availability of spawning products at the depths concerned. For fish species that
reproduce and breed in depth (i.e., European hake) whose larvae do not migrate to
the surface layers, connectivity at depth is a challenging issue that has not been
successfully addressed yet (O’Leary and Roberts 2018).
A difference with foreseeable biological consequences between west-to-east
surface layer and east-to-west intermediate/deep layer hydrodynamic connectivity
arises as for the time a water parcel needs to get through the Strait of Gibraltar from
one basin into the other. It is of only 1–2 days for the surface layer because of
the high speed of the AJ, and of several days, even weeks, for the lower layer as the
speed of the outflow is substantially lower in most of the Strait domain. The
difference obviously affects the potential motility of the spawning products in transit
through the Strait, which in turn is conditioned by the pelagic larval duration before
settlement, since those in the lower layer stay much longer in the zone.
12.3.2 Intra-basin Along Shore Connectivity
Connectivity of different regions in the north shore of the Alboran Sea is favored by
the mean surface circulation (Fig. 12.1). The same applies to the south shore. The
prevailing zonal circulation does not establish significant hydrodynamic barriers for
connectivity, although the variability of the surface pattern may change the direction
in which connectivity would occur. Figure 12.3 sketches some of these patterns that
have been reported in the Alboran Sea. Fig. 12.3a (it replicates Fig. 12.1) corresponds to the most stable mode of surface circulation, which prevails in summertime
(Viudez et al. 1998; Renault al., 2012). In the north shore, it promotes west-to-east
connections along the northern meanders of the AJ in the west and east parts of the
basin and in the opposite direction in the central part. The direction of the flow along
the southern edges of the WAG and EAG makes the east-to-west be the prevailing
direction for connectivity in the southern shores of the basin. Obviously, these
connectivity patterns change when the surface circulation does, which provides
different scenarios in the same geographical area, as suggested by the snapshots in
Fig. 12.3.
From this point of view, the relevant feature of zonal intra-basin hydrodynamic
connectivity would be the time variability. The hydrodynamic situation that prevails
when the biological (spawning) products are available for transport will become the
most suitable pattern, if not the only one, for demographic connectivity. For
instance, surface circulation in summertime matches the pattern sketched in
Fig. 12.3a (Vargas-Yañez et al. 2002; Renault et al. 2012). Therefore, fish species
spawning in this season would be prone to west-to-east connectivity along the
northwestern sector of the Alboran Sea, which would result in quasi-stable patterns
of connected fish stocks. The central area of the north shore, however, would be
under the influence of a weak east-to-west transport coupled to a diminished and
weak CCG, which would favor the enrichment of the Bay of Malaga and, eventually,
endow it with retention characteristics linked to the slow cyclonic circulation of the
CCG (Garcia et al. this book).
12 Biophysical Processes Determining the Connectivity of the Alboran Sea Fish. . .
465
reproduce and breed in depth (i.e., European hake) whose larvae do not migrate to
the surface layers, connectivity at depth is a challenging issue that has not been
successfully addressed yet (O’Leary and Roberts 2018).
A difference with foreseeable biological consequences between west-to-east
surface layer and east-to-west intermediate/deep layer hydrodynamic connectivity
arises as for the time a water parcel needs to get through the Strait of Gibraltar from
one basin into the other. It is of only 1–2 days for the surface layer because of
the high speed of the AJ, and of several days, even weeks, for the lower layer as the
speed of the outflow is substantially lower in most of the Strait domain. The
difference obviously affects the potential motility of the spawning products in transit
through the Strait, which in turn is conditioned by the pelagic larval duration before
settlement, since those in the lower layer stay much longer in the zone.
12.3.2 Intra-basin Along Shore Connectivity
Connectivity of different regions in the north shore of the Alboran Sea is favored by
the mean surface circulation (Fig. 12.1). The same applies to the south shore. The
prevailing zonal circulation does not establish significant hydrodynamic barriers for
connectivity, although the variability of the surface pattern may change the direction
in which connectivity would occur. Figure 12.3 sketches some of these patterns that
have been reported in the Alboran Sea. Fig. 12.3a (it replicates Fig. 12.1) corresponds to the most stable mode of surface circulation, which prevails in summertime
(Viudez et al. 1998; Renault al., 2012). In the north shore, it promotes west-to-east
connections along the northern meanders of the AJ in the west and east parts of the
basin and in the opposite direction in the central part. The direction of the flow along
the southern edges of the WAG and EAG makes the east-to-west be the prevailing
direction for connectivity in the southern shores of the basin. Obviously, these
connectivity patterns change when the surface circulation does, which provides
different scenarios in the same geographical area, as suggested by the snapshots in
Fig. 12.3.
From this point of view, the relevant feature of zonal intra-basin hydrodynamic
connectivity would be the time variability. The hydrodynamic situation that prevails
when the biological (spawning) products are available for transport will become the
most suitable pattern, if not the only one, for demographic connectivity. For
instance, surface circulation in summertime matches the pattern sketched in
Fig. 12.3a (Vargas-Yañez et al. 2002; Renault et al. 2012). Therefore, fish species
spawning in this season would be prone to west-to-east connectivity along the
northwestern sector of the Alboran Sea, which would result in quasi-stable patterns
of connected fish stocks. The central area of the north shore, however, would be
under the influence of a weak east-to-west transport coupled to a diminished and
weak CCG, which would favor the enrichment of the Bay of Malaga and, eventually,
endow it with retention characteristics linked to the slow cyclonic circulation of the
CCG (Garcia et al. this book).
12 Biophysical Processes Determining the Connectivity of the Alboran Sea Fish. . .
465