Biology Reference
In-Depth Information
over turfs is a key interaction that enables kelp forests to regenerate and persist, but
this dominance may be reversed under conditions that favor the persistence of turfs
(Gorman and Connell
2009
). As a consequence, it is clear that variation in algal
assemblages within and among kelp forests can be attributed partly to differences in
the primary canopy-disturbing agents, ocean waves, and temperature (Foster
1975
;
Cowen et al.
1982
; Foster
1982
; Dayton et al.
1984
,
1992
; Seymour et al.
1989
;
Breda and Foster
1985
; Harrold et al.
1988
; Graham
1997
). This, however, can be
highly variable especially on a seasonal scale. For instance, along parts of the west
coast of North America, large ocean waves associated with winter storms remove
large quantities of kelp canopies, typically resulting in maximum kelp canopies in
summer and minimum canopies in winter (Kimura and Foster
1984
; Reed and
Foster
1984
; Dayton et al.
1992
). Consequently, competitive interactions between
the canopy-forming and understory species can vary temporally, further increasing
the overall variation in kelp forest community composition (Pearse and Hines
1979
;
Gerard
1984
; Kennelly
1987a
,
b
; Harrold et al.
1988
; Dayton et al.
1999
). For
example, Edwards and Hern´ndez-Carmona (
2005
) found that along the coast of
Baja California Sur, MEX, the dominant
Macrocystis pyrifera
canopies typically
reduce the abundance of the understory
Eisenia arborea
canopies. However, all the
Macrocystis pyrifera
canopies were lost during the 1997-1998 ENSO, resulting in a
dramatic increase in
Eisenia arborea
canopies that were able to prevent
Macrocystis pyrifera
recovery at its southern range limit for up to 20 years.
7.3.3 Competition in the Face of Climate Change
The role of global environmental change in driving change to macroalgal
communities in marine ecosystems has received heightened attention (e.g.,
Wernberg et al.
2010
,
2011
). While range contractions and extensions have been
forecast as a function of changing climate (e.g., temperature), the effects on
competitive interactions among species are less clear. Unlike kelps, many turf-
forming species are ephemeral and require increased resource availability to enable
their physiology and life history to be competitively superior to perennial species
(Airoldi et al
.
2008
). Coastal waters that facilitate the expansion of turf-forming
algae (e.g., enhanced CO
2
, temperature, and nutrients; Gorgula and Connell
2004
;
Connell and Russell
2010
) tend to maintain their dominance of space at the expense
of canopy-forming algae (e.g., Gorman and Connell
2009
). Much of the global
research effort into forecasting the effects of climate change focuses on the direct
effects, thereby overlooking indirect effects (e.g., competitive effects). As the name
implies, “indirect” effects are not as simple to identify as “direct” effects and can
often yield “unexpected results” (Wootton
1994
). They are unanticipated because
the impact of one species on another (i.e., competitors) requires knowledge of a
third species or mediating component is poorly understood. Research into ocean
acidification (see Chap.
19
by Roleda and Hurd) is a good case in point. Marine
waters absorb approximately 30% of the anthropogenic-derived CO
2
from the
