Surge channels on wave-swept rocky shores are characterized by the violent hydrodynamic mixing that accompanies broken waves. It has been suggested that this mixing rapidly dilutes gametes shed into the surf zone, thereby severely reducing the fraction of eggs that can be fertilized externally. Although surge channels are well mixed within themselves, field experiments show that the exchange of water between these small embayments and the adjacent mainstream is surprisingly slow. Thus, surge channels may act as "containment vessels," limiting the rate at which gametes are diluted, and thereby enhancing the efficacy of external fertilization. Indeed, a mathematical model of fertilization in surge channels suggests that given a sufficient population of adult males within a surge channel, 80-100% of eggs may be fertilized. This result must be tempered, however, by the possibility that the small-scale shears induced by turbulence interfere with fertilization.
Coastal areas are among the most biologically productive, dynamic and valued ecosystems on Earth. They are subject to changes that greatly vary in scale, time and duration and to additional pressures resulting from anthropogenic activities. The aim of this work was to investigate the shoreline evolution and the main environmental changes of the coastal stretch between the towns of Licata and Gela (in the Gulf of Gela, Sicily, Italy). The methodology used in this work included the analysis of: (i) shoreline changes over the long- and medium-term periods (1955–2019 and 1989–2019, respectively), (ii) dune system fragmentation and (iii) the impact of coastal structures (harbours and breakwaters) on coastal evolution. The shoreline change analysis mainly showed a negative trend both over the long- and medium-term periods, with a maximum retreat of 3.87 m/year detected over the medium-term period down-drift of the Licata harbour. However, a few kilometres eastward from the harbour, significant accretion was registered where a set of breakwaters was emplaced. The Shoreline Change Envelope (SCE) showed that the main depositional phenomena occurred during the decade between 1955 and 1966, whereas progressive and constant erosion was observed between 1966 and 1989 in response to the increasing coastal armouring.
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