Red Tide Outbreaks Research Articles

Risk perception, media exposure, and visitor’s behavior responses to Florida Red Tide

ABSTRACT Florida’s Red Tide outbreak, a major environmental disturbance in 2018, not only garnered nationwide attention but also affected both in-state and out-of-state visitors. Guided by the Social Amplification of Risk Framework (SARF), this study examined the relationships between media exposure, risk perception, and visitors’ behavioral responses. Data were gathered from two surveys in late 2018. The findings validate the practicality of applying SARF to the current context. This study also found that both perceived consequences and access to the community are significant predictors of visitor behavior. This study further discussed how to market destinations during turbulent times.

The Monitoring of Harmful Algae Blooms in Sabah, Malaysia

The first record of harmful algae bloom (HAB) in Sabah was in 1976 where 202 victims were reported to be suffering from Paralytic Shellfish Poisoning (PSP) and 7 deaths. The causative organism was Pyrodinium bahamense, a dinoflagellate which produces saxitoxin. Since then, Department of Fisheries Sabah has been doing monitoring to safeguard seafood safety, especially shellfish harvested for food consumption. Cochlodinium polykrikoides bloom for the first time in Sabah in year 2005 where Kota Kinabalu and Tuaran experienced fish kill. Since then, other HAB species such as Gymnodinium catenatum, Gonyaulax polygramma and Noctiluca scintillans were identified in waters of Sabah. Sabah is the only state in Malaysia in which the monitoring program is done consistently throughout the year since 1976. Samples were collected once or twice a month, according to high and low risks areas which have been identified, most of which are in the west coast. The collection frequency may be increased depending on the situation such as whether there is an outbreak of red tide or PSP in the area. Due to this effort, PSP cases involving the public have declined during the last 40 years without duly affecting the income of fishermen and the fisheries industry. After successfully implementing toxin monitoring between 1984 to 2013, it recurred back in 2013 when 3 deaths were reported. The purpose of this paper is to review all HABs incidences that occured in Sabah over the last few years from January 2000 – December 2017.

Research Progress in the Biosynthetic Mechanisms of Marine Polyether Toxins.

Marine polyether toxins, mainly produced by marine dinoflagellates, are novel, complex, and diverse natural products with extensive toxicological and pharmacological effects. Owing to their harmful effects during outbreaks of marine red tides, as well as their potential value for the development of new drugs, marine polyether toxins have been extensively studied, in terms of toxicology, pharmacology, detection, and analysis, structural identification, as well as their biosynthetic mechanisms. Although the biosynthetic mechanisms of marine polyether toxins are still unclear, certain progress has been made. In this review, research progress and current knowledge on the biosynthetic mechanisms of polyether toxins are summarized, including the mechanisms of carbon skeleton deletion, pendant alkylation, and polyether ring formation, along with providing a summary of mined biosynthesis-related genes. Finally, future research directions and applications of marine polyether toxins are discussed.

Relationship between the Occurrence of Red Tides and the Dynamic Response Mechanisms in the Northern Beibu Gulf

Chen, B.; Dong, D.; Qin, X.; Xu, M.; Chen, X., and Shi, M., 2019. Relationship between the occurrence of red tides and the dynamic response mechanisms in the northern Beibu Gulf. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 185–193. Coconut Creek (Florida), ISSN 0749-0208.Unlike the common outbreak mechanism of red tides, the northern Beibu Gulf in the Guangxi Zhuang Autonomous Region of China experiences frequent red tides with distinct characteristics, such as large distances from the mainland and the presence of industrial pollution. By tracing the sources and transport of the high concentrations of nitrogen and phosphorus, the relationship between pollutant transport and the dynamic response mechanisms was explored. The results showed that the concentrations of nitrogen and phosphorus nutrients in the areas of red tide outbreaks near Weizhou Island and in the Qinzhou Gulf in the northern Beibu Gulf were higher than those in the surrounding areas. However, the high concentrations of nitrogen and phosphorus nutrients in the northern Beibu Gulf did not originate from terrestrial pollution from Guangxi Province; rather, these pollutants originated on the east coast of China and were transported through the Qiongzhou Strait. The primary sources were the Pearl River Estuary and the coastal waters of eastern Guangdong. In addition, the differences in the concentration distributions of nitrogen and phosphorus nutrients between the east and west coasts of the Qinzhou Gulf in the northern Beibu Gulf were clearly related to dynamic response mechanisms.

Karstic submarine groundwater discharge into the Mediterranean: Radon-based nutrient fluxes in an anchialine cave and a basin-wide upscaling

Anchialine caves are common in Mediterranean karstic shorelines and elsewhere, delivering point-source fresh groundwater and nutrients to the coastal ocean. Here, we first quantified submarine groundwater discharge (SGD) in a typical karstic system (Zaton Bay, Croatia) receiving groundwater from anchialine caves using a radon (222Rn) mass balance model. We then combine our new observations with the literature to provide a Mediterranean-scale estimate of karstic fresh SGD nutrient fluxes. We found that SGD and related nutrient fluxes in the upper brackish layer were much higher than those in the underlying layer in Zaton Bay. In the upper brackish layer, both SGD (m d−1) and associated nutrient fluxes (mmol m−2 d−1) in the wet season (SGD: 0.29–0.40; DIN: 52; DIP: 0.27) were significantly higher than those in the dry season (SGD: 0.15; DIN: 22; DIP: 0.08). Red tides were observed in the wet season but not in the dry season. Nutrient budgets imply that SGD accounted for >98% of the total dissolved inorganic nitrogen (DIN) and phosphorous (DIP) sources into Zaton Bay. These large SGD nutrient fluxes with high N/P ratios (190–320) likely trigger and sustain red tide outbreaks. Combining our results with 30 previous studies in the region revealed that point-source DIN and DIP fluxes via karstic fresh SGD may account for 8–31% and 1–4%, respectively, of riverine inputs in the Mediterranean Sea. Overall, we demonstrate the importance of karstic SGD as a source of new nutrients with high N/P ratios to the Mediterranean Sea and emphasize how SGD lagging precipitation can drive red tide outbreaks.

Are tintinnids picky grazers: Feeding experiments on a mixture of mixotrophic dinoflagellates and implications for red tide dynamics.

To understand and predict the outbreak of red tides, which are often dominated by mixotrophic dinoflagellates (MTDs), the effects of "top-down" control by co-occurring predators on red-tide MTDs should be taken into consideration. We studied the numerical and functional responses of the tintinnid ciliate Favella ehrenbergii feeding on two red-tide MTDs, Scrippsiella trochoidea and Heterocapsa triquetra, under single and mixed prey conditions. Our results suggest that a mixed diet could support a better growth of predators compared to a monodiet. In addition, the predators preferred to graze S. trochoidea in the mixed diets, suggesting that predators may switch their feeding preference. The grazing by tintinnid predators could potentially inhibit the outbreaks of red tides dominated by MTDs. The findings in this study provide basic data and new insights for understanding the complex predator-prey relationships in marine microbial food webs, and the dynamics of red tides dominated by MTDs.

RNA-Seq Analysis Reveals Genes Related to Photoreception, Nutrient Uptake, and Toxicity in a Noxious Red-Tide Raphidophyte Chattonella antiqua.

Aquaculture industries are under threat from noxious red tides, but harm can be mitigated by precautions such as early harvesting and restricting fish feeding to just before the outbreak of a red tide. Therefore, accurate techniques for forecasting red-tide outbreaks are strongly needed. Omics analyses have the potential to expand our understanding of the eco-physiology of these organisms at the molecular level, and to facilitate identification of molecular markers for forecasting their population dynamics and occurrence of damages to fisheries. Red tides of marine raphidophytes, especially Chattonella species, often extensively harm aquaculture industries in regions with a temperate climate around the world. A red tide of Chattonella tends to develop just after an input of nutrients along the coast. Chattonella displays diurnal vertical migration regulated by a weak blue light, so it photosynthesizes in the surface layer during the daytime and takes up nutrients in the bottom layer during the nighttime. Superoxide produced by Chattonella cells is a strong candidate for the cause of its toxicity to bacteria and fishes. Here we conducted mRNA-seq of Chattonella antiqua to identify genes with functions closely related to the dynamics of the noxious red tide, such as photosynthesis, photoreception, nutrient uptake, and superoxide production. The genes related to photosynthetic pigment biosynthesis and nutrient uptake had high similarity with those of model organisms of plants and algae and other red-tide microalgae. We identified orthologous genes of photoreceptors such as aureochrome (newly five genes), the cryptochrome/photolyase (CRY/PHR) family (6-4PHR, plant CRY or cyclobutane pyrimidine dimer [CPD] Class III, CPD Class II, and CRY-DASH), and phytochrome (four genes), which regulate various physiological processes such as flagellar motion and cell cycle in model organisms. Six orthologous genes of NADPH oxidase, which produces superoxide on the cell membrane, were found and divided into two types: one with 5–6 transmembrane domains and another with 11 transmembrane domains. The present study should open the way for analyzing the eco-physiological features of marine raphidophytes at the molecular level.

Congress takes aim at harmful algal blooms

Florida is facing one of the worst red tide outbreaks in more than a decade. The toxic algae have been plaguing both coasts in the state for the past 10 months, and they show no sign of going away. Reports of dead fish and mammals washing ashore and horrible stenches of rotting sea life are driving many visitors away from Florida, hurting the state’s economy. Neurotoxins produced by algae have also contaminated Dungeness crabs and other shellfish in Alaska, Washington, Oregon, and California, U.S. Sen. Dan Sullivan (R-Alaska), chair of the Senate Subcommittee on Oceans, Atmosphere, Fisheries & Coast Guard, said at an Aug. 28 hearing. Sen. Tammy Baldwin (D-Wis.) noted that “algae blooms are turning hundreds of Wisconsin’s sparkling blue lakes and rivers into green pea soup” and that fish kills are getting worse in Green Bay. Climate change is contributing to the algal blooms as waters warm and

RESEARCH ON HIGH ACCURACY DETECTION OF RED TIDE HYPERSPECRRAL BASED ON DEEP LEARNING CNN

Abstract. Increasing frequency in red tide outbreaks has been reported around the world. It is of great concern due to not only their adverse effects on human health and marine organisms, but also their impacts on the economy of the affected areas. this paper put forward a high accuracy detection method based on a fully-connected deep CNN detection model with 8-layers to monitor red tide in hyperspectral remote sensing images, then make a discussion of the glint suppression method for improving the accuracy of red tide detection. The results show that the proposed CNN hyperspectral detection model can detect red tide accurately and effectively. The red tide detection accuracy of the proposed CNN model based on original image and filter-image is 95.58 % and 97.45 %, respectively, and compared with the SVM method, the CNN detection accuracy is increased by 7.52 % and 2.25 %. Compared with SVM method base on original image, the red tide CNN detection accuracy based on filter-image increased by 8.62 % and 6.37 %. It also indicates that the image glint affects the accuracy of red tide detection seriously.

Feasibility of Changing or Canceling Designated Mariculture Management Areas in Ongjin-gun, Korea

Some of the mariculture grounds near Ongjin-gun, Korea, were designated as mariculture management areas in 2007. Areas are so designated when the environmental quality of the mariculture ground deteriorates or there is an outbreak of hypoxia or harmful red tide that kills mariculture organisms. We s...

A novel method for characterizing harmful algal blooms in the Persian Gulf using MODIS measurements

Biophysical properties of water undergo meaningful variations under red tide (RT) outbreak. A massive Cochlodinium polykrikoids RT began in the eastern Persian Gulf (PG) in October 2008 and extended to the northern PG in December 2008. It killed large fish and hampered marine industries and water desalination appliances. Yet monthly averages of satellite-derived Chl-a (Chlorophyll-a), nFLH (normalized Fluorescence Line Height), and Kd490 (diffuse attenuation coefficient at 490nm) have not been compared in the PG. MODIS (MODerate Resolution Imaging Spectroradiometer) sensor provides global coverage, with short revisit time, and accessible, well validated ocean color products. This study compares the behavior of MODIS Chl-a, nFLH, and Kd490 in both normal and RT conditions. In doing so, their color maps are shown during normal and RT periods. Then, monthly variations of these products are shown as time-series between 2002 and 2008. HOCI (Hybrid Ocean Color Index) is defined by integrating these products to detect RT affected areas. The results gained from 100 locations in the PG show that HOCI >0.18mWcm−2μm−1sr−1mgm−4 and nFLH >0.04mWcm−2μm−1sr−1 discriminates non-bloom waters from algal blooms. Rrs(443)/Rrs(412)>1 is a proper statement to separate Trichodesmium erythtraeum from Noctiluca millaris, Noctiluca scintillans, and diatoms. Rrs(667)/Rrs(443)>1 can differentiate Cochlodinium polykrikoids from T. erythtraeum, N. millaris, N. scintillans, and diatoms as well. So, the combination of HOCI and Rrs(667)/Rrs(443) ratio is useful for detection and quantization of C. polykrikoids.

Submarine groundwater discharge and nutrient loadings in Tolo Harbor, Hong Kong using multiple geotracer-based models, and their implications of red tide outbreaks

Multiple tracers, including radium quartet, 222Rn and silica are used to quantify submarine groundwater discharge (SGD) into Tolo Harbor, Hong Kong in 2005 and 2011. Five geotracer models based on the end member model of 228Ra and salinity and mass balance models of 226Ra, 228Ra, 222Rn, and silica were established and all the models lead to an estimate of the SGD rate of the same order of magnitude. In 2005 and 2011, respectively, the averaged SGD based on these models is estimated to be ≈ 5.42 cm d−1 and ≈2.66 cm d−1, the SGD derived DIN loadings to be 3.5 × 105 mol d−1 and 1.5 × 105 mol d−1, and DIP loadings to be 6.2 × 103 mol d−1 and 1.1 × 103 mol d−1. Groundwater borne nutrients are 1–2 orders of magnitude larger than other nutrient sources and the interannual variation of nutrient concentration in the embayment is more influenced by the SGD derived loadings. Annual DIP concentrations in the harbor water is positively correlated with the precipitation and annual mean tidal range, and negatively correlated with evapotranspiration from 2000 to 2013. Climatologically driven SGD variability alters the SGD derived DIP loadings in this phosphate limited environment and may be the causative factor of interannual variability of red tide outbreaks from 2000 to 2013. Finally, a conceptual model is proposed to characterize the response of red tide outbreaks to climatological factors linked by SGD. The findings from this study shed light on the prediction of red tide outbreaks and coastal management of Tolo Harbor and similar coastal embayments elsewhere.

INVESTIGATION THE BEHAVIOR OF MODIS OCEAN COLOR PRODUCTS UNDER THE 2008 RED TIDE IN THE EASTERN PERSIAN GULF

Abstract. Biophysical properties of water undergo serious variations under red tide (RT) outbreak. During RT conditions, algal blooms spread out in the estuarine, marine and fresh waters due to different triggering factors such as nutrient loading, marine currents, and monsoonal winds. The Persian Gulf (PG) was a talent region subjected to different RTs in recent decade. A massive RT started from the Strait of Hormuz in October 2008 and extended towards the northern parts of the PG covering more than 1200 km of coastlines. The bloom of microorganism C. Polykrikoides was the main specie that generated large fish mortalities, and hampered marine industries, and water desalination appliances. Ocean color satellite data have many advantages to monitor and alarm RT occurrences, such as wide and continuous extent, short time of imagery, high accessibility, and appropriate estimation of ocean color parameters. Since 1999, MODerate Resolution Imaging Spectroradiometer (MODIS) satellite sensor has estimated satellite derived chlorophyll-a (Chl-a), normalized fluorescence line height (nFLH), and diffuse attenuation coefficient at 490nm (kd490). It provides a capability to study the behavior of these parameters during RT and normal conditions. This study monitors variations in satellite derived Chl-a, nFLH, and kd490 under both RT and normal conditions of the PG between 2002 and 2008. Up to now, daily and monthly variations in these products were no synchronously investigated under RT conditions in the PG. In doing so, the MODIS L1B products were provided from NASA data archive. They were corrected for Rayleigh scattering and gaseous absorption, and atmospheric interference in turbid coastal waters, and then converted to level 2 data. In addition, Enhanced Red Green Blue (ERGB) image was used to illustrate better water variations. ERGB image was built with three normalized leaving water radiance between 443 to 560nm. All the above data processes were applied by SeaDAS 7 software package. The Strait of Hormuz was selected as the study area in the eastern part of the PG. Images including high cloud coverage (>50%) over the study area were filtered out. The classification maps of the above products were shown during RT and normal periods. Monthly variations of mentioned products were calculated for the dates before, during, and after RT appearance. The results were demonstrated as time-series diagrams. All the above calculations and presentations were performed in Matlab 7 software package. The results show that MODIS Chl-a, nFLH, and kd490 increased during the 2008 RT. Based on the feedback of these parameters under RT conditions, hybrid ocean color index (HOCI) is defined. HOCI is able to display better water variations during RT outbreak. High values of HOCI show RT affected areas.

A hierarchy of conceptual models of red-tide generation: Nutrition, behavior, and biological interactions

Red tides – discolorations of the sea surface due to dense plankton blooms – occur regularly in coastal and offshore waters along much of the world's coastline. Red tides often cause large-scale mortalities of fish and shellfish and significant losses to the aquaculture and tourist industries of many countries. Therefore, understanding and predicting the mechanisms controlling the outbreak, persistence, spread, and decline of red tides are important concerns to scientists, officials, industry, and the public. With increasing knowledge of red-tide species and red-tide events, new mechanisms have been discovered. Based on the nutrition and behaviors of red-tide organisms and biological interactions among them, red-tide outbreaks can be categorized into a hierarchy of four generation mechanisms (GM1–GM4). In the simplest, GM1, all phototrophic red-tide species were treated as exclusively autotrophic organisms without the ability to swim. However, this GM cannot explain red-tide outbreaks in oligotrophic surface waters offshore. Vertical migration (considered in GM2) and mixotrophy (GM3) enable red-tide flagellates to acquire growth factors from nutrient-rich deep waters or co-occurring prey, respectively. In natural environments, all red tides occur by those species outgrowing co-occurring organisms; red-tide species dominate communities by eliminating other species or reducing their abundances. Thus, GM4 contains the direct biological interactions (i.e., inhibition by physical contact or chemical effects) and indirect biological interactions (i.e., acquiring resources faster than others) that can affect the dominance of red-tide species under given conditions. Correctly choosing one of these four GMs for red tides dominated by one causative species is important because the accuracy of predictions may be outweighed by the costs and time required to acquire the relevant information. In this study, mechanisms describing the outbreak, persistence, and decline of red tides were reviewed, the advantages and limitations of each mechanism were evaluated, and insights about the evolution of the mechanisms were developed.

Monitoring red tide with satellite imagery and numerical models: A case study in the Arabian Gulf

A red tide event that occurred in August 2008 in the Arabian Gulf was monitored and assessed using satellite observations and numerical models. Satellite observations revealed the bloom extent and evolution from August 2008 to August 2009. Flow patterns of the bloom patch were confirmed by results from a HYCOM model. HYCOM data and satellite-derived sea surface temperature data further suggested that the bloom could have been initiated offshore and advected onshore by bottom Ekman layer. Analysis indicated that nutrient sources supporting the bloom included upwelling, Trichodesmium, and dust deposition while other potential sources of nutrient supply should also be considered. In order to monitor and detect red tide effectively and provide insights into its initiation and maintenance mechanisms, the integration of multiple platforms is required. The case study presented here demonstrated the benefit of combing satellite observations and numerical models for studying red tide outbreaks and dynamics.

Mixotrophic dinoflagellate red tides in Korean waters: Distribution and ecophysiology

We investigated the outbreaks of red tides dominated by dinoflagellates in the coastal waters of Korea from 1981 to 2009. During the study period, 693 mixotrophic dinoflagellate red-tide events occurred. Of these, 36.8% were Cochlodinium polykrikoides red tides, with Akashiwo sanguinea, Ceratium furca, and Prorocentrum minimum also frequently forming red tides. Eighty-five percent of mixotrophic dinoflagellate red tides in Korean waters occurred from June to September, in the high water-temperature season. The monthly frequency of outbreaks of mixotrophic dinoflagellate red tides increased from twice in January–March to 228 times in August, but it decreased to 2–9 times in November and December. Eighty-six percent of the outbreak events were recorded in southern coastal waters, 12% in eastern coastal waters, and only 2% in western coastal waters of Korea. There were wide temperature and salinity ranges during red tides associated with A. sanguinea, C. furca, and P. minimum, whereas for C. polykrikoides and Gonyaulax polygramma the temperature and salinity ranges were narrow. The concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) in 1996–2000 were higher than the reported values for the half-saturation concentrations of uptake of nitrate and phosphate for most of the causative mixotrophic dinoflagellates. However, the concentrations of DIN and DIP have decreased gradually since 2000 and the frequency of mixotrophic dinoflagellate red tides has also decreased. Thus, DIN and DIP are likely to be the primary factors influencing the frequency of mixotrophic dinoflagellate red tides in Korean waters. Five novel dinoflagellate species have been discovered in Korean coastal waters since 2005 and their morphological and molecular characteristics have been described as new genera and species. It is thus necessary to monitor their dynamics to investigate whether they can form red tides.

Temporal and spatial distribution of red tide outbreaks in the Yangtze River Estuary and adjacent waters, China

Between 1972 and 2009, evidence of red tide outbreaks in the Yangtze River Estuary and adjacent waters was collected. A geographic information system (GIS) was used to analyze the temporal and spatial distribution of these red tides, and it was subsequently used to map the distribution of these events. The results show that the following findings. (1) There were three red tide-prone areas: outside the Yangtze River Estuary and the eastern coast of Sheshan, the Huaniaoshan–Shengshan–Gouqi waters, and the Zhoushan areas and eastern coast of Zhujiajian. In these areas, red tides occurred 174 total times, 25 of which were larger than 1000 km2 in areal extent. After 2000, the frequency of red tide outbreaks increased significantly. (2) During the months of May and June, the red tide occurrence in these areas was 51% and 20%, respectively. (3) Outbreaks of the dominant red tide plankton species Prorocentrum dong-haiense, Skeletonema costatum, Prorocentrum dantatum, and Noctiluca scientillan occurred 38, 35, 15, and 10 times, respectively, during the study interval.

Nutrient-based method for assessing the hazard degree of red tide: a case study in the Zhejiang coastal waters, East China Sea

The assessment of the hazard degree of red tide is a new research field. The current study analyzes the relationship between the specific growth rate and N/P atomic ratio of red tide to obtain the assessment results of red tide under various N/P atomic ratios. This study aims to develop a nutrient-based method that can assess the hazard degree of red tide disasters based on the algal growth and cell density threshold of red tide outbreaks. This study obtained the following four main findings: (1) a nutrient-based tolerance model of the algal growth that can provide a quantitative description of Shelford’s law of tolerance was established, (2) a method that can assess the hazard degree of red tide disasters based on the time the algal growth reached the cell density threshold of red tide outbreaks was proposed, (3) the hazard degree assessment of red tide disasters was classified into four grades, namely, very high, high, medium, and low, and (4) the spatial distribution map of the Alexandrium tamarense red tide outbreak probability in the Zhejiang coastal waters was generated using the proposed method and the geographic information system and remote sensing technology.

Impacts of nutrients and related environmental factors on distribution and size structure of Noctiluca scintillans populations of the Eutrophic Tha Chin Estuary, Thailand

This study aimed to analyze the impacts of nutrients and related aquatic factors on changes in the Noctiluca population of the Tha Chin estuary, a nutrient-rich estuary located in the inner Gulf of Thailand. Field surveys were carried out at 30 stations during November 2009 to August 2010. The results indicated high levels of dissolved inorganic nitrogen (DIN; 13.89-46.99 μmol/L) and PO(4)(3-)-P (0.20-3.05 μmol/L) where the Noctiluca red tide occurred, particularly during the high-loading period. Dense populations were usually found in the outer part of the estuary with comparatively high salinity (25-29 psu). The highest Noctiluca density was 72,333 cells L(-1) and the cell diameters ranged between 360 and 460 μm. Proportions of small-sized cells (P(s); less than 300 μm) varied over time. In this study, P(s) showed a positive correlation with levels of PO(4)(3-)-P, while the total population density was significantly affected by levels of NH(4)(+)-N and DIN (p < 0.05). Overall, PO(4)(3-)-P influenced the development of the Noctiluca red tide, with the limitation of PO(4)(3-)-P levels to below 1 μmol/L suggested for controlling Noctiluca red tide outbreaks at their origin. To support environmental conservation and maintain sustainable production in the estuary, the levels of PO(4)(3-)-P should be considered for the further effective development of water quality standards in estuarine zones.

The distributions of dissolved nutrients in spring of Sungo Bay and potential reason of outbreak of red tide

There are over 20 years of history of shellfish and seaweed polyculture in Sungo Bay.There had not been reported the outbreak of red tide in the Bay.However,in May 2011,there occured large scale red tide outbreak,which almost spread over the total bay,and which caused higher mortality of cultivated shellfish.It is very important to understand the cause of red tide and to provide data for future environmental protection and aquaculture management.We just carried out one survey of environment monitoring before the outbreak of the red tide.Therefore,in this paper,the distributions of sea water temperature,salinity and dissolved nutrients were investigated in Sungo Bay in April 2006 and 2011,so as to understand the cause of the outbreak of red tide.The results showed that the concentration of dissolved inorganic nitrogen(DIN),phosphate(PO3-4)and silicate(Si)in Sungo Bay of 2011 was 5.6,3.2 and 1.3 times of the same period in 2006,respectively.The mole ratio of DIN/P,Si/P and Si/DIN was(66.33±47.16),(35.12±21.44)and(0.82±0.77),respectively,which was seriously deviated from the Redfield ratio.Dissolved nutrients showed obvious block distribution,their horizontal distribution was characterized by a concentration decrease from the open sea to the inner bay,and there were two sub-peak values near the Yatou River and Bahegang areas,the isolines were almost overlaps with low-salinity isolines.The probable causes of red tide outbreak were discussed from four aspects including nutrients,hydrological characteristics,kelp and temperature.