To understand the vital economy of the open sea, we must recognise the
incalculable abundance of minute unicellular plants, for they form the
fundamental food-supply. Along with these must also be included numerous
microscopic animals which have got possession of chlorophyll, or have
entered into internal partnership with unicellular Algæ (symbiosis).
These green or greenish plants and animals are the _producers_, using
the energy of the sunlight to help them in building up carbon compounds
out of air, water, and salts. The animals which feed on the producers,
or on other animals, are the _consumers_. Between the two come those
open-sea bacteria that convert nitrogenous material, e.g. from dead
plants or animals that other bacteria have rotted, into forms, e.g.
nitrates, which plants can re-utilise. The importance of these
_middlemen_ is great in keeping "the circulation of matter" agoing.
[Illustration: 1. SEA-HORSE IN SARGASSO WEED. In its frond-like tags of
skin and in its colouring this kind of sea-horse is well concealed among
the floating seaweed of the so-called Sargasso Sea.
2. THE LARGE MARINE LAMPREYS (_PETROMYZON MARINUS_), WHICH MAY BE AS
LONG AS ONE'S ARM, SPAWN IN FRESH WATER. Stones and pebbles, gripped in
the suctorial mouth, are removed from a selected spot and piled around
the circumference, so that the eggs, which are laid within the circle,
are not easily washed away.
3. THE DEEP-SEA FISH _CHIASMODON NIGER_ IS FAMOUS FOR ITS VORACITY. It
sometimes manages to swallow a fish larger than itself, which causes an
extraordinary protrusion of the stomach.
4. DEEP-SEA FISHES. Two of them--_Melanocetus murrayi_ and _Melanocetus
indicus_--are related to the Angler of British coasts, but adapted to
life in the great abysses. They are very dark in colour, and delicately
built; they possess well-developed luminous organs. The third form is
called Chauliodus, a predatory animal with large gape and formidable
teeth.]
[Illustration: FLINTY SKELETON OF VENUS FLOWER BASKET (EUPLECTELLA), A
JAPANESE DEEP-SEA SPONGE]
[Illustration: EGG DEPOSITORY OF _Semotilus Atromaculatus_
In the building of this egg depository, the male fish takes stones from
the bottom of the stream, gripping them in his mouth, and heaps them up
into the dam. In the egg depository he arranges the stones so that when
the eggs are deposited in the interstices they are thoroughly protected,
and cannot be washed down-stream.
1, dam of stones; 2, egg depository; 3, hillock of sand. The arrow shows
the direction of the stream. Upper fish, male; lower, female.]
The "floating sea-meadows," as Sir John Murray called them, are always
receiving contributions from inshore waters, where the conditions are
favourable for the prolific multiplication of unicellular Algæ, and
there is also a certain amount of non-living sea-dust always being swept
out from the seaweed and sea-grass area.