Seagrass habitats

Question 1

What are seagrasses

Answer 1

Monocotyledonous with strap like leaves
Not true grasses
Intertidal or subtidal, form seagrass meadows that stabilize the sediment of seabed and provide a source of primary production and habitat
Fully adapted for life in the sea and generally fully submerged but some species can grow intertidal
60 species in 12 genera (low diversity)
Evolved from a single lineage of monocot flowering plant 70-100 mil years ago

Question 2

What are Monocotyledonous plants

Answer 2

Monocotyledons have one seed, flower petals in multiples of 3 or 3, fibrous roots, long thin leaves with parallel veins, lack secondary growth, and its vascular bundle is scattered

Question 3

Seagrass morphology

Answer 3

Horizontal rhizome growth in sediment
Vertical rhizome protrudes above, leaves develop from basal meristem

Question 4

Seagrass growth environment

Answer 4

Most grow in mud or sediment but phyllospadix can be found growing on rocky shelves
Seagrasses make life better for every other organism (they reduce turbidity and trap suspended sediment).
As such, their presence increases light penetration and enhances photosynthesis

Question 5

Photosynthesis in seagrass

Answer 5

Irradiance of at least 11% is required for seagrass photosynthesis
Seagrass leaves lack stomata and produce a thin, porous cuticle to absorb CO2 from water, but levels are low

Question 6

Why are CO2 levels low

Answer 6

Because in seawater, CO2 is found in the forms:
· CO2(aq) + HCO3. + CO32 = [CO2]
· [0.5%] + [89%]+[10.5%] = [CO2]
(at 15C, 35 psu, speciation is bottom line dissolved concentration denoted in[])
So mostly bicarbonate, but seagrasses have developed adaptations to utilise this as a CO2 source.

Question 7

Leaf physiology of seagrasses

Answer 7

They have a single layer of chloroplasts in the epidermis, and a large gas lacunae containing oxygen-enriched gas (probably from photosynthesis).
There is a wide range of depths at which seagrasses can grow but depth limits the photosynthetic capacity of the plant.

Question 8

Tolerance to salinity

Answer 8

Tolerance is relatively narrow and species vary in their response to salinity as can be seen right where leaf extension is measured in 3 species at different salinity levels

Question 9

Globally, estimated habitat loss Is occurring at 7% a year and 44% of seagrass now grows in area just 150km2 size, what are the causes?

Answer 9

Chemical pollution (eutrophicaation
Fungal wasting disease
Reduced water development
Coastal development
Physical damage
Reduced water quality