The early oceanographic expeditions with the vessels like Challenger and EXPLORER had a rather naturalist character and carried out specimen collections from various depths in different areas of the world. Later efforts tended to concentrate on measuring quantitative parameters so as to assess the yield potential of the sea in respect of food resources. Today, contemporary research projects are multi-disciplinary, and are conducted by scientists of different expertise (biologists, chemists, geologists, physicists, mathematicians, computing scientists etc.) and involve many different techniques. Some of the instruments now used are not only miracles of contemporary electronics but, as the measurements being taken have become more extended and also more accurate, these instruments have actually changed our view of the marine environment.

Biological sampling devices

For every category of organism and for every type of water or sediment parameter, several kinds of samplers and devices have been developed and used. Each one has particular advantages and, of course, concomitant disadvantages.

They can be classified into three main categories according to the quality of the results obtained from their use.

Qualitative (mainly traps and dredges): these provide basic information on the fauna by means of the collection of individuals of various species.

Quantitative: these take samples of defined volume (from the water column) or area (from the sediment). Their results provide an estimate of the total abundance or biomass of the area in question. Into this category of samplers come grabs, corers and water bottles (e.g. Niskins bottles). These samplers usually take a small quantity of water (1-12 l) or sediment (area 0.05 - 0.25 m 2 ). Semi-quantitative: here large samples are taken, but their results are reliable mainly:

in respect of proportions (relative abundances) of various taxonomic groups. Dredges and trawls are samplers or this kind.

Organisms collected with samplers such as these are then identified (i.e. their species name is determined) with the aid of binoculars and microscopes. The number of individuals is counted and various conclusions are using advanced mathematical techniques in computers.

Underwater photography and television are also used not only to record marine organisms in a qualitative way but also to make quantitative assessments, as for instance in the case of hard substrate.Imaging methods allow the recording of the whole habitat hetrogeneity and to collect samples in a non-destructive fashion. See Figure 27.

Measurement and recording instruments

While the taxonomic identification of marine organisms is still a labour-intensive process requiring a sustained level of scientific expertise, the measurement of physical and chemical parameters has been

automated to a large extent through the use of specialised electronic equipment. The use of special instruments to measure dissolved oxygen, salinity, and Redox is commonplace nowadays in all marine biology laboratories (Figure 28 Dissolved oxygen meter). There are also automatic recorders of salinity-temperature and oxygen (CTD) (Figure 29 "CTD") which measure all these parameters continuously in vertical profiles (i.e. in all depths) in the water column and store the measurements in incorporated electronic memories.

Most research vessels (but many fishing boats too) use special hydro-acoustic devices (or echo sounders) which are able to detect fish schools. These instruments are based on the principle that sound is reflected when it strikes on a surface separating two materials of different densities. Fish swimbladders present a surface of this type and hence a school of fish, when echo-sounded, will project a view like the one shown in Figure 30.

More recently methods of remote sensing have been developed where the computer analysis of photographs taken from aircraft and satellite leads to valuable indirect conclusions about water movements and its content in various compounds including the temperature.

Analytical instruments

The development of the instruments described below has facilitated the monitoring process considerably, especially in the case of various pollutants, thus saving labour and giving more accuracy to the results.
In modern chemical laboratories most chemical analyses are carried out by special analytic devices which use integrated automated processes: the samples which are to be analysed are placed in cuvette on special racks where a special auto sampler system takes over to bring the sample to the measuring electrode. The whole system is controlled by a computer in the memory of which the results of the analysis are recorded.
Nutrient analysers, Atomic Absorption devices for the detection of heavy metals, Gas Chromatography devices (GC.) and High Performance Liquid Chromatography devices (H.P.L.C.) for the detection of various organic compounds are the most widely encountered examples of this kind of analysers. HÜäƒ >l¨óN;m ‚"ˆØ¢O>ùØ¢ƒ-