1) Are MPAs actually any good at preventing coral loss?
2) What can they realistically protect against?
3) Are MPAs being established in the right areas where they are needed the most?
Now they shall be answered.
A paper by Selig and Bruno (2010) examining the global effectiveness of MPAs in preventing coral loss goes some way to answer the first question. Like with the information given in the previous post, this paper highlights that MPAs have been reasonably useful in the rehabilitation of fish and invertebrates that were overharvested. The idea of 'no-take' and what I have termed 'diminished-take' policy, has lead to optimism that reduced fishing has positive indirect effects on corals. This is primarily through the restoration of food webs that can prevent the outbreak of coral predators. Furthermore, more intact food webs limit the coverage of macroalgae due to greater numbers of the grazer population being present and incourages coral growth. A study by Mumby and Harborne (2010) corroborates this and focuses on the use of herbivorous fish species to restore coral reefs after impacts occur. The researchers found that reductions in algal cover due to an increase in the parrotfish population resulted in a faster rate of coral recovery than those areas where fishing was not prohibited. The study shows that the coral recovery was significantly greater inside a Bahamian reserve than outside over a two and half year period. Moreover, the beneficial role of an intact food web is highlighted by the significant negative correlation between algal cover and coral cover. This proves that MPAs in an indirect way can facilitate coral rehabilitation but the process must be an ecosystem-wide solution.
The direct benefits of MPAs on coral reefs are all mechanical in nature. It prevents destructive fishing techniques, anchor damage and terrestrial runoff. This results in reduced sedimentation and nutrient pollution thereby decreasing the limiting factors that impact coral (these are mentioned earlier on in the blog). Selig and Bruno (2010) state that MPAs can be effective in preventing coral loss. They mention that no change in coral cover over 38 years occurred in reefs within MPAs versus those in unprotected areas which continued to decrease. A key point that needs to be raised from this study is that the effectiveness of MPAs is a function of time. In the Caribbean, the results show that things get worse (14 year decrease after implementation) before they get better indicating a natural lag which is understandable. After X amount of years of coral increase, rates stagnate and level off highlighting that the population recovery reached what they term "saturation point". The study also looked at Indo-Pacific MPAs and the results are different here. They had the same decline as the Caribbean reefs but then increased at 2% per year for 22 years. However, during 1998 there was a strong El Nino which devastated this coral cohort. Despite this, there is a positive message. In older MPAs coral cover change returned to rates around zero. This highlights increased coral resilience which is extremely positive.
Now to the second question. I have found that MPAs do not automatically result in positive effects on coral cover. It is safe to say that on a local scale MPAs have the greatest benefit and whilst the evidence above looks good, the sites used have some significant inconsistencies. Coral loss that is determined by regional or global stressors such as climate change or coral disease is unlikely to be protected by MPAs. due to MPAs having only so much control. They cannot prevent the flow of seawater or pathogens and the transfer of heat. This is shown above with the El Nino example and this quote from the BBC article reaffirms this idea...
"And a recent paper on the demise of the Barrier Reef demonstrates that declaring an area protected does not necessarily shield it from distant influences like over-nutrification."
As such, a little perspective is needed. MPAs whilst beneficial cannot protect against everything but they can, as seen above, help to build resilience so that the impact may be less severe next time round.
Number 3. I get the impression from both academic literature (Selig and Bruno, 2010) and news reports such as the one from the BBC, that whilst MPAs are being introduced at a greater rate and into important areas for conservation, there are a lot of MPAs being declared in areas that do not need them. It almost seems like in some cases they are being implemented for the sake of reaching this target with little thought about where they should be placed. Obviously it is fair enough placing them in areas that have high biodiversity with a number of rare species, but they should also be placed where there are large human populations that have the potential to terminally destroy the reef ecosystem. Focus needs to turn to areas where a large population and high biodiversity exist. More thought and planning is needed by governments it seems as quotes like this from the BBC article are not the most encouraging..."I don't want to knock any of the MPAs but some appear to be easy wins, where you could stick a pin on a map and maybe send a patrol vessel. We need more than that.".
I hope that these are sufficiently answered and you are able to weigh up the pros and cons of MPAs. It seems that their ability to achieve results must be understood correctly as well as where they should be placed and how they should be enforced.
A change to the usual sign off!
Seb
No comments:
Post a Comment