Return to the Sea (TV series)

The episode's first segment, "Life in a Salt Marsh," describes the ways in which a coastal salt marsh – flooded with seawater by the incoming tide and then drained when the tide goes out – is the most productive ecosystem on earth, protecting the land from erosion by waves, filtering and oxygenating water, serving as a nursery for young sea creatures, and providing an economically important source of seafood. The segment documents a North Carolina Maritime Museum field trip to a salt marsh and describes the adaptations and behaviors of plants and animals which live in or visit salt marshes, including pickleweed, marsh periwhinkles, mud snails, hermit crabs, spider crabs, horseshoe crabs, diamondback terrapins, North American river otters, and birds such as rails, egrets, seagulls (highlighting laughing gulls), herons, ibises, and brown pelicans. The segment also discusses threats to salt marshes posed by human encroachment such as habitat destruction, pollution, and boating. The second segment, "Big Sweep," documents activities in North Carolina that were part of Big Sweep – an annual single-day nationwide volunteer event to pick up trash along the beaches, rivers, and lakes of the United States – and emphasizes the special danger plastic trash poses to aquatic wildlife.

A description of the capabilities and operations of the research submarine Johnson Sea Link I as she operates from the mother ship Seward Johnson off Cape Hatteras, North Carolina, to explore the midwater column and the benthos to determine the possible environmental impact of proposed offshore drilling there. The episode culminates in a dive to a depth of 3,000 feet (910 m) to take core samples in a submarine canyon, where the submersible encounters marine snow and a jumbled landscape.

A discussion of the discovery, history of study, causes, symptoms, dangers, and treatment of decompression sickness, known as "the bends." The episode describes the advantages and disadvantages of dive tables and dive computers and the function of a recompression chamber in treating the bends, and explores various still-mysterious and controversial aspects of decompression sickness, including risk factors such as age of the diver and flying after diving. It includes trips to the United States Navy Experimental Diving Unit in Panama City Beach, Florida, and Duke University to see research activities attempting to improve understanding of the bends and a visit to the Divers Alert Network, where volunteers man telephones to provide advice and assistance to divers who contract the ailment.

The story of the World War II sinking of the German submarine U-352 by the United States Coast Guard Cutter USCGC Icarus off North Carolina on May 9, 1942; the discovery of U-352′s wreck in 1975; and its subsequent popularity as a dive site. The episode culminates in a reunion in North Carolina of members of U-352′s and Icarus′s crews for a memorial service for U-352′s crew on the 50th anniversary of her sinking on May 9, 1992. The episode includes interviews with crewmen of both ships and with one of the divers who discovered her wreck.

Divers have only a limited time underwater while exploring a coral reef, and often overlook the smaller things until they examine photographs and video footage later. The episode covers these smaller things, including coral polyps, how they construct reefs, their symbiotic relationship with algae, and coral bleaching; sea anemones; plankton; sea cucumbers; cleaning stations and the tiny cleaner fish such as gobies which base themselves on a coral or a sponge and clean larger fish including groupers, stoplight parrotfish, and barracudas; Pederson's cleaning shrimp, which also cleans fish and hides among the tentacles of the ringed anemone alongside the snapping shrimp; an isopod parasitizing a black bar soldierfish; mollusks, such as the conch, lettuce sea slug, and flamingo tongue snail; how hand-feeding of Nassau groupers has changed their normally skittish behavior around divers; and the anatomy and behaviors of groupers.

A trip to Belize to observe the similarities between the two most diverse and active environments on earth – the coral reef and the tropical rainforest. The episode compares the profusion of corals and the diversity of habitats it creates to the profusion of plants in the rainforest and the wide variety of habitats there; describes the abundance of life in each environment, how organisms in both – such as corals and sponges on the reef and plants in the rainforest – must compete for space, and how insects in the rainforest and small reef creatures colonize every ecological niche; shows parallel survival strategies between reef creatures and plants and animals of the rainforest, such as the use of thorns and spikes to ward off predators and camouflage to deceive them; and discusses modern-day Belize City and the Maya civilization that once thrived in Belize. The episode includes footage of the Belize Barrier Reef – part of the Mesoamerican Barrier Reef System, the world's second-largest after the Great Barrier Reef – and of cays off Belize and the rainforest in the country's interior; of the tapir, margay, jaguar, toucan, ocellated turkey, howler monkey, saga tree, sea urchin, flounder, stonefish, trumpetfish, and green vine snake; of a lizard, termites and their nest, bats in a ruined Mayan temple, and of frigatebirds and boobies on a cay on Lighthouse Reef; and of Belize City, Mayan ruins in Belize, and Tikal in neighboring Guatemala. The episode includes a discussion of damage to the reef through coral bleaching and the careless actions of divers, the destruction of the rainforest to create farmland, and of the Government of Belize's effort to preserve the reef, cays, and rainforest by promoting ecotourism, which makes conservation economically important to the local population. It also highlights the work of the co-owners of the Chan Chich Lodge to create ecotourism to reduce illegal activities in the rainforest and give the local people a financial stake in preserving it, and of Sharon Matola, founder and director of the Belize Zoo, to give the people of Belize a greater appreciation of the rainforest and its animals.

The special's first segment, "Oceans Under Glass," focuses on the operations of the North Carolina Aquariums and highlights the ways in which rivers, sounds, marshes, and barrier islands are important to ocean creatures. The segment covers the aquariums′ field trips, hosting of school visits, and collection of animals in salt marshes; their touch tanks and how they create shipwreck displays; the equipment and techniques they use to make their own salt water, maintain water quality for the organisms in their tanks, and feed the aquarium animals; and their sea turtle rescue and rehabilitation program and research into the causes of sea turtle deaths. The segment also describes the near-extinction, recovery, and nesting and chick-rearing behaviors of the osprey, and visits a tide pool on a rocky outcrop on North Carolina's coast. It includes footage of mosquito larvae, horseshoe crabs, various crabs including a blue crab, filefish, a comb jelly, American alligators, green turtles, loggerhead turtles, an isopod, a sea star, mole crabs, and a striped hermit crab living in a moon snail shell. The second segment, "Swimming With Whales," profiles Dave Woodward – a pioneering recreational diver, scuba instructor, and underwater photographer who in 1976 worked with Marlon Perkins as a still photographer for Wild Kingdom during filming of humpback whales – as he once again swims with them at their wintering and calving grounds at Silver Bank in the Caribbean. The segment includes extensive footage of the whales and discusses their social and mating behaviors, research into their individual identities and overall numbers, and whale songs. The third segment, which derives its title from the D. H. Lawrence poem "Whales Weep Not," documents the death of an emaciated young female sperm whale on the beach at Wrightsville Beach, North Carolina, and the subsequent necropsy that revealed her stomach was full of trash discarded by humans, highlighting the danger human-generated detritus poses to sea creatures.