We studied the effects of NH4+, photosynthetic photon flux (PPF), and temperature on growth rates, together with inorganic carbon (Ci) utilization properties of Gelidiopsis sp. cultivated in tanks. At 25% sunlight, weekly growth rates and dry weight yields increased up to 6-fold with increasing NH4+(0–2 mM); however, at 5% or 100% sunlight the effects were much lower. Contents of photosynthetic pigments (chlorophyll a and phycoerythrin) increased in correlation with increases of NH4+. Maximal chlorophyll a concentrations occurred under high PPF, while phycoerythrin concentrations were higher at low PPF. Ash amounts in Gelidiopsis sp. did not vary significantly with different NH4+ or PPF levels. Optimal temperatures and PPFs for growth were 20–25 °C and 170–320 μmol m−2 s−1, respectively, correlating with short-term photosynthetic O2 evolution measurements. The pH of both thallus surface and bulk medium increased during photosynthesis, reaching average values of 8.75, and resulting in low rates of O2 evolution. Activities of carbonic anhydrase (CA) were detected inside and outside the cells and were apparently involved in the Ci uptake system of Gelidiopsis sp. since both acetazolamide (membrane-impermeable) and ethoxyzolamide (membrane-permeable) inhibited photosynthetic O2 evolution by 89% on average. Half-maximal rates of photosynthetic O2 evolution (K0.5) were reached at 17 μM CO2 at pH 5.0 and 2–3 mM Ci at pH 8.0, indicating high affinity for CO2 and close to saturated photosynthesis at Ci levels of seawater. Thus the Ci uptake system of Gelidiopsis sp. probably uses an extracellular CA catalyzed conversion of HCO3− to yield CO2, which could diffuse into the cells, and an intracellular CA catalyzed HCO3− ↔ CO2 interconversion which may assure CO2 for Rubisco. Direct uptake of HCO3− may also be required based on the K0.5 (CO2) estimated for Gelidiopsis sp. and the pH generated at the thallus surface at which CO2 concentrations would only be approximately 10 μM. Therefore, in addition to limitations of low NH4+ concentrations and high temperatures during the summer, growth of Gelidiopsis sp. from the Israeli Mediterranean may also be restricted by its limited Ci utilization system and the low CO2 concentrations prevailing in seawater.
The present work presents a checklist of marine macroalgal species described for the Israeli Mediterranean shores, based on literature records published within the last century. The eastern Mediterranean (Levant Basin) offers a peculiar macro-habitat, which is radically unique within the Mediterranean Sea. The list includes more than 300 species of red (Rhodophyta), brown (Phaeophyta), and green (Chlorophyta) marine macroalgae found primarily in the intertidal zone, with at least one endemic species (Cystoceira rayssiae, Phaeophyta) described for this area.
A taxonomic list of macro marine algae (seaweeds) described in the literature for the Red Sea during the years 1756–2020 is presented. The list was prepared using existing published studies, local monitoring reports, as well as “grey” or unpublished lists of seaweeds for the area. Altogether, we examined more than 300 publications and compiled more than 900 taxonomic names, of which 576 correspond to valid species, whilst 355 names were considered synonyms for these species. The phylum Chlorophyta (green seaweeds) was represented by 37 currently accepted genera and 133 species (including 74 species synonyms). The phylum Ochrophyta (Phaeophyceae only; brown seaweeds) was represented by 52 genera, 157 species and 99 synonyms; and the phylum Rhodophyta (red seaweeds) by 130 genera, 286 species and 182 synonyms. The brown seaweed Sargassum appears to be a particularly biodiverse genus in the area represented by 58 species and 26 synonyms. Our study shows the inconsistency and lack of long-term taxonomic studies and recent molecular investigations of seaweeds from nearly the whole Red Sea.
The link of the Mediterranean Sea to the Indian and Pacific Oceans was artificially created with the opening of the first Suez Canal in 1897, and the second in 2015, allowing the direct passage of marine organisms into the Eastern Mediterranean Sea. About 307 macroalgae (seaweeds) exist in the Israeli Mediterranean shores. The current study lists marine macroalgae within the Levant basin described after the year 1900, with special focus on species from Israeli shores. We identified 86 species for the whole Levant area regarded as exotic, namely, introduced by artificial vectors derived from human activities, including arrivals via the Suez Canal (Lessepsian invasion). Of those 86 species, 42 are Rhodophyta, 23 are Chlorophyta and 21 are Ochrophyta. Further, about 68% are of Indo-Pacific origin, 20% of Atlantic origin, with 12% of the species of uncertain origin. With precaution, we suggest that about 16% of the marine flora in the Israeli Mediterranean shores are of exotic nature. This survey also indicates that about half of the exotic Ochrophyta are of Atlantic origin, while there are no reports of Chlorophyta of Atlantic origin in the Levant basin. Key aspects when evaluating the exotic nature of marine macroalgae are the trustworthiness of past taxonomic identification and long-term records and description of seaweed collections, both particularly troublesome for the Levant basin.
Two marine macroalgae have recently been identified using drift algal material collected in the Haifa Bay area, Israel. The first is the red seaweed Galaxaura rugosa, first seen south of Haifa Bay during November 2003 and observed thereafter both within seaweeds washed ashore and at 2-4 m deep within the subtidal zone. Galaxaura rugosa was previously described in the Lebanese coasts; therefore its distribution within the Israeli Mediterranean is expected to be far more extensive. The second is the green seaweed Codium adhaerens, which was collected along the northern shores of Haifa Bay during September-October 2007.
Mechanisms of inorganic carbon utilization (i.e., carbon-concentrating mechanisms) in seaweeds involve uptake of HCO3 - and carbonic anhydrase-mediated production of CO2. These mechanisms are needed to cope with the low concentrations of CO2 dissolved in seawater and the low affinities of Rubisco for CO2 in the macroalgal chloroplasts. The current study shows, for the first time, direct evidence that while Ulva rigida photosynthesizes there is continuous production of CO2, apparently generated from an acidification process in its boundary layer. Release of CO2 during light periods was measured using a membrane inlet mass spectrometer, while acidification at the boundary layer was detected in pH-drift experiments. Under repetitive light (4, 70, 300 μmol photons m-2 s-1) and dark cycles, O2 production rates exceeded by 10-fold that of CO2 production under illumination. Photosynthetic release of O2 was largely dependent on the experimental range of light intensities, while CO2 evolution under illumination was significantly reduced at 24 °C as compare to 15 °C. Rapid acidification occuring within the unstirred layer and the consequent CO2 release may account for an additional mechanism of inorganic carbon utilization strategies in Ulva rigida, which previously had been reported to posses an efficient carbonic anhydrase modulated carbon concentrating mechanism.
Absorption and fluorescence spectra, photosynthetic rates, pigment concentrations, and cell size were investigated during photoacclimation of Porphyra leucosticta, a red marine macroalga that thrives during winter in the eastern Mediterranean. Optical properties were measured on intact thalli using image analysis or from crude extracts after disrupting algal tissue. Absorption spectra from crude extracts showed major peaks at 485, 620, and 664 nm for chlorophyll a (chl a) and 500, 564 and 615 nm for phycoerythrin (PE) and phycocyanin (PC). Absorption peaks from intact thalli were less conspicuous than those from crude extracts, possibly due to PE contributing to the bulk absorption of light by chl a in intact cells. Fluorescence emission of intact thalli was about threefold higher than that of crude extracts at 420 and 560 nm. Image analysis revealed differences in maximal fluorescence emissions as related to cell size, cell age, and thallus functional areas, with female cells having nearly a twofold higher emission than vegetative cells or asexual spores. Changes in the fluorescence emissions observed during acclimation to irradiance could reflect the extent of energy transfer from PE and PC to chl a, variable photosynthetic efficiency, or optical properties of the samples. This study suggests that image analysis can provide insights on seaweed photoacclimation that seem to be lost when disrupting their tissues to crude extracts. For example, the high PE to chl a ratios observed with image analysis in fresh tissues may confer a unique photoprotective role of PE when P. leucosticta becomes exposed to high irradiances, even during winter time.