Journal of Plankton Research最新文献

Biodiversity assessment promotes information on the state of an ecosystem. Zooplankton, as a sentinel group at the basis of aquatic food webs, are, thus, an important component to monitor for ecosystem conservation and management. For the first time, we characterized biodiversity of coastal zooplankton along the shallow Northern shoreline of the lower St. Lawrence estuary (LSLE) using an integrated taxonomic and trait-based approach. For 3 years (2019-2021), in July and October, the zooplankton community and environmental parameters were sampled at < 35 m depth. Mesozooplankton were identified at the lowest possible taxonomic level and assigned functional traits. Community structure and diversities revealed high spatio-temporal variations among three different geographic sectors and between seasons, mainly driven by water temperature, Chlorophyll-a concentration and less by salinity. Hotspots of taxonomic and functional diversities occurred in different sectors in the same month, underlining the complementarity of the two approaches. Seasonal shifts in functional diversity hotspots highlight how environmental variability affects biodiversity beyond taxonomic metrics alone. The results of our study in the LSLE establish a first robust baseline to improve our understanding of zooplankton dynamics in the coastal LSLE, to allow future tracking of ongoing change due to the increase of anthropogenic activities and climate changes and to support future monitoring efforts.

The Canary Current Large Marine Ecosystem (CCLME), extending from Cape Spartel in Morocco to Guinea-Bissau, supports high primary and fisheries productivity driven by permanent or seasonal upwelling activity. During the current study, mesozooplankton and hydrographic sampling were conducted across the CCLME in the spring/summer of 2017 and the autumn/winter of 2019. The total mesozooplankton abundance and dry weight were found to be higher in 2017, partly due to the summer reproduction cycle of diplostracans. A prominent latitudinal gradient was observed in both the mesozooplankton standing stock and assemblage structure closely linked to a significant shift in oceanographic regimes at Cape Blanc (21^°N). The area south of Cape Blanc, sampled during the upwelling relaxation in both years, was occupied by warmer South Atlantic Central Waters showing elevated mesozooplankton stock with a tropical assemblage structure. In contrast, cooler and more saline waters north of Cape Blanc, a result of the upwelling regime in that area, explained part of the observed variation in mesozooplankton composition among subregions and sampling periods. Our findings indicate that aside from the upwelling activity, spatiotemporal variation of mesoscale processes and topographical features at a subregional level may also shape mesozooplankton stock and assemblage structure in the CCLME.

Cell size is a critical regulator of many metabolic processes in protists. We explored whether body size and abundances vary consistently in phytoplankton capable of both autotrophy and heterotrophy (mixoplankton) by manipulating environmental stoichiometric conditions in a mesocosm experiment. We applied two allochthonous subsidy treatments: high C: nutrient ratios (leaves) should favour bacterivory through phagotrophy, while low ratios (insects) should favour autotrophy. We identified three focal mixoplankton taxa, common in our study system and that represented facultative (Cryptomonas sp. and Plagioselmis sp) and more obligate phagotrophs (Ochromonas sp.). Ochromonas was largest in the leaf treatment, which were also associated with larger sizes in Cryptomonas (but not the other cryptophyte). The obligately mixotrophic Ochromonas responded more significantly to conditions favouring phagotrophy than did the facultative phagotrophic cryptophytes. All mixoplankton taxa densities declined with insect subsidies that favour autotrophy. Future research should examine a wider range of mixoplankton under varying ecological conditions.

Zooplankton in the Barents Sea has been monitored on an annual autumn survey since the late 1980s, using vertical WP-2 and oblique Multiple Opening and Closing Net and Environmental Sensing System (MOCNESS) tows over the water column. Sampling with MOCNESS is used to describe the vertical distribution and more frequent sampling with WP-2 (~3:1) to describe the horizontal distribution. We use here a large cumulative data set of 874 MOCNESS and 2850 WP-2 stations with data on size-fractioned dry-weight biomass to compare the two zooplankton sampling gears. MOCNESS is consistently collecting more biomass of the large size fraction (>2 mm screen size) by ~20% and less of the small fraction (<1 mm) by ~30% compared to WP-2. This is interpreted to reflect more extrusion of small plankton and less avoidance by larger plankton with the MOCNESS. The data set has been collected by three research vessels. There was a difference in vertical speed in oblique tows of MOCNESS among the ships but no clear effect on volume filtered per unit time. This demonstrates operational consistency and suggests the use of a constant flow factor (distance per flowmeter count) when calculating results over the time series. The issue of calibration of traditional flowmeters on oblique tows needs further examination.

[This corrects the article DOI: 10.1093/plankt/fbae031.].

Eleven years after the publication of the first work applying deoxyribonucleic acid (DNA) metabarcoding to zooplankton communities, the commonly known "miniCOI" barcode is widely used, becoming the marker of choice. However, several primer combinations co-exist for this barcode and a critical evaluation of their performance is needed. This article reviews the misperformance of miniCOI metabarcoding with marine zooplankton communities, comparing them to microscopy and/or other universal markers. In total, misperformances were reported for 26 zooplankton taxa, including 18 copepods and five tunicates. We report a detection failure with Class Appendicularia and contrasting performances for Oithona similis (from good correspondence to detection failure), two worldwide abundant taxa with a crucial role in the marine pelagic realm. A combination of forward primer mismatches, the presence of long poly-T inserts and a low number of reference sequences would explain the failure to detect appendicularians. However, the contrasting performance with O. similis would correspond to distinct numbers of mismatches in the forward primer in different lineages within this cryptic taxon. This is reinforced by the report of similar patterns with other locally abundant zooplankton taxa. Therefore, we strongly call for the use of miniCOI in combination with alternative methods capable of addressing these limitations.

Anthropogenic induced climate perturbations are seen in changes in oceanic circulation patterns, and Arctic water masses defined by salinity are vulnerable to change. Biogeography of marine microbial eukaryotes is expected to be impacted by changes in local environmental conditions and advective processes, but tracking the extent of plankton distribution requires understanding routes for both active and passive tracers. To identify such tracers, we focused on samples collected in the western (Canada Basin) and eastern (Nares Strait); extremes of the Canadian High Arctic that are connected by an east flowing current north of Canada. Sequencing of the V4 region of 18S rRNA revealed that Acantharia, a taxonomically and functionally diverse group of large planktonic protists, were particularly common. Arctic acantharians in our study were dominated by two clades belonging to cyst-forming groups. The distribution of one clade suggested successful advective transport from the Pacific sourced water in the Beaufort Gyre to southern Nares Strait, with cells transported along the northern shelf of the Canadian Arctic. A second clade appeared to be a resident taxon of the Canada Basin whose distribution correlated to local environmental conditions, and detection in deeper samples would be consistent with swarmer formation enabling reestablishment the following year.

As important primary producers and key components of biogeochemical processes, phytoplankton communities are highly diverse and continually adapt to changes in the environment, impacting the entire marine ecosystem. Consequently, it remains important to isolate, culture and properly describe new phytoplankton strains to provide relevant model organisms for laboratory research and accurate reference sequences for identification. Here, 73 phytoplankton strains from the eastern Canadian waters were isolated and genetically characterized using a long rRNA fragment (~4000 bp) covering the 18S, ITS and 28S rRNA regions generated with long-read sequencing technology. While most strains (66%) were accurately identified using the partial 18S rRNA gene (~1200 bp-V4-V9), this study broadens the current 28S rRNA reference database by incorporating 41 distinct strains including 30 unique species. In addition, previously unpublished long-read reference sequences were generated for a few genera, including Picochlorum and Droopiella. Species that were previously poorly described in the eastern Canadian waters were also genetically characterized, including a Chaetoceros similis strain. Overall, this work expands the total number of long-read references, an essential resource for accurate identification of phytoplankton and environmental sequences, thereby advancing the taxonomic resolution that could lead to a better understanding of environmental microbial diversity.

Ecological theory and empirical research show that both direct lethal effects and indirect non-lethal effects can structure the composition of communities. While the direct effects of grazers on marine phytoplankton communities are well studied, their indirect effects are still poorly understood. Direct and indirect effects are inherently difficult to disentangle in plankton food webs. In this study we evaluate the indirect effects of copepod grazers on community function and structure using isolated chemical alarm signals, copepodamides. We expose intact summer and spring communities to direct grazing from copepods, or to chemical alarm cues without the presence of grazers in controlled experiments. The effects of direct grazing on ecosystem function were moderate in both experiments as indicated by levels of chlorophyll and primary production. Indirect and direct effects resulted in changes in the composition of both the eukaryote and prokaryote communities as shown by metabarcoding of 18S and 16S rRNA. Size structure analysis suggests that direct grazing and copepodamide exposure both favoured smaller organisms (< 10-15 μm) corroborating the size-structuring effect of copepod grazers. We conclude that the well-established effect of copepods on phytoplankton communities results from a combination of direct and indirect effects. This is a first attempt to isolate indirect effects of copepods on community structure and the results suggest that a full mechanistic understanding of the structuring effect of copepods will require insights to both direct and indirect effects of consumers as demonstrated for other ecosystems components.