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

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

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

blade holdfast stipe

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

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

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

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

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

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

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 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

Pennate diatoms

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

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

Benthic cyanobacteria Lyngbya

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

The End