When do phytoplankton use asexual reproduction

Samples are taken in the field using plankton nets for collection of specimens. Mesh nets typically work well for capturing phytoplankton, but tiny nanoplankton must be filtered out of a water sample. The amount and type of plankton indicate overall water conditions and show plankton reproduction rates.

Efficient reproductive strategies are a hallmark of phytoplankton. When growing conditions are right, phytoplankton multiply quickly through various means of asexual reproduction. Green algae and bacteria can produce spores that continue dividing inside the parent cell.

Mature endospores are released to form identical offspring. Sexual reproduction involves recombination of genetic material to produce offspring with a unique genome. Biodiversity within a population helps a species adapt to adverse conditions such as heat or drought. Phytoplankton are found near the shore, in standing open water, on ice caps and near the surface of lakes where essential nutrients and sunlight are easily accessible for cell growth and division.

Phytoplankton living in the ocean are normally in the euphotic zone of the water column that is penetrable by sunlight. The euphotic zone is no deeper than feet; average ocean depth is around 13, feet, as estimated by the Woods Hole Oceanographic Institution. The typical life cycle of phytoplankton includes growth, reproduction and death. The life cycle can also include a period of dormancy that happens regularly or only when conditions are not conducive to growth.

For example, chrysophytes can form cysts or spores that remain dormant for months or decades. Some diatoms and dinoflagellates form cysts from winter to spring. Phytoplankton life cycles vary by species. For instance, marine flagellates Phaeocystis pouchetii produce tiny motile cells that keep multiplying until nutrient levels decline. Next, they form colonies surrounded by a sticky mucous coat containing nutrients that allow for continued reproduction. If nutrients drop off altogether, the membrane disintegrates and washes up on shore as smelly, gooey white foam.

Phytoplankton growth fluctuates with the seasons. Reproduction explodes in polar regions each spring when receding ice deposits rich nutrients on the surface of the water. Cool water is ideal for phytoplankton reproduction. In late summer, increased sunlight excites the pigments in floating phytoplankton, resulting in another growth spurt. Penguins have adapted their breeding cycle to coincide with peak times of phytoplankton reproduction. According to the National Snow and Ice Data Center , some of the largest fisheries in the world are located in the Bering Sea where plankton bloom profusely and sustain fish populations.

An abundance of phytoplankton attracts birds, insects, fish and animals, and enhances biodiversity in an aquatic biome. However, excessive reproduction of nontoxic phytoplankton can still be harmful because of resulting oxygen depletion and clogging of fish gills.

Some species of cyanobacteria produce toxins such as microcystin. Toxin producing harmful algal blooms HAB have occurred in every coastal state, according to the National Ocean Service.

HABs can sicken or kill humans in addition to marine life. Drinking water can be contaminated and beaches closed due to noxious odors and risk of infection. HABs occur seasonally in late summer when temperatures and nitrogen pollution spur phytoplankton growth. Lakes and oceans rich in nitrogen, iron and phosphate provide a smorgasbord for countless species of phytoplankton. Blooms often follow in the wake of hurricanes because nutrients get churned up from the bottom.

Growth rate slows when nutrients are in short supply. Other factors influencing reproduction include temperature, depth, light variability and saltwater concentration salinity.

Plankton is not found in many parts of the ocean due to a scarcity of iron in those regions. Depending on the species, phytoplankton meet all their energy needs through photosynthesis, or they can supplement their diet by consuming other living or decaying organisms.

The two major types of phytoplankton employ different strategies for acquiring food. For instance, dinoflagellates hunt and move through the water by swishing their tails; however, they are weak swimmers and cannot go against the current. Examples of planozyotes, which are characterized by two longitudinal flagella arrows instead of one, in Alexandrium minutum left and Alexandrium taylori right. The most common pathway reported until very recently was the transition of the planozygote to a quiescent, environmentally resistant stage known as resting cyst a dormant not motile hypnozygote with a thick wall.

Other types of quiescent stages are cysts with a thin wall and less capacity to withstand adverse environmental conditions than the resting cysts.

These cysts - found in the bibliography with different names such as temporal, pellicle or ecdysal cysts - can be sexual or asexual, this last case being the fastest way to produce a cyst. Examples of resting sexual and pellicle sexual and asexual cysts.

Top row: Resting sexual left and pellicle asexual right cysts in Lingulodinium polyedrum. Middle row: Resting sexual cyst left and multiple pellicle also sexual cyst right in Alexandrium taylori.

Bottom row: Resting sexual left and pellicle asexual right cysts in Alexandrium minutum. However, this general pattern is not always followed, and recently reported life cycles have shown to be quite more complex. In some species for which the sexual cycle has been reported no resting cyst is known e. Karlodinium veneficum , and division of the planozygote meiosis has been documented in an increasing number of other species; therefore this reinforces the idea that the planozygote can skip cyst formation e.

Figueroa and Bravo a, b and implies that meiosis can occur either after quiescence resting or pellicle cyst or without the need of going through a quiescence phase.

In some species of dinoflagellates, meiosis in resting cysts and in planozygotes has been observed through a phenomenon known as nuclear cyclosis e. This is a process associated with the first meiotic division, which consists of the swirling of the chromosomes within the nuclear envelope von Stosch Other recently discovered pathways in the sexual stage are: 1 in culture gametes can revert to an asexual phase and undergo binary fission asexual division rather than fusion e.

Gymnodinium nolleri , G. Uchida did not report planozygote division, but found that planozygotes do not encyst if cell density was below a certain threshold in the species Scrippsiella trochoidea and Gyrodinium instriatum. But what is causing the shift from an asexual to a sexual cycle? Although the reasons are mainly unknown and need further study, it seems that both endogenous and environmental factors can be responsible for the onset of sexuality, and that each species may have its specific triggering conditions.

Sexuality has been traditionally achieved in culture through nutrient depletion, with temperature and light being important modulators of the cyst yield Sgrosso et al. However, gamete pairing and planozygote formation in nature may not be always linked to nutrient shortage, giving that sexuality has been observed either at the termination of blooms Persson et al.

Planozygote nuclei in Gymnodinium nolleri left and Alexandrium minutum right, undergoing meiosis. Mitosis in nuclei of Gymnodinium catenatum left and Alexandrium margalefi right.

There are two basic mating systems in dinoflagellates, homothallism and heterothallism, and both groups have isogamous fusing gametes are similar to each other and anisogamous fusing gametes of different sizes representatives. Isogamous left, Gymnodinium nolleri and anisogamous right, Alexandrium tamutum gamete pairs. Fusing gamete pair in Gymnodinium catenatum left and its nuclei in fusion process. In homothally, the gametes can be genetically identical.

This is the case for example in the species Alexandrium taylori Giacobbe and Yang In heterothally, genetically determined factors in the gametes allow successful mating, sexual fusion and meiosis. In this last case, the sexual compatibility can comprise only two different mating types simple heterothallism , such as in Lingulodinium polyedrum Figueroa and Bravo b or more complex heterothallism , such as in Alexandrium minutum Figueroa et al.

These definitions when applied to resting cyst hypnozygote producing species imply that cyst production and viable progeny are possible within clones of homothallic species self-fertile , whereas two different clonal strains are needed to obtain viable cysts in heterothallic ones self-sterile. However, different mating systems can occur within the same species, and for example a continuum between homothally and heterothally has been described in the species Gymnodinium catenatum Figueroa et al.

Sexual reproduction is thought to be essential for seasonal survival of these species, although asexual resting cysts are also known in Scrippsiella hangoei Kremp and Parrow Dinoflagellate cysts in the sediment can provide the inoculum for future blooms after a long time, given that they can remain viable in the sediments up to years Ribeiro et al. A heteromorphic life stage such as the cyst can represent an advantage because it allows the allocation of the species into different niches planktonic and benthic , and because different life stages of the same organism usually interact with the environment in quite different ways.

In many species, planktonic stages are only an ephemeral phase of the organism's life cycle, dispersion and concentration of the dormant non-motile cells being determined by the same forcing functions that control the dynamics of passive particles in the water and in the sediments.

Dormancy and maturation of resting cysts are biological processes essential for the dinoflagellate population. The dormancy period is a maturation time in which the biological activity growth is suspended. N2 - A rapid method for measuring, simultaneously, the asexual reproduction rates of hundreds of phytoplankton cultures is described.

AB - A rapid method for measuring, simultaneously, the asexual reproduction rates of hundreds of phytoplankton cultures is described. Overview Fingerprint. Abstract A rapid method for measuring, simultaneously, the asexual reproduction rates of hundreds of phytoplankton cultures is described.

Access to Document Link to publication in Scopus. Link to citation list in Scopus. Fingerprint Dive into the research topics of 'A method for the rapid and precise determination of acclimated phytoplankton reproduction rates'. Together they form a unique fingerprint. View full fingerprint. Journal of Plankton Research , 3 2 , In: Journal of Plankton Research , Vol.