GYMNODINIUM CATENATUM: CHARACTERISTICS, LIFE CYCLE, REPRODUCTION - BIOLOGY - 2024

Gymnodinium catenatum is a photosynthetic, atecado dinoflagellate, capable of producing toxins that cause paralyzing shellfish envenomation. This species is always present in seawater, in low concentrations, and its populations periodically undergo exponential growths that produce harmful algal blooms.

This dinoflagellate is capable of forming thick-walled cysts that can withstand long periods in conditions of light and nutrient deficiency. This characteristic allows it to survive even in the ballast waters of boats, which is why it has come to colonize new areas accidentally, due to anthropic action.

Gymnodinium sp. Referential image of a dinoflagellate of the genus Gymnodinium Taken and edited from: Picturepest.

Gymnodinium catenatum has a complex life cycle with cysts that can form directly from haploid vegetative cells, that is, asexually, contrary to what occurs in most dinoflagellates that form cysts with sex cells.

characteristics

Gymnodinium catenatum is a naked dinoflagellate, that is, it lacks teak, it has a transverse and a longitudinal flagellum, as occurs with the rest of the dinoflagellates. These flagella are used for displacement.

They can grow singly (generally during stationary growth stages) or in chains of up to 64 organisms (rapidly growing), however the most common forms are composed of fewer than 10 organisms. They have a gray to brown color due to the presence of photosynthetic pigments.

Cells vary greatly in shape, are generally circular or slightly longer than wide, can measure up to 53 by 45 μm, and have numerous organelles inside. The individual cells and the terminal cells of the chains have conical apices.

The cysts are called dormant cysts and are characterized by having thick walls with a microreticulated surface; its size ranges between 45 and 50 μm in diameter.

Distribution

Gymnodinium catenatum is found in all seas, but its distribution in these is localized and often detected only during algal blooms. Among the countries where it has been observed most frequently are Argentina, Uruguay, Venezuela, Cuba, Costa Rica, Mexico, Spain, Portugal, Egypt, Australia and Japan.

Scientists believe that the presence of Gymnodinium catenatum in many of these localities is due to accidental dispersal in ballast waters. They also believe that they could be cryptic species that are being confused as one.

Reproduction

Gymnodinium catenatum exhibits both asexual and sexual reproduction.

Asexual

Asexual reproduction occurs by oblique binary fission; during this, the diagonal cleavage groove separates the left anterior part of the cell from the right posterior part. Each daughter cell will be in charge of regenerating the component it needs (anterior or posterior), depending on the case.

During cell division, the wall of the newly divided protoplast is continuous with the wall of the progenitor cell and cannot be distinguished from it. The cells in the chains divide synchronously, resulting in chains 2.4, 8, 16, 32, or 64 cells long.

Slowly dividing chains easily break into shorter chains, even cells, or individual cells.

Sexual

Sexual reproduction can occur under conditions of environmental stress, such as growth in a medium deficient in nitrate and phosphate. But these conditions are not essential for this type of reproduction to appear.

The cells that will act as gametes are indistinguishable from vegetative cells. Gametes can be of equal or unequal size. These join in a parallel or perpendicular way. In both cases, the main point of attachment is the sulcus.

The cells are arranged as mirror images, with their longitudinal flagella arranged in parallel. A biconical planozygote is then formed, with a longitudinal double flagellum. The planozygote will gradually become subspherical and will lose one of the longitudinal flagella.

Planozygote can transform into a hypnozygous or resting cyst; for this it loses mobility, undergoes a reorganization and reduction of its cellular content, and secretes a thick cell wall.

Lifecycle

The vegetative cells of Gymnodinium catenatum are normally found in chains of different lengths. This occurs during the rapid growth stage. Then, in the stationary growth phase, the chains break apart to form individual cells.

Gymnodinium fuscum. Referential image of a dinoflagellate of the same genus as Gymnodinium catenatum. Taken and edited from: Picturepest

Under adverse conditions, individual cells can cause resting cells or dormancy cysts. The resting cells are not mobile and secrete an additional protective film. The cysts are spherical and have up to four additional protective layers.

To form dormancy cysts, individual cells can reproduce sexually, or they can do so directly from the vegetative cell. Normally, these cysts can be carried long distances by currents, or be deposited on sea beds.

In the latter case, the cysts can be resuspended in the water during upwelling periods and hatch to give rise to diploid planomeiocytes. These divide and originate haploid vegetative cells, which can enter an exponential growth phase and cause algal blooms.

Nutrition

Gymnodinium catenatum is an autotrophic species, capable of producing its own food from inorganic nutrients, with the help of energy from sunlight. Its growth is limited by the presence of nutrients in the water column.

Among the main nutrients that limit the growth of G. catenatum are selenium, nitrite and nitrate. During the rainy or upwelling seasons, the availability of these nutrients in marine waters near the coast increases.

When the enrichment of nutrients in the water occurs, the populations of G. catenatum do not have limitations to their growth and initiate a period of exponential growth that generates an algal bloom or red tide.

Crippling shellfish poisoning syndrome

It is a syndrome caused by the ingestion of bivalve molluscs that have accumulated a toxin called saxitoxin. This toxin is produced by different species of dinoflagellates.

Gymnodinium catenatum is the only species of atheated dinoflagellates that is involved in this type of poisoning. Mollusks, when ingesting dinoflagellates, accumulate the toxin in their tissues.

The main species of mollusks associated with paralyzing poisoning are clams, mussels, scallops, and cockles. Symptoms of poisoning begin to appear quickly, between 5 and 30 minutes after ingesting the poisoned shellfish.

Symptoms include paresthesia of the mouth and extremities, as well as dizziness, vomiting, and diarrhea. In more severe cases, ataxia, muscle paralysis, and respiratory distress may appear. Fatal cases occur from respiratory paralysis.

To date there is no antidote for saxitoxin, so treatment is symptomatic aimed at maintaining the patient's breathing.

References

1. MA Doblina, SI Blackburnb, GM Hallegraeffa (1999) Growth and biomass stimulation of the toxic dinoflagellate Gymnodinium catenatum (Graham) by dissolved organic substances. Journal of Experimental Marine Biology and Ecology.
2. ML Hernández-Orozco, I. Gárate-Lizárraga (2006). Crippling poisoning syndrome due to consumption of mollusks. Biomedical Journal.
3. SI Blackburn, GM Hallegrae, CJ Bolch (1989). Vegetative reproduction and sexual life cycle of the toxic dinoflagellate Gymnodinium catenatum from Tasmania, Australia. Journal of Phycology.
4. F. Gómez (2003). The toxic dinoflagellate Gymnodinium catenatum: an invader in the Mediterranean Sea. Acta Botanica Croatica.
5. CJ Band-Schmidt, JJ Bustillos-Guzmán, DJ López-Cortés, I. Gárate-Lizárraga, EJ Núñez-Vázquez & FE Hernández-Sandoval (2010). Ecological and Physiological Studies of Gymnodinium catenatum in the Mexican Pacific: A Review. Marine Drugs.
6. FE Hernández-Sandoval, DJ López-Cortés, CJ Band-Schmidt, I. Gárate-Lizárraga, EJ Núñez-Vázquez & JJ Bustillos-Guzmán (2009). Paralyzing toxins in bivalve molluscs during a proliferation of Gymnodinium catenatum Graham in the Bay of La Paz, Mexico. Hydrobiological.