Online Debate: Large no-take areas — Is their total environmental impact positive or negative? With Callum Roberts and Ray Hilborn

Event Date: 
8 October 2013

This debate was held 8 October 2013, and was sponsored by, MPA News, and the EBM Tools Network.

  • Callum Roberts argued that the total environmental impact of large no-take areas — such as Australia’s recently designated 500,000-km2 no-take area in the Coral Sea — is positive. Callum is a professor of marine conservation biology at York University (UK) where he studies the use of no-take areas as tools for biodiversity conservation and fishery management, among other subjects. He authored the books The Unnatural History of the Sea and The Ocean of Life: Fate of Man and the Sea, and has served on advisory panels to multiple ocean studies commissions.
  • Ray Hilborn argued that the total environmental impact of large no-take areas may be negative due to the need to make up food production from other, more environmentally damaging methods, either at sea or on land. Ray is a professor in the School of Aquatic and Fishery Sciences at the University of Washington where he studies conservation, natural resource management, and fisheries stock assessment and risk analysis. He has published over 200 peer-reviewed articles and is author of Overfishing: What Everyone Needs to Know, published by Oxford University Press.

The debate is now closed. The debate transcript is below, followed by a transcript of the audience discussion, which occurred simultaneously to the debate.

RH: Imagine we closed all the oceans to fishing. There is no doubt that fish abundance would rise and most measures of biodiversity status would improve in the oceans. But what else would happen? The food that was not produced by fishing would either be made up by food production with another technology, or someone would eat less. Would the global environment be better or worse? This would depend on the environmental costs of the food production that replaced the fish compared to the benefits of improved ocean environment. If 80 million tons of lost fish production was made up by chopping down rain forest to grow cattle, I think the global environment would be worse off. Capture fisheries produce food at lower environmental cost than livestock and most forms of aquaculture. No water, pesticides, fertilizer or antibiotics are used, and greenhouse gas emissions are lower. These same trade-offs must be considered when large areas of the ocean are closed – what will be the environmental benefits, how much current or potential food production will be lost, and what are the environmental costs of alternatives.

CR: From your opening statement Ray, I think you are trying to debate a different question to the one posed. I read the question as this: Very large no-take areas are being established at an increasing rate worldwide, mainly in remote and so far little-exploited regions. Their creation is warranted given the increasing reach of the global fishing industry and use of sophisticated satellite sensing to guide fishing boats to hotspots of marine life. While they create new challenges in areas of compliance building, surveillance, enforcement and international cooperation, these hurdles do not mean we should not create large MPAs, only that we have important learning to do.

RH: I believe the question we are addressing is whether large no take areas have a net global environmental benefit. The marine conservation community simply does not consider the bigger question of the impact closing large areas has on other marine and terrestrial environments by forgoing current or potential food production.

CR: Ray: You say, fish production has a lower environmental footprint than many other food production systems. Setting aside for a moment that this question is irrelevant to whether or not to establish very large no-take MPAs. The fact that one form of production is more environmentally-friendly than another, does not mean that it is desirable or feasible to continue exploitation of fish at that level, or that decreases in fish production must automatically be substituted by more damaging foodstuffs.

RH: Regarding large vs small, I don't think there is a lot of disagreement that small MPAs can in fact increase food production if the adjacent fisheries are overharvesting

CR: Ray, across much of the world, wild fish production is not sustainable. The calculations you have made on the environmental footprint of production assume sustainability. For a large fraction of the world ocean there is a large and growing unaccounted environmental cost in the form of decline of fish stocks.

RH: The status of fish stocks is very different in different places. Most of the large marine closed areas we are discussing are in countries with well managed fisheries -- the Australian coral sea being a good example. This is not a place that was being overfished. The places that are being overfished are generally not the places that large MPAs are being proposed.

CR: You are right, Ray. In fact where these large MPAs are proposed are generally places with little fishing. Protecting them would 'cost' very little in lost yield. For 10% cover of very large MPAs, I would guess short-term loss of 0.1% to 1% production at most. There are ways we can increase fish availability which don’t require increased fishing: waste less – use discarded bycatch, (estimated at 7 and 20 mt per year). Using forage fish directly rather than via aquaculture would free up 9 mt of fish. Improve management, including rebuilding spawning stocks with MPAs could add 10 to 20mt per year. Together better management might yield a further 26 to 49 mt. This production would not come at the cost of any of the very large MPAs currently under consideration.

[Question submitted by Daniel Cressey: Callum: how much of the total ocean area would you like to see protected as no-take? Ray: how much of the total ocean area would you like to see remain open to fishing? Is there a number you can both agree on for this? Or is it specific, local MPAs that are the source of contention here?]

CR: Reply to Daniel Cressey: I would like to see 30% of the ocean no-take. I think that is justified by the scientific evidence. (I have a review in prep.)

RH: I don't see this question as a scientific one - it is a question of personal choice and my opinion has no more value than anyone else's. I believe it is clear that there is a trade-off between how much of the ocean we close, and food production. This depends a lot on where we close and the management system where those closures occur.

CR: I think the science I have reviewed suggests there is a hump-shaped relationship between protected area coverage and benefits, with benefits rising to begin with, then falling. The benefits peak lies somewhere between 20 and 50% coverage depending on what is being examined (e.g. maximising fishery yield, minimising probability of collapse, representing a given fraction of biodiversity).

RH: This is such old bogus science -- if the fisheries are well managed there is no yield benefit to closing areas. The GBR in Austrialia has seen catches decline proportionally to area closed, with zero benefits from spillover.

CR: You can never 'well manage' all of the species all of the time. This is why we need spatial management in the form of a mix of MPAs and gear restrictions, among other measures. Otherwise a whole bunch of vulnerable species drop out of the system at economic levels of fishing effort. To keep them, we need no-take areas.

RH: With respect to maximizing food production we might want to have some species depleted -- that is certainly how we do it in agriculture. I agree there is a role for small reserves if we want to protect vulnerable species, but don't pretend you will produce more food by doing so.

CR: The problem with this approach is a misleading comparison with agriculture. Simplification of ecosystems, as we know from agriculture, leads to instabilities like pest or disease outbreaks that we fix with chemicals and/or careful husbandry. We have no such recourse in the sea. In this 'wild' place, we need to maintain ecosystem complexity to avoid problems. So 'scallop and prawn' barrens may be good in the short run for some, but in the long run they are highly risky.

RH: Let's get back to large reserves, the topic of the debate. I am not arguing that the environmental cost is necessarily higher than the benefits, but that it MAY be higher and those costs need to be considered. For instance lots of people think we should close the Antarctic and Arctic oceans. Well there will be costs to foregone food production.

CR: There MAY be costs, but as I said earlier, most of the proposed very large MPAs will not cost much in terms of present food production because they aren't fished much. We clearly have to deal with an increasingly hungry planet, but we also need places that protect vulnerable species and ecosystems. It would be a dull and dysfunctional world if all the oceans were intensively exploited.

RH: I am not arguing for any specific amount of the ocean to be protected, but simply highlighting the trade-offs that do occur. Would 99% of the people of the world even know if the all the oceans were exploited (sustainably) or not? I doubt it. Well-managed exploited areas are very much like natural systems. The key is moving to sustainable management in all the world's oceans and another trade-off is the millions (perhaps hundreds of millions) of dollars spent on advocating and setting up MPAs could be used to improve fisheries management.

CR: I agree there is a pressing need for better fisheries management. But an indispensable part of the management package is MPAs. On the subject of increasing global food production, there are many alternatives to increasing fishing. Here are some examples:

Foley et al. Nature (2011) Close the productivity gap for crops between potential and maximal possible productivity on underperforming lands. Switch to crops that have higher production per unit area (e.g. by growing crops better suited to the local climate). Reduce waste in the food production chain. Switch to eating less energy or chemical intensive types of food.

Stehfest et al (2009, Climatic Change)“…a global food transition to less meat, or even a complete switch to plant-based protein food to have a dramatic effect on land use. Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned, resulting in a large carbon uptake from regrowing vegetation.”

McMichael et al. (2007, The Lancet) Reducing the global average red meat consumption from 100g/person/day to 90g would stabilise greenhouse gas emissions from livestock production at present levels, with large benefits for health.

RH: I see no evidence that MPAs are indispensable to good fisheries management in places that have the ability to regulate fishing pressure. In closing let me point out that the chief scientist for The Nature Conservancy (Peter Kareiva) has said that the challenge for preserving biodiversity lies in human used areas, and I believe that the vast funds and energy going into MPA establishment in developed countries would better be applied to improving fisheries management in places that do not have good management systems.

CR: Marine conservation has lagged far behind terrestrial conservation. The most vigorous phase of large protected area creation on land is probably behind us now. But in the oceans it has only just begun. Today’s and future generations deserve large and nearly intact protected areas. Even if you never personally visit, life is enriched by the knowledge that there are wild places in the sea where nature continues in all its richness and wonder.

Sarah Carr: **** And that's a wrap, folks! A huge thanks to our debaters, Ray and Callum, for being willing to do this and to all of our participants, especially those who hung in there through the technical difficulties.****

Sarah Carr: *** If there are any other debates through this forum (without the technical difficulties) you would like to see place, please suggest them in the green box. Or e-mail possible debate topics to info [at]

Audience Questions and Comments

Daniel Stanilovic: Professor Callum Roberts in regards to the Coral Sea no take areas, the management plans for this area and all six bio regions that make up the Australia’s commonwealth marine park network, have not been proceeded by the necessary threat assessment, the threats to these areas have not been identified let alone prioritised. How can you protect this area if you don’t even evaluate what the threats are in the first place?

Keith Lawrence: While there are examples of large no-take zones (eg Chagos), most large scale MPAs are multiple use areas (eg PIPA, Cook Islands, Galapagos, Gt Barrier Reef) with zoning for different uses e.g. tourism, fisheries, protecting critical habitats. How do you view this type of MPA as being different from implementing effective marine spatial planning, or implementing a seascape-scale initiative?

Taylor Gorham: I would like to hear from both of you what you think of creating a large marine protected area (the Blue Halo) in the Sargasso Sea around Bermuda? Is it essential to do this to protect pelagic species? What will the impacts be on Bermuda, both the positive and in terms of opportunity loss?

WeFish: PEW, almost every environmental NGO in Australia, the previous federal government as well as the Australian Greens have all stated that these so called protection areas will not affect recreational fishing as anglers don’t go to these areas, and that they will only affect 1% of commercial fishing in Australia. Have we wasted an opportunity to offer some real protection by taking the soft approach and unfairly targeting the soft targets that have little or no impact, while ignoring the real threats?

TomasT: Prof. Hilborn, we are NOT closing all oceans to fishing,not sure what was the point of your comment. Where is the empirical evidence that closing large aras will have negative effects due to displacement of fishing effort?

bgrassbluecrab: I'm interested in the tradeoffs between easier to declare, large remote areas (like HI) versus smaller, targeted no-take areas that might be harder to wrangle

hydeaway: Is the sea a valuable resource or is it purely an ornament?

Tony G: Professor Callum, please answer Ray's question about the impact of shifting food production to other sources. Then Ray can answer your question about large versus small MPAs. If the answer is you don't know then that is OK and the question must be a part of the equation in a more prominent way. Thanks.

gbustamante: what other options do we have in the Caribbean than no take areas combined with areas of responsible fishing if fisheries regulations are weak and its enforcement even weaker? you tell me.

Pete Flournoy: I agree with Tony G.

JBruno: Tony G, I can answer the question: a) the premise is absurd; we are talking about restricting fishing in small, remote places, b) as is well-known, marine reserves can increase production. Next?

AL KINGSTON: Is a global net economic & environmental benefit guaranteed by the introduction of large widespread NTZ's? Doubt we're anywhere near knowing this but it probably depends largely on what happens outside the NTZ as a result of it's introduction but these wider effects are rarely taken into account in a timely manner.

chris.malin: Ray, it seems to me that you are missing the mark here with the point of no-take reserves. They are not designed to prevent resources from being obtained, but rather for the displacement of fishing for some amount of time, thus allowing for resources to rebuild. In fact, much of the better research on no-take reserves shows that fishing improves after some period of time due to spillover effects. Many fishers have attested, after initial resistance, to the increase in abundance of fisheries species.

marine concern: With respect to Prof. Hilborn; no one is or ever has even suggested closing the oceans to fishing. Humans are part of the eco-system, but with a Global population over 7 billion and growing, and as supposedly 'advanced' beings we should be more responsible for our actions, anything less will surly come back to bite us.

Please keep to the subject in question, not the propaganda normally associated with some in the fishing associations.

John Hocevar: Ray's "question" was a red herring and off-topic, as literally no one is proposing that all fishing be brought to an end.

Francini_Filho: Ray just said: "small MPAs can in fact increase food production if the adjacent fisheries are overharvesting" It is just a matter of scale.

Bsandvicensis: What about anthropogenic effects that affect the MPAs, such as toxic runoff, plastics, and bleaching/acidification? That has a tremendous impact on MPAs regardless of size, therefore its efficacy as a nursery is only as good as the environment within it.

DanielCressey: Callum: how much of the total ocean area would you like to see protected as no-take?

Ray: how much of the total ocean area would you like to see remain open to fishing?

Is there a number you can both agree on for this? Or is it specific, local MPAs that are the source of contention here?

Daniel Stanilovic: Professor Callum Roberts in regards to the Coral Sea no take areas, the management plans for this area and all six Australia’s commonwealth marine park bio regions, have not been proceeded by the necessary threat assessment, the threats to these areas have not been identified let alone prioritised. How can you protect this area if you don’t even evaluate what the threats are in the first place?

SamanthaMurray: Whether looking at MPAs large or small, we have to be careful when making assumptions about the relationship between the % of area closed and the % of fish caught (or not caught). We need to also account for the fact that fishermen tend to be opportunistic and fish elsewhere, not just hang up their gear (though that can happen in some key, heavily fished areas).

marine concern: sorry guys the tech. issues are too much to follow the thread, my screen keeps going blank with an error code. If this can be fixed can this be re-done in the future? A very important issue. 30% no-take, and now! Large or small; varied and dispersed.

AL KINGSTON: why the fixation on 30%

pablogd: The old contention between conservation and management of natural resources still prevails.

marine concern: 30% was the average deemed to be workable by a range of top scientists

WeFish: Would it be possible to pass the question on to both participants so they can be answered at a later time?

SamanthaMurray: Most large MPAs are in remote, unfished areas. Displacement is likely to be very minimal and would not necessarily mean increased reliance on terrestrial sources of protein, such as beef.

Bsandvicensis: What about anthropogenic effects on yield? MPA size isn't the only consideration. These are non-insignificant factors, and highly variable based on location of MPA.

globalsteward: I'm interested in learning more about the spill over effect as it seems to be a benefit for both sides. Do MPAs in palegic habitats increase fish stocks in shallow reef areas and vice versa?

AL KINGSTON: which top scientists? there is still much debate about the merits or otherwise of MPAs of any description, that is why some of us are here.

Tony G: Sorry, but the technology got the better of me. I typed in a long well-reasoned question and it simply disappeared. Please reschedule this fascinating debate when the technology is fixed. Thanks!

WeFish: SamanthaMurray The question then is if you are removing something that isn’t happening, while ignoring the real threats how are you protecting anything?

JBruno: Daniel Stanilovic, the threats in the coral sea and on the GBR are in fact VERY well known and documented. Most are land based threats: CO2 emissions and agriculture

Bsandvicensis: In your models, is "scientific take" permitted in these no-take MPAs? Or are they 100% excluded? Scientists vary on whether this should be allowed.

JBruno: Daniel Stanilovic happy to provide citations. But you can start here

WeFish: My point exactly JBruno the management plans do nothing to address these threats

oceanpeople: 30% was simply a number out of the hat. MPA's are NOT a substitute for good management of human behavior. They have been a fallback position, and a postage stamp solution, to frustrations over our inability to truly manage human impacts on the oceans.

SamanthaMurray: Hey WeFish--I'd say that a mix of 1) small reserves in areas that are being fished, combined with 2) large MPAs in more remote areas to preserve the status quo and ensure that we have protected these places regardless of future advances in technology and gear would be a smart global strategy for MPAs.

glazerr: What about the benefits of closed areas with respect to reducing depensatory processes on reproduction (Allee effects) - especially with highly mobile species? higher densities -> increased per capita reproductive output.

Danny Fox: Prof York why is it that you target fisheries that are well managed and on the other hand you infer they are easy targets for MPA's because they are not overfishing?

oceanpeople: Samantha, You have it right on. But what is essential to protect is the real question.

Thad Murdoch: To RH - surely there is more to consider than just food production. Deleting species willy-nilly to crank up human food seems pretty short-sighted considering we are still learning the functional role of most biota.

Lynn Michele Wilbur: I have to agree with Hillborn on his point that areas of overfishing are not areas under consideration for MPAs. Alaska is in the midst of declining herring stocks and has recently re-opened commercial fishing on nearly depleted yelloweye rockfish. MPAs need to be instated in Alaska other than placing deep water zones off limits along the Aleutian chain. I also agree with Prof. York, too much waste is occurring, and aquaculture (in Alaska's case, salmon hatcheries) use valuable wild fish meal 9 months a

chris.malin: In regards to my earlier comment about spill over effects, there are examples of this from the Gulf of Mexico no-take reserves. For example Madison Swanson marine reserve. Management and proper size of reserve large enough to sustain fisheries of interest (e.g. grouper/snapper) is crucial. Enforcement and areas large enough to protect spawning populations are crucial components to the success of such reserves.

WeFish: I think a lot of people have a misunderstanding of the model of these marine parks they are not designed to protect species in need of protection, but they are supposed to be designed to remove all the threat we can manage so the area is in a better position to look after it self, if the management plans allow the major threats to continue they can only fail.

emilysdarling: Fishing is a real threat, but so are multiple stressors (nutrient and sediment runoff, climate change and invasive species) which are big problems even inside MPAs. The solution is to manage for many problems at one. Inside MPAs, reduce the impact of different local stressors. For global stressors like climate change, we need smarter MPA design, such as MPAs targeted in areas of natural environmental refugia.

bgrassbluecrab: does the flavor of this question (efficacy of large MPAs) change when incorporated in the larger discussion of marine spatial planning?

JBruno: WeFish: I do see your point and I have not read these management plans. In theory, they SHOULD address these issues and Id think at least they would address directly issues from the coast, like runoff from farming.

glazerr: To RH: wouldn't large reserves increase the probability of reproductive encounters in highly mobile species due to increased densities?

JBruno: But as others have said, the point is to protect a place WHILE IT IS STILL CLOSE TO PRISTINE rather than have to restore fishes after overexploitation.

Bsandvicensis: emilysdarling: That was essentially my question regarding the anthropogenic effects on their modeling numbers. Without taking these into account, and foreign items such as derelict fishing gear, plastics, I don't think these estimates are accurate.

tundia: Emily- I agree. The simple default is to ban fishing but the solution is rarely tailored to the problem + the unintended consequences and (especially ecological) costs of displacement are rarely considered. Then the problem of creating the illusion of effective management with the designation of largely meaningless large reserves that have little support by society at large and increase distrust of conservationists.

Thad Murdoch: How about the other costs/benefits of limiting other industries within MPA - such as deep-sea mining or industrial aquaculture?

JBruno: Ie, we anticipate a threat from fishing in these rare places like the coral sea, Galapagos, etc is coming if we dont institute real protection. Like Yellowstone in the US.

Pete Flournoy: the trouble is we are making all these MPAs with no baselines, little enforcement, and insufficient follow-up and no attempt to control; pollution -- just stop fishing! Then we have the mythical large MPAs like Kiribati's which is kind of a joke since fishing there is on the increase -- it isn't closed.

Bsandvicensis: Close to pristine, understood. But you can't stop C02 bleaching, plastics wafting into areas, etc, even if they ARE left pristine. I think the numbers are ambitious unless something can be done to police MPAs from threats such as these and illegal take.

JBruno: "Super-sized MPAs and the marginalization of species conservation" by Dr N Dulvy

defender_of_fish: To both: this debate is framed around "large no-take areas"; I feel that their total environmental impact would depend on their location:

oceanpeople: To RH: Doesn't your concept of "well managed" hinge on the assumption that single species management is a viable way to approach these large ecosystem questions?

AL KINGSTON: I agree with "tundia", displacement and diversification (in NON-NTZ situations) are rarely given enough attention but can be crucial in terms of assessing the outcomes of spatial restrictions.

WeFish: One example of a threat that is allowed to continue un- managed in the Coral Sea no take area, is shipping, there is plenty of peer reviewed research showing the very negative impacts from shipping to our sea mammals. Some environmental groups claim that shipping possesses a larger threat to recovering endangered whale then whale hunting.

bgrassbluecrab: Phf - and if a country gets to check it's environmentalism box by putting a large, perhaps unenforced MPA in then they can step away from more effective actions

defender_of_fish: my question: to CR: do you favor no take areas in both developed and developing countries regardless; why or why not? to RH: do feel their is no circumstance that favors large no take areas?

jdavis: RH: Are there examples of large no-take areas in existence that you believe have *not* had a negative total environmental impact? CR: Are there examples of large no-take areas in existence that you believe have not had much of a positive total environmental impact?

John Gourley: We in the Marianas Islands had serious issues with the 2008 Pew orchestrated environmental campaign to create the Marianas Trench National Monument. Basically, the Monument gave an outgoing President with a poor environmental record a “Blue Legacy” and as a bonus, the US Military got a marine playground - the indigenous people got the shaft. Professor Callum - How does one justify the creation of large no-take MPA’s by political force and not through science?

John Hocevar: "I believe that the vast funds and energy going into MPA establishedment in developed countries would better be applied to improving fisheries management in places that do not have good management systems"... or pay Ray Hilborn to advocate for them.


emilysdarling: Great point John Gourley. Don't forget about local people in MPA planning and implementation process. Co-management improves conservation and social goals of MPA

JBruno: bgrassbluecrab, wefish : I totally agree w that; an unenforced largeMPA is worse than nothing = it is falso advertising, like the bogus cure in World War Z (the book, not the movie)

WeFish: Could public perception that something’s totally protected when it’s not be detrimental to our marine environment?

JBruno: John Gourley, Emiy Darling, there are no "local people" in many of the places we are discussing, eg NWHI, Coral Sea, etc

bgrassbluecrab: So if we're looking to terrestrial parks as a model (debate-able role model), what lessons can be learned from the problems in terrestrial park development?

AL KINGSTON: are we talking science or something else?

defender_of_fish: well that was sort of an interesting debate... kind of anticlimactic...

WeFish: Globally terrestrially we have seen an increase in species loss that almost coincides with the increase in protection areas both

oceanpeople: Sorry, JBruno, but all these places have had traditional indigenous uses for centuries. When we take such broad, sweeping looks at things, the local realities get swept aside - like in the Marrianas.

Lynn Michele Wilbur: Nothing misunderstood about what MPAs are intended for; I have participated in videography of areas of recruitment and rearing for commercially important fish. Some species in Alaska are K-selected species, requiring up to 25 years to mature. Identifying and protecting these areas where these species congregate, (which are are also very rich in species by Alaska standards), from trawling, to anchoring, to hunting marine mammals (nod to WeFish)


Hi everyone, this is Nick Wehner, Project Manager for OpenChannels. I sincerely apologize for the technical difficulties we all encountered during the live debate. It was a live event after all, you can't script life! The Chat system we use is provided by a third party, so it's external to our site. That way a large turnout like we had today (700+ people on the page!) doesn't take down our website. All our previous live chats have been much smaller than this, and our Chat provider simply couldn't keep up with the influx of users. We doubled our plan for with our Chat provider, and even that barely got us through the full hour. We certainly loved the turnout, and we're sorry it wasn't a smooth experience. I'm exploring other Chat providers now. With luck, I'll find one that offers a similar two-screen appearance but with much more server horsepower. If you have any suggestions, send them to me at nwehner[at]openchannels[dot]org - I'd really appreciate the advice! Again, sorry the live debate didn't start off the way we expected, but at least it ended well :) Cheers! -Nick

Thank you for giving us the opportunity to discuss this issue, I am sure it is just as important to people of both sides of the debate, perhaps one day we can all work together on our common goals.

Kudos to your group for bringing this highly emotional topic to the forefront. No doubt that the interest displayed highlights the need to find balance on a simple problem yet complicated solution. Well Done!! Danny

Very interesting discussion here. I'm in favor of MPAs small and large to protect areas, preserve pristine habitat, address ecosystem-wide impacts of fishing, add insurance, etc. I've seen what happened on land: all areas on land not in reserves are way more affected than fished areas in the ocean. The exact proportion protected is a personal and political choice (I'd be happy with 30%). But numerous papers show that MPAs won't improve fisheries yield unless the populations are already overfished. In such cases yield would also improve if overfishing was reversed and rebuilding allowed ("traditional management"). However, JBruno and EmilySDarling strongly argue that the big threats to coral reefs are CO2 output, nutrients, sediment runoff and other problems caused by agriculture. Ray shows that closing large areas to fishing will lead to more food production from other sources, increasing CO2, nutrients, sediment runoff and other problems caused by agriculture. So there are tradeoffs here: closing areas to fishing could lead to worse coral health from terrestrial causes.

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