Turf algae chemically inhibit kelp forest recovery in warming coastal waters

As kelp forests decline in the warming coastal waters of the Gulf of Maine, turf algae – dense mats of red algae replacing kelp in many regions – may chemically interfere with kelp recovery, a new study reports. This complicates efforts to restore these crucial marine ecosystems. Kelp forests are ecologically and economically vital marine ecosystems that support diverse life forms and functions. However, despite their widely recognized importance, kelp forests worldwide are threatened with collapse due to climate change and/or overfishing. In many regions where kelp forests have disappeared, they have been replaced by dense, low-lying mats of chemically rich, filamentous red seaweeds, also known as turf algae. This shift has been linked to declines in biodiversity and major disruptions in coastal ecosystem dynamics. Some research suggests that turf algae may actively hinder the recovery of kelp through allopathy – a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other surrounding organisms. Understanding whether turf algae chemically inhibit kelp recovery is essential to managing and restoring these rapidly changing marine environments.

Shane Farrell and colleagues investigated whether allopathic turf algae suppress the recovery of kelp forests in the warming waters of the Gulf of Maine. Farrell et al. discovered that while kelp forests have persisted in the cooler waters of northeastern Maine, those in the warmer southwest have collapsed and failed to recover, with turf algae now dominating these reefs. By comparing the chemical composition of water and seaweed samples from kelp- and turf-dominated reefs, the authors identified distinct chemical signatures produced by turf algae. Laboratory experiments show that these turf-derived compounds inhibit the early growth stages of kelp. The findings suggest that turf algae alter the chemical ecology of the environment in ways that actively prevent kelp from re-establishing. “Future resilience strategies for marine ecosystems should integrate chemical ecology into climate change models,” write Colette Feehan and Karen Filbee-Dexter in a related Perspective. “By illuminating these hidden processes, we can better develop a fuller picture of how climate change is reshaping ocean ecosystems – and how we might better protect them.”