477 research outputs found
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
Ocean warming and acidification detrimentally affect coral tissue regeneration at a Mediterranean CO2 vent
Among the main phenomena that are causing significant changes in ocean waters are warming and acidification, largely due to anthropogenic activities. Growing evidence suggests that climate change is having more substantial and rapid effects on marine communities than on terrestrial ones, triggering several physiological responses in these organisms, including in corals. Here we investigated, for first time in the field, the combined effect of increasing seawater acidification and warming on tissue regeneration rate of three Mediterranean scleractinian coral species characterized by different trophic strategies and growth modes. Balanophyllia europaea (solitary, zooxanthellate), Leptopsammia pruvoti (solitary, non-zooxanthellate) and Astroides calycularis (colonial, non-zooxanthellate) specimens were transplanted, during a cold, intermediate, and warm period, along a natural pH gradient generated by an underwater volcanic crater at Panarea Island (Mediterranean Sea, Italy), characterized by continuous and localized CO2 emissions at ambient temperature. Our results show a decrease in regenerative capacity, especially in the zooxanthellate species, with increasing seawater temperature and acidification, with demonstrated species-specific differences. This finding suggests that increasing seawater temperature and acidification could have a compounding effect on coral regeneration following injury, potentially hindering the capacity of corals to recover following physical disturbance under predicted climate change
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
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