L9 - Macroalgal seaweeds : red, green, and brown

Question 1

What is the ecology of algae?

Answer 1

Biosphere - 3 life zones, open sea, shore and land. Open sea and shore more ancient. Here, algae play a role comparable to that played by terrestrial plants. Algae often dominate freshwater habitats e.g. ponds, streams and lakes. Important contributors to ecosystem productivity

Question 2

What is macroalgae structure?

Answer 2

Not a half-way development between microalgae and higher plants. Exhibit differentation, but very simplistic relative to higher plants, attach to rocky substrate with holdfast.

Question 3

What is the importance of macroalgae?

Answer 3

Roles at the land-sea margin vital as home and nursery grounds for many animals. Important for biodiversity. Also of value in global carbon budget. Bioindicators of chemical change (nutrient input). Some species are free floating e.g. Sargassum

Question 4

What is the role of macroalgae in ecosystems?

Answer 4

Bring energy (C) into the system, decay of seaweeds (seasonal, accelerated by storm waves) liberates organics for heterotrophic activity. Also, decrease physical energy, allowing more delicate species to live beneath canopy

Question 5

Macroalgae - how do they provide food for others?

Answer 5

Primary producers at base of food chain. Mucus (anti dessication) and cellulose cell walls limit predatory attack. Molluscs (snails, limpets) sea urchins and a few fish consume them, especially juvenile seaweeds. But generally mature seaweeds are robust.

Question 6

Macroalgae - how do they provide cover for others?

Answer 6

Stabilisation of areas by decreasing wave action. Minimising sand abrasion and loss. Provides substrate for animals to live on, between, or in. Bryozoans obtain an elevated position by growing on the macroalgae. Crabs use seaweed for camouflage.

Question 7

What are rocky shores home to?

Answer 7

Larger complex seaweeds; red, brown and green macroalgae. At low tide, zonation reflects positions of species in relation to their ability to survive exposure. Intertidal zone - large fluctuations of humidity, temp, salinity and light, twice a day.

Question 8

What is rocky shore zonation?

Answer 8

Seaweeds show distinct zonation patterns above and below the tide range. Position on shore reflects ecological tolerances for harsh abiotic conditions. Salinity, exposure, abrasion, wave action. Green seaweed typically occupy upper show. Red seaweed cannot survive desiccation well so must live lower down the shore. Brown seaweed very common at depth but also common mid-shore.

Question 9

What factors affect zonation?

Answer 9

At higher exposure the zonation spreads over a greater height relative to tide range. Some reds are parasitic (Polysiphonia on Ascophyllum), ability to survive desiccation. Survival of osmotic shock from extremes of salinity. Abrasion resistance (sand, stone). Flexibility and strength against wave action.

Question 10

What are brown algae - kelp forests?

Answer 10

Offshore, beyond the wave zone, brown kelps form forests. Provide shelter for a diversity of fish and invertebrate animals. Large carnivores find food and refuge here. Including tuna and sea otters. Humans harvest these kelps for food and industrial products.

Question 11

What is the extreme environments that polar seaweeds experience?

Answer 11

Endure months of darkness under sea ice. Seaweeds are also prey to a host of herbivores and microbial pathogens. Physical and biological challenges. Their complex biochemistries structures and life histories reflect adaptations to these challenges.

Question 12

What is the kingdom plantae?

Answer 12

Green (Chlorophyta) algae and red (rhodophyta) algae. Primary endosymbiosis

Question 13

What is the kingdom chromista?

Answer 13

Brown algae (Heterokontophyta/phaeophyceae), Secondary endosymbiosis

Question 14

Why are macroalgae different colours?

Answer 14

Light attenuation in water: sunlight differs in intensity and quality at different depths. White light at surface but only blue-green light at depths >50m. Red light attenuated in shallower water. Pigmentation adjusted accordingly

Question 15

What is the phylum phaeophyta?

Answer 15

Due to their large size, brown seaweeds were given their own division : phaeophyta. But clearly members of the heterokonts (same group as diatoms). Same pigments as diatoms. But brown seaweeds lack silica cell walls that fossilise. However do have a flagellated stage when reproducing.

Question 16

What is the phylum phaeophyta? pt 2

Answer 16

Brown macroalgae, almost entirely marine. Seaweeds of temperate, boreal and polar waters. Only 1500 species. Dominate rocky shore throughout cooler regions of the world.

Question 17

What is the order Fucales of the phylum phaeophyta?

Answer 17

Bladder wrack, Fucus vesiculosus. Large and found on mid shore in high densities.

Question 18

What is the order Laminariales of the phylum phaeophyta?

Answer 18

Kelp, oarweed, laminaria digitata. Can exceed 10m in length. Blades can grow 6 cm/day. Low shore

Question 19

What is Sargassum?

Answer 19

Order fucales, forms immense floating masses in sargasso sea. Double biomass in <20 d. Forms nuisance growth when introduced into non-native areas. Can outcompete and replace native keystone members of fucales and laminariales communities.

Question 20

What is the brown algae body form?

Answer 20

Huge size range up to largest of all seaweeds (kelps). May be taller than a tree but <5cm thick. Basic form = thallus a simple, undifferentiated vegatative body. Thalli may be simple branched filaments e.g. Ectocarpus. Or aggregations of branched filaments (pseudoparenchyma) e.g. Macrocystis. Large brown algae have highly differentiated bodies. Holdfast - physical link to substrate, 3 designs. Stipe - flexible link between fronds and holdfast. Blade (frond) - photosynthetic, held straight to prevailing current, expose both sides to light.

Question 21

What is the brown algae body form? pt 2

Answer 21

Air bladders (pneumatocysts) in some species aid in buoyancy. May be on stipe or blade. Reproductive structures in receptacles. Mucilaginous, intercellular material - algin. Algin (and cellulose) provides flexibility and toughness to withstand mechanical stresses (waves and currents). Prevemts desiccation at low tide and increases buoyancy. Ecologically and biochemically distinct from true plants. But remarkable parallels in body type and life cycles.

Question 22

What are the pigments in brown algae?

Answer 22

Cells contain numerous disc-shaped, golden brown plastids. Similar to plastids of chrysophytes and diatoms. Chlorophyll a and c. Plus variety of xanthophylls e.g. fucoxanthin (give brown algae its characteristic colour) and carotenoids. Suite of pigments permits photosynthesis at numerous levels in ocean.

Question 23

What is brown algae photosynthate?

Answer 23

Storage material = carbohydrate lamminarin stored in vacuoles. May be up to 34% of body weight. Most live in a stable environment (light, nutrients and temperatures). Continuous growth therefore large reserves unnecessary.

Question 24

What is the phylum Rhodophyta?

Answer 24

Red algae, 98% marine, particularly abundant in tropical, warm waters. Many found in cooler regions. Large group; 4000 to 6000 sp in 680 genera. Only a few are unicellular or microscopic filaments. Majority are structurally complex, macroscopic seaweeds.

Question 25

What is the phylum Rhodophyta? pt 2

Answer 25

<100 occur in freshwater. In sea, number of species exceeds that of all other seaweeds. Usually grow attached to rocks, shells, algae, sea grasses. Many are parasitic on other algae e.g. Polysiphonia.

Question 26

What is the body form of red algae?

Answer 26

Most tend to be conspicuous, often beautifuk individuals. Typically smaller and less complex than brown algae. Early ancestral divergence, before evolution of multicellularity, can attain large sizes, but little differentiation of specialisation among cells.

Question 27

How are red algae distinct?

Answer 27

Especially distinct and fascinating. Numerous structural, biochemical, reproductive features not seen in other algae or true plants. Contain accessory pigments aggregated into phycobilisomes. Phycoerythrin gives them their red colour.

Question 28

What are red algae pigments?

Answer 28

Often appear purple, brown or black owing to additional presence of phycocyanin (as in cyanobacteria). Carotenoids and chlorophyll a also present. Suite of pigments allow red algae to exploit a wide niche. Well suited to absorption of green and blue-green light at depth.

Question 29

Red algae pigments examples?

Answer 29

Phycoerythrin (570nm), Phycocyanin (630nm), Allophycocyanin (650nm) collectively all antenna pigments (phycobilisome). Chlorophyll a (670 + 678nm)

Question 30

What is the red algae photosynthate?

Answer 30

Main food reserves are floridean starch. A branched polymer of starch, similar to glycogen. Stored in cytoplasm not chloroplast. Often sugar reserves occur. Indicate red alga carbohydrate metabolism has characteristic features not shared by plants of other algae.

Question 31

What cell walls do red algae have?

Answer 31

In addition to a thin layer of cellulose, contains a thick layer of slimy mucilaginous compounds : a sulphated galactose. Gives characteristic flexible, slippery texture. Continuous production of mucilage layers rid algae of other organisms that may colonise their surfaces.

Question 32

What cell walls do some red algae have?

Answer 32

Certain red algae deposit CaCO3 in their cell wall = coralline algae. Especially tough and stony. Function of calcification is uncertain. May help them to obtain CO2 from water for photosynthesis and prevent predation. 700 million years old in fossil record. Coralline algae common throughout the world.

Question 33

What is coralline red algae?

Answer 33

Jointed coralline algae occur in tidal rock-pools. Coralline officinalis, also occurs as a complex maerl beds. Maerl = important structural ecosystem for numerous marine animals. Priority feature in scottish seas.

Question 34

What is crustose coralline red algae?

Answer 34

Occurs on surf-pounded shoreward surfaces of coral reefs. Important for stabilising reed structure. Large areas of diverse coral reefs owe their survival to crustose coralline red algae.

Question 35

What is the phylum chlorophyta?

Answer 35

Extremely diverse group, both in structure and life history. 7,000 species (90% freshwater). Most are microalgae. Mostly aquatic freshwater, mostly marine. May grow on tree trunks, in soil, in snow. Also in symbiotic associations with lichens, protozoans, sponges and cnidarian.

Question 36

What are some examples of the phylum chlorophyta?

Answer 36

Unicellular flagellates e.g. Chlamydomonas. Simple colonial e.g. Volvox. Complex multicellular e.g. Ulva lactuta (sea lettuce).

Question 37

How is the phylum chlorophyta important from an evolutionary standpoint?

Answer 37

Organism spent 1 billion years at the unicellular level of organisation. Organisation of complex, differentiated, multicellular bodies - only evolved a few times among algae. Some moved onto land - ancestors of plants. Transition to life on land so complex, occurred no more than 2 or 3 times, perhaps only once.

Question 38

What do the phylum chlorophyta show?

Answer 38

Remarkable developmental and metabolic plasticity. Resilient, surviving many disturbances and changes. Bodies composed of several types of specialised cells - have not evolved in most algal groups. Brown and red algae have attained multicellularity. But brown and red algae are metabolically intolerant of ecological changes and few live in freshwater, soil or inside animals

Question 39

What is the classification of green algae?

Answer 39

Traditionally grouped according to outward structure. i.e. unicellular flagellates, filamentous types etc. Studies of mitosis, reproductive cells and molecular similarities reveal several different classes. We will look at two group; Ulvophyceae, Charophyceae, Chlorophyceae (microalgae)

Question 40

Green algae - what is the class Ulvophyceae?

Answer 40

Ulvophytes, primarily marine. Filamentous or composed of flat sheets of cells. Or macroscopic and multinucleate. Only green algae with alternation of generations with sporic meiosis. Dominant diploid life history involving gametic meiosis. Ulva lactuta, sea lettuce. Common marine species on temperate shores. Individuals are laminar sheets, 2 cells thick. Halimeda sp. green alga with calcified cell walls. Generate white sands of tropical waters. Deter herbivores with secondary metabolites.

Question 41

What are indicative of eutrophication?

Answer 41

Ulva and especially Enteromorpha. After disturbance (e.g. recovery from oil spills) these species are also often the first to appear. They are replaced by browns (e.g. Fucus) as the ecosystem recovers.

Question 42

What is the class Charophyta?

Answer 42

Charophytes, mainly freshwater. Unicellular, colonial, filamentous, parenchymatous. Closest relative to plants. Structural, biochemical and genetic similarities. Asymmetrical flagellated cells with multi-layered structures. Phytochrome, flavonoids and cuticle precursors.

Question 43

What are some characteristics of the class Charophyta?

Answer 43

Spirogyra - unbranched, filamentous. Forms frothy/slimy floating masses in fresh waters. Order charales - stoneworts most similar to bryophytes and vascular plants. Apical growth, eggs in archegonia and sperm in antheridia. Zygotes enclosed in sporopollenin.

Question 44

What are products from macroalgae?

Answer 44

Direct source of our food, alginates (brown macroalgae, agar (red macroalgae), carrageenan (red macroalgae). Widely used to thicken, emulsify, and preserve food and drinks. Agar plates.

Question 45

What are products from macroalgae? pt 2

Answer 45

Laminari (brown algae), traditionally used kelp and sand to make glass. Medicinal uses such as cancer therapies, drug/gene delivery, tissue engineering, antioxidant and anti-inflammatory. Seaweeds high in iodine and selenium - thyroid function.