The purpose of marine reserves is to have some places where nature can flourish without human impacts. The recovery of life with release from fishing pressure is not surprising and has been repeatedly demonstrated. The benefits to people vary with the local situation, but include: educational (people can see what nature is like without being fished), spiritual (animals unafraid of people allow close interactions), scientific (understanding of ecology, including food webs, in natural conditions), and socio-economic (tourism, spillover of fish to fished areas).
However, declaring an area “protected” only regulates human activities at that location. These regulations do not enjoy jurisdiction over other human impacts, such as waste nutrients and littler entering the reserves from adjacent waters, including rivers. Neither can they prevent climate change. Thus we often hear comments that reserves cannot protect nature from everything. This is a flawed illogical statement, what Bill Ballantine would have referred to as an “invented problem”. It is comparable to telling somebody that controlling their diet and keeping fit will not protect them from every other risk to their life, like car accidents. Nobody eats well with the expectation that it is a panacea against all risks in life. Similarly, nobody has ever suggested that reserves are a panacea against every risk to nature because that would be equally absurd.
To take this analogy one step further, to live a healthy life does make one resilient to other risks, including diseases and helps recover from illness and accidents. This is common sense. Similarly, theory suggests that where biodiversity is healthy it will be resilient to natural and unnatural disturbances, from storms to diseases, invasive species and climate change.
In general, fisheries are the dominant human impact on marine biodiversity from local to global scales. Thus when MPA prevent fishing the fished populations recover within five and more years (Costello 2014), with consequent effects on their prey and competitors, and the rebalancing of the food web through a trophic cascade (Figure 1). In rocky reef ecosystems, sea urchins are predated by lobsters, crayfish, otters, and large fish. Once these predator populations recover then kelp and other seaweeds flourish where they were previously grazed bare by sea urchins (e.g., Leleu et al. 2012, Remy-Zephir et al. 2012). Thus biogenic habitat can recover as an indirect consequence of recovery of previously fished populations. The natural biodiversity has thus been restored. The increased abundance of top predators, the portfolio effect, and a more naturally functioning ecosystem makes the biodiversity more resilient to natural and anthropogenic disturbances.
Figure 1. The response of different components of biodiversity, from populations to communities and habitats, to release from fishing pressure, and the related mechanisms. The protection paradox is where an MPA may lose more biodiversity due to an environmental disturbance, including climate change, because it has more species and ecological interactions than areas already disturbed (such as due to fishing outside the MPA).
Bates AE, Cooke RSC, Duncan MI, Edgar GJ, Bruno J, Benedetti-Cecchi L, Côté IM, Lefcheck JS, Costello MJ, Barrett N, Bird TJ, Fenberg PB, Stuart-Smith RD. 2019. Climate resilience in marine protected areas and the ‘Protection Paradox’. Biological Conservation 236, 305–314. https://doi.org/10.1016/j.biocon.2019.05.005
Costello 2014. Long live Marine Reserves: A review of experiences and benefits. Biological Conservation 176, 289–296. http://dx.doi.org/10.1016/j.biocon.2014.04.023.
Leleu K, Remy-Zephir B., Grace R., Costello MJ. 2012. Mapping habitat change after 30 years in a marine reserve shows how fishing can alter ecosystem structure. Biological Conservation 155, 193–201.
Remy-Zephir B., Leleu K, Grace R., Costello MJ. 2012. Geographical Information System (GIS) files of seabed habitats and biotope maps from Leigh marine reserve in 1977 and 2006. Accessed at Dryad data archive http://dx.doi.org/10.5061/dryad.6vr28.