Glossary H...

Habitat: An organism's home; for example: in the mid-water, on the seafloor, near the surface or in a tide pool.

Hadal: The deep sea region below 20,000 feet (6,100 meters); the deep trenches.

Hake: A fish, related to cod, that gathers in large schools. Hake live from the surface down to depths of 3,000 feet (914 meters).

Halibut: A large fish with a flattened body adapted for life on the seafloor.

Haptera: Rootlike structures growing from the base of a kelp plant. Haptera form the holdfast that anchors the kelp to the seafloor.

Harems: Large numbers of females that mate with one male.

Harlequin shrimp: A colorful shrimp from the coral reefs of the central Pacific.

Hatcheries: Places where eggs and sperm are fertilised and immature stages are matured. Used in aquaculture.

Haul out: To climb up out of the water. Seals often haul out onto rocks.

Head of the canyon: The shallow part at the beginning of an underwater canyon.

Hectopascals: Unit of measure for high or low pressure systems.

Herbivore: A plant eater.

Hermaphrodite: An animal that has both male and female reproductive organs.

Hermit crab: A crab that protects itself by living inside an empty snail shell. There are many species of hermit crabs, some on land, some in the ocean.

Herring: A small, silvery fish that swims in large schools.

Holdfast: The root-like base of marine algae that anchors or attaches the plant to the substrate. The root-like part of the thallus.

Holding pens: Large tough plastic holding tanks for fish grown in aquaculture.

Hookah: Air pumps in a boat pumping air to divers below through a tube. Used by abalone divers.

Hook and line: Any fishing method which uses a sharp hook (baited or not) attached to a nearly-invisible fishing line. Different hook-and-line methods include longline, troll and pole-and-line.

Horizontal: Side-to-side, or stretched out flat like the horizon (opposite of vertical).

Hull: Frame or body of a ship.

Humus: Nutrient-rich earth formed when plant material decays.

Hydrological cycle: See water cycle.

Hydrodynamics: The study of fluids in motion and the movement of objects through fluid.

Hydrometer: A calibrated instrument for measuring the specific gravity of a liquid.

Hydroid: A body shape often taken on by animals related to sea anemones. A hydroid has a fleshy central stalk topped by a ring of tentacles used for catching food. Anemones are one kind of hydroid; many jellies are hydroids for part of their lives.

Hydrothermal vents: Beaks in rocks where warm or hot fluids seep out.

Hypothermia: A dangerous loss of body warmth, which can cause death.

Hypothesis: A scientific idea about how something works, before the idea has been tested. Scientists do experiments to test their hypothesis and see if the hypothesis is correct.