Photosynthesis in the oceans

vii. Adaptations of Marine Plants.

A. General.

1. Less than 2% of the substrate in the oceans is available for attachment for

marine plants, inasmuch as most of the substrate is too deep for proper light conditions, and some of the shallow areas are unsuitable for attachment (sand, mud, shingles). Thus, the adaptations of the marine plants have gone mainly in the direction of staying afloat (the maintenance of buoyancy) within the euphotic zone of the oceans, especially noted by observing the structures of the diatoms and dinoflagellates.

2. Photosynthetic zones in the oceans :

a. Euphotic zone: where there is sufficient light for photosynthesis to go on

well; this is the surface area in the oceans, down to depths of around 80 meters, in which the production of oxygen by the plants during photosynthesis is greater than the uptake of oxygen by the plants to carry out respiration.

b. Dysphotic zone: where there is light present to carry out

photosynthesis, but not very well. The production of oxygen by photosynthesis is less than that taken up by respiration. This is that layer in the oceans below the euphotic zone and down to depths of no greater than 200 meters.

c. Aphotic zone: where there is not sufficient light present to carry out any
photosynthesis at all.

3. The vegetation of the open sea must be floating freely in the water in order to
be sufficiently near the surface to get enough light.

4. Phytoplankton consists entirely of plants of microscopic size.

a. Sargassum of the Sargasso Sea is really a near-shore, attached plant. It

neverproduces reproductive organs while floating in the Sargasso Sea, whereas it does while attached.

b. All phytoplankton are unicellular, although some form colonial chains

in which the individual one-celled plants are attached to each other.

c. Must mean that small plants have some advantage over large plants as

phytoplankton.

d. Specific gravities:

1). Sea water = 1.02575

2). Protoplasm = 1.02 to 1.06

3). Shells =>1.06