Artificial Reefs May Help Migratory Fish
Human development has started to extend into the ocean, and even below its surface. This phenomenon is called “marine urbanization” or ocean sprawl, and it’s exacerbating changes already occurring due to increased temperatures. On land, we are seeing animals move towards higher latitudes and elevations in response to temperature changes.
Marine animals respond by going deeper and migrating towards the poles. It is thought that in their search for suitable habitats, these species need stepping stones or habitat corridors to facilitate migration. Artificial reefs, created by intentionally sinking large structures, are potentially suitable for this purpose. In fact, artificial reefs are already widespread.
However, little evidence exists that shows an effect of these reefs on biomass along range edges. Generally, populations of a species living at the edge of that species’ range are more adaptable, as they live at the border of their habitat or between two habitats. They are also often genetically unique. Range edge populations are currently especially valuable to study with changing climate conditions.
Researchers at the University of North Carolina at Chapel Hill wanted to find out whether range edge populations of fish could be facilitated by artificial reefs. They conducted diving surveys of 30 warm-temperate reefs hosting a diversity of temperate, tropical and subtropical fish, off the coast of North Carolina. The tropical and subtropical fish that live on warm-temperate reefs are considered range edge populations.
The researchers observed a higher abundance of temperate fish at natural, rocky reefs, but an even higher abundance and biomass of tropical and subtropical fish at artificial reefs that were located at deeper depths (25-35 meters below the surface). This preference is thought to be due to the complexity of the artificial structures, which are on average three times more complex than natural reefs. This provides refuge for prey species of tropical and subtropical fish and the opportunity to establish higher abundance of populations.
This research shows that artificial reefs can act as beneficial habitat and facilitate the movement of fish and other marine animals to deeper depths and higher absolute latitudes. As our climate changes and human populations extend further off the coasts, onto and into our oceans, marine life advocates will need data and creativity to help animals navigate to suitable environments safely. Strategically placed artificial reefs could facilitate this movement along otherwise limited habitat.