiny creatures living in and around these holdfasts to see how diverse the animal communities were. The results revealed a clear story of difference across the coast. In the northern and central sectors, the seaweed forests were dominated by small, young plants. More than 95 percent of the Durvillaea incurvata and 90 percent of the Lessonia spicata individuals had holdfasts smaller than 21 centimeters. This suggested that these areas were either heavily harvested or exposed to strong waves that prevented the plants from growing large. In contrast, the southern sector showed a broader mix of sizes, with larger plants and a richer variety of associated animals, suggesting a slightly more stable environment.

The researchers also looked at the history of the harvest to understand the context of what they were seeing. They analyzed official landing records from the nearby Mansa Bay, which covered a twenty-four-year period from 2000 to 2024. The data showed that the harvest of brown seaweed had surged dramatically after 2009, reaching its highest levels between 2016 and 2019. This period of intense extraction coincided with the time before the protected area had an approved management plan in place. The ecological surveys conducted in 2014 and 2015 took place right as this harvesting pressure was climbing, capturing a snapshot of the ecosystem under increasing stress. The team found that the small size of the seaweed in the northern and central sectors was consistent with the idea that heavy harvesting and environmental exposure were keeping the plants from reaching their full size. However, they could not say for certain which factor was more important, as the two forces often work together.

A crucial part of this project was how the monitoring indicators were chosen. The scientists started with a list of species they thought were important based on scientific literature, but the fishers added their own knowledge to the mix. During workshops, the fishers pointed out specific fish species, such as Calliclinus geniguttatus and Calliclinus nudiventris, that they knew were good indicators of the health of the rocky coast. These fish were not on the scientists' original list. By including them, the monitoring framework became richer and more grounded in the reality of the local ecosystem. The final result was a set of five operational indicators, including the cover of the seaweed canopy, the size of the holdfasts, and the diversity of the small animals living in them. The team established provisional thresholds for these indicators, such as a 40 percent canopy cover or a 6-centimeter holdfast diameter, which would trigger specific management responses if the ecosystem fell below them.

The study also looked at the practical side of keeping this kind of monitoring going. The team estimated that running the program would cost between 70,000 and 100,000 US dollars per year, depending on whether the work was led by the community or by an outside institution. The community-led model, which relied on local fishers for boat access and field assistance, was the more affordable option. This approach highlighted that effective monitoring is not just about collecting data; it is about building a system that is sustainable and owned by the people who live there. The framework does not claim to have solved the problems of the protected area or to have proven that the current management is perfect. Instead, it offers a structured way to watch the ecosystem, learn from it, and adapt management decisions as new information comes in. By linking the physical state of the seaweed forests with the history of harvesting and the knowledge of the people who use them, the study provides a blueprint for how multiple-use marine protected areas can be managed in a way that respects both the ocean and the communities that depend on it.