which have extremely high acidic content and will cause a breakdown in other forms of algae. A clipboard should be used with waterproof paper and pencil for notes and a field notebook to record data immediately after diving. Diving observations should be recorded as soon as possible, preferably while the diver is still on the bottom. Field data should include notes on depth, substrate, terrain, water temperature, current, visibility (clarity), conspicuous sessile animals, herbivores, the date, time, methods used, and the collecting party. If possible, information on available light, salinity, and other environmental factors should be obtained. An assessment of the conspicuous species of plants and the abundance of each should be noted-whether common, occasional, or rare; whether attached to certain substrates, or other peculiarities. In many instances, more than half of the species present are not conspicuous, and require careful microscopic examination. This is usually impossible under field circumstances because of the optical equipment, library facilities, reference collection, and time necessary to make an accurate systematic analysis. Accurate light measurements within a given plant community can only be obtained by measurement in situ. Small, self-contained light meters can be positioned and read by a diver. It is important to understand certain principles before embarking on underwater light measurement of this kind. The use of photographic light meters, incorporating selenium photocells, is unsatisfactory unless restricted spectral regions, isolated with colored filters, are measured. This is because a sensing system which responds differently to different wavelengths is being used to measure light which is becoming increasingly monochromatic with depth. The introduction of colored filters in front of the meter greatly reduces its sensitivity. If an opal cosine collector is added to make the system absorb light more as the plant surface does, then it is of use only in shallow, brightly lit waters. A detailed description of the apparatus necessary to make such measurements is found in Paragraph 7.3. Generally it incorporates a selenium photocell of increased surface area, thereby ensuring increased current output per unit of illumination, a system for easily changing the colored filters, and a sensitive ammeter, the range of which can be altered by current attenuation circuitry. 8.5.3 Specimen Preparation and Preservation It is helpful to examine and make notes on collections while they are still fresh to determine the kinds of macroscopic plants present, especially delicate species. Preparation of herbarium and voucher specimens from fresh material is preferred by many botanists, but this is often not possible in the field. Plants prepared soon after collection tend to retain their natural color better than those that have been preserved. There are standard herbarium methods for pressing plants (Knudsen 1972), with some special variations for marine algae. The usual approach is to float specimens in large, flat trays, and to carefully slide them onto sheets of heavy weight herbarium paper (University of California type, 100 percent rag content, is best). Using water, the plants are arranged on the paper, then the paper is placed on a sheet of blotting paper, topped with a square of muslin or other plain cloth or a piece of waxed paper. This is topped with another blotter, and a corrugated cardboard "ventilator" placed on top. Another layer of blotter-paper-plantcloth-blotter- cardboard is stacked on top, and so on. When 20 or 30 have been stacked, the pile should be compressed, using a weight or pressure from straps wrapped around the plant press. The top and bottom pieces should be stiff, usually boards slightly larger than the herbarium paper and blotters. After several hours (or overnight), the stack should be taken apart and the damp blotters replaced with dry ones. Many small algae dry in one day using this technique, but some, such as the large brown algae, may take a full week to dry completely. A few small filamentous and gelatinous species can be successfully air dried without pressing if they are arranged on a 3" x 5" card. In all cases, it is essential that every sheet be labeled, at least with an identifying station number. The usual method for preserving specimens for later detailed examination and herbarium preparation is simple and effective. For each station, one or more large plastic bags can be used to hold samples of larger plants. Small bags or vials should be used for selected fragile or rare plants. The best general preservative is a buffered solution of 5 percent seawater formalin formalin (commercial liquid formaldehyde diluted with seawater). Specimens will keep successfully, thus preserved, for many years if kept in a cool, dark place. Exposure to light causes preserved plants to fade. Samples from many stations in separate bags can be kept in a single large storage drum that can be sealed tightly to prevent formalin from leaking out. For shipping, most of the preservative can be drained off, as the plants, once preserved, remain in good condition for several weeks if they are damp. Kelps may require special handling because of their large size. Small plants can be preserved in 5 percent seawater formalin, but an alternative method for whole large plants involves soaking them for several hours or days in a solution consisting of 10 percent carbolic acid and 30 percent each of water, alcohol, and glycerin. Specimens thus preserved may be dried and then rolled up for storage. The glycerin helps to keep the plants flexible indefinitely. Another technique suggested by Dawson (1956) involves partially air drying giant kelps on newspaper (in the shade) and rolling the plants, beginning with the holdfast. Rolls are tied, labeled, and wrapped in paper, then left to complete drying. Specimens so prepared can later be resoaked for examination. Coralline algae and rock-encrusting species al require special attention. Air drying specimens in shade, then storing samples in boxes, has proven a satisfactory technique for many large brittle and fragile species. Some small plants can be preserved with general collections, but delicate specimens should be isolated. Retaining small pieces of rock with coralline and encrusting algae attached helps to keep the plants intact. Plants collected for histological study should be preserved in a solution of 90 parts 70 percent ethyl alcohol, 5 parts glacial acetic acid, and 5 parts formalin. In all cases, preserved specimens should be kept as dark as possible. 8.6 MARINE ARTIFICIAL REEFS Artificial reefs are man-made or natural objects. intentionally placed in selected areas of the marine environment to duplicate those conditions that cause concentrations of fishes and invertebrates on natural reefs and rough bottom areas. By increasing the amount of reef habitat, artificial reefs provide the potential for increasing stock sizes of fishes. The main features that appear to attract marine animals to these habitats are shelter, areas of calm water, visual reference points, and food. Artificial reefs also provide access to new feeding grounds, and open new tracts for territorial fishes. Population estimates of reef fishes are made by direct counts of the number and species at the reef sites. These counts are made by two or more swimmers when visibility is 4 or more feet. Each observer makes counts by species for sections of the reef that are then totaled for the entire reef count. The totals of all observers are averaged for a mean count of each species of territorial and schooling fishes, such as black sea bass, Atlantic spadefish, grunts, and most porgies. For seclusive fishes, such as Carolina hake, morays, groupers, and flounders, the highest count obtained by any one observer is used. Although the accuracy of fish population estimates vary with visibility, species, and time of day, it is assumed that if these conditions remain the same the counts represent population density. Artificial reefs can be used in all kinds of water, and can be made in many ways, e.g., old cars, cement, and miscellaneous debris. One of the easiest methods involves the use of old tires (Figure 8-14). Such reefs have been used for over 15 years to improve fishing in normally barren waters (Steimle and Stone 1973). In a recent study, the Figure 8-14 Made From Old Tires Figure 8-15 Underwater Equivalent of a Geologist's Brunton Compass Used for Measuring the Dip and Strike of Underwater Rock Outcrops tires were scattered and piled in the selected area in 20 stacks of four to eight tires, and fastened together with steel rods run through the stacks (Stone and Buchanan 1970). Each stack was weighted causing it to come to rest in an upright position on the bottom. Stacks were arranged in heaps, giving a naturally irregular appearance, in 45 feet of water, with a few single tires randomly distributed. This type of structure has proved highly successful in a number of experiments in other areas. The worn-out tires are cheap, almost indestructible, and make excellent bases on which marine life can grow. The hard, convoluted surfaces are ideal for concentrations of algae and encrusting organisms, and for small fish that find food and shelter in the many holes and crevices in and around the stacks. Larger predatory fish gather around the newly formed "fish havens," as do crustaceans and mollusks. 8.7 GEOLOGY The use of diving has enhanced the geologist's ability to conduct underwater research by giving him direct access to the seafloor. In situ measurements and observations have become a necessary part of the study of the processes of sedimentation and erosion that mold the sea floor in nearshore regions. The initial phase of any offshore geological study is to compile data on the geology of the adjacent shore area, including surficial features and sediments; bore hole data; seismic data; and geological mapping and survey reports. One of the first uses of scuba was the study of the transport of sediment along the seafloor off southern California, Photo Robert Dill (Fisher and Mills 1952). The systematic mapping of seafloor geology began in 1952 during the expansion of offshore oil exploration (Menard et al. 1954). Dill and Shumway (1954) were among the first to document the significance of scuba diving in geological investigations, and presented drawings and photographs of instruments developed to support early studies. Such tools as an underwater equivalent of the Brunton compass (Figure 8-15), the basic instrument that geologists use for geological mapping, were developed by commercial divers and reported by Shumway (1955). This unit was later refined into an instrumented observation board, which included writing board, depth indicator, compass, inclinometer, protractor, ruled edges, bubble levels, pencil holders, accessory straps, and a belt clip. Menard et al. (1954) further utilized diving techniques for underwater geological reconnaissance mapping of the Continental Shelf areas off southern California. The physical measurement of the bottom may utilize techniques previously described; however, a diver may use an accurate compass, an inclinometer, and a tape to acquire physical measurements of sufficient precision for most geological studies. The physical measurement of changing conditions on the seafloor or the creep of the strata of the ocean bottom is another matter, however, requiring measurements of some precision. Dill (1964) describes the use of accurately located and measured stakes to determine the amount of gravity creep and active slumping in submarine canyon sediments. On-site evaluation of topographic data is another important role of the diving geologist. The techniques used for acquisition of topographic data, such as echo ranging and side scan sonar, are not capable of differentiating many topographical features of interest to the geologist. The makeup of the strata in outcroppings, and the direction in which the outcrop slopes, can only be verified by on-site visual observation or photographic techniques. A diver, with a minimum of equipment can measure and record geological features of this type. A diver using a camera can record the strata and sediment conditions in the natural state that cannot be acquired by other methods. The limitation of visibility places severe restraints on the planning of geological and geomorphological work. Most species of animal or algae, a wreck or an amphora, are all sufficiently small for their form and orientation to be readily identifiable in good visibility, and usually identifiable in 2-10 m visibility. However, a cliff, large stack, sand ribbon, or sand wave, cannot be seen all at once even in good visibility. The diver, on first contacting the feature, may not realize what he has found, and will have to swim a ways before he can be sure that the crest of a sand wave is continuous, or the foot of a cliff is horizontal. In this sense the diver's vision, combined with the ability to recognize and integrate the parts of large features with his knowledge of position, becomes a real technique. To aid the search and identification of features divers may swim on a fixed course, or alter course in a programmed way. If a feature is suspected of being in a certain locality the diver should be dropped well to one side so that a traverse in one direction is bound to take him across it. If the features are linear the divers should search on a line normal to the trend until they intersect a trend line. Search techniques are described in detail in Section 7. In this stage of work an aquaplane may be used (Figure 8-1). If the water is deep it is safer to lay a bottom line between buoyed shot weights, marked at intervals to aid position fixing. The buoys can be fixed by sextant or radar. In deep water, it helps to have a shot line for the diver to descend even if he is only giving a visual report on the bottom material or collecting a single sample, especially if there is a current (Woods and Lythgoe 1971). In currents over 1 knot divers have difficulty maintaining their position by swimming during a search. They can be towed on an aquaplane with a screen to protect them from the water flow, or they can work on a fixed bottom line. If the fixed line leads up to the surface vessel, the vertical component of the tension will tend to lift the diver off the bottom. The best method is to attach a light line to the anchor before dropping it, keeping the free end on deck. The diver descends using the combined cable. When reaching the anchor, he streams back on the light line, while the free end is held by an attendant. In this manner, the diver can swim from side to side downstream of the anchor, searching a wide area. He is also in continuous contact with the boat, and can be pulled back to it when he ascends. This system can be worked in 2-3 knots, after which the face mask is pulled off by the current. Observations can include identification, recognition, delineation, the observation of processes, and the detection of change. It is immediately apparent to a diver if: there is size-sorting between crest and trough of ripples; the particles at the crest of ripples are discolored by biological growth while those in the troughs are not; bevelled recesses in a cliff line up to form a continuous notch; sand moves over ripples as a wave passes; or if dead shells on sand are more or less quickly broken up than those on gravel. There are many useful aids to visualization of processes, such as dumping colored sand or gravel, or releasing dyes or neutral density floats into the water to reveal the movement. The best way to prepare a marked sample which will have the same hydraulic characteristics as the natural bottom material is to take a bottom sample, wash it, dry it, spray with aerosol paint, dry again, sieve it to break up agglomerates, and replace it on the sea bed at the point where it was removed. There is the inevitable risk that many of the smallest particles will remain stuck together by paint. This method, however, introduces less error than when dumping completely unnatural or artificial materials, and the method is simple to work in the field. The above techniques are discussed in further detail by Woods and Lythgoe (1971). 8.7.1 Geological Mapping In general, a geologist mapping the seafloor must obtain the same information under water as on land. This usually includes the dip (the angle at which a stratum or any planar feature is inclined from the horizontal) and the strike (the course or Photo lan Macintyre Photo: Laurence Bussey bearing of the outcrop of an inclined bed or stratum on a level surface) of bedrock outcrops. A representative rock sample is also taken to describe the rock type and fossil age of the formation being mapped. The location and information are placed on the regional map for later translation into strati graphic cross-sections and a geological map of the region. Fault contacts can be followed as much as they can on land. The use of aerial photography may save much time and provide an overall context into which the results of underwater geological mapping can be placed. Pictures of bottom topography can often be obtained from aircraft at altitudes. up to 12,000 feet. One of the difficulties of geological mapping under water is finding rock outcrops. A thin cover of overburden can make mapping difficult. However, it is often possible for a geologist to use biological indicators as a means of reaching rock exposures. In many regions sessile organisms such as gorgonian corals and sea fans will extend up through the overburden, showing that a hard substrate is buried beneath a thin cover. Fanning away the sediment with the hand will expose the underlying rock surfaces and permit geological measurements. It is often possible to follow small rockfish to rock exposures after they flee from a diver and seek protection in rock structures. Kelp beds often (but not always) give a surface indication of rocky bottom. The geologist working under water must learn to "read" the environment - it will give many clues about where to find rock outcrops needed to complete geological maps. In many instances, rock outcrops can be anticipated before the dive by looking for bottom irregularities with an echo sounder. Fish associated with rocky areas will also show up as distinct echos above the bottom return and are valuable as indirect indicators of rock bottom. Snapping shrimp that live in rocky areas can be heard as a "crackly" sound when a boat stops over rocky areas. Grapnels towed from outrigger poles over the bottom can also be used as snags for finding isolated rock outcrops. It is advisable to have some breakaway system with a surface buoy to prevent excessive loss of gear. Once a rock outcrop is found, the geologist should swim around the dive site to ensure that the rock to be measured is in place. (In many instances where differential erosion has undercut resistant beds, they will topple and give erroneous readings.) A useful instrument is a writing slate to which is attached an inclinometer and compass (referred to earlier). The dip of rock strata should be determined by measuring the dip bearing (the direction towards which the bed dips) of the outcrop. This value can be later converted into strike by subtracting 90 degrees from the dip bearing value. This method prevents confusion as to which direction the outcrop was facing. The actual dip is measured by placing the straight edge of the writing board on the bedding |