Key Points:
- Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps.
- High nutrient and sediment loads in urban waters may be facilitating the expansion of algal turfs.
Are algal turfs taking over the marine environments as a result of widespread urbanization? That’s the worry of scientists who study marine macroalgae. Algal turfs are expansive beds of sediment-retaining seaweeds, and are common features of urban areas. They have long been black listed by conservationists and many ecologists because they compete directly with foundation species, such as reef-building corals and canopy-forming kelps, which are of considerable importance for marine biodiversity.
Though the term ‘algal turf’ is used to refer to a variety of different types of seaweeds, those in urban areas are typically formed by filamentous algae that are just a few centimeters tall and grow in dense, intertwined matrices or ‘thickets’. Urban algal turfs are thought to consist of opportunistic, pioneer species capable of colonizing novel habitats rapidly and tolerating stressful environmental conditions that may be inhospitable to other organisms.
In particular, urban turfs appear to thrive on elevated nutrient levels (primarily nitrogen and phosphorous from wastewater, sewage, and runoff) and high sediment loads (from coastal construction, dredging, and other sources). Recent studies also suggest urban turfs may be further facilitated by increases in temperature and CO2 associated with climate change.
There is much ongoing research surrounding the proliferation of algal turfs in cities and beyond. Important topics in this area include how turf networks form and persist despite intensive disturbances, the extent to which enhanced populations of herbivores and competitors might constrain turf expansion, and how turf algae affect the diversity of micro-invertebrate, microbial, and fungal epibiota.