Studies on the submerged plant community in Lake Biwa. I. Distribution and productivity of Egeria densa. A submerged plant invader in the south basin [Translation from: Physiol.Ecol.Japan 17, 283-290, 1976]

Egeria densa (PLANCH.) ST. JOHN, a submerged plant invader, forms a wide submerged plant zone, particularly along the west coast of the south basin, Lake Biwa. The macrophyte occupies over 82% of the plant zone in the basin and its biomass reaches 93% of the total. The estimated annual net production was approximately 1 kg dry wt./m2 in a dense area, which is about 4.5 times as much as the net production by phytoplankton in an offshore area of the basin. Although the area covered by the macrophyte is only 5.8% of the total of the basin, it produced about one-tenth of the total annual primary production. In the most productive season Egeria produced 46% of the total primary productivity. Thus, the macrophyte never be neglected when one considers the energy flow or material circulation in the basin. This study was initiated in order to clarify the role of submerged macrophytes, particularly E. densa, in Lake Biwa. The following points are reported in this paper: the distribution of macrophytes in the south basin; seasonal change in standing crop of E. densa; seasonal change in values related to production, utilizing a model proposed by Ikushima with its parameters experimentally determined.

Zonation of submerged vegetation in Lake Kariba, Zimbabwe and its ecological interpretation

The submerged vegetation of Lake Kariba is described in relation to degree of slope (lake morphometry), depth and light transparency. The direct gradient analysis technique - canonical correspondence analysis and the TWINSPAN classification programs were used to analyse the data set. The western end of the lake with low transparency has a low species diversity (with Vallisneria aethiopica dominating). Species diversity increases with increased transparency in the other parts of the lake. The classification revealed monospecific communities for all species as well as mixed communities with Lagarosiphon as the associate species with the broadest distribution. The ordination revealed a first axis strongly related to the depth and transparency gradients and the second axis related to slope.

Abundance of harbor porpoise (Phocoena phocoena) in three Alaskan regions, corrected for observer errors due to perception bias and species misidentification, and corrected for animals submerged from view

Estimating the abundance of cetaceans from aerial survey data requires careful attention to survey design and analysis. Once an aerial observer perceives a marine mammal or group of marine mammals, he or she has only a few seconds to identify and enumerate the individuals sighted, as well as to determine the distance to the sighting and record this information. In line-transect survey analyses, it is assumed that the observer has correctly identified and enumerated the group or individual. We describe methods used to test this assumption and how survey data should be adjusted to account for observer errors. Harbor porpoises (Phocoena phocoena) were censused during aerial surveys in the summer of 1997 in Southeast Alaska (9844 km survey effort), in the summer of 1998 in the Gulf of Alaska (10,127 km), and in the summer of 1999 in the Bering Sea (7849 km). Sightings of harbor porpoise during a beluga whale (Phocoena phocoena) survey in 1998 (1355 km) provided data on harbor porpoise abundance in Cook Inlet for the Gulf of Alaska stock. Sightings by primary observers at side windows were compared to an independent observer at a belly window to estimate the probability of misidentification, underestimation of group size, and the probability that porpoise on the surface at the trackline were missed (perception bias, g(0)). There were 129, 96, and 201 sightings of harbor porpoises in the three stock areas, respectively. Both g(0) and effective strip width (the realized width of the survey track) depended on survey year, and g(0) also depended on the visibility reported by observers. Harbor porpoise abundance in 1997–99 was estimated at 11,146 animals for the Southeast Alaska stock, 31,046 animals for the Gulf of Alaska stock, and 48,515 animals for the Bering Sea stock.

A mechanical device for eradication of submerged aquatic weeds

This paper embodies details and method of operation of a mechanical device developed for eradication of submerged aquatic weeds. The economics of operation is also discussed.

Effect of submerged aquatic vegetation on growth and survival of Penaeus monodon (Fab.)

An experiment was conducted in brackish water ponds with transplanted aquatic weed (Najas sp.) to study the effect of submerged aquatic vegetation on culture of Penaeus monodon. Out of six ponds three were without any aquatic vegetation (T1) while in other three ponds weeds were planted covering 40% of the pond bottom (T2). Hatchery produced post larva of P. monodon (0.006 g) were stocked in all ponds at a density of 40,000/ha. Shrimps were fed twice daily with commercial and formulated feed prepared from locally available ingredients. After 105 days of rearing shrimp of highest average weight (63.18g) was obtained from T2 with a survival rate of 25.90% and the total production was obtained at 654.54 kg/ha. The average weight, survival and total production of shrimp in T1 were 35.0 g, 28.76% and 405.63 kg/ha, respectively.

Influence of nitrogen salts on growth and physiological responses of Rhizophora apiculata Blume in non-aerated water culture

Influence of two different forms of nitrogen on growth and physiological aspects of water-cultured seedlings of Rhizophora apiculata was studied. Of the two forms of nitrogen supplied to the growth medium, ammonium nitrogen was better than nitrate nitrogen by exhibiting increased dry matter production, shoot length, leaf area and also enhanced the contents of carotenoids, chlorophylls and their presence in photosystems and light harvesting protein complex.

Using Remote Sensing and Spatial Information Technologies to Detect and Map Two Aquatic Macrophytes

This paper describes the light reflectance characteristics ofwaterhyacinth [Eichhornia crassipes (Mort.) Solms] and hydrilla [Hydrilla verticillata (L.F.) Royle] and the application of airborned videography with global positioning system (GPS) and geographic information system (GIS) technologies for distinguishing and mapping the distribution of these two aquatic weeds in waterways of southern Texas. Field reflectance measurements made at several locations showed that waterhyacinth generally had higher near-infrared (NIR) reflectance than associated plant species and water. Hydrilla had lower NIR reflectance than associated plant species and higher NIR reflectance than water. Reflectance measurements made on hydrilla plants submerged below the water surface had similar spectral characteristics to water. Waterhyacinth and hydrilla could be distinguished in color-infrared (CIR) video imagery where they had bright orange-red and reddish-brown image responses, respectively. Computer analysis of the imagery showed that waterhyacinth and hydrilla infestaions could be quantified. An accuracy assessment performed on the classified image showed an overall accuracy of 87.7%. Integration of the GPS with the video imagery permitted latitude/longitude coordinates of waterhyacinth and hydrilla infestation to be recorded on each image. A portion of the Rio Grande River in extreme southern Texas was flown with the video system to detect waterhyacinth and hydrilla infestaions. The GPS coordinates on the CIR video scenes depicting waterhyacinth and hydrilla infestations were entered into a GIS to map the distribution of these two noxious weeds in the Rio Grande River.

Influence of Sediment Nutrients on Growth of Emergent Hygrophila

Hygrophila ( Hygrophila polysperma (Roxb.) T. Anderson) is a plants which forms serious aquatic weed problems. Both submerged and emergent growth forms occur. Nutritional studies with a controlled release fertilizer and sediments collected from hygrophila-infested areas were conducted with the emergent growth habit to provide insights into growth of this introduced plant. Plant dry weights for experimental 16- week culture periods with low average temperatures were associated with low amounts of hygrophila biomass as compared to culture periods with high average temperatures. Hygrophila cultured in sand rooting media with the controlled release fertilizer produced as much as 20 times more dry weight than plants cultured in sediments only. First-degree linear regression statistics showed hygrophila dry weights were highly related to ammonia nitrogen, magnesium, sodium, and pH values in the sediments. These findings show the close relationship of the emergent growth habit of hygrophila to sediment nutrients. Analyses for certain sediment characteristics may provide an indication of the potential growth that may be expected for weed infestations of this plant. Hygrophila grows year round in south Florida; however, visual observations of canals and other bodies of water indicate that lower amounts of hygrophila plants occur during the cooler months of year than during the summer season. These findings show the seasonal growth of emergent hygrophila occurs with biomass dependent on both sediment nutrients and temperature.

A Method for siting and prioritizing the removal of derelict vessels in Florida Coastal Waters: test applications in the Florida Keys

Increased boating activities and new waterfront developments have contributed an estimated 3,000 dismantled, abandoned, junked, wrecked, derelict vessels to Florida coastal waters. This report outlines a method of siting and prioritizing derelict vessel removal using the Florida Keys as a test area. The data base was information on 240 vessels, obtained from Florida Marine Patrol files. Vessel location was plotted on 1:250,000 regional and 1:5,000 and 1:12,000 site maps. Type of vessel, length, hull material, engine, fuel tanks, overall condition, afloat and submerged characteristics, and accessibility, were used to derive parametric site indices of removal priority and removal difficulty. Results indicate 59 top priority cases which should be the focus of immediate clean up efforts in the Florida Keys. Half of these cases are rated low to moderate in removal difficulty; the remainder are difficult to remove. Removal difficulty is a surrogate for removal cost: low difficulty -low cost, high difficulty - high cost. The rating scheme offers coastal planners options of focusing removal operations either on (1) specific areas with clusters of high priority derelict vessels or on (2) selected targeted derelicts at various, specific locations. (PDF has 59 pages.)