Posts Tagged 'echinoderms'

Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community

Ocean acidification and warming are likely to affect the structure and functioning of marine benthic communities. This study experimentally examined the effects of ocean acidification and warming on trophic interactions within a maerl bed community by using stable carbon and nitrogen isotope analysis. Two three‐month experiments were conducted in winter and summer seasons with four different combinations of pCO2 (ambient and elevated pCO2) and temperature (ambient and +3°C). Experimental assemblages were created in tanks held in the laboratory and were composed of calcareous (Lithothamnion corallioides) and fleshy algae (Rhodymenia ardissonei, Solieria chordalis, and Ulva sp.), gastropods (Gibbula magus and Jujubinus exasperatus), and sea urchins (Psammechinus miliaris). Our results showed higher seaweed availability for grazers in summer than winter. Therefore, grazers were able to adapt their diet seasonally. Increased pCO2 and temperature did not modify the trophic structure in winter, while shifts in the contribution of seaweed were found in summer. Combined acidification and warming increased the contribution of biofilm in gastropods diet in summer conditions. Psammechinus miliaris mostly consumed L. corallioides under ambient conditions, while the alga S. chordalis became the dominant food source under high pCO2 in summer. Predicted changes in pCO2 and temperature had complex effects on assemblage trophic structure. Direct effects of acidification and warming on seaweed metabolism may modify their abundance and biomass, affecting their availability for grazers. Climate change may also modify seaweeds’ nutritive value and their palatability for grazers. The grazers we investigated were able to change their diet in response to changes in algal assemblages, an advantage given that warming and acidification alter the composition of algal communities.

Continue reading ‘Using stable isotope analysis to determine the effects of ocean acidification and warming on trophic interactions in a maerl bed community’

pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios

The increasing atmospheric CO2 concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pHT showed large variability (7.6–8.1) with low pH conditions during south‐west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pHT: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pHT 7.96 and 7.76 were not affected, whereas the ones at pHT 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pHT 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr2+ as compared to Mg2+ ions. We conclude that although the sea urchins would be affected in future high CO2 waters, at present they are not at risk even during the south‐west monsoon when low pH waters reside on the shelf.

Continue reading ‘pH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios’

Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem

Predator loss and climate change are hallmarks of the Anthropocene yet their interactive effects are largely unknown. Here, we show that massive calcareous reefs, built slowly by the alga Clathromorphum nereostratum over centuries to millennia, are now declining because of the emerging interplay between these two processes. Such reefs, the structural base of Aleutian kelp forests, are rapidly eroding because of overgrazing by herbivores. Historical reconstructions and experiments reveal that overgrazing was initiated by the loss of sea otters, Enhydra lutris (which gave rise to herbivores capable of causing bioerosion), and then accelerated with ocean warming and acidification (which increased per capita lethal grazing by 34 to 60% compared with preindustrial times). Thus, keystone predators can mediate the ways in which climate effects emerge in nature and the pace with which they alter ecosystems.

Continue reading ‘Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem’

The success of the fertilization and early larval development of the tropical sea urchin Echinometra lucunter (Echinodermata: Echinoidea) is affected by the pH decrease and temperature increase

Highlights

• Temperature and pH were tested on embryo-larval development of sea urchins.

• Larval development test proved to be more sensitive compared to gamete fecundity test.

• Low pH as an isolated factor exhibit significant results on fertilization and embryo-larval development.

• Extreme high temperature associated with low pH affect only sea urchin’s embryo-larval.

• Combination of low pH and high temperature causes damages in sea urchin.

Abstract

The decrease in the pH of oceans and the increase in their temperature are the two main problems observed in the marine ecosystems due to the increasing emission of CO2 in the atmosphere. Both conditions can affect the ecological processes of reproduction, recruitment and survival of the marine biota. Thus, the objective of the present study was to evaluate the effects of pH decrease and temperature increase of seawater on the fertilization success and embryo-larval development of a species of tropical sea urchin. For this purpose, fertilization success (gametes) and embryo-larval development rate were determined by exposing gametes and embryos to decreasing pH values (8.0 (control), 7.7, and 7.4) and increasing temperatures (26 (control), 28, 30, 34, and 38 °C). These conditions were tested associated with each other (in synergy). The gamete test was sensitive to all investigated scenarios, the fertilization success was significantly reduced in the conditions of increased temperature (28, 30, 34, and 38 °C) associated with the ideal pH (pH 8.0) and the conditions of reduced pH (pH 7.7, and 7.4), remaining unchanged only in the ideal condition (pH 8.0 + 26 °C). However, the embryo test displayed enhanced sensitivity in the scenarios of temperature increase (28, 30, 34, and 38 °C) associated with pH decrease conditions. A significantly reduction of 29%, 23% and 10% was observed in all tested pH values at 38 °C, when compared to the control group (80%, 79.5% and 63%, respectively). Therefore, the present study suggests that the occurrence of both scenarios may have a significant impact, in the coming years, on the population of Echinometra lucunter.

Continue reading ‘The success of the fertilization and early larval development of the tropical sea urchin Echinometra lucunter (Echinodermata: Echinoidea) is affected by the pH decrease and temperature increase’

Effects of salinity and pH of seawater on the reproduction of the sea urchin Paracentrotus lividus

Fertilization and early development are usually the most vulnerable stages in the life of marine animals, and the biological processes during this period are highly sensitive to the environment. In nature, sea urchin gametes are shed in seawater, where they undergo external fertilization and embryonic development. In a laboratory, it is possible to follow the exact morphological and biochemical changes taking place in the fertilized eggs and the developing embryos. Thus, observation of successful fertilization and the subsequent embryonic development of sea urchin eggs can be used as a convenient biosensor to assess the quality of the marine environment. In this paper, we have examined how salinity and pH changes affect the normal fertilization process and the following development of Paracentrotus lividus. The results of our studies using confocal microscopy, scanning and transmission electron microscopy, and time-lapse Ca2+ image recording indicated that both dilution and acidification of seawater have subtle but detrimental effects on many aspects of the fertilization process. They include Ca2+ signaling and coordinated actin cytoskeletal changes, leading to a significantly reduced rate of successful fertilization and, eventually, to abnormal or delayed embryonic development.

Continue reading ‘Effects of salinity and pH of seawater on the reproduction of the sea urchin Paracentrotus lividus’

Comparative metabolome analysis provides new insights into increased larval mortality under seawater acidification in the sea urchin Strongylocentrotus intermedius

Highlights

• Seawater acidification’s effects on Strongylocentrotus intermedius larvae were investigated.

• A comparative metabolomics analysis was performed.

• Significantly differentially expressed metabolites were identified and annotated.

• Metabolic pathways related to mortality induced by seawater acidification were observed.

Abstract

Mortality and metabolic responses of four-armed larvae of Strongylocentrotus intermedius under CO2-induced seawater acidification were investigated. Gametes of S. intermedius were fertilized and developed to the four-armed larval stage in either current natural seawater pH levels (as Control; pH = 7.99 ± 0.01) or laboratory-controlled acidified conditions (OA1: ΔpH = −0.3 units; OA2: ΔpH = −0.4 units; OA3: ΔpH = −0.5 units) according to the predictions of the Intergovernmental Panel on Climate Change (IPCC). The degrees of spicule exposure and asymmetry and mortality of four-armed larvae of S. intermedius were observed; each had a significant linearly increasing trend as the seawater pH level decreased. Comparative metabolome analysis identified a total of 87 significantly differentially expressed metabolites (SDMs, UP: 57, DOWN: 30) in OA-treated groups compared with the control group. Twenty-three SDMs, including carnitine, lysophosphatidylcholine (LPC) 18:3, lysophosphatidyl ethanolamine (LPE) 16:1, glutathione (GSH) and L-ascorbate, exhibited a linear increasing trend with decreasing seawater pH. Nine SDMs exhibited a linear decreasing trend as the seawater pH declined, including hypoxanthine, guanine and thymidine. Among all SDMs, we further mined 48 potential metabolite biomarkers responding to seawater acidification in four-armed larvae of S. intermedius. These potential metabolite biomarkers were mainly enriched in five pathways: glycerophospholipid metabolism, glutathione metabolism, purine metabolism, pyrimidine metabolism and the tricarboxylic acid cycle (TCA cycle). Our results will enrich our knowledge of the molecular mechanisms employed by sea urchins in response to CO2-induced seawater acidification.

Continue reading ‘Comparative metabolome analysis provides new insights into increased larval mortality under seawater acidification in the sea urchin Strongylocentrotus intermedius’

Do males and females respond differently to ocean acidification? an experimental study with the sea urchin Paracentrotus lividus

Seawater pH lowering, known as ocean acidification, is considered among the major threats to marine environment. In this study, post-spawning adults of the sea urchin Paracentrotus lividus were maintained at three pH values (8.0, 7.7, 7.4) for 60 days. Physiological, biochemical, cellular, behavioural and reproductive responses were evaluated in males and females. Significant differences between sexes were observed, with higher ammonia excretion and lower catalase activity in males. Respiration rate (after 21 days), catalase activity in gonads and total coelomocyte count showed the same increasing trend in males and females under low pH. Ammonia excretion, gonadosomatic index and lysozyme activity exhibited opposite responses to low pH, with an increasing trend in males and decreasing in females. Results demonstrated that exposure to low pH could result in different response strategies of male and female sea urchins at a physiological, biochemical and immunological level. Reduced female gonadosomatic index under low pH suggested decreased energy investment in reproduction.

Continue reading ‘Do males and females respond differently to ocean acidification? an experimental study with the sea urchin Paracentrotus lividus’

Alkaline guts contribute to immunity during exposure to acidified seawater in the sea urchin larva

Larval stages of members of the Abulacraria superphylum including echinoderms and hemichordates have highly alkaline midguts. To date, the reason for the evolution of such extreme pH conditions in the gut of these organisms remains unknown. Here, we test the hypothesis that, analogous to the acidic stomachs of vertebrates, these alkaline conditions may represent a first defensive barrier to protect from environmental pathogens. pH-optimum curves for five different species of marine bacteria demonstrated a rapid decrease in proliferation rates by 50–60% between pH 8.5 and 9.5. Using the marine bacterium Vibrio diazotrophicus, which elicits a coordinated immune response in the larvae of the sea urchin Strongylocentrotus purpuratus, we studied the physiological responses of the midgut pH regulatory machinery to this pathogen. Gastroscopic microelectrode measurements demonstrate a stimulation of midgut alkalization upon infection with V. diazotrophicus accompanied by an upregulation of acid–base transporter transcripts of the midgut. Pharmacological inhibition of midgut alkalization resulted in an increased mortality rate of larvae during Vibrio infection. Reductions in seawater pH resembling ocean acidification conditions lead to moderate reductions in midgut alkalization. However, these reductions in midgut pH do not affect the immune response or resilience of sea urchin larvae to a Vibrio infection under ocean acidification conditions. Our study addressed the evolutionary benefits of the alkaline midgut of Ambulacraria larval stages. The data indicate that alkaline conditions in the gut may serve as a first defensive barrier against environmental pathogens and that this mechanism can compensate for changes in seawater pH.

Continue reading ‘Alkaline guts contribute to immunity during exposure to acidified seawater in the sea urchin larva’

Gene expression patterns of Red Sea urchins (Mesocentrotus Franciscanus) exposed to different combinations of temperature and pCO2 during early development

Red sea urchins were collected and spawned as described in [31]. Briefly, adults were collected from Ellwood Mesa, Goleta, California, USA (34° 25.065’N, 119° 54.092’W) at 14-m depth via SCUBA on February 21, 2018 under California Scientific Collecting Permit SC-1223 and transported to the Marine Science Institute at the University of California Santa Barbara (UCSB). Spawning was induced by injecting 0.53 M KCl into the coelom through the perioral membrane [145]. Eggs from five individual females and sperm from a single male were collected. A subsample of eggs from each female was fertilized with sperm from the male and high fertilization success was examined for each cross (i.e., visually confirming the formation of fertilization envelopes). These subsamples were only used to verify suitable male-female compatibility and were discarded prior to the experiment. An approximately equal number of eggs from each of the five females were gently pooled together. The pool of eggs was fertilized by slowly adding dilute, activated sperm from the male until approximately 98% fertilization success was reached. Performing crosses with a single male ensured that all cultures were composed of full- or half-sibling embryos. This approach was selected in an effort to limit paternal genetic variability and differences in male-female interactions that could otherwise impact the results of the study.

Continue reading ‘Gene expression patterns of Red Sea urchins (Mesocentrotus Franciscanus) exposed to different combinations of temperature and pCO2 during early development’

Effects of low and high pH on sea urchin settlement, implications for the use of alkali to counter the impacts of acidification

Highlights

• Seaweeds and diatoms on settlement plates created low pH and high pH conditions as they respired and photosynthesised.

• Low pH had adverse effects on growth and morphology of sea urchin post-larvae.

• High pH generally had little effect on growth and development, but reduced settlement rates.

• Controlling pH in invertebrate culture systems might improve settlement rates and post-settlement growth.

Abstract

Respiration, photosynthesis, and calcification of cultured organisms and biological substrata can substantially alter the pH and other carbonate parameters of water in aquaculture systems. One such example is the diel cycle of photosynthesis and respiration by diatoms and seaweeds growing on ‘settlement plates’ used to induce metamorphosis of invertebrate larvae and as food for post-larvae. We documented low pH and high pH conditions in nursery raceways and simulated settlement tanks that were as much as 0.26 pH units lower and 0.52 pH units higher than the pH of the source seawater supplied to the systems. To better understand whether the low pH and high pH conditions commonly found in aquaculture culture systems affected the success of the settlement stage of the sea urchin Centrostephanus rodgersii, we induced larvae to settle at pH 7.6, 7.8 (created by injecting CO2), 8.1 (ambient), 8.2, and 8.3 (created by raising total alkalinity), and followed post-settlement growth, development, and survival for 16 d. At metamorphosis, low pH significantly increased the occurrence of abnormalities and reduced the number and length of the sea urchins’ spines and pedicellaria, but did not affect settlement rate or size compared to ambient pH. In contrast, high pH generally had little effect on morphological traits, but settlement was significantly reduced by 14–26% compared to ambient and low pH treatments. After 16 d, juveniles in the low pH treatments were as much as 7% smaller, had 2–4 fewer and 9–13% shorter spines, and had less-developed digestive systems compared to juveniles in ambient or high pH treatments, and there was a non-significant trend towards lower survival in low pH treatments. Our results highlight that the low pH and high pH conditions in invertebrate settlement and nursery culture systems have the potential to hamper production through reduced settlement or growth rates. We need to understand the impacts of fluctuating pH in culture systems, especially day-night oscillations. Treating seawater with alkali chemicals to stabilise pH and counter acidification should be done with caution. Due to the potential for deleterious effects on settlement, dosage regimens will need to be optimised.

Continue reading ‘Effects of low and high pH on sea urchin settlement, implications for the use of alkali to counter the impacts of acidification’


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