Bottom Surface Area Research Articles

Abundance, Composition, and Dynamics of the Invertebrate Fauna of a Tidal Freshwater Wetland

The benthic and epiphytic faunas of Tivoli South Bay, a freshwater tidal wetland on the Hudson River, New York, were studied in the summers of 1986 and 1987. Total macroinvertebrate density in the sediments ranged from 5.0 × 10³ individuals/m² to 11.0 × 10³ individuals/m². Chironomids made up 15 to 50% of the total number of macroinvertebrates in the sediment. Artificial substrates were used to document short-term population dynamics of chironomids. Colonization of artificial substrates placed in the field in June of 1986 was rapid, with the maximum number of chironomid genera being present in <2 wk. Peak abundance on these substrates (8.3 × 10³ individuals/m²) was reached after 22 d of exposure, and densities were comparable to densities of chironomids found on the predominant macrophyte (9.5 × 10³ individuals/m²). Substrates placed in the field later in the summer collected fewer individuals and genera, and there were changes in taxonomic composition. From late June to August, water-chestnut (Trapa natans) thoroughly covered the surface of this bay and was an important habitat for macroinvertebrates. The average abundance of epiphytic invertebrates was consistently greater than 1.0 × 10⁴ individuals/m² of bottom surface area and ranged as high as 3.0 × 10⁴ individuals/m². From June to August, epiphytic invertebrates were more abundant than benthic invertebrates, illustrating the importance of the water-chestnut habitat. In July abundance of epiphytic chironomids declined sharply, with densities dropping from 7.7 × 10³ individuals/m² of bottom surface area to 0.7 × 10³ individuals/m². Emerging adults collected over this period totalled 0.4 × 10³ individuals/m², leaving much of the decline unexplained. Predation by fishes and predatory or competitive interactions among the Chironomidae are possible alternative explanations for the decline.

The vertical distribution of hydropsychid larvae and pupae (Trichoptera: Hydropsychidae) in stream substrates

Vertical stratification of benthic samples at three stations on the Credit and Humber rivers revealed significant between-layer differences in the physical structure of riffles and abundances of larvae and pupal cases of Cheumatopsyche Wallengren and four species of Hydropsyche Pictet (Trichoptera: Hydropsychidae). Rock size and total rock surface area decreased from the top layer to the bottom (surface areas of pebbles excluded). Larvae of all five instars of H. sparna Ross were significantly more abundant (P &lt; 0.05) in the top layer than in the bottom, but pupal cases were more numerous in the middle and bottom layers. Similar patterns were found for larvae and pupal cases of Hydropsyche bronta Ross, Hydropsyche slossonae Banks, and Cheumatopsyche. Pupal cases as well as larvae of Hydropsyche morosa Hagen were more numerous in the top layer. Depth and current conditions influenced sedimentation. Mean current velocities and total accumulation of fine material were greater at downstream stations. Significant variation in deposition of fine and coarse materials was found within the riffle at each station, suggesting that local streambed conditions govern sediment deposition at the microhabitat level.

Comparative characteristics of some ecosystems of the upper regions of the shelf in tropical, temperate and Arctic waters

1. The distribution of biocoenoses in the upper shelf parts of temperate and tropical regions in the western part of the Pacific Ocean, in upper boreal Atlantic waters and in the high latitudes near Franz Josef Land has been investigated employing the quantitative diving method. 2. In bionomically analogous parts of temperate and cold waters of the Northern hemisphere, parallelism in the distribution of biocoenoses can be observed. The leading (dominant) forms are substituted by vicarious species. A series of biocoenoses in these waters corresponds to tropical biocoenoses located at similar depths and on similar grounds. Reef-forming corals, dominant in many tropical biocoenoses, are replaced by macrophytes, especially in cold and temperate waters (convergency on a larger scale). 3. The biomass of bottom biocoenoses attains maximum values in tropical waters and decreases regularly towards the high latitudes of the Arctic Ocean. 4. Population density is maximum in biocoenoses of temperate latitudes; it decreases more or less equally in tropical and Arctic waters. The ratio of the quantity of species to population density per 1 m2 of bottom surface area is maximum in tropical and Arctic biocoenoses and diminishes considerably in temperate waters. 5. The geographical distribution of biocoenoses on similar grounds and at equal depths depends (a) in tropical waters upon the direction of prevalent currents and upon the degree of isolation of island shelves from the ancient continental shelf areas with diverse and abundant populations; (b) in temperate waters, upon the temperature regime of the surface waters (heat exchange between sea and atmosphere; influence of the prevalent water currents); (c) in Arctic waters, upon the solidity and constancy of the ice cover. 6. In tropical and temperate waters, maximum biomass, maximum population density and greatest species diversity are observed at depths ranging from 0 to 10 m, in Arctic waters from about 18 to 25 m, due to ice conditions in the shoals which are unfavourable for life. 7. In all areas investigated, the distribution of biocoenoses reveals a distinct vertical zonation. The zonation is caused in tropical waters (on identical grounds), by the degree of light penetration and by hydrodynamic peculiarities of different layers of the surface water mass; in temperate waters by differences in the thermal regime of the layers of the surface water masses; in the Arctic waters by the degree of light penetration, by the mechanical influence of ice, especially of icebergs, and by the mode of ice conditions prevailing over different depths.

Thermal Aquaculture Design1

ABSTRACTThis paper presents a conceptual design for intensive aquaculture in flowing warm water. Shrimp biology and technology were used as the model, but the concept is applicable to any culturable aquatic species. A culture channel was divided into pens, each successively larger in bottom surface area than the last. Each pen area was proportional to the area of a segment of a typical S‐shaped shrimp growth curve. Heated water was blended with ambient water to maintain a constant water inlet temperature of 27 C. The stream of uniform depth flowed through the channel at a constant rate. Shrimp in culture were allowed to remain in one pen until they attained a density, g per m2, which was constant for all pens. They were moved successively to larger and larger pens until they reached a specified marketable size. Once the system reaches steady‐state, it should be possible to harvest continually, say week after week, the year‐round.