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Calcified macroalgae – critical to coastal ecosystems and vulnerable to change: a review

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Marine and Freshwater Research
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Wendy A Nelson at University of Auckland
Wendy A Nelson
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Abstract

Calcified macroalgae are distributed in marine habitats from polar to tropical latitudes and from intertidal shores to the deepest reaches of the euphotic zone. These algae play critical ecological roles including being key to a range of invertebrate recruitment processes, functioning as autogenic ecosystem engineers through provision of three-dimensional habitat structure, as well as contributing critical structural strength in coral reef ecosystems. Calcified macroalgae contribute significantly to the deposition of carbonates in coastal environments. These organisms are vulnerable to human-induced changes resulting from land and coastal development, such as altered patterns of sedimentation, nutrient enrichment through sewage and agricultural run-off, and are affected by coastal dredging and aquaculture. The consequences of increasing sea surface temperatures and fundamental changes in the carbon chemistry of seawater due to CO2 emissions from anthropogenic activities will have serious impacts on calcifying macroalgae. It is not yet understood how interactions between a range of variables acting at local and global scales will influence the viability of calcifying macroalgae and associated ecosystems. Research is urgently needed on all aspects of the taxonomy, biology and functional ecology of calcifying macroalgae. Without an understanding of the species present, measurement of change and understanding species-specific responses will not be possible.
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www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 2009, 60, 787–801
Calcified macroalgae – critical to coastal ecosystems
and vulnerable to change: a review
W. A. Nelson
National Institute of Water & Atmospheric Research, Private Bag 14-901, Wellington 6241,
New Zealand. Email: w.nelson@niwa.co.nz
Abstract. Calcified macroalgae are distributed in marine habitats from polar to tropical latitudes and from intertidal
shores to the deepest reaches of the euphotic zone. These algae play critical ecological roles including being key to a range of
invertebrate recruitment processes, functioning as autogenic ecosystem engineers through provision of three-dimensional
habitat structure, as well as contributing critical structural strength in coral reef ecosystems. Calcified macroalgae contribute
significantly to the deposition of carbonates in coastal environments. These organisms are vulnerable to human-induced
changes resulting from land and coastal development, such as altered patterns of sedimentation, nutrient enrichment
through sewage and agricultural run-off, and are affected by coastal dredging and aquaculture. The consequences of
increasing sea surface temperatures and fundamental changes in the carbon chemistry of seawater due to CO2emissions
from anthropogenic activities will have serious impacts on calcifying macroalgae. It is not yet understood how interactions
between a range of variables acting at local and global scales will influence the viability of calcifying macroalgae and
associated ecosystems. Research is urgently needed on all aspects of the taxonomy, biology and functional ecology
of calcifying macroalgae. Without an understanding of the species present, measurement of change and understanding
species-specific responses will not be possible.
Additional keywords: calcified green algae, carbonate deposition, Corallinales, ecosystem engineers, invertebrate
recruitment, maerl, ocean acidification, rhodoliths.
Introduction
The vulnerability of calcified marine organisms is being recog-
nised as the impacts of human-induced changes on global climate
and the long-term ecosystem consequences that may result are
being evaluated (e.g. Anthony et al. 2008). Rising temperatures
(both air and sea surface), increased levels of atmospheric carbon
dioxide and resulting decreases in seawater pH and shifts in car-
bon chemistry (Doney et al. 2009), sea level rise, coupled with
increased storm events affecting salinity, physical disturbance,
sedimentation and turbidity (resuspended sediments, increased
terrestrial run-off), as well as changes in ocean circulation and
upwelling patterns are all part of scenarios projected by the Inter-
governmental Panel on Climate Change (IPCC) (Solomon et al.
2007). These changes in global climate are likely to have pro-
found consequences on the physiology of marine species across
many phyla.There will be further pressures on many key marine
species with the impacts of local scale changes in land use
practices and human population growth. This review focuses
on calcified marine macroalgae, highlighting their ecological
importance, the contributions they make to the deposition of
carbonates in coastal environments, and their vulnerability to
anthropogenic changes.
Extracellular deposition of calcium carbonate is found in
members of the phylogenetically diverse brown, green and red
macroalgae. Calcification is infrequently found in species in
the class Phaeophyceae (phylum Ochrophyta), although it is
present in some tropical members of the order Dictyotales,
most notably in the genus Padina. Among green algae (phy-
lum Chlorophyta), there are taxa in the classes Ulvophyceae
and Bryosidophyceae that are calcified, and almost all of these
taxa are tropical (e.g. Acetabularia,Avrainvillea,Halimeda,
Neomeris; Figs 1, 2). Among the red algae in the class Florideo-
phyceae (phylum Rhodophyta), there are several orders in which
some members are calcified. For example, in the Nemaliales cal-
cification is found largely in tropical or subtropical genera, such
as Dichotomaria,Galaxaura,Ganonema,Liagora and Tricleo-
carpa, whereas in the Gigartinales the calcified crustose genus
Peyssonnelia (Peyssonneliaceae) is widely distributed from cold
to tropical seas in both hemispheres, ranging from the inter-
tidal zone to substantial depths, and with more than 74 species
currently recognised (Guiry and Guiry 2008).
It is the red algal order Corallinales, however, that is the
best known of all calcified macroalgal groups, with all species
being calcified and either geniculate (jointed or articulated;
Fig. 3) or non-geniculate (typically crustose; Fig. 4). Geniculate
and non-geniculate corallines are found predominantly grow-
ing epilithically although they are also found as epiphytes, and
growing on mollusc shells and various artificial substrates. In
addition, there are free-living non-geniculate corallines that are
known as rhodoliths or maerl (a Breton word and the term most
typically used in Europe for these growth forms of coralline
algae; Fig. 5). Rhodoliths can accumulate to form large beds –
aggregations of both live and dead material at varying densities
on muddy, pebbly or sandy substrates.
© CSIRO 2009 10.1071/MF08335 1323-1650/09/080787
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