Showing papers by "National Marine Fisheries Service published in 1984"

Model of a coral reef ecosystem

Abstract: The ECOPATH model for French Frigate Shoals estimates the benthic plant production (net primary production in kg wet weight) required to support the atoll food chain. In this section we estimate the benthic net primary production and net community production of the atoll based on metabolism studies of reef flat, knolls, and lagoon communities at French Frigate Shoals Hawaii. Community metabolism was measured during winter and summer. The reef communities at French Frigate Shoals exhibited patterns and rates of organic carbon production and calcification similar to other reefs in the world. The estimate of net primary production is 6.1·106 kg wet weight km-2 year-1±50%, a value remarkably close to the estimate by the ECOPATH model of 4.3·106 kg wet weight km-2 year-1. Our estimate of net community production or the amount of carbon not consumed by the benthos was high; approximately 15% of the net primary production. Model results indicate that about 5% of net primary production is passed up the food chain to mobile predators. This suggests about 10% of net primary production (∼6% of gross primary production) may be permanently lost to the system via sediment burial or export offshore.

Why Do Fish Populations Vary

Abstract: Fish populations vary because of density-dependent and -independent processes that determine recruitment, growth, and natural mortality, and in response to fishing. Most of the natural (non-fishing) variability is associated with recruitment, presumably the density-independent effect of fluctuating environmental factors.

Role of larger herbvores in seagrass communities

Abstract: The nutritional ecology of macroherbivores in seagrass meadows and the roles of grazing by urchins, fishes and green turtles in tropical systems and waterfowl in temperate systems are discussed in this review. Only a few species of animals graze on living seagrasses, and apparently only a small portion of the energy and nutrients in seagrasses is usually channeled through these herbivores. The general paucity of direct seagrass grazers may be a function of several factors in the composition of seagrasses, including availability of nitrogen compounds, presence of relatively high amounts of structural cell walls, and presence of toxic or inhibitory substances. The macroherbivores, however, can have a profound effect on the seagrass plants, on other grazers and fauna associated with the meadow, and on chemical and decompositional processes occurring within the meadow. Grazing can alter the nutrient content and digestibility of the plant, as well as its productivity. Removal of leaf material can influence interrelations among permanent and transient faunal residents. Grazing also interrupts the detritus cycle. Possible consequences of this disruption, either through acceleration or through decreased source input, and the enhancement of intersystem coupling by increased export and offsite fecal production, are discussed. The extent and magnitude of these effects and their ecological significance in the overall functioning of seagrass meadows only can be speculated, and probably are not uniform or of similar importance in both tropical and temperate seagrass systems. However, areas grazed by large herbivores provide natural experiments in which to test hypotheses on many functional relations in seagrass meadows.

A Candidate Magnetic Sense Organ in the Yellowfin Tuna, Thunnus albacares.

Abstract: Single-domain magnetite crystals have been isolated and characterized from tissue located in a sinus within the dermethmoid bone of the skull of the yellowfin tuna, Thunnus albacares. Their chemical composition, narrow size distribution, and distinctive crystal morphology indicate that these crystals are biochemical precipitates. Experiments on the interaction between particles reveal the organization of the particles in situ and suggest a possible form for candidate magnetoreceptor organelles. The consistent localization of such particles with similar arrangement within the dermethmoids of this and other pelagic fishes suggests that the ethmoid region is a possible location for a vertebrate magnetic sense organ.

Utilization of amino acids by planktonic marine bacteria: Importance of clean technique and low substrate additions1,2

Abstract: Rapid turnover of dissolved free amino acids (DFAA) by bacterioplankton in the Gulf of Mexico was observed with techniques designed to eliminate contamination of samples with trace metals and organic compounds. The mean turnover rate of DFAA, based on incorporation of 0.5 nM additions of a mixture of amino acids, was 4.9-d-l for high productivity neritic environments and 1.3.d-’ for low productivity oceanic environments. These rates are faster than those in parallel samples measured by traditional techniques and are consistently faster than previously reported values. Data for multiple level (0.01-7 nM) additions of the mixed substrate were in accord with the Michaelis-Menten enzyme kinetics model. Kinetic parameters derived from this model (V,,,, K, + S,, and R), bacterial cell numbers, and V,,,/cell were highest at photic depths of the neritic zone, intermediate at photic depths of the oceanic zone, and lowest at aphotic depths of the oceanic zone. Estimates of secondary productivity by bacterioplankton (based on V,,,,,) on an equal water volume basis were 6.6 + 1.5% (+-SE, y1 = 5) of the light-saturated primary productivity at the maximum productivity depth. Estimated turnover time of the bacterioplankton community ranged from 2.4 d at 5 m at the highest productivity station to 130 days at 250 m at the lowest productivity

Food selection by young larval gulf menhaden (Brevoortia patronus)

Abstract: Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.

Rapid evolution of a Gulf Stream warm-core ring

Abstract: Satellite images are used to show that major alterations in the structure of Gulf Stream warm-core rings can occur during very short periods of two to five days when an interaction with the Gulf Stream is particularly intense. The role of these interactions in the evolution of a ring are discussed.

Relative contributions of food and water in the accumulation of zinc by two species of marine fish

Abstract: A model food chain, utilizing 65Zn-labeled and nonlabeled food organisms, was used to measure the relative contributions of food and water to Zn accumulation by Gambusia affinis and Leiostomus xanthurus Chlamydomonas sp was fed to Artemia sp which in turn was fed to G affinis and L xanthurus A trace metal-chelate buffer system was used to maintain a stable free Zn ion activity (10-85 mol l-1) in the experimental seawater Food represented 78 to 82% of total accumulation of 65Zn by the fish Thus, food cannot be ignored in assessing the accumulation and toxicity of trace metals

Automated sizing, counting and identification of zooplankton by pattern recognition

Abstract: A computerized system was developed to automate the analysis of zooplankton samples. Classification to major taxonomic group was based on discriminant analysis of morphological features. Images were generated either from preserved organisms or from silhouette photographs. The latter technique simplified large-scale sample storage. Accuracy of correct classification, among organisms regularly occurring in New England coastal waters, exceeded 90%. Critical problems were due to limitations inherent to the imaging of low contrast, randomly oriented objects by a vidicon camera. One solution would utilize an incoherent-to-coherent transducer in a binocular field of observation through which plankton entrained in a flowing medium passed.

Life history of the bowhead whale, Balaena mysticetus (Mammalia: Cetacea)

Abstract: This paper synthesizes data collected from bowhead whales (Balaena mysticetus) landed by Alaskan Eskimos between 1973 and 1982. From these data, and from the literature, length at birth has been estimated to be 4-4.5 m, length at one year to be 8-2 m, length at sexual maturity to be 14 m in females, and maximum length to be 20 m. Sexual activity, possibly mating, has been observed in March through May and the length of gestation is estimated to be 13 months. The calving period appears to extend from March through August, with the peak in births occurring in May. Lactation may extend for one year. Evidence has been provided for a pregnancy rate (percentage pregnant in mature female catch) of 015 and it has been suggested that calving occurs every three to six years. Gross annual reproductive rate (based on calf sightings) is estimated to be at least 3–6%. Sources of mortality are discussed. The sex ratio of animals taken by Eskimos is 0.83: 1.00 (females to males) and is not significantly different from unity. Summary The conclusions drawn in each of the preceding sections are likely to be re-evaluated as more information becomes available. Still, it is suggested that the length at birth is 4–4.5 m, length at one year is 8.2 m, length at sexual maturity is 14 m in females, and the maximum attainable length is 20 m. Conception is most likely to occur in late winter while the whales congregate in Bering Sea polynyas, whereas the peak in calving appears to occur in May. Consequently, it has been hypothesized that the gestation time is greater than one year, but less than two. By analogy with other right whales and sparse data collected, the duration of lactation is assumed to be one year, although this is arguable. The pregnancy rate of mature females, calculated from ovarian data, is 0.15, projecting a calving interval of approximately seven years. The gross annual reproductive rate generated from field data is 3.6–12.4%. The sex ratio of the harvested animals is 0.83: 1.0, and it is assumed that this does not reflect the whole population. Whatever changes are yet to be made in the understanding of the bow-head life history, all of the traits delineated are consistent with those predicted for slowly reproducing animals, the quintessential K-strategist. We are most grateful to the scores of field biologists who have helped us count whales and sample those landed by the Eskimos, and who have contributed ideas and enthusiasm. In addition, we thank R. Tarpley for information on ovaries collected in 1982, J. Breiwick for running several sex ratio estimates, and H. Marsh for her generous assistance with the ovarian histology. Under contract to us R. Davis and W. Koski of L.G.L., environmental research associates, provided the photogrammetric measurements. An earlier, less complete version of our paper was submitted in 1982 as an unpublished report (document SC/34/PS1) to the International Whaling Commission, resulting in many valuable comments from members of the Scientific Committee. P. Best, D. Chapman, and an anonymous reviewer substantially improved the manuscript. Finally, we thank the people of Barrow, Point Hope, Wainwright, Gambell, Savoonga, and Kaktovik for their patience and assistance. Without their support this research would not have been possible.

Marking Otoliths by Immersion of Marine Fish Larvae in Tetracycline

Abstract: Otoliths of the larvae of spot Leiostomus xanthurus and pinfish Lagodon rhomboides were marked with a band that fluoresced in ultraviolet (UV) light after live larvae had been immersed for 1–2 hours in tris-buffered, 100–500-mg/liter solutions of tetracycline in a 1% NaCl solution. Dimethyl sulfoxide did not significantly increase tetracycline uptake. After otoliths were marked, their radii increased approximately 18% in 8 days for spot and 15% for pinfish, but distinct daily growth increments could not be detected even though diel periodicities in feeding and photoperiod were provided in the laboratory. Received October 31, 1983 Accepted March 19, 1984

Viral diseases of marine invertebrates

Abstract: Approximately 40 viruses are known from marine sponges; turbellarian and monogenetic flatworms; cephalopod, bivalve, and gastropod mollusks; nereid polychaetes; and isopod and decapod crustaceans. Most of the viruses can be tentatively assigned to the Herpesviridae, Baculoviridae, Iridoviridae, Adenoviridae, Papovaviridae, Reoviridae, “Birnaviridae”, Bunyaviridae, Rhabdoviridae, and Picornaviridae. Viruslike particles found in oysters might be representatives of the Togaviridae and Retroviridae. Enveloped single-stranded RNA viruses from crustaceans have developmental and morphological characteristics intermediate between families, and some show evidence of relationships to the Paramyxoviridae as well as the Bunyaviridae or Rhabdoviridae. Certain small viruses of shrimp cannot be assigned, even tentatively, to a particular family. Some viruses cause disease in wild and captive hosts, others are associated with disease states but may not be primary instigators, and many occur in apparently normal animals. The frequency of viral disease in natural populations of marine invertebrates is unknown. Several viruses that cause disease in captive animals, with or without experimental intervention, have also been found in diseased wild hosts, including herpeslike viruses of crabs and oysters, iridovirus of octopus, and reolike and bunyalike viruses of crabs. Iridolike viruses have been implicated in massive mortalities of cultured oysters. Baculoviruses, and IHHN virus, which is of uncertain affinities, cause economically damaging diseases in cultured penaeid shrimp. Double or multiple viral infection is common in crabs. For example, a reolike virus and associated rhabdolike virus act synergistically to cause paralytic and fatal disease inCallinectes sapidus. Information on host range, most susceptible stage, and viral latency is available only for viruses of shrimp. One baculovirus attacks five species of New World penaeid shrimp. IHHN virus infects three species ofPenaeus and causes catastrophic mortalities inP. stylirostris, but usually exhibits only inapparent infection inP. vannamei. Some shrimp viruses apparently are latent in larvae, causing disease only when shrimp have reached the postlarval or juvenile stages. Others are equally or more pathogenic in larvae. Studies of shrimp viruses and iridovirus-associated disease in cultured oysters point up the need for rapid and accurate diagnostic methods. Until appropriate cell cultures from marine invertebrates are devised, the viral identifications necessary for understanding of epizootiology, rapid containment of epizootics in cultured animals, and decisions regarding introductions of exotic species will be difficult or impossible.

Thermal dependence of contractile properties of single skinned muscle fibres from Antarctic and various warm water marine fishes including Skipjack Tuna (Katsuwonus pelamis) and Kawakawa (Euthynnus affinis)

Abstract: Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58.

Mitigating Effects of Artificial Riffles and Pools on the Fauna of a Channelized Warmwater Stream

Abstract: The effect of stream channelization on macroinvertebrates, fish, and the sport fishery was studied in the Olentangy River at Columbus, Ohio. Macroinvertebrate abundance, diversity indices, standing stock in the benthos, and drift were significantly lower in a channelized area than in either a natural area or a channelized area mitigated with artificial riffles and pools. Predominant macroinvertebrates were moving-water forms in the natural and mitigated areas, and burrowing forms in the channelized areas. Diversity indices and relative abundance of game fish were significantly lower in the channelized area than in the natural and mitigated areas. However, some nongame species became relatively abundant in the mitigated area when compared to the natural area. Composition of the sport fishing catch and catch rates accurately reflected the predominant fish community in each area. The biota in the area mitigated with artificial riffles and pools was similar to the biota in the natural area.

Zones of coastal hypoxia revealed by satellite scanning have implications for strategic fishing

Abstract: Little is known about the spatial and temporal scales of hypoxic bottom water areas that occur along the inner continental shelf of Texas and Louisiana. Because hypoxia appears to be related to surface chlorophyll and temperature, which can both be measured with the Coastal Zone Color Scanner aboard the Nimbus 7 satellite, an attempt has been made to determine whether conditions favorable for the formation of hypoxia could be detected and monitored from space. A linear discriminant function has identified areas of bottom water hypoxia detected by research vessels up to 10 days after satellite overpass, and predicted hypoxic areas without resort to research vessel data. Such space mapping may be of consequence for marine resource management and exploitation.

Impact of Scallop Harvesting on Eelgrass (Zostera marina) Meadows: Implications for Management

Abstract: Eelgrass (Zostera marina), an important component of estuarine areas from Nova Scotia to North Carolina, is the primary habitat for the economically important bay scallop (Argopecten irradians). The bay scallop fishery in North Caxolina is extensive yet precarious in its dependence on seagrass systems. A balance between habitat integrity and scallop harvest is necessary to sustain the fishery. In this study, we examined the effect of scallop dredging on eelgrass meadows. When the eelgrass was in its vegetative stage, 15 and 30 dredgings were carried out in a hard sand substrate and a soft mud substrate and the results compared to an area of no dredging. Impact was assessed by analyzing the effects of scallop harvesting on eelgrass foliar dry weight and on the number of shoots. The hard bottom had significantly greater overall biomass of eelgrass (P < 0.01, ANOVA) than the soft bottom but fewer differences were apparent for eelgrass shoot density (P < 0.10). Increased dredging led to significantly...

Timing of vertebral-band deposition in tetracycline-injected leopard sharks

Abstract: In late summer 1979, 948 leopard sharks Triakis semifasciata were tagged and released into San Francisco Bay after being injected with the bone-labeling reagent oxytetracycline (OTC). The fluorescent time mark was compared to new growth zones in the vertebral centra of tagged fish recovered over 3 years to determine how often the calcified bands are formed. As of 31 December 1982, 25 vertebral samples were recovered and examined. Although OTC deposition was variable, an intense fluorescent mark was evident in 12 individuals. The results confirm that one opaque (highly calcified) zone and one translucent zone are deposited per year, and that these zones can be used reliably in aging this species within the size group examined. The progression of band formation indicates that opaque zones probably form sometime between May and September. Received July 22, 1983 Accepted March 18, 1984

The sexuality of tropical deepwater shrimps (decapoda: pandalidae)

Abstract: Morphometric studies were carried out as part of resource assessment surveys on deepwater pandalid shrimps in both the northern and southern tropical Pacific Ocean. Previous works have suggested that pandalid shrimps, including those of some tropical species, are typically protandrous hermaphrodites. In this study, however, measurements of certain male secondary sexual characteristics were positively correlated with shrimp size. There was no evidence of degeneration of these characteristics in larger individuals as would be expected with protandrous hermaphrodites. We conclude that shrimps of the tropical pandalid species examined are dioecious and that sex reversal does not occur. Sex reversal in pandalid shrimps was first noted in Pandalus danae (Berkeley, 1929) and, since that time, has been reported for a large number of exploited pandalids from northern temperate waters including P. jordani and P. borealis (Butler, 1964). Butler stated that, with "one or two known exceptions," all pandalid shrimps so far investigated were protandrous hermaphrodites. The usual pattern in hermaphroditic pandalid shrimps is for individuals to mature and function first as males and, at two or three years of age, to change sex and function as females. During the change in sex, the appendices masculinae on the endopods of the second pair of pleopods of the male degenerate during a series of intersex or transitional stages, until these structures are entirely lacking in females. Deepwater pandalid shrimps are also widely distributed in the tropical Pacific Ocean, including Hawaii (Clarke, 1972; Struhsaker and Aasted, 1974), Guam (Wilder, 1977), New Caledonia (Intes, 1978), Fiji (King, in press), Tahiti (Anonymous, 1979), Western Samoa (King, 1980), Vanuatu, west of Fiji (King, 198 la), Tonga (King, 1981b), Papua New Guinea (King, 1982), and the Northern Marianas (Moffitt, 1983). Some species, particularly of the genus Heterocarpus, are found in sufficient abundance to stimulate interest in commercial exploitation (King, 1981c). Shrimps of several of these species including H. ensifer (Clarke, 1972), H. ensifer and H. laevigatus (Wilder, 1977), and H. sibogae and H. laevigatus (King, 1981a) were thought to be protandrous hermaphrodites similar to temperate pandalid species. During studies on the biology and commercial potential of deepwater shrimps in Fiji and the Marianas, at least thirteen different species have been found (Table 1). This paper examines the morphometry and the sexuality of five species which were obtained in sufficient numbers and over a wide size range. The species examined were Plesionika longirostris, H. ensifer, H. sibogae, H. gibbosus, and H. laevigatus in Fiji and P. longirostris, H. ensifer, and H. laevigatus in the Marianas.

Age, Growth, and Mortality of the Little Skate off the Northeast Coast of the United States

Abstract: Age, growth, mortality, and yield per recruit of the little skate Raja erinacea in the Georges Bank-Delaware Bay region were investigated from trawl-survey data collected during 1968–1978. Eight age groups were observed in the population. The parameters of the von Bertalanffy growth equation are asymptotic length L∞ = 52.73 cm; growth coefficient K = 0.352; and hypothetical age at zero length t0 = -0.449 years. The length-weight relationship for both sexes combined over seasons is log10W = -2.641 + 3.229 log10L, where length L is in centimeters and weight W is in grams. Estimates of total instantaneous mortality rates Z for fully recruited ages (age 5 and older) ranged from 0.54 to 1.76 between 1968 and 1978. Natural-mortality values M ranged from 0.4 to 0.5; fishing-mortality values F ranged from 0.14 to 1.36, depending on the value of M assumed. Received May 13, 1983 Accepted March 21, 1984

Zooplankton Feeding Ecology: Contents of Fecal Pellets of the Copepods Acartia tonsa and Labidocera aestiva from Continental Shelf Waters Near the Mouth of the Mississippi River

Abstract: . Feeding habits of adult female Acartia tonsa and Labidocera aestiva and L. aestiva CV copepodites were examined by comparing fecal pellet contents and available phytoplankton. Samples were collected from eight stations in the northern Gulf of Mexico near the mouth of the Mississippi River. Fecal pellets of both copepods contained remains of a wide variety of chain-forming and solitary phytoplankters of various sizes, as well as remains of other crustaceans. Contents of fecal pellets generally mirrored the composition and relative abundance of fluctuating assemblages of available natural phytoplankton. Both species fed upon a wide size range of cells, from solitary centric diatoms of 2–8 um diameter up to large solitary centrics of 33–53 urn diameter. Both copepods also ingested the elongate solitary pennate diatom Thalassiothrix sp. (264–330 urn long) and chain-forming diatoms such as Skeletonema costatum. Remains of large or chain-forming diatoms and crustaceans were more dominant in fecal pellets of L. aestiva. This suggests that L. aestiva is primarily a raptorial feeder, grasping larger particles while A. tonsa is a more typical suspension feeder. Both copepods are opportunistic omnivores, however, and there is considerable overlap in their diets.

Filtering rates of the juvenile Atlantic menhaden Brevoortia tyrannus (Pisces: Clupeidae), with consideration of the effects of detritus and swimming speed

Abstract: From July to September 1982 feeding experiments were conducted with 138-mm fork length Atlantic menhaden Brevoortia tyrannus (Latrobe) (Pisces: Clupeidae) to determine their particle size-specific feeding abilities. Monoculture clearing-rate experiments showed that the minimum size of particles filtered, the minimum size threshold, for 138-mm fish is 7 to 9 μm. Filtration efficiency for three species of phytoplankton below the minimum size threshold. Pseudoisochrysis paradoxa, Monochrysis lutheri, and Isochrysis galbana, averaged 1.0% (n=14). Tetraselmis suecica, Prorocentrum minimum, and 2-celled Skeleionema costatum, phytoplankton which are larger than the minimum size threshold and smaller than the 20-μm upper limit for nanoplankton, were filtered at efficiencies averaging 21% (n=24). S. costatum chains of 3 to 6 cells, prey particles exceeding the size limits of nanoplankton, were filtered at average efficiencies ranging from 22 to 84%. The mean filtration efficiency for Artemia sp. nauplii (San Francisco Bay Brand) of 36% (n=7) was lower than for smaller phytoplankton prey. The presence of detritus at concentrations usually encountered in nature enhanced filtering efficiency and lowered minimum size thresholds at which phytoplankton were retained. For small food particles, filtering efficiency decreased as swimming speed of the menhaden increased. As menhaden grow, their feeding tepertoire shifts to larger planktonic organisms.

Temperature-Induced Changes in Blood Gas Equilibria in the Albacore, Thunnus Alalunga, a Warm-Bodied Tuna

Abstract: Samples of unbuffered, whole blood from freshly-caught albacore (Thunnus alalunga Bonnaterre) were equilibrated at 5, 10, 15, 20, 25, 30 and 35 °C and at 0 and 1 % CO2 for construction of oxygen dissociation curves. A strong Bohr effect (−1.17), a negligible Root effect, and a reverse temperature effect (ΔH = +1.72 for 0% CO2 and +0.26 for 1% CO2) characterized these hyperbolic (Hill9s n = 1.1) curves. The unusual reverse temperature effect was especially pronounced when blood was quickly warmed or cooled, simulating passage through the heat exchanging, countercurrent vascular rete system of this warm-bodied fish. A diagrammatic model of blood gas dynamics in the rete incorporating these in vitro data illustrates protection of arterial oxygen from premature haemoglobin dissociation and consequent loss to the venous circulation as blood warms in the rete. More conventional temperature effects on the carbon dioxide equilibria of albacore blood lower the Pcoco2 of venous blood being cooled in the rete. This reduces the venous-arterial Pcoco2 gradient, thereby minimizing the diffusion of CO2 to arterial blood with resulting haemoglobin-oxygen dissociation via the strong Bohr effect. The temperature range (10–30 °C) over which the albacore haemoglobin-oxygen binding exhibits the reversed thermal effect closely matches the maximum thermal gradient (ambient water-core body temperature) typically present in this fish, suggesting that its highly specialized haemoglobin-oxygen dissociation characteristics evolved within-and now establishes thermal limits upon-the existing geographic distribution of this species.

Zooplankton feeding ecology: contents of fecal pellets of the copepods Temora turbinata and T. stylifera from continental shelf and slope waters near the mouth of the Mississippi River

Abstract: In-situ feeding habits of the copepods Temora turbinata and T. stylifera were investigated by scanning electron microscope examination of fecal pellets, the contents of which reflected copepod gut contents upon capture. Pellet contents were compared with assemblages of available phytoplankton in the water column at the times of zooplankton sampling. Samples were collected in continental shelf and slope waters of the Gulf of Mexico near the mouth of the Mississippi River. Both species ingested a wide size range and taxonomic array of phytoplankters, and to a lesser extent, other crustaceans. Fecal pellets contained primarily the remains of the phytoplankters that were most abundant in the water at times of collection. There was considerable overlap in the food items ingested by adult females of both copepod species, or two stages of T. turbinata copepodites. Thus, T. turbinata and T. stylifera are omnivores, but primarily opportunistic herbivores.