Difference Between Zooplankton and Phytoplankton

Zooplankton vs Phytoplankton

Two of the most important groups of Ecology, as means of energy flow, are zooplankton and phytoplankton. Both phytoplankton and zooplankton cover all the phyla of the animal kingdom including Chordates. Therefore, a taxonomic classification for the plankton is not possible but, either an ecological niche-based, or size based, or life stage based classifications are feasible. Plankton are classified according to their sizes, vary from <2 µm to 200 mm. Pico, nano, micro, meso, and macro are the prefixes for the term plankton according to their sizes arranged ascending. Generally, the phytoplankton store energy via photosynthesis and zooplankton and nekton (large bodied animals that actively move in the water column) feed on those. Humans and other predators feed on nekton and some larger zooplankton in large scale. Also, the human activities, viz. environmental pollution, largely affect negatively on this energy flow that starts from phytoplankton.

What is a Zooplankton?

Zooplankton contains the small animals those swim or float in the water column. According to the developmental stages in their lifecycles, the zooplanktons are divided into two groups, known as meroplankton and holoplankton. Meroplankton contains larvae of cnidarians, crustaceans, molluscs, insects, echinoderms, and some fish. Meroplankton spend only a little time period of their lifecycle as plankton whereas, the holoplankton spend their whole life being plankton. Holoplankton contains Pteropods, Polychaetes, Larvaceans, Copepods, Siphonophores… etc. Zooplankton includes members from almost all the Phyla of the animal kingdom; Protozoa, Cnidarians / Coelenterates, Arthropods, Molluscs, Echinoderms, and Chordates. They are adapted to either swim or float using different techniques viz. fat bodies, oil droplets, pneumatophores, ion-replacement techniques… etc. Zooplankton show a very unique phenomenon called the vertical migration, where they move towards to surface of the water in the nights and move down to deep water during daytime. Vertical migration helps them to be safe from the diurnal predators and allow the phytoplankton to produce food during daytime those could be foraged at the night. During these movements, zooplanktons use water currents as well as active swimming.

What is a Phytoplankton?

Phytoplankton contains the small plant-like organisms in the water column, mostly inhabiting the euphotic zone, aka sunlit volume, of the water body. They are included in the micro, nano, and pico classes of plankton classification according to size. Diatoms (more than 50,000 species), cyanobacteria, dinoflagellates (more than 2000 species), and algae (e.g. red and green algae) are some of the most common groups of phytoplankton. Phytoplankton store the energy of the sunlight in the form of food thus, they are referred as autotrophs of aquatic ecosystems. Phytoplankton are responsible for the world’s maximum primary production, which is almost 200 billion kilocalories per year. Out of the Earths’ primary production, phytoplankton accounts for over 50%. Phytoplankton can not swim against the water current, i.e. those are not active swimmers and therefore, zooplankton and nekton could easily prey on those.

What is the difference between Zooplankton and Phytoplankton?

- Functions of these two ecological niche groups are different and very important.

- Phytoplanktons are autotrophs whereas, zooplanktons are heterotrophs.

- By the terminology also phyto refers to plant-like, and zoo is for animal-like.

- Phytoplankton can not swim actively, while zooplankton can move either actively or passively.

- Presence and absence of vertical migration in respectively zooplankton and phytoplankton also remarks additional variation between those two.