Sea animals can be categorized according to where they live in the ocean -- floating with the currents, swimming in the water column or living on the bottom. If you're setting up a saltwater aquarium to enjoy viewing sea creatures of all types, include zooplankton, benthos and nekton to ensure you have activity and color on every level of your tank.
Here Fishy, Fishy
Fish and other animals that swim freely through the water column in the ocean are classified as nekton. Some of the hardiest and most colorful fish are clownfish, made famous by the movie "Finding Nemo." Other colorful fish suited for the novice saltwater aquarist include damselfish and rabbitfish. The fish will spend most of their time in the midsection of your tank, swimming and feeding along the coral reef or other aquarium decor.
Nourish living coral and fish by culturing zooplankton, free-floating creatures that can't swim faster than ocean currents. They include jellyfish, fry and larval stages of crustaceans and other sea life. Copepods spend their entire lives as plankton, hanging out in the substrate during the day and rising at night to feed on algae and phytoplankton. Fish and coral feed on the copepods. Starter cultures are available at fish stores. Remove protein skimmers from your filtration system to prevent copepods and their food from getting filtered out of the tank.
Along the Bottom
Benthos live primarily on the bottom of the tank. Common aquarium benthos include coral, snails, sea stars, sponges, seahorses, anenomes, crabs, and clams. There are also benthic fish -- such as gobies and mandarin fish -- that have disclike pelvic fins to help them cling to the substrate. Benthic animals help clean the aquarium of leftover food particles and algae. Snails and fish collect detritus from solid surfaces, while coral and clams suck free-floating particles directly from the water.
Here and There
Other animals that live along the bottom don't fall exactly into either the nekton or benthos category. Known as nektobenthos, these animals include aquarium pets such as shrimp, rays and octopi. Shrimp help keep an aquarium free of detritus and provide food for other marine animals. Rays and octopi require special care and large tanks, making them suitable for advanced aquarists. Both do best in tanks by themselves, as they will eat their tank mates for dinner.