Biology Reference
In-Depth Information
Table 15.1
Growth and reproduction thermal limits for the kelps inhabiting the Strait of Gibraltar and the
Alboran Sea
Species
Growth/reproduction
(sporophyte)
Growth/reproduction
(gametophyte)
References
Upper
Lower
Upper
Lower
Laminaria ochroleuca
22-23
C/*
*/*
*/21
C
*/5
C
Luning (
1990
),
Izquierdo et al. (
2002
)
Saccorhiza polyschides
24
C/*
3
C/*
25
C/
<
17
C
þ
/5
C
Norton (
1970
)
Phyllariopsis brevipes
*/*
*/*
20
C/20
C10
C/10
C
Henry (
1987
)
Phyllariopsis purpurascens
*/*
*/*
20
C/20
C10
C/10
C
Unpublished
Lethal limits can be estimated 1-2
C beyond the growth thermal limits
Asterisks
: no data are available
15.2 Abiotic Factors Affecting Distribution of Kelps
in the Alboran Sea and the Strait of Gibraltar
15.2.1 Substratum
The four species of kelps inhabit hard substrata. A singular case is
P. brevipes
,
which always grows on living thalli of the crustose coralline
Mesophyllum alternans
(Foslie) Cabioch &Mendoza (Henry
1987
;P
´
rez-Cirera et al.
1989
). The specificity
for the substratum in
P. brevipes
is possibly due to the requirements of the micro-
scopic gametophyte (Sauvageau
1918
) rather than to those of the sporophyte.
15.2.2 Hydrodynamics
The bottoms where kelps grow in the Strait of Gibraltar are exposed to very strong
currents linked to the semidiurnal tidal cycle, with peaks of 2.5 m s
1
at low or high
tide at spring tides (Lacombe and Richez
1982
). The current may be a factor
controlling the largest blade area that kelps can reach. Blades of 0.1 m
2
of
P. purpurascens
(the largest blade area found) can be detached from the stipe
with current velocities ranging from 2.4 to 3.5 m s
1
and an inverse correlation
was detected between blade area and current exposure on different bottoms (Flores-
Moya et al.
1993
; Flores-Moya
1997
). A similar control by peak currents
decapitating older thalli was suggested for
L. ochroleuca
in the Strait of Messina
(Drew et al.
1982
).
15.2.3
Irradiance
It is accepted that the lower limit of distribution of kelps corresponds to approxi-
mately 1% of the surface solar irradiance (L
€
uning and Dring
1979
) and this
