“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).”

CJA Bradshaw

 

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

 

The so-called ‘spillover effect’ is a long-standing debate in conservation ecology. The idea is relatively simple – put in a marine reserve (or, no-take zone, park, whatever you wish to call it as long as it restricts blanket over-fishing) and the area around the reserve eventually profits from the nearby over-production of fish (and other taxa). The idea is very attractive because even if you’re thick enough not to understand the absolute necessity of marine reserves in our age of mass, global over-exploitation, at least you might have enough grey matter to appreciate the value of more fish ‘spilling over’ into your favourite fishing area. More proposed marine reserves have been sold to the more Luddite ‘stakeholder’ this way than I care to count.

However, as attractive an idea it was, early on in the marine reserve literature (i.e., the early Devonian 1990s), there was limited (Rowley 1994; Willis et al. 2003) or only circumstantial evidence (Russ & Alcala 1996; Roberts et al. 2005) for the effect. Indeed, many have suggested that the spillover benefit, if present, depends entirely on the size of the reserve and whether adjacent areas are managed at all (Allison et al. 1996; McClanahan & Mangi 2000). Others have even suggested that marine reserves can displace fishing effort into smaller areas and change local community structure enough to facilitate invasion by exotic species (Kellner & Hastings 2009).

It is happier time now that we have more than ample evidence that marine reserves do in fact result in species spillover (e.g.,Roberts et al. 2001; Russ et al. 2004; Abesamis & Russ 2005). So it is not with any great claims of novelty that I highlight Garry Russ & Angel Alcala’s latest paper, Enhanced biodiversity beyond marine reserve boundaries: the cup spilleth-over; rather, it’s how they quantify the long-term evidence, the mechanisms for how spillover occurs and how the community changes that they deserve a mention.

Garry Russ, that denizen of marine spillover research, has produced a fine paper showing how communties change in response to the establishment of marine reserves. Using up to 25 years’ worth of data, Russ & Alcala show convincingly that:

• species richness increases linearly with time since reserve establishment, outside of the reserve as well as inside
• the change is not (primarily) due to habitat change
• the effect tapers off with distance from reserve (as has been shown before)
• large, predatory fish are more common inside and just outside reserves than farther away
• the community composition outside the reserves becomes more like that inside over time

It’s these last two points that I find fascinating: 1. The importance of maintaining top predators in guarding ecosystem health cannot be understated (see previous posts here, here and here); and 2. It’s not just an immediate benefit – entire communities slowly spread outward from the area of initial protection like a growing amoeba of recovery.

There are quite a few other titbits to discover in this paper, and certainly a wealth of literature is now available to say once and for all that marine reserves benefit everything within and around them, for fishers and non-fishers alike. Take heed the next time you think you are being relieved of your fishing ‘rights’ when someone proposes a marine reserve in ‘your’ favourite patch. If you want fish in your system for your children and grandchildren to enjoy, embrace such proposals with enthusiasm.

CJA Bradshaw

Russ, G., & Alcala, A. (2010). Enhanced biodiversity beyond marine reserve boundaries: the cup spilleth-over Ecological Applications DOI: 10.1890/09-1197