Surveying Caulerpa (Chlorophyta) species along the shores of the eastern Mediterranean

Caulerpa (Chlorophyta) species inhabiting intertidal and shallow subtidal areas along the Israeli Mediterranean shores were surveyed (i.e. presence/absence) on a seasonal basis from 2007-2009. We recorded the presence of three speciesC. prolifera, C. mexicana, and C. scalpelliformis. These species were noticeable in autumn and inconspicuous during winter, thus, revealing seasonality and population dynamics. There were no indications of well-known invasive species such as Caulerpa racemosa var.cylindracea and Caulerpa taxifolia. This study is the first of a kind that assesses the geographical distribution and seasonality of the genus Caulerpa along the Israeli shores

The measurement of primary productivity in a high-rate oxidation pond (HROP)

A high-rate oxidation pond is studied as a model system for comparing 14C and oxygen evolution methods as tools for measuring primary productivity in hypertrophic aquatic systems. Our results indicate that at very dense algal populations (up to 5 mg chl. a l−1) and high photosynthetic rates, 14C based results may severely underestimate primary productivity, unless a way is found to keep incubation times very short. Results obtained with our oxygen electrode were almost an order of magnitude higher than those obtained by all 14C procedures. These higher values correspond fairly well with a field-tested computer-simulation model, as well as with direct harvest data obtained at the same pond when operated under similar conditions. The examination of the size-fractionation of the photosynthetic activity underscored the important contribution of nannoplanktonic algae to the total production of the syste

Sexual reproduction and biometry of the nonzooxanthellate papillose cup coral Paracyathus pulchellus

Basic information on the reproductive biology of many scleractinian corals species is limited or entirely lacking, particularly from temperate zones, though it is essential for a better understanding of their ecology. This study describes the morphological aspects and the annual cycle of gametogenesis and biometric parameters of the papillose cup coral Paracyathus pulchellus collected at Palinuro (Italy, Southern Tyrrhenian Sea), filling a knowledge gap about the reproductive biology of a widespread Mediterranean and Northern Atlantic coral. Samples of P. pulchellus were collected by SCUBA diving between 5- and 10-meters depth during 18 monthly collections from June 2010 to December 2011. Sexually active polyps displayed either oocytes or spermaries, indicating that P. pulchellus was gonochoric. The sex ratio of sexually active polyps was 1:1. Gametogenesis began with undifferentiated germ cells arose in the gastrodermis that migrated towards the mesoglea of the mesentery where they completed the development. During spermatogenesis, spermary diameter increased from 25 to 83 µm. Oocyte diameter ranged from 9 to 146 µm and during oogenesis the nucleus/cytoplasm ratio decreased due to the accumulation of yolk. The nucleus migrated to the periphery of the oocyte adhering closely to the cell membrane. No embryo was observed in the coelenteric cavity of the polyps, suggesting an external development of planktotrophic larvae due to the small-sized mature oocytes and a possible broadcast spawning reproductive mode. Gonadal index of both females and males increased significantly from August until November and fertilization took place from November to January. Only sexually inactive individuals were observed from February to April, suggesting a quiescence period in both males and females. Seasonal variations in water temperature and photoperiod may have a key role in regulating gametogenesis. The analysis of the main biometric parameters (polyp width, height, dry skeletal mass, volume, surface/volume ratio and bulk skeletal density) showed a negative correlation between size and skeletal density, and no sexual dimorphism

Reproduction of the azooxanthellate coral Caryophyllia inornata is not affected by temperature along an 850 km gradient on the Western Italian coast

The Intergovernmental Panel on Climate Change (IPCC) predicted that ocean surface temperature will rise of 0.6–2.0◦C by 2100. Ocean warming is expected to produce strong impacts on marine ecosystems such as coral reefs, affecting their physiological events including reproductive processes. To date, relatively few studies have examined the effects of climate change on the reproductive success of temperate corals and even less in the azooxanthellate ones. This study examined the reproductive output of the azooxanthellate Mediterranean coral Caryophyllia inornata along a wide latitudinal gradient of seawater temperature and solar radiation. A total of 260 samples, collected from five populations along the Western Italian coast, have been analyzed through histological techniques. The intriguing aspects characterizing all populations of C. inornata along the latitudinal gradient are a strong male-biased sex ratio and the presence of embryos in all stages of development throughout the year in females, males, and sexually inactive individuals. This peculiarity could suggest a mixed strategy of sexual and asexual reproduction in this species as has been observed for some anemones of the genus Actinia. Fecundity and spermary abundance (i.e., the number of reproductive elements per body volume unit), gonadal index (i.e., the percentage of body volume occupied by the germ cells) and fertility (i.e., the number of embryos per body volume unit) in females, males and sexually inactive individuals were unrelated to solar radiation and temperature along the latitudinal gradient. These results suggest that the reproduction in C. inornata is not affected by increasing solar radiation and temperature. The lack of zooxanthellae could make this species less dependent on these environmental parameters, as previously hypothesized for another azooxanthellate species, Leptopsammia pruvoti, investigated along the same gradient

Photosynthetic characteristics of five high light and low light exposed microalgaea as measured with 14C-uptake and oxygen electrode techniques

#Tetraselmis suecica, #Thalassiosira pseudonana, #Chaetoceros calcitrans, #Isochrysis galbana et #Microcystis sp.$ ont été utilisées pour déterminer leurs capacités d'adaptation et pour tester les différences entre les deux méthodes de mesure. Les cultures avaient été exposées à un éclairement fort (HL) ou à un éclairement faible (LL) pendant deux jours avant l'expérience. L'efficacité de la conversion de la lumière (...) et l'activité photosynthétique spécifique maximale par unité de chlorophylle (...) ont été généralement plus élevées pour les cultures LL. Les divers paramètres photosynthétiques mesurés par la méthode de l'électrode à oxygène ont été différents de ceux obtenus par celle du 14C. Les importantes différences de quotient photosynthétique (O2/CO2), observées aussi bien entre cultures HL et LL d'une même espèce qu'entre espèces différentes, soulignent la difficulté de convertir les productions d'oxygène en assimilation de carbone. (D'après résumé d'auteur

A system in balance? ? Implications of deep vertical mixing for the nitrogen budget in the northern Red Sea, including the Gulf of Aqaba (Eilat)

International audienceWe investigated the implications of deep winter mixing for the nitrogen budget in two adjacent systems, the northern Red Sea proper, and the Gulf of Aqaba. Both are subtropical oligotrophic water bodies. The main difference is that in the gulf deep winter mixing takes place regularly, whereas the northern Red Sea proper is permanently stratified. In the Gulf of Aqaba, we observed significantly lower nitrate deficits, i.e. deviations from the Redfield ratio, than in the northern Red Sea proper. Assuming that other external inputs and losses in N or P are very similar in both systems, the higher nitrate deficit can be explained by either lower nitrogen fixation in the (stratified) northern Red Sea, which seems unlikely. An alternative explanation would be higher rates of benthic denitrification than in the gulf. By comparing the two systems we have indirect evidence that benthic denitrification was much lower in the Gulf of Aqaba due to higher oxygen concentrations. This we attributed to the occurrence of deep winter mixing, and as a consequence, the nitrate deficit was close to zero (i.e. N:P ratio close to "Redfield"). If both nitrogen fixation and benthic denitrification take place, as in the northern Red Sea proper, the result was a positive nitrate deficit (i.e. a deficit in nitrate) in the ambient water. The nitrate deficit in the northern Red Sea was observed in spite of high iron deposition from the surrounding desert. Our results strongly support the concept of nitrogen as the proximate, and phosphate as the ultimate limiting nutrient for primary production in the sea. This must not be neglected in efforts for protecting the adjacent reefs against eutrophication

Low and variable pH decreases recruitment efficiency in populations of a temperate coral naturally present at a CO2 vent

Atmospheric carbon dioxide enrichment alters seawater carbonate chemistry, thus threatening calcifying organisms such as corals. Coral populations at carbon dioxide vents are natural acidification experiments that mimic organism responses to seawater pH values projected for 2100. Even if demographic traits are paramount information to assess ecological relationships and habitat suitability, population dynamics studies on corals thriving under acidified conditions are lacking. Here, we investigate the demography and reproduction of popu- lations of the solitary, symbiotic, temperate coral Balanophyllia europaea naturally living along a pH gradient at a Mediterranean CO2 vent. Gametogenesis and larval production were unaffected while recruitment efficiency collapsed at low and variable pH, contributing to coral abundance decline and suggesting that life stages between larval release and early polyp growth are hindered by acidification. Exploring these processes is crucial to assess coral fate in the forthcoming acidified oceans, to preserve coral ecosystems and the socioeconomic ser- vices they provide

Diel 'tuning' of coral metabolism: physiological responses to light cues

Hermatypic-zooxanthellate corals track the diel patterns of the main environmental parameters temperature, UV and visible light - by acclimation processes that include biochemical responses. The diel course of solar radiation is followed by photosynthesis rates and thereby elicits simultaneous changes in tissue oxygen tension due to the shift in photosynthesis/respiration balance. The recurrent patterns of sunlight are reflected in fluorescence yields, photosynthetic pigment content and activity of the two protective enzymes superoxide dismutase (SOD) and catalase (CAT), enzymes that are among the universal defenses against free radical damage in living tissue. All of these were investigated in three scleractinian corals: Favia favus, Plerogyra sinuosa and Goniopora lobata. The activity of SOD and CAT in the animal host followed the course of solar radiation, increased with the rates of photosynthetic oxygen production and was correlated with a decrease in the maximum quantum yield of photochemistry in Photosystem H (PSII) (Delta F'/F-m'). SOD and CAT activity in the symbiotic algae also exhibited a light intensity correlated pattern, albeit a less pronounced one. The observed rise of the free-radical-scavenger enzymes, with a time scale of minutes to several hours, is an important protective mechanism for the existence and remarkable success of the unique cnidarian-dinoflagellate associations, in which photosynthetic oxygen production takes place within animal cells. This represents a facet of the precarious act of balancing the photosynthetic production of oxygen by the algal symbionts with their destructive action on all living cells, especially those of the animal host

The effects of anthropogenic pollution on the Kanev Reservoir (Ukraine) phytoplankton. 1. Phytoplankton dynamics at stations with different levels of pollution

The aim of the investigation was to compare the phytoplankton structure in two zones of the river part of Kanev Reservoir characterized by different levels of urban pollution. Two stations were selected for this purpose: 1, in a relatively pure area of the the river part of Kanev Reservoir; and 2, at the mouth of the Dneiper tributary, the Syrets River, which has been polluted by mineral and organic substances from urban sewage. The “vibrancy” of the phytoplankton was evaluated by determining their biomass, cell abundance, and cell surface area (denoted as B, N, and S, respectively), achieved on the basis of a routine monitoring dataset collected over 24 months at these stations. The investigated zones were characterized by divergent phytoplankton composition and considerably different annual dynamics. The profiles shown by the B, N and S dynamics of the phytoplankton at station 1 were characterized by regular and predictable peaks in summer, formed by the same complex of algal species. Similar-type graphs for station 2 exhibited 3-4 peaks per year formed by completely different groups of algae during different periods. Furthermore, the saprobic zone indicator species, as well as those characterized by highly specific cell-surface estimates, were often observed at station 2. Such species were absent or developed only to a minor extent in phytoplankton of station 1. These facts can be interpreted as symptoms of ecosystem destabilization at station 2, which could be due to the impact of polluted water from the Syrets River on the phytoplankton of the Kanev Reservoir.Исследованы структуры фитопланктона двух точек речной части Каневского водохранилища с разным уровнем загрязнения: ст. 1 – в сравнительно чистом районе его русловой части, ст. 2 – в устье притока Днепра, р. Сырец, загрязненной минеральными и органическими веществами с городских стоков. Динамика фитопланктона была оценена посредством определения его биомассы, численности и площади клеточной поверхности (B, N и S соответственно) на основе мониторинга данных, собранных на протяжении 24 мес. с обеих станций. Исследованные точки характеризовались разным видовым составом фитопланктона и существенно различной годовой динамикой. Кривые динамики B, N и S фитопланктона на ст. 1 характеризовались регулярными и предсказуемыми пиками в летний период, сформированными одинаковым комплексом видов водорослей. Такой же тип графиков для ст. 2 демонстрировал 3-4 пика в год, сформированных совершенно разными группами водорослей в течение разных периодов. Кроме того, водоросли-индикаторы высоких зон сапробности, а также характеризующиеся высокой удельной площадью поверхности клеток, часто наблюдались на ст. 2. Эти виды отсутствовали или развивались только в небольших количествах в фитопланктоне ст. 1, что свидетельствует о дестабилизации экосистемы на ст. 2 из-за влияния загрязненной воды из р. Сырец на фитопланктон Каневского водохранилища.Досліджено структури фітопланктону двох пунктів річкової частини Канівського водосховища з різним рівнем забруднення: ст. 1 – в порівняно чистому районі Дніпра, ст. 2 – в гирлі притоку Дніпра, р. Сирець, забрудненої мінеральними і органічними речовинами з міських стоків. Динаміка фітопланктону була оцінена шляхом визначення його біомаси, чисельності і площі клітинної поверхні (B, N і S відповідно) на основі моніторингу даних, зібраних протягом 24 місяців на обох станціях. Досліджувані пункти характеризувалися різним видовим складом фітопланктону і суттєво різною річною динамікою. Криві динаміки B, N і S фітопланктону на ст. 1 характеризувалися регулярними і передбачуваними піками в літній період, зформованими однаковим комплексом видів водоростей. Такий же тип графіків для ст. 2 демонстрував 3-4 піки на рік, зформовані зовсім різними групами водоростей протягом різних періодів. Крім того, водорості-індикатори високих зон сапробності, а також ті, що характеризуються високою питомою площиною поверхні клітин, часто спостерігалися на ст. 2. Ці види були відсутні або розвивалися в невеликій кількості у фітопланктоні ст. 1, що свідчить про дестабілізацію екосистеми на ст. 2 в результаті впливу забрудненої води з р. Сирець на фітопланктон Канівського водосховища