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Further reasons for local higher production in the area of the Canary Islands are the characteristic oceanic events, such as coastal upwelling, upwelling filaments, Islands’ wakes and eddies (ARÍSTEGUI et al. 1997; BARTON et al. 1998). These mesoscale hydrographic features induce an enhanced zooplankton biomass, creating the nutritional regime necessary to sustain fish larvae and other higher trophic levels (YEBRA et al. 2004). The eggs of most fishes are pelagic and the majority of larvae undergo a pelagic phase in which they inhabit mainly the upper layers of the water column. This is related to the distribution of their food sources, therefore fish larval distribution differs from adult occurrence. Additionally, larvae often drift far away from their spawning areas (ACEVES-MEDINA et al. 2003), as most are not able to overcome current speeds and the flow velocities of mesoscale hydrographic features. The mean swimming velocity of larvae is around 20.5 cm per second, though there are remarkable differences between families (LEIS and CARSON-EWART 1997; LEIS and FISHER 2006). For example apogonids only have an average swimming speed of 6.3 cm per second (LEIS and CARSON-EWART 1997), which is clearly below the flow velocities of on- and offshore currents (MITTELSTAEDT 1983). One possibility for larvae to influence their distribution is the vertical migration. By changing layers with different directional flows they might be able to maintain their location (RODRÍGUEZ et al. 2001). Nevertheless, patterns of ichthyoplankton distribution can be interpreted in terms of the physical characteristics of an area (RODRÍGUEZ et al. 2001). One such physical characteristic of the area of investigation is created by the Canarian archipelago itself. It presents a barrier within the southward flowing Canary Current and acts as a transitional zone from the shelf upwelling region of northwest Africa to the open ocean waters of the eastern North Atlantic (BARTON et al. 1998). As a result of this hydrographic position BARTON et al. (1998) divided the area into four hydrographic subdivisions, which can be seen in Figure 1a-f. The main separation is into a northern and a southern part of the archipelago. In the north the flow of the Canary Current is undisturbed, with an eastern area affected by the African upwelling and an unaffected western area. The southern area is characterized by perturbations caused at the island-ocean interface. Such disturbances are island wakes in connection with winds, island upwelling and island induced eddies (NAVARRO-PEREZ and BARTON 2001). This area is also differentiated between eastern areas which are affected by coastal upwelling and western areas which are not. Due to the perturbation of the Canary Current in its southward flow the current is mixed vertically at the island’s margin (BARTON et al. 1998), resulting in a meandering current (NAVARRO-PÉREZ and BARTON 2001). The Canary Current itself originates from the southward flowing Azores Current which splits into several branches. The easternmost branch, which turns into the Canary Current, flows southward parallel to the African coast and through the Canarian Archipelago (HERNÁNDEZ-GUERRA et al. 2002; JOHNSON and STEVENS 2000; KNOLL et al. 2002). The current consists of different water masses with different properties. The Surface Waters (SW), as the uppermost mixed layer, is created under the influence of local atmospheric conditions (KNOLL et al. 2002). Around the islands the Surface Waters reach a depth of 150 m (KNOLL et al. 2002), though the extension of this layer varies seasonally with a peak during spring (ARÍSTEGUI et al. 2001; BARTON et al. 1998). An increased insolation during summer leads to a strong heating of the SW, producing a temporal thermocline (ARÍSTEGUI et al. 2001; BARTON et al. 1998), which prevents nutrients from permeating the euphotic zone. This limits phytoplankton growth during summer (ARÍSTEGUI et al. 2001). Cooling and wind stress obliterate this thermocline in autumn, resulting in homogenously distributed chlorophyll in the surface mixed layer once again (ARÍSTEGUI et al. 1997). Below the SW, the North Atlantic Central Waters (NACW) flow unaffected by atmospheric conditions, extending to about 700 m depth (KNOLL et al. 2002). These are followed by the Antarctic Intermediate Water (AAIW), which forms an intermediate layer in the depth range of 600 – 1100 m (HERNÁNDEZ-GUERRA et al. 2003; KNOLL et al. 2002; LLINÁS


Inf. Téc. Inst. Canario Cienc. Mar. n°13

Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  
Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  

Technical report consisting on a comprehensive annotated larvae taxa list with the most important taxonomic characters of this region