The pattern of change in the abundances of specific bacterioplankton groups is consistent across different nutrient-enriched habitats in Crete

Abstract

A common source of disturbance for coastal aquatic habitats is nutrient enrichment through anthropogenic activities. Although the water column bacterioplankton communities in these environments have been characterized in some cases, changes in α-diversity and/or the abundances of specific taxonomic groups across enriched habitats remain unclear. Here, we investigated the bacterial community changes at three different nutrient-enriched and adjacent undisturbed habitats along the north coast of Crete, Greece: a fish farm, a closed bay within a town with low water renewal rates, and a city port where the level of nutrient enrichment and the trophic status of the habitat were different. Even though changes in α-diversity were different at each site, we observed across the sites a common change pattern accounting for most of the community variation for five of the most abundant bacterial groups: a decrease in the abundance of the Pelagibacteraceae and SAR86 and an increase in the abundance of the Alteromonadaceae, Rhodobacteraceae, and Cryomorphaceae in the impacted sites. The abundances of the groups that increased and decreased in the impacted sites were significantly correlated (positively and negatively, respectively) with the total heterotrophic bacterial counts and the concentrations of dissolved organic carbon and/or dissolved nitrogen and chlorophyll α, indicating that the common change pattern was associated with nutrient enrichment. Our results provide an in situ indication concerning the association of specific bacterioplankton groups with nutrient enrichment. These groups could potentially be used as indicators for nutrient enrichment if the pattern is confirmed over a broader spatial and temporal scale by future studies.

FIG 1

Sampling map showing the locations of all three sampling sites across the north coast of Crete, the locations of the control and impacted sites, and the codes for the sampling locations at each site. (A) The three sampling sites; (B) impacted (SdI) and control (SdC) sites at Souda; (C) impacted (AgI) and control (AgC) sites at Agios Nikolaos; (D) impacted (StI) and control (StC) sites at Sitia. All images were captured and modified using Google Earth.

FIG 2

UPGMA tree with jackknife support. Samples are named as described in the legend to Fig. 1. The number after the sample name indicates the replicate number. Nodes with more than 75% jackknife support are colored black, while nodes with less than 75% jackknife support are colored gray.

FIG 3

PCoA biplot of samples containing the bacterial groups Pelagibacteraceae (Pel), SAR86, Rhodobacteraceae (Rho), Alteromonadaceae (Alt), and Cryomorphaceae (Cry). Samples are named as described in the legend to Fig. 1. The number after the sample name indicates the replicate number. Black spheres, control samples; gray spheres, impacted samples; white spheres, bacterial groups. The diameters of the spheres are analogous to the group's mean abundance among all samples.