- Dead reckoning
- the process of estimating one's current position based on a previously determined position, or fix, and advancing that position based on known speed, elapsed time, and course.
- Debilitate
- to weaken, deprive of strength
- Decimate
- organism such as a fungus or bacterium that causes decay of dead plants and animals
- Decomposer
- organism such as a fungus or bacterium that causes decay of dead plants and animals
- Delayed implantation
- fertilized egg remains free in the uterus prior to attachment to the uterine wall and placental formation
- Demersal
- living on or just above the bottom of a body of water
- Dentin
- a hard and bone-like tissue that forms most of the tooth
- Dentin
- a hard and bone-like tissue that forms most of the tooth
- Deposit feeder
- animal that feeds by consuming debris (detritus) on or in the seafloor
- Dermal denticles
- tooth like scales embedded in the skin (dermis of elasmobranches (sharks, rays, skates); placoid scales
- Detritus
- particles of organic and inorganic debris from decaying plants and animals
- Diatom
- flowering plant with two seed leaves
- Dicot
- flowering plant with two seed leaves
- Dimorphism
- biological differences between two or more types; having two different distinct forms in the same species, as in sexual dimorphism, where males and females have different characteristics
- Dioecious
- plants that have only male or only female flowers on individual plants
- Disruptive coloration
- type of camouflage where color patterns break up or disrupt body form to make an animal unrecognizable to predators or prey
- Diurnal
- occurring or active during the day
- Diurnal tide
- tide that has only one high and low tide instead of two in each tidal day of 24 hrs 50 min.
- Diversity
- richness of an area in relation to numbers of different types of organisms or groups of organisms in an area or zone
- Dormancy
- period of inactivity brought about by colder temperatures, where breathing and circulation slow slightly
- Dorsal
- pertaining to the back or upper surface
- Downwelling
- sinking of water or water masses below the surface
- Drift algae
- pieces of seaweed that break free of their attachment and drift
