Proximate and elemental composition and energy content of mesopelagic crustaceans from the Eastern Gulf of Mexico

The proximate and elemental chemical compositions of 25 species of pelagic decapod and mysid crustaceans collected from the eastern Gulf of Mexico (27°N; 86°W, 1984 to 1989) was examined. Water level ranged from 63 to 95% and increased slightly with species' increased depth of occurrence. Protein levels were generally high (1.5 to 18.3% wet wt, WW; 27.6 to 62.4% ash-free dry wt, AFDW) and comprised the primary organic component in the majority of species. Protein, both as % WW and % AFDW, decreased with increased depth of occurrence. In contrast to protein, lipid levels were low (0.5 to 8.9% WW; 5.7 to 60.9% AFDW), and increased with increased depth of occurrence. Carbon and nitrogen best mirrored measured lipid and protein levels when considered as non-protein carbon and non-chitin nitrogen, respectively. C:N ratios increased with increased depth, consistent with changes in protein and lipid with depth. Because of their compositional attributes, resident Gulf of Mexico species have a low total wet weight energy content relative to species from more productive regions. Energy content showed no significant trend with depth. Vertical migration patterns were distinctly different between shallow-and deep-living gulf species and these differences were largely responsible for the relationships observed between composition and depth. In migrating species, the protein and nitrogen content were higher, the lipid and carbon contents and C:N ratio lower, than in non-migrating species. Three deep-living species of the genus Acanthephyra were found to be compositionally atypical, resembling shallow, migrating types rather than other deep-living, non-migratory species.     

Proximate composition of Antarctic mesopelagic fishes

Eleven mesopelagic fish species from the Weddell/Scotia Sea region of the Antarctic captured during the austral spring 1983, austral fall 1986, and austral winter 1988, were analyzed for proximate composition. Water, ash level, protein, lipid and carbohydrate were examined in relation to depth of occurrence and season. No depth-related trends were evident, primarily due to a low species diversity and minimal differences in those species' vertical distributions. The Antarctic speciesElectrona antarctica showed a significant increase in lipid level (% wet wt and % ash-free dry wt) between spring, fall and winter. The increase may signify an accumulation over the productive season, possibly as a reserve for the winter months. Lipid levels (% wet wt and % ash-free dry wt) were significantly lower in the Weddell Sea specimens examined in this study than in previously examined identical and congeneric species taken during the same season from a more productive near-shore Antarctic region. Comparisons with congeners and confamilials from tropical-subtropical and temperate systems revealed variable trends. The Antarctic speciesE. antarctica andCyclothone microdon had lower water and protein (% wet wt) levels than similar species from tropical-subtropical or temperate regions. Lipid levels of the two species are similar to temperate individuals, while energy levels are slightly higher. In contrast, species of the genusBathylagus show no trends in composition as a function of latitude. Differences in productivity, water-column temperature-structure, and seasonality are important considerations when examining trends among mesopelagic species.     

Oxygen consumption of midwater fishes and crustaceans from the eastern Gulf of Mexico

Oxygen consumption was measured as a function of temperature, oxygen partial-pressure (P_O2)and species depth of occurrence for twenty-three species of midwater fishes and crustaceans collected from the eastern Gulf of Mexico from June 1981 to July 1985. Q₁₀s (7° to 20°C) of 3.90 and 3.24 were recorded for myctophid and non-myctophid fish groups, respectively, while values of 2.22, 2.19, 2.19 and 2.54 were calculated for sergestid, penaeid, carid and euphausiid crustacean groups, respectively. Q₁₀s were consistent for species within each group. All of the species tested regulated their oxygen consumption to P_O2levels normally encountered within the eastern Gulf. Values of critical partial pressure (P_c) ranged from 20 to 40mm Hg and increased slightly with increasing temperature and respiration rate. Declining respiration with increasing minimum depth of occurrence was primarily a function of temperature alone. Changes in size, dry weight and water content contributed only a small fraction to the observed decrease. This finding contrasts with studies from the eastern Pacific Ocean, where temperature is a minor contributor to changes in respiration rate with depth.     

Chemical composition of midwater fishes as a function of depth of occurrence off the Hawaiian Islands: Food availability as a selective factor?

The variation with depth in water, lipid, protein, carbon and nitrogen contents (% wet weight) of 42 species of midwater fishes, collected in November 1976 off the west coast of Oahu in the Hawaiian Archipelago, was measured. The Hawaiian fishes show significant relationships between these components and depth of occurrence. The slopes of these relationships are not significantly different from those reported for midwater fishes from off California, USA. However, the fishes from Hawaii have significantly lower lipid levels and higher protein levels than do the species from off California. The deep-living Hawaiian species (500 m and deeper) have significantly lower lipid (% wet weight), but there is no significant difference in protein (% wet weight). The difference in lipid contents at all depths appears to be an evolved characteristic, with the greater lipid levels off California being selected for by greater spatial and temporal variation in the food supply for these fishes off the California coast than off Hawaii. The higher protein contents in the shallow-living Hawaiian fishes appear to reflect greater muscle power selected for in these fishes by the greater water clarity, and therefore greater reactive distances, in the surface layers off Hawaii. These conclusions support the general hypothesis that the lower protein contents of bathypelagic fishes are not directly selected by food limitation at depth, but rather result from the relaxation of selection for rapid-swimming abilities at greater depths due to the great reduction at greater depths in the distance over which visual predator-prey interactions can take place. The lower lipid levels in the deeper-living species are apparently made possible by the reduced metabolic rates of these species which reduces their need for energy stores.     

Food availability as a selective factor on the chemical compositions of midwater fishes in the eastern North Pacific

In September and October 1980 we examined the relationships between food availability, depth, and chemical composition among 12 midwater fish species, from three adjacent areas of the eastern North Pacific: the eastern gyre, the California Current, and the transitional region between them. By comparing trends in chemical composition across a geographical productivity gradient, the influence of food availability could be examined both with and without depth as a dependent variable. In general, caloric density, lipids, and water content showed consistent trends along both vertical and horizontal gradients of food availability. Lipids and caloric contents were lowest among bathypelagic species and among fishes from the gyre. Water content was highest in the gyre and among deeper-living species. While protein content as a percentage of the total wet weight declined with depth, there was no clear trend among mesopelagic species between stations. Protein as percent of the total organic content showed no decrease with depth, but was significantly higher in the gyre among mesopelagic species. These findings suggest that compositional trends in water, lipids, and caloric content are correlated with food availability, regardless of any depth-related factors. In contrast, protein did not vary consistently with food availability and thus may be linked to other factors.     

Calorific values of benthic marine algae and their postulated relation to invertebrate food preference

Data are given on the kcal/g dry weight, percent ash, and kcal/ash-free g of dry weight for 1 marine diatom species, 70 macroscopic benthic algae, and 1 marine tracheophyte species. For 41 of these, the data have also been converted to kcal/g wet weight. Calorific values, though relatively homogeneous within genera, appear to be influenced by phyletic affinity, water purity, or depth of immersion, and such ecological properties as growth form, generation time, and relative susceptibility to herbivory. Seasonal factors, portion of the plant combusted and growth rate appear to have little effect. The food preferences of various invertebrate herbivores seem to have evolved more in response to an availability factor than to absolute food value.     

Depth-related enzymic activities in muscle,brain and heart of deep-living pelagic marine teleosts

The activities [units^-1 wet weight tissue] of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH) and isocitrate dehydrogenase (IDH) in white skeletal muscle, brain and heart of 24 pelagic teleost fishes were determined. In addition, for several of the foregoing species, citrate synthase (CS) activities were examined in white skeletal muscle. In muscle, the activities of all these enzymes decrease exponentially with increasing minimum depth of occurrence of the species; this decrease closely parallels the decrease in respiratory rate found previously for these same species. The decline in enzymic activity with increasing minimum depth of occurrence is much greater than the decline in body protein content of the whole fishes, suggesting a disproportionately rapid fall in enzyme concentration in comparison to contractile and structural protein concentrations. The similar reductions in activities of both glycolytic (LDH and PK) and citric acid cycle (CS, MDH and IDH) enzymes with depth indicate that both standard and active metabolisms of deeper-dwelling species are reduced relative to shallower-dwelling forms. There is no suggestion of increased anaerobic capacity with depth or in relation to species, occurrence in the oxygen minimum layer. In brain and heart, there is no significant decrease in enzymic activity with increasing minimum depth of occurrence. These two tissues have similar capacities for metabolism in most fishes, when comparisons are based on enzymic activity per gram wet weight of tissue.     

Allocation of organic material and energy to the holdfast,stipe, and fronds inPostelsia palmaeformis (Phaeophyta: Laminariales) on the California coast

Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g^-1 dry wt and ca. 19 kJ g^-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m^-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone.     

Digestion rates and assimilation efficiencies of siphonophores fed zooplankton prey

Digestion times and assimilation efficiencies are critical factors used in calculations of carbon and nitrogen budgets. Digestion times of natural copepod prey differed significantly among 4 genera of siphonophores (P>0.001), from a minimum of 1.6 h to a maximum of 9.6 h. Assimilation efficiencies, in contrast, were uniformly high; 87 to 94% for carbon and 90 to 96% for nitrogen. Nitrogen assimilation was consistently greater than carbon assimilation. Assimilation efficiencies calculated according to dry weight substantially underestimated assimilation of carbon and nitrogen, while calculations using ash-free dry weights and ash-free to dry weight ratios approached values for carbon assimilation. These values are appreciably higher than most of the assimilation efficiencies previously measured for a few other planktonic carnivores. These results indicate very efficient digestion of food by siphonophores in oceanic environments where prey densities are low.     

Formation and potential trophic significance of marine foam near kelp beds in the benguela upwelling system

The present study investigates the importance of foam in nearshore waters on the west coast of the Cape Peninsula (South Africa) as a possible food resource for consumer organisms. A bacterial density of 3.45x10⁹ cells ml^-1 foam suspension was recorded. Calorific values of up to 15.39 kJ g^-1 ash-free dry weight were noted, and a biochemical analysis of the drained foam suspension gave a composition of 22.85% protein, 10.76% lipid and 3.07% carbohydrates. Field data showed a correlation between peaks of phytoplankton up to 510 mg C m^-3 water temperatures and days of intense foam formation during periods of strong onshore winds. Experimental foam formation in the laboratory indicates that kelp mucilage and phytoplankton contain surface-active agents. An additional feature of kelp mucilage is its capability to improve foam stability. The comparison of the chemical composition of 12 and 120 h-old foam suspension indicates a loss of easily metabolizable components such as trichloroacetic-acid precipitated protein and neutral lipid with time. It is hypothesised that the losses are due to utilisation of these components by consumers.     

Protein composition of white skeletal muscle from mesopelagic fishes having different water and protein contents

The consequences for white skeletal muscle of the whole body variation in water and protein content were examined in 11 mesopelagic fishes taken off the coast of Oregon, USA, in 1983. For such muscles, water content varied from 71 to 91% of muscle wet weight, and protein content ranged from 56 to 141 mg g^-1 muscle wet weight, depending on the species. Dilution by increased water content did not account for the decrease in protein content. Total muscle protein was partitioned into soluble (myogen or sarcoplasmic) and insoluble (myofibrillar) components. Both the myogen and myofibrillar components are reduced in muscle with decreased protein content. The activities (units g^-1 wet wt) of white muscle L-lactate dehydrogenase and L-malate dehydrogenase are higher in fishes undergoing diel vertical migration to surface waters than in fishes that either do not migrate or do not migrate to surface waters. The differences in enzyme activities are not due to a general dilution of muscle protein. The actin content of white skeletal muscle was maintained at a relatively constant level in all 11 species examined and was similar to actin levels observed previously in the white skeletal muscle of scombrids and demersal fishes. This conservation of actin content requires species with a reduced muscle protein content to maintain a significant fraction of their total protein as actin. The specific activities of the myofibrillar Mg²⁺–Ca²⁺-activated adenosine triphosphatases of the mesopelagic species are similar in all 11 species studied. Thus, the ratios of proteins in the isolated myofibrils are probably similar. These results suggest that, in species with decreased muscle protein, there is an increase in the non-myofibrillar form of actin.     

Movements of bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis>) in the northwestern Atlantic Ocean recorded by pop-up satellite archival tags

Pop-up satellite archival tags were implanted into 68 Atlantic bluefin tuna (Thunnus thynnus Linnaeus), ranging in size from 91 to 295 kg, in the southern Gulf of Maine (n=67) and off the coast of North Carolina (n=1) between July 2002 and January 2003. Individuals tagged in the Gulf of Maine left that area in late fall and overwintered in northern shelf waters, off the coasts of Virginia and North Carolina, or in offshore waters of the northwestern Atlantic Ocean. In spring, the fish moved either northwards towards the Gulf of Maine or offshore. None of the fish crossed the 45°W management line (separating eastern and western management units) and none traveled towards the Gulf of Mexico or the Straits of Florida (known western Atlantic spawning grounds). The greatest depth recorded was 672 m and the fish experienced temperatures ranging from 3.4 to 28.7°C. Swimming depth was significantly correlated with location, season, size class, time of day, and moon phase. There was also evidence of synchronous vertical behavior and changes in depth distribution in relation to oceanographic features.Communicated by J.P. Grassle, New Brunswick     

Proximate composition and nucleic acid content of premetamorphic leptocephalus larvae of the congrid eel Ariosoma balearicum

Water, ash, proximate composition (protein, lipid, carbohydrate, hexosamine), and nucleic acid (DNA, RNA) content were measured in premetamorphic larvae of the congrid eel Ariosoma balearicum (Delaroche) collected from the eastern Gulf of Mexico. Specimens ranged from 15.0 to 202.3 mm total length (TL) and 0.0116 to 4.3860 g wet mass (WM). Water content increased linearly with increasing specimen mass over the entire size range; consequently, percent water was uniform and had a mean value of 92.9±1.09% WM. Ash content also increased linearly with specimen mass, but only up to a mass of 2.5 g WM (165 mm TL). Ash content in specimens >165 mm TL showed only a small increase with mass, suggesting an improved osmoregulatory capability in larger individuals. The absolute amount of all proximate components increased with increasing specimen size, but rates of deposition among the components varied, resulting in different patterns in the relative concentrations of each with growth. Protein dominated the ash-free dry mass (AFDM) throughout development (29 to 59% AFDM); carbohydrate and hexosamine occurred in similar proportions (8 to 24% AFDM). Lipid was a significant proportion of the AFDM in only the smallest individuals. Lipid concentrations decreased initially as mass increased in individuals smaller than 0.4 g WM (90 mm TL), indicating a low rate of lipid deposition in small individuals. In specimens >90 mm TL, lipid concentrations were uniform and had a mean of 12% AFDM. Trends for biochemical components and nucleic acids suggest that growth of Phase I leptocephali occurs in two subphases (Ia and Ib). Phase Ia is characterized by cellular proliferation, preferential synthesis of protein and carbohydrate relative to lipid, and growth manifested more as increased length rather than increased mass. For A. balearicum, Phase Ia extends from yolk-sac absorption to 90 mm TL. In Phase Ib, nucleic acid content levels off, lipid deposition increases, and mass increases exponentially.     

Fatty acid composition of the triacylglycerols of the cypris larva of the barnacle Balanus balanoides during metamorphosis

In the free-swimming cypris larva of Balanus balanoides, the mean level of triacylglycerols (triglycerides) was 8% of the ash-free dry weight. During metamorphosis into the juvenile barnacle, the triacylglycerol level in the newly settled non-feeding cypris larva fell to a mean of 2% of the ash-free dry weight. The ratio of fatty acids in the triacylglycerols remained constant throughout metamorphosis, indicating that all species of fatty acids were used as energy sources. There was no evidence for the selective utilisation of particular fatty acids.     

Temperature acclimation of upper and lower thermal limits and freeze resistance in the nonindigenous brown mussel, Perna perna (L.), from the Gulf of Mexico

Acute and chronic upper and lower thermal limits and freeze resistance were investigated in the nonindigenous brown mussel, Perna perna, from the Texas Gulf of Mexico coast in order to assess its potential distribution in North American coastal waters. This species' long-term, incipient lower and upper thermal limits were 7.5°C and 30°C, congruent with the seasonal ambient water temperature range of 10-30°C reported for other populations worldwide. Effects of temperature acclimation and individual size on survival time were most pronounced on chronic exposures to lethal temperatures approaching incipient lower or upper thermal limits. When exposed to temperature increasing at 0.1°C min^-1, the acute upper lethal limit was 44°C regardless of acclimation temperature or individual size. P. perna had a limited freeze resistance, being intolerant of emersion at -2.5°C. This species' narrow incipient thermal limits, limited capacity for temperature acclimation and poor freeze resistance may account for its restriction to subtidal and lower eulittoral zones of cooler subtropical rocky shores. Near extinction of P. perna from Texas Gulf of Mexico waters occurred in the summer of 1997 when mean surface-water temperatures approached its incipient upper limit of 30°C.     

Estimation of the reproductive output of the burrowing shrimp Callianassa tyrrhena : a comparison of three different biometrical approaches

Reproductive output, as the percentage of the mother weight devoted to egg production, was estimated for the burrowing shrimp Callianassa tyrrhena in wet, dry and ash-free dry weight. Three biometrical approaches were used. First, the relationship between the egg mass and the mother weight was determined. A second approach was to estimate the weight loss of the female caused by oviposition. Similar results were obtained from these methods for dry and ash-free dry weight (about 20 and 35%, respectively), but not for the wet weight estimation. The third approach, based on the weight loss of the ovary, did not reveal a constant value for reproductive output throughout the female size range, although it was found that the ovary loses a constant percentage of its weight during oviposition. This discrepancy is due to the fact that the ovary weight shows positive allometry to the weight of the female body. The comparison of the three methods offers insight into the biological events that are related to ovary maturation and oviposition. It is suggested that molting just before oviposition and its inhibition during the yolk accumulation in the ovary play dominant roles in the expression of the reproductive output in the different approaches used. Received: 17 July 1996 / Accepted: 11 September 1996     

Elemental and biochemical composition of salps (Tunicata: Thaliacea)

Carbon and nitrogen content have been measured in the solitary and aggregate generations of 11 species of salps. Regression equations for each species and generation permit estimation of carbon or nitrogen content as a function of length of live individuals. Different species of the same length may have nearly tenfold differences in carbon content. Fractionation and biochemical analysis of some samples revealed that the organic content of salps is approximately 80% protein. Ash-free dry weights average 27% of dry weights; mean carbon content is 29% of ash-free dry weight. Excess ash-free dry weight not accountable as organic material is thought to be water of hydration.     

Triacylglycerols and wax esters in the lipids of deep midwater teleost fishes of the Southern California Bight

Total lipid contents and the proportions of triacylglycerols and wax esters were examined in 23 species of deep-sea fishes collected between 1977 and 1980 in the Santa Catalina, San Clemente and San Pedro Basins off Southern California, USA. Mean total lipid content ranged from 1 to 22% of wet weight. Triacylglycerols accounted for 1 to 91% of total lipids present and were more abundant than wax esters in the lipids of all but a single species. Wax ester contents ranged from 0 to 24% of total lipids but in 20 species were 10% of the lipids. These results do not substantiate the previously suggested idea that wax esters are important constituents of the lipids of deep-sea fishes. Moreover, the hypothesis that wax ester content increases with increasing depth of occurrence is not supported. To assess the importance of the lipids present in bouyancy regulation, the water content and swimbladder inflation of these species were also examined. Neither total lipids nor wax esters appear to play an important role in buoyancy regulation in the majority of these fishes. Eight species have gas-filled swimbladders. Of the species lacking inflated swimbladders, 7 have watery bodies (87 to 95% H₂O) and 6 with low lipid (8.3%) and water (85%) contents may need to swim continuously to maintain their position in the water column. Lipids, largely in the form of triacylglycerols, may be important in the buoyancy of three species with lipid contents>10% of wet weight. Two of these species also possess inflated swimbladders. The reasons for the production of large quantitites of was esters by certain deep-sea teleosts, especially gonostomatids and myctophids, remain unknown.     

Metabolism,enzymic activities and cold adaptation in Antarctic mesopelagic fishes

Several species of Antarctic mesopelagic fishes that have different minimal depths of occurrence but the same environmental temperature were collected in November–December 1983 and in March 1986 between 0 and 1 000 m in the open water near the marginal ice zone in the vicinity of 60°S 40°W (1983) and 65°S 46°W (1986), and oxygen consumption rate (V _{O 2}) and the activity of two metabolic enzymes, lactate dehydrogenase (LDH, an indicator of the anaerobic potential of locomotory muscle) and citrate synthase (CS, an indicator of citric acid cycle activity or aerobic potential), were determined. In four dominant species, whole-individual oxygen-consumption rate (y, ml O₂ individual^–1 h^–1) varied with weight (X, g) according to the equation y=aX ^b, with b values falling between 0.889 and 1.029. The relation of weight-specific LDH activity (y, U g^–1 wet wt) with weight (x, g) was also described by the equation y=aX ^b, with b values varying between 0.229 and 1.025. Weight-specific CS activity declined with weight, with b values from-0.031 to-0.369. V _{2 O}, LDH activity and CS activity all declined markedly with increased species' minimum depth of occurrence (the depth below which 90% of a species' population lives). Comparisons with previous studies on ecologically equivalent species of the California Borderland indicate that depth-related decreases in metabolism are the result of adapted traits of deeper-living species, not declining temperature within the water column. The metabolic rate of Antarctic mesopelagic fishes is approximately twice that of California species at equivalent temperatures; similar rates were found at the normal habitat temperatures of the two groups. Thus, a well-developed compensation for temperature is present in the Antarctic fishes: cold adaptation. Differences in enzymic activity among species, and among different sized individuals of a species are related to differences in metabolic rate and locomotory capacity. Enzymic indices can be used to estimate metabolic rates and evaluate ecological parameters such as predatory strategies and niche separation.     

In situ variation in heart rate of the shore crab Carcinus maenas in relation to environmental factors and physiological condition

Heart rate of Carcinus maenas was recorded continuously for two days in situ, together with water temperature, salinity, depth and light intensity. Of each sex, 25 crabs were used and assigned to groups on the basis of size and colour (the carapace changes colour with prolongation of the intermoult phase). Wet weight:dry weight ratios of midgut gland, muscle, gonads and whole body were examined together with midgut gland lipid content and haemolymph protein concentration. Heart rates and wet wt:dry wt ratios for all the tissues examined were higher in early intermoult than in late intermoult stages of the adult C. maenas (P<0.05). Heart rate, lipid content and haemolymph protein concentrations were higher and wet wt:dry wt ratios of midgut gland, gonads and whole body were lower in juvenile crabs than in adults (P<0.05). The relationship between heart rate and wet wt:dry wt of whole body differed among C. maenas in early and late intermoutl. Heart rate was positively correlated with midgut gland lipid content (a Darwinian fitness parameter) in crabs that were in late intermoult. Physico-chemical environmental parameters, sex and colour accounted for 12% of the variation in heart rate of C. maenas recorded in situ. Temperature and prolonged intermoult were the most important factors influencing heart rate. The findings are discussed in relation to laboratory studies of cardiac activity and observed behaviour of C. maenas in the field.