Environ Monit Assess
(2021) 193:333
1 3
333
Page 8 of 12
positive correlation between peak and high salinity
(38.3 PSU) was found in agreement with Carnicer
et al. (2016), and Abdennadher et al. (2017) showed
that O. cf. ovata had optimal growth at salinity ranging between 35 and 45 PSU. Therefore, salinity is
secondary to temperature in regulating the bloom of
harmful algae (Tester et al., 2020).
In the fish farm, DIN was positively associated
with Ostreopsis sp., and according to van de Poll et al
(2015), nitrogen sources (nitrate, nitrite, and ammonia) might influence phytoplankton abundance. The
low nutrient concentrations recorded in the input water
can be explained by the stratification of the Mediterranean seawater in summer and autumn (Mercado et al.,
2019). Conversely, no relationship was found between
cell abundance and phosphorus. Nevertheless, PO 4 was
the most necessary element for phytoplankton growth
in the mariculture area (Zhaohui et al., 2009). Based
on the present findings, Ostreopsis sp. appears to have
adaptations that allow it to thrive in restricted phosphorus environments where organic phosphorus is the
main source following Ellwood et al. (2020), suggesting
that uneaten feed and fish excreta accumulated in the
mariculture effluents were the likely source of organic
phosphorus. Due to the fact that aquaculture effluents
were rich in nutrients (Qiao et al., 2020), the values
of orthophosphates were much higher compared with
phosphorus in Algerian coastal 0.031 ± 0.012 μmol/L
(Boudjenah, 2019), whereas renewable water or flow
was the main driver of nutrient concentrations (Muñiz
et al, 2019). Furthermore, the genus can bloom in oligotrophic waters (Mediterranean Sea): Vaillancourt
et al. (2018) and Ben Gharbia et al. (2019) reported that
orthophosphates and dissolved inorganic nitrogen were
all weak predictors of phytoplankton blooms. However,
they significantly affect the physiological response of
Ostreopsis sp. (Vidyarathna & Granéli, 2013).
BOD was negatively correlated with Ostreopsis sp.
abundance. Such BOD represents the amount of oxygen
consumed by bacteria and other microorganisms while
they decompose organic matter under aerobic, which
means that there is a competition between cell proliferation and other microorganisms (microalgae community,
parasites…). Moreover, in the fish ponds, Ostreopsis sp.
was not observed during the entire monitoring period,
perhaps due to the competition with other microorganisms that occupied the same ecological niche. Pavaux
(2019) showed that O. cf. ovata inhibits the growth of
competitor diatoms, while the later in return inhibit its
photosynthetic efficiency and growth. Likewise, the
regulation of dinoflagellate by parasites (Pereira et al.,
2011; Zhou et al., 2020) could be the biotic factors regulating Ostreopsis sp. abundance.
Ostreopsis is known to cause airborne disease and
palytoxin-like compound contents were higher during the exponential and stationary growth phases (see
references in, e.g. Zingone et al., 2020; Gémin et al.,
2020), which are related to health disorders (respiratory symptoms and skin irritation) (Vila et al., 2016).
It is necessary to report that no episode of fish death
or outbreak on the farm was observed. Although the
concentration of Ostreopsis cells (6340 cell L
−1
)
recorded in the fish farm does not exceed the alarm
threshold (30,000 cell L
−1
) (Funari et al., 2015;
Vassalli et al., 2018), this concentration is lethal to
some invertebrates (Pavaux et al., 2019). Nevertheless, the monitoring strategies for Ostreopsis bloom in
coastal waters affect cell abundance as the distribution
of cells during blooms is highly complex and variable
(Jauzein et al., 2018). At last, for the safety of consumers, it is recommended that an adult should not ingest
more than 30 µg PLTX kg
−1
in shellfish meat (Pelin
et al., 2018).
Conclusion and recommendation
This study reports the proliferation of Ostreopsis sp.
in the Mediterranean fish farm, rearing Sparus aurata
in a raceway. It should be noted that no threat to fish
health has been observed and that temperature, salinity, and dissolved inorganic nitrogen were the environmental variables influencing the dynamics of the
genus Ostreopsis in the Mediterranean fish farm.
The prediction of harmful algal blooms is a challenge for decision-makers and represents an important economic value. As a result, we recommended
the installation of an efficient upstream filtration
system and the application of stop-feeding therapy
to reduce the sensitivity of fish exposed to harmful
algal blooms. However, the transition towards environmentally friendly practices to remedy fish farm
effluents is necessary. In the end, our results suggest
that mariculture effluents may enhance the proliferation of Ostreopsis sp. and highlight the importance of
monitoring the presence of this harmful dinoflagellate. We also recommended further research on causal
link between this dinoflagellate and human health as
(2021) 193:333
1 3
333
Page 8 of 12
positive correlation between peak and high salinity
(38.3 PSU) was found in agreement with Carnicer
et al. (2016), and Abdennadher et al. (2017) showed
that O. cf. ovata had optimal growth at salinity ranging between 35 and 45 PSU. Therefore, salinity is
secondary to temperature in regulating the bloom of
harmful algae (Tester et al., 2020).
In the fish farm, DIN was positively associated
with Ostreopsis sp., and according to van de Poll et al
(2015), nitrogen sources (nitrate, nitrite, and ammonia) might influence phytoplankton abundance. The
low nutrient concentrations recorded in the input water
can be explained by the stratification of the Mediterranean seawater in summer and autumn (Mercado et al.,
2019). Conversely, no relationship was found between
cell abundance and phosphorus. Nevertheless, PO 4 was
the most necessary element for phytoplankton growth
in the mariculture area (Zhaohui et al., 2009). Based
on the present findings, Ostreopsis sp. appears to have
adaptations that allow it to thrive in restricted phosphorus environments where organic phosphorus is the
main source following Ellwood et al. (2020), suggesting
that uneaten feed and fish excreta accumulated in the
mariculture effluents were the likely source of organic
phosphorus. Due to the fact that aquaculture effluents
were rich in nutrients (Qiao et al., 2020), the values
of orthophosphates were much higher compared with
phosphorus in Algerian coastal 0.031 ± 0.012 μmol/L
(Boudjenah, 2019), whereas renewable water or flow
was the main driver of nutrient concentrations (Muñiz
et al, 2019). Furthermore, the genus can bloom in oligotrophic waters (Mediterranean Sea): Vaillancourt
et al. (2018) and Ben Gharbia et al. (2019) reported that
orthophosphates and dissolved inorganic nitrogen were
all weak predictors of phytoplankton blooms. However,
they significantly affect the physiological response of
Ostreopsis sp. (Vidyarathna & Granéli, 2013).
BOD was negatively correlated with Ostreopsis sp.
abundance. Such BOD represents the amount of oxygen
consumed by bacteria and other microorganisms while
they decompose organic matter under aerobic, which
means that there is a competition between cell proliferation and other microorganisms (microalgae community,
parasites…). Moreover, in the fish ponds, Ostreopsis sp.
was not observed during the entire monitoring period,
perhaps due to the competition with other microorganisms that occupied the same ecological niche. Pavaux
(2019) showed that O. cf. ovata inhibits the growth of
competitor diatoms, while the later in return inhibit its
photosynthetic efficiency and growth. Likewise, the
regulation of dinoflagellate by parasites (Pereira et al.,
2011; Zhou et al., 2020) could be the biotic factors regulating Ostreopsis sp. abundance.
Ostreopsis is known to cause airborne disease and
palytoxin-like compound contents were higher during the exponential and stationary growth phases (see
references in, e.g. Zingone et al., 2020; Gémin et al.,
2020), which are related to health disorders (respiratory symptoms and skin irritation) (Vila et al., 2016).
It is necessary to report that no episode of fish death
or outbreak on the farm was observed. Although the
concentration of Ostreopsis cells (6340 cell L
−1
)
recorded in the fish farm does not exceed the alarm
threshold (30,000 cell L
−1
) (Funari et al., 2015;
Vassalli et al., 2018), this concentration is lethal to
some invertebrates (Pavaux et al., 2019). Nevertheless, the monitoring strategies for Ostreopsis bloom in
coastal waters affect cell abundance as the distribution
of cells during blooms is highly complex and variable
(Jauzein et al., 2018). At last, for the safety of consumers, it is recommended that an adult should not ingest
more than 30 µg PLTX kg
−1
in shellfish meat (Pelin
et al., 2018).
Conclusion and recommendation
This study reports the proliferation of Ostreopsis sp.
in the Mediterranean fish farm, rearing Sparus aurata
in a raceway. It should be noted that no threat to fish
health has been observed and that temperature, salinity, and dissolved inorganic nitrogen were the environmental variables influencing the dynamics of the
genus Ostreopsis in the Mediterranean fish farm.
The prediction of harmful algal blooms is a challenge for decision-makers and represents an important economic value. As a result, we recommended
the installation of an efficient upstream filtration
system and the application of stop-feeding therapy
to reduce the sensitivity of fish exposed to harmful
algal blooms. However, the transition towards environmentally friendly practices to remedy fish farm
effluents is necessary. In the end, our results suggest
that mariculture effluents may enhance the proliferation of Ostreopsis sp. and highlight the importance of
monitoring the presence of this harmful dinoflagellate. We also recommended further research on causal
link between this dinoflagellate and human health as