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Plankton Diversity A. Phytoplankton

Diatoms Class Bacillariophyceae. Phylum Chrysophyta.

• Sometimes called the golden algae, because their characteristic yellow-brown pigments mask their green chlorophyll.

• Dominate the phytoplankton in waters from the temperate to the polar zones. • They either occur as single cells or form chains. • They range in size from 2 µm to 1 mm. • Each cell is encased in a transparent

silica shell of two valves that fit together much like a pillbox. The shell may be covered with spines, or it may be ornamented with a complex series of pores and ridges. The pores are the only connection between the cell and the external environment.

• Planktonic diatoms are usually radially symmetrical (shaped like a pinwheel) and are known as centric diatoms, in contrast to pinnate diatoms, which are bilaterally symmetrical and usually live in sediments (i.e. benthic).

• Diatoms reproduce very rapidly by binary cell division, with one valve going to each daughter cell and serving as the larger valve. A smaller valve is then formed. After several successive generations of cell division, cell size usually decreases to a lower threshold, when gametes are often formed. The smaller diatoms may also form an auxospore, which enlarges and casts off the valves, forms new large valves, and then undergoes asexual divisions. Some diatom species can form asexual resting spores with thickened frustle, which settle to the seabed and may be regenerated later as a planktonic form.

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• Because of their asexual mode of reproduction, diatoms can increase in population size rapidly, when their populations discolor the water, it is known as a bloom.

• Diatoms are most important as primary producers. Those that are not consumed by herbivores eventually die and sink to the ocean floor.

• The cell walls of diatoms that sink to greater depths build up siliceous sediments called the siliceous ooze.

Ooze: If fine sediments from the deep sea are more than 30% fine biogenous sediment by weight, then the sediment is known as an ooze.

Dinoflagellates Class Dinophyceae, Phylum Pyrrophyta or Dinoflagellata

• Exist at lower light levels than diatoms, because they can both photosynthesize like a plant and ingest organic materials like animals (i.e. mixotrophic).

• Some species are parasitic on or live within zooplankton. • Mostly unicellular forms, but some form chains. • They range in size range from 20-200 µm. • They have two flagellae, the transverse

flagellum is located in a groove (the girdle) that divides the cell into two subequal parts. The other flagellum is oriented perpen-dicularly to the transverse flagellum and extends toward the posterior. The two flagellae are resulted in the characteristic spinning movement of dinoflagellates.

• The organism is generally covered with a series of contiguous cellulose plates or theca. Naked dinoflagellates (without theca) are also known.

• Dinoflagellates reproduce asexually by binary fission and have the capacity to reproduce up to several times per day.

• Some dinoflagellates are called fire algae, because they glow with bioluminescence at night.

Dinoflagellate Blooms (Harmful Algal Bloom) and Red Tides

• Red tide is the phenomenon where certain species of dinoflagellate increase rapidly of sufficient magnitude (numbering >108 cells l-1) to color the sea-water a dull red-brown.

• The origin of red tides, like many other sudden blooms of phytoplankton, is an incompletely explained phenomenon. Red tides are often associated with

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sudden influxes of nutrients from land sources into the sea. It is also associated with storms, which may mix nutrients into the surface layer of the ocean and remobilize populations of cysts buried in the bottom sediment, setting the stage for red tides. Along some coasts, the most common times for phytoplankton blooms are in the spring, after winter storms have mixed nutrients into the surface layer of the ocean and when water with warmer temperature, the daylight is longer and the sun light is stronger.

• Some dinoflagellate species produce potent (قوي) toxins. Toxic species are generally not poisonous to shellfish feeding on a bloom, but the toxins are concentrated in the tissue of the shellfish and produce PSP, NSP, or DSP in humans who eat them. Toxins can be transferred through the food web where they affect and even kill the higher forms of life such as fish, birds, marine mammals, and even humans.

a) Paralytic Shellfish Poisoning (PSP): Algal cells contain highly lethal saxitoxin; accumulation of toxin in clams, mussel, scallops and fish lead to poisoning of people who eat them. In cases of severe poisoning, muscle paralysis and respiratory failure occur, and death may occur if the breathing centers are affected. The toxin is not affected by heat, so cooking the shellfish does not neutralize the poison.

b) Neurotoxic Shellfish Poisoning (NSP): algal toxin is brevetoxin (Gymnodinium breve); neurological & gastrointestinal symptoms; aerosols can produce asthma; no deaths reported

c) Diarrhetic Shellfish Poisoning (DSP): Okadaic acid, Dinophysis sp.; gastrointestinal symptoms (diarrhea, cramps تشنج) 30 min after consumption of toxic shellfish, not lethal, recovery ca. 3 days

d) Ciguatera Fish Poisoning (CFP): Ciguatoxin, Symptoms of ciguatera poisoning include headache, nausea, vomiting, abdominal cramps, and reduced blood pressure. Ciguatera poisoning is rarely fatal but in severe cases convulsions, muscular paralysis, and death may occur. Symptoms usually clear in 1 to 4 weeks.

Coccolithophores Phylum Chrysophyta

• Coccolithophores are unicellular and usually nannoplanktonic (mostly <20 µm).

• They are nearly spherical and are covered with a series of calcium carbonate (calcite) plates, or coccoliths.

• Like many phytoplankton, coccolithophorids can form immense blooms which settle down to the ocean floor producing chalk deposits called calcareous oozes or more precisely coccolithophore ooze, including chalk used for classroom chalkboards.

• Reproduce by simple cell division, rarely sexual reproduction.

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Silicoflagellates Phylum Chrysophyta

• Silicoflagellates are unicellular and biflagellate.

• They have numerous chloroplasts and an internal skeleton of silicon dioxide (SiO2) scales or framework.

• Their bloom can block sunlight from reaching underlying parts of the ocean.

Cyanobacteria

Class Cyanophyceae

• Also called blue-green algae, although they are prokaryotic bacteria, not true algae.

• Occur in and may dominate nearshore waters of restricted circulation, as well as brackish water.

• Tiny (roughly 1 µm) unicellular forms have been found ubiquitously throughout the ocean and may be the food of smaller zooplankton.

• Cyanobacteria can undergo nitrogen fixation, in which gaseous atmospheric nitrogen is converted to NH4+, or ammonium ion, and is then available for incorporation into amino acids and proteins.

Fig. The colonial planktonic blue-green cyanobacterium Trichodesmium thiebautii.

Green Algae

Class Chlorophyceae Phylum Chlorophyta

• The true green algae are rarely marine but can dominate the phytoplankton of enclosed estuaries or enclosed lagoons, especially in late summer and fall.

• They can be flagellated with two apical or subapical flagella or nonmotile. • Several species cause nuisance (مزعج) phytoplankton blooms associated with

coastal pollution.

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Cryptomonad Flagellates Class Cryptophyceae Phylum Cryptophyta

• Cryptomonad are a small group of flagellates. They are common in freshwater, and also occur in marine and brackish habitats.

• They are a group of tiny flagellates, only around 10-20 µm in size and flattened in shape, with an anterior groove or pocket.

• There are typically two slightly unequal flagella inserting nearly parallel next to the pocket.

B. Zooplankton Nutritional modes in zooplankton: Herbivores: feed primarily on phytoplankton Carnivores: feed primarily on other zooplankton (animals) Detrivores: feed primarily on dead organic matter (detritus) Omnivores: feed on mixed diet of plants and animals and detritus

Crustacean Zooplankton Phylum Arthropoda

Fig. Some zooplankton: (a) krill, (b) the cladoceran Podon, (c) a foraminiferan, (d) a radiolarian, (e) a comb jelly, (f) an arrow worm, (g) a scyphozoan jellyfish, and (h) a pleustonic siphonophore, the Portuguese man-of-war Physalia physalis.

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• Copepods رجلمجدافيات األ

The most abundant zooplankton in all the oceans and marginal seas, “called insects of the sea“;

The copepods are the largest and most diversified group of crustaceans, account for 70% of crustaceans.

They are either Herbivorous, carnivorous or omnivorous species; They range in length from less than 1 mm to a few millimeters. The calanoid (Suborder Calanoida) are the most of marine planktonic

species. They swim by means of rhythmic strokes of the first pair of anten-nae and the five posterior pairs of thoracic appendages. Calanoid copepods are easily recognized by their longer-than-body frilly (آشكش) antenna.

The harpacticoids usually have benthic adults (epibenthic), but the larvae of some species may dominate the estuarine zooplankton. Their antennae are much shorter than their body length and they look like little torpedoes.

Still the cyclopoid species which are mainly freshwater. Cyclopoids are both planktonic and epibenthic.

The planktonic copepod Euchaeta norvegica

• Krill Family Euphausiidae,

Krill are shrimp like creatures ranging from 15 mm up to 5 cm long. The name Krill comes from the Norwegian word krill meaning "young fry of fish".

They dominate the zooplankton of much of the Antarctic Ocean. They are important as prey for commercial fish (herring, mackerel, salmon, tuna), baleen whales, Mantas, whale sharks, seals, and a few seabird species.

Krill feed on phytoplankton and smaller zooplankton.. All but a single genus of euphausiids are luminescent. Most krill is used for aquaculture and aquarium feeds. In Japan and Russia, krill is also used for human consumption and known as okiami (オキアミ)

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• Cladocera (water flea) براغيث الماء

Cladocera are more important in fresh water than in seawater, but they are sometimes abundant in estuaries. Five marine species, Podon spp., and Evadne spp. are the most common water flea in many waters.

• Other Crustaceans Include mysids, ostracods القشريات الصدفية( ), and cumaceans which are truly planktonic but rarely dominate the zooplankton. A few amphipods (مزدوجات األرجل) are holoplanktonic.

Gelatinous Zooplankton

• Coelenterates Phylum Coelenterata or Cnidaria Class Scyphozoa (the true jellyfish)

Some Cnidaria are holoplanktonic, others have benthis stages. They are Carnivorous, feed on crustaceans and fish They have long tentacles carry nematocysts used to inject venoms into prey; and some such as the sea wasps دبور (Cubomedusae) and the Portuguese man-of-war Physalia physalis (Figure h, page 78) can sicken and even kill human beings, the box jellyfish of Australia (Chironex Fleckeri) for example can kill humans within minutes

Medusae are single organisms of few mm to several meters. Siphonophores such as P. physalis and by-the-wind sailor Velella velella

are colonies of polymorphic –different morphology- animals with specialization: feeding polyps, reproductive polyps, swimming or floating polyps, or protecting polyp protect the colony with stinging cells.

The siphonophore Porpita is about 10 cm across and is stabilized against wind and turbulence by tentacles on the water surface.

The by-the-wind

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• The Comb Jellies Phylum Ctenophora (not cnidarian)

Ctenophores are gelatinous, nearly transparent, and egg shaped.

Comb jellies are distinguished by eight external rows of long fused cilia that look like combs. The beating of the cilia helps move the animal through the water

Some have long tentacles. They don’t have nematocysts and prey on zooplankton (especially copepods), fish eggs, i.e. carnivorous.

Comb jellies are often strongly bioluminescent and light up like flashing bulbs when disturbed.

Important to fisheries due to grazing on fish eggs and competition for fish food

• Salps Phylum Urochordata

Salps are specialized for a free-swimming planktonic existence.

They have intake and exit siphons at opposite ends of the body.

Single or colonies. Pyrosoma, for example, is colonial and shaped like a cylinder closed at one end. Colonies reach over 2 m in length.

Salps are filter feeders; they feed on particles of 1 µm to 1 mm Occur in swarms أسراب, which can wipe the water clean of nanoplankton. They strain phytoplankton and fine particulate matter on a ciliary mucus net. Some salps are important predators on fish larvae.

• Larvacea (Appendicularia) Phylum Urochordata

Usually only a few millimeters in length. The morphology of appendicularians superficially resembles that of the tadpole larvae of most urochordates as they possess a discrete trunk and tail throughout adult life.

The Larvacea live in gelatinous balloons (house) that are periodically abandoned; empty houses provide valuable carbon source for bacteria.

These organisms use their tails to generate a current through the house. The current is strained by a grid of fine fibers, stretched across the anterior house opening, that trap food particles which are passed to the mouth.

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Other Zooplankton

Arrow Worms

Phylum Chaetognatha (spiny jaws)

Arrow worms are torpedo shaped (length is 2-3 cm), with one or two pairs of lateral fins (Figure in page 78).

They swim rapidly by means of rapid contractions of longitudinal trunk muscles.

Head has two rows of movable grasping spines, used to capture food.

Pteropods (the swimming snail) مجنحة األقدام

Pteropods are holoplanktonic snails (belong to mollusks).

They may or may not have a small shell. But they all have wing-like lateral projections from the foot by mean of which they can swim.

Pteropods are suspension feeder. Their carbonate shells produce pteropod ooze on sea floor

Planktonic Polychaetes

A few families of polychaetes are

holoplanktonic and have well-developed locomotory appendages (parapodia) (e.g., the genus Tomopteris).

Heteropods غير متماثلة األقدام

Heteropods are small group of pelagic relatives of snails. The snail foot is developed into a single “fin”; They have good eyes, visual predators.

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Larvae of benthic animals (Meroplankton)

Mollusca: clams and snails produce shelled veliger larvae; ciliated velum serves for locomotion and food collection

Cirripedia: barnacles produce nauplii, which turn to cypris Echinodermata: sea urchins, starfish and sea cucumber produce pluteus larvae of different shapes, which turn into brachiolaria larvae (starfish).

Polychaeta: brittle worms and other worms produce trochophora larvae, mostly barrel- shaped with several bands of cilia

Fig. (a) the veliger of molluscs, (b) the ophiopluteus of brittle stars, (c) the bipinnaria of sea stars, (d) the trochophore of polychaete worms and some molluscs, and (e) the nauplius of many crustaceans.

Decapoda (= 10 legs): shrimps and crabs produce zoëa larvae; they turn into megalopa larvae in crabs before settling to the sea floor

Pisces: fish eggs and larvae referred to as ichthyoplankton; fish larvae retain part of the egg yolk in a sack below their body until mouth and stomach are fully developed

Protistan Plankton

Protists are of major importance in the plankton, especially because they consume very small creatures, such as bacteria, that are largely unavailable to most other zooplankton. Protists are consumed by larger zooplankton and are therefore form a link between microbial forms and the rest of the planktonic food chain.

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• Ciliates Phylum Ciliophora

Ubiquitous in the plankton and often very abundant. They are feed on bacteria, phytoplankton and heterotrophic nanoflagellates Some species may take up phytoplanktonic cells but retain the chloroplasts, which remain functional within the ciliate.

• Foraminifera Phylum Foraminifera

They are relatives of amoeba with calcareous (calcium carbonate) skeleton, which is composed of a series of chambers.

They are range in size from 30 µm to 1-2 mm. Forams sink after death to the bottoms in great numbers forming deep-sea sediments known as foraminifera ooze or globigerina ooze, named after a common foraminiferan genus.

They are bacteriovores; Most abundant 40°N – 40°S.

• Radiolaria

They are spherical, amoeboid cells with silica capsule; 50 µm to several mm The colonial forms can attain several centimeters. Radiolarians are contribute to siliceous ooze sediments in some parts of the ocean in cold water and deep-sea.

They feed on bacteria, small phyto- and zooplankton