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Harmful Algae 4 (2005) 519–524

Prorocentrum minimum bloom and its possible link to

a massive fish kill in Bolinao, Pangasinan,

Northern Philippines

Rhodora V. Azanzaa,*, Yasuwo Fukuyob,Leni G. Yapa, Haruyoshi Takayamac

aThe Marine Science Institute, Velasquez St., University of the Philippines-Diliman, Quezon City 1101, PhilippinesbAsian Natural Environmental Science Center, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

cHiroshima Fisheries Experimental Station, Ondo-Cho, Aki gun Hiroshima, Japan

Received 1 March 2004; received in revised form 1 June 2004; accepted 1 August 2004

Abstract

For the first time, a Prorocentrum minimum bloom at a maximum cell density of 4.7 � 105 cells/L was recorded on January

31 to February 4, 2002 at Bolinao, Pangasinan, Northern Philippines where intensive and extensive aquaculture of Chanos

chanos (milkfish) in fish pens and cages has been practiced for years now. The fish kill, which lasted almost simultaneously with

the bloom of the organism had its peak when the organisms bloom was declining. Lack of oxygen in the cages and pens was the

fundamental cause of the fish kill. Losses due to the fish kill were estimated at six million pesos (equivalent to US$ 120,000),

which includes only the worth of dead cultivated fish. Lack of oxygen in the cages and pens was the fundamental cause of the fish

kill, and toxicity of the Prorocentrum could not be confirmed. The cells had minute spinules equally all over the surface of

valves. Intercalary striae were wide with many ridges perpendicular to valve margin. Outline of cells was rounder than typical P.

minimum cells and similar to P. balticum. Recommendations for future research on the organism are incorporated together with

monitoring and management interventions in order to mitigate or possibly prevent damages in similar future events.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Anoxia; Bolinao; Northern Philippines; Fish kill; Harmful algal bloom; Hypoxia; Prorocentrum minimum

1. Introduction

This is the first report of a Prorocentrum minimum

bloom with negative impacts in the Philippines and

* Corresponding author. Tel.: +63 921 5967; fax: +63 921 5967.

E-mail address: rhod@upmsi.ph (R.V. Azanza).

1568-9883/$ – see front matter # 2004 Elsevier B.V. All rights reserved

doi:10.1016/j.hal.2004.08.006

probably the whole of Southeast Asia, although the

possibility of unreported past blooms should not be

discounted. Since the bloom occurred before and

during a massive fish kill in an area where extensive

and intensive finfish aquaculture is being done, links

between the two events are explored based on

available data and information. A description of the

.

R.V. Azanza et al. / Harmful Algae 4 (2005) 519–524520

organism is included. In view of the socio-economic

and possibly health impacts of its future blooms,

recommendations are made on monitoring and

research directions.

2. Materials and methods

2.1. The study site

The waters of Bolinao, Pangasinan, Northern

Philippines (168–178N latitude, 1198–1218E long-

itude) along with those of neighboring waters, Bolinao

Bay in Lingayen Gulf have been the site for intensive

and extensive aquaculture of Chanos chanos (milk-

fish) being sold locally and in Metropolitan Manila.

The study was limited to the Guiguiwanin Channel

(Fig. 1) where more than a thousand fish pens and

cages were being maintained before and during the

fish kill events in late January to early February 2002.

The channel is about 24 km long, 3 km wide and

approximately 46 m deep. Some fishermen make use

of the area for wild harvest of fin and shellfish. A

Marine Station is being maintained by the University

of the Philippines-Diliman in the area.

2.2. Collection and analyses of phytoplankton

samples

The collection of samples was initiated during the

first week of January 2002 when fishermen and some

students of the Bolinao Marine Laboratory of the

University spotted reddish streaks in the waters of

Guiguiwanin Channel. Samples were collected using

plankton net with 25-mm mesh and a Niskin sampler

for quantification. They were immediately fixed with

Lugols solution but live samples were also kept to be

able to start the culture of the organism. Previous

monthly collections in the Channel (i.e. November and

December 2001) were also analyzed for the presence

of Prorocentrum.

Initial identification of the bloom causative and

other organisms was done at the Marine Science

Institute, University of the Philippines using a

Microstar IV compound microscope (Reichert).

Verification of identification and analysis of the

Prorocentrum samples were done at the University

of Tokyo using the scanning electron microscope

(SEM). Special preparation techniques described

below allowed the better analysis and electron

micrography of the specimens.

2.3. Collection of environmental parameters

Temperature, salinity and light were measured

using thermometer, refractometer, light meter (Licor

II meter), respectively. Using the Wrinkler titration

method by Parsons et al. (1984), dissolved oxygen

(DO) was determined.

2.4. Observations on the cultured fish/dead fish

Observations on the cultured fish were limited to

the times and places, when and where collection of the

water samples were made. Also there were only a few

(three to five) fish samples that were observed each

sampling due to difficulty in obtaining samples from

culture operators. Decaying and more abundant fish

samples on the shoreline were however too smelly and

not suitable for analyses. Only the outer overall

appearance of the fish sample and status of their gills

were observed.

3. Results

3.1. Description of Prorocentrum minimum

(Pavillard) Schiller (1933) Synonyms:

P. mariae-labourae; P. triangulum Martin, 1929.

Cells round to ovate in valve view and lenticulate in

lateral view, measuring 14–18 mm in length; valve

surface and marginal zone covered with many fine

spines; intercalary striae with many ridges perpendi-

cular to valve margin; anterior spine quite low;

spherical nucleus located posteriorly. The cells appear

similar to P. balticum specially using the light

microscope (Fig. 3).

3.2. Phytoplankton count from November to

December 2001 and January to February 2002

There was an increasing dinoflagellate dominance

trend from November 2001 up to the bloom on January

31, 2002 (Fig. 2). The phytoplankton in November

2001 was co-dominated by Gymnodinium sp. and

R.V. Azanza et al. / Harmful Algae 4 (2005) 519–524 521

Fig. 1. Map of Bolinao, Pangasinan where the P. minimum bloom and massive fish kill occurred in January–February 2002.

several diatom species. P. minimum comprised only

1% of the total phytoplankton collected on this month.

By December 2001 Gyrodinium sp. dominated with an

average count of 442 cells/L, representing 60% of the

total phytoplankton for the said month. No P. minimum

organisms were found, however. During the fish kill on

31 January 2002, P. minimum dominated, constituting

99% of the total phytoplankton, reaching a maximum

average density of 4.7 � 105cells/L. The following

day, this number decreased to 1.9 � 105cells/L. Three

days after, diatoms dominated comprising 87% of the

total phytoplankton and P. minimum went as low as

12 cells/L signaling the end of the bloom.

Before the bloom, in the months of November and

December, temperature was fairly constant at an

average of 28 8C. During the bloom, however, the

R.V. Azanza et al. / Harmful Algae 4 (2005) 519–524522

Fig. 2. Percentage composition of phytoplankton in Bolinao Bay, Pangasinan from November 2001 to February 2002.

temperature dropped to 26 8C and increased to 27 8Cwhen the bloom was declining. Salinity before and

during the bloom was at the range of 30–35 ppt. There

was a wide range in the amount of dissolved oxygen

before the bloom in the Channel but during the bloom,

the range narrowed and the values decreased. If the

average of the range of dissolved oxygen is taken, the

trend can be observed as decreasing with the lowest

value (2.1) during the bloom. Light intensity was at a

range between 42 and 1026 mEs�1 m�2 (Table 1).

3.3. General condition and behavior of cultured fish

and other marine animals during and after the

Prorocentrum bloom

During the bloom, fish behavior was normal. The

fish were still eating the feeds given to them by the fish

Table 1

Environmental conditions before and during the P. minimum bloom in G

Date Temperature (8C) Salinity (ppt)

1–2 November 2001 27.9–28.9 30–35

1–3 December 2001 27–28 30–32

31 January 2002 26.35–26.45 33*

February 2002 27* 33.5

Data not available.* c/o C.L. Villanoy and E. Magdaong, Physical Oceanography Labora

pen/cage caretakers. Right after the end of the bloom,

the fish started gasping for breath. They swam on the

surface of the water and some even jumped out of the

water. Hours later, the fish were found floating on the

water, already dead. Not only thousands of milkfish

reared in the fish pens and cages perished, various

dead reef fish, eels, octopus, urchins were washed on

the shore.

4. Discussion

4.1. Association between the P. minimum bloom

and the fish kill

The massive fish kill can be associated with the

P. minimum bloom in terms of oxygen depletion.

uiguiwanin Channel

Dissolve oxygen (mg/L) Light/PAR (mEs�1 m�2)

3.29–7.17 (5.23) 52–1026

1.94–4.86 (3.4) 42–1009

1.95–2.25 (2.1) –

– –

tory, UP-MSI.

R.V. Azanza et al. / Harmful Algae 4 (2005) 519–524 523

Fig. 3. Scanning electron micrographs of Prorocentrum minimum collected from Bolinao, Pangasinan.

R.V. Azanza et al. / Harmful Algae 4 (2005) 519–524524

Although there were some reports on the possible

toxicity of P. minimum, in this particular case for

Bolinao, Northern Philippines, the death of fish was

clearly the result of lack of oxygen mostly from the

collapse of the algal bloom. The optimal level of

dissolved oxygen (DO) is about 5 mg/L for milkfish

growth in tropical waters (Boyd and Lichtkoppler,

1979). The observed DO during the fish kill was

2.1 mg/L (Table 1), three levels below the healthy

level. An ocular inspection in 1999 showed a total of

797 units of fish pens and cages (around 165 ha),

which exceeds the carrying capacity of the area

(Verceles et al., 2000). Thirty-two years (aquaculture

in the area began in 1970) of accumulated nutrient and

waste loading could have led to changes in the water

column and sediments. The sediments of Bolinao were

highly enriched in organic matter and the sediment

metabolism and nutrient regeneration rates were much

higher than found in the surrounding area as well as

rates observed in other tropical sediments (Holmer et

al., 2002). High feed input would lead to large release

of nutrients from the sediments that could have then

favored a P. minimum bloom in January 2002.

Eventually the bloom with brown discoloration of

water, collapsed and the organism’s decomposition

led to further decrease of dissolved oxygen (DO). The

end result therefore was 15 million peso worth of

fish floating dead on the surface of the waters of

Guiguiwanin Channel.

4.2. Implications to future research and monitoring

Constant monitoring of phytoplankton and phy-

sico-chemical parameters related to blooms should be

made in Bolinao, Lingayen Gulf, Northern Philip-

pines. A monitoring body can be pooled which can

comprise fish pen operators, technical students, and

other local government members who can sustain such

a program.

Culture of the organism has been initiated and can

be used for possible toxicity testing and other

biochemical and physiological studies.

Acknowledgements

The authors are grateful to John Dominic for

helping in the collection and identification of

Prorocentrum minimum; Evangeline Magdaong and

Fideliz Pillos for providing the authors the physical

parameters for the month of January 2002; Claudette

Vinluan and Iris Baula for helping in the counting of

phytoplankton and collation of data.

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