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INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 7, ISSUE 12, DECEMBER 2018 ISSN 2277-8616
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Biological And Oceanographic Analyzes Of
Intoxication By Marine Animal Consumption
(IMAC) Precursors In Diego Suarez Bay And
Northern-East Of Madagascar
LANDY SOAMBOLA Amelie, BEMIASA John, RASOAMANENDRIKA Agrippine Faravavy, MAHAZATSAKILA Volatiana
Anissa, RAKOTOJAONASY Fenosoa Edwina, ZIA Florence, MARA Edouard Remanevy
Abstract: Based on a retrospective view, the study aimed at analyzing the Intoxication by Marine Animal Consumption (IMAC) incidents occurred in
north and northeastern Antsiranana. The study took place in September 2016, March 2017 and in July 2017 to February 2018 using oceanographic data
(such as sea surface temperature (SST), rainfall and wind speed) and biological data, including the epidemiological data, the inventory of
Dinoflagellates and chlorophyll a (chl-a). 108 cases were hospitalized. The age group most affected was 18 to 41 years (50%). The overall case fatality
rate was 14%. The animals highlighted are a sea turtle, Sardinella and a Tuna. 40 genera of Diatoms and 09 genera of Dinoflagellates (g Prorocentrum,
g Protoperidinium, g Scippsiella, g Dinophysis, g Gonyaulax, g Gymnodium, g Lingulodium, g Ostreopsis, g Preperidium) are reported throughout the
Diego Suarez Bay. Parameters such as SST, rainfall, wind speed, the importance of terrigenous input and the morphological unit condition the
establishment of Harmful algal blooms (HAB) which is favorable to the IMAC presence. The IMAC may possibly occur 10 days after the harmful algal
bloom.
Index Terms: Planctons, Chlorophyll a, Dinoflagellates, harmful algal bloom, Intoxication by marine animal consumption, oceanographic data, northern-
east of Madagascar; Diego Suarez bay. ————————————————————
1 INTRODUCTION
Unknown cause of the sudden death has been commonly
reported in Madagascar. Intoxication by Marine Animal
Consumption (IMAC) might be part of the causes. Despite the
ministerial regulations on consuming certain marine animals at
risk of IMAC incident during hot season, local people still do
not respect them. IMAC incident victims are often recorded
within the coastal area [1]. For instance, the northern part of
Madagascar does not escape this situation especially during
hot and rainy season [2]. Without a regional and local IMAC
risk alert in a well-located area, the IMAC present a
devastating effect on the area.
It can be observed that direct negative impacts such as loss of
humans, tourism activity and loss of work such as fishing and
other downstream marine product trade channels occur. In
order to be able to, earlier, determine the period and the areas
at risk of IMAC, it is prominent to better know its precursors,
which are mainly part of environmental signals leading to the
blooming of toxic microalgae such as of Dinoflagellates. To do
so, a retrospective study of IMAC into Diego Suarez Bay and
the northern-east of Antsiranana (Diego II or Antsiranana II)
were carried out in order to find out how the indicators of
period and risk zone of IMAC would work. Thus, the present
study has mainly focused on the monitoring of phytoplankton
in Diego Suarez Bay and four parameters including chlorophyll
a, sea surface temperature, wind speed and rainfall in this Bay
and in northeastern Madagascar.
2 METHODOLOGY
2.1 Study areas
Two areas were covered in our study, including Diego Suarez
Bay and the northeastern coast of Madagascar passing
through the Diego Suarez Bay Pass to the Loky River. Those
sites were chosen because of the 2017 and 2018 IMAC
presence in these areas. Diego Suarez Bay consists of four
small bays, including French Bay, Cul de Sac Gallois, Cailloux
Blancs Bay and Tonnerre Bay (see Figure 1).
_______________________________
Landy Soambola Amelie is currently pursuing HDR
degree program in marines sciences in University of
Antsiranana, Madagascar,
E-mail: landyamelie@gmail.com
Bemiasa John is currently pursuing HDR degree degree
program in marines sciences in University of Toliara,
Madagascar. E-mail: j.bemiasa@odinafrica.net
RASOAMANENDRIKA Agrippine Faravavy is currently
pursuing HDR degree program in marines sciences in
University of Antsiranana, Madagascar, E-mail:
faraagrippine@yahoo.fr
MAHAZATSAKILA Volatiana Anissa, RAKOTOJAONASY
Fenosoa Edwina, ZIA Florence are currently pursuing
master’s degree program in marines sciences in
University of Antsiranana, Antsiranana, Madagascar.
E-mail: anistiana.22@gmail.com;
fenosoaedwina@gmail.com; florenceziah@gmail.com
MARA Edouard Remanevy is currently Professor in
Marines Sciences in University of Toliara, Madagascar.
E-mail: maraedouard@yahoo.fr
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Figure 1: Map of Diego Suarez Bay and Antsiranana II coastal
2.2 Methods
A bibliographic study covered the whole period of the
research. The presence of IMAC depends on the algal bloom
(biological factor), which is in turn set and affected by many
parameters, such as physical and chemical factors. The most
important physical factors are source of energy, usually light
and temperature. The chemical factors, whereas, are the
available concentration of carbon dioxide and a contribution of
macronutrient and trace elements [3] and also in mixture and
the concentration of oxygen. For biological parameter view
point, phytoplankton monitoring was firstly used in the four
bays of Diego Suarez during dry and hot season of 2016
(September) and 2017 (March). The fieldwork follows the
method described by Aminot and Kerouel [4]. They focused on
sample collection at the sea surface with plankton net and pills
and, also an observation of 5% formalin-fixed samples in the
Antsiranana Poly Aquaculture Laboratory under an Olympus
OXION microscope. Thus, the cells were identified and
counted. Secondly, chlorophyll a (chl-a), a synthetic product of
phytoplankton cells, was monitored from July 2017 to
February 2018 via data from MODIS Aqua satellite imagery via
EUMETSAT from National oceanographic Data Center
(NODC) of the IH.SM (Institute of Halieutic and Marines
Sciences) of the University of Toliara. These data were
received every five minutes at spatial resolutions of the order
of 1 Km and 4 Km and noted down in the form of rates and
images on the color of the water for chl-a. Sea Surface
Temperature (SST) data were collected at the same time as
chlorophyll-a level via NODC satellite image data in both value
and histogram form whose applied method follows that
described by Bloomfield [5]. As for the parameters influencing
the growth of microalgae or even Dinoflagellates and Diatoms,
we collected information on temperatures, rainfall, water flow
and wind speed. Rainfall data were collected from the
Antsiranana Meteorological Service from 2016 to 2018.
Chlorophyll-a concentration and temperature were
respectively chosen as variables of the study because they
play an important role in the growth of microalgae and reflect
proportionally the presence of phytoplankton whose
Dinoflagellates are integrated parts [6]. Mixed with the
meteorological data, altogether allow the researchers to
predict the favorable conditions for the formation of Harmful
algal blooms (HAB). In addition, rainfall can tell us about the
intake of macronutrients and trace elements in the marine
environment. In turn, the wind speed can give us the relative
information in oxygen concentration in the sea water and on
the possibility of the existence of upwelling. Epidemiological
surveys of Antsiranana hospitals have enabled us to collect
data on the numbers, places of origin of IMAC victims and the
number of intoxicated and dead people.
2.3 Limit of the study
Chl-a, SST, rainfall and wind speeds can’t accurately identify
the presence of toxic microalgae which are responsible for
IMAC: they are only indicators of the possible presence of
these microorganisms. Dissolved oxygen and pH as well are
also factors that may come into with this IMAC phenomenon
3 RESULTS
3.1 Variation of physicochemical parameters
3.1.1 Sea Surface Temperature (SST)
3.1.1.1 In Diego Suarez Bay
The evolution analysis of the sea surface temperature (SST)
shows that, respectively, the temperature varies from 23.82 °C
to 26.52 °C and from 25.36 °C to 29.66 °C respectively during
cold and hot season of 2017 (see Figure 2). In hot season of
2018, it ranges from 26.15 °C to 30.31 °C with an average of
27.53 °C. In all, the average SST is, respectively, 24.43 ° C
and 27.28 ° C during hot and cold season of 2017.
Between 04th July and 09th October 2017 in Diego Suarez Bay,
the temperature of the sea surface is below 25 °C (see Figure
3). After 28 days, from 10th October to 11th November, 2017,
the temperature has gradually been added by 1 °C to continue
to increase by 1 °C more until 11th December 2017. In all,
there was a temperature gradient of 2 °C about two months. In
the following, the temperature of the surface of the sea water
shows a daily variation without falling below 26 ° C.
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The Anova test suggests that the average sea temperatures from
04th July to 07th October 2017 (24, 14 °C), 10th October to 09th
November 2017 (25, 6 °C) and 15th November to 11th December,
2017 (27, 41 °C), significantly differ from one another. This
indicates that surface water is heating up from early October. The
wet season is in full swing from mid-November 2017.
3.1.1.2 In the north-east of Madagascar: Antsiranana II
During cold season, the SST has an average of 26, 14 ° C and
varies from 24, 84 °C to 27, 15 °C (see Figure 4). In hot season,
however, it ranges from 24, 21 °C to 29, 94 °C with an average of
28, 09 °C.
The analysis of the daily SST shows that it oscillates around
26 °C from 04th July 2017 to 11th October 2017, or even almost
during cold period of the year. It reaches 27 °C; another
gradient 18 days later at 29th October 2017 (see Figure 5).
After 20 days, from 30th October to 19th November 2017, the
SST progressively climbed 1 °C more, or 28 °C. 10 days
during 20th to 29th November 2017, the SST shows a rise of a
gradient of more than 29 °C. After that, an irregularity of
oscillation is met on the northeast coast of Madagascar to
continue the increase of SST until 30 °C around 23th February
2018.
According to the Anova test, the temperature from 04th July 2017
to 15th October 2017 differs significantly from that of 16th October
2017 to 29th November 2017. The analysis of the monthly
maximum SST mean variation curve shows that it is slightly
higher in northeastern Madagascar than in Diego Bay during the
dry season. This is not the case during the warm season during
which the shape of the curve is superimposed and indicates the
same average maximum SST (see Figure 6).
3.1.2 Pluviometry
The rhythm of the monthly variation in rainfall varies from one
year to another. In 2016, too much rain occurred in January has
gradually decreased until April. The resumption of increased
rainfall has not occurred until the beginning of the following year,
from January to April, but with less rain. Also during 2017, heavy
rain was observed by the end of the year, from November to
December, and then continues until April of the following year.
The three best rainfall records encountered during the study
period were found in January 2018 (around 667mm) and 2016
(around 420mm) followed by December 2017 (around 234 mm)
(see Figure 7).
3.1.3 Wind
The wind parameter, with high speed at 8 km/h, plays a role in
the upwelling of the bottom to the surface making a large
amount of nutrient available. The case of Antsiranana, the
average wind speed varies from 11 to 25 km/h during hot
season and from 19 to 29 km/h during cold season. Both 2017
and 2018 were significantly windier than 2016 (see Figure 8).
The strong continuous wind encountered in the Diego Suarez
Bay explains the existence of brewing in this place especially
in dry season. Figure 8 also shows a fluctuation of the wind
speed, which looks similar to the other years.
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3.2 Planktonic
Phytoplankton consists of all the microorganisms plant existing
in the sea. The bloom for the concentrations is assumed to be
higher than one million cells per liter.
3.2.1 Taxonomic richness
The result of the plankton study shows that 88% of the planktonic
individuals harvested in Diego Suarez Bay are phytoplankton.
The zooplankton found in the Diego Suarez Bay is divided into 5
branches including Protozoa, Cnidarians, Mollusca, Worms and
Crustaceans. 83.1% of inventoried phytoplankton cells are
Diatoms of 40 genera. The latter are mainly represented by
pinnate diatoms (70%). Thus, 12 genera of centric diatoms such
as g Biddulphia, g Chaetoceros, g Coscinodiscus, g Cymbella, g
Dactyliosolen, g Guinardia, g Lauderia, g Odontella, g
Rhizosolenia, g Skeletonema, g Thalassiosira, g Melosira and 28
genera of pinnate diatoms (g Actinella, g Amphipleura, g
Amphiprora, g Amphora, g Asterionella, g Climacosphenia, g
Cocconeis, g Denticula, g Diploneis, g Encyonema, g Fallacia, g
Gomphosphenia, g Fragilaria, g Gyrosigma, g Halamphora, g
Leptocylindrus, g Licmophora, g Navicula, g Nitzschia, g Nupela,
g Pinnularia, g Placoneis, g Pleurosigma, g Pseudo-Nitzschia, g
Seminavis, g Tabellaria, g Tabularia and g Thallassionema) are
inventoried. 4.5% of inventoried plankton cells were
Dinoflagellates. 09 genera of Dinoflagellates divided into 6
families (including Calciodinellaceae, Dinophysiaceae,
Gonyaulacacea, Gymnodiniaceae, Prorocentraceae,
Protoperidiniaceae) were recorded throughout the Diego Suarez
Bay during our study. 03 genera (g Prorocentrum, g
Protoperidinium (see Plate 1), g Scippsiella) are encountered
during cold season in Cailloux Blancs Bay (20%) and especially
in the French Bay (80%); While, 07 genera were recorded during
the warm season including g Dinophysis, g Gonyaulax, g
Gymnodium (see Plate 2), g Lingulodium, g Ostreopsis, g
Preperidium (see Plate 3), g Prorocentrum in the French Bay,
Tonnerre Bay and Cul de Sac Gallois.
3.2.2 Density
As a result, the average density of plankton varies around 39 583
cells per milliliter. The best density is found in Tonnerre Bay.
Zooplanktons have got a density varying around 3400
zooplankton/ml. For phytoplanktons, the density is slightly high
during the wet season (261 000 cells / ml) than the dry season (214
000 cells / ml). The density of Dinoflagellates varies from 0 to
12,000 per ml. On average, there are 5250 and 1500
dinoflagellates per ml respectively during hot and cold season in
Diego Suarez Bay. It can be argued that the concentration of
dinoflagellates reaches efflorescence during cold and hot season
because the observed concentration seems to have exceeded the
trigger threshold of their efflorescence. It might be stated that the
absence of IMAC cases in 2016 (in the second half) and 2017 (in
the first half) simply means that there are other factors besides
efflorescence of Dinoflagellates that can explain the incident in 7th
December 2017. The best density of Dinoflagellates (i.e., 12 000
cells / ml) was observed during the hot season of the year. The
French Bay has shown a moderate high density in Dinoflagellates
for two seasons of the year (8000 and 4000 Dinoflagellates per ml
respectively during hot and cold season). The lowest density (1000
cells per ml) in Dinoflagellates was found in Cailloux Blancs Bay.
No Dinoflagellates were recorded during cold season in Tonnerre
Bay and Cailloux Blancs Bay.
3.2.3 Synthetic products: Chlorophyll a
The efflorescence of ch-a presents the massive proliferation of
phytoplankton which ,in turn, sets the evolution in the same
direction of the toxic microalgae, Dinoflagellates, which is
responsible for IMAC. This is related to the enrichment of water in
nutrients. The analysis of chl-a rate is reported in Diego Suarez Bay
and northern-east Madagascar from July 2017 to February 2018.
3.2.3.1. Within Diego Suarez Bay
The rate of chlorophyll a in Diego Suarez Bay is generally high,
fluctuating around 2.03mg/m3 during the study period (see Figure
9).
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The analysis of the daily progress of the chlorophyll concentration
curves shows a fluctuation of growth of microalgae or even the rate
of chl-a whose pace differs from one season to another. It can be
seen that the growth of microalgae or even the rate of chl-a occurs
throughout the year. The graph of microalgae is short duration in
cold season varying from 4 to 17 days (see Figure 10) and long
duration in hot season varying from one week (07 days) to 63 days
(two months and three days) (see Figure 11).
Additionally, the lag phase is shorter duration (varying from 1 to 5
days) during dry season explaining the importance in number of
discontinuous growth cycle of microalgae found in there. The long
period of lag phase in hot season can be explained by the
adaptation of algae to new environmental conditions. The
correlation appears to be very weak after the linkage analysis
between fluctuating seawater temperature and chl-a rate. In dry
season, the maximum rate of chl-a was 5,57mg / m3 on 19th
August 2017. During hot season, the best concentration of chl-a
was 6,11 mg/m3 for 2017 and 6.48 mg/m3 for 2018.
The chl-a growth curve consists of four phases, including the
latency phase, the exponential phase, the stationary phase
and the decay phase. The lag phase corresponds to the period
of adaptation of the phytoplankton cells to another condition of
the medium. It was observed at the beginning of hot season
(early November 2017) which was showed by the beginning of
nutrient enrichment in Diego Suarez Bay. It's the shift-up
change. During the exponential phase, phytoplankton cells
divide themselves and increase in number. Then comes the
stationary phase where a balance between division and cell
death occurs. The latter comes at an exponential rate during
the decay phase. Throughout the year, the western part (in
Antsahazo Cove and Cul de Sac Gallois) and south-east
(Andovobazaha Bay along the coast to Ramena to Amoronjia-
Orangea Point) of the interior of Diego Suarez Bay experience
higher enrichments in Chl-a. This result is symmetrical with
respect to degrading reef health in these parts of Diego
Suarez Bay [7].
The average of chlorophyll a rate is around 0.79 mg/m3 during
cold season and 0.52 mg/m3 and 1.03 mg/m3 respectively during
hot season of 2017 and 2018. Maximum chlorophyll analysis
shows that the Ch-a rate varies around 01 mg/m3 from July to
December 2017 and continue with an increase curve of the rate
of a gradient per month until 3.6 mg/m3 maximum in February
2018 (see Figure 12).
3.3. Intoxication by Marine Animals Consumption
3.3.1. Historical
The existence of IMAC in Madagascar has longer been existed
and confirmed by the work as in [8] and [9]. The first work
focused on a retrospective study of 28 cases of children
ichthyosarcotoxism in Tuléar in 1989-1993 [10]. In 1965, a
collective intoxication affecting the people of Antalaha District after
consuming sea turtle Eretmochelys imbricata, whose 60 out of
120 consumers were poisoned and 5 died [11]. From 2010 to
2018, six episodes of IMAC were recorded in Antsiranana and in
the surrounding areas. They are summarized in the table below.
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108 cases were hospitalized, with a male predominance (54%)
with a sex ration 1, 16. The age group most affected age
group was 18 to 41 years (50%). Compared to the IMAC
phenomenon that hit Antsiranana in the past 08 years, the
ones of 2017 and 2018 are the most serious and lethal (with
fatality rate 14%). Regarding the average lethality rate, 9%
and 35% were respectively noted after consuming Clupeidae,
poisoned tunas and sea turtle. Clinical signs are dominated by
general signs, neurologic and gastrointestinal. Regarding
December 2017 incident, almost all the surrounding cities of
Antsiranana were affected. On 24 neighborhoods in
Antsiranana I, IMAC's victims were found among 15 of them.
People who died as a result of sardinella consumption were
adults (over 42 years old) and 6-year old children. No deaths
related to IMAC were recorded for consumption of tunas in
April 2018.
3.3.2. Events
The agents responsible for collective intoxication by consumption
of marine animals are usually microalgae or phytoplankton. Some
of them, especially Dinoflagellates, have the capacity to produce
toxins called "phycotoxins" [12]. Stated by Olivier and al. [13],
among the 3,400 to 4,000 species of phytoplankton, about 70
species, mostly dinoflagellates, have the ability to emit potentially
toxic substances that can affect humans through the fish or
shellfish he consumes. Assimilated by animals, the toxins take a
different name depending on the host Dinoflagellates. During the
wet season of 2017, three types of biotoxins at least, seemed to
be involved in the IMAC observed in Antsiranana, including
clupeotoxin which is a poisoning by consumption of Sardinella,
case of food poisoning of 7th December 2017, chelonitoxism
which is an intoxication derived from the consumption of turtles,
case of IMAC of January 2018; scombrotoxism that is caused by
ingestion of tuna, bonito, mackerel degraded by bacteria, case of
IMAC in April 2018 (see Table1). Despite the prohibition on
sardine fishing and consuming in Madagascar every year from 1
November to 1 March, people still do not respect it [14].
3.3.3. Transfer mechanism
With the wealth of nutrients available in the receiving environment
accompanied by favorable conditions, Dinoflagellates grow and
multiply. According to Nomenisoa [6], the conditions of the
proliferation of toxic microalgae responsible for IMAC were found
from thresholds of SST>= 30°C and chlorophyll a>= 1mg/m³. At
the base of the food chain, Dinoflagellates, which are found in
abundance in the water and in the superficial part of algae, will be
assimilated by planktivorous animals, herbivores (fish) and filter
feeders (shells). In water, Dinoflagellates directly release
phycotoxins that accumulate through the different stages of the
food chain [15]. In turn, these planktivores, herbivores and filter
feeders will be eaten by the largest carnivores. Thus, from
predators to predators, the toxin is transferred to the last link.
Toxins are present in the skin, flesh and viscera of fish [16]. The
toxicity of marine animals is generally related to the level those
aimals occupy in the food chain. Thus, large carnivorous
predators are frequently more toxic because they are consumers
of planktivorous fish, herbivores and filter feeders, carrying toxins.
Humans get intoxicated by taking and consuming these marine
animals regardless of their levels in the trophic chain [13]. The
diet of Sardinelles is based on plankton, especially zooplankton
[16].Turtles can be plankton-eating or herbivores or carnivores or
even spongivores depending on the species. Tunas are
carnivores [17].
4. DISCUSSION AND CONCLUSION
The evolution of the sea surface temperature (SST), shows a
similar trend to Chl-a, that is to say, when the sea surface
temperature increases, phytoplankton proliferation increases as
well. For the Sardinelles study, chl-a concentration acted as good
indicator of the availability of their food [18].The variation of chl-a
shows that Diego Suarez Bay constitutes the basin of proliferation
of the phytoplankton cells throughout the year with a short cycle
of life during dry season which is relatively long during hot
season. This explains the discontinuous and continuous renewal
of nutrients available in the Diego Suarez Bay during hot and dry
season of the year. During dry season, despite the existence of
succession of several growth curves of chl-a with the
achievement of a slight high peak, the absence of stationary
phase does not allow to ensure the good development of the
zooplankton which are the main foods of Sardinella. That point
was different on hot season because the chl-a growth curve
obtained is composed of the following parameters: the growth
phase, the peak, the stationary phase and the decay phase and a
long lag phase (see Figure 10 and 11). If the environmental
conditions required by the chl-a are met, a growth phase can be
recovered at the stationary phase without following a latency
phase immediately (see Figure 11, the fact of the 27th December
2017 to 28th January, 2018). This is the ongoing development of a
significant concentration of phytoplanktonic algae. Obtaining
succession of the complete phase of the biological cycle of
phytoplankton, cells ensure the development, viability and
availability of the zooplankton that feed on them at the second
stage of the food chain. The environmental conditions bring on
the best continuous development of chl-a including an abundance
of rain, an increase of the temperature, a decrease of the wind
velocity or even of the marine current and a nutrient supply by the
terrigenous inputs via the runoff of 23 rivers, in which four of them
flow permanently into Diego Suarez Bay. During this period, the
fish arrive in the rich coastal zone and increase their metabolic
activity. Also, on hot season, from the beginning of the month until
16th November 2017, the chl-a rate is around 0.77 mg/m3. Growth
phase is showed from 18th November, 2017. The stationary
phase goes on until 22nd November 2017 and then, chl a rate falls
to 0.65 mg/m3 on 23rd November 2017. The lag phase continues
until 13rd December, with at a rate of chl-a around 0.9 mg/m3. This
second phase of latency leads to a summer recovery of the
metabolic activity of fish. According Befeno’s study [19] on the
plankton-eating, herbivorous and carnivorous fish in Diego
Suarez Bay, the emptiness of the stomach explaining the low
metabolic activity of fish is mainly encountered during the dry
season. This justifies the presence of intensity of metabolic
activity and the high consumption of fish food in the Diego Suarez
Bay in summer as well as in winter. Thus, for the IMAC incident of
7th December 2017, it can be argued that the Bay has already
experienced continuous enrichment (Chl-a rate is 2.23mg/m3) in
phytoplankton cells since 18th November; 20 days ago. The wet
season is well acquired at this time. The environmental
parameters encountered such as increase of temperature of the
seawater (around 27.12 °C), rain (monthly 70 mm and daily
record of 32 mm), wind speed decrease (around 21 km / h) have
all contributed to the installation of favorable conditions for the
development of toxic microalgae. The wellbeing of the latter
lasted at least five days throughout the Bay. This allowed the
zooplankton to take over, which explains the increase of the
metabolic activity of planktivorous fish such as Sardinella.
Subsequently, the rate of chl-a seems to have resumed growth
only in 13th December, 2018, after the start of the IMAC incident.
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Analysis of each of the four bays shows that three days before
and after and,also during the IMAC incident, the blooming of
phytoplankton cells in Cul de Sac Gallois, French Bay and in the
Cailloux Blancs could reach the value of the highest chl-a rate
(around 10mg/m3, see Plate 4) leading High Risk of IMAC in the
Bay which lasted until February 2018, where our available data is
limited.
Algal bloom in the three bays appears to be related to the
degradation of the coral formation that is encountered there [7].
This confirms the proliferation of seagrass beds after the coral
formation, that supports these algal cells, disappeared. In the
case of Antsiranana II, the concentration of chlorophyll remains
below 1 mg / m3 during cold season and almost during the
beginning of hot season of 2017, despite the increase in the
progressive water temperature collected since the beginning of
November 2017. The algal bloom is encountered 11 days earlier
(12nd January 2018), before Diego II's IMAC incident on 22nd
January 2018, a late period compared to the one in Diego Suarez
Bay (Diego I or Antsiranana I). This situation can be explained by
the fact that the Bay is a semi-closed sea giving importance to
terrigenous influences, but the one in Diego II is due to the open
sea to the Indian Ocean reflecting the strong influence of
globalized change. The environmental conditions during algal
bloom lead the sea surface water temperature to an interval
between 28 and 29 °C and the passage of 02 tropical cyclones
including AVA (5th, 6th, and 7th january 2018) and Berguitta (18th
january 2018) [20]. The latter appears to be related to nutrient
input into coastal areas. Beyond the IMAC incidence period,
chlorophyll concentration remains high until February 04th, 2018.
These results indicate that the semi-closed zone is more sensitive
to algal bloom than the open zone. In conclusion, the
intervention of environmental parameters on the incident of
IMAC acts indirectly due to different factors from hot season,
cold or dry as well in the study area. One can expect, in turn,
only with hot season, a direct influence of the physicochemical
parameters (increase of the temperature of the sea surface,
increase of rainfall, and decrease of wind speed) on the
availability of nutrient which determines the algal bloom and
metabolic activity of predatory marine animals. However, it is
noticed that these environmental elements are not the only
factors explaining the IMAC incident. There is also the
morphological unit of the zone which influences the presumed
period favorable to the presence of the IMAC. With a semi-
enclosed area where terrigenous inputs are continuously
recorded and environmental conditions such as temperature
and rainfall increase; 20 days after harmful algal bloom can be
expected to directly contribute to the IMAC incident. In the
open sea, like the case of Antsiranana II, in the northern-east
of Madagascar, where hydrology depends on the neighboring
Indian Ocean, the variation in environmental parameters is
slower or even delayed. The availability of nutrients can be
done via upwelling due to the passage of tropical depression.
The IMAC event can be expected 11 days after algal bloom.
During hot season, the condition favorable to the
establishment of HAB are gathered rather in the Diego Suarez
Bay but staggered 20 days before the episode of IMAC. Unlike
Antsiranana II, they are gathered later but shifted 11 days
before the presence of IMAC. The IMAC may possibly occur
10 days after the harmful algal bloom. During the study, 09
genera of Dinoflagellates were found in Diego Suarez Bay.
However, it should be noted that the concentration of
chlorophyll a is not the only factor responsible to the
phenomenon even if it is an excellent tracer of potential toxic
water. Consequently, further studies should be considered. As
a recommendation, many data and methods can be integrated
one another to better identify this problem of toxic and / or
harmful microalgae proliferation and improve routine
monitoring and forecasting. Among the possible programs, the
use of near real time satellite data is also needed instead of
focusing on retrospective studies to ensure routine monitoring.
The control of fishing areas or marine products is essential
and oriented according to the main objectives, (Observation,
new zones, new species). In addition, a toxicity study of the
samples of the animals in question would also be necessary.
To mitigate the risks caused by the consumption of marine
products, implementation of observation strategy of these toxic
and / or harmful cells, as well as its culture to identify their
toxin must be integrated.
ACKNOWLEDGMENT
The authors wish to thank A, B, C. This work was supported in
part by a grant from XYZ.
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