Types Of Aquatic Ecosystems Research Articles

Index of Biotic Integrity Based on Fish Assemblages for the Conservation of Streams and Rivers in West‐Central Mexico

The rivers and streams of west‐central Mexico are becoming increasingly degraded and warrant expanded conservation efforts. We have developed an index of biotic integrity based on fish assemblage characteristics to aid in the preservation of the biological integrity and biodiversity of these waters. Our version is an adaptation of previous versions of the index of biotic integrity, which have proven effective in environmental assessment and monitoring in the United States and elsewhere. It consists of 10 fish assemblage attributes, termed metrics, that are related to environmental quality, ecosystem integrity, and biodiversity in west‐central Mexican streams and rivers: number of native species, percentage of benthic species, number of water column species, number of sensitive species, percentage of tolerant species, percentage of exotic species, percentage of omnivores, percentage of native livebearing species, relative abundance, and percentage of diseased or deformed. Data on fish communities from 27 sites on streams and small rivers in the vicinity of the Sierra de Manantlán, southwestern Jalisco, and in the upper Río Duero basin, northern Michoacán, were used to develop expectations and scoring criteria for each metric. The index value for a site was the sum of the scores for the 10 metrics. Index values and associated ratings of biotic integrity for the 27 sites corresponded closely with independent ratings based on habitat and water quality. However, additional tests of the index with independent data and refinement of metrics and scoring criteria are clearly warranted. The index shows promise for identifying key watersheds for the protection of intact native biotic communities and individual endangered and threatened species and for the long‐term monitoring and evaluation of biodiversity and ecosystem integrity in the streams and rivers of west‐central Mexico. Our version could serve as a model for the development of similar indices for other regions and other types of aquatic ecosystems in Mesoamerica.

Primary production required to sustain global fisheries

THE mean of reported annual world fisheries catches for 1988-1991 (94.3 million t) was split into 39 species groups, to which fractional trophic levels, ranging from 1.0 (edible algae) to 4.2 (tunas), were assigned, based on 48 published trophic models, providing a global coverage of six major aquatic ecosystem types. The primary production required to sustain each group of species was then computed based on a mean energy transfer efficiency between trophic levels of 10%, a value that was reestimated rather than assumed. The primary production required to sustain the reported catches, plus 27 million t of discarded bycatch, amounted to 8.0% of global aquatic primary production, nearly four times the previous estimate. By ecosystem type, the requirements were only 2% for open ocean systems, but ranged from 24 to 35% in fresh water, upwelling and shelf systems, justifying current concerns for sustainability and biodiversity.

Disappearance of phenol in water samples taken from the yenisei river and the krasnoyarsk reservoir

Using experimental microecosystems the kinetics of phenol disappearance in river and reservoir water were investigated. In river water the disappearance kinetics could be described by a first-order equation, the same kinetics took place in reservoir water before and after the period of “bloom” of blue-green algae. During the “bloom”, the phenol seemed to be mineralized by bacteria which grew at the expense of another compound, and the model of best fit was the model of exponential growth and low concentration of the test substrate. In the river, two sections differed according to the difference between the mean values of the specific disappearance rates. In the reservoir these rates were lower than those in the river. In general the specific disappearance rate values did not correlate with the values of initial bacterioplankton density, the concentrations of inorganic nutrients nor the chemical oxygen demand. Conclusions about the integral influence of ecosystems on the disappearance rates and dependence of self-purification kinetics on the type of aquatic ecosystem were made.

Macroinvertebrates as ?describers? of morphological and hydrological types of aquatic ecosystems abandoned by the Rh�ne River

Samples of aquatic macroinvertebrates were taken from abandoned beds of the river Rhone in the Bregnier-Cordon area. This sector of the French Upper Rhone is particularly rich in old beds or ‘lones’ which vary in age and morphological type and have more or less direct connections with the river.