Phytoplankton provide food for a large variety of organisms, including the microscopic animals (such as the zooplankton), bivalve molluscan shellfish (like mussels, oysters, scallops, and clams), and small fishes (such as anchovies and sardines). To continue the food chain, these group of animals then provide their own kind of food to other group animals like crabs, starfish, fish, marine birds, marine mammals, and humans (Karl, et al., 2001). Figure 1. Sample food chain involving phytoplankton

Source: (www.planktonfyi.com/images/foodchain.jpg,2006).

Mortality Rate of Phytoplankton

It was recorded that from 1980's to the present, phytoplankton have been continuously increasing in frequency and distribution worldwide. The reason for such continuing increase in biomass is yet to be determined, but scientists have provided several assumptions including (Karl, et al., 2001):

continuously increase of nutrient input to coastal areas because of massive and productive human activities

Climactic changes that are in large-scale forms (such as global warming)

Movement or transport of toxigenic species in ship counterbalanced water

Improved use of coastal resources

Increased surveillance positive intervention of the government health agencies and researchers.

Figure 2. Biomass distribution of phytoplankton

Source: (www.astro.temple.edu/~sanders1/balance.gif,2006)

Figure 3. Generalized Seasonal Changes in Phytoplankton, Sunlight and Dissolved Nutrients

Source: (www.astro.temple.edu/~sanders1/balance.gif,2006)

Figure 4. Generalized Changes in Phytoplankton Biomass

Source: (www.astro.temple.edu/~sanders1/balance.gif,2006)

Biodiversity of Phytoplankton

Despite continued human intervention and technological advancements, which sometimes hindered most marine animals from continuously reproducing, he phytoplankton have survived and have been to be continuously increasing in mortality rate.

In fact, reports revealed that there have been and increasing diversity of marine phytoplankton (Anya, 1996).

This continued diversity in marine phytoplankton can be attributed to their ability to adapt with the environment, however frequent the changes may occur. There are significant deviations in the environment where phytoplankton live and through time, different species have responded differently to changes in the environments (Anya, 1996).

Over time, scientist have been noting how phytoplankton are able to adapt with the evolutionary changes from oceans to calm waters, even from increasing numbers of predators to changing vertical gradients in the light intensity and nutrients which are essential means of growth. Each phytoplankton have been redefining itself and capitalizing on different combinations of the said factors, thereby creating a new and unique shape, size, and physiology helping them for their survival. There are specific types of phytoplankton which are able to response quickly to the ever-changing requirement of the environment. Some phytoplankton are able to develop their own flexible response to the environment. Also there are instances wherein phytoplankton are able to develop high forms of tolerance to a wide range of possible habitats, while other phytoplankton's requirements are more specific. Because of these variations, the quality and forms of phytoplankton existing nowadays are believed to be enormously diverse species assemblage (Anya, 1996).

Logically, these diversions would result to changes in oceans creating uniformity across wide areas. However the diversity of species within phytoplankton can potentially threaten by those which have inputted heavy amounts of nutrients as caused by sewage or large-scale industrial pollution (Anya, 1996).

The abilities of phytoplankton to reproduce, adapt and change over time despite the hindrances and difference in the environment also vary to the type of phytoplankton there is. There are two major groups of large ultra-phytoplankton - the dinoflagellates and the diatoms (which have been showing signs that they can adapt very differently to ocean dynamics). It must be noted that dinoflagellates are considered as one of the most peculiar groups in the ocean. Dinoflagellates are commonly described to have a size one-fifth of a millimeter in diameter, which contains membrane-covered organic shell. Dinoflagellates are most commonly seen on waters because here, they can gather at the surface to photosynthesize and then plunge down again to swallow down the nutrients presented in the deeper water levels. Although dinoflagellates are usually solitary in nature, they are still able to form chains of cells that swim as a unit (Anya, 1996).

It should also be noted that dinoflagellates are the type of phytoplankton that maintain a unique form of highly abundant DNA. These DNA remain condensed into chromosomes throughout the dinoflagellates' cell cycle. Even dinoflagellates, as a specific type of phytoplankton, have varied forms. There are species of dinoflagellates which are partially or wholly herbivorous. There are dinoflagellates that actually eat other phytoplankton even if...

This they do by impaling them, enveloping them in a membrane, and eventually siphoning out the contents (Anya, 1996).
Most famous of the dinoflagellates are the species that congregate in high densities at the surface of water forming "red tide." Majority of the red tide species are known for their potent toxins, which when become concentrated are eaten by filter-feeding shellfish. These are what poison the human consumers (Anya, 1996).

Lethal and poisonous it may seem, these variations in the responses and actions of dinoflagellates are still important to verifying he real capacities and phytoplankton and the impact it can provide to the whole ecosystem in general. There are scientists who suggested that the frequency and intensity of red tides are increasing worldwide, and there are statistical evidences that can prove this. Further proving revealed that the continuous increase in red tides is an evidence for an increase in coastal pollution, since calm, nitrogen-rich waters are ideal for dinoflagellates' continued growth (Anya, 1996).

Like the dinoflagellates, the diatoms are equally unique with its own impact to the ecosystem. Diatoms are phytoplankton with heavy glass shells (called frustules). They are able to sink quickly out of the surface layer of the water level particularly if they have used up all the available nutrients. They would commonly remain to the darker sides of the water to be mixed upward again. The unusual thing for diatoms is the fact that they are dependent on vertical mixing so as to reach the ocean surface again. This then keeps diatoms to maintain their growth. Moreover, by pumping the internal vacuole full of substances lighter than seawater, the diatoms are able to continue living and/or surviving. During complimentary periods, diatoms are able to maximize their growth rates thereby optimizing the time allowed for them to surface and resurface which also allow them to reach high densities, especially in the springtime coastal ocean (Anya, 1996).

Conclusion

Phytoplankton are very unique part of the ecosystem. They have their own capacity to adapt themselves with the environment however fast the changes may be. With this alone, it will be of no doubt that phytoplankton are able to continue surviving and reproducing to higher densities despite the test of time.

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