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.
