- Aphotic Zone
- Zone without light; that portion of the ocean where light is insufficient for plants to carry on photosynthesis
- Zero tide
- average of the lower low tides
- Zonation
- distribution of the plants and animals in a community into recognizable, distinctive zones
- Zooanthellae
- photosynthetic microorganisms that live symbiotically in the tissues of organisms such as corals and jellies
- Zooplankton
- planktonic animals suspended in the water column
- Zygote
- fertilized egg
