Hydrobiological and Bio-Optical Characterization of a Red Tide Occurredin Meda Creek, Porbandar, India

Special Article - Algal Blooms

Austin Environ Sci. 2022; 7(4): 1082.

Hydrobiological and Bio-Optical Characterization of a Red Tide Occurredin Meda Creek, Porbandar, India

Gideon OO1,2,3, Paidi MK1,2 and Mandal SK1,2*

¹Division of Applied Phycology and Biotechnology, CSIRCentral Salt & Marine Chemicals Research Institute, India

²Academic Council of Scientific and Industrial Research, CSIR-Central Salt & Marine Chemicals Research Institute, India

³Biological Sciences Department, Bowen University, Nigeria

*Corresponding author: Subir Kumar Mandal, Division of Applied Phycology and Biotechnology, CSIRCentral Salt & Marine Chemicals Research Institute, Gijubhai Badheka Marg, Bhavnagar-364002, Gujarat, India

Received: August 24, 2022; Accepted: September 27, 2022; Published: October 04, 2022

Abstract

Red tides are becoming more common in aquatic ecosystems, particularly the coastal habitats which are highly influenced by climatic and anthropogenic activities. We provide the first report of a red tide event in Meda creek, west coast of India. Light and scanning electron microscopy were used to identify the bloom forming organism, while physicochemical, biological and biooptical parameters were determined to characterize the aquatic body of the Meda Creek. The dominant bloom forming organisms were observed as unarmored, spherical, dorsoventrally compressed flagellate with truncated apex, notched and rounded hypocone, displaced premedian cingulum and extending sulcus. The length wise size of the cell varied from 20 to 30.83μM, whereas, the width varied from 14 to 27.5μM. The organisms was identified as Gymnodinium sp. High Performance Liquid Chromatography (HPLC) and spectral profile of the bloom indicatedeleven major peaks corresponding to that of 19-but-fucoxanthin (52.75%), astaxanthin (9.62%), fucoxanthin (8.81%), Mgdv (6.45%), prasinoxanthin (3.35%), chlorophyll C2 (3.22%), neoxanthin (3.12%), antheraxanthin (3.14%), diadinoxanthin (2.63%) and diatoxanthin (1.38%). Chlorophyll a concentration in the bloom sample was 38.8μg/L. Water temperature, salinity, NH3-N, NO2-N, NO3-N, PO4-Pwere higher during the bloom period than the non-blooming ones, while metals including Fe, Zn, Cr, Mn and Co were lower. No death of aquatic biota was observed. We propose that eutrophication along with the warm and saline conditions provided enabling conditions for occurrence the bloom. Also, most of the pigments expressed have antioxidant role and might be purposeful for the survival of the organism in the extreme condition of temperature and salinity recorded. Proper management and monitoring measures might help mitigate further occurrences of this bloom in the light changing climate and increasing anthropogenic impacts.

Keywords: Gymnodinium sp.; Red tide; Pigment; Optical spectra; Meda creek; Indian coast

Introduction

Red tide is a natural phenomenon in which species of phytoplankton rapidly accumulate into large biomass or high concentration and discolor a body of water into red, brown, green, or other color depending on the pigment composition of the causative organism [19]. Dinoflagellates like Gymnodinium are linked with this event in fresh, brackish and marine waters of temperate, subtropical and tropical regions [8,42] where events can be sometimes associated with water quality degradation, massive fish and aquaculture kills and toxic effect on humans [4,25,26]. Such blooms have been reported [5,7,12,17,18,36,38,41].

Evidences also exist on increasing incidence and occurrence in new areas where such has not been previously reported [14,17]. Some of these occurrences are attributed to changing hydrogeological conditions associated with climatic change and increasing anthropogenic activities like nutrient enrichment and ballast water discharge [16,34]. Increasing water temperature, salinity and nutrients have been correlated with positive growth rate of Gymnodinium [30,31,36]. Physiological characteristics like high mobility, diurnal vertical migration, mixotrophy and antioxidants e.g., pigments provide ability to survive in some of these conditions [35].

Blooms of Gymnodinium are common in coastal waters like the estuaries, bays and lagoons which are characterized by sudden and wide variations in environmental conditions [3]. These ecosystemshowever provide habitat for diverse biological resources and also grounds for trade and commerce [33]. Considering such functions, occurrences of these blooms could have socio-economic impacts. Meda creek is an estuarine habitat along the west coast of India which serves important functions like fishing, irrigation and minerals. It also provides coastal geomorphic forms like geomorphic forms like beaches, spit, bars, coastal dunes, tidal channels, tidal flats, coastal cliffs, etc. which house various organisms like bivalves, gastropods, corals, algae, fishes, etc. [23].

Meda creek records varying hydrological conditions with influence from freshwater input from Vartu, Sorti, Sindhi, Falku and Kaman rivers during raining season. A dam (Medhakrik dam) constructed along its path in the south provides barrage conditions, hence reducing freshwater inflow, increasing salinity regimes and reducing nutrient availability and movement of aquatic biota. It also receives discharge from famous temples like the ancient Harshad Mata temple and other adjoining areas. Fishing activities are well evident along it [23]. On the 6th of June, 2018, we observed a red tide of Gymnodinium sp. along the creek around Miyani area (Lat. 21.84784oN, Long. 69.36975oE) when we visited for sampling.

Here, we give a first report on the occurrence of red tide of Gymnodinium sp. along the creek and attempt to compare physicochemical parameters in the water body during and outside the period of bloom in other to understand likely factors which could have contributed to bloom. We also examine the pigment profile of the bloom with view to complementing microscopy findings on identity, and to understand physiological status of blooming organism in relation to the environment.

Materials and Methods

Phytoplankton and Water Sample Collection

20 litres of water sample was filtered through a 10 micron mesh size phytoplankton net using a one Liter capacity bowl and subsequently transferred into labelled 100ml phytoplankton bottle. Samples were brought to the laboratory for study. Water samples for the determination of physicochemical parameters were also collected into appropriately labelled plastic containers, and kept in ice packed box for transport to the laboratory. Upon reaching the laboratory, the water samples (with the exception of those for pigment analysis) were stored in 4oC until further analysis. Physicochemical parameters including temperature and salinity were determined at the period of sampling in the field using a portable multi parameter refractometer.

Identification of Causative Species of Red Tide

Light microscopy and scanning electron microscopy was employed for the identification of the causal organism. In the case of light microscopy, aliquot of bloom sample was placed on a glass slide and observed at 40X magnification under a 1X70 inverted Olympus microscope. Morphological features observed were noted and photographs were taken using attached camera [44]. For scanning electron microscopy, 2mL of bloom sample was centrifuged at low speed (2,000 rpm) for 10 minutes, and the supernatant carefully discarded. 1mL of 2% osmium tetraoxide was and then incubated in 4oC for 4 hours. Cells were subsequently washed with filtered seawater, cleaned with hydrogen peroxide and incubated for 24 hours at 30oC. Afterwards, they were filtered on a 25mm diameter 0.45μM pose size membrane under low pressure and rinsed twice with distilled water to remove excess salts. The filter paper was dried in oven at 30oC, after which a small portion was cut from the center, mounted on aluminum stub and coated with gold before viewing under the scanning electron microscope [43].

Physicochemical Analysis of Water Samples

Orthophosphate (PO43-) content: Analysis of orthophosphate in water sample was carried out according to Murphy and Riley (1962). Briefly, 20μL each of ascorbic acid mixture (comprising 1g ascorbic acid dissolved in 5mL MQ water and 9N H2SO4 respectively) and mixed reagent (containing 3.6ml of 10% ammonium molybdate, 10ml 9N H2SO4 and 0.6mL potassium antimony tartrate) were added to 1mL of blank/sample/standard solution of K2HPO4 in 1.5mL Eppendorf tube. Standard solutions of K2HPO4 prepared were 0μM, 2μM, 4μM, 6μM, 8μM and 10μM. Each Eppendorf tube was vortexed to ensure proper mixing, and afterwards incubated for about 20 minute. 200μL aliquot was transferred from each tube into a 96 well plate and optical density was measured against the blank at 880nm wavelength using an Epoch 2 microplate reader. A standard calibration curve of PO43- concentration in known/standard samples against absorbance values was plotted and the relative concentration in the unknown samples was determined.

Nitrate (NO3-) content: 50μL of Gueiss reagent (containing 1 sulphanilamide: 1NED solution) was added to 1mL of blank, water sample and standard solutions of NaNO3 (comprising 0μM, 5μM, 15μM, 20μM, 25μM and 30μM concentration) in 1.5mL tube. Afterwards, all the tubes were vortexed and for 20 minutes at 65oC. Hereafter, 200μL aliquot from each tube was transferred unto a 96 well plate and absorbance was read against blank sample at 540 nm using Epoch 2 microplate reader. The relative concentration of NO3- in the water sample was calculated from the calibration curve of NO32- concentration against absorbance values of the standard solutions [15].

Nitrite (NO2-) content: To each of one milliliter of blank, water sample and standard solutions (0μM, 5μM, 15μM, 20μM, 25μM and 30μM) of NaNO2, 50μL of Guiess reagent was added in a 1.5mL tube. The mixture was vortexed and incubated for 20 minutes. 200μL aliquot was taken from each tube into a 96 well plate, and absorbance was read against the blank at 540nm using Epoch 2 microplate reader. Standard calibration curve was plotted and the unknown concentration in the sample was determined [15].

Ammonia (NH3) content: 5ml of reagent A (Phenol-sodium nitroprusside solution) and B (Alkaline hypochlorite) were respectively added 100μL of blank/water sample/ standard solutions of NH4Cl; 0μM, 10μM, 20μM, 40μM, 60μM, 80μM and 100μM. Each mixture was vortexed and placed in the incubator at 37oC for 15 minutes. After cooling, 200μL aliquot of each transferred into a 96 well plate and absorbance was read at 625nm against the blank. Calibration curve was also constructed and unknown concentration in the sample was obtained [47].

Dissolved oxygen content: Water sample was collected into 150mL reagent bottles, and 2ml each of MnSO4 (winkler A) solution and alkali-iodide-azide (winkler B) agent was added using separate syringe. The bottles were stoppered and inverted a few times to ensure proper mixing. The samples were brought to the laboratory for further analysis. 2mL of conc. H2SO4 was slowly added to the sample through the neck of the bottle. The bottle was stoppered and inverted several times until dissolution of precipitate formed in the previous step was complete and golden to pale yellow colouration was observed. 50mL aliquot was taken and 2 drops of starch solution was added. The mixture was titrated against 0.0125M Na2S2O3 solution until a colorless end point was reached [1,2]. The volume of titrant used was recorded in mg/l, and the dissolved oxygen calculated as thus;