[Coral-List] Macroalgae in the Keys

Curtis Kruer kruer at 3rivers.net
Sun Jun 22 17:32:06 EDT 2008

Hi John,

If Billy Causey's job was only to manage for minimizing macroalgal cover 
cover you might be correct.  But the reality is that the Keys' coral 
reef ecosystem is a mess (for example shoreline mangroves, shallow 
seagrass, marine habitat disturbance and degradation, trap debris and 
trap impacts, loss of hard coral cover in popular dive sites, sacrifice 
zones on seagrass beds where 1000s of partying boats predictably and 
routinely congregate in shallow water, large vessels routinely 
resuspending sediment in coral areas, etc.) and has worsened 
considerably since the designartion of the FKNMS in 1990.  The job of 
the FKNMS was to protect and manage the coral reef ecosystem of the Keys 
for the good of all.   In my view (based on 30+ years of work there), 
and the view of many others, it has failed miserably.  As your email 
arrived I was working through some routine GIS and imagery review I do 
in the Keys utilizing high resolution 2006 color aerial imagery.  You 
should get a set and take a look for yourself.  


So that no one on the list is misinformed possibly you could clarify 
your comment - "....are in my view some of the world's most successful 
reef managers." - and explain that it applies only to macroalgae??  


Curtis Kruer


John Bruno wrote:

>MACROALGAL COVER IN THE FL KEYS:  Dear Chip,  Macroalgal cover in the  
>Florida Keys is only about 10%.  A recent paper based on CREMP  
>monitoring indicates that it was 9.6% in 2000 (Maliao et al. 2008,  
>Marine Biology).  My own unpublished meta-analysis based on CREMP data  
>plus a variety of other sources indicates it was "recently" 12.2 ±  
>0.4% (n=1048 quantative reef surveys performed between 1996 and 2005)  
>and macroalgal cover exceeded 50% in only 2.5% of these surveys.  This  
>is substantially lower than the average in the greater Caribbean of  
>roughly 20% and identical to the Indo-Pacific mean.
>Nobody knows what the historical baseline (i.e., the subregional  
>average, not the value on a single undisturbed reef) of macroalgal  
>cover was in the Keys (or anywhere else), but I doubt that it was any  
>lower than 5%.  So we may have seen a rough doubling of macroalgal  
>cover, but we are very far from a state that could rationally be  
>described as "macroalgal dominated" or "little more than rubble,  
>seaweed and slime".
>Billy Causey and his team are in my view some of the world's most  
>successful reef managers; the quantitative monitoring data indicates  
>that they have been very successful in managing the major threats to  
>reefs that they are capable of mitigating.  They obviously cannot  
>prevent climate change and coral disease outbreaks, but they have done  
>a good job at managing for low-ish macroalgal cover (which will  
>ideally, at some point facilitate coral recovery).  Macroalgal cover  
>the GBR is about 7% (based on AIMS monitoring), but those reefs are  
>10s-100s of km offshore, i.e., very isolated and naturally  
>oliogotrophic compared to the Keys, and didn't suffer the virtual  
>extinction of their key grazer or their dominant coral species as the  
>Keys did due to regional epizootics.  All things considered, at least  
>in terms of macroalgal cover, the Keys are in relatively good shape.   
>Lets give the Keys management team - and all the other successful  
>local reef managers - some credit, base our arguments and discussion  
>on the facts, and focus on the real threats to reefs.
>TOP-DOWN VS. BOTTOM-UP:  Dear Imam, assuming that like most of us you  
>are not swayed by the ideology and anecdotes you have been reading on  
>the list in response to your query, I'd start with Alina Szmant's  
>authoritative review (2002 Estuaries) of the published science on  
>nutrient and grazer control of macroalgal biomass on reefs.  You might  
>also look at Idjadi et al (2006, Coral Reefs), which documented the  
>immediate loss of macroalgal cover (to 6%) as soon as Diadema returned  
>to the scene on a reef purported to be one of the most eutrified in  
>the world.  There are a slew of other peer-reviewed papers that  
>document similar removal of macroalgae on reefs widely described as  
>highly eutrified once grazer populations recover (e.g., Edmunds and  
>Carpenter 2001 PNAS, Carpenter and Edmunds 2006 Ecology Letters, Mumby  
>et al. 2006 Science, etc.).  Also see Williams and Polunin (2001 Coral  
>Reefs); a very powerful and important study that documented the  
>striking negative relationship (r2=0.89) between fish biomass  
>(particularly Scarid biomass) and macroalgal cover.   Finally, if you  
>expand your search beyond the coral reef world, you'd find that in  
>estuaries and in temperate and cold water benthic systems, urchins and  
>other grazers are easily able to control macroalgal production that is  
>far greater, under nutrient concentrations many orders of magnitude  
>higher than those ever seen on reefs.  Just think about Jim Estes'  
>work on Pacific otters-you remove them, urchin populations explode,  
>macroalgae disappears and what remains is an "urchin barren"; and this  
>occurs in upwelling systems with lots-o-nutrients.  This was also seen  
>in the Gulf of Maine after Cod were removed by fishing (at least  
>before people started harvesting urchins, then the macroalgae all came  
>back); see Steneck and Carlton's and Duffy and Hay's very nice reviews  
>of all this the Marine Community Ecology book (eds. Bertness et al  
>2001, Sinauer-http://www.amazon.com/Marine-Community-Ecology-Mark-Bertness/dp/0878930574) 
>.  And look at the recent review by Heck and Valentine (2007 Estuaries  
>and Coasts) which outlines all the evidence for top down control in  
>estuaries around the world.
>If you stick to the hard science, the answer to your question is  
>fairly clear - at least as clear as anything gets in ecology.  Let me  
>know if you have any trouble getting any of these papers.
>John Bruno
>Associate Professor
>Depts. of Biology and Marine Sciences
>UNC Chapel Hill
>>Dear Imam,
>> The relationship between nutrients and algal growth is well  
>>established, and the influences of herbivory on algal growth and  
>>cover have also been demonstrated.  However, as Dr. Goreau stated,  
>>the lack of successful integration of nutrients and herbivory in any  
>>of those studies has contributed to a disconnect.  In Florida, where  
>>a large coastal population has resulted in mesotrophic and more  
>>typically eutrophic coastal waters, we have a high % of algal cover  
>>and biomass.  Add the facts that we do not fish for herbivorous  
>>fishes, and that we have removed a fair % of their predators; it  
>>follows that Florida would have an increase in herbivorous fishes,  
>>and therefore our relative herbivory.  But we are still plagued by  
>>macroalgal dominance, losses of coral and Harmful Algal Blooms. This  
>>suggests that nutrients are indeed an important factor shaping the  
>>algal community.  Hatcher and Larkum (1983, JEMBE 69, pp61-84)  
>>compared grazing and nitrogen concentrations on One Tree Reef in
>> Australia and found both grazing and nitrogen were important in  
>>limiting algal growth.
>>Rex "Chip" Baumberger
>>Biological Scientist, FAU
>>Marine Nutrient Dynamics Dept.
>>Marine Science Division
>>Harbor Branch Oceanographic Inst.
>>5600 US1 North
>>Fort Pierce, FL 34946
>>772-465-2400 x398
>Coral-List mailing list
>Coral-List at coral.aoml.noaa.gov

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