SUMMARY: Charophytes constitute a group of macrophytes that usually inhabit soft bottoms with shallow water. They occur mostly in fresh-water environments but can also be found in brackish waters. Due to their requirement for clear water they are considered sensitive to eutrophication and therefore often used as an indicator for good water quality. The diverse structure of the Estonian coastline with its numerous sheltered bays and shallow, soft-bottom archipelago areas coupled with low salinity conditions provides an excellent habitat for charophytes. To date, seven species have been described in Estonian coastal waters, NE Baltic Sea. Last systematic investigations on charophyte distribution date back 20-30 years. During the summer of 2001 the locations where charophytes have previously been found were revisited and new sites sampled, to describe the present distribution of quantitative and qualitative parameters of charophyte species. Sampling was performed mainly by SCUBA diving; occurrence, abundance and wet weight biomass were estimated for each location. Six species of charophytes were identified. Compared to previously recorded material, no significant changes in the distribution pattern of charophytes were found. The dependence of charophyte distribution on environmental settings was tested, with depth and substrate quality explaining most of the variability in distribution. Salinity within observed range had minor influence on charophytes.Key words: Charophytes, Baltic Sea, depth distribution, salinity.
RESUMEN: DISTRIBUCIÓN DE LAS ESPECIES DE CARÓFITOS EN AGUAS COSTERAS DE ESTONIA (MAR BÁLTICO NE). -Los Caró-fitos son un grupo de macrófitos que por lo general viven en fondos blandos con aguas someras. Se encuentran sobre todo en ambientes de agua continental, pero pueden hallarse asimismo en aguas salobres. Debido a su necesidad de aguas transparentes con frecuencia se les considera sensibles a la eutrofización y, por ello, suelen ser utilizados como indicadores de buena calidad del agua. La estructura variada del litoral de Estonia, con sus numerosas bahías resguardadas y áreas de archipiélagos con fondos blandos y someros, junto a condiciones de baja salinidad, proporciona un hábitat excelente para los carófitos. Hasta la fecha se han descrito siete especies de carófitos en las aguas costeras de Estonia, en el NE del mar Bál-tico. Las últimas investigaciones sistemáticas sobre la distribución de los carófitos se remontan a hace 20-30 años. Durante el verano de 2001 se volvieron a visitar las localidades en las que previamente se habían encontrado carófitos y se muestrearon nuevos emplazamientos, para describir la distribución actual de parámetros cuantitativos y cualitativos relativos a las especies de carófitos. El muestreo se realizó principalmente mediante buceo con escafandra autónoma; para cada localidad se estimaron la presencia, abundancia y biomasa en peso húmedo. Se identificaron seis especies de carófitos. Comparado con el material registrado previamente, no se descubrieron cambios importa...
The in situ grazing experiments were performed in the shallow water rocky habitat of the northern Baltic Sea during ice-free season 2002. In the experiments the effects of algal species and choice on the grazing of the mesoherbivores Idotea baltica (Pallas) and Gammarus oceanicus Segerstra˚le were tested. Salinity, temperature, concentration of nutrients in water and macroalgae and net production of macroalgae were considered as random effects in the analysis. The invertebrate feeding rate was mainly a function of the net photosynthetic activity of Pylaiella littoralis (L.) Kjellman and Fucus vesiculosus L. Feeding rate increased significantly with decreasing algal photosynthetic activity. When the two algal species were incubated together invertebrates fed primarily on P. littoralis. Low selectivity towards P. littoralis coincided with its high photosynthetic activity. The presence of F. vesiculosus did not modify the invertebrate feeding on P. littoralis. The results indicated that (1) the grazing on F. vesiculosus depended on the availability of P. littoralis, (2) the photosynthetic activity of algae explained the best the variation in grazing rate and (3) the grazers are not likely to control the early outbreak of filamentous algae in the northern Baltic Sea by avoiding young and photosynthetically active algae. The likely mechanism behind the relationship is that the increased photosynthetic activity of macroalgae coincides with their higher resistance to herbivory.
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