Chapter 2- The Diving Environment The Diving Environment 51 world. You might see birds such as pelicans or cormorants diving into the water or even see them underwater! Marine mammals include seals, sea lions, walruses, manatees, dugongs, whales, dolphins, and porpoises. Marine mammals are protected in the USA and many other areas, and divers should be aware of the laws to avoid problems. The Food Chain Food chain is a term describing a group of organisms that are linked together primarily by consumption as food items (figure 2-20). The first link in the food chain are the one-celled plants. The phytoplankton (called diatoms and dinoflagellates) exist in their countless millions in the surface layers of the oceans and are eaten by the tiny animals called zooplankton. These, in turn, are eaten by small invertebrates and small fishes, which are eaten by still bigger fish, and so the process goes. By the time you eat a fish, energy has been transferred through several organisms by a food chain of trophic (nutritional) levels in the marine community. The higher the trophic level of the organism, the fewer individuals generally will be found. This is because the organism concerned must pay the high energy costs of converting the food to the energy that is needed for respiration, movement, and reproduction. The conversion of one form of energy to another and the maintenance of the population becomes more and more expensive as higher trophic levels are considered. In the warmer waters of the tropics, there is not much plankton due to a lack of nutrients. Plankton thrive in colder, nutrient-rich water. Because of this, the tropical waters are normally clearer than the temperate waters. When conditions are right and plankton do very well, they may rapidly reproduce and form a bloom, causing a drastic decrease in visibility. An extremely heavy bloom is called a red tide. Several types of organisms, mainly dinoflagellates, have a red pigment, which turns the water brown or reddish. Some plankton produce a toxin, and if a bloom is heavy, it can kill all the fish in an area. Some animals, such as clams and mussels, feed by filtering plankton and concentrate the toxin in their flesh without harm to themselves. If a human eats their flesh, the concentrated toxins can cause serious illness. Most of the concentrating organisms are bivalves, such as clams and mussels. It is always wise to ask about the safety of eating local filter-feeders. Many places that do not have red tides have contaminated shellfish from polluters. It is prudent to avoid eating shellfish from a bay where pleasure boaters anchor. The boat toilets empty directly into the water, and this waste settles to the bottom. Many cases of hepatitis and diarrhea have occurred when people have eaten animals from such a bay. Awareness and avoidance are the best safety guidelines. Hazardous Marine Animals Just how deadly are various species of aquatic animals? How toxic or venomous are they? These are important questions for the modern underwater explorer. The purpose of this section is to familiarize you with some of the more common hazards aquatic animals pose without scaring the wits out of you or perpetuating any myths. Poisonous animals are those creatures whose tissue, either in part or in their entirety, are toxic. In general, marine oral toxins are small molecules that are heat stable or unaffected by cooking. FIGURE 2-20. THE FOOD CHAIN
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