Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word zooplankton is derived from the Greek zoon (ζῴον), meaning "animal", and planktos (πλαγκτός), meaning "wanderer" or "drifter". Individual zooplankton are usually microscopic, but some are larger and visible to the naked eye.
Copepods are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic, some are benthic, a number of species have parasitic phases, and some continental species may live in limnoterrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds, and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as biodiversity indicators.
The biological pump, also known as the marine carbon pump, is, in its simplest form, the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sediments. It is the part of the oceanic carbon cycle responsible for the cycling of organic matter formed mainly by phytoplankton during photosynthesis (soft-tissue pump), as well as the cycling of calcium carbonate (CaCO3) formed into shells by certain organisms such as plankton and mollusks (carbonate pump).
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth, as illustrated on the right. The word "pelagic" is derived from Ancient Greek πέλαγος (pélagos) 'open sea'. The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes from the surface of the sea almost to the bottom. Conditions in the water column change with depth: the pressure increases; the temperature and amount of light decreases; the salinity and amount of dissolved oxygen, as well as micronutrients such as iron, magnesium and calcium, all change.
The spring bloom is a strong increase in phytoplankton abundance that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and coastal waters. Phytoplankton blooms occur when growth exceeds losses, however there is no universally accepted definition of the magnitude of change or the threshold of abundance that constitutes a bloom. The magnitude, spatial extent and duration of a bloom depends on a variety of abiotic and biotic factors. Abiotic factors include light availability, nutrients, temperature, and physical processes that influence light availability, and biotic factors include grazing, viral lysis, and phytoplankton physiology. The factors that lead to bloom initiation are still actively debated.
Meroplankton are a wide variety of aquatic organisms which have both planktonic and benthic stages in their life cycles. Much of the meroplankton consists of larval stages of larger organism. Meroplankton can be contrasted with holoplankton, which are planktonic organisms that stay in the pelagic zone as plankton throughout their entire life cycle.
Iron fertilization is the intentional introduction of iron to iron-poor areas of the ocean surface to stimulate phytoplankton production. This is intended to enhance biological productivity and/or accelerate carbon dioxide sequestration from the atmosphere.
A lake ecosystem or lacustrine ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of lentic ecosystems, which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two fields form the more general study area of freshwater or aquatic ecology.
The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.
Calanus finmarchicus is a species of copepods and a part of zooplankton, which is found in enormous amounts in the northern Atlantic Ocean.
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. Many gelatinous plankters utilize mucous structures in order to filter feed. Gelatinous zooplankton have also been called "Gelata".
The San Francisco Estuary together with the Sacramento–San Joaquin River Delta represents a highly altered ecosystem. The region has been heavily re-engineered to accommodate the needs of water delivery, shipping, agriculture, and most recently, suburban development. These needs have wrought direct changes in the movement of water and the nature of the landscape, and indirect changes from the introduction of non-native species. New species have altered the architecture of the food web as surely as levees have altered the landscape of islands and channels that form the complex system known as the Delta.
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below, which is referred to as the biological pump. Export production is the amount of organic matter produced in the ocean by primary production that is not recycled (remineralised) before it sinks into the aphotic zone. Because of the role of export production in the ocean's biological pump, it is typically measured in units of carbon. The term was first coined by the explorer William Beebe as he observed it from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms which live very deep in the water column.
The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere caused by the Coriolis Effect. They generally form in large open ocean areas that lie between land masses.
Pleurobrachia bachei is a member of the phylum Ctenophora and is commonly referred to as a sea gooseberry. These comb jellies are often mistaken for medusoid Cnidaria, but lack stinging cells.
Phycotoxins are complex allelopathic chemicals produced by eukaryotic and prokaryotic algal secondary metabolic pathways. More simply, these are toxic chemicals synthesized by photosynthetic organisms. These metabolites are not harmful to the producer but may be toxic to either one or many members of the marine food web. This page focuses on phycotoxins produced by marine microalgae; however, freshwater algae and macroalgae are known phycotoxin producers and may exhibit analogous ecological dynamics. In the pelagic marine food web, phytoplankton are subjected to grazing by macro- and micro-zooplankton as well as competition for nutrients with other phytoplankton species. Marine bacteria try to obtain a share of organic carbon by maintaining symbiotic, parasitic, commensal, or predatory interactions with phytoplankton. Other bacteria will degrade dead phytoplankton or consume organic carbon released by viral lysis. The production of toxins is one strategy that phytoplankton use to deal with this broad range of predators, competitors, and parasites. Smetacek suggested that "planktonic evolution is ruled by protection and not competition. The many shapes of plankton reflect defense responses to specific attack systems". Indeed, phytoplankton retain an abundance of mechanical and chemical defense mechanisms including cell walls, spines, chain/colony formation, and toxic chemical production. These morphological and physiological features have been cited as evidence for strong predatory pressure in the marine environment. However, the importance of competition is also demonstrated by the production of phycotoxins that negatively impact other phytoplankton species. Flagellates are the principle producers of phycotoxins; however, there are known toxigenic diatoms, cyanobacteria, prymnesiophytes, and raphidophytes. Because many of these allelochemicals are large and energetically expensive to produce, they are synthesized in small quantities. However, phycotoxins are known to accumulate in other organisms and can reach high concentrations during algal blooms. Additionally, as biologically active metabolites, phycotoxins may produce ecological effects at low concentrations. These effects may be subtle, but have the potential to impact the biogeographic distributions of phytoplankton and bloom dynamics.
Ditylum brightwelli is a species of cosmopolitan marine centric diatoms. It is a unicellular photosynthetic autotroph that has the ability to divide rapidly and contribute to spring phytoplankton blooms.
Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.
Transparent exopolymer particles (TEPs) are extracellular acidic polysaccharides produced by phytoplankton and bacteria in saltwater, freshwater, and wastewater. They are incredibly abundant and play a significant role in biogeochemical cycling of carbon and other elements in water. Through this, they also play a role in the structure of food webs and trophic levels. TEP production and overall concentration has been observed to be higher in the Pacific Ocean compared to the Atlantic, and is more related to solar radiation in the Pacific. TEP concentration has been found to decrease with depth, having the highest concentration at the surface, especially associated with the SML, either by upward flux or sea surface production. Chlorophyll a has been found to be the best indicator of TEP concentration, rather than heterotrophic grazing abundance, further emphasizing the role of phytoplankton in TEP production. TEP concentration is especially enhanced by haptophyte phytoplanktonic dominance, solar radiation exposure, and close proximity to sea ice. TEPs also do not seem to show any diel cycles. High concentrations of TEPs in the surface ocean slow the sinking of solid particle aggregations, prolonging pelagic residence time. TEPs may provide an upward flux of materials such as bacteria, phytoplankton, carbon, and trace nutrients. High TEP concentrations were found under arctic sea ice, probably released by sympagic algae. TEP is efficiently recycled in the ocean, as heterotrophic grazers such as zooplankton and protists consume TEP and produce new TEP precursors to be reused, further emphasizing the importance of TEPs in marine carbon cycling. TEP abundance tends to be higher in coastal, shallow waters compared to deeper, oceanic waters. Diatom-dominated phytoplankton colonies produce larger, and stickier, TEPs, which may indicate that TEP size distribution and composition may be a useful tool in determining aggregate planktonic community structure.
