Biology Reference
In-Depth Information
Exceptions to the notion that macroalgae do not compete strongly for space have
been observed in turf-forming species that can occupy nearly 100% of the substrate
in some places and thereby prevent settlement of other algae (e.g., Hruby and
Norton
1979
), and in areas dominated by encrusting algae which can compete
intensely for space (Steneck and Paine
1986
). On many temperate coasts,
encrusting coralline algae can also occupy up to 80% of hard substrate, dominating
space beneath macroalgal canopies (Irving et al.
2004
). With the creation of
available space (e.g., through storm damage), however, turfs rapidly colonize the
space and overgrow the coralline crusts (Russell and Connell
2005
; Worm et al.
1999
). The morphology of these filamentous turfs allows them to then trap sediment
(Airoldi
1998
; Gorgula and Connell
2004
) and subsequently inhibit the recruitment
of canopy-forming species in localities from a diversity of locations around the
world (Devinny,
1978
; Gorman and Connell
2009
). In addition, recruitment of the
larger macroalgae can occur on the thalli of the turf algae, though the added
hydrodynamic drag on the turf holdfast can result in increased removal rates from
waves and thus low survival (Edwards unpublished data). In an example of compe-
tition among three species of intertidal crustose and turf algae, Padilla (
2003
)
observed coralline turf algae were better competitors than the upright forms for
space, as they were more susceptible to grazing and desiccation. In contrast, two
upright forms were inferior competitors for space but were more resistant to grazing
and desiccation. Thus, the coralline algae coexisted on the rocky shore, though in
different microhabitats. Furthermore, in many temperate systems, if the dominant
kelp canopies are excluded from a reef, turf algae may increase in abundance over
time and ultimately become the dominant space occupiers, especially in areas
where the canopies have been removed (e.g., Edwards
1998
; Connell
2003b
).
Competition for space itself can be strongly mediated by both physical (distur-
bance) and biological (competition) factors. For example, Kastendiek (
1982
)
observed three species of algae at Santa Catalina Island, CA, USA, competing
strongly with each other but that the nature of this competition differed greatly
between species pairs, each of which was influenced by physical disturbances
differently. Specifically, the kelp
Eisenia arborea
forms canopies that excludes
(or reduces its abundance) the brown alga
Halidrys dioica
, thereby allowing the turf
alga
Pterocladia capillacea
to dominate the substrate under the canopy. However,
if the
Eisenia arborea
canopy is removed,
Halidrys dioica
recruits in high
abundances and dominates the substrate, thus excluding
Pterocladia capillacea
from the area. This switch between competition for light and competition for space
appears to be driven by disturbance to the dominant
Eisenia arborea
canopy.
Similarly, competition for space may be strongly dependent on species identity
and whether the interaction is interspecific or intraspecific. For example, Santelices
et al. (
2003
) observed that in the intertidal region of Chile, when the holdfasts of the
intertidal red algae
Mazzaella laminarioides
and
Nothogenia fastigiata
come into
contact, one outcompetes the other resulting in its death. However, when the
holdfasts of either species come into contact with a member of their own species,
the holdfasts coalesce and both individuals survive, suggesting that the populations
might be chimeric. Finally, competition for space may be integral in regulating
