the mean flow (Armi and Farmer 1985, 1988; Garcia-Lafuente et al. 2000) with the
result of a quasi-permanent eastward direction of the AJ regardless the tidal conditions. West of Tarifa, where the Strait broadens, tidal currents overcome the mean
flow and tidally induced reversals of the AJ are the rule.
12.5 Species Life History Effects and Constraints
in the Connectivity Processes
12.5.1 Influence of Hydrographic Patterns at Early Life
Stages of Fish
Hydrodynamics is pivotal in the fish egg and larval environmental scenario, most
particularly in the case of pelagic species originating from adult fish, which are
adapted to recurrent and permanent hydrographic patterns. Hydrodynamics causes
the passive drifting of small pelagic offspring until finding areas where processes of
enrichment, concentration, and retention confluence (the “Bakun triad”, Bakun
1996). If these conditions are positionally retained in the form of a nursery ground,
ontogenic development is favored until attaining early juvenile stages in which they
can overcome the constraints imposed by local hydrography.
The Alboran Sea is a sharp trans-continental ecosystem with the potential of early
life stages connecting European and African coasts, which are separated by the
AJ. Another example of such an ecosystem in the Mediterranean is provided by the
Strait of Sicily where a surface current of Atlantic origin too, the Atlantic Ionian
Stream (AIS), may disengage the respective coastal marine ecosystems. Hydrodynamics there strongly conditions the life stages of small pelagics.
Establishing connectivity by the import of early life history stages (ELHSs) from
one distant spawning ground to another site is crucial to incorporate vital developmental rates that condition survival probabilities at critical ontogenic stages. GarciaLafuente et al. (2002) analyzed the coupling of the AIS in the Strait of Sicily with the
European anchovy (Engraulis encrasicolus) and showed spatially asymmetric distributions of eggs and larvae originated by the southeastwards alongshore advection
of these products by the main branch of the AIS. The geostrophic front associated
with the stream facilitates the pumping of nutrients and trophic resources for the
alongshore drift of larvae until they concentrate in a cyclonic vortex off the southernmost Sicily, where they feed and grow in favorable conditions provided by
upwelling linked to the vortex (Garcia-Lafuente et al. 2002). Biological evidence
of this transport is supported by the estimated daily ages and sizes of larvae, which
significantly increases as larvae drift southeast. Larvae of 11 mm have an estimated
age of 14 days, a sufficient pelagic larval duration (PLD) for reaching the vortex
from the northern spawning grounds. But the AIS apparently represents a hydrographic barrier for the exchange of ELHS individuals between the Tunisian and
Sicilian shores. In fact, lagrangian simulations confirm that high mortality rates at
12 Biophysical Processes Determining the Connectivity of the Alboran Sea Fish. . .
473
result of a quasi-permanent eastward direction of the AJ regardless the tidal conditions. West of Tarifa, where the Strait broadens, tidal currents overcome the mean
flow and tidally induced reversals of the AJ are the rule.
12.5 Species Life History Effects and Constraints
in the Connectivity Processes
12.5.1 Influence of Hydrographic Patterns at Early Life
Stages of Fish
Hydrodynamics is pivotal in the fish egg and larval environmental scenario, most
particularly in the case of pelagic species originating from adult fish, which are
adapted to recurrent and permanent hydrographic patterns. Hydrodynamics causes
the passive drifting of small pelagic offspring until finding areas where processes of
enrichment, concentration, and retention confluence (the “Bakun triad”, Bakun
1996). If these conditions are positionally retained in the form of a nursery ground,
ontogenic development is favored until attaining early juvenile stages in which they
can overcome the constraints imposed by local hydrography.
The Alboran Sea is a sharp trans-continental ecosystem with the potential of early
life stages connecting European and African coasts, which are separated by the
AJ. Another example of such an ecosystem in the Mediterranean is provided by the
Strait of Sicily where a surface current of Atlantic origin too, the Atlantic Ionian
Stream (AIS), may disengage the respective coastal marine ecosystems. Hydrodynamics there strongly conditions the life stages of small pelagics.
Establishing connectivity by the import of early life history stages (ELHSs) from
one distant spawning ground to another site is crucial to incorporate vital developmental rates that condition survival probabilities at critical ontogenic stages. GarciaLafuente et al. (2002) analyzed the coupling of the AIS in the Strait of Sicily with the
European anchovy (Engraulis encrasicolus) and showed spatially asymmetric distributions of eggs and larvae originated by the southeastwards alongshore advection
of these products by the main branch of the AIS. The geostrophic front associated
with the stream facilitates the pumping of nutrients and trophic resources for the
alongshore drift of larvae until they concentrate in a cyclonic vortex off the southernmost Sicily, where they feed and grow in favorable conditions provided by
upwelling linked to the vortex (Garcia-Lafuente et al. 2002). Biological evidence
of this transport is supported by the estimated daily ages and sizes of larvae, which
significantly increases as larvae drift southeast. Larvae of 11 mm have an estimated
age of 14 days, a sufficient pelagic larval duration (PLD) for reaching the vortex
from the northern spawning grounds. But the AIS apparently represents a hydrographic barrier for the exchange of ELHS individuals between the Tunisian and
Sicilian shores. In fact, lagrangian simulations confirm that high mortality rates at
12 Biophysical Processes Determining the Connectivity of the Alboran Sea Fish. . .
473