Multicellular Algae: Seaweeds
Eukaryotic
Primary producers
Not weeds, but algae.
Most biologists agree that macrophyte is a much better name, macroalgae too
Lack true leaves, stems, and roots
Physical Characteristics
Thallus = the complete body
Blade = leaf like, flattened portions
Pneumatocysts = gas filled bladders, keep upright so towards sunlight
Stipe = stem-like
Holdfast = attaches seaweed to a substrate
Types of Algae Classes
Chlorophyta = Green
Phaeophyta = Brown
Rhodophyta = Red
Macroalgae: Green algae
Have the same pigments as land plants (chlorophyll)
More than 7,000 species
Phaeophyta: Brown Algae
Largest (size) and most complex of the algae
Nearly all are marine (~1500 spp.)
Brown color comes from accessory pigments (fucoxanthin)
Kelps
Kelps are the largest seaweed we encounter in the ocean. They are also the most complex.
Due to this large size, many of the kelps are harvested for food!
Giant Kelp, Macrocystis pyrifera
-The largest of the kelps.
-Anchors itself to the sea floor by use a massive holdfast.
-Extensive pneumatocysts used for buoyancy.
-Pneumatocysts= keep the seaweed close to the surface to maximize photosyhthesis
Macrocystis pyrifera
-This kelp obtains huge proportions growing as much as 0.5m/day!
-Kelp forest are great for sheltering all sorts of marine life, fish, invertebrates seals and sharks.
-Harvest of the upper sections of the blades for food.
Rhodophyta-red algae, are more numerous than the green and brown algae combined(including aquatics).
--Corallina, a coralline algae, deposits CaCO
3
within its cell walls which provides structural support and often encrusting many surrounding surfaces.
Products from Seaweed:
• Phycocolloids—form gels and increase viscosity of liquids
• Algin—stabilizer in ice cream (Macrocystis)

• Carageenan—emulsifier (Irish Moss, Chondrus)
• Agar—jellies (and of course all your plates in microbiology,
• Gelidium, Pterocladiella)
• Certain alga can be used to make agar or as stabilizer in gelatin and ice cream
• Thickener and help smooth for many foods and milk-products
• Toothpaste
• Beauty creams
• Paints
• Medical products- like bacterial culture plates, time-release pills, and dental impression gels
Flowering Plants
• Flower, reproductive organ
• Photosynthetic
• Eukaryotes
• True stems, roots, leaves
• Dominant on Land, few Marine species
True Flowering Plants: Seagrasses
Salt Tolerant Plants =
Salt Marsh grasses
Mangroves
Seagrasses have rhizomes, or horizontal stems which grow beneath the sediment.
--Provides habitat for juveniles and larvae of many marine species
--Anchors sediments
--Helps stabilize soft bottoms
--Protects coast from turbulence and erosion
Salt Marsh plants
Salt water tolerant species = halophytes
Do not tolerate total submergence
Act as water purification system
Habitat and breeding grounds for many fishery species
Protect against erosion
Examples Salt Marsh Plants
Salt Wort, Cordgrass
Mangroves
-Mangroves thrive in salty environments and are able to obtain freshwater from saltwater.
-Some spp. secrete excess salt through their leaves while other block absorption of salt at their roots.
-Mangrove Impacts
• -Trap and cycle organics, chemical elements, sediment and minerals.
• -Provide shelter for marine organisms.
• -Leaf litter important for decomposition, recycling nutrients.
• -Provide shelter/habitat for marine organisms—often economically important ones.
• -Nearly all commercially/recreationally important fisheries spend a portion of life in mangroves and/or seagrass
• -Stabilize the coastline, reducing erosion from storm surges, currents, waves, and tides.