This study assessed the impact of N. scintillans HABs and evaluated the biodiversity losses from the ten stations at the Gulf of Mannar (GoM), the Southeast coast of India. The results of surface water temperature (SST) (Fig. 2), Chlorophyll, and wind velocity of the study showed that chlorophyll a' (17.5mg/m− 3 in 2021) (Fig. 3) and temperature (29.22C°) values were high during the N. scintillans bloom whereas the variation of wind velocity (7.79 m/sec) was low (Fig. 4).
N. scintillans were found in water temperatures of 14.2–24.2°C, and salinities of 28.0–36.5 (Table 1). The temperature increased gradually at Station 1 from an initial 16.2°C in August to a maximum of 22.5°C in February, while salinity fluctuated between 34.6 and 36.5. At Station 4, both temperature and salinity showed greater variation, fluctuating between 14.2 and 24.2°C, and between 28.0 and 36.0, respectively. The chlorophyll concentration in the surface waters at the Port Hacking offshore station, measured within 2 days of the sampling for Noctiluca, was highest in September when concentrations reached 2.9 µg L− 1 (Table 1). Apart from this, and small increases in December and June, concentrations remained low (< 1 µg L− 1) throughout the study period.
Table 1
List of marine invertebrates and vertebrates found during the bloom event.
S. No
|
Species list
|
S1
|
S2
|
S3
|
S4
|
S5
|
S6
|
S7
|
S8
|
S9
|
S10
|
1
|
Abudefduf septemfasciatus
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
2
|
Amphiprion sebae
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
3
|
Amphiprion clarkii
|
-
|
+
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
4
|
Ambassis nalua
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
5
|
Arothron caeruleopunctatus
|
-
|
+
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
6
|
Arothron hispidus
|
-
|
+
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
7
|
Chaetodon collare
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
-
|
8
|
Dascyllus reticulatus
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
9
|
Dascyllus trimaculatus
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
10
|
Decapterus russelli
|
-
|
+
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
-
|
11
|
Diodon holocanthus
|
+
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
+
|
12
|
Diodon hystrix
|
+
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
13
|
Epinephelus chlorostigma
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
+
|
14
|
Epinephelus diacanthus
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
15
|
Epinephelus coioides
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
+
|
+
|
16
|
Gazza achlamys
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
17
|
Gymnothorax favagineus
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
18
|
Gymnothorax flavimarginatus
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
19
|
Gymnothorax meleagris
|
+
|
+
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
20
|
Gymnothorax monostigma
|
+
|
+
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
21
|
Gymnothorax pictus
|
-
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
22
|
Leptoscarus vaigiensis
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
23
|
Platax orbicularis
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
24
|
Plectorhinchus schotaf
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
25
|
Pomacanthus semicirculatus
|
-
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
26
|
Pomadasys argyreus
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
27
|
Sargocentron rubrum
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
-
|
28
|
Scarus rubroviolaceus
|
+
|
+
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
29
|
Scarus russelii
|
+
|
+
|
+
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
30
|
Siganus canaliculatus
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
31
|
Siganus javus
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
32
|
Siganus vermiculatus
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
+
|
33
|
Teraporn jarbua
|
-
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
+
|
+
|
34
|
T. puta
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
Crustaceans
|
35
|
Atergatis integerrimus
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
36
|
Charybdis natator
|
-
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
37
|
Neocallichirus sp.
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
38
|
Scylla serrata
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
39
|
Thranita crenata
|
-
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
Cephalopods
|
40
|
Sepia sp.
|
-
|
-
|
-
|
-
|
-
|
+
|
-
|
-
|
-
|
-
|
Sea Anemone
|
41
|
Stichodactyla haddoni
|
-
|
-
|
-
|
-
|
+
|
+
|
-
|
-
|
-
|
-
|
Sea Hourse
|
42
|
Hippocampus kuda
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
43
|
Hippocampus kelloggi
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
-
|
Sea Cucumber
|
44
|
Holothuriya sp
|
-
|
-
|
+
|
+
|
+
|
+
|
+
|
+
|
+
|
-
|
Sea hare
|
45
|
Dolabella sp
|
-
|
-
|
-
|
-
|
+
|
+
|
+
|
-
|
-
|
-
|
Polychaete worms
|
46
|
Arenicola sp
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
-
|
47
|
Eurythoe sp
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
-
|
Molluscs (Bivalve)
|
48
|
Donax cuneatus
|
+
|
-
|
-
|
+
|
+
|
+
|
+
|
-
|
-
|
-
|
In Total of 48 marine vertebrates and invertebrate organisms were identified, of which 34 fish (16 families), 5 crustaceans, 2 polychaetes, single species of bivalve, cephalopod, sea anemone, sea hare, and two endangered animals of the sea horse, sea cucumber were reported from the of HABs areas (Table 1). Compared to all stations, 48 vertebrates and invertebrates were recorded at Kilakarai station, and 8 were recorded from Mundal. The fish mortality was assessed at a total of 7.2 tones, among these the lowest 0.037 tonnes was from Valinokkam and the highest 1.1 tonnes from Keelakarai were recorded.
Fish mortalities were determined by the fish weight percentage, including families such as Muraenidae (44%), Pomacentridae (12%), Serranidae (6%), Siganidae (11%), Scaridae (4%), Tetraodontidae (6%) Terapontidae (0.004%), Haemulidae (1%), Diodontidae (9%), Carangidae (2%), Ambassidae (1%), Leiognathidae (0.002%), Chaetodontidae (0.004%), Ephippidae (0.004%), Pomacanthidae (1%) and Holocentridae (0.003%) (Fig. 5). Whereas the mass mortality weight (0.83 tonnes) recorded in the Pomacentridae family was less than three folds compared to the Muraenidae family. However, the maximum number of fish mortality of Pomacentridae family fish viz damselfish species of Dascyllus reticulatus, D. trimaculatus, and other species Adudefduf septemfasciatus, were 0.83 tonnes, which is equivalent to nearly 9 million fish killed in only 3 days and the minimum number of Leiognathidae (162 kg) family fish viz Gazza achlamys occurred due to N. scintillans HABs. High fish mass mortality was recorded at the Kilakarai and Sethukarai stations (Fig. 6). The results of the analysis of variance (ANOVA) showed that there were significant variations (P > 0.5; F > 000) among the total weights estimated between the stations, indicating the severe impact of N. scintillans HABs.
The results from this study revealed mass mortality by 34 fishes at all ten stations. It was divided into commercially important 14 fish species and the remaining 20 fish were non-commercially important (Fig. 7). The maximum commercially important fish were recorded at Kilakarai (4,701 kg) followed by Sethukarai (4,027 kg) and the minimum was recorded at Valinokkam (378 kg) (Fig. 8). In particular, the fish families of Siganidae and Serranidae were affected at all the stations. In the case of non-commercially important fish, the maximum was recorded at Kilakarai (15,986 kg), followed by Sethukarai (12,612 kg), and the minimum was recorded at Mundal (2,125 Kg). The Muraenidae (31,874 kg) fish family was highly affected by N. scintillans HABs. Fishes can suffocate due to the low oxygen level in seawater (Diaz and Rosenberg, 1995). In various parts of the world, the mass mortality of fish has been recorded due to low dissolved oxygen caused by harmful algal blooms. Similarly, the present study also shows that the mass mortality of fishes and invertebrates, particularly damselfish were killed huge number.
The enriched nutrient content (ammonia and phosphate), disposal of ballast water, and short-term hypoxic conditions from the Gulf of Mannar have been suggested as key factors of HABs (Gopakumar et al., 2009; Baliarsingh et al., 2016; Diraviya et al., 2020; Shunmugaraj et al., 2020). Various environmental factors might have contributed to the high cell abundance and persistence of the N. scintillans bloom in the Gulf of Mannar, the Southeast coast of India. Similarly, meteorological factors such as rainfall, wind velocity, and wind direction are also triggering the N. scintillans bloom in coastal waters (Miyaguchi et al., 2006). According to earlier studies, N. scintillans severely impacted the variety of coral reef fishes such as rabbitfish, moray eels, goatfish, parrotfish, damselfish, clownfish, mollusks, and sea snakes from Pudumadam to Periapattinam and Manpdapam group of Islands at Gulf of Mannar region (Gopakumar et al., 2009; Shunmugaraj et al., 2020).
The N. scintillans bloom event washed nearly 14 tons of commercially important fishes at the Gulf of Mannar, the Southeast coast of India (Gopakumar et al., 2009). However quantitative analysis of family-wise mortality rate, and commercially important fish economic value data was not recorded for the Gulf of Mannar region. In the present study, the intense N. scintillans bloom killed an amount of 0.83 tonnes of damselfish, equivalent to approximately 9 million fish in only 3 days (Fig. 9), which is now considered the large mass mortality of damselfish ever caused by an N. scintillans bloom. In addition, N. scintillans bloom killed an amount of 1.67 tonnes of commercially important fish which is equivalent to US$ 11.5 M. The earlier study reported that N. scintillans bloom caused losses of nearly 100 M of shrimp Penaeus orientalis, which is valued at US$ 1M (Chen and Gu, 1993). In addition, Muhammad, (2016) found that the N. scintillans bloom event occurred in the East Bay of Ormara, Pakistan. Due to the extreme density of N. scintillans triggered the reduction of dissolved oxygen in the East Bay region causing mass mortality of commercially important finfish and shellfish i.e. mullets, Chinese pomfrets, Groupers, shrimps, and crabs.
Recently, Diraviya raj et al., (2020) observed that the intense dinoflagellate bloom of N. scintillans occurred in 2019 at GoM, Southeast Coast of India. This bloom created temporary hypoxic conditions (DO below 2 mg L− 1) which resulted in the fast-growing coral such as Acropora, Montipora, and Pocillopora being severely affected at GoM Southeast Coast of India. Similarly, Fire et al., (2009) reported that the New England coastal waters are highly devastated by toxic producing Alexandrium bloom. The extremely high densities of Alexandrium bloom events produced Saxitoxin, causing mortality on shortnose sturgeon Acipenser brevirostrum in 2009 at Sagadahoc Bay, Maine, USA. In addition, the toxic Alexandrium bloom is considered a major threat to the health of the shortnose sturgeon fish population. The recent study also found that the Pseudo-nitzschia bloom event occurred at Chunnamber backwater of Puducherry, Southeast coast of India. During this event, 1 metric ton of mass mortality of backwater fish is killed (Mishra et al., 2021).
The Chilean coastal zone has severely affected by the Alexandrium catenella bloom in the summer of 2009 and 2016. The exceptional bloom outbreaks spread over the Chilean coast causing economic losses in the Chilean salmon farm industry of over $10 M USD (Mardones et al., 2010). The same coast has been massively impacted by Pseudochattonella cf. verruculosa and A. catenella in 2016. The high density of Pseudochattonella cf. verruculosa and A. catenella bloom event killed 27 million salmon (Salmo Oncorhynchus kisutch and Oncorhynchus mykiss) and trout fishes resulting in 39,000 tons (Montes et al., 2018). Michel et al., (2017) found that the multispecies mass mortality of marine fauna is massively impacted by toxic dinoflagellate Alexandrium tamarense bloom in Belle-Isle and Cabot, Canada. The intense algal bloom contains a mixture of Paralytic shellfish toxins (PST) and it extensively spread all over the St. Lawrence Estuary, as a consequence of this event mass mortality of multispecies such as beluga (Delphimapterus leucas) harbor porpoise (Phocoena phocoena) juvenile fin whale (Balaenoptera physalus) and Seals killed.
Similar predictive strength was found for the temperate fish species rainbow wrasse (Coris julis) off the Azores (Fontes et al., 2016). However, caution is needed when considering environment-recruitment correlations as they seldom hold when extending the original time series (Myers, 1998). Also, remote sensing data only capture the surface manifestation of the bloom and may therefore not necessarily represent a larger part of the water column. Superimposed on these stresses, climate change is already leading to temperature increases in some areas of the earth’s oceans, and warmer waters could affect the occurrence of HABs (Moore et al., 2008; Backer and Moore, 2011; Hallegraeff, 2010; Gowen et al., 2012). Specifically, changes in the frequency, intensity and geographic extent of HABs may occur, but the possible responses are likely to be highly species-specific, given the diverse toxicity, physiology, biology, and ecology of HABs organisms.