Autotrophic Plankton

The initial, primary, endosymbiosis occurred about

1.5 billion years ago, when a eukaryotic heterotroph engulfed (or was invaded by) a cyanobacterium to form the photosynthetic plastids of the Plantae, the group that includes land plants and red and green algae. About 500 million years later, a secondary endosymbiosis occurred (figure below), in which a different eukaryotic heterotroph captured a red alga. Over time, the red-algal endosymbiont was transformed into the plastids of the Stramenopiles, the group that includes diatoms, brown macroalgae and plant parasites. Gene transfer continued from the red-algal nuclear and plastid genomes to the host nucleus. At least 170 red-algal genes have been identified in the nuclear genome of diatoms.

The reaction complex

Anoxygenic phototrophs have just one type, either type I (green shading above) or II (lavendar shading above), while all oxygenic phototrophs have one of each type. The primary distinguishing feature of the two types of RCs are the early electron acceptor cofactors, which are FeS centers in type I RCs and pheophytin/quinone complexes in type II RCs

the most significant physiological and ecological differences are between oxygenic and anoxygenic phototrophic bacteria

Both of these groups have representatives living in the marine environment. In the marine intertidal zone, both oxygen‐producing cyanobacteria and anoxygenic purple and green phototrophic bacteria often occur close together and may form colored blooms and microbial mats.

richodesmium is unusual in a few ways

First, it is visually prominent, especially during surface blooms Second, Trichodesmium is unusual in that it simultaneously photosynthesizes and carries out nitrogen fixation. Normally, oxygen is poisonous to the process of nitrogen fixation, but in this case the oxygen is detoxified because its production is spatially and temporally segregated from nitrogenase within the cell. Third, Trichodesmium can transform dissolved phosphorus into phosphonate - which is not readily consumed by other organisms. Living in low-phosphorus environments, this gives Trichodesmium a potential advantage over its competitors and, as nutrient supplies to the ocean change with climate, could shift the composition of phytoplankton communities in the ocean.

Life history:

Holoplankton are organisms that spend their entire life cycles in the water column. Meroplankton spend only part of their life cycles as plankton and spend other parts as either benthic organisms on the seafloor and as larger, free-swimming nekton.

Functional grouping of plankto

Resource acquisition Life history Allometries

Allometries

Size may not seem like a functional group at first blush, but allometric scaling is used to relate cell or body size to factors including metabolic rate and predator-prey relationships.

Pyrrhophyta

The Dinoflagellata are sometimes called Pyrrhophyta , meaning "fire plants." This is because some species are capable of bioluminescence, in which chemicals made by the organism produce light in a chemical reaction. The dinoflagellates begin to glow as it gets dark, but will brighten considerably when agitated, such as in the wake of a ship. The phenomenon was first noted in the genus Noctiluca, which resulted in its name ("night light"), but the reaction is now known to occur in several marine species.

Diatoms may be divided into two main groups based on their morphology and life cylces

The centric diatoms, or Centrobacillariophyceae, exhibit radial symmetry The pennate diatoms, or Pennatibacillariophyceae, typically exhibit bilateral symmetry

diatoms

The most diverse group of phytoplankton 200,000 different species, ranging in size from a few micrometres to a few millimetres and existing either as single cells or as chains of connected cells. About one-fifth of the photosynthesis on Earth is carried out by diatoms. Diatom photosynthesis in the sea generates about as much organic carbon as all the terrestrial rainforests combined. unlike much of the carbon generated by trees, the organic carbon produced by diatoms is consumed rapidly and serves as a base for marine food webs.

defensive trichocysts

These are discharged upon rapid hydration, ejecting long rod-shaped protein filaments similar to those found in ciliates like Paramecium. The effect is much like an exploding can of spray-string.

Resource acquisition:

Traditionally plankton were subdivided into the phytoplankton (photosynthetic plankton) and the zooplankton (heterotrophic plankton). As our understanding of plankton has grown, we now include mixotrophic categories (capable of both auto- and hetero- trophy).

Molecular-clock-based estimates suggest that diatoms arose in the

Triassic period, perhaps as early as 250 Myr ago, although the earliest well-preserved diatom fossils come from the Early Jurassic, some 190 Myr ago. Before the diatoms, the phytoplankton consisted primarily of cyanobacteria and green algae only slightly larger than bacteria.

Cryptophytes

acquired photosynthesis by secondary endosymbiosis, and their plastids possess four membranes. They have retained the nucleus of their endosymbiont in a miniaturized form called a nucleomorph. Nucleomorphs were first described in cryptomonads as tiny double-membrane-bound bodies nested between the inner and outer pairs of plastid membranes, with nuclear pore-like structures and an electron-dense region resembling a nucleolus. asymmetric cell shape. They have a cell invagination at the ventral side lined with ejectosomes (explosive organelles) and flagella

Cell size is ultimately restored through sexual reproduction Pennates

also have a size requirement for the initiation of sexual reproduction, but seem to form gametes only when they find an appropriate mate of the opposite sex, a seemingly less risky option. When paired, pennate cells produce morphologically identical gametes, which are unable to swim and instead move towards one another in an amoeba-like fashion and fuse to create the zygote and auxospore, which breaks free of the old cell wall.

The green nonsulfur bacteria (Chloroflexaceae)

also known as filamentous and gliding green bacteria are anoxygenic phototrophic bacteria that contain bacteriochlorophyll c or d in their chlorosomes. They move by gliding, are tolerant to oxygen, and grow preferably as photoheterotrophs. They have been observed microscopically in marine habitats, but pure cultures of marine representative do not exist. These bacteria are adapted to hot freshwater environments.

plastid acquisition

an event in evolutionary history happening million of years ago, some modern unicellular organisms ingest algae and utilize them as temporal chloroplasts (kleptoplasts) for weeks to months before digesting them. One example involves a cryptomonad. The dinoflagellate Nusuttodinium aeruginosum ingests the cryptomonad Chroomonas sp. and enlarges the kleptoplast with the aid of the cryptomonad nucleus.

photosynthesis

ancient process that originated not long after the origin of life and has evolved via a complex path to produce the distribution of types of photosynthetic organisms and metabolisms that are found today.

The purple sulfur bacteria (Chromatiaceae and Ectothiorhodospiraceae) and the purple nonsulfur bacteria

anoxygenic phototrophic bacteria that contain bacteriochlorophyll a or b in the light‐harvesting complexes located in the cytoplasmic membrane and various kinds of invaginations of it. Bacteria of this group are the most prominent and abundant anoxygenic of phototrophic bacteria in marine environment. Purple sulfur bacteria can form spectacular mats in the intertidal zone.

The green sulfur bacteria (Chlorobiaceae)

anoxygenic phototrophic bacteria that contain bacteriochlorophyll c, d, or e in light‐harvesting complexes located in special light‐harvesting organelles, the chlorosomes. They are obligately phototrophic, require strictly anoxic growth conditions, and have a low capacity to assimilate organic compounds. They mainly use sulfide ions as electron donors. Depending on the pigment content, a number of green‐colored and corresponding brown‐colored species are known. Several species have been found in marine and also hypersaline environments, in which under appropriate conditions intensively colored, visible mass developments are formed.

Of the three domains of life, Bacteria, Archaea, and Eukarya, chlorophyll-based photosynthesis has only been found in the ____ and ____ domains.

bacterial and eukaryotic

The life cycle of coccolithophores

characterized by an alternation of diploid and haploid phases. They alternate from the haploid to diploid phase through syngamy and from diploid to haploid through meiosis. In contrast with most organisms with alternating life cycles, asexual reproduction by mitosis is possible in both phases of the life cycle.

Mixotrophs

combine photosynthesis and food ingestion to harvest both energy and nutrients, and are quite common in marine phytoplankton, with the diatoms being a noteworthy exception. Mixotrophy can be found in all dinoflagellate orders, even if evidence is stronger in some taxa. Most dinoflagellates have complex life cycles, and in some cases mixotrophic behavior is only apparent in some life stages. For example, P. piscicida lacks chloroplasts and is heterotrophic for most of its life, except in its flagellated zoospore stage where the cells contain functional kleptochloroplasts stolen from ingested cryptophytes.

Coccoliths

complex architecture (see photos below); they may have spines or an elaborated rim, and come in an amazing variety of shapes -- pentagons, muffin-shapes, baskets, donuts, or even trumpet-like shapes are known. These plates are formed by deposition within the Golgi apparatus, and are often embedded in mucilage. Variations in coccolith morphology and coccolith combinations form the basis for classifying coccolithophores, although recent observations have shown that coccolithophores once regarded as separate taxa with different cell coverings are actually diploid and haploid phases of a single life cycle.

Photosynthetic phyla

cyanobacteria, proteobacteria (purple bacteria), green sulfur bacteria, heliobacteria, the green nonsulfur bacteria (filamentous anoxygenic phototrophs), and acidobacteria. Essentially all members of the cyanobacteria phototrophic.

eukaryotic photosynthesis originated from

endosymbiosis of cyanobacterial-like organisms, which ultimately became chloroplasts

Eukaryotes are thought to have evolved the capacity for photosynthesis through a process called

endosymbiosis, in which a protist host encapsulated a photosynthetic cyanobacterium. The first such endosymbiotic event gave rise to the group called archaeplastida, which includes glaucophytes, red algae, green algae, and land plants. Phytoplankton groups that occur as photosynthetic cells belong to the informal taxonomic group Protista. As with the photosynthetic bacteria, we can use functional groups to organize protists based on how they acquire nutrients and energy.

Haptophytes

golden-brown color because of the presence of the yellow-brown accessory pigments, diadinoxanthin and fucoxanthin, a feature they share with other Chromista. These are contained in the one or two plastids that are present in the cell. The name Haptophyta was originally applied to the group because of the presence of the unique organelle, the haptonema. This is a peg-like structure that extends out from the cell near the point where the two flagella are attached. The haptonema was originally thought to be a third flagellum, but has since been found to have a quite different morphology, and its function is unknown.

Green Algae

green phytoplankton (Chlorophyta) in the ocean is poorly known because most studies have focused on groups with large cell size such as diatoms or dinoflagellates that are easily recognized by traditional techniques such as microscopy. Representatives of green algae are mostly found in small size fractions, in particular the picophytoplankton (cells from 0.2 to 2 µm) and nanophytoplankton (cells from 2 to 20 µm). They are mixotrophic, using photosynthesis and ingestion of bacteria and other organic matter for energy. Evolution of photosynthesis in the Chlorophytes originates from primary endosymbiosis so they have a chloroplast surrounded by only two membranes and possess chlorophyll b as the main accessory chlorophyll. These plankton can occur either as as solitary coccoid green cells or as loose colonies or aggregates. They are morphologically diverse, including flagellates with one to eight flagella and non-motile, coccoid cells. The cells of many species are covered with organic body scales; others are naked. Reproduction may be asexual or isogamous sexual.

Phototrophic organisms

have the ability to grow on the basis of light‐mediated energy transformation as the principal source of energy.

Photosynthetic organisms

have the ability to perform light‐mediated energy transduction.

Cyanobacteria carry out nitrogen fixation

in which gaseous N2 is converted to NH4+ (ammonium), which is then available for use in the synthesis of amino acids and protein

The most common means of producing more dinoflagellates is

is asexual cell division, or mitosis. This process "splits" the organism, producing two identical copies. The theca may be shed (and regrown in each of the daughters), or it may be divided, with each daughter receiving half and regrowing half. A few genera grow as filaments. These are formed when the cells do not separate after dividing. dinoflagellates are haploid, so when the sexual cycle begins, gametes are formed by simple mitosis. They may be naked or armored, looking like small versions of the "parent". The "male" and "female" gametes may or may not look alike, but they are always free-swimming. Upon fusion of the two gametes, a planozygote may be formed . This is an actively swimming zygote, as compared to the "usual" non-motile zygote of plants and animals. It is the zygote stage which may form a cyst called an hystrichosphere or hypnozygote (5 in figure) under unfavorable conditions. This is a dormant capsule which protects the dinoflagellate until favorable conditions return

Photosynthetic dinoflagellates have eyespots

light-sensitive organelles composed of lipid droplets packaged within stacked layers of membranes. These contain carotenoid compounds, which are light- excitable, allowing the organism to detect the direction of the light source. A few rare species have a more complex structure, the ocellus, which uses a refracting lens to focus a projected image on the retinoid lining membrane. Not bad for a unicellular critter!

have two dissimilar flagella,

long clusters of protein strands which can be manipulated for movement. The two flagella are of different sorts-- that is, they are constructed and move in different ways. One flagellum lies in a groove, the sulcus that runs between the thecal plates from the center of one side, to the posterior end of the cell. When this posteriorly oriented flagellum beats backs and forth, it propels the dinoflagellate in the opposite direction -- anteriorly. The other flagellum is flattened and ribbonlike and lies in a groove, the cingulum, that encircles the cell, dividing it into its two primary regions. This flagellum allows the dinoflagellate to turn and maneuver, as well as providing forward movement. The combined action of these two flagella may cause the dinoflagellate to slowly turn on its axis as it moves through the water, and this is where the group gets its name.

Coccolithophores

marine haptophytes that produce calcareous scales called coccoliths inside the cell that are subsequently extruded to form an exoskeleton, termed a coccosphere. 300 different species. The morphological diversity of their coccoliths is preserved in a continuous and complete fossil record spanning the last 200 million years. Coccolithophores are generally considered to be phototrophs. However, there is an increasing body of evidence that coccolithophores are mixotrophic, engulfing small organic particles and taking up other simple carbon molecules from seawater.

Diatoms reproduce primarily by

mitotic divisions interrupted infrequently by sexual events. Diatoms only construct new walls during cell division. After the cell divides, the epitheca and hypotheca separate, and new valves are laid down between them. Because the frustule cannot grow once it has been laid down, the mean size of a dividing population of diatoms gets smaller and smaller with time.

organisms that can use photosynthesis, prey upon other organisms or feed on organic material dissolved in the ocean = Organisms that use photon capture to produce complex organic compounds in sufficient enough concentration to grow = bacteria that use water as photosynthetic electron donorsand produce molecular oxygen = bacteriathat use reduced substrates such as sulfide or ferrous iron as photosyntheticelectron donors but do not produce oxygen during photosynthesis =

mixotroph phototroph oxygenic phototroph anoxygenic phototroph

Cell size is ultimately restored through sexual reproduction centric

occurs differently in centric and pennate diatoms. In centric diatoms , only small cells are receptive to an environmental trigger and can become either sperm, which break free of the wall, or eggs, which remain encased within the wall. Sperm swim to an egg, gain entry past the glass wall, and fertilize the egg nucleus. The resultant zygote swells to form a specialized cell known as the auxospore, sheds its old cell walls and produces a much larger wall, restoring cell size. This is risky for a centric diatom because if sperm are unable to find eggs in the dilute ocean, the gametes will die.

Plankton nets

of different mesh sizes can be used to target specific size classes, but nets can damage plankton that do not have strong structural parts.

Planktonic organisms

organisms that cannot actively swim against currents. In contrast nekton are organisms that can swim strongly against currents.

The Cyanobacteria (including those known as prochlorophytes)

phototrophic bacteria performing an oxygenic type of photosynthesis. In addition, some representatives are able to use reduced sulfur compounds as photosynthetic electron donors and under these conditions use only one photosystem in an anoxygenic type of photosynthesis.

Silicoflagellates

planktonic marine chromists (Dictyochophyceae) that contain chromatophores for photosynthesis. Silicoflagellates are mixotrophic and capable of phagocytosis. Their internal silica skeletons are composed of a network of bars and rings Silicoflagellate skeletons may vary considerably within a single species, making it difficult to define species. first appear in the Early Cretaceous and become common in the Late Cretaceous. They were somewhat more diverse in the early Cenozoic than they are today. Silicoflagellate skeletons usually comprise 1-2% of the siliceous component of marine sediments; they are thus much less abundant than diatoms. However, they are widely distributed throughout the world ocean. Living silicoflagellates propel themselves with one long eukaryotic flagellum, or undulipodium. The spines on the skeleton may function in retarding sinking, which is of obvious importance to a photosynthetic organism. sexual reproduction by isogamy and asexual reproduction by aplanospores and statospores.

Aerobic bacteriochlorophyll‐containing bacteria ("ABC‐bacteria")

represent chemoheterotrophic bacteria with the potential to produce photosynthetic pigment‐protein complexes and to perform light‐mediated photosynthetic electron transport processes. From what is known about these bacteria, it is reasonable to assume that they grow just as other chemotrophic aerobic bacteria in the dark of the deep sea but make use of their photosynthetic apparatus in illuminated environments to gain additional metabolic energy.

Diatoms are

single-celled organisms which secrete intricate skeletons. The skeleton of a diatom, or frustule, is made of very pure silica coated with a layer of organic material. This skeleton is divided into two parts, one of which the epitheca overlaps the other the hypotheca like the lid of a box or petri dish. Both epitheca and hypotheca are made up of two or more parts: the valve, a more or less flattened plate, and at least one hoop-like rim called either a pleural band or cingulum. Both parts of a frustule may be highly perforated. Pennate diatoms show a long slit, the raphe, along the long axis. Through the raphe, the living diatom secretes mucilage, with which it may attach to a substrate or move by gliding over the substrate.

Archaea

some chemoheterotrophic Archaeans possess retinal‐containing proteins that function as proton pumps and establish a light‐driven transmembrane proton gradient. They gain selective advantage in illuminated environments by this ability to use light‐driven membrane energetization.

Water bottle samplers

that are submerged and automatically closed at depth are used to capture fragile or extremely small planktonic organisms.

Distribution

the most dominant types of phytoplankton in the world's oceans, with Prochlorococcus ruling much of the globe and bigger diatoms dominating nearer the poles.

Dinoflagellates

unicellular eukaryotes that appeared ~400 MYA and still thrive today in most marine and freshwater ecosystems. surrounded by a complex covering called the amphiesma, which consists of outer and inner continuous membranes, between which lie a series of flattened vesicles. In armored forms, these vesicles contain the thecal plates, cellulose plates that are the "armor". This armor may be lacking (the cells are "naked"), and some species shed their theca under certain environmental conditions. Armored dinoflagellates have two major plate regions composed of between 2 and 100 individual plates The edges of the plates overlap, sliding apart as the cell increases in size and allowing the cell to expand. Some species have ridges or crests. In some, the crests may be hollow and house cyanobacteria which provide fixed nitrogen to the host. This is most common in nitrogen-poor waters.

Cyanobacteria usually inhabit

upper part of the photic zone in the sea. The most abundant phototrophic organism in the global ocean environment, most likely, is a very small oxygenic phototrophic prokaryote, Prochlorococcus marinus.

Anoxygenic phototrophic bacteria

use reduced substrates such as sulfide, hydrogen, ferrous iron, and a number of simple organic substrates as photosynthetic electron donors but do not produce oxygen during photosynthesis

Oxygenic phototrophic bacteria

use water as photosynthetic electron donors and produce molecular oxygen (cyanobacteria),

The filamentous cyanobacterium Trichodesmium

was first noticed in the ocean near Australia by the explorer Captain Cook. Trichodesmium is encountered in high abundance in western boundary currents (for example, the Gulf Stream, Kuroshio), in tropical portions of the central gyres, and in several ocean margin seas. The water column of these environments is generally very stable, with the upper mixed layer often around 100 m. This zone is characterized by low nutrient concentrations, very clear waters, and deep light penetration.

Diatoms tend to dominate phytoplankton communities in

well-mixed coastal and upwelling regions, as well as along the sea-ice edge, where sufficient light, inorganic nitrogen, phosphorus, silicon and trace elements are available to sustain their growth. In polar environments, where glaciers and permafrost limit photosynthesis on land, diatoms are critical components of the food webs that sustain both marine and terrestrial ecosystems. Larger species of diatoms can move up and down through the water column by controlling their buoyancy. Certain open-ocean species can move between well-lit but nutrient-depleted surface waters, in which they photosynthesize, and nitrate-rich waters at a depth of about 100 m, where they take up and store the nutrients necessary to keep dividing. Diatoms seem to have exquisite communication capabilities, using a nitric-oxide-based system that mediates signalling between and within cells and regulates the production of aldehydes, which can be harmful to grazing copepods

symbiotic partners

zooxanthellae may be found in many marine invertebrates, including sponges, corals, jellyfish, and flatworms, as well as within protists, such as ciliates, foraminiferans, and colonial radiolarians. In each case, the host organism is able to swallow the dinoflagellate and incorporate it into its own tissues without harming it. The dinoflagellate then divides repeatedly to increase its numbers, and begins to manufacture carbohydrates which are provided to the host. The degree of interdependence varies greatly -- the sea anemone Anemonia can survive quite well without its zooxanthellae, while certain corals rely almost exclusively on the food from their symbionts, and build reefs much faster with the dinoflagellates present in their tissues.