Limnetic Region Research Articles

Fitoplâncton de um reservatório eutrófico (lago Monte Alegre), Ribeirão Preto, São Paulo, Brasil

Este trabalho teve por objetivo apresentar a flora planctônica de um pequeno reservatório eutrófico, localizado no Sudeste brasileiro, baseado em amostras coletadas quinzenalmente durante o período de abril de 1988 a março de 1989 em uma estação localizada no centro da região limnética. Foram identificadas 93 espécies, 9 variedades, 5 formas taxonômicas e 9 táxons determinados em nível genérico -3 foram listados em suas respectivas classes, em um total de 119 táxons pertencentes a 9 classes taxônomicas (13 Cyanophyceae, 55 Chlorophyceae, 15 Zygnemaphyceae, 14 Euglenophyceae, 05 Bacillariophyceae, 3 Xanthophyceae, 6 Chrysophyceae, 4 Cryptophyceae e 4 Dinophyceae). Foi verificada uma considerável complexidade na composição florística, conforme registrado para outros lagos e reservatórios tropicais, com maior contribuição da divisão Chlorophyta (59%). As espécies fitoplanctônicas foram utilizadas como um dos aspectos para a caracterização trófica do ambiente.

Palaeolimnological investigations in Poland based on Cladocera (Crustacea)

The results of subfossil Cladocera analysis obtained from deposits of 26 lakes throughout Poland have been presented. For years throughout Poland a broad range of palaeolimnological studies have been conducted. Their aim is to discover the historical development of water basins and climatic changes in the course of the last 13,000 years and also to investigate the gradual influence of man on the ecosystem with particular emphasis on the last few decades. The hitherto obtained results of palaeolimnological studies, including the results of Cladocera analysis, have yielded information about the development of lakes and provided the basis for plans of certain reservoirs and their basins. Over the past years, analysis of subfossil Cladocera has become one of the leading palaeolimnological methods. The results of detailed qualitative and quantitative analysis of Cladocera remains from sediments of 15 lakes allowed for a reconstruction of the lakes' development. The littoral and limnetic regions, changing trophy, from oligotrophy to advanced eutrophication, changes in pH and fluctuation of water levels, as well as changes resulting from settlement — from Mesolithic and Neolithic through Medieval times until the present — have been reconstructed. For individual lakes, phases of Cladocera development and periods of eutrophication were indicated which partially correlated with certain pollen zones as well as periods of human impact and geochemical effects.

Fossil Continental Diatoms: Paleolimnology, Evolution, and Biochronology

Diatoms are golden brown algae (class Bacillariophyceae) whose cellular contents are enclosed between two valves or shells of silica. They are classified into groups with radial symmetry (centric diatoms) and axial symmetry (pennate diatoms). The latter are subdivided as raphid and araphid diatoms according to the presence or absence of raphes (slit-like structures) that allow diatoms to move along firm surfaces. Many centric and some araphid diatoms are planktonic, maintained by turbulence in the limnetic region of a lake, whereas raphid diatoms live on the lake bottom or are attached to objects in the illuminated zone.

Distinctive aspects of the zooplankton of large lakes in Australasia, Antarctica and South America

Not only has the degree of species-level cosmopolitanism amongst zooplanktonic organisms been considerably overestimated, but differences between the different classical biogeographic regions (established from terrestrial studies) occur at supra-specific levels as high as family or even suborder. The Centropagidae, and particularly the genus Boeckella, are found in New Zealand, most of Australia, southern and high altitude regions of South America, and around the periphery of Antarctica. The biogeography and ecology of this family is discussed in detail. Most predaceous families of Cladocera are entirely absent from the Australian and Neotropical regions. The genus Daphniopsis occurs in salt lakes in Australia and South America and in freshwater lakes in Antarctica. In southern Australia numerous species of ostracod have colonized the limnetic region of salt lakes, and the largest of these prey on species of Calamoecia, Daphniopsis and small ostracods. Chaoboridae are absent from New Zealand as, too, are obligate planktivorous fish. The Chilean flamingo, Phoenicopterus chilensis, and Wilson's phalarope, Phalaropus tricolor, are significant predators on Boeckella poopoensis in salt lakes on the Andean Altiplano and elsewhere in South America.

Size-Structured Morality in a Treespine Stickleback (Gastrosteus aculeatus) – Cutthroat Trout (Oncorhynchus clarki) Community

In a 112-ha bog lake on the Queen Charlotte Islands, British Columbia, small fish comprised the major element in the diet of cutthroat trout (Oncorhynchus clarki). Despite the presence of juvenile salmon and char in the lake, threespine stickleback (Gasterosteus aculeatus) was the most common fish in the diet (99.5%). Foraging activity appeared to be more frequent in littoral than in limnetic regions. Mark–recapture methods indicate an average population of 220 trout and 75 000 adult stickleback. Trout consumed an estimated 308 770 stickleback yearly (145 kg) of which 65% were taken during summer. Seventy-three percent of all fish consumed were young of the year and 2% were adults, the latter representing 4% of the adult population in the lake. There was a 75% reduction in total mortality between successive year classes of stickleback (0,1,2,3 +). This consumption curve, which resembles a typical survivorship curve of fish, is a function of the size-structure of the populations and includes interactions between size availability of stickleback, prey-size preferences of the trout, and length frequency distributions of trout. Total weight of stickleback consumed by trout comprised about 40% of that previously calculated for 16 species of avian piscivores in the lake.

Coherence and horizontal movements of pathces of Holopedium gibberum (Cladocera).

The horizontal spatial dynamics of Holopedium gibberum in a small lake was followed during two summers. H. gibberum individuals aggregated into a single patch measured in tens of meters. Patch movement was extensive throughout the limnetic region, bore no apparent relationship to wind action, and patch structure remained cohesive regardless of weather conditions. Grazing activity by H. gibberum within the patch was intensive, reducing phytoplankton density to half that outside the patch.

A light trap to sample littoral and limnetic regions of lakes

(1981). A light trap to sample littoral and limnetic regions of lakes. SIL Proceedings, 1922-2010: Vol. 21, No. 2, pp. 776-781.

Spine deficiency and polymorphism in a population of Gasterosteus aculeatus: an adaptation to predators?

A population of Gasterosteus aculeatus from a muskeg lake on the Queen Charlotte Islands shows a spine polymorphism, with 80% lacking the second dorsal spine and 68% lacking the pelvic spines. Females were more prevalent among phenotypes with greater spine number, and males were more common among those with fewer spines. Adult females, as well as juveniles of both sexes with pelvic spines, were more frequent in the limnetic habitat, whereas adult males and juveniles without pelvic spines were common in the littoral region.Five species of piscivorous birds, each in low numbers, foraged in the lake. Extensive predation in the limnetic region by Gavia immer and, secondarily, Podiceps spp. is implicated as a selective pressure favouring the greater spined phenotype.Odonate Nymphs (Aeshna spp.) consumed juvenile fish in predation experiments and in the lake proper. Nymphs were common in the littoral zone, where submerged debris provided substrate for foraging. It is proposed that spine loss in this population of G. aculeatus is an adaptation to the hunting technique of Aeshna, whereby reduced external structures such as spines minimize frictional contact for a grappling predator. Experimental data and other gasterosteid populations are discussed with reference to these proposals.

Enriching effects of Urban runoff on the productivity of a mesotrophic lake

Sewage was diverted from Lake Sammamish in September, 1968, and since then there have been no significant responses by trophic indicators which indicate the lake is beginning to recover. To explain this delay in response, extensive urban development in the lake's watershed was considered as a factor which might be acting to inhibit the lake's recovery. In vitro uni-algal experiments with water from 13 streams which drain urban and undeveloped areas showed that about half of the streams stimulated algal growth significantly, but these streams constitute less than 14 per cent of the lake's total water income. Of these six streams only two drain urban areas and account for less than 2 per cent of the water income. In situ experiments showed that no streams were significantly stimulatory to natural populations of phytoplankton. Other in situ studies showed that one urban stream and two from undeveloped areas caused substantial increases in periphyton growth after a 12-day period, although these increases were not statistically significant. Additional in situ nutrient limitation experiments in August of 1970 and 1971 revealed that P and N were limiting only in combination. Results from these studies do not support the contention that urban runoff is seriously enriching the limnetic region of Lake Sammamish.

Limnetic Larval Fish in Northern Wisconsin Lakes

The open water of two northern Wisconsin lakes was sampled for larval fish at night with fine-mesh conical townets. Those collected were identified to genus or species and enumerated. The majority of larval fish were captured in the limnetic region but a few never strayed from the littoral region.The seasonal changes of the limnetic species were similar for the two lakes and 3 years of study. Their abundance varied greatly from year to year but yellow perch, sunfish, and black crappies always dominated.