Lecture 32- Seagrasses and Mangroves

Question 1

What do seagrasses and mangroves have in common?

Answer 1

-live in sheltered environments

Question 2

What are the characteristics of seagrasses?

Answer 2

• flowering plants: have shoots and leaves, rhizomes, roots and flowers, pollen and seeds
• all are monocotyledons
• all are capable of asexual propagation via rhizomes

Question 3

What is the main difference between seaweed and seagrass?

Answer 3

-seagrasses are flowering plants

Question 4

How does pollination of seagrasses occur?

Answer 4

• under water by means of water currents
• have male and female flowers
• flowers and pollen are underwater
• largest pollen in the world: the pollen strands get carried in the water (so being long is an advantage)
• seagrass flowers are inconspicous, male and female flower alternate on the plant (the flower is less than 2mm)
• the flowers don’t need to attract bees or birds

Question 5

What are the habitat requirements for seagrasses?

Answer 5

• usually in soft sediments (different to seaweed)
• sheltered environments (one species lives in rock pools)
• most species are subtidal
• shallow waters
• wide range of salinity, can exist in fully saline water as well as fresh water
• have higher light requirements than seaweed so occur in shallower water
• very common in estuaries

Question 6

What is the distribution of seagrasses?

Answer 6

• about 60 species worldwide
• occur in tropical and temperate regions
• about 20 species in southern Australia and NZ, at least 14 species are endemic

Question 7

What are some local seagrasses?

Answer 7

1. Zostera/Heterozostera: intertidal and subtidal, can be luxurious if subtidal, if intertidal grows less as it is exposed
2. amphibolis: rockpools as well as soft sediments, very large pollen, doesn’t look that grass like, interesting life history: when fertilisation occurs= female flower retained on the parent then floats, and holds seedling in place until it can
3. Posidonia: strap weed, high rhizome and root biomass (50-90%) most of the biomass is under the soil, the high biomass allows it to withstand more wave action than other seagrasses asexual propagation more than seed production, not as common
4. Halophila: paddleweed, leafs are leaflike, temperate and tropical, marine and freshwater, not extensive beds,

Question 8

What is the ecological importance of seagrasses?

Answer 8

• seagrass grows above sediment and in it, each part has animals associated with it, invertebrates in the sediment also on the leafs, many other animals
• if you dig up a sample of sediment with seagrasses and compare to bare sediment= the faun would differ a lot

Question 9

What are the roles of seagrasses in the ecosystem?

Answer 9

1. stabilise sediment and provide habitats
2. provide substrate (for other species to attach, mostly seaweed)
3. food for iconic species (dugong, black swans, and only a few fish species= too much cellulose for fish)
4. nursery areas (provide habitat and shelter for the juveniles we value commercially, king george whiting)

Question 10

What is the problem with humans and seagrasses?

Answer 10

• need sheltered habitat and people destroy it
• many seagrass areas lost in the 70s and 80s
• e.g 85% of seagrass beds in western port
• the reasons for different places where seagrass beds were lost is often different

Question 11

How do humans impact seagrass beds?

Answer 11

• catchment runoff
• small boat anchoring (clearing a patch on the ground)
• dredging
• shiping

Question 12

What is the seagrass watch?

Answer 12

• organization created to facilitate community based monitoring of seagrass beds
• increase community awareness about the importance of seagrass beds

Question 13

What are the characteristics of mangroves?

Answer 13

• trees and shrubs: adapated for intertidal
• 50+ species
• largely tropical
• halophytes= salt loving
• largely estuarine
• grow in soft sediments
• live in sheltered environment (need it)
• provide shelter for coastlines

Question 14

What is special about Australia’s mangroves?

Answer 14

• mangroves at highest latitude in the world

- odd patch in williamstown= between basalt boulders

Question 15

What are the two types of mangrove roots?

Answer 15

1. Pneumatophores (type of aerial roots, designed to be submerged and exposed at some times)
2. Prop roots (aerial roots that help support it in the sediments)
   - have long root (cable root) under sediment

Question 16

How do mangroves cope with salt?

Answer 16

• reduce salt intake= selectively permeable roots, allow water in but not salt in
• reduce water loss=thick waxy cuticle, fewer stomata
• increase salt loss=salt glands, salt transported there and crystalizes out
• isolate salt=push it into old leaves and these are shed sometimes

Question 17

What is the mangrove food web like?

Answer 17

• high depositional environment
• lot of nutrition
• complex substrate
• fish will move in with the tide

Question 18

What is Avicennia marina the local mangrove species like?

Answer 18

• in tropics: grows bigger, faster and fruits faster
• seed germinates on tree, drops off, floats about for 3 days, then sinks, adrift for up to 5 months before it finally takes root

Question 19

What are the threats to mangroves?

Answer 19

• poor public image: muddy, smelly and lot of mozzies
• reclamation and development
• changed the patterns of water flow
• now called wetlands

Question 20

What is a salt marsh?

Answer 20

• can only be submerged occassionally, higher up from the sea
• high intertidal areas of grasses, succulents and small shrubs
• the definition of saltmarsh recently broadened
• like mangroves: halophytes, lergely estuarine, soft sediments, sheltered environments

Question 21

What are the sorts of plants in saltmarshes?

Answer 21

• have water in
• squishy
• pig face is one

Question 22

What is the pattern in occurrence of seagrasses, mangroves and saltmarshes?

Answer 22

• seagrass in sheltered and subtidal
• mid intertidal to high intertidal= mangroves
• the places that are infrequently indendated= saltmarsh