Biogeography and community assembly of demersal fishes across continental shelf seas
Life is not distributed randomly on our Ocean planet but is organized by the environment, evolutionary history, and human-induced disturbances. These effects are multifaceted but only in recent years have scientific observations touched large expanses of the oceans to test regional- and global-scale drivers which shape marine biodiversity. Fish are valuable model taxon for testing ecological patterns in the oceans due to their high diversity, dispersal capacity, and newly widespread data availability. The primary objective of this dissertation is to disentangle patterns of marine fish biomass, geographic breakpoints in community composition, and drivers of trait compositions which are proxies for species ecological functions. To do this, I collated and analyzed scientific bottom trawls throughout continental shelf seas in the Northern Hemisphere. The first manuscript (Chapter 2) focuses on biomass distributions of four demersal species which dominate biomass in the Baltic Sea to describe spatiotemporal biomass shifts and the primary environmental covariates to each species. The second and third manuscripts (Chapter 3–4) scale outwards to include community-wide patterns of composition and traits from scientific trawls in the North Atlantic and northeast Pacific oceans. Together, I show (i) evidence for substantial changes in species biomass distributions in the Baltic Sea when modelling biomass at yearly and seasonal scales, (ii) large-scale biogeographic divides in fish community networks weighted by differing co-occurrence frequencies, and (iii) that fish traits have been primarily shaped by environmental filtering, with a unique degree of evolutionary conservatism in the northeast Pacific. Scaling from a marginal sea to continental-scale ocean shelves, and from select species to community-wide data, this work offers novel insight into macroecological patterns which explain the distribution of highly diverse fishes in the modern oceans.
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