20 UNDERWATER GUIDE TO MARINE LIFE 



Support and anchorage are big problems in such gooey substrata. Sea spiders 

 (pycnogcnids) creep about on long legs. Crinoids and glass sponges have long 

 stalks on which they are supported, and some crabs have hairy feet. Brittle stars 

 are abundant and support themselves on their long arms. The largest known 

 crustacean is the Japanese spider crab with legs that may span 1 5 feet, lives here. 



THE NERITIC PROVINCE 



This is the realm of the underwater swimmer. Whereas oceanic diving has 

 been done and will be important in the future, the shallow waters near shore 

 offer greater variety of life and less harsh conditions; almost anyone is able 

 to enjoy these waters. The boundaries of this zone are the shore line and the 

 outer limit of the continental shelf (if it is present) at a depth of about 600 

 feet. Therefore, the majority of the neritic province is euphotic or well lighted. 

 This province is variable in almost every respect, including nature of bottom, 

 temperature, animals and plants, and water movements. 



The Neritic-Pelagic Zone. There is an overlap between the oceanic-pelagic 

 and the neritic-pelagic. Most of what has been said about the oceanic-pelagic 

 also applies to this zone. However, many of the animals of this zone are 

 dependent on the bottom during some time of their life. Pelagic invertebrate 

 larvae usually settle to transform to sessile, benthic adults, and many of these 

 pelagic animals at least feed on or near the bottom. Actuallv, onlv a few 

 habitually neritic animals and plants are free of the bottom throughout the whole 

 of their lives, and these are mostly planktonic ones, small species such as diatoms 

 or some crustaceans. 



The life of this zone includes planktonic larvae, jellyfish, fish eggs, crustaceans, 

 pteropods, squids, the great majority of sharks and rays, and most bony fishes. 

 Most of these cannot survive if they stray into the oceanic province. 



The IN eritic-Benthic or Littoral Zone. Of all the zones of the sea, this one 

 shows the greatest diversity of life, especially in a special subdivision of this 

 zone, the coral reef, which will be considered presently. 



It is rather difficult to decide how to subdivide this area. From the point of 

 view of water movement, there is said to be an eulittoral or tidal zone, which 

 is bounded by the high- and low-water marks of the highest spring tides and 

 which varies in extent with the geographical location, and a sublittoral or non- 

 tidal zone, which extends from low-water to the edge of the continental shelf. 

 Within each of these are several zones which define the all-important 

 communities of the neritic province. 



Some nektonic species such as small fishes are so intimately connected to the 

 benthic region that they may be spoken of as being nekto-benthic. Among these, 

 the reef fishes are notable examples. But mostly, the zones of these benthic 

 regions are characterized by algae or sessile, plantlike animals or other 

 invertebrates. 



THE EULITTORAL OR TIDAL SUBZONE 



This is the harshest environment of the sea, and the only one that can be 

 thought of as having weather as we know it on land. As the tides cover and 



