Phytoplankton diversity and community structure affected by oceanic dispersal and mesoscale turbulence. (8th August 2014)

• Record Type: Journal Article
• Authors: Lévy, Marina; Jahn, Oliver; Dutkiewicz, Stephanie; Follows, Michael J.
• Is Part Of: Limnology and oceanography, fluids and Environments. Volume 4(2014)
• Page Start: 67
• Page End: 84
• Publication Date: 2014-08-08
• Subjects: phytoplankton -- biodiversity -- resource competition -- dispersal -- mesoscale eddies; Limnology -- Periodicals; Oceanography -- Periodicals; Fluid dynamics -- Periodicals; 551.48
• DOI: 10.1215/21573689-2768549
• Languages: English
• ISSNs: 2157-3689

Abstract

Lay Abstract: Phytoplankton are an extremely diverse set of floating, microscopic organisms, which are freely transported by water movements (current, eddies, etc.) and make up the base of the oceanic food web. This work explores how their diversity is affected by dispersal by different scales of motions in the ocean. Previous theoretical studies, based mostly on terrestrial ecosystems, have suggested that the number of phytoplankton types able to coexist at the same location should increase with increasing levels of dispersal. Here we test this hypothesis for a realistic range of oceanic conditions using a set of computer simulations of phytoplankton ecology coupled with a turbulent ocean circulation model. Our results indicate that oceanic communities become dominated by a smaller number of phytoplankton types as dispersal increases, but they have a larger ability for coexistence in larger home range areas. Dispersal due to oceanic eddies contributes significantly to these changes. Moreover, mixing of communities can only partially explain the increase in local coexistence, and we believe that dispersal allows more phytoplankton types to become equally competitive. Abstract: We explore the role of oceanic dispersal in setting patterns of phytoplankton diversity, with emphasis on the role of mesoscale turbulence, using numerical simulations that resolve mesoscale eddies and a diverse set of phytoplankton types. The model suggests that dispersal of phytoplankton by oceanic transport processes increases phytoplankton diversity at the local scale of O(10–100) km (α‐diversity), extends the range of many phytoplankton types, and decreases the ability of rare types to persist in isolated areas. As a consequence, phytoplanktonic assemblages are modified and diversity decreases at the regional scale of O(1000) km ( γ ‐diversity). By progressively accounting for different classes of motion, we show that the increase of α ‐diversity ensues from vertical mixing of the organisms, dispersal by mean lateral currents, and in slightly larger proportion, dispersal due to eddies. With the progressive inclusion of mechanisms of dispersal, the community becomes dominated by a smaller number of types but with larger degree of coexistence, in larger home range areas. From a resource competition perspective, physical transport can reduce the effective concentration R* of a limiting resource R, thus allowing more types to become equally fit. In addition, mixing of nearby populations allows coexistence of types with unequal fitness. The simulations suggest that mesoscale turbulence plays a particular role, concomitantly providing a means for different phytoplankton types to achieve comparable fitness and extending the exclusion time scale for less competitive types.