Biology Reference
In-Depth Information
ameliorated by cross-shore delivery of nutrients via internal waves. Consequently,
while the individuals near the edge of the forests may be healthy, individuals in the
interior can become nutrient stressed and appear less healthy during periods of low
nutrient availability, though this varies considerably with forest size (Bernstein and
Jung
1979
; Dayton et al.
1984
). This nutrient limitation may also be important to
reproduction in many species. For example, Reed (
1990
) concluded that both
interspecific and intraspecific competition between the microscopic gametophytes
of
Macrocystis pyrifera
and
Pterygophora californica
was intense when they
settled at high densities but not when they settled at low densities. He attributed
this to competition for nutrients even though the culture media was changed
regularly. In contrast, Vadas (
1972
) found no evidence of competition among the
gametophytes of
Nereocystis luetkeana
, though this may have been because his
overall densities were substantially lower than those used by Reed. Further, Carney
and Edwards (
2010
) observed that delaying development as 1-2 celled
gametophytes for 1-3 months can ameliorate the negative effects of intraspecific
competition among kelp gametophytes, though she did not test how this impacts
eventual sporophyte recruitment.
7.3 Competition in Complex Environments
7.3.1 Synergistic Effects of Different Factors
While it is true that limitation of one or more resources can be important to the
recruitment, survival, and reproduction in many macroalgae, synergistic effects
among numerous environmental factors may result in substantial variability in how
species respond to these limitations. For example, Fujita (
1985a
,
b
) reports that when
nutrients are plentiful, the green algae
Ulva
spp. (formerly
Enteromorpha
) are able to
outcompete the red algae
Gracilaria tikvahiae
for space in the intertidal due to its
greater uptake and growth rates. However,
Gracilaria tikvahiae
possesses greater
nutrient storage capabilities and therefore outcompetes
Ulva
during periods when
nutrients are limited. Likewise, on the New England, USA coast, where the brown
alga
Fucus vesiculosus
is the dominant competitor for space over
Ulva
spp. in the
absence of grazers,
Ulva
spp. is the competitive dominant species when grazers are
present. This occurs because the grazers remove the fast growing young stages of
Ulva
spp., thus allowing the slower growing grazer-resistant
Fucus
to grow. Along
the Pacific coast of Baja California, MEX, the giant kelp
Macrocystis pyrifera
forms
a surface canopy above the stipitate kelp
Eisenia arborea
and thus outcompetes
Eisenia arborea
for light. However,
Eisenia arborea
is more resistant to low nutrient
conditions such as those observed during El Ni˜o Southern Oscillation (ENSO)
events (Hern´ndez-Carmona et al.
2001
) and thus is able to persist during periods
when
Macrocystis pyrifera
dies. Following the ENSO,
Eisenia arborea
is able to
form dense subsurface canopies that exclude
Macrocystis pyrifera
recruitment and
