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842 records · Page 47Linked to original sources
USGS2021

Exposure to domoic acid is an ecological driver of cardiac disease in southern sea otters

Harmful algal blooms produce toxins that bioaccumulate in the food web and adversely affect humans, animals, and entire marine ecosystems. Blooms of the diatom Pseudo-nitzschia can produce domoic acid (DA), a toxin that most commonly causes neurological disease in endothermic animals, with cardiovascular effects that were first recognized in southern sea otters. Over the last 20 years, DA toxicosis has caused significant morbidity and mortality in marine mammals and seabirds along the west coast of the USA. Identifying DA exposure has been limited to toxin detection in biological fluids using biochemical assays, yet measurement of systemic toxin levels is an unreliable indicator of exposure dose or timing. Furthermore, there is little information regarding repeated DA exposure in marine wildlife. Here, the association between long-term environmental DA exposure and fatal cardiac disease was investigated in a longitudinal study of 186 free-ranging sea otters in California from 2001 – 2017, highlighting the chronic health effects of a marine toxin. A novel Bayesian spatiotemporal approach was used to characterize environmental DA exposure by combining several DA surveillance datasets and integrating this with life history data from radio-tagged otters in a time-dependent survival model. In this study, a sea otter with high DA exposure had a 1.7-fold increased hazard of fatal cardiomyopathy compared to an otter with low exposure. Otters that consumed a high proportion of crab and clam had a 2.5- and 1.2-times greater hazard of death due to cardiomyopathy than otters that consumed low proportions. Increasing age is a well-established predictor of cardiac disease, but this study is the first to identify that DA exposure affects the risk of cardiomyopathy more substantially in prime-age adults than aged adults. A 4-year-old otter with high DA exposure had 2.3 times greater risk of fatal cardiomyopathy than an otter with low exposure, while a 10-year old otter with high DA exposure had just 1.2 times greater risk. High Toxoplasma gondii titers also increased the hazard of death due to heart disease 2.4-fold. Domoic acid exposure was most detrimental for prime-age adults, whose survival and reproduction are vital for population growth, suggesting that persistent DA exposure will likely impact long-term viability of this threatened species. These results offer insight into the pervasiveness of DA in the food web and raise awareness of under-recognized chronic health effects of DA for wildlife at a time when toxic blooms are on the rise.

California↗
USGS2021

The tide turns: Episodic and localized cross-contamination of a California coastline with cyanotoxins

The contamination of coastal ecosystems from a variety of toxins of marine algal origin is a common and well-documented situation along the coasts of the United States and globally. The occurrence of toxins originating from cyanobacteria along marine coastlines is much less studied, and little information exists on whether toxins from marine and freshwater sources co-occur regularly. The current study focused on the discharge of cyanotoxins from a coastal lagoon (Santa Clara River Estuary) as a consequence of an extreme tide event (King Tides; December 3–5, 2017) resulting in a breach of the berm separating the lagoon from the ocean. Monthly monitoring in the lagoon throughout 2017 documented more than a dozen co-occurring cyanobacterial genera, as well as multiple algal and cyanobacterial toxins. Biotoxin monitoring before and following the King Tide event using Solid Phase Adsorption Toxin Tracking (SPATT) in the lagoon and along the coast revealed the co-occurrence of microcystins, anatoxin, domoic acid, and other toxins on multiple dates and locations. Domoic acid was ubiquitously present in SPATT deployed in the lagoon and along the coast. Microcystins were also commonly detected in both locations, although the beach berm retained the lagoonal water for much of the year. Mussels collected along the coast contained microcystins in approximately half the samples, particularly following the King Tide event. Anatoxin was observed in SPATT only in late December, following the breach of the berm. Our findings indicate both episodic and persistent occurrence of both cyanotoxins and marine toxins may commonly contaminate coastlines in proximity to cyanobacteria-laden creeks and lagoons.

California↗
USGS2021

Acute oral toxicity and tissue residues of saxitoxin in the mallard (Anas platyrhynchos)

Since 2014, widespread, annual mortality events involving multiple species of seabirds have occurred in the Gulf of Alaska, Bering Sea, and Chukchi Sea. Among these die-offs, emaciation was a common finding with starvation often identified as the cause of death. However, saxitoxin (STX) was detected in many carcasses, indicating exposure of these seabirds to STX in the marine environment. Few data are available that describe the effects of STX in birds, thus presenting challenges for determining its contributions to specific mortality events. To address these knowledge gaps, we conducted an acute oral toxicity trial in mallards ( Anas platyrhynchos ), a common laboratory avian model, using an up-and-down method to estimate the median lethal dose (LD 50 ) for STX. Using an enzyme-linked immunosorbent assay (ELISA), we tested select tissues from all birds and feces from those individuals that survived initial dosing. Samples with an ELISA result that exceeded approximately 10 µg 100 g −1 STX and randomly selected ELISA negative samples were further tested by high-performance liquid chromatography (HPLC). Tissues collected from mallards were also examined grossly at necropsy and then later by microscopy to identify lesions attributable to STX. The estimated LD 50 was 167 µg kg −1 (95% CI = 69–275 µg kg −1 ). Saxitoxin was detected in fecal samples of all mallards tested for up to 48 h after dosing and at the end of the sampling period (7 d) in three birds. In those individuals that died or were euthanized <2 h after dosing, STX was readily detected throughout the gastrointestinal tract but only infrequently in heart, kidney, liver, lung, and breast muscle. No gross or microscopic lesions were observed that could be attributable to STX exposure. Given its acute toxicity, limited detectability, and frequent occurrence in the Alaska marine environment, additional research on STX in seabirds is warranted.

Harmful Algae↗
USGS2022

A validation of satellite derived cyanobacteria detections with state reported events and recreation advisories across U.S. lakes

Cyanobacteria harmful algal blooms (cyanoHABs) negatively affect ecological, human, and animal health. Traditional methods of validating satellite algorithms with data from water samples are often inhibited by the expense of quantifying cyanobacteria indicators in the field and the lack of public data. However, state recreation advisories and other recorded events of cyanoHAB occurrence reported by local authorities can serve as an independent and publicly available dataset for validation. State recreation advisories were defined as a period delimited by a start and end date where a warning was issued due to detections of cyanoHABs over a state's risk threshold. State reported events were defined as any event that was documented with a single date related to cyanoHABs. This study examined the presence-absence agreement between 160 state reported cyanoHAB advisories and 1,343 events and cyanobacteria biomass estimated by a satellite algorithm called the Cyanobacteria Index (CI cyano ). The true positive rate of agreement with state recreation advisories was 69% and 60% with state reported events. CI cyano detected a reduction or absence in cyanobacteria after 76% of the recreation advisories ended. CI cyano was used to quantify the magnitude, spatial extent, and temporal frequency of cyanoHABs; each of these three metrics were greater ( r > 0.2) during state recreation advisories compared to non-advisory times with effect sizes ranging from small to large. This is the first study to quantitatively evaluate satellite algorithm performance for detecting cyanoHABs with state reported events and advisories and supports informed management decisions with satellite technologies that complement traditional field observations.

Harmful Algae↗
USGS2022

Are little brown bats (Myotis lucifugus) impacted by dietary exposure to microcystin?

The cyanobacterium, Microcystis aeruginosa, can produce the hepatotoxin microcystin. When toxic M. aeruginosa overwinters in the sediments of lakes, it may be ingested by aquatic insects and bioaccumulate in nymphs of Hexagenia mayflies. When volant Hexagenia emerge from lakes to reproduce, they provide an abundant, albeit temporary, food source for many terrestrial organisms including bats. Little brown bats, Myotis lucifugus , feed opportunistically on aquatic insects including Hexagenia . To determine if microcystin moves from aquatic to terrestrial ecosystems via trophic transfer, we combined a dietary analysis with the quantification of microcystin in bat livers and feces. In June 2014, coincident with the local Hexagenia emergence, bat feces were collected from underneath a maternity roost near Little Traverse Lake (Leelanau County, Michigan, USA). Insects in the diet were identified via molecular analyses of fecal pellets from the roost and from individual bats. Livers and feces were collected from 19 female M. lucifugus , and the concentrations of microcystin in these liver tissues and feces were measured using an enzyme-linked immunosorbent assay (ELISA) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). We show that the majority of the bats’ diets consisted of aquatic insects and that microcystin was detected in high concentrations (up to 129.9 μg/kg dw) in the bat feces by ELISA. Histopathological examination of three bat livers with the highest concentrations of microcystin showed no evidence of phycotoxicosis, indicating that M. lucifugus may not be immediately affected by the ingestion of microcystin. Future work could examine whether bats suffer delayed physiological effects from ingestion of microcystin.

Michigan↗
USGS2022

Paralytic shellfish toxins associated with Arctic Tern mortalities in Alaska

Harmful algal blooms produce biotoxins that can injure or kill fish, wildlife, and humans. These blooms occur naturally but have intensified in many locations globally due to recent climatic changes, including ocean warming. Such changes are especially pronounced in northern regions, where the effects of paralytic shellfish toxins (PSTs) on marine wildlife are of growing concern. In Alaska, seabird mortality events have increased in frequency, magnitude, and duration since 2015 alongside anomalously high ocean temperatures. Although starvation has been implicated as the apparent cause of death in many of these die-offs, saxitoxin (STX) and other PSTs have been identified as possible contributing factors. Here, we describe a mortality event at a nesting colony of Arctic Terns ( Sterna paradisaea ) near Juneau, Alaska in 2019 and report elevated concentrations of PSTs in bird, forage fish, and mussel samples. Concentrations of STX and other PSTs in tern tissues (2.5–51.2 µg 100g −1 STX-equivalents [STX-eq]) were of similar magnitude to those reported from other PST-induced bird die-offs. We documented high PST concentrations in blue mussels (>11,000 µg 100g −1 STX-eq; Mytilus edulis spp.) collected from nearby beaches, as well as in forage fish (up to 494 µg 100g −1 STX-eq) retrieved from Arctic Tern nests, thereby providing direct evidence of PST exposure via the terns’ prey. At maximum concentrations measured in this study, a single 5 g Pacific Sand Lance ( Ammodytes personatus ) could exceed the median lethal STX dose (LD 50 ) currently estimated for birds, offering strong support for PSTs as a likely source of tern mortality. In addition to describing this localized bird mortality event, we used existing energetics data from adult and nestling Arctic Terns to calculate estimated cumulative daily PST exposure based on ecologically relevant concentrations in forage fish. Our estimates revealed potentially lethal levels of PST exposure even at relatively low (≤30 ug 100g −1 STX-eq) toxin concentrations in prey. These findings suggest that PSTs present a significant hazard to Arctic Terns and other northern seabirds and should be included in future investigations of avian mortality events as well as assessments of population health.

Alaska↗
USGS2025

Phytoplankton assemblage structure, drivers, and thresholds with a focus on harmful algal bloom ecology in the Lake Okeechobee system, Florida, USA

Untangling the complexities of harmful algal bloom (HAB) dynamics is an ongoing effort that requires a fundamental understanding of spatiotemporal phytoplankton patterns and the environmental filters through which assemblages are structured. To this aim, monthly field surveys were conducted from 2019 to 2021 at 21 sites in Lake Okeechobee, Florida – a large, shallow, eutrophic, and heavily managed lake with coastal connectivity that experiences intense and recurrent HABs. Phytoplankton assemblages were strongly spatially structured forming 7 distinct lake zones with significant dissimilarity in composition and total abundance. While successional patterns were not apparent across seasons or wet/dry periods, total phytoplankton abundance was significantly greater towards the end of the wet season. Distance-based linear models using 16 abiotic variables were used to identify significant explanatory variables of spatial and temporal patterns. The spatial model explained 93 % of the variability suggesting deterministic processes largely control spatial patterns. The temporal model explained only 48 % of the temporal variability suggesting stochasticity in lake-wide shifts in assemblages over time. However, the strong spatial structuring of assemblages may preclude lake-wide succession patterns. Total algal abundance metrics were inversely related to nitrate, orthophosphate, and total alkalinity, the strongest explanatory variables of assemblage patterns, suggesting a lag between peak resources and peak abundance as phytoplankton cycle “boom-to-bust” phases. Consistent with this inverse relationship, Threshold Indicator Taxa Analysis returned almost exclusively negative responder indicator taxa for all three explanatory variable gradients. The assemblage-level threshold defined the gradient boundary between boom- and bust-associated indicator taxa. These data contribute novel information about HABs ecology pertinent to management strategies.

Florida↗
USGS2025

Dominant Dolichospermum and microcystin production in Detroit Lake (Oregon, USA)

The excessive growth of harmful cyanobacteria, including Dolichospermum (formerly known as Anabaena ), in freshwater bodies has become a pressing global concern. However, detailed information about the role of Dolichospermum in shaping bloom dynamics and producing cyanotoxins is limited. In this study, a bloom event dominated by Dolichospermum spp. at Detroit Lake (Oregon, USA) was examined from 2019 to 2021. In 2019, early summer cyanobacterial community succession reached up to 8.7 % of total phytoplankton abundance. Dolichospermum was the major microcystin (MC)-producing genus, with peak MC levels of 7.34 μg L −1 . The presence of MCs was strongly correlated with the abundance of Dolichospermum ( r = 0.84, p < 0.05) and MC synthetase gene, mcyE-Ana ( r = 0.63, p < 0.05). Metabolic analyses further showed that the presence of nif / pst genes linked to nitrogen and phosphorus metabolism was dominated by Dolichospermum from the bloom onset until September. In addition, the abundance of Dolichospermum was significantly correlated with the abundance of nitrogen-fixing nif-Ana gene ( r = 0.62, p < 0.05). As the lake experienced a longer N and P scarcity period (May to September), the N 2 -fixing Dolichospermum was able to dominate over other non-fixing cyanobacteria present, including Microcystis and Planktothrix . Overall, our results facilitate a better understanding of the organism and will help working toward managing/predicting future blooms.

Oregon↗
USGS2025

Paralytic shellfish toxins and seabirds: Evaluating sublethal effects, behavioral responses, and ecological implications of saxitoxin ingestion by common murres (Uria aalge)

Paralytic shellfish toxins (PSTs), including saxitoxin (STX) and its congeners, are neurotoxins that can be produced during harmful algal blooms and cause illness or death in humans, fish, seabirds, and marine mammals. Since 2014, multiple large-scale seabird mortality events have occurred in Alaska waters, with STXs detected in some carcasses. To investigate the sublethal behavioral and ecological effects of STX on seabirds, we conducted captive dosing trials with common murres ( Uria aalge ). We gavaged purified STX (dehydrated STX dihydrocholoride, STX-diHCl) or an Alexandrium catenella culture extract into murres, monitored behavioral responses and recovery times, and assessed tissue concentrations in individuals that died or were euthanized. Using a modified up-and-down dose-finding scheme, we estimated a median effective dose (ED 50 ) of 89 µg STX-equivalents (eq) kg -1 for STX-diHCl and 366 µg STX-eq kg -1 for the A. catenella extract based on ecologically relevant behavior. Differences between the ED 50 estimates could reflect uncertainties in toxin equivalency factors for PST congeners, which are based on studies using purified toxins in mice and may vary across taxa or toxin matrices. Post-dosing concentrations of STX varied by tissue type across individuals, with quantifiable levels ranging from 3 to 379 µg STX-eq 100g -1 . Evidence of biotransformation of STX in A. catenella extract-dosed birds was observed. We also measured the chronic effects of dosing with sublethal levels of STX-diHCl over seven-days, which resulted in lower fish intake among treatment birds compared to controls (-187 g day -1 ). This investigation improves our understanding of the ecological effects of PSTs on seabird health.

Alaska↗
USGS2025

Cyanotoxin and domoic acid occurrence, relation with salinity, and potential recreational health risks in U.S. coasts in the 2015 US EPA National Coastal Condition Assessment

In the first nationwide study of cyanotoxins in U.S. estuaries, algal toxins, cyanotoxins, chlorophyll, and salinity were measured in samples collected during the National Coastal Condition Assessment 2015. Anatoxin-a (ANAA), cylindrospermopsin (CYLS), domoic acid (DMAC), and microcystins (MCs) were detected by LC/MS/MS in 0.6, 0.9, 8.3, and 2.0 % of samples with mean concentrations of detections of 0.13, 0.13, 0.53, and 0.49 µg/L, respectively. MCs by ELISA were also evaluated, and 4.0 % of samples had measurable MCs with a mean of 0.78 µg/L. While ANAA and CYLS were detected south of 40° latitude, MCs by ELISA and DMAC occurred nationwide. Results were compared to freshwater recreational health thresholds from the World Health Organization and US Environmental Protection Agency to evaluate potential recreational exposure to MCs and CYLS since marine thresholds do not currently exist. Cyanotoxins were categorized using the 2021 World Health Organization Alert Level Framework for recreational exposure with 99.4, 99.1, 94.7, 98.0, and 44.7 % of samples being at the Vigilance Level for ANAA, CYLS, MCs (ELISA and LC/MS/MS), and chlorophyll, respectively with the remaining samples at Alert Level 1. Chlorophyll had 19.9 and 9.9 % of samples at Alert Level 1 and Alert Level 2, respectively. All cyanotoxins were below US EPA health advisory thresholds. ANAA, CYLS, DMAC, and MCs by ELISA were detected in samples with a wide range of salinities, while MCs by LC/MS/MS only occurred in samples with salinity <5 part per thousand (PPT). The source of cyanotoxins is likely a combination of inland transport and in situ estuarine production.

contiguous United States↗
USGS2025

Cyanotoxin production in shallow subtropical lakes is driven by nutrient enrichment and primary producer abundance on the millennial scale

Increased cyanotoxin concentrations from harmful algal blooms (HABs) in lake systems pose a global challenge to water quality. Although progress has been made in monitoring cyanotoxins in modern environments over recent decades, identifying the triggers of cyanotoxin release by cyanobacteria has yielded mixed results from experimental and analytical studies. Paleolimnological reconstructions can reveal whole-lake long-term changes, but few studies have directly measured cyanotoxins alongside other water quality proxies. Here, we investigated the drivers of sedimentary total microcystin (MC) concentrations on millennial scales in hypereutrophic Lakes Dora and Marian in central Florida, USA. We analyzed dated sediment records using paleolimnological techniques to reconstruct nutrient deposition, cyanobacteria abundance (photosynthetic pigments), and cyanotoxins (total MCs). The objective was to investigate the linkage between MC concentrations in the sediments with both biotic (cyanobacteria and other primary producers) and abiotic factors (nutrients and climate). We found that MC production occurred throughout the ∼7000-year period, progressing from periods of moderate to low, and then to high concentrations in both lakes. Statistical analyses showed that historical MC concentrations were correlated with sedimentary measurements of total phosphorus (TP), cyanobacteria abundance, and other primary producer groups, such as cryptophytes. However, there was only a minimal correspondence with climate proxies, such as charcoal and pollen, suggesting that internal nutrient cycling and human pressures were the dominant drivers of MC deposition. Our study demonstrates that cyanotoxins have occurred for millennia in both lakes with maintained relationships to nutrients and other environmental factors that existed both in historic and modern limnological conditions.

Florida↗
USGS2026

Revisiting chlorophyll a thresholds for San Francisco Bay: Insights from observations of phytoplankton molecular abundance

Harmful Algal Blooms (HABs) are a hazard for coastal environments worldwide; identifying screening thresholds of chlorophyll- a (chl- a) associated with increased risk of HABs is a management priority. Molecular surveillance of coastal phytoplankton and bivalve biotoxins could be used to link chl- a with HAB risk, but requires an understanding of whether the HAB risks increase uniformly as chl-a rises, or whether some taxa are disproportionately favored, and if these relationships vary by season. In this study, we present a novel use of molecular abundance data to investigate the scientific bases for estuarine chl- a thresholds protective against HABs. In San Francisco Bay (SFB), California, the relationship between molecular relative abundance (as measured by 18S metabarcoding) of nine different HAB taxa, absolute quantitative polymerase chain reaction (qPCR) abundance, and mussel toxin concentrations of a subset of the taxa were investigated for thresholds as a function of increasing chl- a . Our results show most HAB taxa did not increase in absolute or relative abundance during SFB’s spring bloom interval, when chl- a levels were highest (>10 µg/L) but the assemblage was dominated by non-harmful diatoms. However, several flagellated, mixotrophic taxa did increase above their molecular baseline in fall, and the combined probability of any HAB occurring above baseline was elevated when chl- a reached ∼4.6 µg/L in the fall. This work demonstrates the promise of molecular approaches in disentangling the seasonally complex interplay between stressors and phytoplankton/HAB community responses and has the potential to provide clearer, more cost-effective monitoring and mitigation strategies for managers.

California↗
USGS2009

Monitoring benthic aIgal communides: A comparison of targeted and coefficient sampling methods

Choosing an appropriate sample unit is a fundamental decision in the design of ecological studies. While numerous methods have been developed to estimate organism abundance, they differ in cost, accuracy and precision.Using both field data and computer simulation modeling, we evaluated the costs and benefits associated with two methods commonly used to sample benthic organisms in temperate kelp forests. One of these methods, the Targeted Sampling method, relies on different sample units, each "targeted" for a specific species or group of species while the other method relies on coefficients that represent ranges of bottom cover obtained from visual esti-mates within standardized sample units. Both the field data and the computer simulations suggest that both methods yield remarkably similar estimates of organism abundance and among-site variability, although the Coefficient method slightly underestimates variability among sample units when abundances are low. In contrast, the two methods differ considerably in the effort needed to sample these communities; the Targeted Sampling requires more time and twice the personnel to complete. We conclude that the Coefficent Sampling method may be better for environmental monitoring programs where changes in mean abundance are of central concern and resources are limiting, but that the Targeted sampling methods may be better for ecological studies where quantitative relationships among species and small-scale variability in abundance are of central concern.

Algae↗