Germination fluctuation of toxic Alexandrium fundyense and A. pacificum cysts and the relationship with bloom occurrences in Kesennuma Bay,Japan

While cyst germination may be an important factor for the initiation of harmful/toxic blooms, assessments of the fluctuation in phytoplankton cyst germination, from bottom sediments to water columns, are rare in situ due to lack of technology that can detect germinated cells in natural bottom sediments. This study introduces a simple mesocosm method, modeled after previous in situ methods, to measure the germination of plankton resting stage cells. Using this method, seasonal changes in germination fluxes of toxic dinoflagellates resting cysts, specifically Alexandrium fundyense (A. tamarense species complex Group I) and A. pacificum (A. tamarense species complex Group IV), were investigated at a fixed station in Kesennuma Bay, northeast Japan, from April 2014 to April 2015. This investigation was conducted in addition to the typical samplings of seawater and bottom sediments to detect the dinoflagellates vegetative cells and resting cysts. Bloom occurrences of A. fundyense were observed June 2014 and February 2015 with maximum cell densities reaching 3.6 × 10⁶ cells m⁻² and 1.4 × 10⁷ cells m⁻², respectively. The maximum germination fluxes of A. fundyense cysts occurred in April 2014 and December 2014 and were 9.3 × 10³ cells m⁻² day⁻¹ and 1.4 × 10⁴ cells m⁻² day⁻¹, respectively. For A. pacificum, the highest cell density was 7.3 × 10⁷ cells m⁻² during the month of August, and the maximum germination fluxes occurred in July and August, reaching 5.8 × 10² cells m⁻² day⁻¹. Thus, this study revealed the seasonal dynamics of A. fundyense and A. pacificum cyst germination and their bloom occurrences in the water column. Blooms occurred one to two months after peak germination, which strongly suggests that both the formation of the initial population by cyst germination and its continuous growth in the water column most likely contributed to toxic bloom occurrences of A. fundyense and A. pacificum in the bay.     

Recurrent vernal presence of the toxic Alexandrium tamarense/Alexandrium fundyense (Dinoflagellata) species complex in Narragansett Bay,USA

The vernal occurrence of toxic dinoflagellates in the Alexandrium tamarense/Alexandrium fundyense species complex in an enclosed embayment of Narragansett Bay (Wickford Cove, Rhode Island) was documented during 2005 and 2009–2012. This is the first report of regular appearance of the Alexandrium fundyense/Alexandrium tamarense species complex in Narragansett Bay. Thecal plate analysis of clonal isolates using SEM revealed cells morphologically consistent with both Alexandrium tamarense Lebour (Balech) and Alexandrium fundyense Balech. Additionally, molecular analyses confirmed that the partial sequences for 18S through the D1–D2 region of 28S were consistent with the identity of the two Alexandrium species. Toxin analyses revealed the presence of a suite of toxins (C1/2, B1 (GTX-5), STX, GTX-2/3. Neo, and GTX-1/4) in both Alexandrium tamarense (6.31 fmol cell⁻¹ STX equiv.) and Alexandrium fundyense (9.56 fmol cell⁻¹ STX equiv.) isolated from Wickford Cove; the toxicity of a Narragansett Bay Alexandrium peruvianum isolate (1.79 fmol cell⁻¹ STX equiv.) was also determined. Combined Alexandrium tamarense/Alexandrium fundyense abundance in Wickford Cove reached a peak abundance of 1280 cells L⁻¹ (May of 2010), with the combined abundance routinely exceeding levels leading to shellfishing closures in other systems. The toxic Alexandrium tamarense/Alexandrium fundyense species complex appears to be a regular component of the lower Narragansett Bay phytoplankton community, either newly emergent or previously overlooked by extant monitoring programs.     

Grazing-induced morphological and growth rate changes in Anarthrophyllum rigidum,a Patagonian leguminous shrub

Grazing influences the morphology and growth rate of shrubs, and consequently, their population dynamics. It has been shown that grazing directly affects the growth of shrubs. On the other hand, the reduction of grass biomass by herbivores reduces soil–water competition between grasses and shrubs, and indirectly, could enhance the growth of shrubs. However, the assessment of the long-term effects of grazing on the growth of shrubs in the arid Patagonia has been hampered by the lack of long and homogeneous records of plant population dynamics and primary production. In this study, we combined growth-ring and allometric analyses to assess the long-term effect of grazing on individuals of Anarthrophyllum rigidum, a leguminous shrub widely distributed across the Patagonian steppe. A. rigidum has evergreen leaves rich in proteins that constitute an important complement to the diet of sheep, particularly in winter when the abundance of grasses is reduced. Our observations indicate that individuals of A. rigidum nearby the water source used by livestock were smaller in size (35.5 cm vs. 67.39 cm), presented a larger number of basal branches (23 vs. 12), and showed slower rates of growth (8.2 mm year^?1 vs. 14.3 mm year^?1) than individuals located far from the water source. This first quantification of the long-term effects of grazing on A. rigidum in the dry Patagonian steppe suggests that beneficial effects of grazing through the reduction of grasses that compete with shrubs for soil–water should be more obvious for livestock non-preferred than preferred shrubs     

Empirical models of toxigenic Pseudo-nitzschia blooms: Potential use as a remote detection tool in the Santa Barbara Channel

The Santa Barbara Channel, CA is a highly productive region where wind-driven upwelling and mesoscale eddies are important processes driving phytoplankton blooms. In recent years, the spring bloom has been dominated by the neurotoxin-producing diatom, Pseudo-nitzschia spp. In this paper, we relate a 1.5-year time series of Pseudo-nitzschia spp. abundance and domoic acid concentration to physical, chemical, and biological data to better understand the mechanisms controlling local Pseudo-nitzschia spp. bloom dynamics. The data were used to define the ranges of environmental conditions associated with Pseudo-nitzschia spp. bloom development in the Santa Barbara Channel. The time series captured three large toxic events (max. particulate domoic acid concentration, pDA ～6000 ng L^?1; max. cellular domoic acid concentrations, cDA ～88 pg cell^?1) in the springs of 2005–2006 and summer 2005 corresponding to bloom-level Pseudo-nitzschia spp. abundance (>5.0 × 10⁴ cells L^?1). In general, large increases in Pseudo-nitzschia spp. abundance were accompanied by increases in cDA levels, and cDA peaks preceded pDA peaks by at least one month in both the springs of 2005 and 2006. Statistical models incorporating satellite ocean color (MODIS-Aqua and SeaWiFS) and sea surface temperature (AVHRR) data were created to determine the probability that a remotely sensed phytoplankton bloom contains a significant population of toxic Pseudo-nitzschia spp. Models correctly estimate 98% of toxic bloom situations, with a 7–29% rate of false positive identification. Conditions most associated with high cDA levels are low sea surface temperature, high salinity, increased absorption by cDOM (412 nm), increased reflectance at 510/555 nm, and decreased particulate absorption at 510 nm. Future efforts to merge satellite and regionally downscaled forecasting products with these habitat models will help assess bloom forecasting capabilities in the central CA region and any potential connections to large-scale climate modes.     

Density-dependent effects of snail grazing on the growth of a submerged macrophyte,Vallisneria spiralis

In order to better understand the role of herbivorous snails in freshwater ecosystems, we conducted experiments investigating food preference of the snail Radix swinhoei on leaves of the submerged plant Vallisneria spiralis with and without periphyton coverage. The effects of snail grazing on the growth of V. spiralis were assessed in a no-snail control and at three snail densities (80, 160, 240 individuals m^?2). Results showed that the snails chose preferentially leaves covered by periphyton. Grazing activity at low snail density (80 individuals m^?2) was found to stimulate V. spiralis growth, but at higher snail density (240 individuals m^?2), plant growth was apparently suppressed. An increase observed in nutrient concentrations in water column with increasing snail density may be attributed to nutrient release by snails. This study suggests that the nature of the relationship between herbivorous snails and macrophytes in freshwater ecosystems depends on the abundance of the snails. At low snail density, the relationship may be a mutualistic one, but at high density snail herbivory may impact negatively on macrophyte biomass in lakes.     

Mesozooplankton and microzooplankton grazing during cyanobacterial blooms in the western basin of Lake Erie

Lake Erie is the most socioeconomically important and productive of the Laurentian (North American) Great Lakes. Since the mid-1990s cyanobacterial blooms dominated primarily by Microcystis have emerged to become annual, late summer events in the western basin of Lake Erie yet the effects of these blooms on food web dynamics and zooplankton grazing are unclear. From 2005 to 2007, grazing rates of cultured (Daphnia pulex) and natural assemblages of mesozooplankton and microzooplankton on five autotrophic populations were quantified during cyanobacterial blooms in western Lake Erie. While all groups of zooplankton grazed on all prey groups investigated, the grazing rates of natural and cultured mesozooplankton were inversely correlated with abundances of potentially toxic cyanobacteria (Microcystis, Anabaena, and Cylindrospermopsis; p < 0.05) while those of the in situ microzooplankton community were not. Microzooplankton grazed more rapidly and consistently on all groups of phytoplankton, including cyanobacteria, compared to both groups of mesozooplankton. Cyanobacteria displayed more rapid intrinsic cellular growth rates than other phytoplankton groups under enhanced nutrient concentrations suggesting that future nutrient loading to Lake Erie could exacerbate cyanobacterial blooms. In sum, while grazing rates of mesozooplankton are slowed by cyanobacterial blooms in the western basin of Lake Erie, microzooplankton are likely to play an important role in the top-down control of these blooms; this control could be weakened by any future increases in nutrient loads to Lake Erie.     

The emergence of Dinophysis acuminata blooms and DSP toxins in shellfish in New York waters

The dynamics of Dinophysis acuminata and its associated diarrhetic shellfish poisoning (DSP) toxins, okadaic acid (OA) and dinophysistoxin-1 (DTX1) as well as pectenotoxins (PTXs), were investigated within plankton and shellfish in Northport Bay, NY, USA, over a four year period (2008–2011). Over the course of the study, Dinophysis bloom densities ranged from ~10⁴ to 10⁶ cells L⁻¹ and exceeded 10⁶ L⁻¹ in 2011 when levels of total OA, total DTX1, and PTX in the water column were 188, 86, and 2900 pg mL⁻¹, respectively, with the majority of the DSP toxins present as esters. These cell densities exceed – by two orders of magnitude – those previously reported within thousands of samples collected from NY waters from 1971 to 1986. The bloom species was positively identified as D. acuminata via scanning electron microscopy and genetic sequencing (cox1 gene). The cox1 gene sequence from the D. acuminata populations in Northport Bay was 100% identical to D. acuminata from Narragansett Bay, RI, USA and formed a strongly supported phylogenetic cluster (posterior probability = 1) that included D. acuminata and Dinophysis ovum from systems along the North Atlantic Ocean. Shellfish collected from Northport Bay during the 2011 bloom had DSP toxin levels (1245 ng g⁻¹ total OA congeners) far exceeding the USFDA action level (160 ng g⁻¹ total OA of shellfish tissue) representing the first such occurrence on the East Coast of the U.S. D. acuminata blooms co-occurred with paralytic shellfish poisoning (PSP) causing blooms of Alexandrium fundyense during late spring each year of the study. D. acuminata cell abundances were significantly correlated with levels of total phytoplankton biomass and Mesodinium spp., suggesting food web interactions may influence the dynamics of these blooms. Given that little is known regarding the combined effects of DSP and PSP toxins on human health and the concurrent accumulation and depuration of these toxins in shellfish, these blooms represent a novel managerial challenge.     

Differences in swimming pattern between life cycle stages of the toxic dinoflagellate Alexandrium fundyense

Different life stages of Alexandrium fundyense have different swimming behavior; gametes often are said to “swarm” or “dance” before mating. This behavior was studied, and quantitative measures of these motility patterns in two-dimensions were generated using motion-analysis software applied to video records of individual-cell movements. Behavior, swimming patterns, and growth were studied in two strains of A. fundyense and compared in encystment medium and growth medium. Vegetative cells swam straight, rotating around the apical axis until they hit something and then swam straight in a different direction. Gamete swimming behavior was slower and characterized by frequent direction changes and circular motion. Gametes contacted other cells frequently (>5 cell contacts min⁻¹ cell⁻¹). Zygotes swam slowly when newly formed and later became nearly immobile; these cells continued to contact other cells and also surfaces. The results are in accordance with field observations of long swimming distances for vegetative cells, accumulation in thin layers of gametes, and sinking of developing resting cysts attached to marine snow for zygotes.     

Controls on the initiation and development of blooms of the dinoflagellate Cochlodinium polykrikoides Margalef in lower Chesapeake Bay and its tributaries

Massive blooms of the dinoflagellate Cochlodinium polykrikoides occur annually in the Chesapeake Bay and its tributaries. The initiation of blooms and their physical transport has been documented and the location of bloom initiation was identified during the 2007 and 2008 blooms. In the present study we combined daily sampling of nutrient concentrations and phytoplankton abundance at a fixed station to determine physical and chemical controls on bloom formation and enhanced underway water quality monitoring (DATAFLOW) during periods when blooms are known to occur. While C. polykrikoides did not reach bloom concentrations until late June during 2009, vegetative cells were present at low concentrations in the Elizabeth River (4 cells ml⁻¹) as early as May 27. Subsequent samples collected from the Lafayette River documented the increase in C. polykrikoides abundance in the upper branches of the Lafayette River from mid-June to early July, when discolored waters were first observed. The 2009 C. polykrikoides bloom began in the Lafayette River when water temperatures were consistently above 25 °C and during a period of calm winds, neap tides, high positive tidal residuals, low nutrient concentrations, and a low dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorous (DIP) ratio. The pulsing of nutrients associated with intense but highly localized storm activity during the summer months when water temperatures are above 25 °C may play a role in the initiation of C. polykrikoides blooms. The upper Lafayette River appears to be an important area for initiation of algal blooms that then spread to other connected waterways.     

Monitoring,management, and mitigation of Karenia blooms in the eastern Gulf of Mexico

Annual blooms of the toxic dinoflagellate Karenia brevis in the eastern Gulf of Mexico represent one of the most predictable global harmful algal bloom (HAB) events, yet remain amongst the most difficult HABs to effectively monitor for human and environmental health. Monitoring of Karenia blooms is necessary for a variety of precautionary, management and predictive purposes. These include the protection of public health from exposure to aerosolized brevetoxins and the consumption of toxic shellfish, the protection and management of environmental resources, the prevention of bloom associated economic losses, and the evaluation of long term ecosystem trends and for potential future bloom forecasting and prediction purposes. The multipurpose nature of Karenia monitoring, the large areas over which blooms occur, the large range of Karenia cell concentrations (from 5 × 10³ cells L^?1 to >1 × 10⁶ cells L^?1) over which multiple bloom impacts are possible, and limitations in resources and knowledge of bloom ecology have complicated K. brevis monitoring, mitigation and management strategies. Historically, K. brevis blooms were informally and intermittently monitored on an event response basis in Florida, usually in the later bloom stages after impacts (e.g. fish kills, marine mammal mortalities, respiratory irritation) were noted and when resources were available. Monitoring of different K. brevis bloom stages remains the most practical method for predicting human health impacts and is currently accomplished by the state of Florida via direct microscopic counts of water samples from a state coordinated volunteer HAB monitoring program. K. brevis cell concentrations are mapped weekly and disseminated to stakeholders via e-mail, web and toll-free phone numbers and provided to Florida Department of Agriculture and Consumer Services (FDACS) for management of both recreational and commercial shellfish beds in Florida and to the National Oceanic and Atmospheric Administration (NOAA) for validation of the NOAA Gulf of Mexico HAB bulletin for provision to environmental managers. Many challenges remain for effective monitoring and management of Karenia blooms, however, including incorporating impact specific monitoring for the diverse array of potential human and environmental impacts associated with blooms, timely detection of offshore bloom initiation, sampling of the large geographic extent of blooms which often covers multiple state boundaries, and the involvement of multiple Karenia species other than K. brevis (several of which have yet to be isolated and described) with unknown toxin profiles. The implementation and integration of a diverse array of optical, molecular and hybrid Karenia detection technologies currently under development into appropriate regulatory and non-regulatory monitoring formats represents a further unique challenge.     

Estimating spatial variation in the abundance of potential microcystin-producing Microcystis spp. using real-time PCR during summer bloom in Lake Taihu

Lake Taihu, which is the third largest freshwater lakes in China, is a hypertrophic shallow lake in eastern China that has experienced lake-wide cyanobacterial blooms annually during the last few decades. In this study, quantitative real-time PCR assays targeting on phycocyanin intergenic spacer (PC-IGS) and a microcystin synthetase gene mcyD were established, respectively. Water samples collected from eight sampling sites (including Zhushan Bay (N5), Meiliang Bay (N2), Gonghu Bay (N4), West lake areas (W2 and W4), south-middle lake areas (S2, S4 and S5)) in August of 2009 and 2010 were analyzed using real time PCR for the distribution and abundance of toxic and total Microcystis populations. The results showed that Microcystis exists as a mixed population of potential toxic and non-toxic genotypes, and there was significant spatial changes in the abundance of potential toxic Microcystis on the basis of quantification by quantitative real-time PCR analysis: the abundance of toxic Microcystis population in 2009 and 2010 varied from 4.08 × 10⁴ to 8.28 × 10⁶ copies mL^?1, from 4.45 × 10⁵ to 5.22 × 10⁷ copies mL^?1, respectively. Meanwhile the ratio of the mcyD subpopulation to the total Microcystis varied considerably, from 5.7% to 41.1% in 2009 and from 10.3% to 65.8% in 2010 in all sampling sites, and the value is high in Zhushan Bay and Meiliang Bay with the high level of eutrophication. Correlation analysis showed the abundance of toxic and total Microcystis being strongly related (P < 0.01). However, there is different effects of environmental factors on the abundance of toxic and non-toxic Microcystis populations. The abundance of toxic and total Microcystis populations were positively correlated with chlorophyll-a (Chl-a) concentration (P < 0.01) suggesting that Microcystis is dominated genera of cyanobacterial bloom in Lake Taihu. It was also found that the abundance of toxic Microcystis and the proportion of toxic subpopulation to the total Microcystis were positively correlated with total phosphorus and orthophosphate concentrations (P < 0.01), whereas there was no significant correlation with total nitrogen and nitrate concentration (P > 0.05). All data suggest that phosphorus concentration is a critical factor for determining the abundance of toxic Microcystis population.     

Zooplankton community composition and copepod grazing on the West Florida Shelf in relation to blooms of Karenia brevis

Blooms of the toxin producing dinoflagellate Karenia brevis occur routinely on the West Florida Shelf of the Gulf of Mexico. Nutrient supplies are thought to play a large role in the formation and maintenance of these blooms. The role of top-down control has been less well studied, but grazing, or the lack thereof, on these toxic species may also enhance the formation of large biomass blooms in this region. Zooplankton community structure and copepod species composition were analyzed from samples collected on the West Florida Shelf (WFS) during a NOAA funded ECOHAB regional Karenia Nutrient Dynamics project during October 2007–2010. In 2008 there was no statistical difference in the abundance of zooplankton at bloom and non-bloom stations, however in 2009 there was a statistically significant difference (p < 0.05) between the abundance of zooplankton at stations with Karenia present. To investigate copepod ingestion rates in relation to K. brevis, shipboard and laboratory experiments of the single label method of ¹⁴C labeled phytoplankton culture, and time course ingestion experiments with isolated copepods were performed. Calculated ingestion rates suggest that the copepod species Centropages velificatus, and Acartia tonsa ingested K. brevis, however rates were variable among collection sites and K. brevis strains. Parvocalanus crassirostris did not ingest K. brevis in any of the experiments.     

Brevetoxin persistence in sediments and seagrass epiphytes of east Florida coastal waters

A bloom of Karenia brevis Davis developed in September 2007 near Jacksonville, Florida and subsequently progressed south through east Florida coastal waters and the Atlantic Intracoastal Waterway (ICW). Maximum cell abundances exceeded 10⁶ cells L⁻¹ through October in the northern ICW between Jacksonville and the Indian River Lagoon. The bloom progressed further south during November, and terminated in December 2007 at densities of 10⁴ cells L⁻¹ in the ICW south of Jupiter Inlet, Florida. Brevetoxins were subsequently sampled in sediments and seagrass epiphytes in July and August 2008 in the ICW. Sediment brevetoxins occurred at concentrations of 11–15 ng PbTx-3 equivalents (g dry wt sediment)⁻¹ in three of five basins in the northern ICW during summer 2008. Seagrass beds occur south of the Mosquito Lagoon in the ICW. Brevetoxins were detected in six of the nine seagrass beds sampled between the Mosquito Lagoon and Jupiter Inlet at concentrations of 6–18 ng (g dry wt epiphytes)⁻¹. The highest brevetoxins concentrations were found in sediments near Patrick Air Force Base at 89 ng (g dry wt sediment)⁻¹. In general, brevetoxins occurred in either seagrass epiphytes or sediments. Blades of the resident seagrass species have a maximum life span of less than six months, so it is postulated that brevetoxins could be transferred between epibenthic communities of individual blades in seagrass beds. The occurrence of brevetoxins in east Florida coast sediments and seagrass epiphytes up to eight months after bloom termination supports observations from the Florida west coast that brevetoxins can persist in marine ecosystems in the absence of sustained blooms. Furthermore, our observations show that brevetoxins can persist in sediments where seagrass communities are absent.     

Combined physical,chemical and biological factors shape Alexandrium ostenfeldii blooms in The Netherlands

Harmful algal blooms (HABs) are globally expanding, compromising water quality worldwide. HAB dynamics are determined by a complex interplay of abiotic and biotic factors, and their emergence has often been linked to eutrophication, and more recently to climate change. The dinoflagellate Alexandrium is one of the most widespread HAB genera and its success is based on key functional traits like allelopathy, mixotrophy, cyst formation and nutrient retrieval migrations. Since 2012, dense Alexandrium ostenfeldii blooms (up to 4500 cells mL⁻¹) have recurred annually in a creek located in the southwest of the Netherlands, an area characterized by intense agriculture and aquaculture. We investigated how physical, chemical and biological factors influenced A. ostenfeldii bloom dynamics over three consecutive years (2013–2015). Overall, we found a decrease in the magnitude of the bloom over the years that could largely be linked to changing weather conditions during summer. More specifically, low salinities due to excessive rainfall and increased wind speed corresponded to a delayed A. ostenfeldii bloom with reduced population densities in 2015. Within each year, highest population densities generally corresponded to high temperatures, low DIN:DIP ratios and low grazer densities. Together, our results demonstrate an important role of nutrient availability, absence of grazing, and particularly of the physical environment on the magnitude and duration of A. ostenfeldii blooms. Our results suggest that predicted changes in the physical environment may enhance bloom development in future coastal waters and embayments.     

The interactive roles of nutrient loading and zooplankton grazing in facilitating the expansion of harmful algal blooms caused by the pelagophyte,Aureoumbra lagunensis,to the Indian River Lagoon,FL, USA

Confined to Texas, USA, for more than 20 years, brown tides caused by Aureoumbra lagunensis emerged in the Indian River Lagoon and Mosquito Lagoon, Florida, USA, during 2012 and 2013, affording the opportunity to assess whether hypotheses developed regarding the occurrence of these blooms are ecosystem-specific. To examine the extent to which top-down (e.g. grazing) and bottom-up (e.g. nutrients) processes controlled the development of Aureoumbra blooms in Florida, nitrogen (N) uptake, nutrient amendment, and seawater-dilution, zooplankton grazing experiments were performed and the responses of Aureoumbra and competing phytoplankton were evaluated. During the study, Aureoumbra comprised up to 98% of total phytoplankton biomass, achieved cell densities exceeding 2 × 10⁶ cells mL⁻¹, and contained isotopically lighter N compared to non-bloom plankton populations, potentially reflecting the use of recycled N. Consistent with this hypothesis, N-isotope experiments revealed that urea and ammonium accounted for >90% of N uptake within bloom populations whereas nitrate was a primary N source for non-bloom populations. Low levels (10 μM) of experimental ammonium enrichment during blooms frequently enhanced the growth of Aureoumbra and resulted in the growth rates of Aureoumbra exceeding those of phycoerythrin-containing, but not phycocyanin-containing, cyanobacteria. A near absence of grazing pressure on Aureoumbra further enabled this species to out-grow other phytoplankton populations. Given this alga is generally known to resist zooplankton grazing under hypersaline conditions, these findings collectively suggest that moderate loading rates of reduced forms of nitrogenous nutrients (e.g ammonium, urea) into other subtropical, hypersaline lagoons could make them susceptible to future brown tides caused by Aureoumbra.     

Potential impact of an exceptional bloom of Karenia mikimotoi on dissolved oxygen levels in waters off western Ireland

In the summer of 2005 an exceptional bloom of the dinoflagellate Karenia mikimotoi occurred along Ireland's Atlantic seaboard and was associated with the mass mortality of both benthic and pelagic marine life. Oxygen depletion, cellular toxicity and physical smothering, are considered to be the main factors involved in mortality. In this paper we use a theoretical approach based on stoichiometry (the Anderson ratio) and an average K. mikimotoi cellular carbon content of 329 pg C cell⁻¹ (n = 20) to calculate the carbonaceous and nitrogenous oxygen demand following bloom collapse. The method was validated against measurements of biochemical oxygen demand and K. mikimotoi cell concentration. The estimated potential oxygen utilisation (POU) was in good agreement with field observations across a range of cell concentrations. The magnitude of POU following bloom collapse, with the exception of three coastal areas, was considered insufficient to cause harm to most marine organisms. This indicates that the widespread occurrence of mortality was primarily due to other factors such as cellular toxicity and/or mucilage production, and not oxygen depletion or related phenomena. In Donegal Bay, Kilkieran Bay and inner Dingle Bay, where cell densities were in the order of 10⁶ cells L⁻¹, estimated POU was sufficient to cause hypoxia. Of the three areas, Donegal Bay is considered to be the most vulnerable due to its hydrographic characteristics (seasonally stratified, weak residual flow) and hypoxic conditions (2.2 mg L⁻¹ O₂) were directly observed in the Bay post bloom collapse. Here, depending on the time of bloom collapse, depressed DO levels could persist for weeks and continue to have a potentially chronic impact on the Bay.     

Changes in abundances of Alexandrium tamarense resting cysts after the tsunami caused by the Great East Japan Earthquake in Funka Bay,Hokkaido, Japan

The 2011 Great East Japan Earthquake and the subsequent huge tsunami greatly affected both human activity and the coastal marine ecosystem along the Pacific coast of Japan. The tsunami also reached Funka Bay in northern Japan and caused serious damage to the scallop cultures there, and this tsunami was believed to have affected the coastal environments in the bay. Therefore, we investigated the changes in the spatial abundance and distribution of the toxic dinoflagellates Alexandrium tamarense cysts before the tsunami (August 2010) and after the tsunami (May 2011, August 2011, May 2012 and August 2012) in the bay. Further, monthly sampling was conducted after the tsunami to identify seasonal changes of Alexandrium catenella/tamarense cysts and vegetative cells. Significant increases were observed in the populations of A. catenella/tamarense cysts, comparing the abundances before the tsunami (in August 2010; 70 ± 61 cysts g⁻¹ wet sediment) to those just after it (in May 2011; 108 ± 84 cysts g⁻¹ wet sediment), and both A. tamarense bloom (a maximum density was 1.3 × 10³ cells L⁻¹) and PSP (Paralytic Shellfish Poisoning) toxin contamination of scallops (9.4 mouse unit g⁻¹ was recorded) occurred in the bay. Seasonal sampling also revealed that the encystment of A. tamarense and the supply of the cysts to bottom sediments did not occur in the bay from September to April. These results strongly suggested that the mixing of the bottom sediments by the tsunami caused the accumulation of the toxic A. tamarense cysts in the surface of bottom sediment through the process of redeposition in Funka Bay. Moreover, this cyst deposition may have contributed to the toxic bloom formation as a seed population in the spring of 2011.