Metabolic adaptation of Cancer irroratus developmental stages to cyclic temperatures

Metabolic-temperature responses of the developmental stages of the sublittoral crab Cancer irroratus cultured at 10° to 20°C daily cyclic and 15°C constant temperatures were determined. Generally, the metabolic rate increased with temperature in the lower range with Q₁₀'s (temperature coefficients) above 2, compensated in the midrange with Q₁₀'s between 1 and 2, and declined at the higher temperatures with Q₁₀ values less than 1. For the larvae cultured at a constant temperature of 15°C, the compensatory response range narrowed with development from first zoeae to the later zoeal stages. In contrast, the compensatory response of the first zoeae, megalops, and crab stages within the range 10° to 25°C was interrupted by a zone of thermal sensitivity between 15° and 20°C for those individuals cultured in the 10° to 20°C cyclic regime. The compensatory response range is narrower for the third stage zoeae and broader for the second, fourth, and fifth stage zoeae. Metabolic rate-temperature (M-T) patterns of C. irroratus developmental stages cultured under the cyclic regime varied from those held at constant temperature by increased respiration and metabolic rate compensation between 20° and 25°C, and by an extension of the metabolically active range towards higher temperatures.     

Metabolic adaptation of Zostera marina (eelgrass) to diurnal periods of root anoxia

The temperate seagrass Zostera marina L. is common in coastal marine habitats characterized by the presence of reducing sediments. The roots of this seagrass grow in these anoxic sediments, yet eelgrass is highly productive. Through photosynthesis-dependent oxygen transport from leaves to roots, aerobic respiration is supported in eelgrass roots only during daylight; consequently, roots are subjected to diurnal periods of anoxia. Under anoxic root conditions, the amino acids alanine and -amino butyric acid accumulate within a few hours to account for 70% of the total amino acid pool, while glutamate and glutamine decline. Little ethanol is produced, and the pool size of the organic acid malate changes little or declines slowly. Upon the resumption of shoot photosynthesis and oxygen transport to the roots, the accumulated -amino butyric acid declines rapidly, glutamate and glutamine pools increase, and alanine declines over a 16-h period. These adaptive metabolic responses by eelgrass to diurnal root anoxia must contribute to the successful exploitation of shallow-water marine sediments that have excluded nearly all vascular plant groups. A metabolic scheme is presented that accounts for the observed changes in organic and amino acid pool sizes in response to anoxia.     

Temperature and salinity adaptation in the purple shore crab Hemigrapsus nudus: An in vitro physiological study with excised gills

The alkali-soluble polysaccharides of the cell wall from 7 different marine diatoms were shown to contain the monosaccharides rhamnose, fucose, galactose, mannose and xylose. The relative amounts of rhamnose and fucose varied widely from one species to another, from the very rhamnose-rich Chaetoceros affinis to Thalassiosira gravida, where no rhamnose was found. All Chaetoceros species were found to have a high content of rhamnose. Also the proportion of mannose to galactose varied widely from species to species. The observed change in monomer composition from the logarithmic to the stationary growth phase is explained by assuming the alkali-soluble fraction to be a mixture of polysaccharides. The soluble, extracellular polysaccharides from 4 of the diatoms were also investigated. The products from C. affinis and C. curvisetus were homogeneous and composed of only 3 monomers: rhamnose, fucose and galactose. The extracellular polysaccharide composition in all species investigated was quite different from the composition of the cellular alkali-soluble fraction. The ecological aspects of these soluble polysaccharides may prove of considerable interest.     

Freezing tolerance in the intertidal red algaeChondrus crispus andMastocarpus stellatus: Relative importance of acclimation and adaptation

The effect of repeated daily freezing on photosynthesis, growth and phenotypic acclimation to freezing was studied in the red algaeChondrus crispus Stackhouse andMastocarpus stellatus (Stackhouse in With.) Guiry. Algae used for experiments were collected from Chamberlain, Maine, between March and August 1987, and field observations and experiments were carried out at Chamberlain and Kresge Point, Maine between March 1987 and March 1989. After ca 30 d of daily freezing for 3 h at –5°C photosynthesis ofC. crispus was reduced to 55% of control values. Growth rates ofC. crispus were also reduced in fronds frozen daily compared to unfrozen controls, and eventually fronds became bleached and fragmented resulting in biomass losses. Fronds ofC. crispus, frozen daily, had higher photosynthetic rates following freezing events than unfrozen controls indicating that this species can acclimate to freezing conditions. Acclimation to freezing involves the light-harvesting reactions of photosynthesis. In contrast, photosynthesis and growth inM. stellatus were unaffected by repeated daily freezing for 3 h at –5°C for 36 d. No differences in photosynthesis following freezing were observed between frozen and control fronds suggesting thatM. stellatus does not phenotypically acclimate to freezing. The greater freezing tolerance ofM. stellatus relative toC. crispus results, in part, from genetic adaptations associated with plasma membranes and the light-harvesting reactions of photosynthesis.     

Temperature and salinity adaptation in the purple shore crab Hemigrapsus nudus: An in vitro metabolic flux study with excised gills

The effects of temperature and salinity acclimation on intermediary metabolism in excised gill homogenates from Hemigrapsus nudus were examined. In general, a decrease in salinity was followed by an increase in the oxidation of the substrates glucose-1-¹⁴C, acetate-1-¹⁴C and glycine-¹⁴C to ¹⁴CO₂. Also, there was an increase in amino acid incorporation into the protein fraction. Both of these metabolic parameters were differentially temperature-sensitive. An enzymic model which may explain the increase in respiration rate observed in several intertidal invertebrates meeting an hypo-osmotic stress is proposed, using data from these experiments and also from the literature.     

Metabolic responses to changing environmental conditions in the brackish water polychaetes Marenzelleria viridis and Hediste diversicolor

The metabolic strategies of the polychaete Marenzelleria viridis (Verrill 1873), a successful immigrant into Baltic shallow eutrophic coastal waters with meso-to oligohaline salinities since the 1980's, were determined by simultaneous calorimetry and respirometry. Resistance to oxygen deficiency under varying ecological conditions was also examined. The results of the studies with this immigrant were compared to those with the common indigeneous polychaete Nereis (Hediste) diversicolor (O.F. Müller). At 10 and 20 °C and the average habitat salinity of 5 M. viridis gradually reduced its metabolic activity with declining oxygen partial preessures (pO₂), whereas H. diversicolor maintained its metabolic activity. The metabolism of both species remained fully aerobic down to a pO₂ of 2 kPa. An additional hyposmotic stress of 0.5 salinity at a temperature of 20 °C led to a decrease in the rate of oxygen consumption in H. diversicolor below a pO₂ of 10 kPa, whereas metabolic heat dissipation remained constant. M. viridis, however, further reduced both, metabolic heat dissipation and oxygen consumption. The metabolic rates of both species under anoxia were similar, amounting to ca. 20% of the normoxic rate. The resistance of the two species to oxygen deficiency was also similar, ranging between 21 and 290 h (median survival time LT₅₀), depending on temperature and salinity. Specimens used in the present study were collected from the Southern Baltic coastal inlet of Darß-Zingster-Boddenkette during 1992 and 1993.     

Oxygen and acid-base status of the sea urchin Psammechinus miliaris during environmental hypoxia

The respiratory and acid-base responses to hypoxia of the sea urchin Psammechinus miliaris Gmelin have been studied both in the laboratory and in the field. Sea urchins were collected from the Clyde Sea area, Scotland, between March and July 1993. Individual urchins were unable to regulate their oxygen uptake during hypoxia. The partial pressure of oxygen (P_{O 2}) in the coelomic fluid was lower than ambient P_{O 2} during normoxia but still decreased with a decrease in environmental P_{O 2}. There was a significant increase in pH and in the concentrations of bicarbonate, magnesium and calcium in the coelomic fluid, but a significant decrease in the partial pressure of carbon dioxide (P_{CO 2}), in response to declining P_{O 2}s. The disturbance of respiratory parameters in urchins accompanying hypoxic exposure in rock pools was similar to that observed in the laboratory, although not as severe as might have been expected on the basis of the laboratory experiments.     

Metabolic responses of the prawns Palaemon elegans and P. serratus (Crustacea: Decapoda) to acute hypoxia and anoxia

Using prawns, Palaemon elegans (Rathke) from intertidal pools on the Isle of Cumbrae, Scotland, and P. serratus (Pennant) from the subtidal at Plymouth, England, some metabolic responses to hypoxia and anoxia have been studied. P. elegans was found to have a greater tolerance of severe hypoxia than P. serratus. Tolerance of totally anoxic conditions, however, was limited to only 4 h in P. elegans and to approximately 1 h in P. serratus. exposure to moderate hypoxia (30 torr) resulted in little change in the concentration of L-lactate in the blood or in the tissues of either P. elegans or P. serratus. When exposed to extreme hypoxia (10 or 5 torr for P. elegans), however, there was a progressive increase in the concentration of L-lactate in the blood and in the tissues of both species. After normoxic conditions had been restored, the concentration of L-lactate in the blood and in the tissues returned to normal resting levels more rapidly in P. elegans than in P. serratus. Under hypoxic conditions, both P. elegans and P. serratus showed an increase in the concentration of blood glucose and a slight reduction in the glycogen content of the tissues. The concentrations of blood glucose and of tissue glycogen returned to normal levels within 6 h of the prawns being returned to normoxic conditions. The results of an in situ study in April and August 1986 to examine the metabolic responses of P. elegans to the hypoxic conditions normally experienced in high-shore rock pools are also presented. The ecological significance of the differing abilities of these species to survive hypoxic exposure is discussed.     

Distributions and population structures of two intertidal estuarine polychaetes in the lower St. Lawrence Estuary,with special reference to environmental factors

An intensive study of the spatial distribution ofNereis virens (Sars) andNephtys caeca (Fabricius) was conducted during the spring and autumn of 1986 in the lower St. Lawrence estuary. Statistical analysis showed that spatial variations in density, individual body weight and sexual maturity, particularly in the case ofNereis virens, are correlated with the intertidal level, with certain sediment characteristics, and with the thickness of the colonizable sediment layer. The density ofN. virens increases in an offshore-onshore direction, whereas that ofNephtys caeca decreases in the same direction. For both species, mean body weight increases downshore from the upper intertidal level. Other specific relationships exist in relation to sediment characteristics. Sexually matureNereis virens are found only at the lower intertidal level; sexual maturity inNephtys caeca was not studied. There were no changes in spatial distribution patterns between spring and autumn. The spatial distribution ofNereis virens parallels depth contours and may reflect its ability to inhabit environments which become more physically unstable in an offshore-onshore direction. This spatial distribution is consistent with a model whereby larvae are recruited in the upper intertidal zone and juveniles migrate downshore.     

Adaptation of the polychaete worm Scoloplos armiger to hypoxic conditions

The anaerobic metabolism of the intertidal polychaete Scoloplos armiger, its recovery from anaerobiosis and the importance of anaerobic energy production during low tide in the field were investigated. Under anaerobic conditions S. armiger produces energy in the same manner as Arenicola marina, a prototype of an euryoxic invertebrate from the intertidal. Energy is produced from the phosphagen stores and from the breakdown of glycogen to volatile fatty acids, mainly propionate and to a lesser extend acetate. However, S. armiger cannot reduce its energy demand to the same degree as A. marina. This and the relatively small pool of glycogen may be the reason for its only moderate resistance to anoxia. The recovery from anaerobiosis proceeds in S. armiger significantly slower than in A. marina. S. armiger is able to maintain a fully aerobic metabolism down to a Pw_{O 2}of ca. 20 torr and even at a Pw_{O 2}of 10 torr a partly aerobic metabolism was retained. In the field during low tide S. armiger ascends into the oxidative layer, where it is able to maintain an aerobic metabolism even at parts without remaining puddels on the surface.     

Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage

Despite the great interest in characterizing the functional structure and resilience of functional groups in natural communities, few studies have examined in which way the roles and relationships of coexisting species change during community succession, a fundamental and natural process that follows the release of new resources in terrestrial and aquatic ecosystems. Variation in algal traits that characterize different phases and stages of community succession on rocky shores are likely to influence the magnitude, direction of effects, and the level of redundancy and complementarity in the diverse assemblage of herbivores. Two separate field experiments were conducted to quantify per capita and population effects and the functional relationship (i.e., redundancy or complementarity) of four herbivore species found in central Chile during early and late algal succession. The first experiment examined grazer effects on the colonization and establishment of early-succession algal species. The second experiment examined effects on the late-successional, dominant corticated alga Mazzaella laminarioides. Complementary laboratory experiments with all species and under natural environmental conditions allowed us to further characterize the collective effects of these species. We found that, during early community succession, all herbivore species had similar effects on the ephemeral algae, ulvoids, but only during the phase of colonization. Once these algae were established, only a subset of the species was able to control their abundance. During late succession, only the keyhole limpet Fissurella crassa could control corticated Mazzaella. The functional relationships among these species changed dramatically from redundant effects on ephemeral algae during early colonization, to a more complementary role on established early-successional algae, to a dominant (i.e., keystone) effect on late succession. This study highlights that functional relationship within consumer assemblages can vary at different phases and times of community succession. Differentiation in herbivore roles emphasizes the need to evaluate consumer's impacts through different times of community succession, and through experimental manipulations to make even broad predictions about the resilience or vulnerability of diverse intertidal assemblages to human disturbances.     

Photosynthetic response to temperature and desiccation of the intertidal alga Mastocarpus papillatus

When exposed to air during low tide, intertidal macroalgae experience a terrestrial environment and often encounter extreme levels of heating and desiccation. Two aspects of photosynthesis may be influenced by this increase in temperature and decrease in water content during exposure to air: (1) the rate of aerial photosynthesis itself, and (2) the rate at which aquatic photosynthesis recovers upon immersion in water at high tide. This laboratory study examines the effect of air temperature and desiccation on photosynthesis of the intertidal macroalga Mastocarpus papillatus Kützing. Plants were collected at Hopkins Marine Station, California, USA (36°37N; 121°54W) between July and December 1990. When apical tips were exposed to 15 to 25°C air for 2 h, photosynthesis was rapidly recovered upon reimmersion in seawater. Recovery was delayed, but complete, when tissue was exposed to 30°C air, but did not occur after exposure to 35°C air. Desiccation did not influence either the rate or the ultimate level of recovery upon reimmersion. Photosynthesis in air generally decreased with increasing desication, with no net photosynthesis occurring below 25% relative water content. Net photosynthesis of hydrated thalli increased with air temperature from 15 to 30°C, then decreased at 35°C. Dark respiration of hydrated thalli increased over the entire temperature range. This study indicates that thallus heating and desiccation during periods of exposure to air can potentially influence the total carbon budget of M. papillatus.     

Metabolic cold adaptation in Antarctic fishes: evidence from enzymatic activities of brain

To evaluate the concept of metabolic cold adaptation (MCA) in fishes, we compared - in brain, red muscle, and white muscle of Antarctic notothenioid fishes and tropical/subtropical fishes - the activities of two enzymes of ATP-generating pathways, citrate synthase (CS), an indicator of citric acid cycle activity (aerobic metabolism), and lactate dehydrogenase (LDH), an indicator of potential for ATP production through anaerobic glycolysis. Brain was chosen because, unlike locomotory muscle, its metabolic activity is not likely to be influenced by a species' level of activity or nutritional status, so MCA should be readily observed if present. CS and LDH activities in brain exhibited a high level of MCA, but compensation to temperature was not complete (48% for CS; 46% for LDH). CS and LDH activities in red and white muscle varied widely among species, according to the general level of locomotory activity. The 'mode of life'-related enzymatic activities in locomotory muscle show that study of MCA at the level of whole organism metabolism is fraught with difficulties and experimental ambiguities. In contrast, the low variation among species within each group in enzymatic activities in brain, and the large differences between groups in CS and LDH activity, show that brain is an excellent study system for evaluating metabolic compensation to temperature.     

Modelling spatial distribution of hard bottom benthic communities and their functional response to environmental parameters

In this study we analyzed and modelled spatial distribution of hard bottom benthic communities in the Lagoon of Venice, and used the model to derive functional response of these communities to changing environmental conditions.     

Metabolic suppression in thecosomatous pteropods as an effect of low temperature and hypoxia in the eastern tropical North Pacific

Many pteropod species in the eastern tropical North Pacific Ocean migrate vertically each day, transporting organic matter and respiratory carbon below the thermocline. These migrations take species into cold (15–10°?C) hypoxic water (<20?μmol O₂ kg^?1) at depth. We measured the vertical distribution, oxygen consumption and ammonia excretion for seven species of pteropod, some of which migrate and some which remain in oxygenated surface waters throughout the day. Within the upper 200?m of the water column, changes in water temperature result in a?~60–75?% reduction in respiration for most species. All three species tested under hypoxic conditions responded to low O₂ with an additional?~35–50?% reduction in respiratory rate. Combined, low temperature and hypoxia suppress the metabolic rate of pteropods by?~80–90?%. These results shed light on the ways in which expanding regions of hypoxia and surface ocean warming may impact pelagic ecology.     

Freezing rate and duration determine the physiological response of intertidal fucoids to freezing

Differential thermal analysis (DTA) was used to measure the freezing temperature of nine species of red brown intertidal macroalgae from the coast of Maine, USA in 1991. Using slow and rapid cooling rates approximating those found in the field for Ascophyllum nodosum (L.) Le Jol. we found that, for a given rate, the freezing points of all species were similar: -7.06 to -8.02°C for slow cooling (ca. 0.25°C min^-1) and -3.42 to -4.56°C for rapid cooling (ca. 5.0°C min^-1). In the low shore species, Fucus evanescens C. Ag., photosynthesis was inhibited to a greater extent when plants were frozen or thawed rapidly than after slow freezing or thawing. However, in the upper shore species, F. spiralis (L.), photosynthesis recovered rapidly and completely regardless of freezing rate. Rapidly frozen F. evanescens also experienced greater loss of plasmalemmal integrity, evidenced by a greater loss of cellular contents on re-immersion, than those frozen slowly. Light-limited photosynthesis following freezing was more severely inhibited than light-saturated photosynthesis. Respiration was generally enhanced immediately after freezing, but then declined to rates below those of unfrozen controls within 2 h following re-immersion, with control rates of respiration being achieved after a 24 h recovery period. Our data suggest that the physiological consequences of winter emersion at sub-zero temperatures may vary widely between individual plants of freezing-susceptible species, due to the wide variations in freezing rate associated with microhabitat effects.     

Bioavailability of a hydrocarbon from water and sediment to the marine worm Arenicola marina

The uptake, accumulation and depuration of a labelled hydrocarbon (¹⁴C-1-naphthalene) by the marine annelid Arenicola marina were studied. Naphthalene was chosen because it is an important component of oil and is known to be toxic to marine organisms. The bioavailability of the hydrocarbon to the worm from contaminated sediment is examined and the results discussed with reference to the rehabilitation of oiled environments, as A. marina is thought to be capable, in high numbers, of greatly reworking sediments.     

Use of environmental DNA in assessment of fish functional and phylogenetic diversity

Assessing the impact of global changes and protection effectiveness is a key step in monitoring marine fishes. Most traditional census methods are demanding or destructive. Nondisturbing and nonlethal approaches based on video and environmental DNA are alternatives to underwater visual census or fishing. However, their ability to detect multiple biodiversity factors beyond traditional taxonomic diversity is still unknown. For bony fishes and elasmobranchs, we compared the performance of eDNA metabarcoding and long-term remote video to assess species’ phylogenetic and functional diversity. We used 10 eDNA samples from 30 L of water each and 25 hr of underwater videos over 4 days on Malpelo Island (pacific coast of Colombia), a remote marine protected area. Metabarcoding of eDNA detected 66% more molecular operational taxonomic units (MOTUs) than species on video. We found 66 and 43 functional entities with a single eDNA marker and videos, respectively, and higher functional richness for eDNA than videos. Despite gaps in genetic reference databases, eDNA also detected a higher fish phylogenetic diversity than videos; accumulation curves showed how 1 eDNA transect detected as much phylogenetic diversity as 25 hr of video. Environmental DNA metabarcoding can be used to affordably, efficiently, and accurately census biodiversity factors in marine systems. Although taxonomic assignments are still limited by species coverage in genetic reference databases, use of MOTUs highlights the potential of eDNA metabarcoding once reference databases have expanded.     

Physiological and behavioural responses of the intertidal scavenging gastropod Nassarius festivus to salinity changes

Physiology (oxygen consumption and ammonia excretion) and behaviour (feeding and activity) of the intertidal gastropod Nassarius festivus (Powys) at five different salinities [15, 20, 25 (control), 30 and 35‰] were studied for 4 weeks. Oxygen consumption and ammonia excretion rates were reduced immediately after salinity was either elevated or reduced. Subsequently, both rates were increased while the O:N ratio was decreased at all salinities, including the control, in the first 2 weeks and then levelled off. Such changes were probably attributed to osmotic adjustment and reproductive activity. Activity and feeding were reduced at low salinity, particularly in the first week. Reproductive output, in terms of the total number of egg capsules and the mean number of eggs per capsule, was also lowered at reduced salinities. Nevertheless, individuals at all salinities are able to maintain a positive energy balance. Results are discussed with respect to the distribution of N. festivus in Hong Kong waters. Received: 14 April 1997 / Accepted: 9 May 1997