68
J. Collina-Girard
(Fig. 5.14b). On the coastline or on the islands, the fortunate conjunction of geology
and meteorology thus provides the opportunity of all-weather refuge anchoring.
There is no doubt that this did not escape the Greeks marines during Antiquity when
they settled in Marseilles in the sixth century before our era.
5.4.3 Wind Conditions and “Thermal Landscape”
During the fair season, wind conditions cause the displacement of warm water fronts
(23–24
◦ C) brought in by the east wind and pushed out by the Mistral. This surface
warm water lies on much colder deep waters (13
◦ C). When the Mistral blows, this
water column is pushed out behind Sicié Cap while the cold and deep waters rise to
the surface, causing the water temperatures in diving locations to plummet rapidly.
When the wind changes, the surface warm water is no longer pushed seaward by the
Mistral and flows back into the Bay above the deep cold water, creating a violent
surface current. The thermocline between superficial warm waters and deep cold
waters moves vertically with these wind patterns, thereby modifying the diver’s
“thermal landscape”. These rapid variations in temperature also affect others, such
as the pelagic fish that follow the movements of this tepid surface water.
5.4.4 Temperature Patterns and Landscape
The seasonal temperature variations associated with the Mistral and northeast wind
frequency changes are accompanied by changes in water temperatures. Certain phenological events, which are remarkable for the diver, set the immersed landscape
in a seasonal calendar through the cyclical perception of the underwater landscape
(Dupuy and Harmelin 2000; Collina-Girard 2012).
In spring, the onset of the fair season is initiated by the proliferation of the asparagopsis alga which carpets the seabed and walls. The disappearance of this alga
then marks the imminence of summer warming. At the same time, shellfish such as
sea spiders migrate towards the coast in the spring while the first octopuses put in an
appearance.
The summer and early autumn mark the arrival of abundant pelagic fish, rare
during the winter: “dentis”, bream, zebra seabream, liches, tuna. New species to these
waters have appeared on a regular basis in the past twenty years, such as the barracuda,
which was uncommon west of Toulon up until recently. During midsummer and the
autumn, the electric blue fry damselfish hatch (chromis chromis). At the same period
we can observe murex hatches, piles of eggs similar to expanded polystyrene. Erect
holothurians ejecting their gametes during reproduction are also characteristic of this
season, during which warm water temperatures stabilize at around 20
◦ C or more.
The octopuses weaken and die at the end of the autumn, a season which can extend
until mid-November in Marseilles. The summer and winter fish; large seabream,
J. Collina-Girard
(Fig. 5.14b). On the coastline or on the islands, the fortunate conjunction of geology
and meteorology thus provides the opportunity of all-weather refuge anchoring.
There is no doubt that this did not escape the Greeks marines during Antiquity when
they settled in Marseilles in the sixth century before our era.
5.4.3 Wind Conditions and “Thermal Landscape”
During the fair season, wind conditions cause the displacement of warm water fronts
(23–24
◦ C) brought in by the east wind and pushed out by the Mistral. This surface
warm water lies on much colder deep waters (13
◦ C). When the Mistral blows, this
water column is pushed out behind Sicié Cap while the cold and deep waters rise to
the surface, causing the water temperatures in diving locations to plummet rapidly.
When the wind changes, the surface warm water is no longer pushed seaward by the
Mistral and flows back into the Bay above the deep cold water, creating a violent
surface current. The thermocline between superficial warm waters and deep cold
waters moves vertically with these wind patterns, thereby modifying the diver’s
“thermal landscape”. These rapid variations in temperature also affect others, such
as the pelagic fish that follow the movements of this tepid surface water.
5.4.4 Temperature Patterns and Landscape
The seasonal temperature variations associated with the Mistral and northeast wind
frequency changes are accompanied by changes in water temperatures. Certain phenological events, which are remarkable for the diver, set the immersed landscape
in a seasonal calendar through the cyclical perception of the underwater landscape
(Dupuy and Harmelin 2000; Collina-Girard 2012).
In spring, the onset of the fair season is initiated by the proliferation of the asparagopsis alga which carpets the seabed and walls. The disappearance of this alga
then marks the imminence of summer warming. At the same time, shellfish such as
sea spiders migrate towards the coast in the spring while the first octopuses put in an
appearance.
The summer and early autumn mark the arrival of abundant pelagic fish, rare
during the winter: “dentis”, bream, zebra seabream, liches, tuna. New species to these
waters have appeared on a regular basis in the past twenty years, such as the barracuda,
which was uncommon west of Toulon up until recently. During midsummer and the
autumn, the electric blue fry damselfish hatch (chromis chromis). At the same period
we can observe murex hatches, piles of eggs similar to expanded polystyrene. Erect
holothurians ejecting their gametes during reproduction are also characteristic of this
season, during which warm water temperatures stabilize at around 20
◦ C or more.
The octopuses weaken and die at the end of the autumn, a season which can extend
until mid-November in Marseilles. The summer and winter fish; large seabream,