1,344 research outputs found
Latitudinal trends in shell production cost from the tropics to the poles
Get PDFThe proportion of body mass devoted to skeleton in marine invertebrates decreases along latitudinal gradients from large proportions in the tropics to small proportions in polar regions. A historical hypothesis—that latitudinal differences in shell production costs explain these trends—remains untested. Using field-collected specimens spanning a 79°N to 68°S latitudinal gradient (16,300 km), we conducted a taxonomically controlled evaluation of energetic costs of shell production as a proportion of the total energy budget in mollusks. Shell production cost was fairly low across latitudes at <10% of the energy budget and predominately <5% in gastropods and <4% in bivalves. Throughout life, shell cost tended to be lower in tropical species and increased slightly toward the poles. However, shell cost also varied with life stage, with the greatest costs found in young tropical gastropods. Low shell production costs on the energy budget suggest that shell cost may play only a small role in influencing proportional skeleton size gradients across latitudes relative to other ecological factors, such as predation in present-day oceans. However, any increase in the cost of calcium carbonate (CaCO3) deposition, including from ocean acidification, may lead to a projected ~50 to 70% increase in the proportion of the total energy budget required for shell production for a doubling of the CaCO3 deposition cost. Changes in energy budget allocation to shell cost would likely alter ecological trade-offs between calcification and other drivers, such as predation, in marine ecosystems
Disturbance, dispersal and marine assemblage structure: A case study from the nearshore Southern Ocean
Get PDFDisturbance is a key factor in most natural environments and, globally, disturbance regimes are changing, driven by increased anthropogenic influences, including climate change. There is, however, still a lack of understanding about how disturbance interacts with species dispersal capacity to shape marine assemblage structure. We examined the impact of ice scour disturbance history (2009–2016) on the nearshore seafloor in a highly disturbed region of the Western Antarctic Peninsula by contrasting the response of two groups with different dispersal capacities: one consisting of high-dispersal species (mobile with pelagic larvae) and one of low-dispersal species (sessile with benthic larvae). Piecewise Structural Equation Models were constructed to test multi-factorial predictions of the underlying mechanisms, based on hypothesised responses to disturbance for the two groups. At least two or three disturbance factors, acting at different spatial scales, drove assemblage composition. A comparison between both high- and low-dispersal models demonstrated that these mechanisms are dispersal dependent. Disturbance should not be treated as a single metric, but should incorporate remote and direct disturbance events with consideration of taxa-dispersal and disturbance legacy. These modelling approaches can provide insights into how disturbance shapes assemblages in other disturbance regimes, such as fire-prone forests and trawl fisheries
The extremes of disturbance reduce functional redundancy: Functional trait assessment of the shallow Antarctic benthos
Get PDFThermal reaction norms and the scale of temperature variation: latitudinal vulnerability of intertidal Nacellid limpets to climate change
Get PDFThe thermal reaction norms of 4 closely related intertidal Nacellid limpets, Antarctic (Nacella concinna), New Zealand (Cellana ornata), Australia (C. tramoserica) and Singapore (C. radiata), were compared across environments with different temperature magnitude, variability and predictability, to test their relative vulnerability to different scales of climate warming. Lethal limits were measured alongside a newly developed metric of “duration tenacity”, which was tested at different temperatures to calculate the thermal reaction norm of limpet adductor muscle fatigue. Except in C. tramoserica which had a wide optimum range with two break points, duration tenacity did not follow a typical aerobic capacity curve but was best described by a single break point at an optimum temperature. Thermal reaction norms were shifted to warmer temperatures in warmer environments; the optimum temperature for tenacity (Topt) increased from 1.0°C (N. concinna) to 14.3°C (C. ornata) to 18.0°C (an average for the optimum range of C. tramoserica) to 27.6°C (C. radiata). The temperature limits for duration tenacity of the 4 species were most consistently correlated with both maximum sea surface temperature and summer maximum in situ habitat logger temperature. Tropical C. radiata, which lives in the least variable and most predictable environment, generally had the lowest warming tolerance and thermal safety margin (WT and TSM; respectively the thermal buffer of CTmax and Topt over habitat temperature). However, the two temperate species, C. ornata and C. tramoserica, which live in a variable and seasonally unpredictable microhabitat, had the lowest TSM relative to in situ logger temperature. N. concinna which lives in the most variable, but seasonally predictable microhabitat, generally had the highest TSMs. Intertidal animals live at the highly variable interface between terrestrial and marine biomes and even small changes in the magnitude and predictability of their environment could markedly influence their future distributions
Long-term effects of altered pH and temperature on the feeding energetics of the Antarctic sea urchin, Sterechinus neumayeri
Get PDFLong-term effects of altered PH and temperature on the feeding energetics of the Antarctic sea urchin, Sterechinus neumayeri
Get PDFThis study investigated the effects of long-term incubation to near-future combined warming (+2 °C) and ocean acidification (−0.3 and −0.5 pH units) stressors, relative to current conditions (−0.3 °C and pH 8.0), on the energetics of food processing in the Antarctic sea urchin, Sterechinus neumayeri. After an extended incubation of 40 months, energy absorbed, energy lost through respiration and lost as waste were monitored through two feeding cycles. Growth parameters (mass of somatic and gonad tissues and the CHN content of gonad) were also measured. There were no significant effects of combined ocean acidification (OA) and temperature stressors on the growth of somatic or reproductive tissue. Despite more food being consumed in the low temperature control, once food processing and maintenance costs were subtracted, there were no significant effects of treatment on the scope for growth. The biggest significant differences were between amounts of food consumed during the two feeding cycles. More food was consumed by the low temperature (0 °C) control animals, indicating a potential effect of the changed conditions on digestive efficiency. Also, in November, more food was consumed, with a higher absorption efficiency, which resulted in a higher scope for growth in November than September and may reflect increased energetic needs associated with a switch to summer physiology. The effect of endogenous seasonal cycles and environmental variability on organism capacity is discussed
Warming by 1°C drives species and assemblage level responses in Antarctica’s marine shallows
Get PDFForecasting assemblage-level responses to climate change remains one of the greatest challenges in global ecology [1
, 2
]. Data from the marine realm are limited because they largely come from experiments using limited numbers of species [3
], mesocosms whose interior conditions are unnatural [4
], and long-term correlation studies based on historical collections [5
]. We describe the first ever experiment to warm benthic assemblages to ecologically relevant levels in situ. Heated settlement panels were used to create three test conditions: ambient and 1°C and 2°C above ambient (predicted in the next 50 and 100 years, respectively [6]). We observed massive impacts on a marine assemblage, with near doubling of growth rates of Antarctic seabed life. Growth increases far exceed those expected from biological temperature relationships established more than 100 years ago by Arrhenius. These increases in growth resulted in a single “r-strategist” pioneer species (the bryozoan Fenestrulina rugula) dominating seabed spatial cover and drove a reduction in overall diversity and evenness. In contrast, a 2°C rise produced divergent responses across species growth, resulting in higher variability in the assemblage. These data extend our ability to expand, integrate, and apply our knowledge of the impact of temperature on biological processes to predict organism, species, and ecosystem level ecological responses to regional warming
Seasonality of oxygen consumption in five common Antarctic benthic marine invertebrates
Get PDFThe waters of the Southern Ocean exhibit extreme seasonality in primary production, with marine life living below 0 °C for much of the year. The metabolic cold adaptation (MCA) hypothesis suggests that polar species need elevated basal metabolic rates to enable activity in such cold which should result in higher metabolic rates, or at least rates similar to temperate species. This study aimed to test whether any of the five common marine invertebrates around Adelaide Island (Western Antarctic Peninsula) displayed MCA: the suspension-feeding holothurian Heterocucumis steineni, the grazing limpet Nacella concinna, and the omnivorous brittle star, cushion star and sea-urchin Ophionotus victoriae, Odontaster validus and Sterechinus neumayeri, respectively. We also tested a second hypothesis that secondary consumers will exhibit less seasonal variation of metabolic rate than primary consumers. Routine oxygen consumption was measured in both the austral summer and winter using closed circuit respirometry techniques. Metabolic rates for all the species studied were low compared with temperate species, in a fashion consistent with expected temperature effects on biological systems and, therefore, the data do not support MCA. All the species studied showed significant seasonal differences for a standard mass animal except N. concinna. In two species N. concinna and H. steineni, size affected the seasonality of metabolism. There was no difference in seasonality of metabolism between primary and secondary consumers. Thus, for secondary consumers seasonal factors, most likely food availability and quality, vary enough to impact metabolic rates, and produce seasonal metabolic signals at all trophic levels. Other factors such as reproductive status that are linked to seasonal signals may also have contributed to the metabolic variation across trophic levels
Limpet feeding rate and the consistency of physiological response to temperature
Get PDFThermal reaction norms are fundamental relationships for geographic comparisons of organism response to temperature. They are shaped by an organism’s environmental history and provide insights into both the global patterns of thermal sensitivity and the physiological mechanisms underlying temperature response. In this study we conducted the first measure of the thermal reaction norm for feeding, comparing the radula rasping rate of two tropical and one polar limpet species. The consistency of thermal response was tested through comparisons with limpet duration tenacity. Feeding and duration tenacity of limpets are ecologically important muscular mechanisms that rely on very different aspects of muscle physiology, repeated concentric (shortening) and isometric (fixed length) contraction of muscles, respectively. In these limpets the thermal reaction norms of feeding limpets were best described by a single break point at a maximum temperature with linear declines at higher (Siphonaria atra) or lower temperatures (Nacella concinna and Cellana radiata) rather than a bell-shaped curve. The thermal reaction norms for duration tenacity were similar in the two tropical limpets. However, the rasping rate in Antarctic N. concinna increased linearly with temperature up to a maximum at 12.3 °C (maximal range 8.5–12.3 °C) when feeding stopped. In contrast, duration tenacity in N. concinna was maximal at 1.0 °C (−0.6 to 3.8 °C) and linearly decreased with increasing temperature. The thermal reaction norms of muscular activity were, therefore, inconsistent within and between species, indicating that different mechanisms likely underlie different aspects of species sensitivities to temperature
Extreme phenotypic plasticity in metabolic physiology of Antarctic demosponges
Get PDFSeasonal measurements of the metabolic physiology of four Antarctic demosponges and their associated assemblages, maintained in a flow through aquarium facility, demonstrated one of the largest differences in seasonal strategies between species and their associated sponge communities. The sponge oxygen consumption measured here exhibited both the lowest and highest seasonal changes for any Antarctic species; metabolic rates varied from a 25% decrease to a 5.8 fold increase from winter to summer, a range which was greater than all 17 Antarctic marine species (encompassing eight phyla) previously investigated and amongst the highest recorded for any marine environment. The differences in nitrogen excretion, metabolic substrate utilization and tissue composition between species were, overall, greater than seasonal changes. The largest seasonal difference in tissue composition was an increase in CHN (Carbon, Hydrogen, and Nitrogen) content in Homaxinella balfourensis, a pioneer species in ice-scour regions, which changed growth form to a twig-like morph in winter. The considerable flexibility in seasonal and metabolic physiology across the Demospongiae likely enables these species to respond to rapid environmental change such as ice-scour, reductions in sea ice cover and ice-shelf collapse in the Polar Regions, shifting the paradigm that polar sponges always live “life in the slow lane.” Great phenotypic plasticity in physiology has been linked to differences in symbiotic community composition, and this is likely to be a key factor in the global success of sponges in all marine environments and their dominant role in many climax communities
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