460 



numbers, in relatively sparse populations. 

 The lack of vegetation and exposed rocks 

 is paralleled by the relative scarcity of 

 species that Uve attached to such firm sur- 

 faces. Instead, the soft ooze covering the 

 bottom places a premium upon species ad- 

 justed for burrowing, or those having long 

 stems for deep anchorage, or long legs 

 capable of elevating the body. 



The sessile or passive benthos includes 

 sponges, characteristically abundant long- 

 stemmed hydroid sea pens, long-stemmed 

 crinoids, a few alcyonarian corals, bryo- 

 zoans, and tunicates. The active benthos in- 

 cludes sea cucumbers, a few bivalves, and 

 long-legged pycnogonids and crabs. Among 

 the last is the largest Hving crustacean, the 

 crab Kaempfferia kaempfferi, with a maxi- 

 mum leg expanse of about 5 meters. The 

 nekton consists chiefly of fishes, typically 

 unicolorous, slender, and with large jaws 

 {Macrostomias, Stylophthalmus, Gastrosto- 

 mus, Mancalias, Caulophryne) . 



Marine Sediments 



In closing this section on stratification in 

 the marine habitat, a brief discussion of 

 marine sediments is pertinent since the 

 character of the floor is of great importance 

 in primary community gradients. 



Shallow coastal waters, which support 

 the marine Uttoral and subhttoral zones, 

 have a dense population of animals, and 

 sometimes there is a considerable growth 

 of rooted vegetation. An example of the 

 latter is seen in the notable development 

 of mangroves and associated vegetation 

 along subtropical and tropical shores. This 

 mangrove colonization has been the sub- 

 ject of study along the Florida coast by 

 Davis (1940). The mangrove and as- 

 sociated plants comprise a number of dis- 

 tinct zones or belts which are more or less 

 related to water level and to the degree of 

 salinity of the surface and soil water. There 

 is a trend from offshore pioneer zones to 

 upland, fresh-water, nonhalophytic zones 

 inland from the mangrove swamps. The first 

 offshore zone is dominated by the red man- 

 grove, Rhizophora mangle, and in addition 

 includes marine algae and marine aquatic 

 seed plants. This first zone is inextricably 

 associated with the marine aquatic offshore 

 biota and is best developed on submerged 

 shoals. This pioneer zone is followed shore- 

 ward by a mature forest swamp which oc- 



THE COMMUNITY 



cupies an outer zone along the coast, or 

 completely covers young islands, which are 

 flooded by salt water. This forest swamp 

 stratum is composed almost entirely of 

 medium-sized to large, red mangroves 

 wliich grow with interlocking, arched prop 

 or buttress roots. Mangrove roots form 

 tangles that hold the plants in the loose, 

 shifting soil. The mutually supporting root 

 tangles cooperate in stabiUzing the zone 

 and, in addition, act as natural weirs, catch- 

 ing sediments and debris and hence are of 

 material importance in the building of soil. 



The Httoral, especially, is subject to con- 

 tinuous augmentation of miscellaneous sub- 

 stances from streams, as well as the periodic 

 accumulation of debris as a consequence of 

 tidal action, and aperiodic deposits through 

 storm action. The floor of these two zones 

 is variously covered, therefore, by two 

 types of sediment, (1) neritic, and (2) 

 terrigenous. 



The neritic deposits are composed of 

 earth mixed with organic substances of 

 shallow waters; for example, the remains 

 of moUusks, crustaceans, the tubes of an- 

 nelids, sea urchin tests, and remains of 

 fishes. 



Terrigenous deposits are composed of 

 mineralized substances carried into the sea 

 from rivers. Their chief component is siUca, 

 which may run as high as 70 per cent. 

 These substances form the shallow water 

 sands and muds and may be diversely 

 colored: deep red by iron oxides, blue 

 by manganese oxides, and green by silicates 

 of iron or potassium (glauconites). The 

 terrigenous deposits also include volcanic 

 materials. 



The httoral and sublittoral zones have 

 substantially the same floor, but are differ- 

 entiated physically by tidal factors and non- 

 tidal influences such as wave action. The 

 conclusion is that the basic organismal 

 stratification is the resultant of bottom and 

 tidal influences. 



The abyssal zones are not affected by 

 tidal movements. Their floors are recipients 

 of the third type of marine deposits, namely, 

 the pelagic. Pelagic deposits are commonly 

 separated into "red clay" and several 

 "oozes" by oceanographers (Steuer, 1911; 

 Murray and Hjort, 1912; Coker, 1938; 

 Sverdrup, Johnson, and Fleming, 1942). 

 As a group, these oozes comprise those 

 organic remains that continually settle from 



