“One measure that often meets great resistance from fishermen, but is beloved by conservationists, is the establishment of marine protected or ‘no take’ areas.” Stephen J. Hall (1998)
I’m going to qualify this particular post with a few disclaimers; first, I am not involved in the planning of any marine protected areas (henceforth referred to as ‘marine parks’) in Australia or elsewhere; and second, despite blogging on the issue, I have never published in the discipline of protected area design (i.e, ‘conservation planning’ is not my area of expertise).
That said, it seems to becoming more imperative that I enter the fray and assess not only how marine parks should be designed, but how effective they really are (or can be). I’ve been asked by several conservation NGOs to provide some insight into this, so I thought I should ‘think aloud’ and blog a little mini-review about marine park effectiveness.
Clearly there is a trend to establish more marine parks around the world, and this is mainly because marine conservation lags so far behind terrestrial conservation. Indeed, Spalding et al. (2008) showed that only 4.1 % of continental shelf areas are incorporated within marine parks, and ~ 50 % of all marine ecoregions have less than 1 % marine park coverage across the shelf. Furthermore, marine protection is greatest in the tropical realms, while temperate realms are still poorly represented.
The question of whether marine parks ‘work’ is, however, more complicated than it might first appear. When one asks this question, it is essential to define how the criteria for success are to be measured. Whether it’s biodiversity protection, fisheries production, recreational revenue, community acceptance/involvement or some combination of the above, your conclusion is likely to vary from place to place.
Other complications are, of course, that if you cannot ensure a marine park is adequately enforced (i.e., people don’t respect the rules) or if you don’t actually place the park anywhere near things that need protecting, there will be no real net benefit (for any of the above-mentioned interest groups). Furthermore, most marine parks these days have many different types of uses allowed in different zones (e.g., no fishing, some fishing, recreational diving only, no boat transport, some shipping, etc., etc., etc.), so it gets difficult to test for specific effects (it’s a bit like a cap-and-trade legislation for carbon – too many rules and often no real net reduction in carbon emissions – but that’s another story).
All these conditions aside, I think it’s a good idea to present what the real experts have been telling us about marine park effectiveness from a biodiversity and fishing perspective over the last decade or so. I’ll summarise some of the major papers here and give an overall assessment at the end. I do not contend that this list is even remotely comprehensive, but it does give a good cross-section of the available evidence.
- McClanahan & Mangi (2000): For Kenyan coral reef parks, total wet mass of catches per trap, the mean size of the trapped fish, and the number of fish species caught per trap declined as a function of the distance away from the park edge. This relationship was truncated on the unmanaged side of the park which also had smaller catches, smaller fish, and fewer species than the managed side.
- McClanahan & Kaunda-Arara (2002): In Kenyan coral-reef lagoons on seven reefs over 6 years, most fish species within the park showed recovery after fisher exclusion.
- Gell & Roberts (2003): In a short review, these authors conclude that reserves and fishery closures benefit species as diverse as molluscs, crustaceans and fish of many sizes, life histories and mobilities. Benefits develop within 2-5 years of marine reserve establishment and continue to build for decades. Reserves work in coral reefs, kelp forests, temperate continental shelves, estuaries, seagrass beds, rocky shores and mangroves.
- Halpern (2003): Probably the most comprehensive review of 89 marine park studies concluded that on average, density, biomass, size of organisms, and diversity (except for invertebrate biomass and size) were higher inside reserves compared to outside (or after reserve establishment versus before) for all species and examining each functional group (carnivorous fishes, herbivorous fishes, planktivorous fishes/invertebrate eaters, and invertebrates) separately.
- Mumby et al. (2006): In Caribbean coral reef systems, these authors showed that marine reserves benefit both grazers and their predators, but more so for algal grazers. This, in turn, benefits coral reefs by removing competing algae biomass.
- Shears et al. (2006): In New Zealand marine parks (one with full fisher exclusion, the other with partial exclusion), legal-sized spiny lobster (Jasus edwardsii) were 11x more abundant and biomass 25x higher in the no-take marine park following park establishment, while in the partially protected marine park there was no measurable change in numbers.
- Stelzenmüller et al. (2007): In a Mediterranean reserve system, catch-per-unit-effort (CPUE) of total fish and CPUE and length of common pandora (Pagellus erythrinus) increased close to the reserve. CPUE and length of striped red mullet (Mullus surmuletus) slightly increased also near the reserve.
- Stewart et al. (2009): In another comprehensive review of temperate marine parks, these authors found higher density, biomass and species richness in reserves compared to adjacent exploited areas.
- Kellner & Hastings (2009): Demonstrated that displacement of fishing into smaller areas by the establishment of marine parks can facilitate the invasion of marine pests.
So the general conclusion is yes, marine parks benefit biodiversity and help to recover fish populations depleted from fishing (with the possibility of some unintended consequences though for community composition). There are also a host of studies looking at the socio-economic advantages/disadvantages of marine reserves that I won’t attempt to get into. It does seem however from that perspective that marine reserves are generally considered, despite initial resistance, positive components of coastal human communities.
I’ll leave you with some words by Ben Halpern in his 2003 review:
“Despite the popularity of marine reserves as a management tool, few reserves appear to have been created or designed with an understanding of how reserves affect biological factors or how reserves can be designed to meet biological goals more effectively (e.g., attaining sustainable fish populations).”
McClanahan, T., & Mangi, S. (2000). Spillover of exploitable fishes from a marine park and its effect on the adjacent fishery Ecological Applications, 10 (6), 1792-1805 DOI: 10.1890/1051-0761(2000)010[1792:SOEFFA]2.0.CO;2
McClanahan, T., & Kaunda-Arara, B. (1996). Fishery Recovery in a Coral-reef Marine Park and Its Effect on the Adjacent Fishery Conservation Biology, 10 (4), 1187-1199 DOI: 10.1046/j.1523-1739.1996.10041187.x
Gell, F. (2003). Benefits beyond boundaries: the fishery effects of marine reserves Trends in Ecology & Evolution, 18 (9), 448-455 DOI: 10.1016/S0169-5347(03)00189-7
Halpern, B. (2003). The impact of marine reserves: do reserves work and does reserve size matter? Ecological Applications, 13 (sp1), 117-137 DOI: 10.1890/1051-0761(2003)013[0117:TIOMRD]2.0.CO;2
Mumby, P. (2006). Fishing, Trophic Cascades, and the Process of Grazing on Coral Reefs Science, 311 (5757), 98-101 DOI: 10.1126/science.1121129
Shears, N., Grace, R., Usmar, N., Kerr, V., & Babcock, R. (2006). Long-term trends in lobster populations in a partially protected vs. no-take Marine Park Biological Conservation, 132 (2), 222-231 DOI: 10.1016/j.biocon.2006.04.001
Stelzenmuller, V., Maynou, F., & Martin, P. (2007). Spatial assessment of benefits of a coastal Mediterranean Marine Protected Area Biological Conservation, 136 (4), 571-583 DOI: 10.1016/j.biocon.2007.01.002
Stewart, G., Kaiser, M., Côté, I., Halpern, B., Lester, S., Bayliss, H., & Pullin, A. (2009). Temperate marine reserves: global ecological effects and guidelines for future networks Conservation Letters, 2 (6), 243-253 DOI: 10.1111/j.1755-263X.2009.00074.x
Kellner, J., & Hastings, A. (2009). A reserve paradox: introduced heterogeneity may increase regional invasibility Conservation Letters, 2 (3), 115-122 DOI: 10.1111/j.1755-263X.2009.00056.x