18 THE RELATION OF PLANTS TO TIDE-LEVELS 
2. THE BOTTOM VEGETATION OF THE HARBOR FROM -5 TO +1.5 FEET 
(THE SUB LITTORAL AND LOWER LITTORAL BELTS). 
The present belt includes 1.5 feet of the lower part of what Kjellman calls 
the “ littoral region,” 1. e., of the strip between low and high tide marks. It 
also includes 5 feet vertically of bottom below the mean low-water level, 4. ¢., 
5 feet of what Lorenz calls the “ submerged littoral region.” 
The plants forming the bottom vegetation of this harbor consist of (A) plants 
of the loose soil; (B) algz attached to stones or shells; (C) epiphytes living 
chiefly on members of group A. 
A. PLANTS ON LOOSE SOIL (THE ENHALID FORMATION OF WARMING). 
This formation includes two seed plants, Zostera and Ruppia, which are 
rooted in the soft bottom, and only two important alge, Ulva lactuca and 
Enteromorpha clathrata. Most of these latter are unattached, and either 
simply rest on the bottom or are weighted down by mud or mussels. The Ulva 
grows in sheets, the Hnteromorpha in tangles. In looking down on the bottom 
of the harbor from the neighboring hills at low tide, 1. e., with the water- 
surface at —1 foot, the bottom over most of its area appears green in color. 
This green color is due to the presence of the more or less uniform covering 
either of Ulva lactuca or of Zostera marina, or, on some smaller areas, of 
Enteromorpha clathrata. The most considerable bare area on the part of the 
bottom, exposed by the lowest tides, is that at the north and northwest portions 
of the harbor, which lies between the —1-foot level and the 2-foot level. Besides 
this there are two or three narrow strips, 12 to 15 feet wide, and trending more 
or less northward from the mouth of the main fresh-water stream at 200 north 
by 550 east, which are rather constantly bare. (See plates 11 and vit.) There 
are other smaller changeable bare spots on various parts of we bottom outside 
the Zostera belt. 
Of those portions of the harbor bottom still covered a the water is at 
—1 foot, the bottom of the tide-channel starting near the wharf of the Research 
Laboratory at 1,100 north by 400 west, and emptying into the deep hole at 1,400 
north by 400 east, is nearly bare of Ulva and Zostera. Likewise, the greater por- 
tion of the deep hole itself, and of the channel leading from it to the Outer 
Harbor, have a rather bare, sandy, shelly, or pebbly bottom, except for that 
portion to the east and south of the deep spot which is indicated on the map as 
covered with Zostera. The plants of Ulva found under these more swiftly 
moving waters are small attached plants which are evidently being carried along 
with their supports. ‘The area occupied by a dense growth of Zostera is indi- 
cated on the map by a wavy outline marked Z. Its distribution will later be 
described in some detail. 
The rest of the harbor bottom below the 1.5-foot level, aside from the bare 
areas mentioned above, is rather completely covered with Ulva. This Ulva 
occurs in the form of innumerable detached flattish, or crumpled, or bullate 
and often perforate and ragged sheets, of all sizes from a few decimeters to 10 
meters across. The distribution of much of this Ulva over the bottom is more 
or less inconstant. Often the bottom is covered completely for hundreds of 
square meters, e. g., 400 to 1,000 north by 200 west to 400 east. In other 
portions of the harbor only one-half or three-fourths of the bottom is actually 
hidden by the Ulva, e. g., near the west side at 0 to 600 north, or near 200 north 
by 400 west. 
