Effects of ocean warming and acidification on survival,growth and skeletal development in the early benthic juvenile sea urchin (Heliocidaris erythrogramma)

Co‐occurring ocean warming, acidification and reduced carbonate mineral saturation have significant impacts on marine biota, especially calcifying organisms. The effects of these stressors on development and calcification in newly metamorphosed juveniles (ca. 0.5 mm test diameter) of the intertidal sea urchin Heliocidaris erythrogramma, an ecologically important species in temperate Australia, were investigated in context with present and projected future conditions. Habitat temperature and pH/pCO₂ were documented to place experiments in a biologically and ecologically relevant context. These parameters fluctuated diurnally up to 10 °C and 0.45 pH units. The juveniles were exposed to three temperature (21, 23 and 25 °C) and four pH (8.1, 7.8, 7.6 and 7.4) treatments in all combinations, representing ambient sea surface conditions (21 °C, pH 8.1; pCO₂ 397; Ω_Ca 4.7; Ω_Ar 3.1), near‐future projected change (+2–4 °C, ?0.3–0.5 pH units; pCO₂ 400–1820; Ω_Ca 5.0–1.6; Ω_Ar 3.3–1.1), and extreme conditions experienced at low tide (+4 °C, ?0.3–0.7 pH units; pCO₂ 2850–2967; Ω_Ca 1.1–1.0; Ω_Ar 0.7–0.6). The lowest pH treatment (pH 7.4) was used to assess tolerance levels. Juvenile survival and test growth were resilient to current and near‐future warming and acidification. Spine development, however, was negatively affected by near‐future increased temperature (+2–4 °C) and extreme acidification (pH 7.4), with a complex interaction between stressors. Near‐future warming was the more significant stressor. Spine tips were dissolved in the pH 7.4 treatments. Adaptation to fluctuating temperature‐pH conditions in the intertidal may convey resilience to juvenile H. erythrogramma to changing ocean conditions, however, ocean warming and acidification may shift baseline intertidal temperature and pH/pCO₂ to levels that exceed tolerance limits.     

Sensitivity of sea urchin fertilization to pH varies across a natural pH mosaic

In the coastal ocean, temporal fluctuations in pH vary dramatically across biogeographic ranges. How such spatial differences in pH variability regimes might shape ocean acidification resistance in marine species remains unknown. We assessed the pH sensitivity of the sea urchin Strongylocentrotus purpuratus in the context of ocean pH variability. Using unique male–female pairs, originating from three sites with similar mean pH but different variability and frequency of low pH (pH_T ≤ 7.8) exposures, fertilization was tested across a range of pH (pH_T 7.61–8.03) and sperm concentrations. High fertilization success was maintained at low pH via a slight right shift in the fertilization function across sperm concentration. This pH effect differed by site. Urchins from the site with the narrowest pH variability regime exhibited the greatest pH sensitivity. At this site, mechanistic fertilization dynamics models support a decrease in sperm–egg interaction rate with decreasing pH. The site differences in pH sensitivity build upon recent evidence of local pH adaptation in S. purpuratus and highlight the need to incorporate environmental variability in the study of global change biology.     

Ocean warming and acidification alter the behavioral response to flow of the sea urchin Paracentrotus lividus

Ocean warming (OW) and acidification (OA) are intensively investigated as they pose major threats to marine organism. However, little effort is dedicated to another collateral climate change stressor, the increased frequency, and intensity of storm events, here referred to as intensified hydrodynamics. A 2‐month experiment was performed to identify how OW and OA (temperature: 21°C; pH_T: 7.7, 7.4; control: 17°C‐pH_T7.9) affect the resistance to hydrodynamics in the sea urchin Paracentrotus lividus using an integrative approach that includes physiology, biomechanics, and behavior. Biomechanics was studied under both no‐flow condition at the tube foot (TF) scale and flow condition at the individual scale. For the former, TF disk adhesive properties (attachment strength, tenacity) and TF stem mechanical properties (breaking force, extensibility, tensile strength, stiffness, toughness) were evaluated. For the latter, resistance to flow was addressed as the flow velocity at which individuals detached. Under near‐ and far‐future OW and OA, individuals fully balanced their acid‐base status, but skeletal growth was halved. TF adhesive properties were not affected by treatments. Compared to the control, mechanical properties were in general improved under pH_T7.7 while in the extreme treatment (21°C‐pH_T7.4) breaking force was diminished. Three behavioral strategies were implemented by sea urchins and acted together to cope with flow: improving TF attachment, streamlining, and escaping. Behavioral responses varied according to treatment and flow velocity. For instance, individuals at 21°C‐pH_T7.4 increased the density of attached TF at slow flows or controlled TF detachment at fast flows to compensate for weakened TF mechanical properties. They also showed an absence of streamlining favoring an escaping behavior as they ventured in a riskier faster movement at slow flows. At faster flows, the effects of OW and OA were detrimental causing earlier dislodgment. These plastic behaviors reflect a potential scope for acclimation in the field, where this species already experiences diel temperature and pH fluctuations.     

Noncalcifying larvae in a changing ocean: warming,not acidification/hypercapnia,is the dominant stressor on development of the sea star Meridiastra calcar

Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the noncalcifying lecithotrophic larvae of the sea star Meridiastra calcar was investigated in the setting of predicted ocean warming (+2 to 4 ^°C) and acidification (?0.4 to 0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula‐larvae) was negatively effected by a +2 to 4 ^°C warming and there was a negative effect of ?0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2 ^°C warming and larval growth was impaired at +4 ^°C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.     

Unshelled abalone and corrupted urchins: development of marine calcifiers in a changing ocean

The most fragile skeletons produced by benthic marine calcifiers are those that larvae and juveniles make to support their bodies. Ocean warming, acidification, decreased carbonate saturation and their interactive effects are likely to impair skeletogenesis. Failure to produce skeleton in a changing ocean has negative implications for a diversity of marine species. We examined the interactive effects of warming and acidification on an abalone (Haliotis coccoradiata) and a sea urchin (Heliocidaris erythrogramma) reared from fertilization in temperature and pH/pCO(2) treatments in a climatically and regionally relevant setting. Exposure of ectodermal (abalone) and mesodermal (echinoid) calcifying systems to warming (+2°C to 4°C) and acidification (pH 7.6-7.8) resulted in unshelled larvae and abnormal juveniles. Haliotis development was most sensitive with no interaction between stressors. For Heliocidaris, the percentage of normal juveniles decreased in response to both stressors, although a +2°C warming diminished the negative effect of low pH. The number of spines produced decreased with increasing acidification/pCO(2), and the interactive effect between stressors indicated that a +2°C warming reduced the negative effects of low pH. At +4°C, the developmental thermal tolerance was breached. Our results show that projected near-future climate change will have deleterious effects on development with differences in vulnerability in the two species.     

Temperature effects on photosynthesis in gametophytic and sporophytic stages of the freshwater red alga Sirodotia delicatula (Rhodophyta,Batrachospermales) under a global warming perspective

The increase in Earth's global mean temperature due to human influence has become a major concern, with ecological consequences already being reported around the world. In tropical streams, benthic red algae belonging to the order Batrachospermales contribute to a large fraction of the community energy input and play an important role in sustaining autotrophic food webs. The Batrachospermales also have a unique life history, with heteromorphic life stages (gametophytes and sporophytes) occurring seasonally and with distinct ecological roles. Through “in vivo” chlorophyll fluorescence and dissolved oxygen evolution techniques, we evaluated the effects of projected temperature increases of two future scenarios (RCP 4.5 and RCP 8.5) on the photosynthetic response of Sirodotia delicatula gametophytes and sporophytes. In general, both chlorophyll fluorescence and dissolved oxygen showed that the RCP 8.5 scenario could severely jeopardize the photosynthetic performance of the sporophytes during the summer while also providing a stressful physiological situation to the gametophytes. Due to the crucial role of sporophytes in the development of this species, results indicate that this predicted scenario could affect this species. Given the position of these organisms at the base of the food web in tropical lotic environments, especially in shaded low‐order streams, such impact could generate unforeseen cascade effects on higher trophic levels.     

Effects of EHF radiation and cytoactive substances on fertilization and early embryonic development of the sea urchin Strongylocentrotus intermedius

This study examines the influence of extremely high frequency (EHF) electromagnetic radiation (42.2 GHz, 100 μW/cm², impulse modulation 1000 Hz) on the gametes and embryos of the sea urchin Strongylocentrotus intermedius. Preliminary radiation treatment reduces the number of fertilized egg cells and the survival rate of embryos at early stages of development up to the pluteus. Methyluracil reduces the degree of expression of biological effects of EHF radiation.     

The stunting effect of a high CO2 ocean on calcification and development in sea urchin larvae,a synthesis from the tropics to the poles

The stunting effect of ocean acidification on development of calcifying invertebrate larvae has emerged as a significant effect of global change. We assessed the arm growth response of sea urchin echinoplutei, here used as a proxy of larval calcification, to increased seawater acidity/pCO₂ and decreased carbonate mineral saturation in a global synthesis of data from 15 species. Phylogenetic relatedness did not influence the observed patterns. Regardless of habitat or latitude, ocean acidification impedes larval growth with a negative relationship between arm length and increased acidity/pCO₂ and decreased carbonate mineral saturation. In multiple linear regression models incorporating these highly correlated parameters, pCO₂ exerted the greatest influence on decreased arm growth in the global dataset and also in the data subsets for polar and subtidal species. Thus, reduced growth appears largely driven by organism hypercapnia. For tropical species, decreased carbonate mineral saturation was most important. No single parameter played a dominant role in arm size reduction in the temperate species. For intertidal species, the models were equivocal. Levels of acidification causing a significant (approx. 10–20+%) reduction in arm growth varied between species. In 13 species, reduction in length of arms and supporting skeletal rods was evident in larvae reared in near-future (pCO₂ 800+ µatm) conditions, whereas greater acidification (pCO₂ 1000+ µatm) reduced growth in all species. Although multi-stressor studies are few, when temperature is added to the stressor mix, near-future warming can reduce the negative effect of acidification on larval growth. Broadly speaking, responses of larvae from across world regions showed similar trends despite disparate phylogeny, environments and ecology. Larval success may be the bottleneck for species success with flow-on effects for sea urchin populations and marine ecosystems.     

Elucidating the sponge stress response; lipids and fatty acids can facilitate survival under future climate scenarios

Ocean warming (OW) and ocean acidification (OA) are threatening coral reef ecosystems, with a bleak future forecast for reef‐building corals, which are already experiencing global declines in abundance. In contrast, many coral reef sponge species are able to tolerate climate change conditions projected for 2100. To increase our understanding of the mechanisms underpinning this tolerance, we explored the lipid and fatty acid (FA) composition of four sponge species with differing sensitivities to climate change, experimentally exposed to OW and OA levels predicted for 2100, under two CO₂ Representative Concentration Pathways. Sponges with greater concentrations of storage lipid, phospholipids, sterols and elevated concentrations of n‐3 and n‐6 long‐chain polyunsaturated FA (LC PUFA), were more resistant to OW. Such biochemical constituents likely contribute to the ability of these sponges to maintain membrane function and cell homeostasis in the face of environmental change. Our results suggest that n‐3 and n‐6 LC PUFA are important components of the sponge stress response potentially via chain elongation and the eicosanoid stress‐signalling pathways. The capacity for sponges to compositionally alter their membrane lipids in response to stress was also explored using a number of specific homeoviscous adaptation (HVA) indicators. This revealed a potential mechanism via which additional CO₂ could facilitate the resistance of phototrophic sponges to thermal stress through an increased synthesis of membrane‐stabilizing sterols. Finally, OW induced an increase in FA unsaturation in phototrophic sponges but a decrease in heterotrophic species, providing support for a difference in the thermal response pathway between the sponge host and the associated photosymbionts. Here we have shown that sponge lipids and FA are likely to be an important component of the sponge stress response and may play a role in facilitating sponge survival under future climate conditions.     

Temperature limits to early development of the New Zealand sea urchin Evechinus chloroticus (Valenciennes, 1846)

Seawater temperature is an important environmental factor for the early life stages of marine invertebrates. In this study we evaluated and described the effects of temperature during early development of E. chloroticus, identifying the optimum temperature range and upper thermal limit for successful development. The temperature range evaluated was between 15–24 °C which included the normal seawater temperatures during the spawning season in northern New Zealand, as well as the highest temperature projected by the IPCC for this region due to global warming (1–3 °C by the year 2100). Gametes from several females and males were used in the experiment. Fertilization was carried out at different temperatures and development was monitored at different time points after fertilization in each temperature. The development rate of E. chloroticus increased with an increase in seawater temperature. However, at temperatures higher than 21.5 °C the amount of abnormal development reached ∼30%. The optimum temperature for early development was between 15–21 °C, whereas the upper thermal limit was ∼24 °C. Therefore, early development of E. chloroticus is negatively affected by an increase in seawater temperature of ∼3–4 °C above current seawater temperature levels in northern New Zealand. The thermal sensitivity of early life stages of E. chloroticus could affect survival rates during early development of this species in a global warming scenario, which could impair recruitment in populations which are exposed to higher temperatures, leading to possible distributional shifts of this species.     

The effect of ocean acidification and temperature on the fertilization and embryonic development of the Sydney rock oyster Saccostrea glomerata (Gould 1850)

This study investigated the synergistic effects of ocean acidification (caused by elevations in the partial pressure of carbon dioxide pCO₂) and temperature on the fertilization and embryonic development of the economically and ecologically important Sydney rock oyster, Saccostrea glomerata (Gould 1850). As pCO₂ increased, fertilization significantly decreased. The temperature of 26 °C was the optimum temperature for fertilization, as temperature increased and decreased from this optimum, fertilization decreased. There was also an effect of pCO₂ and temperature on embryonic development. Generally as pCO₂ increased, the percentage and size of D‐veligers decreased and the percentage of D‐veligers that were abnormal increased. The optimum temperature was 26 °C and embryonic development decreased at temperatures that were above and below this temperature. Abnormality of D‐veligers was greatest at 1000 ppm and 18 and 30 °C (≥90%) and least at 375 ppm and 26 °C (≤4%). Finally prolonged exposure of elevated pCO₂ and temperature across early developmental stages led to fewer D‐veligers, more abnormality and smaller sizes in elevated CO₂ environments and may lead to lethal effects at suboptimal temperatures. Embryos that were exposed to the pCO₂ and temperature treatments for fertilization and embryonic development had fewer D‐veligers, greater percentage of abnormality and reduced size than embryos that were exposed to the treatments for embryonic development only. Further at the elevated temperature of 30 °C and 750–1000 ppm, there was no embryonic development. The results of this study suggest that predicted changes in ocean acidification and temperature over the next century may have severe implications for the distribution and abundance of S. glomerata as well as possible implications for the reproduction and development of other marine invertebrates.     

气候变化背景下全球陆地干湿变化研究综述

气候变化背景下,全球水循环加剧,出现了大气变干与植被变绿等陆地干湿变化趋势的解耦现象,旱区面积变化也存在争议。为回答上述问题,在梳理常见干湿指标变化趋势与驱动因素的基础上,根据指标变化方向对其进行归类,然后从机理角度解析影响不同指标趋势耦合或解耦的关键要素,并提出未来干湿变化研究展望。结果表明,气候变化背景下,饱和水汽压差、干燥度指数和土壤水分指标显著变干,植被绿度和生产力显著变湿(增加),降水、径流、陆地水储量和其他复合指标区域分异明显、但整体趋势不显著。二氧化碳浓度增加、气温升高和土地利用变化是导致不同指标趋势分异的重要因素,不同指标的趋势分异也解释了旱区面积评估在不同维度上的差异。未来研究中应开展干湿变化的综合评估,其综合性主要体现在以下四个方面：1)关注大气-生态-水文多维度评估;2)解析自然与人类双重压力下,不同维度要素间的关联、互馈过程,及其对系统干湿演变的促进、限制与调节作用;3)重视干湿演变程中的极端灾害事件和空间上以旱区为代表的气候变化敏感性区域;4)构建以脆弱性评估与适应性治理为核心的气候变化应对路径。