Oct. 1

Seagrasses:
 
The seagrases evolved like the mangroves in the Tethys Sea during the
Cretaceous period.  They evolved from terrestrial grasses.  Several
 genera were able to evolve before the Atlantic
and Pacific formed.  There are now 12 genera with 50 species.  All are
rooted in soft mud or sand substrates and are found offshore of
salt marshes and mangroves, here they are protected form the full force of
wave action.  All seagrasses have horizontal stems and regular roots.
Seagrasses have very high productivity, up to 600 g/m2/ yr.  (A good
amount of this biomass is epiphytic, with algae growth on the blades.)  

There are 3 morphs found in seagrasses; blades, tubular stems, and spoon
or ovid stems.  Some species are monecious (male or female), and some are
diecious (both).  Pollen is released into the water and transported to the
female.

Zostera is an example of a seagrass that pollinates via the air.  This is
because this species can tolerate low tides and is found growing in areas
with a lesser amount of water than usual.

In the temperate regions (20 C or less) there are 5 genera, and 7 genera
are found in the tropical regions (greater than 20 C).  If a species is
euryhalic, it can take a wide variety of salinities.  

Manatees and turtles are associated with the seagrasses, as well as
mollusks and crustaceans.  

In the division Anthophyta there are 3 families.
1.  Hydrocharitacea
	Thallasia (turtlegrass) - this is the most common seagrass, found
in the tropics.
	Halophila - deepest growing, up to 85 m.
	Enhalus - found in the intertidal zone with Zostera.
2.  Potamogetonaceae
	Zostera - second most common seagrass, found in temperate and
tropic regions, 	there are 10 species.
	Heterozostera - close relative to Zoestra.
	Philospandix - 5 species are found in the temperate zones.
	Ruppia (widgeon grass) - tropical.
	Posidonia - temperate.
3.  Zannichellaceae
	Cymodaceae - tropical.
	Thalasodendron - 3 tropical species, all in Indonesia.
	Halodule (shoal grass) - 3 tropical species.
	Syringodium - manatee grass.

Some uses of seagrasses are as dolls, mats, and baskets (especially
Zostera and Thallasia by native Indians). The Misquito Indians also ate
the seeds of Thallasia.  Seagrasses are also beds for predatory
gastropods,  helmet shells and conchs which makes them valuable.




Diseases in seagrass beds:
1931 - East coast,  Zostera marina hit with wasting disease.
1932 - Wasting disease showed up in Europe.
1933 - 90-99% of this species gone, took decades for Zostera to recover.

The biggest problem now for seagrasses seems to be dredging.

There are several methods for revegetation:
	transplanting new beds - estimated costs are $2000/acre in 3 ft.
of water, and $200,000/acre in 8 ft. of water.
Non-anchoring methods include:
	plugs
	cans with bottoms cut out - transplant cans.
	direct seeding
	transplanting mats

      Anchoring methods include:
	use of ties or rubber bands
	weaving into plastic or paper mesh

R. Felger observed the Seri Indians in the Gulf of California and wrote
two papers on their practices.  The first described how Zoestra was washed
to the beach and then collected and used as a food source.  The second
discussed the indigenous practice of turtle hunting, which was passed on
to the Mexican people .  This sharing of knowledge quickly wiped out the
turtle population living in seagrass beds.

Oct. 8

Mangroves:

The zonation of mangroves is based on salt tolerance and temperature.

White				Black 				Red
(Lagunclaria)	  		(Avicennia)
(Rhizophera)
needs freshwater influence	tolerates saltwater		completely
salt tolerant
least cold tolerant		cold tolerant			most cold
tolerant

The theory of propagule sorting states that the trees with the largest
fruits are found in the front (Red) and the smallest fruit bearing trees
are found in the back (White).  This is because the tides carry the
smallest seeds to the back of the mangrove, while the big ones stick to
the front.









1.  Shoots/Leaves
	Mangroves are not very good at spreading vegetatively, instead
they    
inch seaward using reclining branches.  Rhizophera is a good example of
this, its reclining branches reach down to the ground and then take root.
The stilt roots prop the tree up.  	The leaves are all almost uniform
in shape and size.  Common features are leathery leaves to tolerate
flooding, tannins to protect against fungi, and the leaves are succulent
for salt balance.  Avicennia has salt excreting glands, the whole leaf
surface can be covered in NaCl crystals.  Rhizophera does not have salt
excreting glands.  Both of these species have cell sap that is saltier
than seawater. 
	The Rhizophera stem has many small vesicles (50-100 microns) that
are used to carry water instead of a few larger ones.  The high osmotic
pressure of seawater causes the water that is carried in these vesicles to
be pretty pure.  Because this system is under high negative pressure, it
is in danger of collapsing.
	    
2.  Roots
	Roots are used to anchor the plant and for aeration of soils.  In
Rhizophera, there is a long cable of anchoring roots above the surface.
These are aerial roots with lenticles (holes) which allow air into the
plant.  Sometimes these roots can be knee to chest high.
	Avicennia also has a cable root but it is growing underground with
pnuematophores reaching above ground.  The pnuematophores obtain oxygen
for the plant.  In Asia, an extension of the cable root has produced root
knees, which are small nubs above ground.
	Both of these species have long, extensive root systems because
they are only rooted about a foot beneath the soil.

3.  Propagules
	Mangroves are pollinated by everything from bats, birds, mice,
insects, butterflies, and the wind.  Their flowers are well developed and
very 'showy' to attract pollen spreaders.  
	The fruits of mangroves are well adapted to marine environments.
They are vivipary, meaning that the seed germinates and grows on the
parent plant before it is released into the marine environment.  In
Rhizophera, the radicle grows out of the end of the fruit until it is
mature.  It then falls of and the hypocoyl becomes the root of the plant.
The plumule becomes the leaves.

Uses of mangroves:
The wood of mangrove trees has been traditionally used for lumber, fuel,
poles, and for its tannins and dies.  Modern uses include conversion to
farmlands, shrimp farms, salt pans for salt production, and urban uses
such as marinas and subdivisions.