12 Seaweeds, Sea Grasses, and Benthic Microorganisms

Notes for Marine Biology: Function, Biodiversity,

EcologyBy Jeffrey S. Levinton

©Jeffrey S. Levinton 2001

Seaweeds

1. Usually connect to a substratum2. Take up nutrients from surrounding water3. Need not have the support structures requiredof terrestrial plants

Seaweeds 2

1. Individual seaweed attached to substratumis a thallus, varies from a tarlike crust, to thinsheet, to erect branching forms2. Thallus is often attached to surface by meansof a holdfast3. Stipe is the usually tubular and sturdyStructure that connects holdfast to rest of Thallus4. Flattened section of a thallus is known as ablade

holdfaststipe

blade

(a) (b) (c)

(d)(e)

Variation of form in seaweeds

(a) Ulva sp. (b) Codium fragile(c) Corallina sp. (d) Polysiphonia sp. (e) Laminaria sp.

Seaweeds 3

Seaweed growth:

In smaller seaweeds, can occur nearlyanywhere on thallus

In larger seaweeds, occurs in specializedgrowth areas known as meristems

Seaweeds 4

Seaweed classification

On basis of pigments used in gathering lightfor photosynthesis, by storage products, andby type of flagellae in spores

Seaweeds 5Seaweed Group Photosynthetic

PigmentsStorage

ProductsCell Wall

Green algae Chlor. a, b Starch Cellulose (not all)

Brown algae Chlor. a, c Fucoxanthin

Laminarin Mannitol

Alginate

Red algae Chlor. a, d Phycoerythrin, Phycocynanin

Floridian starch

Agar, Carageenan

Seaweeds 6Seaweeds have complex life cycles:

Haploid (N chromosomes) often alternateswith diploid (2N) phase

Gametophyte produces gametes, released fromgametangia (single cells or more complex structures)

Gametes merge to form zygote --> sporophyte

Seaweeds 7

N

N2N

N

2N

2N

N

N

N

N

N2N

Isomorphic Heteromorphic Single morph. phase

G S G S G

Ulva CodiumLaminaria

G = gametophyte, S = sporophyte

Life history types

Seaweeds 8

Seeweed Groups

Green seaweeds (Chlorophyta)

• Similar photosyn. Pigments to higher plants

• Range of form from one cell to filmy forms such as Ulva to finger shaped Codium

Green seaweed Enteromorpha, with red coralline algae

Brown seaweeds (Phaeophyta)

• Range from small filamentous forms to common seaweeds on the shore such as Fucus, to enormous kelps (e.g. Macrocystis)

• Get color from pigments xanthophyll and carotene

• Contain phycocoloids, alginates, other substances used by people in toothpaste, pills, salad dressing, potash and acetone also extracted from some species

Brown seaweed Fucus sp.

Pacific coast brown seaweed Hedophyllum sessile

Red seaweeds (Rhodophyta)

• Phycoerythrin is the pigment giving them color

• Complex life cycles• Great range of forms, including calcareous

forms common on coral reefs, rocky subtidal reefs

• Carageenan obtained from Irish Moss for material used in cream cheese, ice cream. Agar is extracted from Gracilaria

Coralline algae with chiton

Sea Grasses• Flowering plants, including eel grass Zostera

marina, turtle grass Thalassia testudinum• Flowers are not fancy (no animal pollinators)• Pollen floats along until encountering a

receptive stigma• Seeds move a short distance before setting

and germinating, turtle grass fruit can travel longer distances

Sea grass Phyllospadix

Sea Grasses 2• Usually grow asexually by means of

rhizome system, which extends beneath the sediment surface

• Often have high cellulose content, difficult to graze (eel grass hardly grazed at all)

Benthic Microorganisms

• Occur as single cells or chains of cells, cells can move in sediment pore water

• Skeleton made of silica• Benthic forms dominated by pennate

diatoms• Cell division main form of growth, but

also sexual reproduction• Most occur singly, but some are colonial

Diatoms

Pennate diatoms

Benthic Microorganisms 2

• Occur as single cells or in connected groups

• Crucial in decomposition• Bacterial reproduction through cell

division, genetic exchange between cells possible

• Most are heterotrophic, but there are a wide variety of types, acting on many different substrates

Bacteria

Benthic Microorganisms 3

• Occur free living but also as symbionts with plants and animals

• Photosynthetic but also capable of nitrogen fixation

• Commonly multicellular arranged in cell rows (trichomes), grouped into filaments

• Nitrogen fixation occurs in larger cells, heterocysts

• Blue greens can make resting spores

Blue-Green Bacteria (Cyanobacteria)

Benthic cyanobacteria Lyngbya

Benthic Microorganisms 4

• Very common in marine environment

• Usually heterotrophic, extremely important in decomposition processes of particulate organic matter

Fungi

The End