finishes, strong surface current, produced by winds from NW-W,
are formed just off the Basque Coast and circulates parallel to the coast in
a W -? E direction and S -> N off the French coast (IBAÑEZ, 1979).
AII this coincides with a mixture of both surface and deep waters off the
Basque coast which produces an enrichment in nutrients in the surface layers.
(It would be interesting in later works to take samples from deeper
waters, up to 1000 m, in order to establish the true magnitude of this
In October, according to MANRIQUEZ et al. (1978) the nitrate and phosphate values seem to be slightly higer still off Galicia, at least in
the coastal area (1).
Whit reference to the effects which this cycle of nutrients may have on
the intertidal benthic algae, there are some ephemeral algae (species which
usually persist for only a few months) like Porphyra linearis which
develops in the winter months in the upper mid-Iittoral or upper shore area
(depending on the force of the waves at this time). There are also other
long life species such as Corallina officinalis, Halopteris scoparia, C/adostephus
spongiosus (var. spongiosus and verticillatus) and Bifurcaria
rotunda, whose biomass per surface unit diminishes notably in the winter
due to the storms, and which present a lower Margalef index precisely at
this time (IRASTORZA & IBAÑEZ, in press).
It seems that the combined effect of the storms and an increase of
nutrients favours the fall of the old part and the active growth of new
branches, which produces a minimum value of Im.
However apparen contradictions are seen in some nitrophylic algae
Enteromorpha, which forms dense "grass" in the upper mid-Iittor~1
area and which reaches a maximum in the months of June-July, later
disappearing in winter (fig. 22).
This disappearance is possibly due to the active '.grazing" by the
moluscs Patella intermedia, Gibbula umbilicaris and Monodonta
lineata, this last in lesser degree, in the community of green seaweeds.
Less insolation in the winter months, the force of storms etc... may also
have an adverse effect on this time.
Indeed, a little sandy blanket which the algae grow on, develops on flat
surfaces as in Zumaya. In December this blanket disappears completely
leaving the bare rock and with it the community of Enteromorpha disappears
In Mompas we can see how the belt of Enteromorpha which completely
covers the upper mid-Iittoral area ascends in the winter months. And the Enteromorpha
disappears from the lowest levels and develops at the lower extreme of
the upper shore.
Possibly adverse conditions such as absence of insolation cause a
disequilibrium between the algae production and the grazing of the phito-
phagous molluscs, so that they can only develop in areas where the molluscs
have limited access (upper-shore) and where sufficient humidity exists in
winter to permit the development of Enteromorpha in precarious
(1) According lo MILLOT (1979) and HUA & THOMASSET (1979),
well localized coaslal upwellings are produced with different Iypes of wind
depending on the coastaI geometry.