plankton

 

The term plankton has been derived from Greek and it supports the meaning of drifting or wandering. In scientific world, the term refers to the astoundingly diverse categories of plants and animals whose life cycles are spent fully or partly by wandering or drifting in either sea water or freshwater lakes. Though a large number of these organisms are empowered of mobility, typically they are not able move about without the help of waves and currents. Hence the lack of ability to swim, significantly distinguishes the plankton organisms from nekton such as fish that have the capacity of controlling their locomotion abilities in the water. The planktonic organisms vary in sizes and types with some being noticeably large and measuring up to a meter or more. However, generally the plankton organisms are much smaller in size than nekton and as such can only be properly viewed through a microscope. As the plankton comprises of a complex enigma of diverse organisms, they have been reclassified in multiple ways. The plant plankton is termed as the phytoplankton while the animal plankton is termed as the zooplankton. The plankton is also segmented according to their taxonomy and life cycles within the plankton (Dr. William Hamner, 2003). This report describes the various segmentations within the plankton life and its taxonomy. 

Significance of binomial nomenclature for scientific investigators

All sorts of identified species on earth are generically named with a two part scientific term which is known as binomial nomenclature. The scientific terms are important particularly for scientific investigators as they facilitate a universal language for communiatning unambiguously in relation to various animal species. Additionally the scientific naming system is designed in a manner to prescribe about a specific animal’s relationship to other animals. The generic epithet which denotes the name of the genus and the specific epithet contained in the name will ensure a more effective classification for each species. The first step in taxonomic organisation is related to the genus as all the species which are identified to be most generically related are confined together within a genus (Dewey T 2006).     

Another important aspect of binomial nomenclature lies in its descriptive nature. The name is an indication about the animal. According to Tanya Dewey (2006) the long ear sunfishes are named such due to their hardened structure and conspicuous operculum flaps that looks as if they have long ears and this particular long ear sunfish is scientifically named as megalotis which translates as big years.  Some names are given with a reference to the specific region in which they are found in abundance like the Eubalaena Australis given to the Southern right whales which translates in to a similar meaning like “Southern true baleen’.    

Defining Species

Despite the enhanced opportunities today to perceive even the finest details relating to organisms, there is ongoing debate on what actually constitutes of a species and how to define a species. According to past research (The process of speciation 2002) a definition of species is categorised in two main camps. The two main concepts are based on the biological species and the morphological species.

Does species definition apply to all life?

Morphological species

This indicates the structure and form relating to an organism or its parts. The concept widely supports the theory that members of a particular species are recognised as individuals who are similar from one to the other. This definition though attractive has its limitations mainly due to its arbitrary nature. Investigators have found many samples which look similar but do not mate with each other proving them to be different species despite belonging to the same population.

Biological species 

This defines species as a group of individuals who are potentially or actually interbreeding and who are secluded reproductively from other similar groups. The definition emphasizes that species is of evolutionary nature and that members of one species share genes with their own members and not with those of other species. Despite the widespread support for this concept it also has its own limitations. The theory cannot be tested on fossil data or museum specimens. It cannot describe the existence of species in lineage such as fossil horses. The theory is also not applicable to many living organisms such as hybrid created in zoos or species that lives in different places.

Comparison of phytoplankton and the zooplankton

The phytoplankton and the zooplankton are the two different but prime formations of the plankton. While phytoplankton is represented in the absolute bottom level of the food chain as they are in plant form the zooplankton is represented by the animal forms of the plankton. Examples for the phytoplankton are golden algae, diatoms, cyanobacteria and green algae. Some organisms of the phytoplankton are unicellular and range in the sizes between 1 millimetre to 10 meters. Examples for the zooplankton include small crustaceans, protozoa, worms, jellyfish etc. Some of these species are single celled and they have the ability to colonize. The zooplanktons represent the second level of the food chain as they depend on phytoplankton and bacteria to provide their substance. The phytoplankton being plants depend on the conversion of sunrays in the photosynthesis from the water in which they live. As they have to depend on the sun for their prime substance, phytoplankton can be seen living on the water surfaces allowing them plenty of access to the sun’s rays. However, zooplankton contains more nocturnal habitats as they prefer dark areas. As such they remain mostly in the deeper recess of the water where the minimum of sunlight is penetrated. They travel to the water surface mainly during the night times for their feeds.  

Both organisms play an important role for the marine ecosystem stability and both are valuable indicators of the water’s health. The plankton is easily influenced by temperature changes, acidity levels, increase or decrease of nutrients levels arising from farm runoffs as well as pollution. Harmful algae blooms are effective indicators of an environmental imbalance known as the red tide. A massive overgrowth of these algae can cause toxin production leading to the death of many marine species creating a dead zone within the water. The phytoplankton is also the contributor for half of the oxygen level produced in the world. In addition to being the creators of the marine food chain base these organisms are highly useful for safeguarding the general atmosphere in which we live (source E-How).

Comparison of holoplankton & meroplankton

Due to the extreme diversity of the plankton organisms and to appreciate the assemblage of them it has been further classified in to two more groups which are named as the holoplankton and the meroplankton. The holoplantonic species live through out their entire life by wandering or drifting within their plankton. As such they produce, live and die within the planktonic community. Examples for these organisms are diatoms which also fall in to phytoplankton category and copepods which are represented by the zooplankton. Scientists claim that copepods who analogues in to insects to be the most abundantly seen animals in the world. They are also identified as the primary grazers of the phytoplankton which forms another significant link within the marine food chain.

On the other hand meroplanktonic organisms spend only a part of their lives by drifting within the plankton. They live within it during the development period known as the larvae. The larvae are a unique stage as it does not in any way resemble the adult formation and they need metamorphosis at the time they arrive at a suitable habitat.  Nearly all zooplankton are represented as meroplanktonic and some single species possess multiple larval stages. The development stages of some fish, benthic invertebrates such as clams and worms are examples (Source Marine biology field trip – internet).

Recruitment and its significance to marine organisms

The planktonic life typically covers a massive range of life forms as well as life histories. Nearly all benthic invertebrates and benthic algae has planktonic phase within their lifecycles as mentioned earlier. As such the larvae should survive their period within the plankton before initiating their benthic way of life in a different habitat or hard substrate. This transition from a pelagic form of life to a benthic habitat through a process of recruitment is known to be one the most highlighted and important occasions in the life history of these marine organisms.

 

However, the entire process of recruitment has not been defined clearly to date and it is not based on a specific life stage, process or history. According to Keough and Downes in 1982 the recruitment process reflects a mishmash of settlement and post settlement periods of random length which in most cases is ascertained by the time length before the settling organism is noted by an observer.  

The incorporation of these young organisms to an adult population which is termed as the recruitment process is important to all types of marine organisms. However, in the case of benthic organisms the process has added emphasis. For example mollusks spend a larvae period in their planktonic phase for approximately 6 weeks within a temperate zone. In the presence of tidal currents the mollusks parent population lives apart from their colonization patches. The mollusks select a substratum that would enhance their chance of survival and as such this selection process is also vitally important in their life cycle. The larvae can decide on the appropriateness of their substrate through a process of recognition mechanisms. One such example is the attraction by individual organisms contained in the adult population. This acts as a good indication and proof that a particular substratum can support the continued existence of individuals belonging to the same species.  

Conclusion

Due to the ongoing taxonomic chaos at present there is concern about the taxonomic stability as many scientists do not subscribe to the same concepts and theories regarding species. As a result of the species debate some species consisting of a variety of subspecies have been divided into multiple species. Even though the massive diversity of life circles and the body plans consisted within the plankton can at first glance seem overwhelming, it is heartening to acknowledge that all organisms should essentially achieve similar goals in respect of growth, reproduction and survival. In the context of life within the plankton the complex behavioural mechanisms and a process of settlement and recruitment will set the scene for complex adult interactions that will ensue.