[Coral-List] Parrotfish not quick fix

[tim mcclanahan]

Peter
 
We did run a 14-year study to try to assist the recovery of parrotfish in a
mid-size fishery closure in Belize with an appropriate fished control. It
did not work out very well - it seems they recover slowly or not to levels
that can reverse erect algal dominance, as they did not reverse or really
even change the abundant erect algae after 14 years of closure. Supportive
findings were found in a Kenyan study where we found parrotfish were among
the slowest taxa to recover and not clearly associated with changes in the
benthos.
 
In both cases sea urchin numbers went down before parrotfish herbivory
recovered completely, so one could actually produce a low herbivory
transition when establishing fisheries closures.  We also think small
fisheries closures may not be able to achieve high recovery of parrotfish
and so closure size and time are expected to influence the results of
closures experiments.
 
So, while parrotfish may play an important herbivory role, I see the current
evidence to control and especially to reverse shift as equivocal. This may
be because of the low coral cover in most Caribbean reefs but also because
many of these taxa are actually avoiding the erect algae in favor of more
delectable turfs and other algal taxa. They may play some role in preventing
but a weaker role in reversing erect algal dominance. I think more
large-scale and long-term experiments and critical/skeptical evaluations of
the existing research are warranted given the many conflicting findings.
There seems to be selective citation of the few correlational reports of
parrotfish positive effects relative to the many unsupportive findings in
large scale closures, which are essentially large scale experiment that you
rightly request. 
 
These early results are unfortunate for those proposing a quick fix for
Caribbean reefs based on this single factor. It does, however, make sense to
just not fish parrotfish and to keep their numbers high everywhere to
prevent erect algal dominance where coral cover has not been degraded. Of
course, this will reduce yields to fisheries where even in Belize parrotfish
were a large part of the yield before they were banned.  The current ban in
Belize should produce some interesting results on the potential of
parrotfish to control algae on various scales of space and time. My guess is
the response will be slow and weak but I hope to be proved wrong.
 
See the paper abstracts below that give some of the key results and these
points are discussed in more detail in the papers.
 
Tim McClanahan
 
 
Belize Study
 
AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS
Aquatic Conserv: Mar. Freshw. Ecosyst. 21: 658­675 (2011)
 
Testing for top-down control: can post-disturbance fisheries closures
reverse algal dominance?
 
T.R. MCCLANAHANa,* N.A. MUTHIGA and R. A. COLEMAN
 
 
ABSTRACT
1. The response of fish, sea urchins, benthic cover, herbivory, and
predation on  sea urchins were studied over a 14-year period in and out of a
recently established  fully closed and fished atoll reef lagoon of the
remote Glover¹s Reef, Belize.
2. Closure from fishing was predicted to result in the recovery of predatory
fish and herbivores, herbivory rates, and subsequently reduce erect algae
and lead to the recovery of herbivore resistant and calcifying taxa such as
hard corals and calcifying algae. Recovery of predatory fishes was the
largest response to closure and the herbivore response was weak and no
corals and calcifying algae changed in the predicted direction.
3. Hard corals declined where they were most abundant and all sites appear
to have reached a stable point of ~15% cover by the end of the study.
Generalized and possibly opportunistic carnivores, such as jacks, barracuda,
groupers, snappers, grunts, and sparids showed the greatest increases and
there was a trend towards more small-bodied herbivores such sea urchins and
damselfish in the open and a slight gain in large herbivores in the closed
area, but this had little effect in increasing total herbivory.
4. Factors that may have influenced this unexpected response include: (1) a
complex food web that did not produce a simple cascade response; (2)
attenuation of the cascade effect towards the lower trophic levels; (3)
insufficient compliance, closure time, and space; (4) a post- rather than
pre-disturbance establishment of the closure; 5) habitat or site
specificity; and (6) overriding environmental disturbances, such as
oceanographic oscillations and a warming climate.
5. The results suggest a need to further evaluate fisheries management
systems, contingencies, and interventions that will promote coral reef
resilience to climate change and ecosystem sustainability.
 
 
Kenyan Study
 
MARINE ECOLOGY PROGRESS SERIES
Vol. 497: 13­23, 2014
 
Recovery of functional groups and trophic relationships in
tropical fisheries closures
Timothy R. McClanahan*
Wildlife Conservation Society, Marine Programs, Bronx, New York
10460, USA
 
 
ABSTRACT: Ecological changes associated with Kenya¹s fisheries closures
were examined using a space-for-time substitution chronosequence based on 5
fisheries closures that ranged in age since closure from 5 to 41 yr. The
chronosequence allowed estimates of the rates of change and recovery of key
ecological processes and functional groups. I asked if ~35 yr was sufficient
time for the ecosystem to recover and stabilize from fishing effects. Total
consumer biomass peaked at 15-20 yr, but the magnitude and time scale of
other functional group responses varied and were not always predictable
based on assumed successional rates of recovery (i.e. plants > herbivore
>carnivore > piscivore). For example, piscivore recovery was minor and
variable while the biomass of herbivorous fishes was slow and had not
clearly stabilized by the end of the time series. In contrast, predation
rates on sea urchins were a key process that increased slowly and sea urchin
biomass declined to very low levels at ~20 yr of closure. Against
predictions, total herbivory estimates and fleshy erect algae and hard coral
cover did not change with the age of the closures, indicating the importance
of multiple types of herbivores and climate disturbances. For benthic cover
groups, time since closure was a strong predictor (R2 > 0.50) for seagrass
and red coralline algae, which increased over time, and sand and calcareous
green algae, which declined over time. These changes were complete on the 20
to 30 yr time scale. Consequently, processes were generally slow and
functional group recovery was not fully complete by ~35 yr of closure. I
speculate that recovery processes and times in these closures are likely to
be influenced by human disturbances in the surrounding seascape and that
permanent, old, and large closures are needed to represent fully restored
tropical reef lagoon ecosystems.
 
 
Size and time of closure study in Kenya
 
MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 504: 119­132, 2014
 
Differential impacts of coral reef herbivores on algal succession in Kenya
A. T. Humphries, T. R. McClanahan, C. D. McQuaid
 
ABSTRACT: In shallow-water systems, fisheries management influences
herbivory, which mediates ecosystem processes by regulating algal biomass,
primary production, and competition between benthic organisms, such as algae
and corals. Sea urchins and herbivorous fishes (scrapers, grazers, browsers)
are the dominant herbivores in Kenya’s fringing coral reef and their grazing
influences coral-macroalgal dynamics and dominance. Using experimental
substrata and grazer exclusions, we tested the hypothesis that herbivores
differentially affect algal composition and succession using 3 levels of
fisheries management: fished reefs, community-managed closures (<10 yr old,
<0.5 km2), and government-managed closures (20 to 40 yr old, 5 to 10 km2).
In fished reefs and government closures, herbivores facilitated maintenance
of early successional algal species, such as turfs, associated with sea
urchins in the former and scraping fishes in the latter. Crustose coralline
algae were only abundant in government closures, and video recordings showed
that fish grazing was greatest at these sites, most notably for parrotfishes
(scrapers). A combination of sea urchins and small grazing and detritivorous
fishes was present in community closures, which allowed macroalgae to
quickly develop from turf into early then late successional stages. These
reefs may represent an intermediate or transitional system of herbivore
dominance characterized by macroalgae. Consequently, reefs in heavily fished
seascapes initially protected from fishing may require additional management
efforts to facilitate the recovery of larger-bodied scraping fishes,
including bans on capturing parrotfishes and restricting gear (e.g.
spearguns) that target these species.
 
On 7/9/14, 7:00 PM, "coral-list-request at coral.aoml.noaa.gov"
<mailto:coral-list-request at coral.aoml.noaa.gov>
<coral-list-request at coral.aoml.noaa.gov>
<mailto:coral-list-request at coral.aoml.noaa.gov> wrote:
 
>If all the ostensibly no-take MPAs across the Caribbean were functional,
>we'd have plenty of parrot fishes.  If just one decently scaled experiment
>that enhanced herbivory had been run, or if just one of the governmental
>decisions to protect parrot fishes was implemented with appropriate BACI
>monitoring so there would be data to evaluate, we might actually know if
>restoring herbivory will push the system back through the phase shift (not
>a given).