SECOND 



sea slick — An area of sea surface, variable in size 

 and markedly different in appearance, with color 

 and/or oiliness; usually caused by plankton 

 blooms. 



sea slide — A submarine sediment slump or mass 

 movement which may evolve into a turbidity 

 flow. Analogous to a landslide. (2) 



sea slug — See nudibranch. 



sea snake — A reptile of the family Hydrophiidae ; 

 a group comi^rising about 50 species of truly 

 marine forms distantly related to the cobras and 

 possessing similar venom. All are inhabitants 

 of warm coastal waters of the Indian Ocean and 

 western Pacific with one exception, the yellow- 

 bellied sea snake, which is oceanic and ranges 

 entirely across both the Indian and Pacific 

 Oceans in low latitudes. 



sea snow — (also called plankton snow, marine 

 snoio) . Particles of organic detritus and living 

 forms. The downward drift of these particles 

 and living forms, especially in dense concentra- 

 tions, appears similar to a snowfall when viewed 

 by underwater investigators. 



seasonal current — A current that changes with 

 seasonal winds. 



sea spider — (or pycnogonid) . One of a class 

 (Pycnogonida) of spiderlike benthic arthro- 

 pods which range from shallow water to great 

 depths. The species inhabiting shallow waters 

 range in size from a fraction of an inch to a few 

 inches; the deep water species may attain a 

 spread of several feet. 



sea squirt — See ascidian. 



sea stack — A tall, columnar rock isolated from the 

 coast by differential wave erosion. (2) 



sea star — (or starfish). One of a class (Asteroi- 

 dea of echinoderms having a flat, usually five- 

 armed body. The body wall contains embedded 

 calcareous plates bearing spines or tubercles. 

 Some spines are modified into pincerlike organs, 

 called pedicellariae, which in some tropical 

 species are dangerously venomous to humans. 



sea state — (or state of the sea). The numerical 

 or written description of ocean surface rough- 

 ness. For more precise usage sea state may be 

 defined as the average height of the highest one- 

 third of the waves observed in a wave train, 

 referred to a numerical code which covers an 

 increasing range of such heights as indicated by 

 "WMO Code 75 table below : 



Code Wave height (feet) 







1 0-% 



2 %-l% 



3 1%^ 



4 4-8 



5 8-13 



6 13-20 



7 20-30 



8 30-45 



9 1 Over 45 



sea turtle — Any of various large marine turtles 

 belonging to the reptilian order Testudinata and 

 having the feet modified into paddle-like appen- 

 dages, including the leatherback, hawksbill, log- 

 gerhead, green, and Ridley turtles, and being 

 widely distributed in warm seas. 



sea urchin — One of a class (Echinoidea) of 

 echinoderms in which the body is covered by 

 a hard shell (or test) composed of fitted im- 

 movable plates; spines articulated at their bases 

 and of various sizes, often large, and sharp are 

 present on the test; members of the class may be 

 spherical (the regular sea urchins), depressed 

 spherical (the cake urchins) , discoidal (the sand 

 dollars), or ronnd elongate (the heart urchins) . 

 Many species of urchins have venomous spines. 



sea valley — See valley. 



sea wall — A manmade structure of rock or con- 

 crete built along a portion of coast to prevent 

 wave erosion of the beach. (2) 



sea walnut — A transparent, luminescent cteno- 

 phore {3Inemiopsis) . Often seen in large 

 swarms on the surface in coastal waters. 



seaward beach — The seaward facing beach of the 

 reef islands. (56) {See figure for atoll.) 



seaward reef margin — The seaward edge of the 

 reef flat, marked in places by an algal ridge and 

 cut by surge channels, which are the landward 

 extensions of the reef-front grooves. (56) 

 {See figure for atoll.) 



sea water — The water of the seas, distinguished 

 from fresh water by its appreciable salinity. 

 The amount of the salinity greatly affects the 

 water's physical characteristics. 



The distinction between the usage of salt water 

 and sea water is not very sharply drawn. Com- 

 monly, sea water is used as the antithesis of 

 specific types of fresh water, as river water, lake 

 water, rain water, etc., whereas salt water is 

 merely the antithesis of fresh water in general. 



seawater batteries — Silver-zinc batteries activa- 

 ted by flow of sea water through them. 



seaweed — (or weed). Any macroscopic marine 

 alga or seagrass. 



Secchi disc — A white, black, or varicolored disc, 

 30 centimeters (about 11.7 inches) in diameter, 

 used to measure water transparency (clarity). 

 The disc is lowered in the water and the depth 

 (in meters) at which it disappears from sight is 

 averaged with the depth at which it reappears. 

 This average value is used to represent sea water 

 transparency. 



second — 1. A term used to describe distance or 

 depth ; one second refers to about 4,800 feet, or 

 the distance that sound will travel through sea 

 water during one second. Two ships may be 

 said to be 10 seconds apart when their jjositions 

 are separated by about 48,000 feet. 



2. The sixtieth part of a minute of angular 

 measure. 



143 



