In aquatic ecosystem the limiting factor for the productivity is

What is Ocean Productivity? Ocean productivity largely refers to the production of organic matter by " phytoplankton," plants suspended in the ocean, most of which are single-celled. Phytoplankton are " photoautotrophs," harvesting light to convert inorganic to organic carbon, and they supply this organic carbon to diverse " heterotrophs," organisms that obtain their energy solely from the respiration of organic matter. Open ocean heterotrophs include bacteria as well as more complex single- and multi-celled " zooplankton" (floating animals), " nekton" (swimming organisms, including fish and marine mammals), and the " benthos" (the seafloor community of organisms). The many nested cycles of carbon associated with ocean productivity are revealed by the following definitions (Bender et al. 1987) (Figure 1). "Gross primary production" ( GPP) refers to the total rate of organic carbon production by autotrophs, while " respiration" refers to the energy-yielding oxidation of organic carbon back to carbon dioxide. "Net primary production" ( NPP) is GPP minus the autotrophs' own rate of respiration; it is thus the rate at which the full metabolism of phytoplankton produces biomass. " Secondary production" ( SP) typically refers to the growth rate of heterotrophic biomass. Only a small fraction of the organic matter ingested by heterotrophic organisms is used to grow, the majority being respired back to dissolved inorganic carbon and nutrients that can be reused by autotrophs. Ther...

By:Michael F. Chislock( Department of Fisheries and Allied Aquacultures, Auburn University),Enrique Doster( Department of Animal Sciences, Auburn University),Rachel A. Zitomer( Department of Biological Sciences, Humboldt University)&Alan E. Wilson( Department of Fisheries and Allied Aquacultures, Auburn University)©2013Nature Education Eutrophication is characterized by excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis (Schindler 2006), such as sunlight, carbon dioxide, and nutrient fertilizers. Eutrophication occurs naturally over centuries as lakes age and are filled in with sediments (Carpenter 1981). However, human activities have accelerated the rate and extent of eutrophication through both point-source discharges and non-point loadings of limiting nutrients, such as nitrogen and phosphorus, into aquatic ecosystems (i.e., cultural eutrophication), with dramatic consequences for drinking water sources, fisheries, and recreational water bodies (Carpenter et al. 1998). For example, aquaculture scientists and pond managers often intentionally eutrophy water bodies by adding fertilizers to enhance primary productivity and increase the density and biomass of recreationally and economically important fishes (Figure 1) via bottom-up effects on higher trophic levels (Boyd & Tucker 1998). However, during the 1960s and 1970s, scientists linked algal blooms to nutrient enrichment resulting from ant...

Marine ecosystems are aquatic environments with high levels of dissolved salt, such as those found in or near the ocean. Marine ecosystems are defined by their unique biotic (living) and abiotic (nonliving) factors. Biotic factors include plants, animals, and microbes; important abiotic factors include the amount of sunlight in the ecosystem, the amount of oxygen and nutrients dissolved in the water, proximity to land, depth, and temperature. Sunlight is one of the most important abiotic factors for marine ecosystems. It’s so important that scientists classify parts of marine ecosystems—up to three—by the amount of light they receive. The topmost part of a marine ecosystem is the euphotic zone, extending down as far as 200 meters (656 feet) below the surface. At this depth, there is sufficient light for regular photosynthetic activity. Most marine life inhabits this zone. Below the euphotic zone is the dysphotic zone, which can reach from 200 to as deep as 1,000 meters (656 to 3,280 feet) below the surface. At these depths, sunlight is still available, but only enough to facilitate some photosynthesis. Below the dysphotic zone lies the aphotic zone, which does not receive any sunlight. Types of Marine Ecosystems Scientists divide marine ecosystems into several broad categories, although there are discrepancies depending on the source about what qualifies as a marine ecosystem. The number of marine ecosystems is actively debated. Although there is some disagreement, several...