Evidence of small-scale spatial structuring of phytoplankton alpha- and beta-diversity in the open ocean

TY - JOUR

T1 - Evidence of small-scale spatial structuring of phytoplankton alpha- and beta-diversity in the open ocean

AU - Mousing, Erik Askov

AU - Richardson, Katherine

AU - Bendtsen, Jørgen

AU - Cetinić, Ivona

AU - Perry, Mary Jane

PY - 2016/11/1

Y1 - 2016/11/1

N2 - Phytoplankton assemblages in the open ocean are usually assumed to be mixed on local scales unless large semi-permanent density discontinuities separating water masses are present. Recent modelling studies have, however, suggested that ephemeral submesoscale oceanographic features leading to only subtle density discontinuities may be important for controlling phytoplankton alpha- and beta-diversity patterns. Until now, no empirical evidence has been presented to support this hypothesis. Using hydrographic and taxonomic composition data collected near Iceland during the period of the 2008 spring bloom, we show that the distribution of phytoplankton alpha- and beta-diversity was related to submesoscale heterogeneity in oceanographic conditions. Distinct phytoplankton communities as well as differences in richness were identified on either side of a front delimiting surface waters of slightly different (˜0.03) salinities. Alpha-diversity was significantly higher on the high salinity side of the front compared to the low salinity side. This difference was primarily driven by the presence of several large diatom species in the high salinity region, especially of the genus Chaetoceros which dominated the biomass here. By investigating beta-diversity in relation to environmental and spatiotemporal variables, we show that the regional distribution of phytoplankton taxa was influenced by both different environmental conditions on either side of the front and dispersal limitation across the front. Changes in beta-diversity were primarily driven by turnover rather than nestedness and were apparently controlled by different processes in each region. Synthesis. This study shows that small-scale and ephemeral density discontinuities created by submesoscale frontal dynamics can play a major role in structuring patterns of phytoplankton diversity. Evidence is presented that they can generate changes in environmental conditions (leading to environmental filtering) and act as physical (dispersal) barriers for phytoplankton transport. The study suggests that dispersal barriers are potentially of much greater importance for phytoplankton diversity at local scales than currently recognized and indicates that drivers of marine phytoplankton diversity are similar to those structuring diversity of land plants.

AB - Phytoplankton assemblages in the open ocean are usually assumed to be mixed on local scales unless large semi-permanent density discontinuities separating water masses are present. Recent modelling studies have, however, suggested that ephemeral submesoscale oceanographic features leading to only subtle density discontinuities may be important for controlling phytoplankton alpha- and beta-diversity patterns. Until now, no empirical evidence has been presented to support this hypothesis. Using hydrographic and taxonomic composition data collected near Iceland during the period of the 2008 spring bloom, we show that the distribution of phytoplankton alpha- and beta-diversity was related to submesoscale heterogeneity in oceanographic conditions. Distinct phytoplankton communities as well as differences in richness were identified on either side of a front delimiting surface waters of slightly different (˜0.03) salinities. Alpha-diversity was significantly higher on the high salinity side of the front compared to the low salinity side. This difference was primarily driven by the presence of several large diatom species in the high salinity region, especially of the genus Chaetoceros which dominated the biomass here. By investigating beta-diversity in relation to environmental and spatiotemporal variables, we show that the regional distribution of phytoplankton taxa was influenced by both different environmental conditions on either side of the front and dispersal limitation across the front. Changes in beta-diversity were primarily driven by turnover rather than nestedness and were apparently controlled by different processes in each region. Synthesis. This study shows that small-scale and ephemeral density discontinuities created by submesoscale frontal dynamics can play a major role in structuring patterns of phytoplankton diversity. Evidence is presented that they can generate changes in environmental conditions (leading to environmental filtering) and act as physical (dispersal) barriers for phytoplankton transport. The study suggests that dispersal barriers are potentially of much greater importance for phytoplankton diversity at local scales than currently recognized and indicates that drivers of marine phytoplankton diversity are similar to those structuring diversity of land plants.

U2 - 10.1111/1365-2745.12634

DO - 10.1111/1365-2745.12634

M3 - Journal article

SN - 0022-0477

VL - 104

SP - 1682

EP - 1695

JO - Journal of Ecology

JF - Journal of Ecology

IS - 6

ER -