What we know about coral loss

See updates below in red

Without empirical evidence that a population or guild of critters is declining it is pretty hard to understand why they are becoming scarce or to justify any remediation. This kind of work is essentially ecological bookkeeping. Or a form of empirical environmental journalism. I hear all the time from science colleagues that “we already knew that was happening” or “we already know enough to stop…”. Perhaps. But I think it is impossible to build consensus about a problem if you can’t demonstrate it exists.

Is coral cover changing?

The null hypothesis is that there is no change in coral cover (for a species or all corals). And the one-tailed alternative is that there has been a decline. If we find evidence for the latter, we ask what is the rate of decline, how does it vary with space and time, etc. Inevitably, it is messy and complicated. Many reefs recover from natural and anthropogenic disturbances. But slightly more do not. Thus in general, we see a slow, downward trend in coral cover nearly everywhere data are available.

There are hundreds of single or multiple site papers documenting change in coral cover on reefs (including coral recovery). For example, an influential classic is Hughes 1994 (Science PDF here): one of the first studies to demonstrate really drastic declines in coral cover. Terry resurveyed nine reefs off the north coast of Jamaica in the 1970s then again in the 1990s. The definition of a “phase shift”:Screen Shot 2013-09-13 at 7.13.32 PM

Below is a list of the key papers that either synthesize existing data or cover a large geographic range and many survey sites.

1) Gardner et al. 2003 (Science PDF here) and Cote et al. 2005. The first meta-analysis of coral cover loss across an entire region. The results really shocked the world and suggested the results of Hughes 1994 were at least somewhat general (but see Bruno et al 2009 PDF). The definition of grim: Screen Shot 2013-09-14 at 8.35.07 AM

2) Bellwood et al. 2004 (Nature PDF here) analyzed coral cover surveys of the Great Barrier Reef for the first time and showed even the world’s “most pristine and best managed reef” was losing it’s corals: Screen Shot 2013-09-13 at 8.19.33 PM

3) Bruno and Selig 2007* (PLOS One link). We expanded on what had been done in these two studies by looking at coral cover trends across most of the Pacific ocean:

We compiled and analyzed a coral cover database of 6001 quantitative surveys of 2667 Indo-Pacific coral reefs performed between 1968 and 2004. Surveys conducted during 2003 indicated that coral cover averaged only 22.1% (95% CI: 20.7, 23.4) and just 7 of 390 reefs surveyed that year had coral cover >60%. Estimated yearly coral cover loss based on annually pooled survey data was approximately 1% over the last twenty years and 2% between 1997 and 2003 (or 3,168 km2 per year). The annual loss based on repeated measures regression analysis of a subset of reefs that were monitored for multiple years from 1997 to 2004 was 0.72 % (n = 476 reefs, 95% CI: 0.36, 1.08).

4) Bruno et al. 2009 (Ecology PDF here) analyzed 3581 quantitative surveys of 1851 reefs performed between 1996 and 2006 to determine reef state in terms of coral and macroalgal cover around the world. We found that the replacement of corals by macroalgae was less common and less geographically extensive than assumed. The figure below shows absolute living coral and macroalgal cover from the surveys in each region (the most recent survey from each site.) Screen Shot 2013-09-14 at 8.29.51 AM

5) Schutte et al. 2010* (MEPS PDF here) We expanded Gardner et al., taking the data through 2006 and increasing the number of surveyed reefs by nearly 10X.  The database included 3777 coral cover surveys from 1962 sites surveyed between 1971 and 2006. More grim, but signs of hope since coral and macroalgal cover had not changed much since the early 1980s, when the big drop in coral cover due to the white band disease outbreak occurred: Screen Shot 2013-09-13 at 10.02.04 PM

*note the data from these two papers was also used in Butchart et al. 2010 (Science PDF here)

6) Death et al. 2013 – read all about this study documenting frightening coral loss on the GBR here. The AIMS GBR database on which this study was based has been used in a number of other coral cover trends papers, several of which wrongly argued that coral cover was not changing on the GBR, e.g., Sweatman et al which I criticized here and here PDF. Death et al. 2013 found:

“from 1985 to 2012, mean coral cover declined nonlinearly from 28.0% to 13.8%”

This is an incredible if sobering finding. It suggests that the mean coral cover of the GBR is no higher than the Caribbean average (which according to Schutte et al. 2010, was 16.0 ± 0.4% (n = 1547) from 2001 to 2005. Fig-2-Death-et-al

7) Ateweberhan et al. 2011 (Coral Reefs PDF): ~ 2000 surveys of 366 reef sites between 1977 and 2005 across the Indian Ocean. Although there was evidence for substantial coral loss due to the 1998 El Nino (via related bleaching), most reefs have recovered and overall, there is little to no evidence for long-term coral cover loss. (HT to Doug Fenner for reminding me of this study)

Screen Shot 2013-09-17 at 8.48.07 PM

There are dozens of other reports on coral loss including the influential Status of Coral Reefs series put out by the IUCN (produced by the GCRMN in association with AIMS and then the RRRC until recently when IUCN took over coordination of the GCRMN) and the Reefs at Risk reports. These all have a quasi-quantitative quality to them and none are peer reviewed.  They do all contain valuable information, but rarely really dig in and synthesize and analyze the data.  Also note there are several ongoing projects that are amassing huge databases of tens of thousands of reef surveys and using cutting edge statistics and models to analyze the trends; e.g., the Jeremy Jackson-led IUCN project which published a preliminary report here (PDF). (See the final IUCN report here, but note there are numerous errors in it, including the authors flawed interpretation of the causes of coral losses).

Take home summary

As far as we can tell, the coral cover average of most regions is well below 20% and often closer to 10%. Therefore, I think we have lost at least 50% of living coral cover and more likely 60 or 70%.  And in some regions quite possibly as much as 80-90%.

By not indicting whether I meant absolute or relative losses in this initial summary, Ive managed to confuse quite a few people and even facilitated yet another Fenner-Goreau email spat. Im sorry for not being more clear. I am generally critical of the use of relative loss values, as they can exaggerate seemingly innocuous losses, e.g., from 4% to 2% cover = 50% loss!  So, I have attempted to clarify my summary below. 

Based on current coral cover (10-20% in most regions) and assuming the coral cover baseline (the historical regional average, not the average of undisturbed reefs or the maximum potential cover) was ~ 50%, there has been an absolute loss of 30-40% (coral cover) and a relative loss of 60-80%.  If you assume a higher baseline, the loss values obviously increase.  

Caveats galore: Since we don’t know what the coral cover baseline is, it is impossible to say exactly how much coral we’ve lost. The views among coral reef scientists vary quite a lot about what is “natural” in terms of coral cover. A recent survey indicated that 50-75% was the most common answer (90/207 respondents) to the question “What is the Indo-Pacific baseline for coral?” Yet a sizable number of people answered 25-50% or >75%. The same is true for the Caribbean, where both 25-50% and 50-75% were popular answers. (read more about coral reef baselines here). Additionally, both the baseline and the loss varies from reef to reef and region to region. Many of the word’s reefs are very poorly sampled. So our estimates of recent and current coral cover are not especially precise and maybe not particularly accurate. Finally, it is complicated because we haven’t really lost entire reefs. Instead we have lost coral cover on them. Corals are being thinned, rather than entirely removed. This is different from habitat loss in rain forests, and many other habitats and the loss values do not translate perfectly.

I think I need to add a shout out to Reef Check in particular but also to all the other scientists and groups that collected and shared their survey and monitoring data with me and others.  Thanks! 

Gomez et al 1981: I should have mentioned this in my post initially.  This is the mother of all large scale coral reef surveys.  Ed Gomez and his team surveyed 619 sites in the late 1970s (download the PDF here).  

Note, there are a few papers on trends for other metrics of “reef health” including Caribbean fishes (Paddack et al. 2009 PDF) and reef complexity (Alvarez-Filip et al. 2009 PDF). Yet much more of this type of work is needed. Why coral cover is changing is even more complex and fodder for another post.

25 Responses to “What we know about coral loss”

  1. So here we sit watching the demise of coral reefs and associated inhabitants while an endless debate persists regarding what constitutes acceptable baseline parameters.
    (Science can be extremely frustrating). There needs to be an “expedite” button that when pressed, determines that the point has been settled. Otherwise, this will go on until there is little or nothing left. At that point baselines won’t really matter will they. Wait, more likely the argument will then shift to whether or not coral reefs ever existed at all.

  2. Douglas Fenner says:

    First, I don’t think Sweatmann said that coral cover was not declining on the GBR. He said it was declining a lot slower than Hughes et al were claiming. His statements were based on hard data, the AIMS transect data. Check his reply to Hughes et al, and you find out that the graph which Bellwood and Hughes put in their paper, which they gave no source for, was clearly the AIMS transect data for the late years, and some other source for the early years (since AIMS was not collecting data back then) Most likely that data came from the Connell studies on the Heron Is reef flat, based on 1 m sq quadrats and never intended to show whether the whole reef was declining or not. That would explain the high variability.
    The low levels reached on the GBR shown in the paper by De’ath, Sweatmann et al. were based on manta board surveys. Those surveys produce data giving lower coral cover levels than transects, because people choose transect locations so they are in coral, no use of surveying sand or rubble or bare rock. But for tow board surveys, you can’t easily stop the tow board each time you hit a patch of sand, so they get recorded. Bear in mind both surveys are only done on one side of the reefs, on some of the GBR reefs, the other side is just an apron of sand or rubble. Ask a geologist whether those are parts of the reef or not, and you’ll get the answer that they are because they are reef carbonate. There is no easy answer to where reefs begin and end, and excluding areas that don’t have high coral cover will boost the amount of coral cover you record. No surprise. But the reality is that there are high coral cover areas and low coral cover areas, and different methods bias the results one way or another. There is no rigorous justification for any one absolute percentage of coral cover at one time, since it depends on where you measure.
    In addition, the De’ath paper reported results from manta board, which were taken by visual estimate! Not mentioned in the methods, but should have been. I’ve asked Hugh Sweatmann what the transect results are now showing, because his paper on the transect results didn’t include the most recent years. He says that the shape of the decline in the transect data is similar to that in the towboard data. So the decline is real, and if you look at the De’ath data the decline in the last couple years is the steepest (but if you look at variability in early years you could be excused for wondering if the apparent decline in the last 2 years might turn out to be statistical variation.
    One of the caveats that doesn’t seem to be discussed in these papers that average for whole ocean basins is that the sites from which the data come from are not the same each year. VERY far from it. Not the fault of the people doing the metanalysis, but, but, if you aren’t comparing the same sites, the changes in the average can be driven in part or in whole by which sites were measured in which years. That’s the explanation of the Bellwood and Hughes graph, one study using one method in one place in the first half of the time period, another study using different methods in different areas in the second half. The overall trend was produced by comparing apples and oranges at different times. This seems to me to be something that is a weakness in all the studies reporting absolute levels, other than local studies reporting the same sites, like the original Discovery Bay, Jamaica study by Hughes- there can be no doubt of the decline there because he surveyed the same sites (didn’t he?). Changes over time, however, could be computed for each site, and then the rates of change could be averaged over the whole ocean basin.
    The decline is way beyond any doubt, and it affects every ocean basin. The absolute value of coral cover averages for any basin, however, are less secure due to this sampling problem.

  3. Douglas Fenner says:

    I do, however, very much agree with Steve Mussmann. While we are trying to figure out more accurately what the changes have been and where, it is obvious that we have lost a great deal, and the time is long past for us to make serious efforts to stop the decline.
    There have been a lot of efforts to stop the decline, but as the NOAA review a few years ago concluded, while a lot of good things have been done, the reefs are still declining. They are still going down the tube.

  4. Douglas Fenner says:

    I DO think it is important to try to figure out how much we have already lost, where, and why. I don’t think why is the only thing we need to know, but yes it is critical to know why.
    I’d add that in figuring out how much we have lost, studies on the most pristine reefs that we can find, can supplement our study of what data was collected early on as well as later to find trends. For fish, study of very remote reefs that have had little if any fishing pressure has stunned most of us with the finding that they are dominated by large predatory fish like sharks and/or giant trevallies. We have known since Jeremy Jackson’s presentation at the Panama ICRS that megafauna on reefs were originally far beyond what we can imagine now. He was mainly talking of things like sea turtles and monk seals That has been added to with data from near-pristine reefs that shows that big reef fish, mostly predators, are amazingly abundant.
    This is relevant to the coral and algae questions, because surveys of near-pristine reefs also show that not all are near 100% coral cover as some have suggested. There are two Vroom papers that demonstrate that in the US Pacific islands. Another paper by McManus reviewed the data from near-pristine reefs he could find. In fact, macroalgae as well as other types of algae are surprisingly common on reefs humans have had little or no impact on, and coral cover is much less than sometimes supposed, coral cover less than 50% is common. Those sorts of figures don’t support the view that we have lost 80 or 90% of our coral.
    Another weakness in the metanalyses is that the sites were never chosen randomly, and there may have been some strong biases. There were only a few early studies doing transects and reporting quantitative coral cover. The locations were most likely not chosen without bias. One example is that Tom Goreau Sr. (wisely, I think) chose the best reef system he could find, to locate his marine lab, on the north shore of Jamaica. He says that in his writings. Others likely did the same. That bias could easily produce unrealistically high coral covers in early surveys. Look at the curve in the Jackson report for the early years. Huge, wild ocillations in the coral cover. Most likely not real at all, but due to data coming from areas of high coral cover at one time and low another. Average them out and you won’t get such high coral cover estimates.
    On the flip side, in many areas the largest data set is from Reef Check and it heavily influences the data from later years. One of the instructions to survey teams is to survey the best sites in their areas. Done for good intentions, and if the data now shows low coral cover then the actual situation is worse than we thought. But it is a source of bias, and we shouldn’t forget that.
    I think we have to work hard not to let our desire to show huge declines, which is driven by an admirable desire to boost conservation by showing huge losses, to color our collection, analysis, presentation, and interpretation of data. The pleas for conservation need to follow the science, not bias our science.

    Vroom, P. S. 2010. “Coral dominance: a dangerous ecosystem misnomer?” Journal of Marine Biology 2011: 164127.

    Vroom, P. S., Page, K. N., Kenyon, J. C., and Brainard, R. E. 2006. Algae-dominated reefs. American Scientist 94: 430-437.

    Fenner, D. 2009. The largest reef fish species were gone most places in the world
    even before scientists knew about it.

    McManus, J.W., Vallejo, B., Meñez and Coronado, G. (1995) ReefBase: an international database on coral reefs. In: Marine/Coastal Biodiversity in the Tropical Region (workshop proceedings). East-West Center, Honolulu.

    • John Bruno says:

      Dear Doug,Thanks for your comments.

      •I certainly agree, the goal here is an unbiased documentation of trends in nature. When the data suggests “good news” I publish it just as readily as the doom and gloom, re Bruno et al 2009, Schutte et al. 2010. Ive had many a reviewer claim doing so was “dangerous”.

      “surveys of near-pristine reefs also show that not all are near 100% coral cover as some have suggested. There are two Vroom papers that demonstrate that in the US Pacific islands. Another paper by McManus reviewed the data from near-pristine reefs he could find. In fact, macroalgae as well as other types of algae are surprisingly common on reefs humans have had little or no impact on, and coral cover is much less than sometimes supposed, coral cover less than 50% is common. Those sorts of figures don’t support the view that we have lost 80 or 90% of our coral.”

      •My point that some reefs have lost ~90% of their coral cover was based on places like the Florida Keys, Jamaica, Belize, Mexico, The Bahamas, etc where coral cover is close to 5%, assuming a baseline of 50%… I do agree that a baseline of 100% or even close to that is unlikely. And I agree completely with your broader point (see our paper on exactly this with Peter Vroom here).

      •Reef Check: The direction to survey the healthiest reefs is unfortunate, however, I have not been able to find any evidence that it actually happens or biases the outcome; e.g., see the Supp Text 4 “Potential biases in survey techniques and site selection”
      doi:10.1371/journal.pone.0000711.s004 for our 2007 paper here. Also, if the surveys were biased in this way, this would cause an underestimation of coral loss (which I think contradicts your broader point). I am very concerned about potential biases then and now in which reefs we survey. And sorting our which biases are important is complicated. I actually dont think there was an early bias to survey high cover reefs: few such surveys exist and that was the heyday of disturbance ecology, when many reef ecologists were gleefully documenting mass coral loss!

      •Sweatman et al 2009: the problem was not their analysis of their data at hand (at the time) but their assumption that the 1986 AIMS data represents the GBR baseline. Although there is little GBR data pre-AIMS monitoring, that is not the case for many other places. Go here for a thorough discussion of this.

      Finally, re Death et al 2013: I am sure their observed GBR decline is not a statistical artifact: the losses were the result of well-documented disturbances, eg COTS and storms. The big question is, to what degree those drivers of coral loss are natural and human-caused.


      • Douglas Fenner says:

        Note: I included the point about Reef Check that didn’t fit with the view I was proposing, precisely because it didn’t fit, I don’t want to cherry pick the data.

  5. John Parker says:

    It’s nice to know that Steve has “settled” this point. What a great way to avoid debate.
    Stating that coral reefs will disappear is the same alarmist BS spewed by Al Gore in his convenient lie.
    The history of coral reefs is change. They wax and wane. Our lifetime is a blink of the eye in this cycle. Try looking at the big picture once in a while. We’ll all be gone long before coral reefs are.

    • Douglas Fenner says:

      Yes, reefs do naturally wax and wane, in part from disturbances such as hurricanes. Coral cover increases in the absence of hurricanes, then a hurricane brings it down. Humans, of course, have changed that with a wide variety of human impacts, all of which are chronic unlike the hurricane, and cause sustained loss of corals. The Caribbean has lost much of its coral, as has the Indian Ocean. The Caribbean’s losses have been sustained so far. That’s all well documented.
      It is quite true that the geological structure of coral reefs will be here long after most of us are gone. However, the coral reef ecosystem may well not be. It is partly a matter of definition. If you define a community that is dominated by algae and has a tiny amount of coral (say, 4% coral cover or maybe 1% cover) as a coral reef because it sits on the geological structure called a coral reef, then yes indeed coral reef ecosystems will outlast you and I. But if you think that the word “coral” in “coral reef” means that corals must be abundant enough to function as one of the major reef builders, then you are very likely to be quite wrong. Increasing sea surface temperatures will reach the present threshold temperatures for mass coral bleaching within 3 decades. Events like El Nino which boost temperatures well above the averages (in some areas) will then be able to kill large parts of the world’s coral, much as it did in 1998 when it is estimated to have killed 16% of the world’s coral.
      We do know that corals can acclimate and/or adapt some. However, we don’t know how fast they can acclimate or adapt, or how much they can. That is the major wild card in predictions. No one at this point really knows how much they can adapt.
      So we can continue with business as usual and hope that the corals adapt and most of them don’t die, or we can try to take precautionary measures to head off what may well be a disaster. Many in the dive industry seem to be choosing to stick their heads in the sand and hope everything will be OK.
      Of course, global warming has a lot of other effects that will cost humanity dearly, far more than taking action to avoid it.

  6. John McManus says:

    Great article, especially regarding the ‘thinning’ of coral cover point. Just a correction: the Reefs at Risk reports were indeed peer reviewed, and extensively so. Recognizing the fact that existing, publicly available time series on coral reefs have been extremely patchy and strongly biased towards reefs that are convenient, popular and inexpensive to access, they used modern GIS modelling procedures to extrapolate existing information on reef threats. A much better approach would be to have monitoring sites distributed in an unbiased manner around the world, as described by Jeremy Jackson in his ICRS plenary last year. Several of us spent many years trying to organize such an effort, but it has been impossible so far to find a funding approach to support this. Good luck to the new effort, which will hopefully spread outside the Caribbean. In the meantime, these meta-analyses are a very helpful complement to the GIS-based analyses, and further integration of these two approaches will improve the analyses.

    Note that the early version of ReefBase was aimed specifically at meta-analyses. However, at the time, most scientists considered field data to be “capital”, for personal or institutional use only, even when funded by tax dollars. Now, with the advent of ocean monitoring programs and a crack-down by NSF on its data release policies, hopefully that will change and more substantial field data will become widely available.

    • John Bruno says:

      Thanks John, esp for the clarification, re RaR.
      Crazy that we don’t have a solid global monitoring program for reefs yet:(

  7. Dean Jacobson says:

    On a polluted atoll, the coral disease/COTS/algal overgrowth scenario is reducing coral to 5% or less (baseline above 75%) and increasing algae from less than 5% to over 80%”. But even an “unpolluted” site is getting in the act. On next-door Arno atoll, which has recently experienced serious COTS predations, I find that macroalgae varies from 80% within a kilometer of leeward ocean shore (high algae to the south). Fish/nutrient levels cannot possibly vary that much on this small spatial scale. This Microdictyon mystery deserves a closer look (COTS alone cannot explain it)!

  8. John Bruno says:

    This is from Gregor Hodgson via the CoralList (Sep 15 18:09:21 EDT 2013):

    Since 1997, Reef Check has carried out a global monitoring program of coral reefs using a standardized method based on about 30 indicators including living coral and recently killed coral, bleached and diseased coral. Prior to 2005, Reef Check teams were trained and led by Masters or PhD level scientists who were responsible for field level Q & A. Since 2005, all Reef Check data has been collected by individuals who have been through a formal training program, tested and certified to collect data. In fact about 75% of the data has always been collected by research scientists because Reef Check methods have been adopted by many countries and research institutes as part of their core monitoring program. Independent researchers such as John Bruno et al., have used the database for local and regional meta analyses. The database is available to any researcher. Our WRAS online coral reef database has been taken offline to transition it from a GIS to a Google Earth platform, and to merge it with our California NED online rocky reef database. http://ned.reefcheck.org/ An analysis of the 15 year coral reef dataset is due out in 2014. For a list of peer reviewed and other technical publications based on or related to Reef Check data please see: http://reefcheck.org/about_RC_Reef/Publications.php

    Reef Check offers regular training programs throughout the world using our local coordinators. If you think it is important to track coral reefs during the next 20 years of global warming, please contact rcinfo at reefcheck.org to arrange a training or if you would like to help coordinate surveys in a country where we do not have a coordinator.

    I am noticing two problems when researchers try to compare baselines now with pre-1980s data:
    1. there is a shifting baseline in new cohorts of coral reef researchers who have a hard time understanding what reefs actually were like 40 years ago, but typically have not read the old descriptive literature from pre-1970s such as Saville-Kent that provide exceedingly detailed descriptions of what the shallow reefs were like;
    2. a problem with meta-analyses that do not take into account the fact that in 2013, there are no “zero coral cover” data from former reefs or zones of reefs that are no longer reefs because they experienced 100% die off and so researchers no longer monitor them. Some former reef zones that were populated by Acropora palmata can still be seen, as the dead skeletons are still in place, but those formerly populated by the more fragile A. cervicornis are often simply gone. This means that the current regional and global coral cover estimates are probably underestimating the decline as researchers no longer include reefs that died and have not recovered.

    Gregor Hodgson, PhD
    Executive Director
    Reef Check Foundation
    PO Box 1057 (mail)
    17575 Pacific Coast Highway (overnight)
    Pacific Palisades, CA 90272 USA
    T: +1 310-230-2371 or 2360
    Gregorh at reefcheck.org
    Skype: gregorh001

    • John Bruno says:

      Gregor and I have disagreed about this many times: I don’t agree there are (many) reefs that are literally gone and no longer surveyed. The one exception might be the buried patch reefs in the inner GBR that Roff et al (2013) recently described.

      George Roff, Claire Reymond, Jian-xin Zhao, Yuexing Feng, Laurence McCook, Terry Done, John Pandolfi (2013) Palaeoecological evidence of a historical collapse of corals at Pelorus Island, inshore Great Barrier Reef, following European settlement. Proceedings of the Royal Society B (in press)

  9. Jez says:

    Hey John, where is that figure from (https://theseamonster.blog/wp-content/uploads/Screen-Shot-2013-09-14-at-8.43.04-AM1.png)? I couldn’t find it in the Jackson et al. 2012 link – it’s a more interesting figure than anything else in that pdf!

    • John Bruno says:

      Hi Jez: The figure came from the “final report” which is not yet public. I was also asked to remove the figure from the post…

  10. John Bruno says:

    Peter Sale just made this comment on the coral list:

    I second Gregor Hodgson’s comments on how younger reef scientists have no direct knowledge of how reefs used to be 40 years ago. That is one of the reasons why we assembled the booklet, Reef Reminiscences. It captures the memories of a number of older reef scientists concerning the places they worked in their youth. Yes, we may be wearing rose-colored glasses (or perhaps rose-colored cataracts), but I think we all tried to describe what we remembered without exaggerating.

    The document is available for download at http://inweh.unu.edu/wp-content/uploads/2013/05/Reef-Reminiscences.pdf

    Share it with your (younger) friends.
    Peter Sale

    Peter F. Sale
    Assistant Director
    United Nations University
    Institute for Water, Environment and Health

    • John Bruno says:

      Thanks Peter. We have highlighted the RR report (which I love) here several times. I think it is an invaluable resource. But I also think you underestimate the impact it and dozens of other reports, papers, lectures, videos, the Shifting Baselines site, etc. going back to Jeremy’s 1996 lecture & paper “Reefs Since Columbus” all making the same point, have had on “younger” ecologists. We hear you loud and clear! In fact, a few months ago when I asked coral-listers what they thought was “natural” on coral reefs, old timers like you and young pups including students gave the same answers (see the report on the survey here), suggesting to me that your work on this has been successful.

      • There is no easy answer to what is the ‘normal’ or pre-stress coral cover on a reef. I have wrestled with that question for many years.

        Back in the late 1970s Edgardo Gomez coordinated the largest survey in the world when he looked at many Philippine reefs. To aid communication he used a simple metric: 100-75% = excellent; 75-50% = good; 50-25% = fair; 25-0% = poor. Those were excellent means of communicating reef status in SE Asia to decision makers for reefs especially those in the belt between 7 deg N & S where there is virtually no influence of cyclones or major wave action. One example is Ambon Bay where the early descriptions were of ~100+% cover; now with all the pollution, sedimentation and destructive fishing, cover is close to zero.

        If one is to look at mid-Pacific reefs, the metrics above were not meaningful; the reef fronts and sides of many Pacific reefs can be pristine with 20 – 30% coral cover (or less), because wave action will clean out any branching and plating corals.

        I have often considered we need a scale of cover to fit the location, if there is sufficient anecdotal information or we have a good handle on coral cover vs the natural environment at that site i.e. wave fetch, storm frequency etc. You quote replies from questionnaires; these should be calibrated against the geographic location. Many GBR reefs rarely get above 30 – 50% because frequent cyclones prune them back; now cover is declining with a series of other impacts including COTS and pollution.

        There are raw data available from 1986 for 7 countries in the Caribbean if anybody wants to repeat these transect studies: Wilkinson, C., Nowak, M., Miller, I., Baker, V. (2013). Status of Caribbean coral reefs in seven countries in 1986. Marine Pollution Bulletin, 70: 7-9.

        The Status of Coral Reefs of the World series were produced by the GCRMN in association with AIMS and the RRRC. IUCN only recently took over coordination of the GCRMN. We attempted to get all chapters ‘peer’ reviewed and in most instances each chapter had 2 reviews, but often deadlines for publication and launches meant that some were summarily reviewed.

  11. John Bruno says:

    And more on coral baselines from Dennis Hubbard via the coral list:

    One other thing to consider in all of this relates to a discussion we all
    had at the RSMAS “Coral Reef Love IN” run by Bob Ginsburg back when reefs
    were just “declining”. One of the exercises was to have everyone present
    data on reefs that they started working on 20-30 years earlier (now 40-50
    years). The admitted blind spot in this approach was that, when everyone
    thought back, not a single one of us had chose the crummiest, nastiest
    reefs we could find. As a result, our “typical” reefs were initially chosen
    because they were the “biggest”, “best”, “most populated”, “most diverse”
    or some other descriptor that might suggest that they had little chance of
    improving and that chances were better than even that they might decline in
    subsequent years.

    None of this is to say that the evidence of decline is not compelling.
    However, the “shifting baseline” may work a bit in the opposite direction
    than is typically discussed. I guess my point here is that data or
    recollections from those of us who are fortunate to have taken 60+%
    abundance for granted are not perfect either.

  12. Douglas Fenner says:

    I would add to the key papers that synthesize existing data and cover a large geographic area the paper in Coral Reefs by Ateweberhan et al. 2011. They synthesized coral cover data from the Indian Ocean over time. They found that coral cover initially averaged about 38%, fell to about 10% right after the 1998 ENSO mass coral bleaching event, increased over the next 4 years, then stabilized at about 30%. Their analysis went up to 2005, so it would be interesting to see what has happened since then. But unlike the Caribbean and Pacific, there is no gradual decrease in coral cover, and there was a major increase after the losses caused by the 1998 bleaching. Also, the coral cover at the end of the study was the highest of the three oceans.
    I think this needs to be added to discussions.
    Also of some interest is the finding that coral cover seems to have stabilized in the Caribbean now, at least for the moment. At much lower levels than it should be, but stability is better than continuing to decrease.
    That fact along with the Indian Ocean study, suggest some caution when concluding that “the reefs are continuing to go down the tubes.” True for some areas, maybe not true for some others. That said, the future threats are immense, particularly climate change.

    Ateweberhan, M., McClanahan, T.R., Graham, N.A.J., and Sheppard, C.R.C. 2011. Episodic heterogeneous decline and recovery of coral cover in the Indian Ocean. Coral Reefs 30: 739-752.

  13. Christian says:

    Very interesting debate. Are there any data available for the Red Sea?

    • John Bruno says:

      I am sure there are but Ive never been able to get ahold of Red Sea data. Yossi Loya has certainly been monitring RS reefs (Eilat) since the 1960s (in fact he pioneered some of the survey techniques used today and not only on reefs). For Bruno and Selig, we tried to extract data on coral cover from his various papers and to get the data from him; in both cases unsuccessfully.

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