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Preview: Journal of Plankton Research - current issue

Journal of Plankton Research Current Issue

Published: Thu, 18 Jan 2018 00:00:00 GMT

Last Build Date: Thu, 18 Jan 2018 06:45:54 GMT


2017 David Cushing Prize

Thu, 18 Jan 2018 00:00:00 GMT

Pseudo-nitzschia species composition varies concurrently with domoic acid concentrations during two different bloom events in the Southern California Bight

Fri, 22 Dec 2017 00:00:00 GMT

The San Pedro Shelf (SPS) region of the Southern California Bight has witnessed an increase of Pseudo-nitzschia spp. blooms during the past decade, although the domoic acid (DA) concentrations observed during these events have varied considerably. This study compared the extent, timing and environmental controls of Pseudo-nitzschia blooms that were observed in two consecutive years on the SPS. Environmental conditions were characterized during shipboard surveys during spring 2013 and 2014 along an onshore–offshore transect at surface and subsurface depths. A Pseudo-nitzschia bloom of similar cell abundances was observed during each year, yet maximal DA concentrations differed by nearly two orders of magnitude. Environmental parameters were favorable for Pseudo-nitzschia spp. growth in both years, but few factors could be identified that specifically pertained to DA, with the exception that toxicity correlated negatively with dissolved silicic acid concentrations. Automated ribosomal intergenic spacer analysis for Pseudo-nitzschia species indicated that the relative abundance of toxin-producing species had a strong influence on DA concentrations between years, with high-DA concentrations corresponding to Pseudo-nitzschia communities dominated by P. australis/P. seriata. Factors explaining the preferential growth of particular Pseudo-nitzschia species remain enigmatic but are important for predicting toxic events attributable to these taxa.

Effects of water column processes on the use of sediment traps to measure zooplankton non-predatory mortality: a mathematical and empirical assessment

Wed, 13 Dec 2017 00:00:00 GMT

Zooplankton populations can at times suffer mass mortality due to non-predatory mortality (NPM) factors, and the resulting carcasses can be captured by sediment traps to estimate NPM rate. This approach assumes sinking to be the primary process in removing carcasses, but in reality, carcasses can also be removed by ingestion, turbulent mixing and microbial degradation in the water column. We present mathematical formulations to calculate NPM from sediment trap data by accounting for carcass removal by processes in addition to sinking, and demonstrate their application in a study in Lake Shira, Russia. Carcass abundance of the major calanoid copepod Arctodiaptomus salinus decreased with depth, indicating the effect of carcass removal from the water column. The estimated NPM values (0.0003–0.103 d−1) were comparable with previously reported physiological death rates. We further used independent data to partition carcass removal due to detritivory, turbulent mixing and microbial degradation. Estimated ingestion by the amphipod Gammarus lacustris could account for the disappearance of copepod carcasses above the traps. Wind-driven turbulence could also extend the carcass exposure time to microbial degradation. Collectively, these water column processes would facilitate the remineralization of carcasses in the water column, and diminish the carcass carbon flux to the benthos.

Effects of salinity on cellular growth and exopolysaccharide production of freshwater Synechococcus strain CCAP1405

Tue, 05 Dec 2017 00:00:00 GMT

The picocyanobacterium Synechococcus is ubiquitous in freshwater and high–saline marine ecosystems. The cellular response of freshwater Synechococcus to salinity variations is not well understood. Herein, we compare cellular physiology, cell division and exopolysaccharide production of freshwater Synechococcus CCAP1405 when grown under different salinity conditions. A comparable growth rate between salinity 0 and 10 indicates that this strain is capable of adapting to such moderate salinity change. The photosynthetic efficiency and the growth were significantly lower at salinity 20 and 30 suggesting that cells experienced stress above salinity 10. For the first time, we record bimodal DNA distribution pattern for a freshwater Synechococcus strain with cell division synchronized to light–dark cycle. Pre-replication (G1) and synthesis (S) phase durations were significantly longer at high salinity, pointing to slower growth. However, post-replication (G2) phase duration was not influenced by a change in salinity. The soluble and attached exopolysaccharide production increased with salinity and age of the culture. Increased exopolysaccharide production in the vicinity of the cell-boundary facilitated its survival and microaggregate formation under salinity stress conditions. These findings indicate that flux of freshwater Synechococcus into estuarine and marine conditions would influence its growth, exopolysaccharide production and picophytoplankton carbon flow in the food web.

Meroplankton distribution in South Pacific islands, implications for larval connectivity

Tue, 05 Dec 2017 00:00:00 GMT

The knowledge on the mechanisms of population connectivity through larval stages and its implications across time and spatial scales is crucial to assess possible biological outcomes of marine protected areas (MPA) network designs. We re-analyzed available data on meroplankton distribution in the Rapa Nui ecoregion around Easter Island (27° S, 109°22′ W) and Salas y Gómez Island (26°28′S, 105°21′W) together with in situ and satellite physical and biological information to evaluate its implications for mechanisms of populations connectivity. The geostrophic flow near the coast of Easter Island included vertical and horizontal shears which, combined with vertical migration behavior of the larvae, would promote larval retention. Larval duration in the plankton and a possible effect of connection through seamounts between islands could cause the distribution pattern of ichthyoplankton endemic species between both islands. Finally, we studied the role of sub-mesoscale structures (<10 km) in the distribution of chlorophyll and meroplankton using the finite size Lyapunov exponent (FSLE). Lagrangian coherent structures which are identified as ridges of FSLE were related to higher in situ depth integrated chlorophyll, higher insular and oceanic ichthyoplankton abundances, and explained differences in the ichthyoplankton community structure around Salas y Gómez island.

Resting eggs in free living marine and estuarine copepods

Tue, 21 Nov 2017 00:00:00 GMT

Marine free living copepods can survive harsh periods and cope with seasonal fluctuations in environmental conditions using resting eggs (embryonic dormancy). Laboratory experiments show that temperature is the common driver for resting egg production. Hence, we hypothesize (i) that seasonal temperature variation, rather than variation in food abundance is the main driver for the occurrence of the resting eggs strategy in marine and estuarine copepod species; and (ii) that the thermal boundaries of the distribution determine where resting eggs are produced and whether they are produced to cope with warm or cold periods. We compile literature information on the occurrence of resting egg production and relate this to spatio-temporal patterns in sea surface temperature and chlorophyll a concentration obtained from satellite observations. We find that the production of resting eggs has been reported for 42 species of marine free living copepods. Resting eggs are reported in areas with high seasonal variation in sea surface temperature (median range 11°C). Temporal variation in chlorophyll a concentrations, however, seems of less importance. Resting eggs are commonly produced to cope with both warm and cold periods and, depending on the species, they are produced at the upper or lower thermal boundaries of a species’ distribution.

“Fake prey”: planktonic ostracods negatively affect the predatory performance of Chaoborus larvae

Tue, 21 Nov 2017 00:00:00 GMT

Previous laboratory experiments have indicated that Chaoborus larvae may be confused when exposed to a single prey species at a high density, resulting in decreased attack efficiency. Here, we hypothesized that a prey less vulnerable to Chaoborus larvae, such as Physocypria schubarti ostracods, could affect the predatory performance of Chaoborus on a more vulnerable prey, such as Ceriodaphnia silvestrii neonates. We predicted that fewer neonates would be ingested by Chaoborus larvae in the presence of ostracods at high densities due to the decreased attack efficiency caused by the confusion effect. This hypothesis was tested by combining predation assays and direct visual observations of live organisms. There was a significant decrease in the consumption of neonates when they were offered together with ostracods at high densities; however, this was not related to the ingestion of ostracods as an alternative prey or to decreased attack efficiency on neonates caused by the confusion. The energy wasted due to the numerous attacks on the ostracods (“fake prey”) possibly led the chaoborids to exhaustion, reducing their predatory performance on neonates. In ecological terms, high densities of ostracods in the water column may theoretically minimize the strong impact of Chaoborus sp. larvae on more vulnerable prey.

Temperature effects on growth and buoyancy of Microcystis aeruginosa

Wed, 08 Nov 2017 00:00:00 GMT

Batch cultures of Microcystis aeruginosa (M. aeruginosa) were cultivated at seven different temperatures to measure the specific growth rate at each temperature. A relationship between temperature and specific growth rate was established. We propose a cardinal temperature model for M. aeruginosa with the inflection point (optimal temperature) located at 27.5°C. The model describes 98% of the variability of experimental data from 5°C to 35°C. A digital inline holographic microscope was employed to visualize and analyze the buoyancy of the M. aeruginosa colonies at two different temperatures. The results demonstrated a five times difference in buoyant velocities of colonies at 17.5°C and 28°C. A model was derived to calculate the density of a colony using the buoyant velocity and colony size. The findings provide a better understanding of temperature effects on the growth and buoyancy of M. aeruginosa. The results could facilitate the prediction and mitigation of harmful algal blooms in aquatic ecosystems.

Evidence for a size-structured explanation of partial diel vertical migration in mysids

Wed, 08 Nov 2017 00:00:00 GMT

Mysids are known for benthic-pelagic diel vertical migration (DVM), where the population is benthic by day and pelagic by night. However, historical and recent observations in members of the Mysis relicta complex suggests populations exhibit partial DVM, with some remaining benthic at night. We used pelagic net and benthic sled tows to assess diel habitat use by Mysis diluviana at two stations (60 and 100 m deep) in Lake Champlain, USA, during June–November 2015. At both stations, mysids were on the bottom both day and night, but the extent of pelagic habitat use by Mysis varied by site depth. At 60-m, pelagic densities were an order of magnitude lower during the day compared to at night, indicative of benthic-pelagic DVM. Contrary to expectations, we found no diel difference between pelagic and benthic sled density estimates at 100-m, suggesting an equal number of Mysis are benthic day and night, and an equal number are pelagic-day and night at deeper sites. Mean body length of benthic-caught mysids was greater than pelagic-caught individuals, a pattern that was evident both day and night at 100-m. Our findings indicate Mysis partial DVM is common across seasons and influenced by body size and depth.