Botanica Marina 2019; 62(2): 97–108 Soultana Tsioli*, Sotiris Orfanidis, Vasillis Papathanasiou, Christos Katsaros and Athanasios Exadactylos Effects of salinity and temperature on the performance of Cymodocea nodosa and Ruppia cirrhosa: a medium-term laboratory study https://doi.org/10.1515/bot-2017-0125 Received 14 December, 2017; accepted 2 October, 2018; online first 8 November, 2018 Abstract: The effects of salinity and temperature on the photosynthetic and growth performance of the seagrasses Cymodocea nodosa and Ruppia cirrhosa were studied to understand their local seasonality and distribution. Cymodocea nodosa shoots were collected from Cape Vrasidas, and R. cirrhosa shoots from the coastal lagoon Fanari, all from the Eastern Macedonian and Thrace Region, Greece. Effective quantum yield (∆F/Fm′), leaf chlorophyll-a content (mg g−1 wet mass) and growth (% of maximum) were tested at different temperatures (10–40°C) and salinities (5–60). The results showed that: (a) R. cirrhosa was more euryhaline (5–55/60) than C. nodosa (10–50), (b) the upper thermal tolerance of C. nodosa (34–35°C) was higher than that of R. cirrhosa (32–34°C), (c) C. nodosa could not tolerate 10°C, whereas R. cirrhosa could, and (d) the growth optimum of C. nodosa was 30°C and that of R. cirrhosa 20–30°C. The thermal optima and tolerances of growth and photosynthesis confirm the seasonal patterns of R. cirrhosa but not of C. nodosa. However, the sensitivity of C. nodosa to low salinities and temperatures may explain its absence from shallow coastal lagoons. Ruppia cirrhosa could be vulnerable to future climate change. Keywords: benthic macrophytes; chlorophyll fluorometry; factorial experiments. *Corresponding author: Soultana Tsioli, Benthic Ecology and Technology Laboratory, Fisheries Research Institute (Hellenic Agricultural Organization-DEMETER), Nea Peramos, Kavala 64007, Greece, e-mail: stsioli@inale.gr Sotiris Orfanidis and Vasillis Papathanasiou: Benthic Ecology and Technology Laboratory, Fisheries Research Institute (Hellenic Agricultural Organization-DEMETER), Nea Peramos, Kavala 64007, Greece Christos Katsaros: Section of Botany, Department of Biology, National and Kapodistrian University of Athens, Athens 15784, Greece Athanasios Exadactylos: Department of Ichthyology and Aquatic Environment, School of Agricultural Sciences, University of Thessaly, Fytokou str., Volos 38446, Greece Introduction Cymodocea nodosa and Ruppia cirrhosa are perennial species living side by side (Signorini et al. 2008) in many contrasting Mediterranean environments, while their coexistence has not been observed in eastern Macedonian and Thrace coastal habitats. Cymodocea nodosa is regarded as a “warm-temperate” species, common in the Mediterranean Sea (Den-Hartog 1970). Its optimal temperatures for growth and photosynthesis have been shown to be 24.5°C (Peduzzi and Vukovic 1990) and 30–32°C (Terrados and Ros 1995), respectively. The salinity range in which C. nodosa can survive has been indicated at approximately 17–56 (Fernández-Torquemada and Sánchez-Lizaso 2011). Light and temperature are the major factors controlling the seasonality of Cymodocea growth and peak biomass was observed during summer months (Pérez and Romero 1992). Ruppia cirrhosa is regarded as a “temperate” species that inhabits Mediterranean lagoons (Triest and Sierens 2010). Ruppia cirrhosa survives at salinities 0–75 (Adams and Bate 1994) and temperatures between 0 and 38°C (Comín et al. 1990) and exhibits optimal growth (growth above 80% of maximum value) at salinities above 36 (Verhoeven 1979). Studies on the seasonality of R. cirrhosa stated that its biomass increases exponentially starting in early spring until September (Menéndez and Comín 1989) while its peak has been observed in October (Calado and Duarte 2000). The genetic differentiation of Cymodocea nodosa across the Mediterranean–Atlantic transition region (Alberto et al. 2008) and within the Aegean Sea (Gkafas et al. 2016) strongly indicates the existence of local ecotypes. A significant differentiation of populations of Ruppia cirrhosa between the western and eastern basins of the Mediterranean Sea also exists (Triest and Sierens 2010). Although species may adapt to different environments through phenotypic plasticity, the responses of local ecotypes of C. nodosa and R. cirrhosa to thermal and osmotic stress are not adequately known. Authenticated | stsioli@inale.gr author's copy Download Date | 5/2/19 11:57 AM