Larval fish dynamics in coastal and oceanic habitats in the Canary Current Large Marine Ecosystem (12 – 23°N)

Abstract

Understanding processes that regulate dispersal patterns and survival of larval fish in relation to habitat structures as bottom-up drivers in upwelling ecosystems is the objective of this dissertation. To what extent do larval fish assemblages reflect species-specific adaptations to the physical environment in marine ecosystems? That’s only one of several remaining questions that have received much attention in the past, yet remain unanswered for all globally important marine ecosystems. The abundant small pelagic fish species in the southern Canary Current Upwelling Ecosystem (CCUE) provide livelihoods for millions of people, but the physical processes that drive abundance and distribution of these species are not well known. In order to understand vital processes in the CCUE that control the dispersal of larval fish assemblages, four surveys at sea were conducted between 2014 and 2016. The data framework, which was used to answer central research questions, was based on a combination of field work (expeditions with larval fish sampling), in-situ measurements of environmental parameters (salinity, fluorescence, conductivity, temperature, depth – CTD), community analysis (e.g. Cluster Analyses, Discriminant Analyses, Similarity Percentage Analysis (SIMPER), Multivariate Analysis of Variance (MANOVA), Random Forest Models, and Generalized Additive Models (GAMs)), and satellite based remote sensing data (sea surface temperature, sea surface chlorophyll-a, wind regime, absolute dynamic topography and geostrophic current vectors). Results from data collection served as the basis for preparation of my dissertation and are presented in the form of three scientific publications (Chapter I – III). • In Chapter I, a spatiotemporal niche-partitioning of larval habitats was detected for the two most dominant small pelagic species, round sardinella (Sardinella aurita) and European sardine (Sardina pilchardus), constrained by species-specific upwelling regimes. • In Chapter II, active larval vertical migration behaviour was revealed in an offshore upwelling cell. Species that occurred in the inner upwelling cell took advantage of a passive retention to circumvent a loss of larvae into unproductive oceanic regions during an upwelling event. • In Chapter III, two larval fish assemblages were observed, each inhabiting one of two water masses that were trapped by two mesoscale eddies along a front.