Knowledge of global patterns of biodiversity is fundamental for contemporary studies in ecology, evolution and conservation. Recent studies on global patterns of species diversity are predominantly conducted across heterotrophic taxa, but do not consider the major oceanic and coastal primary producers. Using macroalgae as a model, we aim to understand their biogeography along spatial and latitudinal gradients, and to detect potential drivers behind their distribution.
Using the geographical range of macroalgae extracted form online databases (AlgaeBase and OBIS), we created global distribution maps of macroalgal species richness. We examined latitudinal patterns of species richness and range sizes and compared them with those predicted by mid-domain models. By formulating and fitting of global spatial regression models (GLS), we determined to what extent environmental variables could predict macroalgal species richness. Finally, we delimited biogeographical realms for benthic macroalgae.
Macroalgal richness is highest in the Pacific Ocean, specifically in South East Asia, for all taxonomic levels and macroalgal groups. Red and brown seaweeds show an increased richness in temperate regions. Latitudinal gradients for macroalgae show the same bimodal pattern observed for most marine organisms. Deviations from mid-domain effect expectations indicate a lower diversity in polar regions and the tropics, and a peak in biodiversity in the northern temperate zone. GLS show that sea surface temperature and nutrients are important predictors of macroalgal genus richness at a global scale. Delimitation of the optimal number of biogeographic realms varies between groups. We found strong support for the delimitation of nine distinct marine realms for macroalgae.
Macroalgae originated from temperate areas, as reflected in the high values of richness at latitudinal and spatial scales. The lower values of model coefficients indicate that biotic interactions (such as competition and predation) affect their presence in the tropics.
