User:NatalieRHolmes/Planktivore

Forms of Plankton
Phytoplankton are usually photosynthetic one-celled organisms. These organisms are usually found near the surface of the water due to their need for light energy for their photosynthetic processes. Phytoplankton provide most of the oxygen that is in the water and provide a large amount of food for other organisms in the water column.

Zooplankton are heterotrophic plankton, which are animals that ingest nutrients rather than producing them via chemical reactions. Zooplankton can provide an important food source for juvenile fish. Some taxa are planktonic for only part of their life cycle.

Forms of Planktivory
Most fish are planktivores during part or all of their life cycles, especially when they are larvae. There are obligate planktivores, which feed only on plankton, and facultative planktivores, which take plankton when available but eat other types of food as well. The gizzard shad (Dorosoma cepedianum), for example, has a voracious appetite for various forms of plankton across its life cycle. It is an obligate planktivore when it is a juvenile, in part due to its very small mouth size. As it grows it becomes an omnivore, taking phytoplankton, zooplankton, and larger pieces of nutritious detritus. Adult gizzard shad consume large volumes of zooplankton until it becomes scarce, then turn to organic debris for food.

Planktivores obtain food in two ways. Particulate feeders eat planktonic items selectively. Filter feeders process volumes of water and strain food items en masse. "Tow-net" filter feeders swim rapidly with mouths open to filter the water, and pumping filter feeders suck in water via pumping actions. The latter includes stationary animals, such as corals. Another form of filter feeding is a "gulping" behavior, in which the animal takes boluses of water; the alewife (Alosa pseudoharengus) feeds in this manner.

Marine
Some examples of marine planktivores include: reef manta ray, humpback whale , right whale, bowhead whale sea salp , and coral. There are also marine invasive species, which are destructive organisms that are non-native and damage the habitat they have invaded. One example of a marine invasive planktivore is the sea walnut.

Planktivores disproportionately contribute to the Indo-Australian Archipelago (IAA) biodiversity hotspot. Within the IAA, planktivorous coral reef fishes are especially concentrated around Indonesia, Papua New Guinea, the Philippines, and the Solomon Islands. Allochthonous particle transportation to coral reefs by ocean currents and tides provides an important food source for planktivorous fish.

Freshwater
Some examples of freshwater planktivores include: Rainbow smelt, Emerald shiner, American gizzard shad , Alewife , Golden shiner , Bigmouth buffalo , White perch, and Yellow perch. Some examples of invasive freshwater planktivores include: Bighead carp, Spiny water flea , zebra mussel , and Silver carp.

Ecological and Biogeochemical Significance
Plankton species are ecological indicators, meaning their presence gives insight into whether a system is functioning to the benefit of the organisms living within the ecosystem. Since planktivores eat plankton, planktivore presence and their abundance also indicates the health of an ecosystem by implying changes to water quality, water temperature, trophic level interactions, and sources of nutrients flowing to and from a water body. Understanding these changes can aid in assessing the appropriate conservation plans for more than just one species, especially larger, more charismatic species commonly highlighted for fundraising for conservation efforts such as basking sharks, seabirds, and sea turtles.

Effects on water quality
Seasonal bottom hypoxia is an expanding problem for water quality in marine and freshwater ecosystems. This form of hypoxia is caused by anthropogenic agricultural run-off and run-off from urban areas that result in the addition of chemicals and nutrients into surrounding water systems. Hypoxia affects the pelagic food web by reducing the amount of oxygenated water available for pelagic fishes and invertebrates to breathe. Although pelagic fishes and planktivores are restricted by hypoxic zones, zooplankton species have discovered how to use this to their advantage. Zooplankton species have been observed to seek refuge in hypoxic zones to avoid predation by planktivores that are unable to hunt in low oxygen areas with high temperatures. This causes the predation in layers of lakes, such as the epilimnion, metalimnion, and hypolimnion to be disrupted.

Effects on productivity
Seasonal upwelling of ocean and freshwaters occurs annually and can cause nutrients to mix around in the water column. This also causes plankton species to mix around instead of primarily existing above the thermocline.

Role in nutrient cycling
Studies on planktivores and plankton allow humans to better-understand marine management issues surrounding biogeochemical processes, such as ocean acidification. Ocean acidification impacts the ability of some planktviores to form their calcium-based skeletons, such as corals. The increased solubility of calcium carbonate shells and skeletons is due to the addition of carbon dioxide (CO 2 ) which interacts with water (H 2 O) to make carbonic acid that acidifies the waters. Carbon dioxide bioaccumulates in marine systems and adds to greenhouse gases which promotes climate change.