"First reports show that the artificial reef may be developing into an ecosystem similar to a natural reef", said Doug Mecum, Acting Administrator for the Alaska Region of NOAA Fisheries. "The reef is already supporting a greater diversity of marine life than the natural hard bottom site."
The artificial reef was installed in 2006 near Whittier in Smitty's Cove on Prince William Sound. It is serving as a test to see if such concrete structures will work in the cold near-shore waters of Alaska to encourage settlement of plants and invertebrates while providing shelter and a forage base for fish.
Scientists are comparing the artificial reef area to a natural hard-bottom site and a natural rocky reef. To date, the artificial reef contains a more diverse kelp and fish community than the hard bottom site, but is not yet as diverse as the life in the natural reef.
"We're guardedly optimistic that the artificial reef, given enough time, will come to resemble the natural reef," said biologist Brian Lance of NOAA Fisheries Habitat Conservation Division in Alaska. "At first pass it looks like algae, kelp and fish communities moved in relatively quickly. Marine life in the artificial reef is not as diverse as life in the natural rocky reef, but we think it's moving in that direction."
The artificial reef is built of concrete balls and pyramids that have openings for fish to move inside. The reef units were deployed in three paired patches on a declining slope (30 to 40 feet in depth) over mixed soft and hard sediment substrate. NOAA Fisheries intends to monitor the artificial reef site for another three years to see if the expected ecosystem complexity develops, or if maturation of the ecosystem at the artificial reef is influenced by structural differences in the types of reefs used.
The artificial reef site was only 16 months old at the time of the last survey in September, 2007. The natural reef is perhaps centuries to millennia old.
Both the natural reef and the artificial reef were dominated by species such as rockfish and ling cod, which were not commonly found at the natural hard bottom site. Also found in the reefs were sculpin, ronquil, Pacific halibut, cod and rock sole.
Researchers dove to check the sites. They also set fish traps, used hook and line to catch larger-bodied fish, and watched images from underwater video cameras, monitoring the sites monthly from June until September.
Scientists placed transmitters on rockfish that were captured at the artificial and at the natural reef.
They found that the rockfish captured, given transmitters, and released at the artificial reef stayed put.
Of the dozen rockfish captured at the natural reef and then released with transmitters at the artificial reef, five returned to the natural reef within one week. However, five established residence at the artificial reef for the duration of the project (two and a half months), which indicates that the quality of habitat at the artificial reef was attractive enough to hold the fish in their new home.
A side-benefit of the artificial reef is that it has attracted recreational divers as well as scientists. The artificial reef is situated in an area that is increasingly used for recreational fishing, boating, and diving.
Continued development around Whittier has the potential to degrade the local marine habitat. The study will show whether or not the concrete artificial reef structures can be used to mitigate the effects of development.
"It is important to understand the colonization rate and species composition of algae, kelp, invertebrates and fish that may use the reef so we can determine the effectiveness of these reefs as an enhancement tool for degraded or unproductive areas," said Lance.