Seagrass meadows, key ecosystems supporting fisheries, carbon sequestration and coastal protection, are globally threatened. In Europe, loss and recovery of seagrasses are reported, but the changes in extent and density at the continental scale remain unclear. Here we collate assessments of changes from 1869 to 2016 and show that 1/3 of European seagrass area was lost due to disease, deteriorated water quality, and coastal development, with losses peaking in the 1970s and 1980s. Since then, loss rates slowed down for most of the species and fast-growing species recovered in some locations, making the net rate of change in seagrass area experience a reversal in the 2000s, while density metrics improved or remained stable in most sites. Our results demonstrate that decline is not the generalised state among seagrasses nowadays in Europe, in contrast with global assessments, and that deceleration and reversal of declining trends is possible, expectingly bringing back the services they provide.

No abstract

During the last decade, the Palmones River estualy has undergone severe eutrophication followed by a green tide episode; two species ofUlva, rotundata Blid. and Ulva curvata (Kutz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P) of Ulva species, as well as some physicochemical variables in the estualy. Maximum biomass (up to 375 g dly wt.m-2 in some spots, corresponding to a thallus area index of nearly 17 m2 Ulva m-2 sediment) were observed in June and December. However, the biomass vaned among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates obseroed. Growth rates were estimated directly i n the field. The rates were generally higher i n Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The dqerence between both estimates was used to quantijj the importance of the processes causing loss of biomass, which were attrib utable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme selfshading. Maximum chlor@hyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water, However, the absolute concentrations of tissue N and P were always higher than the cn'tical h e l s for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estualy. I n addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass. K q index words: eutrophication; growth; primaly p r e duction; Ulva Local proliferations of masses of green algae are often found in estuaries and coastal waters of areas undergoing eutrophication (Geertz-Hansen et al.

The diel variation and regulation of the enzyme nitrate reductase (NR) were examined in the diatom Thalassiosira weissflogii (Gru.) Fryxell et Hasle. NR was purified, and polyclonal antibodies were raised to a 98‐kD polypeptide. The antibodies cross‐reacted only with proteins from closely related diatom species, suggesting significant epitopic variation of this enzyme within algal divisions. Neither NR enzymatic activity nor protein was detected in cells grown with ammonium as the sole nitrogen source; the addition of ammonium to cells growing on nitrate decreased both protein levels and enzyme activity by 40% within 2 h. In cells grown on a 12:12 h LD cycle, NR activity and NR protein levels were highly correlated, with a peak at midday, a decrease toward the end of the photoperiod, and an increase in activity beginning near the end of the dark period. The addition of actinomycin D (an inhibitor of RNA synthesis) and cycloheximide (an inhibitor of protein synthesis) affected NR activity and NR protein levels identically, strongly suggesting that this nuclear‐encoded protein is regulated primarily at a transcriptional level. The diel pattern of NR protein and activity ceased immediately following transfer to continuous light, indicating that the periodicity is not directly controlled by a circadian rhythm. Time‐lagged cross‐correlation analysis revealed a 6‐h phased difference between the minimum enzyme activity or protein levels and the maximum cellular carbon pool. On the basis of the experimental results, we develop a model proposing that (1) NR activity is regulated primarily by transcriptional regulation of NR synthesis and that (2) the level of expression of the enzyme during a given day is correlated with the integrated pool of organic carbon accumulated during the preceding photoperiod.

Summary• Several Cape species of the genus Erica are known to present seeder and resprouter phenotypes, and this variation seems to have a genetic basis. Therefore, this genus provides ideal model systems for using to elucidate the evolution of nonsprouting or seeder and resprouter life-histories in woody, fire-recruiting plants.• A simple simulation model was developed to identify, under life-history optimality, the ecological conditions ( viz. rainfall conditions and fire frequency) that conferred a selective advantage to the seeder phenotype over the resprouter in a given Cape Erica species.• The model illustrated that the seeder life-history was able to invade and replace a resprouter population only under a mild mediterranean climate, with short, moderate summer droughts.• This simulation approach will contribute to a better understanding of the biogeographical pattern of seeder and resprouter lineages of one of the paradigmatic fynbos woody taxa throughout the Cape floristic region.

The present study assessed the effect of seawater ammonium enrichment on survival and growth of the seagrass Zostera noltii Hornem. Ammonium enrichment had an inhibitory effect on shoot, rhizome and root elongation rates, as well as on primary production. The inhibitory effect was partially alleviated by phosphate addition. The frequency of ammonium pulses also affected growth negatively, with a maximum effect at both low and high pulse frequencies. Similar results were obtained when the experiment was run in the field during a winter trial. However, when the field experiment was repeated in spring at higher mean temperature and irradiance levels, opposite results were obtained, with ammonium enrichment causing a substantial increase in growth rates and productivity. These responses were related to the internal balance of non-structural carbohydrates (especially sucrose) with respect to C and N cell metabolism. Thus, there was a mobilisation of sucrose in both above-and belowground tissues to meet C increased demands arising from ammonium assimilation in winter, with sucrose concentrations reaching critical levels in relation to the total internal C pool. In contrast, sucrose accumulated in the tissues when ammonium pulses were applied in spring, indicating an enhanced C turnover that was able to meet the increased demands arising from ammonium assimilation into organic N compounds.

No abstract

The primary production of Ulva populations relies on their photosynthetic perfrmance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic perjimance of two different species (Ulva rotundata Blid., Ulva curvata (Kutz.) De Toni) blooming in the Palmones river estuav. Light within canopies d i f f e d from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. I n addition, light was spectrally jiltered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/ PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are ji-equently found covering the intertidal mudjats, and therejbre, thalli within these mats may be suijected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspen& differences were observed for light-saturated photosynthetic rates (P,,,J and light compensation points (Lcp), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima wtre recorded in winter for P,,, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (Rd was not seasonally affected, and a maximum L, was found in summer. To extrapolate these data toJield situations, the temperature dependence of photosynthesis should be considered. The values were 2.44 for Rd and 1.79 for P, , , whereas the photosynthesis rate at subsaturating light levels was unaffected. The Qro values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal dijierences on P,,, were damped.