80 UNDERWATER GUIDE TO MARINE LIFE 



It may grow in sand, or mud, in tidepools, or on wharves and rocks. It is tem- 

 perate and tropical in distribution. The sponge seaweed, Codium, has a 

 spongy texture and is branching. It is very common in the warm waters of both 

 coasts. It grows to a height of about 8 inches. A few green algae are calcified 

 as are many red algae. Halimeda is a tropical reef-building calcareous alga. One 

 of the oddest of green algae is the tropical merman's shaving brush, Penicillus 

 Cfig. 43^. It grows to 5 inches high, and the name perfectly describes its shape. 



The green algae are probably the ancestors of all later plants. They show 

 strong similarity to higher plants in their pigment chlorophyll, which is carried 

 in typical bodies in the plant cells called "chloroplasts." Chlorophyll is green, 

 so it absorbs all colors of the spectrum except green, which it reflects. Therefore, 

 the chief light rays used in photosynthesis are of the red and blue ends of the 

 spectrum. Because there is very little red left in water below 15 to 20 feet, 

 the green algae cannot photosynthesize efficiently there and are rarely found 

 in this greenish water. Surprisingly enough, some green algae live deeper than 

 any other photosynthetic plants. Some are found at depths of 200 feet where 

 they use the dim blue light that is available. 



BROWN ALGAE: Phylum Phaeophyta— F/^wrt'^ 20 and 21 



This is an almost exclusively marine group of over a thousand species and 

 includes the largest and most conspicuous of all algae, the kelps. The color is 

 brown to olivaceous and is caused by the presence of fucoxanthin, an accessory 

 pigment which increases absorption of green light. Fucoxanthin passes the 

 energy it absorbs on to chlorophyll for utilization. Chlorophyll itself absorbs 

 reds and blues for photosynthesis. Thus, brown algae are the most successful 

 utilizers among algae of a wide range of the colors of the spectrum and are, 

 therefore, the most conspicuous and most varied algae of the sea, both in form 

 and habitat. 



The brown algae are typical of rocky shores from the tidal zone to depths 

 of 50 or 100 feet or more. The deeper ones are long, however, and are able to 

 reach up into shallower waters for light. The temperate to arctic zones see 

 the greatest variety and abundance of them, though they are present in tropical 

 seas also. 



There is a great variety of form among these algae. Most of the following are 

 of temperate to arctic distribution and are found on both coasts. Ectocar^us 

 grows to 12 inches and is filamentous and branched. It frequently grows on 

 other algae, that is, is an epiphyte. Fiicus, rockweed, is very common on rocky 

 shores in the tidal zone. This is the alga that makes whole shores look brown. 

 It has little buoying bladders along the stem, which, when dry, make a popping 

 noise as they are burst underfoot. Rockweed is not found in tropical waters 

 but is the most common seaweed north of Cape Hatteras and central California. 

 Ascofhylhim is like rockweed but reaches tropical waters. It grows in the same 

 places as rockweed, but there is no midrib on its stem as there is on Fucus. 

 Desmarestia is a large genus of bushy, branched algae which grow on rocks 

 and is abundant only in the warmer months. The branching identifies them, 

 being pinnate, that is, branches extend from the main stem on both sides of the 

 central stem, which is not itself branched. Most Desmarestia species are small, 

 but some reach 6 feet in length. Sargasso weed, Sargasswn, was discovered by 



