Changes to rocky reefs, like the loss of kelp forests, can have a ripple effect throughout the ecosystem, impacting species that depend on these habitats. Understanding interactions between aquaculture and rocky reef ecosystems is key to ensuring the sustainability of both.
The magnitude of interactions between aquaculture and rocky reef ecosystems depends on the proximity of farms to rocky reefs, the intensity of farming, local hydrodynamics and the sensitivity of the rocky reef ecosystem.
Salmon aquaculture releases organic waste (including uneaten feed and fish waste) into the environment. Some of this organic matter is dissolved in the water column (dissolved waste), while some forms particles (particulate waste) which float in the water column and then sink to the seafloor at varying rates. This waste can be transported to nearby rocky reef ecosystems and may result in organic enrichment, which can alter rocky reef ecosystems in several ways.
Excess nutrients can lead to the rapid growth of opportunistic algae (characterised by rapid growth and reproduction) and epiphytic algae (algae that grows on the surface of other algae). Although this is the environment’s mechanism for adjusting to increased nutrients, sustained growth of opportunistic and epiphytic algae can smother other species and reduce light penetration, causing shifts in the reef ecosystem.
Kelp and other canopy-forming algae create underwater forests, providing shelter and food for marine life. If the kelp canopy is removed (e.g. via wave action during storms) from a reef experiencing nutrient enrichment, opportunistic algae is more likely to rapidly recolonise bare space, making it difficult for the kelp to grow back.
Organic matter can act as a food source and attract scavenger species. While this might help clean up the waste, it can also disrupt local food webs if certain scavengers become overly abundant.
Our research points toward several key strategies for managing interactions between aquaculture and rocky reef ecosystems:
Research is ongoing to better understand how aquaculture interacts with rocky reef ecosystems, particularly for new aquaculture sectors like seaweed farming. Difficulties remain in knowing whether nutrient enrichment in reef ecosystems is a result of aquaculture or other nutrient sources (e.g. river inputs, run-off from land, marinas), or a combination of both. Differentiating aquaculture interactions from other interactions is an area of ongoing active research. By better understanding these interactions and using this understanding to inform management, the goal is to ensure that aquaculture can coexist with, and even support, healthy marine ecosystems.
