Ch. 6: Multicellular Primary Producers

Ch. 6: Multicellular Primary Producers: Seaweeds and Plants When we think of photosynthesizers we think of plants But in the ocean they are photosynthetic bacteria, unicellular algae (from Ch. 5) and seaweeds! They are considered plant-like because they are all primary producers They can photosynthesize

Seaweeds A type of Algae Play an important role in coastal environments Use solar energy to produce organic matter for food webs Organisms live on or in their tissues Produce oxygen for organisms in the ocean and on land Can Photosynthesize

6.1 Multicellular Algae: The Seaweeds The most familiar types of marine algae are seaweeds They’re not weeds, so some biologists called them macrophytes or macroalgae They are multicellular and eukaryotic More complex structure and reproduction than unicellular algae less complex than plants Kingdom Protista

General Structure Don’t have roots, stems or leaves like plants The body is known as the thallus The leaf-like structures are blades Large, flat surface for photosynthesis

Gas-filled bladders called pneumatocysts keep it near the surface to get more sunlight The stipe is like a stem; it provides support The holdfast attaches the thallus (body) to the bottom Cannot anchor in sand, needs a hard bottom Water and nutrients are absorbed across the surface of the whole alga

Three types: green, brown & red B. Types of Seaweeds Three types: green, brown & red Turn paper to the back and make 3 columns labeled green, brown, and red

1. Green Algae – -phylum Chlorophyta LEAST COMPLEX!!! Only 10% of 7,000 species are marine Found in freshwater, terrestrial, and marine habitats Simple thallus Same pigments and food reserves as plants; thought to have evolved into land plants

Green Cont. Common on rocks in shallow water and tide pools Different sea lettuce (genus Ulva) species are widespread; from polar to tropical waters Halimeda is a calcareous green alga that has deposits of calcium carbonate in its thallus As they die and accumulate they help build coral reefs

Green Seaweed (Algae)

Brown Algae – phylum Heterokontophyta, class Phaeophyta Color varies from olive green to dark brown Has more yellow- brown pigments, like fucoxanthin, than chlorophyll Almost all 1,500 species are marine

Brown Algae Cont. Dominant primary producers on temperate and polar rocky coasts The largest and most complex seaweeds Rockweeds (genus Fucus) is found on Atlantic and Pacific coasts of N. America

Brown Algae Cont. In warm waters (Gulfs of Mexico and California) Sargasso weed (Sargassum) are found Pneumatocysts keep the blades afloat Some grow on rocks, some float offshore in huge masses The Sargasso Sea gets name from it

Brown Cont. The kelps are the largest and most complex of the brown algae Most found below the tide level in temperate and sub- polar regions Huge forests grow providing food and shelter for many organisms Laminaria consists of a single large blade up to 10 ft long ¨ Harvested for food in several parts of the world

The blade of Alaria can be 80 ft. long Bull kelp, Nereocystis, has a 90 ft. long stipe with a large pneumatocysts and several blades at the top Macrocystis is the largest of the kelp ¨ Massive holdfast is attached to hard bottoms ¨ Several long stipes and long blades ¨ A pneumatocysts at the base of each blade ¨ Have been found over 300 ft tall! ¨ Can grow 20 inches per day Kelp beds or kelp forests are among

Kelp beds or kelp forests are among the most productive marine environments ¨ Found in the colder waters of the North and South Pacific ¨ The tops are chopped off to harvest food and several other natural products

Red Algae – phylum Rhodophyta Almost all of the 4000 species are marine More species than all green and brown combined Have red pigments called phycobilins, which mask the green chlorophyll Inhabit most shallow-water marine environments Some are parasites of other seaweeds Some have no chlorophyll and depend solely on their host

Red Algae Cont. Can grow as dense clumps in upper tidal areas or long, flat branches in deeper water Coralline algae deposit calcium carbonate within their cell walls Encrusting grows on rocks or branched (articulated) like a plant Their secretions help form coral reefs by cementing it together

STOP WRITING ON CHART!! CONTINUE NOTES Seaweed Life Cycle Seaweed produces in two ways: Asexual (vegetative reproduction) is common and more important than sexual reproduction Thallus fragments of Sargassum can grow into new individuals Spores are resistant cells that can disperse to new locations Zoospores have flagella for movement In sexual reproduction gametes from different parents fuse to recombine the genetic information Each generation shows genetic variation Cells divide and multiply by mitosis; gametes are formed by meiosis

During a seaweed’s life cycle they may exist as one of four different types One type of thallus is a diploid sporophyte will produce haploid spores The spores divide and grow into another type of thallus, a haploid gametophyte The gametophyte produces haploid gametes The gametes fuse to form a diploid zygote that grows into a sporophyte This type of life cycle is called alternation of generations Sometimes the sporophyte looks just like the gametophyte, sometimes the gametophyte is much smaller

Economic Importance People around the world harvest seaweed for many uses Mostly as a food source Also used for fertilizer, animal feed, and wound dressing Mariculture, the farming of seaweed, is big business in China, Japan & Korea Seaweeds produce gelatinous phycocolloids used in foods They produce viscous gels

Algin – used as a stabilizer and emulsifier in dairy products like ice cream & cheese ¨ It gives it a smooth texture ¨ Keeps frosting and pies from becoming dry ¨ Also found in shampoo, shaving cream, plastics, rubber, paper, paints, cosmetics, and pesticides ¨ The giant brown kelp, Macrocystis, is a major crop for algin ¨ Harvesting ships off the California coast cut stipes and fronds (blades) to a depth of six feet below the surface

Carrageenan – used as an emulsifier ¨ Obtained from red algae ¨ Gives body to dairy products and pudding Agar – used for its ability to form jellies ¨ Protects ham, fish, and meats during canning ¨ Used in low-calorie foods, since it is not digestible by humans ¨ Used as a thickener, in laxatives, and in cosmetics ¨ Used by biologists to grow bacteria in Petri dishes

6.2 Flowering Plants Of the 250,000 species of plants only a few live in the ocean They are more evolved than algae, and have true leaves, stems and roots with tissues to transport water and nutrients

Seagrasses Not really grass, evolved from land plants (the lily family) About 60 species Live mostly submerged in shallow waters, such as bays and estuaries

B. Salt-Marsh Plants Cordgrasses are members of the grass family Not marine, but can tolerate high salt areas (halophyte) Salt marshes and coastal mudflats Salt glands in the leaves excrete excess salt

Mangroves Adapted to life along tropical and subtropical shores Land plants that can tolerate salt Like muddy or sandy shores protected by waves Include about 80 mostly unrelated species of trees and shrubs

Mangroves Cont. Have adapted to an environment where salinity is high, water loss from leaves is high, and sediments are soft and poor in oxygen Thick leaves reduce water loss Seeds germinate while still attached to the parent Foot-long seedlings fall and stick into the soft ground like a knife or float in the water to disperse to new locations