Patrícia Ventura, Jacqueline Gautier-Debernardi, Eugenio Di Franco, Patrice Francour, Antonio Di Franco, Alexis Pey, Habitat-specific response of fish assemblages in a small fully protected urban MPA, ICES Journal of Marine Science, Volume 81, Issue 8, October 2024, Pages 1575–1583, https://doi.org/10.1093/icesjms/fsae100
Protecting Our Oceans
Marine Protected Areas (MPAs) are one of several conservation tools we use to help protect critical ocean environments and species. They establish a safe zone where certain protections are enacted and enforced. Examples include bans on fishing/trawling or limiting boat traffic. Fish have been shown to significantly increase in density, size and biomass as a result, which is known as the ‘reserve effect.’
There are four key factors that determine the effectiveness of an MPA.
- Level of protection
- Size
- Length of protection
- Enforcement
Typically, the greater these factors, the greater the reserve effect. However, the reserve effect for each individual area still seems to depend on external environmental factors. In the Mediterranean Sea, many established MPAs with this effect are isolated. They exist in low human density locations or along islands with minimal disturbance. As we continue to expand and develop coastlines, isolation won’t be an option in helping protect fish populations.
Urbanization
Conservationists are now looking at urban MPAs to combat this loss of isolation. These are like other protected areas, just in or next to a large population center. With its proximity to human disturbances like tourism, boat traffic, and pollution, the question becomes; can these be as effective as their more isolated counterparts?
Researchers went to Monaco to study the Larvotto MPA to see if urban MPAs have a reserve effect. In Monaco, 90% of the coastline and shallow habitats have been modified or changed by human disturbance. The Larvotto MPA was established in 1976 and sits right along the city’s coastline, protecting the only Posidonia oceanica meadow in Monaco. This critical habitat is important for many fish species in the Mediterranean and is an important carbon capturer.
Larvotto Example
Two habitats in the Larvotto MPA were compared to nearby unprotected areas:
- Artificial rocky substrates
- Posidonia oceanica meadow
Species richness and biomass were significantly higher for artificial rocky substrates in the Larvotto MPA compared to unprotected areas. However, there was no significant difference between protected and unprotected P. oceanica meadows.
The presence of the reserve effect in the artificial rocky substrates but not the P. oceanica meadows was surprising. The main reason the MPA was established in the first place was to protect the P. oceanica meadows, but they displayed little to no difference to unprotected areas further away. One reason for this outcome could be high predation that masks the effects the protection has on the community.
The reserve effect on the rocky substrate saw substantial increases in high trophic predators (predators at the top of the food chain). They could be moving into the meadows to hunt on surplus food, reducing fish populations to similar levels seen outside the MPA. Nevertheless, this outcome demonstrates how dynamic habitat responses can be to protective measures in such a small area.
Urban MPA Solution?
Even though size is considered an important factor in MPAs, with larger areas having greater reserve effects, this study demonstrates that small MPAs that are highly enforced can be effective as well. Not only that, but the Larvotto MPA is benefiting an ecosystem next to a large population center. This seems counterintuitive with isolation considered the best barrier to protect the natural environment. Urban MPAs could be a bridge between the public and conservation with their proximity being a visual reminder of the benefits of protecting marine habitats. This can facilitate investment and interest from concerned citizens and stakeholders Not only promoting enforcement of its protections, but possibly grow our network of marine protected areas.
I am a recent MSc graduate in marine biology from Bangor University, where I studied population dynamics of elasmobranchs off the coast of Wales. My interests lie in ecological data analysis to understand environmental processes and identify natural patterns. However, nothing beats being in the field and interacting directly with the marine life.
