1. 12 Seaweeds, Sea Grasses, and Benthic Microorganisms
Notes for Marine Biology: Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001

2. Seaweeds Usually connect to a substratum
Take up nutrients from surrounding water
Need not have the support structures required
of terrestrial plants

3. Seaweeds 2 Individual seaweed attached to substratum
is a thallus, varies from a tarlike crust, to thin
sheet, to erect branching forms
2. Thallus is often attached to surface by means
of a holdfast
3. Stipe is the usually tubular and sturdy
Structure that connects holdfast to rest of
Thallus
4. Flattened section of a thallus is known as a
blade

4. blade
holdfast
stipe

5. Variation of form in seaweeds
(c)
(b)
(a)
Ulva sp.
(b) Codium fragile
(c) Corallina sp.
(d) Polysiphonia sp.
(e) Laminaria sp.
(d)
(e)
Variation of form in seaweeds

6. Seaweeds 3 Seaweed growth: In smaller seaweeds, can occur nearly
anywhere on thallus
In larger seaweeds, occurs in specialized
growth areas known as meristems

7. Seaweeds 4 Seaweed classification
On basis of pigments used in gathering light
for photosynthesis, by storage products, and
by type of flagellae in spores

8. Photosynthetic Pigments Chlor. a, d Phycoerythrin, Phycocynanin
Seaweeds 5
Seaweed Group
Photosynthetic Pigments
Storage Products
Cell 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

9. Seaweeds 6 Seaweeds have complex life cycles:
Haploid (N chromosomes) often alternates
with diploid (2N) phase
Gametophyte produces gametes, released from
gametangia (single cells or more complex
structures)
Gametes merge to form zygote --> sporophyte

10. Seaweeds 7 Life history types Codium Ulva Laminaria G S G S G
Isomorphic Heteromorphic Single morph.
phase
G = gametophyte, S = sporophyte

11. Seaweeds 8
Seeweed Groups

12. 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

13. Green seaweed Enteromorpha, with red coralline algae

14. 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

15. Brown seaweed Fucus sp.

16. Pacific coast brown seaweed Hedophyllum sessile

17. 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

18. Coralline algae with chiton

19. 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

20. Sea grass Phyllospadix

21. 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)

22. Benthic Microorganisms
Diatoms
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

23. Pennate diatoms

24. Benthic Microorganisms 2
Bacteria
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

25. Benthic Microorganisms 3
Blue-Green Bacteria (Cyanobacteria)
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

26. Benthic cyanobacteria Lyngbya

27. Benthic Microorganisms 4
Fungi
Very common in marine environment
Usually heterotrophic, extremely important in decomposition processes of particulate organic matter

28. The End