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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Plankton | 4/7 | https://en.wikipedia.org/wiki/Plankton | reference | science, encyclopedia | 2026-05-05T07:36:10.175954+00:00 | kb-cron |
=== Zooplankton === Zooplankton (from Greek zoon, or animal) are small protozoans or metazoans (e.g. crustaceans and other animals) that feed on other plankton. Some of the eggs and larvae of larger nektonic animals, such as fish, crustaceans, and annelids, are included here.
=== Mixoplankton === Mixoplankton (from Greek mixis, or mixture) have a mixed trophic strategy. In recent years, there has been a growing recognition that perhaps the majority of plankton can act in both the above modes. Traditionally, plankton were divided into just the first two broad trophic groups: plant-like phytoplankton which make their own food, usually by photosynthesis, and animal-like zooplankton that eat other plankton. In recent years, there has been a recognition that many plankton, perhaps over half, are mixotrophic. Plankton have traditionally been categorized as producer, consumer, and recycler groups, but some plankton are able to benefit from more than just one trophic level. This mixed trophic strategy means mixoplankton can act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. In this manner, mixoplankton can use photosynthesis for growth when nutrients and light are abundant, but switch to eating phytoplankton, zooplankton or each other when growing conditions are poor. As a result of these findings, many unicellular plankton formally categorized as phytoplankton, including coccolithophores and dinoflagellates, are longer included as strictly phytoplankton, as they not only produce their own food through phototrophy but can also ingest other organisms. These organisms are now more correctly termed mixoplankton. This recognition has important consequences for how the functioning of the planktonic food web is viewed.
Mixotrophs can be further divided into two groups; constitutive mixotrophs which are able to perform photosynthesis on their own, and non-constitutive mixotrophs which use phagocytosis to engulf phototrophic prey that are either kept alive inside the host cell, which benefits from its photosynthesis, or they digested, except for the plastids, which continue to perform photosynthesis (kleptoplasty). Recognition of the importance of mixotrophy as an ecological strategy is increasing, as well as the wider role this may play in marine biogeochemistry. Studies have shown that mixoplankton are much more important for marine ecology than previously assumed. Their presence acts as a buffer that prevents the collapse of ecosystems during times with little to no light. Mixoplankton have ancient origins and have been recognized by scientists for over a century. However, it is only in recent years that the widespread significance of mixoplankton has been gaining recognition in mainstream marine science.
=== Decomposers === Instead of directly building biomass, decomposers break organic nutrients down into inorganic forms which can be recycled (an approach which metabolically can be costly). Fungi: Mostly tiny mycoplankton (microfungi), yeast, or mobile zoospores, that can recycle organic matter through a process called the mycoloop which involves parasiting plankton. Bacteria/Archaea: often called bacterioplankton. These minute prokaryotes (typically <0.001mm) return organic nutrients to inorganic forms by breaking down particulate and dissolved organic matter through the process called the microbial loop. This process recycles nutrients, like nitrogen and phosphorus, back into the water for primary producers like phytoplankton to use again. Some convert ammonium in animal waste to nitrate, while others transform nitrate to nitrogen gas. Viral infections likely destroy many, while others are eaten by protist zooplankton and mixoplankton, which use their nutrients for photosynthesis. However details of their ecology is complex and it is not clear what sustains them. Viruses: Typically 10 to 100 times smaller than bacteria and also the most abundant (~100 billion per litre), viruses infect other plankton and larger organisms. It is thought they efficiently halt vast plankton blooms within days, by turning biomass into dissolved organic matter that supports bacterial growth through a process called the viral shunt. Being host-specific, they also likely influence the biological and microbial carbon pumps.
== Other groups ==
=== Gelatinous zooplankton ===
Gelatinous zooplankton are fragile animals that live in the water column in the ocean. Their delicate bodies have no hard parts and are easily damaged or destroyed. Gelatinous zooplankton are often transparent. All jellyfish are gelatinous zooplankton, but not all gelatinous zooplankton are jellyfish. The most commonly encountered organisms include ctenophores, medusae, salps, and Chaetognatha in coastal waters. However, almost all marine phyla, including Annelida, Mollusca and Arthropoda, contain gelatinous species, but many of those odd species live in the open ocean and the deep sea and are less available to the casual ocean observer.
=== Ichthyoplankton ===
Ichthyoplankton are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals. Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about 1 millimetre (0.039 in). The newly hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac (for nourishment), and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae. In time fish larvae become able to swim against currents, at which point they cease to be plankton and become juvenile fish.
=== Pseudoplankton ===