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