Kelp forest

Kelp are large brown algae, not flowering plants. They attach to submerged rocks with root-like holdfasts; stem-like stipes and broad blades extend upward toward sunlight. Some species have gas-filled bladders that help keep blades near the surface. Where conditions allow, kelp grow in dense stands that form a vertically layered underwater habitat. Kelp forests occur around the world in subtidal coastal regions, particularly in temperate and polar waters where temperatures, light, nutrients and currents are suitable.

The canopy, midwater fronds and rocky seafloor beneath a kelp forest create different places for organisms to feed, hide and reproduce. Fish, invertebrates, marine mammals and seabirds use these habitats in different ways. Kelp are primary producers: through photosynthesis they convert light into organic matter and contribute to coastal food webs. The physical structure also modifies local water movement and can provide shelter from waves and predators. Kelp ecosystems support human activities such as fishing, recreation and wildlife observation, and contribute to nutrient cycling and coastal carbon processes.

Kelp forest extent depends not only on the algae themselves but also on ecological interactions. Sea urchins and other grazers eat kelp; predators that limit grazers can therefore influence whether a forest persists. When predator abundance falls or grazer numbers rise, intense grazing can transform a kelp-dominated reef into an urchin barren. These changes are not identical in every region: local species, ocean conditions and food-web structure affect how forests respond and recover.

Marine heatwaves and sustained warming can reduce kelp growth, reproduction and survival. Poor water quality, sediment runoff, habitat disturbance and imbalances between predators and grazers can also damage forests. The relative importance of these pressures differs among places. Monitoring must therefore track local species and conditions rather than assume that one cause explains every loss. Conservation approaches include reducing manageable pressures, protecting key species and habitats, and restoring kelp where ecological conditions make recovery feasible.