If you watch the animated series SpongeBob SquarePants, you surely know Sheldon J. Plankton, the green copepod and main antagonist of Mr. Krabs. This portrayal is rather unfortunate because, in reality, plankton plays a crucial role in the aquatic environment.

Freshwater and marine organisms primarily depend on plankton for food, as it forms the productive base of aquatic ecosystems. A collapse in plankton populations can severely disrupt the entire food web and negatively impact fisheries. Conversely, an abnormal increase in a single species can also harm fisheries. Therefore, studying plankton is an important aspect of fisheries research, providing insights into the health of aquatic ecosystems that must be considered in fisheries production and conservation programs.

Composition and classification

Plankton comes from the Greek word “planktos,” meaning “drifter” as they freely float in water, primarily because they are too small, weak, or non-motile to swim against currents.

A single drop of water from a lake or ocean can contain thousands of microscopic plankton, including algae, bacteria, protozoans, crustaceans, mollusks, coelenterates, and other animals in their early life stages. Plankton composition varies with the seasons and nutrient availability in the water.

It can be classified in several ways, with common categories based on nutritional requirements, size, lifespan, or habitat. Plant-like plankton that produce food through photosynthesis are called phytoplankton, while animal-like communities are referred to as zooplankton. Technically, these unique organisms are neither fully plant nor animal and are classified under Kingdom Protista.

Plankton can range from 0.002 to 200 cm in size. Based on size, they are categorized as femtoplankton, picoplankton, nanoplankton, microplankton, mesoplankton, macroplankton, or the largest, megaplankton.

Organisms that spend their entire life cycle as plankton are known as holoplankton, while those that only spend part of their life cycle as plankton are referred to as meroplankton. Plankton in marine waters are called haliplankton, while those in freshwater are known as limnoplankton.

Identifying phytoplankton

In recent years, research on phytoplankton has increased due to its role in primary productivity, climate impact, and as an indicator of water quality. Understanding and accurately identifying phytoplankton species is crucial for addressing issues they pose to fisheries, including harmful algal blooms or ‘red tide.’

Phytoplankton is primarily classified into two major groups: dinoflagellates and diatoms. The main difference is that dinoflagellates have whip-like tails that propel them through the water, while diatoms rely on currents for movement.

Dinoflagellate species can be either armored or unarmored. Armored dinoflagellates possess intricate shell-like structures called theca, which are absent in unarmored, or naked, dinoflagellates. The pattern and arrangement of thecal plates in armored dinoflagellates vary by species, making them important for identification. During blooms, they may form chains of two or more, depending on the species.

Diatoms, in contrast, can be bilaterally symmetric pennate or radially symmetric centric species. They contain chlorophyll pigments and are encased in a rigid, transparent, glass-like cell wall, allowing them to form colonies or chains under favorable environmental conditions.

Tools and techniques in identifying phytoplankton

When Antonie van Leeuwenhoek first observed protozoa in 1674 using a crude compound microscope, he saw a hidden world of microscopic organisms. Today, microscopes remain essential tools for studying these organisms. Light and compound microscopes are the simplest options for quickly assessing phytoplankton communities in the field.

Powerful microscopes, such as electron, scanning electron, and transmission electron microscopes, have allowed scientists to examine the intricate physical characteristics of phytoplankton that distinguish them from other species. These advanced tools are particularly useful for comparing similar-looking species. Special preparation techniques, including staining solutions, enhance the observable features of phytoplankton. Combined with morphological identification, genetic studies have led to the discovery, renaming, and taxonomic regrouping of several phytoplankton species.

In 2020, Dr. Garry Benico discovered a new species of toxic unarmored dinoflagellate in Philippine waters, named Karlodinium azanzae. This discovery was based on comparisons of physical form, structure, and molecular characteristics among 26 species within the same genus from Japan and the Philippines.

These countless, often invisible yet powerful species in aquatic environments can confuse an untrained eye when distinguishing between plankton species under the microscope. Therefore, systematic nomenclature is crucial for researchers and fisheries managers to sustain the challenging task of phytoplankton identification and monitoring, ultimately helping to mitigate the impacts of “red tide” on seafood safety and security.

Capacitating fishery researchers on plankton identification

To enhance the knowledge and technical skills of fishery researchers and managers in identifying phytoplankton species, personnel from DA-NFRDI and DA-Bureau of Fisheries and Aquatic Resources (BFAR) participated in a phytoplankton identification and analysis training on September 16-19, 2024 in Quezon City.

As bio-indicators of aquatic ecosystem health, plankton composition is a key parameter studied under the Save Manila Bay Program. This training aimed to bolster the skills of its proponents and other fisheries researchers and managers.

Valeriano Borja of NFRDI-Capture Fisheries Research and Development Division (CFRDD) and Professor Garry Benico of Central Luzon State University (CLSU) served as resource speakers on phytoplankton taxonomy and analytical tools used in identification.

The training emphasized the importance of accurate phytoplankton identification for assessing primary productivity, water quality, pollution indicators, and other key phenomena. Participants engaged in lectures and hands-on activities, observing live and preserved specimens under microscopes. Under expert guidance, they successfully identified various phytoplankton species.

NFRDI Executive Director Dr. Lilian Garcia commended the project proponents for initiating the training and stressed that researchers and managers must embody the values of attitude, ability, and availability in their work. Meanwhile, CFRDD Chief Elsa Furio said, “We need patience and continuous application of the skills we’ve gained in phytoplankton taxonomy to build our confidence in this area.”

One of the participants, Karl Mikel Pregon of BFAR Vessel Operation Center, expressed his gratitude: “I thank NFRDI for this training. This new skill will aid us in identifying phytoplankton during our surveys. Although I was not fond of microscopic work during my undergraduate years, I now enjoy it and feel more knowledgeable in phytoplankton identification.” ### (Norvida Gatdula)