African Journal of Marine Science 2006, 28(2): 215–217Printed in South Africa — All rights reserved

Copyright © NISC Pty LtdAFRICAN JOURNAL OF

MARINE SCIENCEISSN 1874–232X

Occurrence and predominance of the fish killer Cochlodinium polykrikoideson the Pacific coast of Costa Rica

M Vargas-Montero1*, E Freer1, R Jiménez-Montealegre2 and JC Guzmán2

1 Centro de Investigación en Estructuras Microscópicas, Universidad de Costa Rica, Ciudad de la Investigación, Finca 2,San Pedro de Montes de Oca, CP 2060, Costa Rica2 Parque Marino del Pacífico, Puntarenas, Costa Rica * Corresponding author, e-mail: vmontero@cariari.ucr.ac.cr

Introduction

Cochlodinium polykrikoides is known to be associated with

extensive fish kills, which result in severe economic losses in

Japan and Korea (Yuki and Yoshimatsu 1989, Kim 1998,

Okaichi 2003). Similar harmful effects have only recently

been noted in Costa Rica. In 2002, on the Pacific coast of

Costa Rica, fish mortalities and airborne human intoxication

were noted for the first time during a bloom of C. poly-krikoides (Vargas and Freer 2004a). Although the subject is

of much interest, the mechanism behind its toxicity remains

unclear (Taylor 1987). Laboratory cultures of C. polykrikoideshave been shown to produce 40% mortality in juveniles of

the fish Leiognathus nuchalis (pargo mancha) during the first

eight hours of contact (Yuki and Yoshimatsu 1989). C.polykrikoides has known haemolytic properties that can

adversely affect aquatic organisms. In fish bioassays at

densities of above 1 000 cells l–1, fish showed signs of

respiratory distress, loss of equilibrium, and an inability to

maintain position in the water column (Landsberg 2002).

Earlier reports of outbreaks of C. polykrikoides on the

Pacific coast of Mexico were in 1999 in Manzanillo Bay

(Morales-Blake et al. 2001) and in 2000 in the Gulf of

California (Gárate-Lizárraga et al. 2000), possibly related to

the La Niña phenomenon. On the Pacific coast of Costa

Rica, the persistent trade winds produce turbulence in the

water column, particularly in the upwelling area in the north

(Jiménez 2001). It has been suggested that the environ-

mental conditions arising from trade winds are conducive to

the development of blooms of C. polykrikoides (Vargas and

Freer 2004a).

This study presents the temporal distribution of C. poly-krikoides along the Pacific coast of Costa Rica and the

possible environmental effects that contribute to the estab-

lishment of these extensive blooms.

Material and Methods

Surface water samples for taxonomic analysis were collected

every 15 days from January 2003 to June 2004, at 14 stations

located over the main fishing grounds along the Pacific coast

of Costa Rica (Figure 1). The samples were collected using a

1-litre acrylic Niskin bottle and a 20µm plankton net, fixed with

acid Lugol’s solution and subsequently analysed using a

Sedgewick-Rafter chamber under a Nikon light microscope.

Wind data from various meteorological stations on the

Pacific coast of Costa Rica were also collected.

Results

During the period of sampling, water discolourations owing

to C. polykrikoides started in September 2003, and reached

Water samples were collected at several points along

the Pacific coast of Costa Rica (10°00’N, 84°15’E) fort-

nightly from January 2003 to June 2004. During this

period, dense red-ochre discolourations dominated by

Cochlodinium polykrikoides were observed, particu-

larly over the dry season. In 2003, the highest cell

density of 1.75 X 108 cells l–1 was observed in October.

During April and June 2004, extensive blooms were

present, with the highest cell density (3.8 X 108 cells l–1)

occurring in April. These blooms were accompanied by

a strong fetid odour and large quantities of yellow

foam. Fish mortalities also occurred near some coastal

areas. The observed discolourations tended to be

associated with the strongest north-west winds on the

North Pacific coast of Costa Rica. To date, blooms

caused by C. polykrikoides have been increasing in

frequency and in extent. The previously unreported

high cell densities and the increase in the duration and

extent of these harmful algal blooms suggest that the

environmental conditions have changed to the benefit

of C. polykrikoides over other phytoplankton species

that usually bloom at that time of year. The fish mortal-

ities associated with C. polykrikoides blooms are

cause for concern, as are the possible environmental

changes contributing to the production of these exten-

sive blooms.

Keywords: Cochlodinium polykrikoides, fish kill, Pacific coast

Vargas-Montero, Freer, Jiménes-Montealegre and Guzman216

the highest average cell density of 1.75 X 108 cells l–1 in

October (Figure 2). The cells were generally present as

chains of 4, 6 or 8 cells, each containing a red stigma. Large

numbers of resistant cysts were also present in the water

samples. At the beginning of January 2004, the bloom had

reached its broadest spatial extent of approximately 50km2.

The maximum concentration of 3.8 X 108 cells l–1 was attained

in April 2004, by which time the bloom had decreased in size

and was concentrated within a few kilometres from the coast.

The major discolourations were observed during the dry

season (December–May), generally after the strongest north-

easterly winds (Figure 2). These discolourations were red-

ochre in colour, and associated with a strong fetid odour and

large amounts of yellow foam. Hundreds of dead fish,

comprising members of the families Carangidae, Lutjanidae,

Muraenidae, Engraulidae and Soleidae, were observed near

the central Pacific coast.

Discussion

Although small blooms of C. polykrikoides have been

observed since 1981, this is the first report of a large-scale

bloom on the Pacific coast of Costa Rica. Extensive dis-

colourations were observed over a period of less than one

year and were associated with foam production, a fetid smell,

and large fish mortalities. Fish kills associated with HABs are

unusual in Costa Rican waters. However, in 2002 a large

number of dead fish washed up on the beaches (Vargas and

Freer 2004a). In 2004, fish and coral reef mortalities were

observed in diverse sectors of the coast in close proximity to

blooms of C. polykrikoides. It is possible that, owing to the

high cell densities of C. polykrikoides, anoxic conditions

following bloom decay could have contributed to some of

these mortalities. The potential toxicity of C. polykrikoideshas not been established in laboratory tests.

The first report of a HAB by C. polykrikoides (then named

C. catenatum) on the Pacific coast of Costa Rica was in

1981 (Hargraves and Víquez 1981). Two decades later, in

2002, a bloom of this species was reported in the central

Pacific region of Costa Rica, together with the cyanobac-

terium Trichodesmium erytraeum (Vargas and Freer

2004a). HAB events in general have become increasingly

frequent and more persistent in Costa Rica since 2000.

More specifically, C. polykrikoides blooms have increased

in frequency and persistence since 2002 (Vargas and Freer

2003, Vargas et al. 2004), extending over the whole Pacific

coast but concentrated in the main fishing area of the Gulf

of Nicoya (Vargas and Freer 2004a). This recent increase

suggests that environmental conditions along the coastal

areas of Costa Rica may have changed to the benefit of

previously unrecorded non-desirable micro-organisms.

The high cell concentrations reported in this study have

not been observed previously along the Pacific coast of

Costa Rica. This is indicative of a shift in species domi-

nance from toxic phytoplankton species that usually pro-

duce blooms, such as Pyrodinium bahamense and

Gymnodinium cf. catenatum, to C. polykrikoides (Hargraves

and Víquez 1981, Víquez and Hargraves 1995, Vargas and

Freer 2003, 2004b). Blooms of C. polykrikoides are

generally quasi-monospecific, with only very low concentra-

tions of other species present. Other species encountered

were the dinoflagellates Ceratium dens, Gonyaulaxspinifera, Heterocapsa sp. and Heterolobatum sp., as well

as the cyanobacterium Trichodesmiun erytraeum.

The average wind speed for the upwelling area in the

north along the Pacific coast of Costa Rica indicates that

the strongest north-westerly winds occur during April, the

period when an extensive bloom was observed. Along the

central Pacific coast (Gulf of Nicoya) some of the blooms

were also observed during the dry season. The period

December–March is characterised by strong winds, which,

by promoting turbulence, disrupt water column stratification

and increase the availability of nutrients. Such conditions

favour the emergence of cysts near the coast (Mcgillicuddy

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Figure 1: Map of the Pacific coast of Costa Rica showing the

locality of the sample stations (Stations 1–3 are in the Gulf of

Papagayo and Stations 6–9 in the Gulf of Nicoya)

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Figure 2: Monthly average wind speed and average cell density in

surface waters along the Pacific coast of Costa Rica between

January 2003 and June 2004. Seawater temperature ranged

between 25°C and 28°C during the sampling period

African Journal of Marine Science 2006, 28(2): 215–217 217

et al. 2003). Winds are very important in the formation and

maintenance of HABs along some Central American coasts

(Alonso and Ochoa 2004). Strong trade winds from the

north-east could be, among others, a significant factor in

the increase of HABs in Costa Rica — more so than the

availability of nutrients, particularly for mixotrophic species

like C. polykrikoides.

Acknowledgements — We appreciate the contribution of the Vice-

rrectoría de Investigación of the University of Costa Rica to this

research, which forms part of project no. 810-A4043. We also thank

the Ministry of Science and Technology and the Netropica Foundation

for their contribution. Dr Steve Hanson and two anonymous reviewers

are thanked for their comments on an earlier version of the manuscript.

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Received January 2005; accepted January 2006