Biogeographic patterns in major marine realms: function not taxonomy unites fish assemblages in reef, seagrass and mangrove systems

Abstract

We examine the effects of different biogeographic histories on assemblage composition in three major marine habitats in two biogeographically distinct marine realms. Specifically, we quantify the taxonomic and functional composition of fish assemblages that characterise coral reef, seagrass and mangrove habitats, to explore the potential effects of biogeographic history and environment on assemblage composition. The three habitats were surveyed in the Caribbean and on the Great Barrier Reef using a standardised underwater visual census method to record fish size and abundance data. The taxonomic composition of assemblages followed biogeographic expectations, with realm-specific family-level compositions. In marked contrast, the functional composition of assemblages separated habitats regardless of their biogeographic locations. In essence, taxonomy characterises biogeographic realms while functional groups characterise habitats. The Caribbean and Indo-West Pacific have been separated for approximately 15 million years. The two realms have different taxonomic structures which reflect this extended separation, however, the three dominant shallow-water marine habitats all retain distinct functional characteristics: seagrass fishes are functionally similar regardless of their taxonomic composition or biogeographic location. Likewise, for coral reefs and mangroves. The results emphasise the advantages and limitations of taxonomic vs. functional metrics in evaluating patterns. Taxonomy primarily reflects biogeographic and evolutionary history while functional characteristics may better reflect ecological constraints. IntroductionHistorical and ecological biogeographic processes have a profound effect on the distribution of organisms and how they interact with their environment (Wiens and Donoghue 2004). The species-rich tropics offer an ideal setting to study how these mechanisms have shaped the structure of the communities we recognise today (Floeter et al. 2008, Mouillot et al. 2013a. Coral reefs, in particular, have triggered the interest of researchers as they provide an opportunity to study a high-diversity system which operates at global biogeographic scales (Mouillot et al. 2014, Leprieur et al. 2016. This research has underpinned a fast-growing ResearchBiogeographic patterns in major marine realms: function not taxonomy unites fish assemblages in reef, seagrass and mangrove systems

Below the Mesophotic

“…Few studies have investigated historical depth transitions between shallow- and deep-reef taxa. Most research on the general structure of tropical reef-fish faunas at the regional level has focused on the phylogeography of shallow faunas and the relationship between faunal structure and the usage of reefs vs. other habitats 41 – 44 . However, research attention needs to be expanded to resolving phylogenetic relationships among reef-fish assemblages inhabiting different depth zones, as that is central to understanding the evolutionary origins and current composition of local and regional reef-fish faunas inhabiting shallow as well as deep reefs.…”

The evolution of traits and functions in herbivorous coral reef fishes through space and time

“…Functional biogeography (sensu [9]) provides an important framework for analysing large-scale patterns in trait combinations [11,12]. However, the role of history remains largely unexplored, despite promising insights from high-diversity systems, such as coral reefs [13]. These high diversity environments have been shaped through time & 2019 The Author(s) Published by the Royal Society.…”

Ecological functioning of mudflats: global analysis reveals both regional differences and widespread conservation of functioning

“…Thus, to ensure the continued provision of ecosystem services, the conservation of biological trait diversity may be more important than preventing the loss of taxonomic diversity (e.g. Frid et al 2008, Cadotte 2011, Hemingson & Bellwood 2018. Although marine ecosystems have not been subjected to the same level of scrutiny as terrestrial ecosystems (e.g.…”

“…Although marine ecosystems have not been subjected to the same level of scrutiny as terrestrial ecosystems (e.g. Hendriks & Duarte 2008), investigations of macroscale patterns of functional diversity and/or ecological functioning have been conducted in seagrass and mangrove habitats and for coral reef fish populations (Stuart-Smith et al 2013, Hemingson & Bellwood 2018. However, no global scale analyses of ecosystem functioning have been undertaken for soft sediment systems.…”

“…The subsequent lack of faunal exchange, changes in ocean currents (e.g. formation of the Gulf Stream) and increasing salinity in the Atlantic led to the development of distinct faunas (Schneider & Schmittner 2006, Hemingson & Bellwood 2018.…”