1. NOTE
Location, location, location: small shifts in collection site result
in large intraspecific differences in macroalgal palatability
Kathryn N. Keeley • Jolie D. Stroh •
Diem Samantha C. Tran • Caitlin R. Fong •
Peggy Fong
Received: 17 May 2014 / Accepted: 11 February 2015
Ó Springer-Verlag Berlin Heidelberg 2015
Abstract The role of herbivorous fishes in coral reef
resilience has increased interest in the process of herbivory
and has focused attention on herbivore feeding behavior,
making it important to evaluate experimental methods used
to assess herbivore decisions. We tested whether small-
scale differences in collection site play a role in within-
species palatability of macroalgae. Baseline grazing assays
using algae collected on a fringing reef in Moorea, French
Polynesia, revealed that herbivore preferences among three
common species ranked Padina boryana [ Sargassum
mangarevense ) Amansia rhodantha. Comparing grazing
preferences between individual thalli of the same species
collected 15 m apart revealed that consumption of
intertidal S. mangarevense was nearly six times greater
than for conspecifics collected from the adjacent subtidal
reef flat. The same trend occurred for P. boryana but was
not significant. This demonstrated that algal palatability
can vary on a very small spatial scale, presenting a
potential trap for the unwary when setting up experiments;
we encourage researchers to consider this potential com-
plication in experimental studies of herbivory.
Keywords Spatial variability Á Herbivore choice Á
Macroalgae Á Palatability Á Herbivory
Introduction
Studies of the relative palatability of coral reef macroalgae
have become increasingly common over the last 30 years,
as coral reefs have shifted from dominance by coral to
dominance by various forms of algae (e.g., Bellwood et al.
2004). We define palatability in terms of relative con-
sumption of available algae (similar to selectivity in
Mantyka and Bellwood 2007a, b). Early studies demon-
strated that herbivory controlled algal community structure
across a reefscape, with undefended forms of macroalgae
only proliferating in reef areas that functioned as refuges,
such as intertidal reef flats and off-reef sand plains (e.g.,
Hay et al. 1983). These studies stimulated much research
into the responses of algae to herbivory, especially how
anti-herbivore defenses reduce palatability (for a recent
review see Fong and Paul 2011). More recent studies have
sought to understand the role of individual species of
herbivorous fish in supporting this key grazing function by
assessing their level of functional redundancy or com-
plementarity within the herbivore community (e.g., Man-
tyka and Bellwood 2007a, b; Burkepile and Hay 2008,
2011; Brandl and Bellwood 2014; Rasher et al. 2013).
Taken together, these recent studies suggest that herbivore
specialization on different types of algae is more common
than previously thought, though whether this has always
been the case or is in response to modern reefs supporting
more algae (and therefore more choices) is not clear. What
is clear, however, is that herbivore choice experiments
have become important to further our understanding of the
functional roles of both herbivores and algae on modern
coral reefs.
While studies of within-species differences in palat-
ability are less common, the available evidence suggests
that there is considerable spatial variation that may be
Communicated by Biology Editor Dr. Hugh Sweatman
K. N. Keeley (&) Á J. D. Stroh Á D. S. C. Tran Á P. Fong
Department of Ecology and Evolutionary Biology, University of
California, Los Angeles, CA 90095-1606, USA
e-mail: k.n.keeley@gmail.com
C. R. Fong
Department of Ecology, Evolution, and Marine Biology,
University of California, Santa Barbara, CA 93106, USA
123
Coral Reefs
DOI 10.1007/s00338-015-1274-2

2. associated with environmental context (e.g., Bolser and
Hay 1996; Taylor et al. 2003). For example, spatial var-
iation in intraspecific palatability has been attributed to
differences in tissue nutrient content through bioassay
experiments comparing grazing of algae cultured under
ambient and enriched conditions in order to model spatial
differences in nutrient supply. In some cases, enrichment
enhanced consumption (e.g., Fong et al. 2006; Chan et al.
2012), while in others, it lowered consumption by
increasing anti-herbivory defenses (S J Bittick, personal
communication). Spatial variation in palatability may also
be attributed to an individual alga’s history of herbivory, as
defenses can be induced by specialist grazers (Pavia and
Toth 2000), though differences in grazing history may not
always explain spatial patterns (Taylor et al. 2003). How-
ever, while studies have demonstrated that intraspecific
macroalgal palatability can vary at a relatively large spatial
scale (e.g., *8–30 km between inshore and offshore
locations separated by coastal barrier islands; Taylor et al.
2003), it is unknown whether palatability varies on smaller
scales.
It is especially important to understand this variability in
intraspecific palatability at small scales because algae used
in palatability experiments are often collected at the scale
of a reef (e.g., Rasher et al. 2013), reef zone (e.g., Hay et al.
1983; Hoey and Bellwood 2009), or potentially even
smaller scales (e.g., a single algal patch in Fong et al. 2006;
Smith et al. 2010; or within a 100 m length of reef slope in
Chan et al. 2012), although the actual size of collection
sites is rarely stated. In contrast, when studies do give
details of exact collection locations for multiple species of
algae offered in choice experiments, algae may be col-
lected from widely different locations for a single experi-
ment (e.g., Mantyka and Bellwood 2007a, b). This may be
necessary in some instances, as very palatable algae rarely
co-occur with highly unpalatable species that are common
on reefs (e.g., Hay et al. 1983). However, this method
assumes that palatability of algal species varies little in the
spatial scale that such collections are made. Here, we
describe an instance on a fringing reef in French Polynesia
where algal species varied substantially in palatability
between sites only 15 m apart.
Methods
To evaluate whether small-scale spatial differences in
collection site affected herbivory rates among common
species of coral reef macroalgae, we conducted surveys to
characterize the herbivorous fish community and two
experiments to evaluate herbivore choice. The first
experiment established a baseline consumption rate when
algal species were offered individually. We then conducted
choice experiments that offered the same algal species
collected 15 m apart. All research was done in February
and March of 2014 on a fringing reef along the north shore
of Moorea, French Polynesia (17°290
S, 149°510
W), an area
of high topographic complexity from dead coral heads
killed during a recent crown-of-thorns starfish (Acanthaster
planci) outbreak. Herbivorous fish in the families Acan-
thuridae, Scaridae, Siganidae, and Kyphosidae were sur-
veyed along 50 9 2 m belt transects between 0900 and
1500 hrs (modified from Xavier et al. 2012). Surveys
(n = 15) were conducted on the subtidal reef slope where
choice experiments were deployed. No fish were observed
in the intertidal reef zone. All experiments occurred in a
*10 9 10 m area at a depth of 2–3 m. For our baseline
herbivory experiment, the macroalgae Padina boryana,
Sargassum mangarevense, and Amansia rhodantha were
selected, as they were common (personal observation) and
congeners or similar functional forms were deemed pala-
table in previous studies (Mantyka and Bellwood 2007a, b).
Padina boryana and S. mangarevense were also used to
assess intraspecific palatability and were collected low
either in the intertidal zone or in the adjacent subtidal area
(*0.5–1.5 m deep). While P. boryana and S. mangar-
evense sites were B15 m apart, the algae were noticeably
different; intertidal algae were darker and thicker, with no
visible grazing scars (personal observation). Amansia
rhodantha was never found intertidally.
The first experiment assessed the palatability of the three
macroalgal species when herbivores were presented with a
single choice. For this experiment, P. boryana and S. man-
garevense were collected intertidally and A. rhodantha
subtidally. Macroalgae were collected haphazardly, but
limited to whole thalli. Macroalgae were cleaned of visible
epiphytes and invertebrates, spun in a salad spinner for 60 s,
wet weighed, and attached to 12 9 12 cm hardware cloth
experimental units. Each unit was comprised of 8 g of only
one of the algal species, n = 6 for each species. Ex-
perimental units were deployed approximately 2–3 m deep
on the fringing reef, at least 1 m apart. Damselfish territories
were avoided (Ceccarelli et al. 2005). After 4.75 h, experi-
mental units were collected and algae wet weighed (as
above). Herbivory rates were as calculated as percent loss,
where [(initial mass - final mass)/initial mass] 9 100.
Hourly rates were calculated by dividing biomass loss by the
hours algae were deployed. Data did not meet assumptions
even after transformations; therefore, a nonparametric
Kruskal–Wallis test compared hourly herbivory rates among
algal species, and a Wilcoxon sign rank was used to identify
where means differed.
Our second experiment evaluated whether the collection
location for P. boryana and S. mangarevense (intertidal or
shallow subtidal) had an effect on intraspecific herbivory
rates. Separate experimental units for each algal species
Coral Reefs
123

3. contained 6 g of intertidal and 6 g of shallow subtidal
macroalgae, with n = 19 for S. mangarevense and n = 10
for P. boryana. Units were deployed for 5 h and hourly
rates calculated. Data met assumptions, and paired t tests
tested for differences between means.
Results and discussion
Only herbivorous fish in the families Acanthuridae and
Scaridae were present in surveys. The mean abundance of fish
in the Acanthuridae (54.8 9 100 m2
± 12.9, mean ± SD)
was nearly five times higher than those in Scaridae
(11.5 9 100 m2
± 6.7). Common species include Cte-
nochaetus striatus, Acanthurus nigrofuscus, and Zebrasoma
scopas. Siganidae and Kyphosidae were never observed in the
study site.
When baseline experimental units containing only one
of the three algal species were exposed to herbivory, there
was a significant difference in hourly consumption rates
between the three species (Kruskal–Wallis, p = 0.0006;
Fig. 1). Post hoc analysis revealed significant differences
between all treatments (Wilcoxon pairwise controlled for
error using a sequential Bonferroni, 0.0001 for all three
comparisons). Padina boryana was consumed nearly six
times more than A. rhodantha but only 1.5 times more than
S. mangarevense. Sargassum mangarevense was consumed
nearly four times more than A. rhodantha.
Padina and Sargassum were among the most palatable
of the 12 species of algae offered in choice experiments on
the Great Barrier Reef (Mantyka and Bellwood 2007a, b),
though members of neither genus were identified to species
in these studies. In contrast, Sargassum polyceratium was
one of the least palatable in a comparative study using six
species in the Caribbean (Chan et al. 2012). Different
herbivore species vary considerably in their choices (e.g.,
Burkepile and Hay 2011), and therefore, these regional
and/or congeneric differences may be driven by differences
in the herbivore community. Taken together, these results
suggest that relative palatability among algae may vary
between regions and congeners, and therefore, it is im-
portant to consider algal palatability within a local and
species-specific context.
Herbivory rates were higher overall for algae collected
from the intertidal site versus the subtidal site (Fig. 2).
Sargassum mangarevense thalli collected intertidally were
consumed nearly six times more than thalli collected from
the adjacent shallow subtidal zone (paired t test,
p 0.00001). While intertidal P. boryana also appeared to
be consumed at a faster rate than subtidal P. boryana, this
difference was not significant (paired t test, p = 0.1372).
Our study demonstrated that, within a single species,
macroalgal palatability can vary greatly on very small
spatial scales. It is likely this difference is a result of
phenotypic responses to environmental conditions or levels
of herbivory that may vary between the two habitats, de-
spite their close proximity. The nutrient content of
macroalgal tissue can vary across kilometers, likely as a
function of differences in nutrient supply (Fong et al.
2001), and that tissue nutrient content affects herbivory
rates (Chan et al. 2012). Herbivores can induce defenses
(Pavia and Toth 2000), and herbivory is lower in intertidal
reef flats (Hay et al. 1983). Thus, it is possible that our
intertidal algae were more enriched, less defended, or both
Fig. 1 Rates of consumption of Padina boryana, Sargassum
mangarevense, and Amansia rhodantha by herbivores when each
species was presented separately. Bars represent mean ± SE. n = 6
for each species
Fig. 2 Rates of consumption of a Sargassum mangarevense (n = 19)
and b Padina boryana (n = 10) collected from the intertidal and
shallow subtidal reef flat. Bars represent mean ± SE. Asterisk
indicates significant differences between treatments
Coral Reefs
123

4. compared to their subtidal conspecifics, making them more
palatable to herbivores. Regardless of the underlying
mechanism, our study is the first demonstration that
palatability can change on the scale of meters. This implies
that care must be taken when collecting algae for choice
experiments so that results are not confounded by differ-
ences in palatability caused by small-scale differences in
environmental or biotic context.
Acknowledgments We thank the UCLA Department of Ecology
and Evolutionary Biology, the UCLA Office of Instructional Devel-
opment, and the Holmes O. Miller Endowment for their support. We
also appreciate Director Frank and Hinano Murphy, as well as the
staff at the UC Berkeley’s Gump South Pacific Research Station for
welcoming us and facilitating our work. This is contribution number
209 from the Richard B. Gump South Pacific Research Station.
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