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Abstract:The present paper aims to describe the marine flora occurring on the continental shelf of Gökçeada Island (North Aegean) based on the review of the long-term researches which provided qualitative information on many taxa including Cyanobacteria, Chlorophyta, Ochrophyta, Rhodophyta and Tracheophyta.Eight species (Polysiphonia brevearticulata, Ceramium codii, Gymnothamnion elegans, Spermothamnion repens, Lophosiphonia cristata, Hydrolithon cruciatum, Leathesia marina, Caulerpa racemosa) and one variety (Caulerpa racemosa var. cylindracea) recorded during the present study are the new records for Gökçeada Island. The new recorded species belonging to Rhodophyta were found as opportunistic-filamentous and crustose epiphytic forms on Posidonia oceanica leaf blades during the years 2009-2016. The presence of Caulerpa racemosa, the Mediterranean invasive algae and its dispersal around the island proves the ecological threat on the coastal ecosystem of the island due to the touristic boat achorings and bottom trawling.Rhodophyta had the highest number of species dominated the macroalgal composition with 178 species followed by the contributions of Ochrophyta and Chlorophyta and Cyanobacteria with 78, 64 and 25 species, respectively. As for the marine phanerogams (Tracheophyta) that contribute as key ecosystems to the biological diversity were recorded as 1% of the systematic groups in the region presenting three genus (Cymodocea, Posidonia, Zostera) but covering vast areas.After all the future goals of this research are to develop a checklist of marine flora along the littoral zones of Gökçeada Island (North Aegean) presenting the last biodiversity situation and a detailed herbarium collection for the museum of Istanbul University Gökçeada Marine Research Department.

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Epiphytic microalgae attached to Posidonia oceanica leaves play a significant role through primary production, nutrient cycling and trophic fluxes in benthic ecosystems. Due to their sensitivity, epiphytic microalgae respond to environmental alterations more quickly than their host. The aim of this study is therefore to evaluate the ecological quality in Gökçeada Underwater Park (North Aegean) using epiphytic microalgal composition and abundance. In this respect, P. oceanica shoots are collected at 6m, 15m and 28m in May, July, October 2009 and January 2010 to estimate the microalgal composition and abundance. Also, P. oceanica descriptors and physico-chemical parameters in the water column of the meadow lower limit are measured. Leaf surface improvement through greater depths, have provided a convenient substratum for epiphytic colonization. A total of 56 taxa belonging to epiphytic microalgae are composed of Bacillariophyceae (91%), Cyanophyceae (7%) and Dinophyceae (2%). Temporal and bathymetric dynamics of the epiphytic community structure and abundance depend on the environmental parameters; such as leaf surface, nutrients and turbidity. Also, a mucilage phenomenon, resulted in a low diversity due to the dominancy of filamentous cyanobacteria. Necessary data is supplied for a less evaluated region affected by agricultural activities and urbanization in the recent years.

Aquatic macrophytes are one of the key components of freshwater ecosystems and contribute to ecosystem functioning and environmental sustainability. They are assumed to be an ideal biomonitoring tool in long-term monitoring programs implemented by the EU Water Framework Directive due to their sensitivity to environmental factors. Therefore, this study focuses on the evaluation of the ecological status in Lake Sapanca using macrophyte composition and abundance in order to make future predictions on the health of aquatic ecosystems and to form effective management. Submerged macrophyte assemblages related to environmental parameters were investigated from February to November of 2017. A total of 12 submerged macrophyte species were recorded in the littoral zone of the lake. The main findings on the most dominant 7 species of this community indicated significant differences among stations and seasons. They also revealed that submerged macrophyte density was shaped in relation to environmental variables, particularly temperature and nutrients. Submerged macrophyte assemblages reached their highest species number and biomass value (5312 gm-2) in summer, while no species was recorded in winter. High biomass values of these species corresponded with lower macrophyte diversity. The macrophyte index results demonstrated that Lake Sapanca is at a critical level in terms of nutrient enrichment. More frequent observation of species such as Ceratophyllum demersum and Elodea canadensis, which indicated "massive" nutrient enrichment, revealed that the ecological status of the lake varies from meso-to eutrophic at the local level.