Recovery of underwater forests offers hope for ocean restoration around the world

Human activity has degraded ecosystems around the world and damaged biodiversity, but ecosystem restoration offers hope for the future. Scientists studying the restoration of underwater kelp forests, which provide food and shelter for other species, found that 10 years of restoration efforts helped damaged forests grow back as richly and robustly as those of never-disturbed forests.

„Macroalgal forests are found on more than a third of the world’s coastlines and underpin entire ecosystems,” said Dr. Emma Cebrian of the Center d’Estudis Avançats de Blanes, corresponding author of the study. Frontiers in Marine Science.

„In 2011, a restoration operation took place in the Bay of Mao, Menorca, where a macroalgae species was reintroduced to an area where it thrived. 10 years later, we found that associated algal species had returned to the habitat. They, the ecosystem functions they provide.”

Under the sea

Seprian and his team used a trait-based approach to investigate the functional recovery of kelp forests: the link between restoration efforts and the forest functioning as it did before it was damaged. The team studied five areas of Kongolaria barbata, one of the 'canopy-forming’ species essential to maintaining kelp forests, to understand how the restoration of these species could work to restore ecosystems.

„Among all sponges, the macroalgae that form the canopy provide structure to the ecosystem, similar to the trees in a terrestrial forest,” said Cristina Calobart, first author of the study, which is based at the Center d’Estudies Avignons de Plains. „For example, they affect the local environment by changing light and water flow. These changes in the environment create ecological niches where other species can profit.”

Evaluation of restoration projects takes place on short time scales, especially in marine ecosystems, where these projects are less established. However, as slow-maturing species recovery projects require longer periods of time for evaluation, and as we understand how plant composition and species diversity are restored, questions remain about how an ecosystem returns to function.

To measure function, it is necessary to study measurable traits in target species that capture the health of the ecosystem. The team chose to look at a set of 14 characteristics, such as the size of the specimens and whether they belonged to a long-lived or slow-growing species. The presence of species that require more time to mature or grow larger may indicate a healthier ecosystem, better able to support them.

The team studied an intensively restored area where restoration efforts had been ongoing for 10 years, a nearby area where restored macroalgae had spread beyond the boundaries of the initial restoration area, a neighboring area that was not restored, and two reference sites. Not disturbed. Samples were collected from each of these locations for identification and analysis, then dried and weighed to measure the abundance of each species.

Grow strong

They found that the restored area was composed of more diverse species than the untouched area and the area where restoration efforts had spread, with a similar species composition to the reference samples. The reforested area was functionally richer than one of the reference forests, even though it wasn’t exactly populated by the species scientists expected.

The species that make up restored ecosystems may differ from the original ones, while filling the same niche in supporting local biodiversity. The restored area contained species with greater structural complexity and longer lifespans, an important sign of long-term recovery that increases the potential shelter the forest provides for other species. The added diversity also offers potential benefits for the future: more diverse kelp forests can better respond to environmental challenges.

„We demonstrated that a restoration action and removal of the cause of degradation can lead to recovery not only of a species but also of associated ecosystem functions,” Cebrian said. „Adding information from other restoration efforts will help us fully understand how recovery works in different habitats, species or environmental conditions.”