Unique habitats: Artificial Reefs

An artificial reef by definition is a man-made underwater structure usually built for a purpose of promoting marine life. It is widely accepted in the scientific community that artificial reefs are very beneficial. They can increase local populations such as algal growth, coral reefs and fish. They also can prevent coastal erosion and force waves to deposit energy away from the coastline. In addition, they can promote natural reef restoration by attracting attention away from suffering populations, allowing time for the natural populations to revive and thrive.  

Artificial reef where some algae and plants are growing. Fish swimming under it.
Part of a ship wreck in the National Park of the Bothnian Bay (Photo by Janos Honkonen, Metsähallitus).

Artificial reefs are often built using objects meant for other purposes such as old ships or construction debris, while other artificial reefs are designed and manufactured specifically for creating new reefs. These artificial reefs are usually made of PVC, concrete or any other material that creates a hard surface for marine life such as algae and invertebrates to grow.  Some new techniques are using 3D printing for artificial reef fabrication to restore the declining coral reefs communities. Additionally, many popular diving sites in the world are methodically placed around shipwrecks that were purposefully sunk as artificial reefs. This promotes tourism and can also boost the economy.

Polyps growing on the surface of a buoy in the underwater nature trail (Photo by Janos Honkonen, Metsähallitus).
Polyps on a chain (Photo by Lari Pihjanjärvi, Metsähallitus).

Now this does not mean we can just go around throwing any unused object into the sea. See ‘Trash Talk’ blog! Most artificial reefs are created purposefully, but without careful planning and monitoring of artificial reefs, natural habitats can be damaged or dramatically changed, creating an unbalanced natural environment that can attract unwanted species and be a catalyst for invasive species as well. Furthermore, it is important to be aware of what materials are being released when creating artificial reefs. For example, if not prepared properly, various chemicals, toxins and even plastics can be released into the seas, further damaging the marine ecosystem. 

A large metallic thing at the bottom of the sea.
One of the many trash that our marine team found in Summer 2018 (Photo by Suvi Saarnio, Metsähallitus).

So, what about in the Bothnian Bay? Species in the Bothnian Bay are well adapted to this unique environment with its low salinity and brackish waters, so how these artificial reefs impact the biological diversity of the Bothnian Bay is unknown. At least in other parts of the Baltic Sea, artificial reef balls have previously been deployed and resulted in an immediate and noticeable growth in species occurring in or around the balls.

In the SEAmBOTH area, where a lot of the bottom substrate is either sand or other soft material, artificial reefs like wind mill bases (concrete blocks) or ship wrecks can create a new surface for organisms to grow on. For example, filamentous algae, water mosses, hydra and the sponge animal Ephydatia fluviatilis can’t grow on soft substrates. Adding hard substrates to areas of mostly soft substrates will increase the heterogeneity of the area and create more habitats for various kinds of organisms. Water mosses and algae in the area attract invertebrates for feeding and the artificial reef itself creates hiding places and shelter which all attract fish to the area to feed, hide, rest or spawn. This way both accidental and planned artificial reefs, no matter if they were meant to be artificial reefs or serve some other purpose, may increase the biodiversity of the area.

Ephydatia fluviatilis growing on a log (Photo by Suvi Saarnio, Metsähallitus).

Though there are few intentional reefs in the Bothnian Bay, many accidental reefs have been created and many plans for off shore wind mill areas are in the works. The SEAmBOTH team and other Metsähallitus teams have experienced just how everyday materials can create an unintentional home for marine species. We just have to wait and see how these reefs will grow and impact the biological status of this area.

Water pygmyweed (Crassula aquatica) growing on a log (Photo by Ashley Gipson, Metsähallitus).

Written by Ashley Gipson

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