Introduction.

By definition, a “naturalist” is someone versed in natural history (not to be confused with a “naturist”, who is someone who sunbathes naked), so by definition, someone versed in aquatic natural history is an “underwater naturalist”. To some extent, then, you’re already a naturalist – whether you realize it or not.

Think about your diving experiences. Whether you’ve made only a few dives or hundreds, or whether you dive in salt water or fresh, you’ve seen and become familiar with aquatic organisms and some of their characteristics. Even if you don’t know them by name, you know how they behave or where they “belong”, so that you recognize where to expect them. For example, if you’ve previously encountered octopus in wholes in our favourite reef, you might think to look for octopus in similar holes on a similar reef. In this sense you’re already an underwater naturalist.

This section takes your experiences and builds upon them. You’ll understand more about the animals and plants you see underwater and learn how the environment dictates their form and behaviour. You’ll learn to put aside conclusions drawn from land organisms, and instead comprehend underwater plants and animals in light of their aquatic environment. Most importantly, this section shows you how you fit in, how your actions affect organisms that you interact with, and how to visit the aquatic world in a responsible manner.

Introduction To The Aquatic Realm.

Imagine walking into the living room of someone you’ve never met. Glance around the room, you spot an, expensive stereo and classical music compact disks. In the corner stands a piano and next to it a cello. Immediately you conclude that for this person, music is very important, and not just any music, but classical music. In a rudimentary sense, this person’s environment tells you about the person who lives there. Similarly, underwater naturalists observe the aquatic environment to understand the organisms that live there.

With this in mind, a study of underwater life begins with ecology, which is “the study of the interrelationship of living things and their environment”. Ecology examines not just organisms and their relationship with their environments, but also ecosystems, which are “the complex of living things and their environment functioning as a unit”.

An ecosystem can be large and general, or small and specific, depending upon your context. The earth is an ecosystem, but so is a vegetable garden or a puddle of rainwater. Underwater naturalists focus on aquatic (underwater), rather than terrestrial (land) ecosystems, so comparing the physical and structural differences between the two environments lays the foundation for understanding the differences between the organisms that live in water versus on land.

Terrestrial And Aquatic Environments – Physical Characteristics.

You don’t have to be a diver to realize that the big difference between terrestrial and aquatic environments is that on land, organisms are surrounded by air, and underwater they’re surrounded by water.

But you do have to be a diver to experience firsthand how existence differs from one environment to other.

Density.

Water is 800 times denser than air, which is in fact, the main cause for most of the differences between terrestrial and aquatic environments. Water density restricts motion, so that fast moving animals (primarily fish) have streamlined shapes to minimize water resistance. Only terrestrial animals that move fast enough to encounter significant air resistance, such as birds, show comparable streamlining. The cheetah, for example, runs faster than many fish swim, yet has far less streamlining by comparison.

Gravity.

Water exerts far more buoyancy than air, so for practical purposes, aquatic organisms can exist in a nearly “weightless” environment. While land organisms must have a rigid structure to resist gravity, some aquatic organisms such as the jellyfish grow quite large with virtually no rigid structure at all. This makes it possible for some aquatic organisms to live their entire life floating in the water column, never or rarely touching the bottom; many fish species have a special organ – the air bladder – specifically for controlling “weightlessness”. By contrast in the terrestrial environment gravity is ever-present; even birds spend a significant amount of their lives perched.

Even among aquatic animals with rigid structure, the absence of gravity often affects energy use and potential size. A 225 kg/500 lb fish barely flicks a fin to hover motionlessly, but a tiny hummingbird beats its wings at a blur to accomplish the same – and no 225kg / 500 lb terrestrial animal can hover in air at all. Even the smaller whales dwarf the largest terrestrial animal, the elephant. Dinosaurs, which were the largest terrestrial animals that ever lived, are small compared to the great whales (especially the blue whale). The potential for large size is greater when organisms are not restrained by gravity.

It’s worth nothing while buoyancy practically negates gravity underwater; the aquatic world isn’t truly weightless in the sense of being in outer space. Aquatic organisms feel and respond to gravity, as demonstrated by fish swimming “right side up”. In true weightlessness, no reference to up or down exists.

Movement. Air has wind, water has currents and both affect their respective ecosystems. You’re probably familiar with seeds that drift in the breeze, small spiders that ride “web balloons” or other organisms that drift that drift with the wind, but these are insignificant compared to analogues underwater organisms that drift “weightless” in currents. Plankton (which means wanderers) is a community of micro-organisms that drifts through the aquatic realm. The abundance of plankton is such that many aquatic animals don’t have to forage to feed – sponges, tube worms, corals and other organisms spend their entire lives attached to one spot, straining the plankton they eat from the water.

While a few terrestrial plants use the wind to aid reproduction, the majority of aquatic invertebrates and many vertebrates release their larvae into the water, where they float long distances to new habitats. Many aquatic animals release sperm and eggs into the water; permitting fertilization outside the parents’ bodies.

Light. Life gets most of its energy from the sun. Plants use light directly, whereas animals use it indirectly either by eating plants or other animals that eat plants. For practical purposes, air doesn’t affect the life–providing light spectrum, making land the ideal environment for plants. Water absorbs light (and therefore colour) unevenly, first absorbing red in shallow depths, then orange, yellow, green, blue, indigo and violet. In the clearest water, light cannot reach deeper than about 180 meters/600 feet, and in many aquatic environments it cannot even penetrate a tenth that deep. Consequently, plant life survives only at the shallower depths, where, depending on depth, it may have only part of the spectrum available. In contrast, terrestrial plants are limited by temperature, altitude and availability of water.

Oxygen. In air, oxygen is evenly distributed and plentiful, making up about 21 percent of the atmosphere (at altitude, the oxygen pressure is lower, but the distribution is the same 21 percent). In water, oxygen may be unevenly distributed; for example in a lake, the shallows may have more oxygen compared to stagnant bottom waters. Proportionately little oxygen exists in water, requiring aquatic organisms to have gills. , which compared to terrestrial lungs are significantly more efficient at gathering oxygen. Other aquatic animals – notably marine mammals, reptiles and amphibians – return to the surface periodically to breathe air.

Terrestrial And Aquatic Environments – Structural Characteristics.

The physical differences between terrestrial and aquatic environments explain the differences in the structures of their ecosystems and organisms. Plants. On land, plants dominate. Their large rigid structure, which combats gravity, makes them massive and difficult to move. This makes plant ecosystems relatively stable compared to aquatic plant ecosystems. Long-lived plant communities control short – lived animal communities. Terrestrial ecosystems tend to be described in plant-terms: redwood forest, grass prairies, rain forest etc. Underwater the majority of plants tend to be small and primarily microscopic.

Small aquatic animals easily eat aquatic plants, so that plant-consuming animals play the role of bringing plant-energy into the ecosystem. Animal populations dominate many aquatic ecosystems, which are referred to in animal-terms: coral reef, oyster beds, clam beds, etc. Food Chains. Because large animals eat the stable-population plants directly, terrestrial food chains tend to be shorter than aquatic food chains. For example: grass converts light into chemical energy, grass eaten by antelope, antelope eaten by lion. This is a three –link food chain.

In aquatic environments, small and microscopic animals eat the plant plankton, adding at least one immediate link. For example: Algae converts light into chemical energy, algae eaten by animal plankton is eaten by small fish, small fish are eaten by dolphins. This is a four-link food chain.

Human Perceptions Of Aquatic Life.

One-way human beings handle unfamiliar situations is by drawing analogies from previous experiences. This is why as you read, you’re referred back to your entry-level class or to common experiences, both of which help you learn by drawing upon what you already know. In the underwater world, you do the same thing consciously or not.

For example, when you clear your mask at 18 meters/60 feet, you’ve made the (obvious) comparison to clearing your mask in a pool and concluded that doing it on a reef or in a quarry doesn’t differ significantly. In this case, it helps you react correctly. On the other hand, suppose you approach a coral reef without knowing anything about coral.

How do you interact with coral? Your experience tells you animals move. Coral doesn’t.  Compared to terrestrial organisms, coral seems to be a plant (or even inanimate rock) rather than an animal. You can stand on many plants (or rock) without harming them, but if you treat coral accordingly, you will kill it. Therefore, your terrestrial experiences with organisms have only limited value in understanding aquatic organisms, because they can lead to misconceptions, such as about “dangerous” marine organisms and about the nature of aquatic organisms in general.

Aquatic Life Mythology.

Probably the most wide spread misconception about the underwater world is that some aquatic creature seek out and attack human beings. There’s no denying that some aquatic organisms present potential hazards.  But, experience shows that tall tales, fiction tales, fiction and false assumptions fuel our fears. As a diver learning underwater naturalism, you need to avoid character judgements about an organism based on whether it may sometimes pose a hazard. An organism’s form and behaviour spring from its survival needs, and nothing more. While you can’t ignore potentially hazardous organisms, you can learn to understand the organism and to avoid the hazard. As you probably know, the vast majority of all aquatic life injuries are avoidable.

When you think of “dangerous” aquatic animals, what species come to mind?  Usually sharks, barracuda, eels, jellyfish, orca, crocodiles and snakes – those that might seem to “attack” by moving or acting in a way that you could interpret as malicious. You know that fire coral, sea urchins and crown-of-thorns sea stars are potentially dangerous, but since they lack intelligence or an obvious ability to move, you’re less likely to attribute injuries from them to an “attack”. Stepping on a sea urchin with bare feet causes a painful injury, but no one would think the urchin wilfully attacked by manoeuvring itself under your feet.

This brings up three important points regarding “dangerous” aquatic life. Animals rarely attack unprovoked. The vast majority of “attacks” are defensive reactions. If, without looking first, a diver reaches in a moray eel’s hole, the eel will more than likely be terrified (how would you feel if a giant arm suddenly thrust in through your front door and started groping around) and defend itself by biting he diver.

The fact the diver intended no harm is irrelevant; the eel reacts according to instinct. Realizing this, you avoid injuries caused by defensive actions by being able to recognize potentially hazardous animals, by knowing the potential severity of an injury, and by acting in ways that don’t threaten them.

In the case of the eel, this means knowing what an eel looks like, knowing that it can bite, and knowing that reaching into holes is a good way to startle it into doing so. The same principle applies to a sea urchin or fire coral – recognizing it, realizing that it can stick or sting, and understanding that merely touching it can cause the injury.

Animals do not attack out of malice. Not all injuries from aquatic animals are defensive, but even these can be attributed to natural behaviour. Animals don’t seek humans out of malice, revenge or anger, which is what makes many fictional portrayals unrealistic. Animals may initiate an attack for one of four reasons; to defend themselves, to defend territory, a mate or young, to obtain food and by mistake.

In the previous discussion, you saw how a diver could provoke a defensive response. Animals such as the black-tip reef shark are known to be territorial and will defend their territory if they perceive a diver as a competitor. Likewise, baleen whales and dolphins, which are normally docile around humans, become quite agitated when they perceive a diver as a threat to offspring.

As with avoiding a defensive “attack”, you want to know which aquatic animals have territorial behaviour or protect their young and mates, and avoid being mistaken as a threat to territory, young or mate. Animals also attack for food, which rules out divers. You’re not natural prey for any aquatic organism.  More of a concern, however, is that an aquatic animal may mistake a diver for prey or food. At some dive sites, some animals learn to eat out of diver’s hands.

If an unfortunate diver’s finger resembles food to a nearsighted moray or grouper, an “attack” may result. In other areas, a surfer with arms and legs dangling from a board may look like a turtle or sea lion to a shark below. This may have precipitated attacks from sharks that prey on turtles and seal lions. To avoid these types of “attacks”, you must understand what aquatic animals fed on, what triggers feeding behaviour, and how to not accidentally resemble the animal’s idea of food.

Underwater animal attacks seem worse than terrestrial animal attacks. Because humans are so vulnerable in the water, aquatic animal attacks cause more sensation and emotional reaction. We understand terrestrial animals better because we’re terrestrial, and in many areas we’ve killed off or displaced most of those terrestrial animals we fear (not necessarily intentionally).

The reality is, to most aquatic organisms, you’re not worth attention. They’re too busy going about surviving to give you much notice unless you seem to threaten survival or enhance it as a food source. Because aquatic life behaviour is predictable, however you can avoid unpleasant interactions by obtaining local orientations to aquatic life, by reading about aquatic organisms and by acting on what you learn. For example, if you know sharks frequent an environment, and you realize that bleeding and struggling fish attract them (looking for food), you may want to avoid spear-fishing in that area. Likewise, if you’re river diving and spot a snapping turtle, you avoid handling it based on the knowledge that it may bite.

Responsible Interactions With Aquatic Life.

Types of Interaction.

As soon as you enter an aquatic environment, you interact with the organisms living there, whether you intend to or not. You may not intend to involve aquatic life at all in your dive plan-such as a search and recovery dive, or aquatic life maybe your focus, such as in underwater photo and video, fish feeding, fish watching, shell-collecting or gathering tropical fish for aquariums. Some of these interactions are relatively passive and have little negative affect on aquatic life; others may have tremendous negative affect, such as those that kill the organism. Besides your intent, your awareness can be important because your interaction can kill, injure or terrorise aquatic animals without you being aware that you’re doing so. You can classify interactions into several categories, each with varying degrees of negative affect on aquatic life.

Passive interactions.

Passive interactions are those with the least affect. Most passive interaction falls into the category of observing aquatic life-organisms themselves, organism interactions, and interactions between divers and organisms. You can learn a great deal about aquatic life by watching it.

Touching and handling aquatic life.

Humans are naturally curious, so there is a tendency to want to touch and handle aquatic organisms. For many organisms, this is terrifying and sometimes kills them. For a diver, ignorantly touching the wrong organism can be painful or even life threatening experience. In general, touching and handling aquatic life should be done by those experienced with the particular organism. This action should not harm or disrupt the organism’s natural behaviour, and doing so should provide some sights into the organism’s natural history without compromising its health. Otherwise, leave it alone.

Riding aquatic life.

If you consider your own reaction when an uninvited insect drops on your back, then you can relate to how manta ray, turtle or manatee feels when an uninvited diver does the same. There are no circumstances in which riding an animal benefits it, and in some cases, (Particularly sea turtles since they need to surface for air) doing so may injure it.

Spear fishing and gathering aquatic life.

Taking aquatic life, even for human consumption often has a detrimental effect on the aquatic environment. (It certainly has a detrimental effect on the organism). These practices should only be done within the guidelines established by local law, which exist to help ensure a healthy underwater community and long-term survival of the species you gather. Don’t harm aquatic animals that you must measure for minimum size before taking.

Collecting aquatic life for aquariums and collections.

As in spear fishing and gathering aquatic life to eat, taking aquatic life for aquariums and collections may have a negative effect because the organism no longer fills its place in the environment. If you collect, do so responsibly, keeping in mind that in many areas it is illegal and/or requires special licensing.

Feeding fish and aquatic life.

At first, feeding aquatic animals sounds like an interaction that benefits the aquatic environment. When conducted responsibly, fish feeding can be rewarding and can help you understand animal behaviours, but you need to avoid some practices. First, feed with food you bring on the dive.  Don’t kill one organism to feed another.

Second, feed fish sparingly so you don’t seriously interrupt their natural behaviour, including normal feeding and mating. These are important in retaining the balance in the local ecosystem. Remember that feeding in the same location again and again may change local animal behaviours, affecting an entire local ecosystem. Those who see such animals wont witness their natural behaviours.

Underwater photography and videography.

Underwater imaging, done with forethought and consideration of the environment, gives you a rewarding way to “capture” aquatic life with little negative effect. Provided that you’re careful not to damage coral, river grasses or other aquatic life, that you don’t capture, chase or harass animals for the sake of your camera and that you apply good buoyancy skills, you can enjoy years of underwater photo and video while causing little damage to the underwater environment. Its perhaps one of the most rewarding interactions you can have underwater. See the sections on underwater photography and videography for more information.

Dive Techniques That Preserve.

Compared to acid rain, offshore dumping and other forms of pollution that damage reefs, divers inflict little damage to the underwater world. Of that damage, most is unintentional and can be prevented with a little bit of care and forethought. Although divers probably aren’t a major threat to the world’s reefs, as the underwater world’s ambassadors and advocates, it’s our responsibility to set a good example.

Here are a few guidelines that will help you swim through your favourite dive site with minimal damage.

Secure dangling equipment.

Dangling submersible pressure gauges, alternate air sources and other accessories drag across the bottom and reefs, destroying and killing. Use Velcro-type fasteners, clips, snaps and other holders to keep your equipment and accessories tucked in close to your body and not dragging. This not only helps the environment, but minimizes snags, reduces wear on your equipment and saves energy through streamlining.

Dive carefully.

Use good diving techniques.  Stay properly weighted, neutrally buoyant and off the bottom. Swim in a horizontal position (not with your feet down).  This keeps your fins farther from the bottom so you don’t kick (and destroy) aquatic life. Try to glide quietly through the water: you’ll disturb the environment less, and you’ll se more natural behaviour. Also, avoid touching anything on the bottom with your hands. Most bottom dwelling aquatic organisms are very delicate. A simple bump or touch can do harm.  If you’re a boater, avoid anchoring over delicate reef bottoms. Anchor over sandy areas or better yet, go out of your way to use mooring buoys.