The change in a marine biological community from freshly dead to remineralization

1. The change in a marine biological community from freshly dead to remineralization Y.Parker, L.Nefdt, O.Matinisi 7 59 words Introduction: Change in the chemical composition of the ocean under certain conditions may lead to the death of many microorganisms, in particular plankton species. Most of the marine food supply of the benthos is provided by the downward transport of organic matter produced by the decomposition of phytoplankton on the ocean surface. Zooplankton assists in the modification of the sinking and suspended particles; this in turn has a significant effect on the material fluctuation on the benthos. Approximately 25 to 50% of the organic matter produced in the surface waters of the ocean are consumed by organisms living at the bottom of the ocean, the benthos. The organic matter in coastal waters is re mineralised at the bottom of the ocean, which results in a low nitrogen to phosphorus ratio. Surface interactions: Phytoplankton are usually found close to the surface of the ocean, they are known as the most common marine primary producers, therefore most marine organisms depend on them either directly or indirectly. Zooplankton are known to feed mostly on phytoplankton (diatoms and dinoflagellates), therefore their population size depends on the fluctuation of the diatoms/dinoflagellate blooms. The change of ocean chemistry, high surface temperatures in the ocean, high salinity and calm seas may affect the phytoplankton and zooplankton in a negative way, in that the acidity interferes with their ability to produce calcium carbonate which affects their physical functioning and reproduction, which may lead to death. When dinoflagellates (Figure 1), (a type of phytoplankton) bloom they are found concentrated in a specific area; the reddish-brown droplet within their cells cause the ocean water to appear as a red/brown colour (Figure 2). These blooms of dinoflagellates are called “Red tide”. In the process of a red tide, the dinoflagellate cells are known to die and their dead cells are decomposed by bacteria. During the decomposition of the dinoflagellate dead cells, the bacteria require a large amount of dissolved oxygen which has a negative effect on the marine organisms within the community. When a large amount of dissolved oxygen is being used up, fish and other marine organisms within the community that also require dissolved oxygen, suffocate due to a lack of oxygen in the areas that are exposed to red tide. Toxins released from dinoflagellates during a red tide are not toxic but have a negative effect on those individuals that consume organisms, such as shellfish that carry these toxins. Figure 1: Dinoflagellate colonies. Available from: http://www.marinebio.net/marinescience/03ecology/mlplankton.htm Decomposition: Figure 2: Dinoflagellate bloom . Sinking organic matter from the surface results from either decaying phytoplankton (Figure 3), faecal pellets produced by zooplankton which have consumed phytoplankton or the decay of any marine organisms on the surface. This forms the particulate organic matter (POM). Decomposition of nitrogen and phosphorus from the particulate organic matter from the phytoplankton occurs. During the decomposition of phytoplankton, communities of bacteria attach to the particulate organic matter (dead phytoplankton). Figure 3: Phytoplankton Available from: http://en.wikipedia.org/wiki/Phytoplankton Figure 4: Zooplankton Available from:http://www.biyolojiegitim.yyu.edu.tr/k/zoplnktnm/pages/zooplankton_jpg.htm Remineralization: Organic matter in the surface coastal waters of the ocean is remineralized at the bottom of the ocean (benthos) which results in a low nitrogen and phosphorus ratio. Denitrification on the benthos is responsible for the loss of fixed nitrogen during decomposition in the underlying sediment. It has been tested that decomposition has a thirty day storage. During the decomposition of phytoplankton, initially all the dissolved organic nitrogen released is remineralized. The remineralization of nitrogen and phosphorus is temperature dependant. The remineralization eventually slows down so that equal amounts of nutrients are remineralized after a thirty day storage. Marine snow is the main form of transport for decomposing phytoplankton as well as other dead organic material in the ocean. Bacteria help to solubilize and re mineralize the aggregated particles of plankton. Organic solutes leak out of the sinking aggregates which guide the zooplankton towards the aggregates. Zooplankton (Figure 4) is responsible for approximately 9% of the remineralization at the bottom of the ocean (benthos). The zooplankton is able to modify the sinking suspended particles, or aggregates of marine snow, which have a significant effect on the change of the organic material. Remineralization occurs until equal amounts of nutrients are re mineralized. The marine snow which reaches the benthos, forms part of the benthic sediment and provides a source of nutrients for many benthic organisms, such as scavengers and crustaceans. In some cases the marine snow will contain toxins from the dinoflagellate blooms which results in the decrease in oxygen concentration in the ocean and the death on some crustacean species (Figure 5, 6 and7). Figure 5: Anoxia caused by red tide. Available from: http://www.mnn.com/sites/default/files/user71/hypoxia.jpeg Figure 6: crustacean (crab) feeding on benthos. Available from: http://www.topnews.in/usa/2-new-crustaceans-found-iberian-peninsula-28098 Figure 7: crustacean (crayfish) feeding on benthos. Available from:http://www.indianetzone.com/43/crustaceans.htm