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12 Seaweeds, Sea Grasses, and Benthic Microorganisms

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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

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