Seasonality and dynamics in coral reef macroalgae:
variation in condition and susceptibility to herbivory
Carine D. Lefe
David R. Bellwood
Received: 27 May 2009 / Accepted: 15 December 2009 / Published online: 28 January 2010
Ó Springer-Verlag 2010
Abstract Seasonal variation in coral reef macroalgal size
and condition is well documented, yet seasonal variability of
herbivory on macroalgae by coral reef ﬁshes is unknown.
Herbivore feeding intensity was quantiﬁed monthly on an
inner-shelf reef on the Great Barrier Reef, using Sargassum
bioassays. Removal rates of transplants displayed high levels
of variation with signiﬁcantly higher rates of removal during
the summer months. Differences in Sargassum plant size and
condition suggest that the variability in herbivore feeding
intensity is attributed primarily to the variation in the con-
dition of the macroalgae, especially epiphyte loads. The
dramatic changes in macroalgal removal reveal a consider-
able decrease in herbivore activity in the winter. This high-
lights the clear distinction between ‘summer’ and ‘winter’
months in terms of reef processes, emphasizing the high
seasonal variation in macroalgal removal rates at different
time of the year.
Recent decades have witnessed increasing concern
regarding the effect of human-induced disturbances on
coral reefs (Wilkinson 2002; Hughes et al. 2003; Pandolﬁ
et al. 2003). Much of the debate has been centred on
coral–algal phase shifts, where dramatic increases in the
abundance of macroalgae outcompete corals following
eutrophication and/or loss of herbivores (Hughes et al.
1999; Smith et al. 2001; Bellwood et al. 2004; Graham
et al. 2006; Mumby et al. 2006). Coral reefs are highly
heterogeneous systems, with numerous studies demon-
strating that the occurrence of macroalgae on Indo-Paciﬁc
reefs differs markedly over both spatial and temporal scales
(McCourt 1984; Steinberg 1992; Vuki and Price 1994;
Vroom et al. 2005).
Algal assemblages of the Great Barrier Reef (GBR) show
marked latitudinal, cross-shelf and within-reef variations in
composition and abundance (e.g. Wismer et al. 2009). In
contrast to mid-shelf and outer-shelf reefs, inshore or coastal
reefs typically have abundant and conspicuous macroalgal
communities (Diaz-Pulido et al. 2007; Wismer et al. 2009).
The reef ﬂat zone in particular is often dominated by dense
and highly productive beds of large ﬂeshy brown macroal-
gae, predominantly Sargassum (Fucales, Phaeophyta) (e.g.
McCook 1997; Schaffelke and Klumpp 1997).
Many benthic macroalgae are strongly seasonal in their
occurrence, growth and reproduction (Nizamuddin 1970;
Price 1989; Ateweberhan et al. 2006). Dominant canopy
algae such as Sargassum show pronounced peaks in bio-
mass during the summer and retain low biomass during the
winter (Martin-Smith 1992; Schaffelke and Klumpp 1997;
Diaz-Pulido and McCook 2005). Sargassum beds are thus
characterized by large and dense canopies of healthy and
relatively clean macroalgae in summer, but persist largely
as basal parts only, after a severe seasonal dieback in
winter (senescence) during which time they become
heavily epiphytized (Martin-Smith 1992). The effect of this
variability on ﬁshes, the dominant coral reef herbivores, is
Communicated by D. Goulet.
Electronic supplementary material The online version of this
article (doi:10.1007/s00227-009-1376-x) contains supplementary
material, which is available to authorized users.
C. D. Lefe
vre (&) Á D. R. Bellwood
Australian Research Council Centre of Excellence for Coral
Reef Studies and School of Marine and Tropical Biology,
James Cook University, Townsville, QLD 4811, Australia
Mar Biol (2010) 157:955–965