2. The aim was to differentiate metric variation caused by human or natural processes and thereby to (1) select reliable metrics and (2) develop user-friendly protocols for cost-effective monitoring programmes for coastal lagoon water quality.3. Eight different sites dominated by macrophyte communities characterized by two angiosperms (Ruppia cirrhosa and R. maritima), two opportunistic macroalgae (Ulva sp. and Chaetomorpha linum), and Cyanobacteria colonies were quantitatively and destructively sampled twice.4. Structural metrics showed highest heterogeneity at a local site-specific scale, while functional metrics showed highest heterogeneity at the scale of habitat. As a result the structural metrics appeared inappropriate as indicators of lagoon water quality changes. By contrast shifts of habitat dominated by angiosperms to opportunistic macroalgae owing to nutrient excess, especially nitrogen, can be identified by functional metrics, especially with EEI.

No abstract

The photoperiod alone or in combination with temperature may affect macroalgal growth, reproduction, and development. This study aimed to investigate the responses of Ericaria barbatula, a perennial fucalean species collected from Kavala Gulf, Greece, to photoperiod and temperature. Maximum quantum yield (F v /F m ), wet biomass (g), relative growth rate (day−1), and reproduction (receptacles and zygote formation) were monitored in two laboratory experiments, the first one in two consecutive phases (A and B), that lasted at least seven months. While in Experiment 1, phase A, specimens were cultivated under long-day (LD) and short-day (SD) conditions at a constant temperature, in Experiment 1, phase B, they were cultivated at a seasonally changing temperature. The results indicated that E. barbatula reproduced in both phases under SD conditions and grew better in winter to early spring under seasonally changing temperatures. The cultivation under night-break (NB) daylength and seasonally changing temperatures (Experiment 2) indicated that E. barbatula is a facultative (quantitative) SD plant, a result that needs further examination. However, the induction of reproductive organs under SD conditions has been confirmed. It secures the release of zygotes and the germlings’ growth in the field from April to June/July under non-stressful Mediterranean Sea temperatures.

Stuckenia pectinata, a submerged macrophyte of eutrophic to hyper-eutrophic fresh to brackish waters, faces management and climatic-forced increment of salinity and irradiance in Vistonis Lake (Greece) that may endanger its existence and the ecosystem functioning. A pre-acclimated clone under low irradiance and salinity conditions was treated to understand the effects of high salinity and irradiance on a suite of subcellular (chlorophyll a fluorescence kinetics and JIP-test, and chlorophyll content) to organismal (relative growth rate—RGR) physiological parameters. The responses to high irradiance indicated the plant’s great photo-acclimation potential to regulate the number and size of the reaction centers and the photosynthetic electron transport chain by dissipation of the excess energy to heat. A statistically significant interaction (p < 0.01) of salinity and irradiance on Chl a, b content indicated acclimation potential through adjusting the Chl a, b contents. However, no significant (p > 0.05) difference was observed on Chl a/b ratio and the RGR, indicating the species’ potential to become acclimatized by reallocating resources to compensate for growth. Thus, the regulation of photosynthetic pigment content and photosystem II performance consisted of the primary growth strategy to present and future high salinity and irradiance stressful conditions due to eutrophication management and the ongoing climatic changes.