• Ochrophytes are of diverse organization and include unicellular, colonial, filamentous and parenchematous thalli. • They are characterized by the presence of chlorophylls a and c in their as well as xanthophylls (e.g. ) and other carotenoids that mask the chlorophylls (Table 2). • Due to the presence of these pigments, many ochrophytes have a yellowish-green, or brown appearance. • As storage products, they accumulate oils and Heterokontophyta chrysolaminarin (C) in cytoplasmic vesicles, but never starch. () • walls contain cellulose, and in certain they contain silica. • Cells possess one or more plastids, each with an envelope formed by two membranes of and two membranes of chloroplast . • Thylacoids, in stacks of three, in most ochrophytes are Fig. Semidiagrammatic drawing of a light surrounded by a band of , girdle lamella, just and electron microscopical view of the basic organization of a cell of the beneath the innermost membrane. Chrysophyceae. (C) Chrysolaminarin • Ochrophytes have flagellated cells with two vesicle; (CE) chloroplast envelope; different flagella, an anterior tinsel (mastigonemes) and (CER) chloroplast endoplasmic reticulum; (CV) ; (E) posterior whiplash (smooth) (Fig. ). eyespot; (FS) flagellar swelling; (G) Golgi • In this group of algae, mastigonemes consist of three body; (H) hair of the anterior flagellum; parts, a basal, tubular and apical part formed by fibrils. (MB) muciferous body; (MR) microtubular root of flagellum; (N) nucleus.

Chrysophyceae and related groups The following classes are commonly recognized in this division and will be discussed here: • Chrysophyceans (Golden-) are mostly unicellular 1. Chrysophyceae (golden-brown algae) organisms. 2. Synurophyceae • Some are amoeboid or coccoid. 3. Eustigmatophyceae • Most of the species in the Chrysophyceae are freshwater, occur in 4. Pinguiophyceae unpolluted and soft waters (low in ). 5. (silicoflagellates) • Some are strictly marine algae and part of the nanoplankton. 6. • Some have a single functional flagellum like Chromulina, while others 7. can form colonies like the freshwater Uroglena. 8. Bacillariophyceae () 9. Raphidophyceae (chloromonads) 10.Xanthophyceae (yellow-) 11. 12.Phaeophyceae (brown algae)

• Phylogenetic analysis using rDNA nucleotide sequences of the 16S subunit have shown that the classes Chrysophyceae, Synurophyceae, Eustigmatophyceae, Raphidophyceae, Pelagophyceae and Dictyochophyceae are evolutionarily close. Phaeophyceae, Xanthophyceae, Phaeothamniophyceae, Pinguiophyceae and are also related, and Bacillariophyceae and Chromulina Uroglena Bolidophyceae form an isolated group.

• The are parietal and • Many of the Chrysophyceae have a usually only a few in number, often tinsel flagellum that is inserted at the only one or two. anterior end of the cell parallel to the • Chlorophylls a, c1, and c2 are cell axis and a whiplash flagellum that present, with the main carotenoid is inserted approximately perpendicular being fucoxanthin which give them a golden color. to the tinsel flagellum. • The chloroplasts are surrounded by • The posterior whiplash flagellum is two membranes of chloroplast E.R., usually the shorter flagellum and has a the outer membrane of which is swelling at its base on the side toward usually continuous with the outer the cell contains an electron-dense membrane of the nuclear envelope. area referred to as the photoreceptor. • The thylakoids are usually grouped • The flagellar swelling fits into a three to a band. depression of the cell immediately • are common in beneath which, inside the chloroplast, chloroplasts of the Chrysophyceae. is the eyespot. • The storage product is chrysolaminarin (leucosin), a β- • The eyespot consists of lipid globules 1,3 linked glucan, supposedly found inside the anterior portion of the in a posterior vesicle (C). chloroplast, between the chloroplast • Contractile vacuoles in the anterior envelope and the first band of portion of the cell (CV). Semidiagrammatic drawing of a light and electron thylakoids. Semidiagrammatic drawing of a light and electron microscopical view of the basic organization of a cell of microscopical view of the basic organization of a cell of the Chrysophyceae. (C) Chrysolaminarin vesicle; (CE) the Chrysophyceae. (C) Chrysolaminarin vesicle; (CE) chloroplast envelope; (CER) chloroplast endoplasmic chloroplast envelope; (CER) chloroplast endoplasmic reticulum; (CV) contractile vacuole; (E) eyespot; (FS) reticulum; (CV) contractile vacuole; (E) eyespot; (FS) flagellar swelling; (G) Golgi body; (H) hair of the flagellar swelling; (G) Golgi body; (H) hair of the anterior flagellum; (MB) muciferous body; (MR) anterior flagellum; (MB) muciferous body; (MR) microtubular root of flagellum; (N) nucleus. microtubular root of flagellum; (N) nucleus.

١ • Most of the Chrysophyceae are sensitive to changes in the environment and • The presence of cellulose in cell walls is common, and some species survive the unfavorable periods as statospores. are covered with scales or protected by an organic sheath called the • The formation of a cyst or statospore or resting is one character by (L), an envelope around the protoplast, but not generally which a member of the Chrysophyceae or Synurophyceae may be recognized. attached to the protoplast as a wall is. • Statospores, are shaped like a small, externally ornamented bottle enclosed in a silicified wall with a terminal pore closed by nonsilicified plug (P). • Scales (if they are present) are made of silica and are radially or • A vegetative cell forms a statospore internally. biradially symmetrical • Very few chrysophyceans are naked. • When a statospore germinates, there is a dissolution of the plug or separation of it from the spore wall. The protoplast then moves out of the statospore by amoeboid motion, forming flagella as it moves out.

Chrysococcus rufescens. (a) Whole cell. (b) Cell Formation of a statospore or cyst Statospore of Ochromonas sphaerocystis. undergoing reproduction. (c) Ultrastructure of in Ochromonas tuberculata. (a)– vegetative cell. (B) Branched cytoplasmic process; (E) (c) The formation of the eyespot; (G) Golgi; (L) lorica; (LV) leucosin vesicle; (LF) statospore. (d) A mature long flagellum; (N) nucleus; (SF) short flagellum; (V) statospore as seen from the collar contractile vacuole. end. (C) Chloroplast; (Co) collar of statospore; (Cr) chrysolaminarin vesicle; (CV) contractile vacuole; (D) discobolocyst; (N) nucleus; (P) plug in pore of statospore; (S) statospore wall; (SDV) silica deposition vesicle; (Sp) spine.

• Two different types of projectiles occur in the • Nutrition in the Chrysophyceae can be either phototrophic, Chrysophyceae, muciferous bodies and phagotrophic, or mixotrophic (photosynthetic organism capable of discobolocysts. taking up particles and molecules from the medium). • On discharge the contents of the vesicle in • Food particles include both living (, small algae, or even muciferous bodies (MB) often form a fibrous network cells of its own kind) and non-living (detritus, fecal material). outside the cell. • The mixotrophic chrysophytes, Epipyxis pulchra have the ability to • The discobolocysts (D) are in the outer layer of cytoplasm and consist of a single membrane select or reject specific food item. bounded vesicle with a hollow disc in the outward facing part of the vesicles. The discharge is explosive, taking place by the expansion of the projectile into a thin thread 6 to 11 µm long.

Semidiagrammatic drawing of a light and electron microscopical view of the basic organization of a cell of the Chrysophyceae. (MB) muciferous body. Phagotrophy in Epipyxia pulchra. The cell has a posterior stalk by which it is attached to a lorica. (a) The long tinsel flagellum beats in such a way that water and suspended particles are drawn to the cell. (b) A particle is seized by the long tinsel flagellum. (c) The particle is maneuvered between the (a) Ochromonas tuberculatus. (D) discobolocyst; (b) two flagella. (d) A feeding cap from the cell envelopes the particle. (e) The particle is enclosed within Charged and discharged discobolocysts. a food vacuole within the cytoplasm. The stalk has pulled the cell into the lorica.

• Chrysophytes are notorious for their production of fishy or rancid smells, reflecting release of unsaturated aldehydes derived from the high cell content of polyunsaturated acids. • Mitotic division is the most • These chemicals are classified as algal volatile organic common mechanism of compounds (AVOCs). . • is rare, but when it occurs, are anisogamous. • Vegetative cells are haploid, and meiosis is the first division of the zygote. • In some cases, zygotes are statospores, representing a resting phase.

Three unsaturated fatty-acid derivatives produced by chrysophytes that result in rancid or fishy odors. The cycle of .

٢ • Eustimatophytes are yellow-green unicells that • Synurophyceae are flagellate algae occur in freshwater, brackish water, and seawater as covered with silica-scales (S). well as in the soil. • They are closely related to the Chrysophyceae. • They produce naked . • The Synurophyceae differ from chrysophyceans in • Most bear a single pleuronematic (mastigonemes ) the following: the Synurophyceae lack chlorophyll c2, the flagella are inserted into the cell flagellum, but some have two flagella. approximately parallel to one another (Fig. ), there • They are characterized by the presence of a large is a photoreceptor (P) near the base of each orange red extraplastidial (outside the chloroplast) flagellum, there is no eyespot, the contractile stigma. vacuole (CV) is in the posterior portion of the cell and the loss of the ability to carry out phagocytosis. • Other characteristics of the class include a basal swelling of the tinsel flagellum (FS) adjacent to the • Biflagellate unicellular forms can live in colonies. • Of the 200 species that compose this group, most eyespot, only , chloroplasts without girdle of them belong to the cosmopolitan genera lamellae and no peripheral ring of DNA, and and Synura. chloroplast endoplasmic reticulum not connected to • Sexual reproduction occurs by , vegetative the nuclear envelope. cells are haploid, and zygotes may remain as cysts • The chloroplasts of the Eustigmatophyceae have β- when environmental conditions are unfavorable. ,carotene and two major xanthophylls, violaxanthin and • ٍAs they inhabit relatively unpolluted freshwater vaucheriaxanthin. Violaxanthin is the major light- they are good indicators of water quality. harvesting pigment in the Eustigmatophyceae • Several members of the Synurophyceae thrive in acidic lakes. As environmental concerns over the (a) Diagrammatic representation of the basic acidification of lakes by acid rains increase, these Semidiagrammatic drawing of the cytology of morphology of a of the Eustigmatophyceae. species will probably be more widely used as Synura, showing the characteristic cytology of (C) Chloroplast; (CER) chloroplast endoplasmic indicators of lake acidification. the Synurophyceae. (CV) Contractile vacuole; reticulum; (E) eyespot; (F) long flagellum; (FB) basal (F) flagella; (G) Golgi; (L) chrysolaminarin body of short flagellum; (FS) flagellar swelling; (LV) vesicle; (N) nucleus; (P) photoreceptor; (S) lamellate vesicles; (N) nucleus. scale; (SV) scale vesicle.

are unicellular flagellate algae, also known as • The life cycle of • Raphidophyceae antiqua involves a vegetative Chloromonads. propagation phase and a non- • The anterior flagellum is commonly tinsel, whereas the posterior flagellum is motile dormant phase. naked. • The vegetative diploid cells grow • Their plastids contain chlorophylls a and c, and two membranes of chloroplast by binary fission under normal endoplasmic reticulum. growth conditions. • Unlike other ochrophytes, the endoplasmic reticulum membrane that envelops • Small haploid cells are produced the chloroplast is not connected to the membrane surrounding the nucleus. when the are depleted • The cells have like in . in the medium. • There are about 15 species, most of which are marine algae. • These haploid cells change into • The freshwater species of the Raphidophyceae cysts under low-light conditions and spend several months are green, whereas the marine forms are Chattonella antiqua dormant in bottom sediments. yellowish and contain the carotenoid fucoxanthin. • The period of dormancy usually • Many of the marine species produce neurotoxic lasts from the end of summer to compounds that are similar to . the following spring and is enforced by low temperatures. • Uptake of the toxin by fish results in depolarization of nerves supplying the heart. • Swarmers germinate from the This reduces the heart rate, thereby lowering cysts and somehow become blood pressure, which in turn affects the transfer diploid, although how of oxygen to the gill lamellae, creating hypoxic diploidization occurs is not conditions that lead to fish mortality. known. • Toxic red-tide blooms of the marine Chattonella • The resulting diploid vegetative antiqua and Heterosigma carterae have cells complete the life history. reported in Japan. In 1972, a bloom of C. The life cycle of Chattonella antiqua. antiqua killed 500 million dollars worth of caged yellow-tail fish in the Seto Inland Sea in Japan (a) Heterosigma carterae. (b) Fibrocapsa japonica. (C) Chloroplast; (M) mucocyst.

Bacillariophyceae • Bacillariophyceans, or diatoms, constitute the largest class of Ochrophyta. • About 10,000 benthic and planktonic species are known, and they can be found in both freshwater and marine environments. • This group is responsible for 25% of of the sea. • Diatoms are unicellular, and in some cases, live in colonies with a filamentous appearance, formed by numerous loosely-joined individuals.

Some common diatoms that might occur in your field samples. (1) sp.; (2) Thalassiothrix sp.; (3) costatum; (4) Coscinodiscus sp.; (5) sp.; (6) sp.; (7) Rhizosolenia sp; (8) gravida; (9) Nitzschia pungens, chain.

٣ • The is composed of two overlapping halves, the smaller fitting into the larger like a Petri dish • The outer half is the and the inner the hypotheca. • Each is composed of two parts, the valve, a more or less flattened plate, • The most distinctive feature of diatoms is their rigid translucent wall, and the connecting band, attached to the edge of the valve. The two connecting or frustule, consisting of silicon dioxide (SiO2) and traces of other bands, one attached to each valve, are called the girdle or cingulum. substances, such as aluminum, , and titanium. • Occasionally there are one or more additional bands. • The inorganic component of the frustule is enveloped by an organic component or “skin”, the latter composed of amino acids and sugars with the hydroxyproline, uronic acid and collagen present. • Cellulose is never present.

• In discussing diatoms and silica, there is often confusion over terminology in regard to silicon. – Silicon is the element. – Silica is a short convenient designation for silicon dioxide (SiO2) in all of its crystalline, amorphous, and hydrated or hydroxylated forms.

– Silicate is any of the ionized forms of monosilicic acid [Si(OH)4]

Semidiagrammatic representation of a cell of Melosira varians composed of two valves, V and V, two girdle band series: 1, 2, 3, and, underlapping these, the younger series 1, 2, 3.

• The use of scanning microscopy has revealed the complexity of frustule • When looking at the frustule from the top or bottom, the structures. faces of the can be seen in a valvar view, while • The siliceous material of the frustule from the side, a girdle or cingular view can be observed. is laid down in certain regular patterns that leave the wall ornamented. • The ornamentation of the frustule is very complex and each species has a configuration of specific spines, pores or striae.

• Diatoms can be classified in four basic groups based on the ornamentation of diatoms : (1) centric and radial, where the structure is arranged according to a central point (Fig. a) (2) trellisoid, where the structure is arranged uniformly over the surface without reference to a point or line (Fig. b) (3) gonoid, where the structure is dominated by angles (Fig. c); (4) pennate, where the structure is symmetrically arranged upon either side of a central line (Fig. d)

The basic patterns of ornamentation in the Bacillariophyceae. (a) Centric and radial (example Coscinodiscus). (b) Trellisoid, with structure arranged margin to margin (example Eunotia). (c) Gonoid, with structure supported by angles (example Triceratium). (d) Pennate, symmetrical about an apical line (example ).

٤ • Besides the raphe, there are basically two types of wall perforations within • Some pennate diatoms have a raphe the Bacillariophyceae: system composed of the raphe (r) (a • the simple pore or hole, longitudinal slot in the theca), divided into • and the more complex chambers known as loculi (singular loculus or two parts by the central nodule (cn). areola) (Figs. 17.6, 17.12) • Each half of the raphe terminates in a • The structure of the valve wall with loculi resembles a honeycomb. swelling of the wall called the polar nodule (pn). • The ornamentation in the pennate diatoms is bilaterally symmetrical around the raphe. • In those pennate diatom valves that do not have a raphe system, there is instead an unornamented area running down the center of the valve, which is called the pseudoraphe. • Diatoms with only one or two raphes are able to move due to the production of a mucilaginous material that flows out of the raphe and holds the cell to the substrate. • The contraction of this material and the production of new mucilage cause a sliding movement of the cell.

Fig. 17.6 The types of openings in frustule walls. (a) Hole or pore (Chaetoceros didymos var. (a) A cell with a raphe system ( viridis). anglica). (b) Loculus opening outward (Coscinodiscus linatus). (c) Loculus opening inward (cn) Central nodule; (pn) polar nodule; (r) raphe. (b) A (Thalassiosira wailesii). (h) Hole; (lp) lateral pore or pass pore; (sm) sieve membrane; (sp) cell with a pseudoraphe (pr) sieve pore.

• The valve surface can have extensions, called • Pores or loculi (punctae) in a single row are referred to as stria processes, whose main function appears to be to (plural striae). maintain contact between contiguous cells and to assist colony formation. • These processes are given different names: – Cornuate processes are horn-like; – strutted processes are ones that have been reduced to a boss at the apex of a valve;

Fig. 17.4 Climaconeis colemaniae. Light and scanning electron micrographs of the frustule. The valve contains linear striae, each with 6–8 poroid aerolae. The valve contains a raphe opening. Two pores – spinulae are very small processes; occur in the area of the central nodule. – awns or setae are hollow and elongated. • Special pores (mucilage or slime pores) through which mucilage is secreted are known in many diatoms. In the pennate diatoms, these pores usually occur singly near one or both poles of the valve and generally occupy thickenings in the walls.

• Asexual reproduction occurs by bipartition. • The protoplasm is located inside the frustule; in their plastids thylakoids form packs of three surrounded by the girdle lamella. • When occurs, the two valves are separated and each produces a new hypotheca, so that the hypotheca of the parental • Photosynthetic pigments are chlorophylls a and c (c1, and c2), as well as cell always acts as the epitheca of the daughter cells. the carotenoids fucoxanthin (giving the cells their golden-brown color), diatoxanthin and violaxanthin. • After successive cell divisions over time, there is an effect on the average cell size of the diatom population. • The most common storage products are chrysolaminarin and lipids. • This phenomenon has been observed in natural populations. • Diatoms contain unique 4α-methyl sterols, such as 4-desmethylsterol and cholesterol. • The mean diameter of the population progressively decreased until a minimum mean diameter was reached, at which point cell size suddenly increased due to the formation of called auxospores. • Auxospores were generally the result of sexual reproduction processes, but in some cases they were produced asexually.

Light microscopical drawing of valve (a) and girdle (b) views of the diatom . (c) Drawing of a transverse section of M. grevillei in the transmission electron microscope. (Ch) Chloroplast; (CN) central nodule; (E) elongate chamber of a septum; (GB) girdle band; (I) intercalary band; (IBE) intercalary band of the epitheca; (IBH) intercalary band of the hypotheca; (LT) locule tubule;(O) oil; (R) raphe; (S) stria.

٥ Extracellular mucilage • Diatoms produce five types of mucilaginous aggregation: • Sexual reproduction of diatoms is rare in nature and usually occurs as described before. • (1) tubes, • The life cycle is diplontic with isogamy in pennate diatoms (both • (2) pads, gametesarenonflagellated) and • (3) stalks, in centric diatoms (the male is motile, whereas the • (4) fibrils,and female gamete (egg) is nonmotile). • (5) adhering films • In some cases, formation is a consequence of selfing: the • A substantial part of the fixed by benthic diatoms is secreted fusion of two haploid nuclei produced by the same diploid cell. as extracellular mucilages • Auxospore formation can also be caused by changes in environmental conditions of temperature, light and available nutrients.

• Sexual reproduction in diatoms can occur only after two general conditions have been met. – First, cells must reach a minimum size range, typically 30–40% of their maximum size. – Second, there must be the presence of correct environmental conditions. These include combinations of temperature, light, nutrients, trace metals, organic growth factors, and osmolarity. • Contrary to most other algal groups, sexuality is primarily a means of size restoration, and is not normally a factor in dormancy or dispersal

Forms of extracellular mucilage in diatoms.

Motility Biolfouling • Some diatoms are able to glide over the surface of a substrate. • Diatoms are ubiquitous fouling , attaching to Gliding is restricted to those pennate diatoms with a raphe submerged structures by secreting insoluble mucilages. Achnanthes (described previously) and those centric diatoms with labiate longipes is a common marine fouling diatom that is highly resistant processes (L). to toxic antifouling coatings. It produces a stalk that elevates it • Nearly all motile diatoms must adhere to above the toxic coatings on ship bottoms. Fouling of ship bottoms the substratum in the area of their raphe in increases the frictional drag, leading to excess fuel consumption. for movement to occur. Cleaning ship hulls coasts millions of dollars each year, leading to • The labiate processes have a pore in the an additional loss of revenue. center, and the mucilage is secreted through the pore. • Diatoms can glide only when the valve containing a raphe is in contact with the surface. If the diatom cell settles with the girdle contacting the substrate, the diatom secretes a mucilaginous tether from the portion of the raphe near the central nodule. The tether attaches to the substratum and the cell pulls itself onto a valve containing a raphe using the tether.

Fig. 17.17 Scanning electron micrographs of Achnanthes longipes. (a) Whole cell showing the pad, shaft, (b) A cell that has settled on the girdle bands. Tether and collar of the mucilaginous stalk. Also shown is a path of mucilage left by the gliding diatom and mucilage is secreted from the raphes of each valve. surface film (SF) of mucilage left on the substratum. (b) The attachment of the collar (C) of the stalk (Sh) The tether mucilage is attached to the substrate. (c) on the cell. (R) Raphe. (c) The attachment of the pad to the substratum. Tether mucilage extending from the raphe in the central nodule area to the substrate.

Resting spores and resting cells • Some diatom cells form thick, ornamented walls at different times in their life cycle and become resting spores. If such cells are planktonic, they fall to the bottom where, presumably, they await more favorable conditions. • Resting cells have the same morphology as vegetative cells and do not form a protective layer, thereby differing from resting spores. • Diatoms that are attached to a substrate and are motile on the substrate have the advantages of –(1)being held in position in moving water; –(2)avoiding burial by moving up and over sediments; –(3)moving to colonize vacant areas; and –(4)moving to areas with more light and/or nutrients

(a), (b) Ditylum brightwelli. (a) Vegetative cell. (b) Resting spore. (c), (d) Amphora coffaeformis. Drawings of the ultrastructure of a vegetative cell (c) and a resting cell (d). (C) Chloroplast; (L) lipid; (N) nucleus; (V) vacuole.

٦ • Auxospore formation is a second mechanism (in addition Rhythmic phenomena to resting spores) for reestablishing the original size of the cell. The auxospores are formed by the fusion of two • It is possible to synchronize the division of diatom cells in gametes. a culture in a couple of different ways. • Depending on the species, – Removal of silicon from cultures of Navicula pelliculosa stops auxospores develop in one of growth of the cells at a stage prior to cytokinesis. When silica is three different ways added to the culture, all of the cells then divide synchronously. • 1 Isodiametric auxospores. Centric diatoms such as Melosira • 2 Properizonial auxospores. – Another way of obtaining synchronized cell divisions is by Centric diatoms such as keeping the diatoms in the dark for a long period followed by Chaetoceros produce non- exposure to light. In Nitzschia palea the shortest time that can be isodiametric (non-spherical) obtained between cell divisions is 16 hours. If the cells are grown mature auxospores. on an 8 hour light : 8 hour dark cycle, synchronously dividing • 3 Perizonial auxospores. cells are obtained. If the cycle is shortened to 6 hours light : 6 Pennate diatoms such as hours dark, then cell division occurs every second dark period Navicula form this type of non- because there is insufficient time for the diatom to prepare itself isodiametric mature auxospore for the next division. Diagrammatic summary of the three types of sexual auxospores in diatoms.

• The effects of heavy metals on diatoms can be Physiological issues divided into three groups: • Silicon cannot be replaced by any of the elements similar to it in – (1) Cu, Zi, and Ge affect the biochemical pathway of physical and chemical properties or in atomic radius, such as Ge, C, silicon metabolism; Sn, Pb, As, P, B, Al, Mg, or Fe.

– (2) Hg, Cd, and Pb interfere with cell division and • Concentrations of germanium dioxide (GeO2) above 1.5 mg liter1 cause morphologically distorted cells to be produced; will specifically suppress the growth of diatoms. The finding that GeO2 specifically inhibits diatom growth was a welcome one for and phycologists working on algal cultures. – (3) Cr, Ni, Se, and Sb (Antimony) have no effects up to a concentration of 1 µM, well above the • In addition to responding adversely to germanium in solution, diatoms are sensitive to copper. Concentrations of 0.25 ppm copper concentrations that show effects with other toxic as CuSO4.5H2O are normally used to control algal blooms without metals. affecting fish in freshwater lakes.

Amnesic shellfish poisoning occurs when shellfish filter diatoms from the genera Nitzschia, Pseudo-nitzschia, and Amphora from marine waters.

• Some normally photosynthetic diatoms are able to grow under heterotrophic conditions with as the sole carbon source. • When the organism is growing in the light, it does not have the mechanism for the utilization of glucose in the medium. It requires about 24 hours in the dark in a glucose medium before it is able to use the glucose as a carbon source. This lag period indicates that the lack of light induces an uptake and/or assimilation system for the glucose. • It was suggested that such facultative heterotrophy enables these diatoms Nitzschia to settle into bottom deposits, live heterotrophically for long periods, then Pseudo-nitzschia Amphora rise and begin again. • Subsequent ingestion of the shellfish by • Although the above diatoms still have functional chloroplasts, there are man and birds results in memory loss some colorless apochlorotic diatoms lacking functional chloroplasts. (amnesia), abdominal cramps, vomiting, disorientation, and even death. • Species of Nitzschia, are able to grow with lactate or succinate as the sole • The diatom produces domoic acid, a organic carbon source. derivative of the neuroexcitatory amino acid L-glutamic acid. • In nature, some Apochlorotic diatoms live on decaying marine vegetation • Domoic acid is especially prevalent in and the mucilages of large moribund cells of the diatom and can be induced by depriving the cells of nutrients, particularly silicate and phosphate.

٧ • Diatoms cells contain large quantities of highly unsaturated fatty acids such as eicosanoic acid (Fig. a) in vesicles in the cytoplasm. Chemical defense against predation • Death of cells during feeding by invertebrates results in the release of the unsaturated fatty acids into the seawater which convert into the unsaturated short-chain aldehydes 2,4-decadienal and 2,4,7-decatrienal (Fig. b). • Diatoms are preferred food for invertebrates such as . • These short chain fatty-acid aldehydes are toxic to developmental stages of Some diatoms (e.g., Phaeodactylum tricornutum, Skeletonema a range of invertebrates including copepods, sea urchins, polychaetes, and pseudocostatum) have evolved a mechanism to reduce predation by ascidians, reducing the numbers of the next generation of these grazers. releasing chemicals that reduces the fecundity of the next • Future generations of grazers are sabotaged, encouraging the survivability generations of invertebrates. of diatom populations. • Interestingly, the released aldehydes also are toxic to diatoms. However, the diatoms cells are being destroyed by the grazing and are already out of the gene pool.

(a) The reaction by which a non-toxic highly unsaturated fatty acid is converted by a phospholipase into a reactive unsaturated fatty-acid aldehyde that is toxic to invertebrates. The reaction is initiated by wounding of the diatom cell. (b) Two unsaturated fatty-acid aldehydes, decatrienal and decadienal, that are toxic to invertebrates and a saturated fatty-acid aldehyde, tridecanal, that is not toxic. Phaeodactylum tricornutum Skeletonema

Spring diatom increase Some ecological aspects • The spring diatom bloom is a strong increase in abundance (especially the diatoms) that typically occurs in the early spring and lasts until • Diatoms comprise the main component of the open-water marine late spring or early summer. flora and a significant part of the freshwater flora. • This seasonal event is characteristic of temperate North Atlantic, sub-polar, and coastal waters. • In the marine environment the colder the water is, the greater the • The magnitude, spatial extent and duration of a bloom depends on a variety of diatom population. environmental conditions, such as light availability, nutrients, temperature, and stratification of the water column. • The maintenance of oceanic diatoms in the water column involves some adaptation of the cells to make them buoyant. • Adaptations of large and heavy cells (large diatoms) to reduce sinking, and to maintain near neutral buoyancy and vertical position in the euphotic zone, include – chain formation and cell extensions that provide a high surface area: volume ratio. Cell extensions increase frictional drag and also increase the effective size of phytoplankton cells, which makes them more difficult for grazers to capture and ingest. – production of gas vacuoles and the accumulation of fats and oils, which are lighter than water. • Cell aging and nutritional state of phytoplankton cells are physiological conditions that affect cell density. Post-bloom - starved diatoms tend to sink significantly faster than nutrient-rich diatoms.

Idealized diagram tracing changes in phyto-, zooplankton, light, and nutrients during the year in a temperate-boreal inshore body of water.

Spring diatom increase mechanism diatoms • The siliceous of diatoms have been well preserved in the • During winter, wind-driven turbulence (often derived from storms) and cooling water fossil record. temperatures break down the stratified water column formed during the summer. • This breakdown allows vertical mixing of the column. • Diatomaceous fossil deposits, known as or • This mixing replenishes nutrients from depth to the surface waters and the rest of the diatomite, are exploited in many parts of the world and have euphotic zone. important industrial applications as abrasives, refractory ceramic • In winter, phytoplankton use these nutrients to perform photosynthesis. However, and filters. vertical mixing also causes high losses, as phytoplankton are carried below the euphotic zone (so their respiration exceeds primary production). In addition, reduced illumination • The industrial uses of diatomaceous earth are varied. (intensity and daily duration) during winter limits growth rates. – One of the first uses was as a mild abrasive in toothpaste and metal polishes. • In the spring, more light becomes available and stratification of the water column – Diatomaceous earth was also used as an absorbent for liquid occurs as increasing temperatures warming the surface waters (referred to as thermal nitroglycerin to make dynamite that could be transported with stratification). As a result, vertical mixing is inhibited and phytoplankton and nutrients are held at the surface. This coupling of nutrients and phytoplankton promotes comparative safety. The inert medium used in the present-day exponential increases in photosynthetic activity, and, thus, . manufacture of dynamite is wood meal. • Spring blooms typically last until late spring or early summer, at which time the bloom – Probably the most extensive industrial use of diatomaceous earth is in collapses due to nutrient depletion in the stratified water column and increased grazing the filtration of liquids, especially those of sugar refineries. pressure by zooplankton. – Another major use is in the insulation of boilers, blast furnaces, and • Phytoplankton die or are ingested and egested by zooplankton, sinking below to great other places where a high temperature is maintained. depths. Because of the stabilization of the water column, these materials and other nutrients are not returned to the surface from the bottom.

• The onset of relatively quiet summer conditions further stabilizes the water column.

• Toward the end of summer, with the advent of fall storms, the thermocline may be disrupted, bringing some nutrients toward the surface from the bottom in shallow water. This may result in a fall increase of phytoplankton.

٨ Order 2 Bacillariales (): pennate or trellisoid ornamentation; • The systematic arrangement of diatoms has traditionally been based one or two chloroplasts; raphes possibly present with gliding; no on morphology and consists of a single class called Bacillariophyceae. flagellated spermatozoids; sexual reproduction by conjugation. • The Bacillariophyceae can be divided into two orders as follows: • Common genera include Nitzschia, Pseudo-nitzschia, Navicula, Order 1 Biddulphiales (Centrales): radial (centric) or gonoid Amphora, Cymbella, and Pinnularia ornamentation; many chloroplasts; no raphe; resting spores formed; motile spermatozoids with a single tinsel flagellum; oogamous sexual reproduction. – Melosira, a common golden-brown diatom found in marine and freshwater environments, consists of cylindrical cells with a greater length than Breadth – Chaetoceros has more than 160 species, the largest number of any planktonic diatom. The genus is widespread in warm and cold waters.

Nitzschia palea Pseudo-nitzschia Navicula

Chaetoceros Melosira granulata Amphora Cymbella Pinnularia

Dictyochophyceae • These golden-brown algae are characterized by tentacles or rhizopodia on basically amoeboid vegetative cells. • Amoeboid cells are relatively rare among the algae, being mostly restricted to the Dictyochophyceae and the Xanthophyceae. Classification: The Dictyochophyceae can be divided into three orders: • Order 1 Rhizochromulinales: marine and freshwater unicells with tentacles. • http://www.microscopyview.com/ • has amoeboid non-flagellated vegetative cells with many fine beaded-filipodia and fusiform zoospore has a single tinsel flagellum • http://cfb.unh.edu/phycokey/phycokey.htm • Order 2 : unicells with a long anterior flagellum and a second flagellum reduced to a basal body. Their body is covered with scales, usually three to six chloroplasts (if chloroplasts are present) are located in a • http://blacksea- ring surrounding the nucleus, which occupies a central position. Some species are capable of emitting and catch small organic education.ru/phytoplankton.shtml particles, marine and freshwater. • http://www.microscopyview.com/MENU/40 0-DIATOM/406-MID/H406-7700.html

a) hexacostata in the light and electron Rhizochromulina marina. Vegetative cell (a) and microscope. (c) spinifera zoospore (b).

• Order 3 Dictyocales: or silicoflagellates are a group of cosmopolitan marine PELAGOPHYCEAE (constitute a prominent part of the phytoplankton in the cold seas) unicells • The Pelagophyceae are a group of basically (have one emergent flagellum) with a silicified skeleton and represented unicellular algae that are cytologically similar to the by only one extant genus Dictyocha. Chrysophyceae • The cytoplasm surrounds the skeleton and contains golden discoid plastids. • The cells are very small (3–5 µm) members of the •In Dictyocha speculum, the skeleton-bearing cells multiply vegetatively by mitotic ultraplankton and appear as small spheres with division. Cells connected by bridges develop and give rise to large spherical cells indistinct protoplasm under the light microscope. without skeletons that become multinucleate. Uninucleate swarmers with a single • Members of the class are economically important flagellum develop in the large spherical cells. The swarmers are released and grow because some of the algae produce “brown tides.” into large multinucleatecells, which are probably a form of resting cell. All of the • is the causative agent of cells are of the same level and sexual reproduction is not known. brown tides in Texas. Aureoumbra lagunensis is able to grow at its maximum rate at salinities as high as 70 PSU (practical salinity units; seawater is about 35 fine structure of Dictyocha PSU). Few algae are able to survive these fibula. (b), (c) Side and hypersaline conditions. In addition, the surface of the front views of the skeleton cells are covered with a slime layer that reduces of Dictyocha. (ar) Apical predation. A combination of these advantages ring; (br) basal ring; (c) enables A. lagunensis to outcompete other algae. chloroplast; (cb) cell boundary; (m) • anophagefferens forms brown tides along the coasts of New itochondrion; (n) nucleus; Jersey, New York, and Rhode Island. The numbers of cells in brown tides (p) pseudopodium; (rs) can be so large that they can exclude light from the benthic eelgrass radial spine; (s) silica (Zostera marine), resulting in elimination of the eelgrass. The larvae of the skeleton; (sb) supporting bay scallop feed off eelgrass and the bay scallop industry was virtually bar. wiped out for a number of years after a brown tide in the waters off the northeast United States. • A. anophagefferens is a psychrophilic alga that is able to grow at low temperatures and survive extended periods of darkness. This explains its ability to form algal blooms. Growth stages of the silicoflagellate Dictyocha speculum.

٩ • Flagellate cells have two lateral or apical insertion heterokont flagella with a Xanthophyceae and related groups forwardly directed tinsel flagellum and a posteriorly directed whiplash flagellum. • The organization of xanthophyceans, or Tribophyceae, • The eyespot (E) in motile cells is always in varies from simple filaments to amoeboid cells to siphonous thalli. the chloroplast, and the chloroplasts are • The chloroplasts contain chlorophylls a and c, lack fucoxanthin, and are surrounded by two membranes of colored yellowish-green. chloroplast endoplasmic reticulum. The • As storage products, they accumulate chrysolaminarin, paramilo (β-1,3 outer membrane of the chloroplast E.R. is linked glucan similar to paramylon), sugars and oils. usually continuous with the outer membrane of the nucleus. • Their cell walls contain cellulose and often silica scales. • In most non-motile cells the wall is • Sexual reproduction is only known in three genera with a haplontic life cycle. composed of two overlapping halves that fit • Some species form resistant cysts with silica walls, closed by a cap. together as do the two parts of the • Xanthophyceans, despite their green color, can be distinguished from bacteriologist’s Petri dish. chlorophytes by their lack of chlorophyll b and by their heterokont flagella. • Most of the 600 known xanthophyceans species live in freshwater and moist soil, and only a few are marine species. • The freshwater and marine genus has a cylindrical body consisting of a branched coenocytic filament with many discoid plastids and numerous nuclei.

Light and electron microscopical drawing of a zoospore of a typical member of the Xanthophyceae, Mischococcus sphaerocephalus. (C) Chloroplast; (CV) contractile vacuole; (E) eyespot; (FS) flagellar swelling; (LF) long flagellum with hairs; (N) nucleus; (SF) short flagellum; (V) vacuole. Vaucheria coronata, coenocytic filament and Oogonium

• The class Phaeothamniophyceae includes freshwater filamentous • The heterotrichous genera Giraudyopsis and Chrysomeris belong to the forms, which can be simple or branched, without chrysolaminarin. class Chrysomerophyceae, characterized by a lack of alginates. • They produce biflagellate zoospores as in Phaeothamnion. • This class is most closely related to the Xanthophyceae and Phaeophyceae and the cytology of these three classes is similar. • The Phaeothamniophyceae is the only class of algae where fucoxanthin and heteroxanthin occur together.

A filament and zoospore of Phaeothamnion polychrysis. Some algae classified in the Phaeothamniophyceae. Also included is the fine structure of a zoospore.

Phaeophyceae • Pinguiophyceae include marine planktonic unicellular flagellates as in Phaeomonas, or no flagellate as in Pinguiochrysis, with a high content in • Phaeophyceans are known as brown algae, whose color is due to the omega-3 fatty acids. presence of large amounts of the xanthophyll fucoxanthin in their chloroplasts, which conceals the rest of the pigments as well as from the • These fatty acids are the basis for choosing the latin noun “Pingue” phaeophycean that might be present. (meaning fat, grease) as the root of the class name. • Phaeophyceans are found almost exclusively in marine and are an • The high percentage of unsaturated fatty acids, and the lack of a , important component of the benthic vegetation in the rocky shores of the make these algae desirable as a source of unsaturated fatty acids and of northern and southern hemispheres. feed. • Some brown algae live more than a hundred meters deep due to fucoxanthin, that allows them to use the blue part of the radiation spectrum. • Some occupy the , as in certain fucoids, and can resist desiccation for hours or even for days ( canaliculata). • Laminariales form extensive subtidal “forests”. • Only five genera live in freshwater, but many are found in brackish waters of .

Algae classified in the Pinguiophyceae Pelvetia canaliculata Laminariales

١٠ • Some phaeophyceans have air bladders or vesicles in their thalli which increase their buoyancy, allowing them to live upright and • There are no unicellular or colonial organisms and the algae are basically rooted to the substrate, as in nodosum, or floating, as filamentous, pseudoparenchymatous, or parenchymatous. in natans. • Many phaeophyceans such as are branched filaments. • Large concentrations of the latter algae gave its name to a region of • When branched filaments of one or several axial filaments are joined by the Atlantic known as the Sargasso Sea. mucilages, they form pseudoparenchymatic thalli called haplostichous, as • Brown algae provide and a food source for many marine in . . • The thalli called polystichous are parenchymatic, as in Sphacelaria. • Traditionally, they have been used by man as for their high • Polystichous thalli originate by the division of their cells in all directions, phosphate content. causing a thickening of the and cell differentiation: an outer layer • Some, like Laminariales, accumulate iodine in a concentration consisting of pigmented cortical cells and an inner medullar layer of 10,000 times higher than that found in the sea. unpigmented cortical cells.

Ectocarpus Leathesia Sphacelaria Ascophyllum nodosum Sargassum natans

• The greater morphological complexity of Phaeophyceae, and of • As characteristic storage products, they accumulate the laminarin, an insoluble polymer algae as a whole, is found in the order Laminariales, in which thalli composed mainly of β-linked glucans. have three distinct parts: the holdfast, stipe and blade. • The cell wall consists of an inner layer of cellulose • The parenchymatous Phaeophyceae have plasmodesmata or pores fibers and an outer external layer of mucilage, comprising colloidal substances called phycocolloids, between most of the cells. These pores are bounded by the such as alginates, which are salts of , and plasmalemma, and protoplasm is continuous from one cell to the the substance fucoidan (or fucoidin), which is mainly next through them. composed of sulfated . • Both alginates and fucoidan are of commercial interest. • In the phaeophycean Padina, calcium carbonate deposits (i.e., calcification of the wall) are present in the form of aragonite. • The cells contain a single nucleus with small Diagram of a hypothetical brown algal chromosomes and one or more chloroplasts, whose cell. (ce) Chloroplast envelope; (cen) structure can be laminar, perforated, discoid or centrioles; (cer) chloroplast endoplasmic lenticular. reticulum; (d) dictyosome; (er) • The chloroplasts also have chlorophylls a, c , and c . endoplasmic reticulum; (f) DNA fibrils; 1 2 (m) ; (ne) nuclear • Plastids have their own membrane and two membranes from the endoplasmic reticulum. envelope; (nu) nucleolus; (p) ; (ps) pyrenoid sac; (v) vacuole. • Sometimes, the outer membrane of the chloroplast E.R. is continuous with the outer membrane of the nuclear envelope. • Pyrenoids, when present, accumulate reserve polysaccharides around them. • Thylakoids are arranged in packs of three, surrounded by a girdle lamella.

Padina

• Generally the motile cells of the • Asexual reproduction is by means of zoospores, fragmentation or Phaeophyceae (always the specialized multicellular structures called propagules, which are able reproductive cells such as to produce adult individuals. zoospores or gametes, as there • Sexual reproduction occurs by isogamy, or oogamy. are no motile vegetative cells) • Life cycles are isomorphic haplo-diplontic or heteromorphic with a have a long anterior tinsel dominance of or (Laminariales). flagellum with tripartite hairs and a shorter posteriorly directed • and Durvilleales have a diplontic cycle. whiplash flagellum with a swelling (fs) near the base fits into a depression of the cell immediately above the eyespot. • The eyespot (stigma) (e) consists of lipid globules arranged in a single layer between the outermost band of the thylakoids and the chloroplast representation of a male gamete of Ectocarpus envelope. siliculosus showing the distribution of cellular • The eyespot acts as a concave organelles. (af) Anterior flagellum; (c) chloroplast; mirror focusing light onto the (e) eyespot; (fh) flagellar hairs (present along entire flagellar swelling, which is the length, for clarity only shown on part of the flagellum); photoreceptor site for (fs) proximal swelling of the posterior flagellum; (g) Golgi apparatus; (li) lipid body; (m) mitochondrion; (mb) in brown-algal flagellate cells. microbody; (mt) ; (n) nucleus; (p) pyrenoid; (pf) posterior flagellum; (v1) physode; (v2) storage granule; (v3) vesicles with cell wall or adhesive Branches with propagules in different development stages . material.

١١ Brown algae consist of more than 250 genera and about 1,500 species. • Two types of sexual reproductive structures (sporangia or gametangia) can be observed in Phaeophyceae. – One type has multilocular (plurilocular) structures , in which each cavity produces a flagellate cell by mitosis. This type can be produced either in gametophytes or in sporophytes. – Other reproductive structures are unilocular, formed by a single cell, in which 16 to 128 flagellate haploid spores are formed by meiosis. This type is mainly produced in sporophytes.

Diversity in brown algae. A. dudresnayii. B. pinnatifi da. C. Ectocarpus fasciculatus, plurilocular (a) and unilocular (b) sporangia. ochroleuca. D. .

• Most phaeophyceans with simple thalli and isomorphic reproductive cycles belong to the and physodes order . • Ectocarpus is cosmopolitan; thalli are • Phlorotannins (phaeophycean tannins) are stored in physodes (Fig. ) uniseriate branched filaments with in the cytoplasm of many brown algae. Phlorotannins are formed by heterotrichous organization and diffuse Golgi by polymerization of phloroglucinol (1,3,5-tri-hydroxybenzene) intercalary growth. • The tannins are non-glycosidic (do not contain sugars), bind proteins, • The haploid gametophytes and diploid have strong reducing action, and are astringent to the taste. They are sporophytes are morphologically identical. readily oxidized in air, resulting in the formation of a black pigment, • The gametophytes produce multilocular hycophaein, giving dried brown algae their characteristic black color. (plurilocular) gametangia that generate male and female gametes, which are • Phlorotannins have been postulated to function in morphologically identical but have a different – (1) deterring grazing by , behavior. – (2) absorbing ultraviolet radiation, and • Male gametes are chemotactically attracted – (3) serving as a component of cell walls towards female gametes by the substance, sporophytes ectocarpene. • Phlorotannins are not normally secreted outside the cell. It is necessary for the cells to be damaged before the phlorotannins are released. • After gamete fusion, the zygote, without a resting stage, originates a , in which gametophytes either unilocular sporangia or plurilocular sporangia are produced. The latter originates diploid asexual spores that can generate diploid sporophytes. • Gametes can also produce new gametophytes by parthenogenesis, and even haploid zoospores can fertilize to produce sporophytes. •In Ectocarpus, multilocular structures are Chemical structure of phloroglucinal, the basic building formed on both haploid and diploid thalli. The life cycle of Ectocarpus siliculosis. Transmission electron micrograph showing physodes block of polyphenols and the chemical structure of the around the nucleus. polyphenol procyanidin.

• The order Cutleriales is • contains characterized by biflagellate gametes. a single family with two genera, • The male gamete is much smaller than the female one, which produces the Desmarestia and sporophytes Himantothallus, both with multifidene that attracts male pseudoparenchymatous thalli gametes. and heteromorphic life cycles, • The order includes species with life cycles with heteromorphic alternation of microscopic gametophytes and generations, as in , in which the oogamous sexual reproduction. is predominantly • This order is distributed sporophytes composed of dichotomously branched worldwide in temperate and cold flat thalli that produce micro and waters. megagametangia grouped in sori. • The sporophyte is flat and and was described as a different genus named Aglaozonia. •In Zanadinia, the life cycle shows gametophytes isomorphic alternation of generations. gametophytes

Desmarestia The life cycle of Desmarestia. ( The life cycle of Cutleria multifida.

١٢ • In the order , thalli are flat, • consists dichotomous or fan-shaped, growing by one or more of several genera distributed apical cells. from temperate to tropical • Sporangia and gamentangia are grouped in sori. waters. • Sporangia (unilocular) produce four or eight immobile • The thallus is a small tuft of haploid meiotic spores. branches with a parenchymatous • Sexual reproduction occurs by oogamy. gametophytes construction in which growth is • The life cycle of involves the isomorphic by a prominent apical and alternation of generations. pigmented cell. sporophytes • Gametophytes are dioecious, and the oogonia are • For asexual reproduction, the arranged in sori, each oogonium produces a single thallus develops specialized immobile cell (egg) which liberated through the wall branches called propagules. • In multilocular gametangia, male thalli develop • Fertilization can be oogamous, pyriform sperm with two laterally inserted flagella. as in Cladostephus and • Only the pleuronematic (tinsel) flagellum is externally sporophytes Halopteris, or isogamous as in visible, since the other flagellum is reduced to the basal body. Sphacelaria.

gametophytes

The life cycle of .

Left figure: Diagrams of reproductive structures of Dictyota in cross section of the thallus. (a) Sorus with The life cycle of Sphacelaria antheridia. (b) Sorus with oogonia. (c) Tetrasporangium

• The order is characterized by a life cycle • Fertilization takes place during spring tides in the warmer months, when eggs Laminariales and sperm are discharged. involving the heteromorphic alternation of generations, between large sporophyte and microscopic gametophyte. • The egg secretes the pheromone dictyotene • Sexual reproduction by oogamy and plastids without pyrenoids. • Many species of this order, such as Dictyota dichotoma or fan-shaped Padina pavonia, are common in temperate and warm coasts. • Sporophytes reach several meters in height and have a marked morphological differentiation. • Species of Dictyota produce terpenoids, such as pachydictyol and (6R)-6- hydroxydichotoma-3, 14-diene-1,17,dial, that inhibit grazing of Dictyota by • They are attached to the substrate by a system of rhizoids, herbivorous fish, amphipods, and sea urchins called haptera, from which a cylindrical stipe rises, ending in a widening laciniate blade consisting of several layers of cells. • Growth in length is due to an intercalary meristem located between the end of the stipe and the blade. • can live for several years and each year it renews its blade. In winter a new meristem inserted in the base of the blade generates a new blade, and the old one is destroyed at the apex. • The thalli increase in thickness by a layer of cells with meristematic activity known as meristoderm (MR).

Dictyota dichotoma Thallus with regular dichotomous branching Padina pavonia

Cross section of the blade of Laminaria. CX: cortex. ME: medulla. MR: meristoderm luetkeana

• The stipe of Laminaria is cylindrical. In cross section, it shows a meristoderm that produces small pigmented cells outwards and cortical unpigmented cells inwards. • Gametophytes in Laminaria, as in • Cortical cells increase in size from the outside inwards. all Laminariales, are microscopic. • Mucilaginous ducts (canals) are located in the outer cortical layers. These • Female gametophytes consist of ducts are formed by a ring of secretory cells. few cells. Oogonia produce a • Inside the stipe, a medulla is formed by elongated cells with a narrow lumen, single egg, which when mature known as hyphae or trumpet cells (TC), arranged in a network. the oogonium through a pore, but remains attached to the • Trumpet cells are widened at their ends and consist of sieve plates, through oogonium wall. which there is a transport of substances similar to vascular . • Some species of Laminaria can live for several years and produce a growth • Male gametophytes are branched sporophytes filaments. Male unicellular ring per year in their old stipes. gametangia produce a single biflagellate gamete.

• After fertilization, the diploid gametophytes sporophytes grow on the female gametophyte.

Trumpet Hyphae The life cycle of Laminaria japonica

١٣ • Laminariales are subtidal algae which form large populations in temperate and cold seas, comprising the biggest algae such as • The order Fucales comprises pyrifera which can reach 50 meters in length. phaeophyceans in which the life • Species of Laminaria (L. hyperborea, L. digitata, L. ochroleuca) and cycle is diplontic, and thalli are thought to grow by an apical cell that are common in Atlantic coasts. generates a promeristem. • In Pacific coasts, other genera, such as Macrocystis, Nereocystis • In these algae, adult plants are and are dominant. diploid so that meiosis is gametic. • Laminariales, collected in nature or cultivated, are the main source •In , the thalli are dichotomous, of alginates and other compounds such as mannitol and iodine. ribbon-shaped, with a central thickening or midrib, fixed to the substrate by means of a disc. • The reproductive organs are arranged at the apex of the thallus, in widened parts known as receptacles, constituted by multiple cavities or sunk in the thallus. • Inside the conceptacles, male gametes are found in the antheridia and eggs in oogonia, together with sterile filaments or paraphyses that project outside the through an ostiole.

Macrocystis pyrifera Laminaria Macrocystis Nereocystis The life cycle of Fucus sp. (F. vesiculosus and F. serratus).

• Antheridia are on branched filaments, producing 64 biflagellate sperms after meiosis. • Species of the genus Fucus (F. vesiculosus, F. spiralis, F. serratus) • Antheridia have two walls. The breakage of the outer wall releases the are common in cold and temperate coasts of the northern sperm in a package, and then the second wall breaks and the sperm swim hemisphere, while other fucoids, as numerous Sargassum species attracted by the sexual pheromone, fucoserratene, produced by the egg. live in tropical waters worldwide. • The oogonia have three walls that surround eight eggs. Breakage of the • is a genus that may have originated in the Mediterranean outer envelope releases the entire assembly, and after the disruption of the and is characteristic of well structured coastal communities. remaining walls, the eggs float until they are fertilized. • Caulocystis and Horrmosira are common in the waters of the South • The zygote produces a cellulose wall, and then it attaches to the substrate Pacific. and begins to divide to give a new sporophyte.

Cystoseira Life cycle of a monoecious species of Fucus

• is the Japanese name for the dried macroalgae that is derived from a mixture of Laminaria species and used as food. These include L. longissima, L. japonica, L. angustata, L. coriacea and L. ochotensis. • These are all harvested from natural sources. • The first three of the above are the main components of the harvest. • The plants grow on rocks and reefs in the sublittoral zone, from 2 to 15 m deep. They prefer calm water at temperatures between 3 and 20 C. The • Phaeophyceae are thought to have evolved from naturally growing plants are biennial and are ready for harvesting after 20 months. Harvesting is from June to October. ancestors that had reproductive life cycles with the • As demand grew in the 1960s, isomorphic alternation of generations, fertilization by attempts were made to develop artificial cultivation methods, but anisogamy or isogamy and simple morphological types, the 2 yr cycle meant the costs like Ectocarpus. were too high. • In the 1970s, forced cultivation • They evolved towards forms with a progressive reduction was introduced, reducing the of the gametophyte and increased morphological cultivation period to 1 yr, similar to the system developed in China in complexity of the sporophyte, as in Laminaria. the early 1950s. • Diplontic life cycles and fertilization by oogamia, as in • Today, about one third of Japan’s requirements come from Fucus, are considered the most advanced characters cultivation, with the remaining two after an extreme reduction of the haploid generation. thirds still coming from natural resources. • For cultivation, Laminaria must go through its life cycle (d) Long line with Laminaria after 8 months of growth (Yellow Sea, China). (e) Long line showing attached Laminaria plants (South Korea). (f ) Young sporophytes growing on long line

١٤ • Another exploited the Undaria sp., known as , which together with • Laminaria species contain about 10% protein, 2% fat, and useful amounts Laminaria sp. is one of the two most economically important edible algae. of minerals and vitamins, though generally lower than those found in nori. • U. pinnatifida is the main species cultivated; it grows on rocky shores and bays in the For example, it has one tenth the amounts of vitamins but three times the sublittoral zone, down to about 7 m, in the temperate zones of Japan, the Republic of amount of iron compared with nori. Korea, and China • Brown macroalgae also contain iodine, which is lacking in nori and other red • Undaria is an annual with a life cycle similar to Laminaria. macroalgae. • It has an alternation of generations with the large macroalga as the sporophyte and a microscopic gametophyte as the alternate generation. • In China, haidai is regarded as a health vegetable because of its mineral • Undaria is processed into a variety of food products. and vitamin content, especially in the north, where green vegetables are scarce in winter. • The crude protein content of wakame and kombu is 16.3 and 6.2 g (g/100 g), respectively, and both algae contain all essential amino acids, which account for • It is usually cooked in soups with other ingredients. 47.1% of the total amino acid content in wakame and for 50.7% in kombu. • In Japan, it is used in everyday food, such as a seasoned and cooked kombu that is served with herring or sliced salmon.

Brown Algae Ecological Significance • Hizikia fusiforme is another brown algae popular as food in Japan and the Republic of Korea known as Hiziki. • It is collected from the wild in Japan and cultivated in the Republic of Korea. • The protein, fat, carbohydrate, and vitamin contents are similar to those found in kombu, although most of the vitamins are destroyed in the processing of the raw macroalgae. • The iron, copper, and contents are relatively high, certainly higher than in kombu. Like most brown macroalgae, its fat content is low (1.5%) but 20–25% of the fatty acid is eicosapentaenoic acid (EPA).

• Japan produces also okamuranus. The harvested macroalgae are washed, salted with 20–25% salt, and let to dehydrate for about 15 days. Drained fronds are sold in wet, salted form in packages.

Productivity: Up to 1 kg C / m2 / y (Graham et al. 2008)

Brown Algae Ecological Significance Brown Algae Viewing Sites

Point Lobos State Preserve, CA (just south of Monterrey CA)

١٥ Brown Algae Economic Significance Brown Algae Viewing Sites

Brown Algae Economic Significance

Alginate

١٦