Biology Reference
In-Depth Information
15.2.5
Inorganic Nutrients
There are no time series of inorganic nutrients in the area. However, they must be
high due to the permanent cold, rich-nutrient upwelling in the kelp forests. It can be
hypothesized that the perennial
L. ochroleuca
stores nutrients as other perennial
nutrient storage strategy is very different in the annual
P. purpurascens
from the
Strait of Gibraltar. The C:N and N:P ratios increased from spring (when recruitment
of sporophytes took place) to summer (when the thalli reached the greatest size and
the production of sori began), and they remained constant until the first storm period
in the autumn when the sporophytes were detached. The ratios suggested that the
growth of
P. purpurascens
could be limited by both N and P, but the time course of
the C:N:P Redfield ratio (Redfield
1934
; Atkinsons and Smith
1984
) showed that
the growth was P-limited (Flores-Moya et al.
1995
).
P. purpurascens
shows external carbonic anhydrase (CA) activity (see also
(the most abundant inorganic carbon species in seawater) to CO
2
which diffuses
into the cells. However, under fast flowing water due to tidal currents the extracel-
lular CA may be physically removed from the thallus surface (Flores-Moya and
Fern´ndez
1998
).
15.3 Growth and Reproduction
An estimate of the mean age of
L. ochroleuca
individuals of about 4-6 m length
collected at 45 m depth at Alboran Island (assuming one annual cycle per pair of
bands formed by the meristoderm; Klinger and DeWreede
1988
) resulted in an age
of 8-11 years (Flores-Moya, unpublished data). Similar age structure was found in
the populations growing at 60 m depth in the Strait of Messina (Drew
1972
).
S. polyschides
and both species of
Phyllariopsis
can be considered as “monocarpic”
(the term used for flowering plants which die after setting fruit) since the thalli
become senescent after sorus formation. The basic difference between the two
genera is that the
S. polyschide
s thalli sometimes do not become fertile during the
first year (i.e., they could be considered biennial) whereas growth and reproduction
in
Phyllariopsis
occurs in less than 1 year (Flores-Moya et al.
1993
). The thalli are
recruited in spring and are detached from the substratum in autumn-winter.
L. ochroleuca
bears sori all year long but the highest percentage of fertile blades
occurs in the spring and summer. The optimal temperature range for both zoospore
germination and growth of gametophytes is 15-18
C (Table
15.1
); gametogenesis
is inhibited at temperatures below 10
C. Growth of young sporophytes is maximal
at irradiances of 20-40
mol photons m
2
s
1
(Izquierdo et al.
2002
).
S. polyschides
and both species in
Phyllariopsis
become fertile in summer (Flores-Moya et al.
1993
). Gametophytes of both species of
Phyllariopsis
are dioecious but unusually
m
