Autumn larval fish assemblages in the northwest African Atlantic coastal zone

摘要

A study on the assemblage composition and vertical distribution of larval fish was conducted in the southern area of the Moroccan Atlantic coast in Autumn 2011.A total of 1 680 fish larvae taxa were identified from 21 families.The majority of the larvae were present in the upper layers.Clupeids were the most abundant larvae taxa followed by Myctophidae,Gadidae and Sparidae,hence the larval fish assemblages (LFA) were variable in different depth layers.Total fish larvae showed a preference for surface layers,and were mainly found above 75 m depth,with some exceptions.The maximum concentration of fish larvae was concentrated up to 25 m essentially above the thermocline,where chlorophyll a and mesozooplankton were abundant.Spatially,neritic families were located near the coast and at some offshore stations especially in the northern part,while oceanic families were more distributed towards offshore along the study area.Cluster analysis showed a segregation of two groups of larvae.However,a clear separation between neritic families and oceanic families was not found.Multivariate analysis highlighted the relationship between the distribution of larvae of different families and environmental parameters.Temperature and salinity seem to have been the factors that acted on associations of fish larvae.Day/night vertical distributions suggest there was not a very significant vertical migration,probably due to adequate light levels for feeding.