Artificial reefs created from sunken ships in Madeira and Porto Santo help support marine biodiversity, but cannot reproduce all the ecological functions of natural reefs, a scientific study has concluded.
The findings are based on nine years of fish monitoring by Madeira’s marine biodiversity programme, BioMa, which has been operating across the archipelago since 2016.
Pedro Neves, a researcher at the Oceanic Observatory of Madeira, said the study compared two natural reefs and one artificial reef on each island. The research was carried out in partnership with Madeira’s Institute of Forests and Nature Conservation and the University of Las Palmas.
The two artificial reefs studied were created by sinking former Portuguese Navy corvettes: the Afonso Cerqueira off Madeira and the General Pereira d’Eça off Porto Santo.
“We concluded that artificial reefs behave like natural reefs in some respects, because more or less the same species are found in both places,” Neves told Lusa. “However, the species living around the artificial reefs do not perform all the same ecological functions as those found on natural reefs. Artificial reefs remain very important, for example for diving, tourism and the local economy, but we cannot regard them as substitutes for natural reefs,” he said.
In Madeira, where fish communities are richer and more functionally diverse, the differences between natural and artificial reefs were less pronounced. The artificial structures appear to act mainly as an extension of the island’s existing network of marine habitats.
In Porto Santo, however, the differences between sites were more evident. The artificial reef displayed high levels of functional diversity compared with a natural reef exposed to greater fishing pressure.
Researchers recorded 52 fish species during the study, including several considered particularly important for conservation and the functioning of the marine ecosystem. These included large predators and ecologically distinct species such as grouper, triggerfish, dogfish and several types of ray.
Neves said artificial reefs are valuable because they create additional habitats, but stressed that natural environments must continue to be protected, warning that conservation decisions should not be based solely on the number of species found in one location. Instead, marine protected areas should encompass a mosaic of different environments, including sandy seabeds, rocky reefs and kelp fields.
“We cannot protect only a natural reef because it has more species than a sandy bottom, or just an artificial reef because it has a higher density than a natural reef,” he said. “We have to try to preserve a little of everything.”
The next challenge is to translate the programme’s scientific observations and data into clear information that can be used by policymakers.
In addition, BioMa currently carries out surveys twice a year, in summer and autumn, returning to the same locations to photograph and record marine life in coastal habitats.
The programme covers 19 sites around Madeira and Porto Santo, including rocky reefs, sandy seabeds, rhodolith fields and artificial structures. Its researchers have so far catalogued around 85 fish species and more than 70 coastal invertebrate species, as well as identifying species previously unknown in the region and, in some cases, to science.
Most monitoring dives currently reach depths of about 30 metres, but newly acquired technology will allow researchers to begin systematically exploring deeper and largely unknown areas.
The Oceanic Observatory now has equipment including a remotely operated vehicle, or ROV, and autonomous underwater vehicles.
Neves said the region has technological capabilities that compare favourably with those available in many other areas, creating new opportunities to investigate Madeira’s deep-sea habitats.
“There is still a great deal that we are only now beginning to observe,” he said. “In the coming years, this will certainly produce very interesting results and information.”
Work in deeper habitats remains embryonic, with scientists still testing and preparing the complex equipment. Nevertheless, Neves said he had high expectations for what could be discovered.
“Every dive we make with the remotely operated vehicle and every mission with the autonomous vehicles brings us new information, because we knew nothing about these areas,” he said.
Until now, discoveries from Madeira’s deeper waters have often been sporadic. Museum collections may contain a specimen caught by a fisherman on one occasion, for example, but with little information about where it lived or whether it was ever found again.
“We know that there is a great deal we do not know,” Neves said. “We now need to visit more places, more frequently, at greater depths and across different habitats to understand what exists.”
The programme may eventually be expanded to areas not yet routinely monitored, including Madeira’s north coast and the Desertas and Selvagens islands.
Researchers are also comparing marine protected areas with locations that are not formally protected. However, Neves cautioned that even after a decade of monitoring, it remains too early to draw firm conclusions about long-term changes in species or the effects of human activity.
A species may be absent from a particular site for natural reasons rather than because of human interference, he explained. Only long-term, repeated observation can distinguish between short-term fluctuations and lasting ecological change, and provide a reliable basis for future conservation decisions.
Samantha Gannon
info at madeira-weekly.com
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