Structural and functional vulnerability to elevated pCO2 in marine benthic communities

The effect of elevated pCO₂/low pH on marine invertebrate benthic biodiversity, community structure and selected functional responses which underpin ecosystem services (such as community production and calcification) was tested in a medium-term (30 days) mesocosm experiment in June 2010. Standardised intertidal macrobenthic communities, collected (50.3567°N, 4.1277°W) using artificial substrate units (ASUs), were exposed to one of seven pH treatments (8.05, 7.8. 7.6, 7.4, 7.2, 6.8 and 6.0). Community net calcification/dissolution rates, as well as changes in biomass, community structure and diversity, were measured at the end of the experimental period. Communities showed significant changes in structure and reduced diversity in response to reduced pH: shifting from a community dominated by calcareous organisms to one dominated by non-calcareous organisms around either pH 7.2 (number of individuals and species) or pH 7.8 (biomass). These results were supported by a reduced total weight of CaCO₃ structures in all major taxa at lowered pH and a switch from net calcification to net dissolution around pH 7.4 (Ω_calc = 0.78, Ω_ara = 0.5). Overall community soft tissue biomass did not change with pH and high mortality was observed only at pH 6.0, although molluscs and arthropods showed significant decreases in soft tissue. This study supports and refines previous findings on how elevated pCO₂ can induce changes in marine biodiversity, underlined by differential vulnerability of different phyla. In addition, it shows significant elevated pCO₂-/low pH-dependent changes in fundamental community functional responses underpinning changes in ecosystem services.     

Post-larval development of two intertidal barnacles at elevated CO2 and temperature

Ocean acidification and global warming are occurring concomitantly, yet few studies have investigated how organisms will respond to increases in both temperature and CO₂. Intertidal microcosms were used to examine growth, shell mineralogy and survival of two intertidal barnacle post-larvae, Semibalanus balanoides and Elminius modestus, at two temperatures (14 and 19°C) and two CO₂ concentrations (380 and 1,000 ppm), fed with a mixed diatom-flagellate diet at 15,000 cells ml⁻¹ with flow rate of 10 ml⁻¹ min⁻¹. Control growth rates, using operculum diameter, were 14 ± 8 μm day⁻¹ and 6 ± 2 μm day⁻¹ for S. balanoides and E. modestus, respectively. Subtle, but significant decreases in E. modestus growth rate were observed in high CO₂ but there were no impacts on shell calcium content and survival by either elevated temperature or CO₂. S. balanoides exhibited no clear alterations in growth rate but did show a large reduction in shell calcium content and survival under elevated temperature and CO₂. These results suggest that a decrease by 0.4 pH_(NBS) units alone would not be sufficient to directly impact the survival of barnacles during the first month post-settlement. However, in conjunction with a 4–5°C increase in temperature, it appears that significant changes to the biology of these organisms will ensue.     

Cuttlebone calcification increases during exposure to elevated seawater pCO2 in the cephalopod Sepia officinalis

Changes in seawater carbonate chemistry that accompany ongoing ocean acidification have been found to affect calcification processes in many marine invertebrates. In contrast to the response of most invertebrates, calcification rates increase in the cephalopod Sepia officinalis during long-term exposure to elevated seawater pCO₂. The present trial investigated structural changes in the cuttlebones of S. officinalis calcified during 6 weeks of exposure to 615 Pa CO₂. Cuttlebone mass increased sevenfold over the course of the growth trail, reaching a mean value of 0.71 ± 0.15 g. Depending on cuttlefish size (mantle lengths 44–56 mm), cuttlebones of CO₂-incubated individuals accreted 22–55% more CaCO₃ compared to controls at 64 Pa CO₂. However, the height of the CO₂-exposed cuttlebones was reduced. A decrease in spacing of the cuttlebone lamellae, from 384 ± 26 to 195 ± 38 μm, accounted for the height reduction The greater CaCO₃ content of the CO₂-incubated cuttlebones can be attributed to an increase in thickness of the lamellar and pillar walls. Particularly, pillar thickness increased from 2.6 ± 0.6 to 4.9 ± 2.2 μm. Interestingly, the incorporation of non-acid-soluble organic matrix (chitin) in the cuttlebones of CO₂-exposed individuals was reduced by 30% on average. The apparent robustness of calcification processes in S. officinalis, and other powerful ion regulators such as decapod cructaceans, during exposure to elevated pCO₂ is predicated to be closely connected to the increased extracellular [HCO₃ ⁻] maintained by these organisms to compensate extracellular pH. The potential negative impact of increased calcification in the cuttlebone of S. officinalis is discussed with regard to its function as a lightweight and highly porous buoyancy regulation device. Further studies working with lower seawater pCO₂ values are necessary to evaluate if the observed phenomenon is of ecological relevance.     

Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

Early life stages of marine crustaceans respond sensitively to elevated seawater PCO₂. However, the underlying physiological mechanisms have not been studied well. We therefore investigated the effects of elevated seawater PCO₂ on oxygen consumption, dry weight, elemental composition, median developmental time (MDT) and mortality in zoea I larvae of the spider crab Hyas araneus (Svalbard 79°N/11°E; collection, May 2009; hatch, December 2009). At the time of moulting, oxygen consumption rate had reached a steady state level under control conditions. In contrast, elevated seawater PCO₂ caused the metabolic rate to rise continuously leading to a maximum 1.5-fold increase beyond control level a few days before moulting into the second stage (zoea II), followed by a pronounced decrease. Dry weight of larvae reared under high CO₂ conditions was lower than in control larvae at the beginning of the moult cycle, yet this difference had disappeared at the time of moulting. MDT of zoea I varied between 45 ± 1 days under control conditions and 42 ± 2 days under the highest seawater CO₂ concentration. The present study indicates that larval development under elevated seawater PCO₂ levels results in higher metabolic costs during premoulting events in zoea I. However, H. araneus zoea I larvae seem to be able to compensate for higher metabolic costs as larval MDT and survival was not affected by elevated PCO₂ levels.     

The functional morphology and development of the alimentary tract of larval and juvenile barnacles (Cirripedia: Thoracica)

The alimentary tract of the nauplius larva of Balanus spp. consists of cuticle-lined foregut and hindgut, with intervening endodermal midgut constricted into anterior and posterior regions. The anterior midgut cells in the region of the constriction (constriction cells) secrete proteins (probably digestive enzymes). The remaining anterior midgut cells, often containing lipid droplets, form the absorptive region of the tract. Glycoprotein globules and lipid droplets within anterior midgut cells are the remants of the yolk in a pre-hatched larva, this yolk additionally supporting the larva through the non-feeding first nauplius stage. Nauplius Stages II to VI are actively feeding planktonic stages which increase in size and build up lipid reserves. These accumulated reserves support the non-feeding cyprid, first through its planktonic life and then through settlement and subsequent metamorphosis to the juvenile barnacle. Juvenile barnacles start to feed between 2 and 5 days after metamorphosis.     

Brooded coral larvae differ in their response to high temperature and elevated pCO2 depending on the day of release

To evaluate the effects of temperature and pCO₂ on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179′N, 120°44.85′E), were exposed to ambient (419–470 μatm) and high (604–742 μatm) pCO₂ at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F _v/F _m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO₂ × temperature interaction in 2012; F _v/F _m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO₂ interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO₂ in 2010, but in 2012, high pCO₂ depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.     

Tolerance to high temperatures and potential impact of sea warming on reef fishes of Gorgona Island (tropical eastern Pacific)

Knowledge of upper thermal-tolerance limits of marine organisms in the tropical eastern Pacific (TEP) is important because of the influence of phenomena such as El Niño and global warming, which increase sea temperature. Laboratory experiments were conducted to determine the critical thermal maximum (CTM) of reef fishes from the TEP. In 15 reef fishes of Gorgona Island (TEP) the CTM was between 34.7°C and 40.8°C. None of these CTMs was exceeded by sea temperature in the TEP during any of the strongest El Niño events in this century (32°C during El Niño 1982-1983 and 1997-1998), which indicates that all species studied here may tolerate El Niño maximum temperatures. In addition, the CTM of the least-tolerant species was 8°C above the current mean sea temperature in a wide range of latitudes in the TEP. This suggests that fishes live far from their upper thermal tolerance limits and that the current global-warming trend is still unlikely to be dangerous for these species. If sea temperature continues to increase at the current rate, in about a century sea temperature could exceed the thermal tolerance of some reef fishes and threaten them with extinction. Such risk, however, might occur sooner if the sea temperature during El Niño also increased in step with the global warming, but also because other processes involved in maintaining population, such as reproduction, can be affected at lower temperatures. The possible ability of reef fishes to adapt to increases in sea temperature is discussed.     

The swimming kinematics of larval Atlantic cod, Gadus morhua L., are resilient to elevated seawater pCO2

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO₂ conditions (control-370, medium-1800, and high-4200 μatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO₂—at beyond near-future ocean acidification levels—affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO₂ levels. Nonetheless, cod larvae cultured at the highest pCO₂ concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious.     

大气CO2体积分数升高环境温度与土壤水分对农田土壤呼吸的影响

植物-土壤生态系统土壤呼吸与温度、水分环境因子的关系对评价目前大气CO2浓度持续升高背景下陆地生态系统土壤碳库的变化趋势具有重要意义.依托FACE(free air carbon dioxide enrichment)技术平台,利用阻断根法,采用LI-6400红外气体分析仪(IRGA)-田间原位测定的方法,研究了大气CO2体积分数升高对稻(Oryza sativa L.)/麦(Triticum aestivum L.)轮作制中麦田的土壤呼吸、基础土壤呼吸和呼吸主要影响因子,分析了大气CO2体积分数升高后温度与水分对土壤呼吸的影响.结果表明,在整个测定期间,土壤呼吸与基础土壤呼吸速率呈明显的季节变化,与气温和土壤温度季节变化趋势基本一致,呼吸速率与温度具有显著的相关性,是影响土壤呼吸的控制性因素;呼吸速率与土壤含水量无显著的相关性,土壤水分是研究区麦田土壤CO2排放的非限制性因素,且温度与土壤含水量间的交互效应对土壤呼吸的影响不显著.基础土壤呼吸比作物下的土壤呼吸更易受温度影响,土壤温度比气温能更好地解释土壤CO2排放的季节性变化.而CO2体积分数增加降低了温度与呼吸速率间的相关系数和Q10,表明温度对土壤CO2排放的影响程度下降.但高CO2体积分数环境中植物-土壤生态系统的土壤呼吸对温度增加敏感性的降低,有利于减缓土壤碳分解损失的速度.结果有助于评价未来高CO2体积分数气候变暖背景下植物-土壤系统下的农田生态系统土壤碳的固定潜力.     

Influence of delayed metamorphosis on survival and growth of juvenile barnacles Balanus amphitrite

Competent cyprid larvae of the barnacle Balanus amphitrite Darwin were prevented from metamorphosing in the laboratory for 3 or 5 d using three different techniques (holding at low temperature, crowding, and detaining on a silanized surface). We then assessed the effects of prolonging larval life on post-metamorphic growth and survival, in comparison with control individuals that metamorphosed soon after they were competent to do so. Seven experiments were conducted over 2 yr (July 1987 to September 1989). In all experiments (each with six replicates per treatment), postponing larval metamorphosis for 3 or 5 d dramatically depressed postmetamorphic growth rate (P<0.05), although metamorphic success and post-metamorphic survival were not affected (P>0.10). The results suggest that B. amphitrite cyprids deferring their metamorphosis in the field may be less successful in competing for space, at least during the first few weeks of postlarval life.     

Comparing the effect of elevated pCO2 and temperature on the fertilization and early development of two species of oysters

This study compared the synergistic effects of elevated pCO₂ and temperature on the early life history stages of two ecologically and economically important oysters: the Sydney rock oyster, Saccostrea glomerata and the Pacific oyster, Crassostrea gigas. Gametes, embryos, larvae and spat were exposed to four pCO₂ (375, 600, 750, 1,000 μatm) and four temperature (18, 22, 26, 30°C) levels. At elevated pCO₂ and suboptimal temperatures, there was a reduction in the fertilization success of gametes, a reduction in the development of embryos and size of larvae and spat and an increase in abnormal morphology of larvae. These effects varied between species and fertilization treatments with S. glomerata having greater sensitivity than C. gigas. In the absence of adaptation, C. gigas may become the more dominant species along the south-eastern coast of Australia, recruiting into estuaries currently dominated by the native S. glomerata.     

Acute toxicity and sublethal behavioral effects of copper on barnacle nauplii (Balanus improvisus)

This study documents the effects of short-term (24h) sublethal copper exposures on undirected swimming activity and photobehavior of Balanus improvisus stage II nauplii. All Cu treatments were static, with temperature and salinity conditions at 20°C and 15 or 30. The 24h LC 50 estimate for Cu is 88 ppb at 15 and >200 ppb at 30. Sub-lethal Cu concentrations cause reductions in swimming speed, which decrease progressively with increasing Cu dose. At 50 ppb Cu, this was significant primarily at light intensities below the phototactic threshold. At higher Cu concentrations, significant reductions in mean linear velocity occurred at most light intensities tested. At 30, 50 and 100 ppb Cu also reduce the positive phototactic response and 150 ppb Cu causes reversal of phototaxis at optimal intensities. Photokinesis is reduced at 100 ppb Cu and disappears at 150 ppb Cu. At 15, the behavioral effects of 50 ppb Cu resemble those occurring with 150 ppb Cu at 30. Swimming speed and photobehavior show promise as sensitive behavioral indicators of copper toxicity. Additional research is required to determine if these responses apply to a broad range of pollutants and to other planktonic organisms. There is also a need to further evaluate the significance of these behavioral effects ecologically.Contribution No. 181 from the EPA Environmental Research Laboratory, Narragansett, RI 02882, USA     

Effects of elevated pCO2 and the effect of parent acclimation on development in the tropical Pacific sea urchin Echinometra mathaei

Effects of acclimation to projected near-future ocean acidification (OA) conditions on physiology, reproduction and development were investigated in the tropical sea urchin Echinometra mathaei. Following 6 weeks in control or one of the three elevated pCO₂ (pH_NIST 7.5–8.1; pCO₂ ~485–1,770 μatm) conditions, adult urchins exhibited a slight decline of growth in low pH treatments and moderately reduced respiration at intermediate levels. At 7 weeks, gametes from adults were used to produce larvae that were reared in their respective parental treatments. To assess whether larvae from acclimated parents are more resilient to elevated pCO₂ than those not acclimated, larvae from control animals were also reared in the elevated pCO₂ treatments. There was no difference in female ‘spawnability’ and oocyte size between treatments, but male spawning ability was reduced in increased pCO₂ conditions. In elevated pCO₂ treatments, the percentage of normal larvae and larval size decreased in the progeny of control- and elevated pCO₂-acclimated parents, and arm asymmetry increased. Thus, acclimation of the parents did not make the progeny more resilient or sensitive to OA effects. Negative effects of increased pCO₂ on reproduction and development may impact on recruitment and population maintenance of this species.     

Physiological and behavioral responses of temperate seahorses (Hippocampus guttulatus) to environmental warming

The aim of the present study was to evaluate, for the first time, the effect of environmental warming on the metabolic and behavioral ecology of a temperate seahorse, Hippocampus guttulatus. More specifically, we compared routine metabolic rates, thermal sensitivity, ventilation rates, food intake, and behavioral patterns at average spring temperature (18 °C), average summer temperature (26 °C), temperatures that they endure during summer heat wave events (28 °C), and in a near-future warming scenario (+2; 30 °C) in Sado estuary, Portugal. Both newborn juveniles and adults showed significant increases in metabolic rates with rising temperatures. However, newborns were more impacted by future warming via metabolic depression (i.e., heat-induced hipometabolism). In adult stages, ventilation rates also increased significantly with environmental warming, but food intake remained unchanged. Moreover, the frequency of swimming, foraging, swinging, and inactivity did not significantly change between the different thermal scenarios. Thus, we provide evidence that, while adult seahorses show great resilience to heat stress and are not expected to go through any physiological impairment and behavioral change with the projected near-future warming, the early stages display greater thermal sensitivity and may face greater metabolic challenges with potential cascading consequences for their growth and survival.     

Acquisition and loss of cold-tolerance in adult barnacles (Balanus balanoides) kept under laboratory conditions

In the laboratory, Balanus balanoides (L.) barnacles maintained without food at 5°C over the winter to summer period remained cold-tolerant. Winter animals maintained at 5°C and fed Artemia nauplii under a controlled light-dark regime until mid-summer lost this cold-tolerance. Summer animals, maintained without food at 5° or 15°C until midwinter, became cold-tolerant. Summer and winter animals subjected to increased (or decreased) ambient salinity for 48 h showed a small decrease (or increase) in their lower median lethal temperature (MLT—defined as the temperature at which 50% of the animals die after 18 h exposure to air). Summer animals subjected to desiccation for 48 h also showed a small decrease in their lower MLT. It is concluded that the seasonal changes in cold-tolerance of adult barnacles are probably induced by a combination of environmental factors including food availability, light intensity, day-length and changes in ambient sea-water temperatures. Development of cold-tolerance in the winter did not depend upon fertilisation. Changes in intra-cellular solute concentration which accompany adaptation to changes in ambient salinity or desiccation do not appear to be related to the seasonal changes in cold-tolerance.     

Scanning electron microscopy of metamorphosis in four species of barnacles (Cirripedia Thoracica Balanomorpha)

Metamorphosis and early juvenile development was followed in the laboratory in Balanus amphitrite and B. improvisus (family Balanidae) and in Semibalanus balanoides and Elminius modestus (family Archaeobalanidae) from cyprid settlement until 24 h after ecdysis. Stages of development were studied in vivo and with scanning electron microscopy. Events in metamorphosis and early juvenile development are very similar in all four species and can be interpreted in terms of a highly modified moult. Notably, there was no indication whatsoever of the amorphous decorticated settler previously described from metamorphosis of B. amphitrite. The shape of a juvenile barnacle with cirri and incipient shell plates is apparent immediately after the shedding of the cypris carapace, and rudimentary peduncle can be distinguished below the developing wall plates. A basal row of cuticular hairs encircles the peduncle in all species except S. balanoides. These hairs seem to serve a restraining function during early development, when the juvenile barnacle is only attached by the initially secreted cyprid cement. Similarly situated hairs are also present in very young juveniles of the lepadomorph Scalpellum scalpellum. In Semibalanus balanoides nothing indicates that the rostrum originates from the fusion of two latera as previously claimed, since this plate is single as soon as it can be distinguished.     

Responses of marine benthic microalgae to elevated CO2

Increasing anthropogenic CO₂ emissions to the atmosphere are causing a rise in pCO₂ concentrations in the ocean surface and lowering pH. To predict the effects of these changes, we need to improve our understanding of the responses of marine primary producers since these drive biogeochemical cycles and profoundly affect the structure and function of benthic habitats. The effects of increasing CO₂ levels on the colonisation of artificial substrata by microalgal assemblages (periphyton) were examined across a CO₂ gradient off the volcanic island of Vulcano (NE Sicily). We show that periphyton communities altered significantly as CO₂ concentrations increased. CO₂ enrichment caused significant increases in chlorophyll a concentrations and in diatom abundance although we did not detect any changes in cyanobacteria. SEM analysis revealed major shifts in diatom assemblage composition as CO₂ levels increased. The responses of benthic microalgae to rising anthropogenic CO₂ emissions are likely to have significant ecological ramifications for coastal systems.     

会泽铅锌尾矿区自然生长的3种豆科植物铅锌耐性的研究

为了解会泽铅锌尾矿区自然发生的豆科植物对重金属的耐性,研究了该地区自然发生的3种豆科植物在Pb2＋/Zn2＋单盐和双盐胁迫下种子萌发及其幼苗生长的情况。研究表明：在本实验所设的浓度范围内,Pb2＋/Zn2＋单独胁迫时,对供试植物种子及幼苗的生长主要表现为抑制作用,除苕子（Vicia Cracca L.）外,金属离子的质量浓度越大抑制作用越强;Pb2＋/Zn2＋共同胁迫时出现复杂的交互作用。对于苕子的种子及幼苗的生长,Pb2＋/Zn2＋呈现明显的相互加强抑制作用;对于其它2种植物,当Zn2＋浓度在低质量浓度时,Pb2＋似乎对Zn2＋抑制有缓解作用,同样当Pb2＋浓度在低质量浓度时,Zn2＋似乎对Pb2＋抑制有缓解作用,但是当Pb2＋/Zn2＋高浓度时,Pb2＋/Zn2＋呈现明显的相互加强抑制作用。不论是单盐还是双盐,苕子对的耐性最强,其次为白三叶（Trifolium repens L.）,紫花苜蓿（Medicago sativa L.）最弱。会泽铅锌尾矿区重金属含量高是该区植被恢复的最大障碍,进一步研究植物对Pb2＋及Zn2＋的耐受性对于铅锌尾矿区的植被恢复有极其重要的意义。