Interplay between r- and K-strategists leads to phytoplankton underyielding under pulsed resource supply

Fluctuations in nutrient ratios over seasonal scales in aquatic ecosystems can result in overyielding, a condition arising when complementary life-history traits of coexisting phytoplankton species enables more complete use of resources. However, when nutrient concentrations fluctuate under short-period pulsed resource supply, the role of complementarity is less understood. We explore this using the framework of Resource Saturation Limitation Theory (r-strategists vs. K-strategists) to interpret findings from laboratory experiments. For these experiments, we isolated dominant species from a natural assemblage, stabilized to a state of coexistence in the laboratory and determined life-history traits for each species, important to categorize its competition strategy. Then, using monocultures we determined maximum biomass density under pulsed resource supply. These same conditions of resource supply were used with polycultures comprised of combinations of the isolated species. Our focal species were consistent of either r- or K-strategies and the biomass production achieved in monocultures depended on their efficiency to convert resources to biomass. For these species, the K-strategists were less efficient resource users. This affected biomass production in polycultures, which were characteristic of underyielding. In polycultures, K-strategists sequestered more resources than the r-strategists. This likely occurred because the intermittent periods of nutrient limitation that would have occurred just prior to the next nutrient supply pulse would have favored the K-strategists, leading to overall less efficient use of resources by the polyculture. This study provides evidence that fluctuation in resource concentrations resulting from pulsed resource supplies in aquatic ecosystems can result in phytoplankton assemblages' underyielding

Nitrogen as the main driver of benthic diatom composition and diversity in oligotrophic coastal systems

Phytoplankton is the main indicator group for eutrophication in coastal ecosystems, however its high dispersal potential does not enable the assessment of localized effects of coastal nutrient enrichment. Benthic diatoms are sessile microalgae associated with sandy substrates and have the potential to reflect more localized pollution impacts. Although benthic diatoms are widely used bioindicators in freshwater systems, they have rarely been used for assessing the eutrophication status of oligotrophic environments such as the eastern Mediterranean Sea. In the present study, we assess the efficiency of benthic diatoms as bioindicators of nutrient enrichment in oligotrophic coastal systems, by investigating the effect of different physicochemical conditions and nutrient concentrations on the assemblage composition, diversity and individual species populations. To do this, we sampled along a eutrophication gradient formed by anthropogenic nutrient inputs from a metropolitan area. The main driver of assemblage composition, diversity and biomass of diatoms was nitrogen concentration and its temporal and spatial changes. Nitrogen loadings were positively correlated with increased biomass of Cocconeis spp. and negatively correlated with Mastogloia spp. Our findings suggest that in coastal ecosystems of oligotrophic marine ecoregions, benthic diatom assemblage structure and specific taxonomic groups can be reliable predictors of coastal eutrophication offering higher spatial resolution compared to phytoplankton

Meloneis Gen. Nov., a New Epipsammic Genus of Rhaphoneidaceae (Bacillariophyceae)

The diatom family Rhaphoneidaceae is characterized by high generic diversity and low species diversity with most genera known to have long stratigraphic ranges. The genera within this family are neritic marine, and mostly epipsammic. A new modern and epipsammic genus, Meloneis gen. nov., is described herein and is compared to all genera within Rhaphoneidaceae and especially to Rhaphoneis Ehrenberg s.l. Within Meloneis three new species and one variety are distinguished and described herein: M. mimallis sp. nov., M. mimallis var. zephyria var. nov., M. akytos sp. nov., and M. gorgis sp. nov

The show cave of Diros vs. wild caves of Peloponnese, Greece - distribution patterns of Cyanobacteria

The karst cave ‘Vlychada’of Diros, one of the oldest show caves in Peloponnese, sustains extended phototrophic biofilms on various substrata – on rocks inside the cave including speleothems, and especially near the artificial lighting installation (‘Lampenflora’). After a survey of the main abiotic parameters (Photosynthetically Active Radiation -PAR, Temperature -T, Relative Humidity -RH, Carbon Dioxide -CO2) three clusters of sampling sites were revealed according to Principal Component Analysis (PCA): i) the water gallery section predominately influenced by CO2, ii) the dry passages influenced by RH and PAR, and iii) the area by the cave exit at the dry section influenced by temperature. The collected samples from the water gallery section and the dry passages of the cave revealed a total of 43 taxa of Cyanobacteria, with the unicellular/colonial forms being the most abundant. The applied non-metric Multi-dimensional Scaling Ordination (nMDS) of the cumulative species composition showed a clear distinction between the water gallery section and the dry passages of the cave. Further comparison with previous data from other wild caves of Peloponnese (‘Kastria’, ‘Francthi’, and ‘Selinitsa’) was conducted revealing a distinction between the show cave and the wild ones. Apart from the human impact on cave ecosystems – through aesthetic alteration (‘greening’) of cave decorations by the ‘Lampenflora’, and by the cleaning treatments and restoration projects on the speleothems – identification of the organisms constituting the ‘Lampenflora’ might provide taxonomically and ecologically significant taxa

External valve views of <i>Meloneis mimallis</i> sp. nov. under SEM.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank"><b>Figure 2A</b></a><b>. </b><i>M. mimallis</i> with two pseudocelli consisting of 5 pores (lower valve apex) & 6 pores (upper valve apex); note the two sizes of edge papillae, the larger ones usually in groups of 3–4 between the areolae rows. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank"><b>Figure 2B</b></a><b>.</b> Detail of the valve apex showing the circular pattern of pseudocellus consisting of 6 pores (black arrow); grey arrow indicates the external opening of the rimoportula; black arrow with white outline points to the extra incomplete row of small papillae (see also the complete rows in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank">Fig. 2C</a>). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank"><b>Figure 2C</b></a><b>.</b> Note the presence of an extra short continuous row of fine papillae at each pole (arrows) (cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank">Fig. 2B</a>). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank"><b>Figure 2D</b></a><b>.</b> A specimen with two pseudocelli, consisting of 3 pores (black arrow) & 4 pores (white arrow). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank"><b>Figure 2E</b></a><b>.</b> Detail of the valve end showing the round to ovate rota-type areolae with central pits. [Scale bars: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank">Figures 2A, C, D</a> = 10 µm, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank">Figure 2B</a> = 1 µm, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g002" target="_blank">Figure 2E</a> = 2 µm].</p

Characters of valve morphology differentiating the four taxa of <i>Meloneis</i>.

<p>Characters of valve morphology differentiating the four taxa of <i>Meloneis</i>.</p

Internal valve views of <i>Meloneis mimallis</i> sp. nov. and <i>Meloneis akytos</i> sp. nov. under SEM.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank"><b>Figure 3A</b></a><b>.. </b><i>M. mimallis</i> with diagonally positioned rimoportulae in relation to the apical axis. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank"><b>Figure 3B</b></a><b>.</b> Detail of the apex showing the elongated slit-like internal opening of the rimoportula (black arrow), and the pseudocellus consisting of 4 fine pores (black arrow with white outline). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank"><b>Figure 3C</b></a><b>.</b> A specimen of <i>M. akytos</i> with distant striae and diagonally positioned rimoportulae in relation to the apical axis. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank"><b>Figure 3D</b></a><b>.. </b><i>M. akytos</i> showing the elongated slit-like internal opening of the rimoportula (white arrow), and the pseudocellus with 2 fine pores (black arrow). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank"><b>Figure 3E</b></a><b>.</b> Tilted specimen of <i>M. akytos</i>; note the two (white arrow) or three (black arrowhead) struts of the rotae in the areolae. [Scale bars: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank">Figures 3A, C</a> = 10 µm, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank">Figure 3B</a> = 1 µm, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032198#pone-0032198-g003" target="_blank">Figures 3D, E</a> = 2 µm].</p

Valve morphology - according to the available literature and photodocumentation cited in this paper - differentiating <i>Meloneis</i> from the related genera of the family Rhaphoneidaceae (for the genus <i>Rhaphoneis s.s.</i> characters of the type species <i>Rhaphoneis amphiceros</i> were considered).

1<p>Fo = fossil, R = recent.</p>2<p>Mu = multipolar, La = lanceolate, Rh = rhomboid, Ell = elliptic, Li = linear, Elo = elongate.</p>3<p>So = solid, Pe = perforate, Co = concentric.</p>4<p>SRa = presence of a single row of areolae even around the apices, SRna = presence of a single row of areolae but not around the apices.</p>5<p>Ps = pseudocellus, RP₁ = apical pore field reduced to 1 pore.</p>6<p>x = number, M = many, F = few.</p>7<p>Ci = rather circular, Di = rather disorganised, Rd = rather radiating.</p>8<p>Rimoportula (R) and Apical Pore Field (Ps, RP₁) in relation to vE = valve edge, and in relation to Lr = last transverse row of areolae. For instance: (R-Lr) = rimoportula positioned between the areolae of the last transverse row, vE→ Ps = pseudocellus positioned next to the valve edge. The question marks indicate unclear position of the rimoportula in relation to pseudocellus and to the last transverse row.</p>9<p>P = presence, A = absence.</p>10<p>Sp = spines, Pa = papillae, A = absence of protrusions.</p

Potential mechanisms of coexistence between two globally important Pseudo-nitzschia (Bacillariophyta) species

To understand the mechanisms leading to coexistence and exclusion, it is essential to establish information on the nutritional needs of species. We focused on the frequently coexisting Pseudo-nitzschia species, P. delicatissima and P. galaxiae, capable of forming blooms and producing domoic acid. We employed monoculture experiments to determine growth kinetic parameters important for understanding resource use (i.e. maximum specific growth rate, half-saturation coefficients for growth and cell quotas), and we coupled mixed-culture experiments and numerical modelling to explore the role of resource competition relative to unknown factors, such as allelopathy. Experimental results showed that both species had a high requirement for nitrogen (N) and low requirement for phosphorus (P), consistent with field observations of Pseudo-nitzschia blooms in N-rich conditions. The model accurately predicted the outcome of competition; P. galaxiae outcompeted P. delicatissima when considering only resource competition, but the population trajectories were better predicted when allelopathic effects were added. Since the competitive exclusion of P. delicatissima by P. galaxiae in our laboratory experiments is not consistent with observations of coexistence in the natural environment, the model was further modified to explore realistic ranges of population loss factors, such as sinking, demonstrating how coexistence is possible when these are considered