The collection and observation of living organisms in the sea, including the quantitative determination of their abundance in time and space. The biological survey of the ocean depends to a large extent on specially equipped vessels. Sampling in intertidal regions at low tide is one of the few instances where it is possible to observe and collect marine organisms without special apparatus.
A primary aim of marine biology is to discover how ocean phenomena control the distribution of organisms. Sampling is the means by which this aim is accomplished. Traditional techniques employ the use of samplers attached to wires lowered over the side of a ship by means of hydraulic winches. These samplers include bottles designed for enclosing seawater samples from particular depths, fine-meshed nets that are towed behind the ship to sieve out plankton and fish, and grabs or dredges that are used to collect animals inhabiting the ocean bottom. These types of gear are relied upon in many circumstances; however, they illustrate some of the problems common to all methods by which the ocean is sampled. First, sampling is never synoptic, which means that it is not possible to sample an area of ocean so that conditions can be considered equivalent at each point. Usually, it is assumed that this is so. Second, there are marine organisms for which there exists no sampling methodology. For example, knowledge of the larger species of squid is confined to the few animals that have been washed ashore. A third problem concerns the representativeness of the samples collected. The open ocean has no easily definable boundaries, and organisms are not uniformly distributed. The actual sampling is regularly done out of view of the observer; thus, sampling effectiveness is often difficult to determine. Furthermore, navigational systems are not error-free, and therefore the position of the sample is never precisely known. All developments in methods for sampling the ocean try to resolve one or more of these difficulties by improving synopticity, devising more efficient sampling gear, or devising methods for observation such that more meaningful samples can be obtained.
Direct and remote observation methods provide valuable information on the undersea environment and thus on the representativeness of various sampling techniques. Personnel-operated deep-submergence research vessels (DSRVs) are increasingly being employed to observe ocean life at depth and on the bottom, and for determining appropriate sampling schemes. The deep-submergence research vessels are used with cameras and television recording equipment and are also fitted with coring devices, seawater samplers, and sensors of various types. Cameras are deployed from surface ships on a wire. Other cameras are operated unattended at the bottom for months at a time, recording changes occurring there. Scuba diving is playing a larger role, especially in open-ocean areas, and is used to observe marine organisms in their natural habitat as well as to collect the more fragile marine planktonic forms such as foraminifera, radiolaria, and jellyfish. Remotely piloted vehicles (RPVs) will continue to assume greater importance in sampling programs since they can go to greater depths than can divers, and they overcome a limitation in diving in that remotely piloted vehicles can be operated at night. Optical sensors carried aboard Earth-orbiting satellites can provide images of ocean color over wide areas. Ocean color is related to the turbidity and also to the amount of plant material in the seawater. This thus establishes a means by which sampling programs carried out from ships can be optimized. See also Diving; Seawater fertility; Underwater photography; Underwater television; Underwater vehicle.
