A substance that releases hydrogen ions when dissolved in water. Any solution with a pH of less than 7 is acidic.

See "base."

A substance that releases hydroxide ions (OH-) when dissolved in water. Any solution with a pH of more than 7 is basic, or alkaline.

The process by which living things produce minerals.

calcium carbonate
A colorless or white crystalline compound occurring naturally in rocks like chalk, limestone, and marble and in the shells of marine creatures like shellfish, coral, and sea

An element consisting of atoms with six protons. Carbon is present in all known forms of life.

carbon dioxide
A molecule consisting of one carbon atom and two oxygen atoms (CO2). This colorless, odorless gas is naturally present in the atmosphere.

A molecule consisting of one carbon atom and three oxygen atoms (CO3).

Average weather conditions of a region, including temperature, precipitation, and winds.

A phylum comprising four taxonomic classes: Hydrozoa (hydroids), Cubozoa (sea wasps and box jellies), Scyphozoa (jellyfish), and Anthozoa (corals and sea anemones). Hydroids are considered the most primitive of the four classes; the other three classes probably evolved from hydroids. Scyphozoa spend most of their lives in the medusa stage, while Anthozoa spend most of their lives as polyps.

A marine animal within the phylum Cnidaria that is composed of anatomical units called polyps and that typically forms a solid underskeleton of calcium carbonate (as in the “stony corals”), or an internal skeleton of calcareous spicules or complexes of protein and carbohydrates (as in the “soft corals”). Corals can be composed of single polyps, known as solitary corals, or multiple polyps, known as colonies. Colonial, stony corals that form large, rigid skeletons are sometimes known as reef-building corals to distinguish them from smaller stony corals and more flexible soft corals.

coral reef
(1) An underwater geological structure, made largely of calcium carbonate, that is secreted by corals and other organisms (such as coralline algae, sponges, bryozoans, and mollusks) over long periods of time; (2) the biological community and ecosystem associated with such structures.

development (biological)
The process by which organisms and their biological components change over time, especially in the earliest stages.

An animal in the earliest stages of development.

All the external factors that affect an organism during its lifetime.

The scientific theory for how groups of living things change over time.

greenhouse gases
Gases that increase global temperatures by absorbing the radiation emitted by Earth's surface. Greenhouse gases include carbon dioxide, water vapor, methane, and nitrous oxide.

An animal without a backbone.

An atom with a positive or negative charge.

larva (pl. larvae)
The early form of an animal (as a frog or sea urchin) that at birth or hatching is fundamentally unlike its parent and has yet to develop adult characteristics.

Relating to the sea.

marine calcifier
An ocean organism that builds its shell out of calcium carbonate.

The smallest unit of matter into which an element or a compound can be divided and still retain its chemical and physical properties. It consists of a single atom or group of like or different atoms bonded together by chemical forces.

ocean acidification
When the ocean becomes more acidic due to the absorption of an increasing amount of carbon dioxide from the atmosphere.

A measure of how acidic or how basic a solution is. pH is based on the concentration of hydrogen ions in the solution.

See "plankton."

Small or microscopic organisms that passively float in great numbers in fresh or salt water, especially at or near the surface. They serve as food for fish and other larger organisms, forming the base of the marine food web. Plankton include phytoplankton, tiny plants such as algae, and zooplankton, tiny animals that generally feed on phytoplankton.

The larval stage of coral and other Cnidarians.

An underwater flowering plant which, like land plants, has leaves, stems, and a root system.

A group of individuals, usually identifiable by a set of distinctive features, with a unique evolutionary history. Classically, the members of a species can interbreed only with each other to produce fertile offspring.