RESUMEN
Turbulence is one of the least investigated environmental factors impacting the ecophysiology of phytoplankton, both at the community and individual species level. Here, we investigated, for the first time, the effect of a turbulence gradient (Reynolds number, from Reλ = 0 to Reλ = 360) on two species of the marine diatom Pseudo-nitzschia and their associated bacterial communities under laboratory conditions. Cell abundance, domoic acid (DA) production, chain formation, and Chl a content of P. fraudulenta and P. multiseries were higher for intermediate turbulence (Reλ = 160 or 240). DA was detectable only in P. multiseries samples. These observations were supported by transcriptomic analyses results, which suggested the turbulence related induction of the expression of the DA production locus, with a linkage to an increased photosynthetic activity of the total metatranscriptome. This study also highlighted a higher richness of the bacterial community associated with the nontoxic strain of P. fraudulenta in comparison to the toxic strain of P. multiseries. Bacillus was an important genus in P. multiseries cultures (relative abundance 15.5%) and its highest abundances coincided with the highest DA levels. However, associated bacterial communities of both Pseudo-nitzschia species did not show clear patterns relative to turbulence intensity.
Asunto(s)
Bacterias , Diatomeas , Diatomeas/genética , Diatomeas/crecimiento & desarrollo , Bacterias/genética , Bacterias/clasificación , Bacterias/aislamiento & purificación , Bacterias/metabolismo , Ácido Kaínico/análogos & derivados , Ácido Kaínico/metabolismo , Fitoplancton/genética , Clorofila A/metabolismo , Fotosíntesis , TranscriptomaRESUMEN
Phytoplankton and bacteria form the foundation of marine food webs. While most studies on phytoplankton bloom influence on bacteria dynamics focus on diatom-dominated blooms due to their global ecological significance, it is unclear if similar patterns extend to other species that compete with diatoms like Phaeocystis spp. This study aimed to contribute to the understanding of associations between phytoplankton and bacteria in a temperate ecosystem. For this, we studied the dynamics of phytoplankton and bacteria, combining 16S metabarcoding, microscopy, and flow cytometry over 4 years (282 samples). Phytoplankton and bacterial communities were studied throughout the year, particularly during contrasting phytoplankton blooms dominated by the Haptophyte Phaeocystis globosa or diatoms. We applied extended local similarity analysis (eLSA) to construct networks during blooming and non-blooming periods. Overall, the importance of seasonal and species-specific interactions between phytoplankton and bacteria is highlighted. In winter, mixed diatom communities were interconnected with bacteria, indicating a synergistic degradation of diverse phytoplankton-derived substrates. In spring, despite the intensity variations of P. globosa blooms, the composition of bacterial communities remained consistent over several years, suggesting establishing a stable-state environment for bacterial communities. Specific associations between monospecific diatom blooms and bacteria were evidenced in summer.
Asunto(s)
Bacterias , Diatomeas , Ecosistema , Haptophyta , Fitoplancton , Estaciones del Año , Diatomeas/crecimiento & desarrollo , Fitoplancton/crecimiento & desarrollo , Bacterias/clasificación , Bacterias/genética , Bacterias/aislamiento & purificación , Bacterias/crecimiento & desarrollo , Haptophyta/crecimiento & desarrollo , Eutrofización , Agua de Mar/microbiología , Agua de Mar/química , Microbiota , ARN Ribosómico 16S/genéticaRESUMEN
This study investigated the drivers of the blooms of Pseudo-nitzschia seriata and Pseudo-nitzschia delicatissima complexes in the eastern English Channel and southern North Sea. Phytoplankton data series acquired from 1992 to 2020 were analyzed with a multivariate statistical approach based on Hutchinson's niche concept. P. seriata and P. delicatissima complexes were found to be typically present year round, but they bloomed at different periods because they occupied different realized ecological niches. P. delicatissima complex occupied a more marginal niche and was less tolerant than P. seriata complex. P. delicatissima complex typically bloomed in April-May at the same time as Phaeocystis globosa while P. seriata complex blooms were more frequently observed in June during the decline of low intensity P. globosa blooms. P. delicatissima and P. seriata complexes were both favored by low-silicate environments and relatively low turbulence but they responded differently to water temperature, light, ammonium, phosphate and nitrite + nitrate conditions. Niche shifts and biotic interactions played important roles in the control of the blooms of P. delicatissima and P. seriata complexes. The two complexes occupied different sub-niches during their respective low abundance and bloom periods. The phytoplankton community structure and the number of other taxa presenting a niche overlapping the niches of P. delicatissima and P. seriata complexes also differed between these periods. P. globosa was the taxa contributing the most to the dissimilarity in community structure. P. globosa interacted positively with P. delicatissima complex and negatively with P. seriata complex.
Asunto(s)
Diatomeas , Haptophyta , Mar del Norte , Fitoplancton , EcosistemaRESUMEN
Temporal dynamics of Syndiniales Group II were investigated combining 18S rDNA amplicon sequencing and direct microscopy counts (fluorescence in situ hybridization-tyramide signal amplification [FISH-TSA]) during 5 years. The study was undertaken in meso-eutrophic coastal ecosystem, dominated by diatoms, the haptophyte Phaeocystis globosa and exhibiting relatively low dinoflagellate abundance (max. 18.6 × 103 cells L-1 ). Consistent temporal patterns of Syndiniales Group II were observed over consecutive years highlighting the existence of local populations. According to sequencing data, Syndiniales Group II showed increasing abundance and richness in summer and autumn. Dinospores counted by microscopy, were present at low abundances and were punctuated by transient peaks. In summer dinospore highest abundance (559 × 103 L-1 ) and prevalence (38.5%) coincided with the peak abundance of the dinoflagellate Prorocentrum minimum (13 × 103 L-1 ) while in autumn Syndiniales Group II likely had more diversified hosts. Although, several peaks of dinospore and read abundances coincided, there was no consistent relation between them. Ecological assembly processes at a seasonal scale revealed that stochastic processes were the main drivers (80%) of the Group II community assembly, though deterministic processes were noticeable (20%) in June and July. This latter observation may reflect the specific Syndiniales-dinoflagellate interactions in summer.
Asunto(s)
Dinoflagelados , Haptophyta , Parásitos , Animales , Ecosistema , Parásitos/genética , Biodiversidad , Hibridación Fluorescente in Situ , Dinoflagelados/genética , Haptophyta/genética , Estaciones del AñoRESUMEN
Assessing the relative contributions of the interacting deterministic and stochastic ecological processes for phytoplankton community assembly is crucial in understanding and predicting community organization and succession at different temporal and spatial scales. In this study, we hypothesized that deterministic and stochastic ecological processes regulating phytoplankton, present seasonal and repeating patterns. This hypothesis was explored during a 5-year survey (287 samples) conducted at a small spatial scale (~15km) in a temperate coastal ecosystem (eastern English Channel). Microscopy and flow cytometry quantified phytoplankton abundance and biomass, while metabarcoding data allowed an extended evaluation of diversity and the exploration of the ecological processes regulating phytoplankton using null model analysis. Alpha diversity of phytoplankton was governed by the effect of environmental conditions (environmental filtering). Temporal community turnover (beta diversity) evidenced a consistent interannual pattern that determined the phytoplankton seasonal structure. In winter and early spring (from January to March), determinism (homogeneous selection) was the major process in the phytoplankton community assembly. The overall mean in the year was 38%. Stochastic processes (ecological drift) prevailed during the rest of the year from April to December, where the overall mean for the year was 55%. The maximum values were recorded in late spring and summer, which often presented recurrent and transient monospecific phytoplankton peaks. Overall, the prevalence of stochastic processes rendered less predictable seasonal dynamics of phytoplankton communities to future environmental change. IMPORTANCE While ecological deterministic processes are conducive to modeling, stochastic ones are far less predictable. Understanding the overall assembly processes of phytoplankton is critical in tracking and predicting future changes. The novelty of this study was that it addressed a long-posed question, on a pluriannual scale. Was seasonal phytoplankton succession influenced by deterministic processes (e.g., abiotic environment) or by stochastic ones (e.g., dispersal, or ecological drift)? Our results provided strong support for a seasonal and repeating pattern with stochastic processes (drift) prevailing during most of the year and periods with monospecific phytoplankton peaks.