A unique study on an international level to determine the impact recreational diving has on marine ecosystems in artificial reefs was carried out for the first time using a sunken ship off the coast of Portimão. The findings were published last week in the Journal of Coastal Conservation.
This study was conducted using the ‘NRP Oliveira e Carmo’ corvette which was sunk on October 30, 2012 to become part of the underwater park Ocean Revival in Alvor, Portimão.
The park features four former ships of the Portuguese Navy which were deliberately sunk to create artificial reefs for recreational diving. Before they were sunk, the ships were rigorously cleaned to remove all polluting elements.
It is located 2.5 nautical miles off the coast of Alvor (Portimão).
The ‘NRP Oliveira e Carmo’ became an interesting subject for the study by chance: the vessel was broken into two pieces during big storms in the first months of 2013. The smaller stern section (1/3 of the vessel) remained where it sank while the longer and heavier bow section (2/3 of the vessel) was dragged 200m away by ocean currents.
Instead of being viewed as a problem, this was considered a unique opportunity. The bow continued to welcome divers, while the stern became “uninteresting” given its small size and has been off-limits to divers since the winter of 2013, thus free from human interference.
This gave Gonçalo Calado, a biologist at Lisbon’s Universidade Lusófona and the man in charge of monitoring the Ocean Revival project, and João Encarnação, from Portimão diving company Subnauta, a chance to study how divers can impact the “early colonisation stages of two artificial reefs in the same underwater conditions”.
According to Calado, this is exactly what made the study “unique on an international level”.
While similar studies had been carried out, never had researchers studied two artificial reefs that were subjected to the same conditions and variables, the only difference being that one was visited by divers and the other wasn’t.
“As far as we know, it is the first time that such an experiment was done,” Calado told the Resident.
“We didn’t find any other study like this published. It is very rare for a ship to break in half at the bottom of the ocean and for there to be a piece of it that is not visited by divers,” he added.
The results of the study confirmed that divers did have an impact on the species inhabiting the two artificial reefs.
Researchers found that there were significantly fewer sea fans (gorgonians) in the bow section. Sea fans are described as part of the family of corals, anemones and jellyfish and resemble small, pink-coloured trees.
Direct human interference affected the more fragile species and damage was mostly due to divers’ flippers, the study revealed.
On the other hand, thoracica, a superorder of crustaceans, adapted better to the bow section where they could better attach and protect themselves, taking over some spots that belonged to the sea fans.
Said Calado: “Through these results, some lessons can be learned and applied on management plans in natural ecosystems, such as restriction periods for visitors while benthic communities are being established.”
He also added that it remains to be seen if species that are subject to divers’ interference can overcome these disturbances, adapt and evolve into stable communities similar to natural reefs.
Although not comparable to the amount of dives registered in other destinations like the Red Sea, recreational diving has some room to grow in the Algarve, said the biologist. Underwater tourism is on the rise in the Algarve and 70% of dives carried out by Subnauta take place at the Ocean Revival park, which keeps natural reefs from becoming overloaded, “which isn’t even the case yet”.
Article by kind permission of http://portugalresident.com
See also: 'Marine Life Threats We Need to Be Seriously Concerned About'
