Secondary Productivity Research Articles

Toward an Integration of Landscape and Food Web Ecology: The Dynamics of Spatially Subsidized Food Webs

We focus on the implications of movement, landscape variables, and spatial heterogeneity for food web dynamics. Movements of nutrients, detritus, prey, and consumers among habitats are ubiquitous in diverse biomes and can strongly influence population, consumer-resource, food web, and community dynamics. Nutrient and detrital subsidies usually increase primary and secondary productivity, both directly and indirectly. Prey subsidies, by movement of either prey or predators, usually enhance predator abundance beyond what local resources can support. Top-down effects occur when spatially subsidized consumers affect local resources by suppressing key resources and occasionally by initiating trophic cascades. Effects on community dynamics vary with the relative amount of input, the trophic roles of the mobile and recipient entities, and the local food web structure. Landscape variables such as the perimeter/area ratio of the focal habitat, permeability of habitat boundaries, and relative productivity of trophically connected habitats affect the degree and importance of spatial subsidization.

CLIMATE CHANGE, HURRICANES AND TROPICAL STORMS, AND RISING SEA LEVEL IN COASTAL WETLANDS

Global climate change is expected to affect temperature and precipitation patterns, oceanic and atmospheric circulation, rate of rising sea level, and the frequency, intensity, timing, and distribution of hurricanes and tropical storms. The magnitude of these projected physical changes and their subsequent impacts on coastal wetlands will vary regionally. Coastal wetlands in the southeastern United States have naturally evolved under a regime of rising sea level and specific patterns of hurricane frequency, intensity, and timing. A review of known ecological effects of tropical storms and hurricanes indicates that storm timing, frequency, and intensity can alter coastal wetland hydrology, geomorphology, biotic structure, energetics, and nutrient cycling. Research conducted to examine the impacts of Hurricane Hugo on colonial waterbirds highlights the importance of long-term studies for identifying complex interactions that may otherwise be dismissed as stochastic processes. Rising sea level and even modest changes in the frequency, intensity, timing, and distribution of tropical storms and hurricanes are expected to have substantial impacts on coastal wetland patterns and processes. Persistence of coastal wetlands will be determined by the interactions of climate and anthropogenic effects, especially how humans respond to rising sea level and how further human encroachment on coastal wetlands affects resource exploitation, pollution, and water use. Long-term changes in the frequency, intensity, timing, and distribution of hurricanes and tropical storms will likely affect biotic functions (e.g., community structure, natural selection, extinction rates, and biodiversity) as well as underlying processes such as nutrient cycling and primary and secondary productivity. Reliable predictions of global-change impacts on coastal wetlands will require better understanding of the linkages among terrestrial, aquatic, wetland, atmospheric, oceanic, and human components. Developing this comprehensive understanding of the ecological ramifications of global change will necessitate close coordination among scientists from multiple disciplines and a balanced mixture of appropriate scientific approaches. For example, insights may be gained through the careful design and implementation of broad-scale comparative studies that incorporate salient patterns and processes, including treatment of anthropogenic influences. Well-designed, broad-scale comparative studies could serve as the scientific framework for developing relevant and focused long-term ecological research, monitoring programs, experiments, and modeling studies. Two conceptual models of broad-scale comparative research for assessing ecological responses to climate change are presented: utilizing space-for-time substitution coupled with long-term studies to assess impacts of rising sea level and disturbance on coastal wetlands, and utilizing the moisture-continuum model for assessing the effects of global change and associated shifts in moisture regimes on wetland ecosystems. Increased understanding of climate change will require concerted scientific efforts aimed at facilitating interdisciplinary research, enhancing data and information management, and developing new funding strategies.

Secondary productivity (3H-leucine and 3H-thymidine incorporation), abundance and biomass of the epiphytic bacteria attached to detritus of Typha domingensis pers. in a tropical coastal lagoon

Senescent, naturally dried leaves of Typha domingensis were incubated inthe littoral region of a coastal lagoon and epiphytic bacterial volume,abundance, biomass and secondary productivity were measured during 127 daysof decomposition. The peak of cell abundance was registered at t =127 days when expressed per leaf surface area (10.07×107cells cm-2; 7.26 µgC cm-2), and at t= 26 days when expressed per biofilm dry mass (38.10 ×107 cells (mgDM biofilm)-1, 30.52 µgC(mgDM biofilm)-1). The highest values of bacterial biovolumesand lower turnover time were usually obtained in the beginning of thecolonization. Leu:Tdr ratios were also higher in the beginning of thecolonization, when bacterial community presented unbalanced metabolism.Consequently, the highest discrepancies between the bacterial secondaryproduction estimated by leu and Tdr incorporation were observed in the first2 days of decomposition. On average, the bacterial secondary productivityestimated by leu incorporation was 2.1 times higher than the valuesestimated by Tdr incorporation when the empirical factor for Tdr wasobtained from the relationship between Tdr and biomass increment. Thisdifference increased to 4.2 when the empirical factor was obtained from therelationship between Tdr and cell numbers increment. An average of bothmethods (0.0037 to 0.1397 µgC cm-2 h-1)produced results that fall within the range reported in the literature forepiphytic bacteria of freshwater ecosystems.

Annual cycle of autotrophic and heterotrophic production in a small, monomictic Piedmont lake (Lake Oglethorpe): Analog for the effects of climatic warming on dimictic lakes

Lake Oglethorpe, Georgia, is a small, monomictic impoundment in the southeastern U.S. Piedmont region. Seasonal differences in ecological processes correspond to the two major stratification patterns and result in seasonal differences in pelagic community structure. The winter mixed period (November–March) provides light and temperatures suitable for active nutrient regeneration and uptake, population growth of edible phytoplankton and crustacean zooplankton, and low bacterial abundance and production. Monthly estimates of daily primary productivity are in the mesoeutrophic range (40–1,420 mg C m‒2 d‒1); however, mean annual primary productivity is in the eutrophic range (500 mg C m‒2 yr‒1) because of greater activity in winter and an extended “growing season.” The stratified period (April–October) is characterized by rapid development of hypolimnetic anoxia, high bacterial production, cyanobacteria and large algae, heterotrophic flagellates, ciliates, rotifers, small cyclopoid copepods, and Chaoborus. Heterotrophic activity, HPLC chlorophyll a, and grazer activity were highest at the epilimnetic‐metalimnetic boundary. Bacterial abundances (1.5–32 × 106 cells ml‒1) increased in the hypolimnion during the stratified period. Long‐term (1978–1994) warming within the water column (0.061–0.10°C yr‒1) follows midwinter (January) air temperature trends. Using Lake Oglethorpe as an analog, we predict as consequences of climatic warming in northern dimictic lakes: increases in nutrient cycling rates, winter primary and secondary productivity, summer heterotrophic production, and microbial components of the food web.

The Promise And Problems of Enhanced Oil Recovery Methods

Abstract Enhanced oil recovery (EOR) methods are outlined in a systematic and balanced manner, and the current impact of these methods is assessed in light of field experience. The main EOR methods are described briefly, their current status is described, and the reasons for the lack of success are examined. The paper does not rely on voluminous statistics, nor does it give another set of screening criteria. Rather it develops the process discussion in terms of mobility ratio and capillary number. Successful EOR methods such as SAGD are modifications of standard methods to unusual reservoir conditions. Certain EOR methods, such as chemical floods, have inherent limitations, explaining the lack of success in the field in contrast to laboratory. Introduction Primary oil recovery can vary from zero to over 50% of the original oil in place (OOIP), depending on the type of hydrocarbon and the reservoir drive. Primary recovery from oil sands is zero, whereas that for a water drive in a light oil reservoir can reach 50%, or even more in the case of an efficient gravity drive. Secondary recovery is usually taken to mean waterflooding, and can again vary from zero (oil sands) to a few per cent (heavy oils) to 20 - 50% of the initial oil in place (IOIP) for a light oil. Enhanced oil recovery usually implies recovery beyond the secondary stage. In the case of very viscous oils and oil sands, with little or no primary and/or secondary productivity, EOR may refer to the recovery techniques employed from the start. We are thus concerned with a whole range of unconventional-usually costly oil recovery methods, only a few of which have been shown to be commercially successful, under favourable conditions. Improved oil recovery (IOR) sometimes signifies measures taken during-not after-the primary and secondary stages to increase oil recovery. This is often the case in offshore oil reservoirs where the economics would not permit operation beyond the secondary stage. As the conventional oil reserves in U.S.A. and Canada decline, EOR is gaining increasing importance. The extensive survey published every two years by the Oil & Gas Journal (Moritis(l)) shows that the EOR production in Canada and U.S.A. is about 25% and 10%, respectively, of the total oil production, and is increasing. Table 1, based on the survey, gives the oil production rates for various EOR method, for 1994. Miscible displacement is the dominant recovery method in Canada, with steam injection gaining fast. The latter is the principal recovery method in U.S.A., with miscible carbon dioxide flooding a distant second. In Canada, steam injection will continue to increase in importance, as the heavy oil/bitumen resources are exploited. In U.S.A., steam is limited to California heavy oil reservoirs, and carbon dioxide flooding to areas with inexpensive sources. Chemical flooding methods have declined with the drop in oil prices over the last decade. These methods have the promise of recovering oil from depleted light oil reservoirs. Hundreds of EOR projects are being operated. Many are experimental.

Estimation of the biomass production of Artemia with regard to its use in aquaculture: Temperature and strain effects

Secondary productivity was estimated for one sexual species of the brine shrimp Artemia (Artemia tunisiana) and for two inland and two coastal parthenogenetic diploid and polyploid strains ( Artemia parthenogenetica), reared in semi-intensive cultures under different natural temperature conditions. Standing biomass and productivity were affected by temperature conditions, mode of reproduction, ploidy level and habitat temperature characteristics. At high temperatures (24–30 °C), diploid and polyploid parthenogenetic Artemia strains attained the highest biomass values and productivity of the coastal parthenogenetic diploid strain was 13 times higher than that of polyploids. Differences between the inland and coastal parthenogenetic diploid strains studied may be due to genetic adaptation to habitat temperature conditions. At low temperatures (under 15 °C) only the sexual species survived, and its production values were ten times lower than those of polyploid strains during spring and summer. Productivity was directly related to standing biomass and inversely related to individual biomass. On the basis of these results, an empirical model to predict Artemia productivity from biomass and individual dry weight data is proposed. This study provides useful information for the selection of the most suitable non Artemia franciscana strains to introduce in salterns from the Old World with a given temperature regime and it also supplies practical guidelines for the easy determination of Artemia productivity.

“Seamount effects” in the zooplankton community near Cobb Seamount

Oceanic seamounts often support large nektonic stocks. Since the mid-1950s it has been believed that this high productivity results, in part, from biological response to the physical interaction between oceanic currents and the abrupt topographic profiles represented by most seamounts. The “classic theory” for the production/maintenance of seamount nektonic stocks suggests that (i) the combination of localized upwelling and the trapping/concentrating action of closed anticyclonic vortices (i.e. Taylor cones) enhance local primary production, (ii) thereby promoting local secondary productivity that, (iii) supports local nektonic populations. Here we test one element of this theory: whether proximity to a shallow seamount is associated with changes in zooplankton abundance and species composition. Zooplankton samples were collected near Cobb Seamount, a shallow (< 100 m) northeast Pacific seamount 50-km west of Vancouver Island. Both upwelling and closed recirculations occur at Cobb Seamount, but the latter is confined to depths > 100 m and is not an effective retention mechanism. Total zooplankton abundance did not vary significantly on- versus off-seamount. However, using a variety of nonparametric multivariate techniques we demonstrate that a “seamount effect” on zooplankton-community composition is detectable up to 30 km from the seamount summit. This effect is superimposed on (and locally much stronger than) the expected slow decline in resemblance as between-sample geographic distance increases. Possible mechanisms by which this effect operates include: differential growth or reproduction, differential mortality and behavioral or migratory effects. The on-off seamount differences are accounted for largely by the increased relative abundances of two fast-growing opportunists, doliolids ( Dolioletta sp) and larvaceans ( Oikopleura sp.), near Cobb Seamount. Predation pressure from seamount fish and active avoidance of the seamount by zooplankton may also play a role in generating the seamount effect. The absence of an effective trapping mechanism and the fact that total zooplankton abundance does not increase near the seamount lead us to conclude that the bottom-up model of localized energy transfer proposed under the “classic hypothesis” is incorrect for Cobb Seamount: nektonic stocks at Cobb Seamount (and, possibly, other shallow seamounts) are more likely supported by flow-through (i.e. advected) rather than local production.

Silicone-stimulated anthraquinone production and release by Morinda citrifolia in a two-liquid-phase system

A 2.5-fold increase in the release of intracellular anthraquinones was obtained by adding 1 ml L-1 silicone A to suspension cultures of Morinda citrifolia. Cell growth and secondary metabolite production were not affected even at high silicone A concentrations. Performance of the silicone treatment in a two-liquid-phase system (5 ml n-hexadecane/50 ml medium) resulted in a 150% increase of the overall secondary metabolite productivity.

Linking Marine and Terrestrial Food Webs: Allochthonous Input from the Ocean Supports High Secondary Productivity on Small Islands and Coastal Land Communities

This study quantifies the flow of energy and biomass from a productive marine system to a relatively unproductive terrestrial system. Biomass from marine food webs (here, the Gulf of California) enters the terrestrial webs of islands and coastal areas through two conduits: (1) shore drift of algal wrack and carrion and (2) colonies of seabirds. Both conduits support dense assemblages of consumers: arthropods are 85-560 times more abundant in the supralittoral than inland and 2.2 times more abundant on islands with seabird colonies than those without. Marine input (MI), not terrestrial primary productivity (TP) by land plants, provides most energy and biomass for terrestrial communities on 16 of 19 study islands. The ratio of perimeter to area (P/A) significantly predicts arthropod abundance on islands and is the major determinant of the relative importance of allochthonous flow; we expect P/A ratio to be important wherever transport of nutrients, detritus, and organisms among habitats occurs. Similar transport phenomena generally take place, often with significant impact, on coastal habitats and islands worldwide. Such input subsidizes a diverse array of terrestrial consumers; in many cases, subsidized consumers reach extraordinarily high densities and thus can depress their in situ resources. In general, we propose that such flow is often a key feature of the energetics, structure, and dynamics of populations, food webs, and communities whenever any two habitats, differing in productivity, are juxtaposed.

Scale-dependent correlation of sperm whale distribution with environmental features and productivity in the South Pacific

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 135:1-9 (1996) - doi:10.3354/meps135001 Scale-dependent correlation of sperm whale distribution with environmental features and productivity in the South Pacific Jaquet N, Whitehead H The purpose of this study was to investigate sperm whale Physeter macrocephalus distribution in relation to underwater topography, temperature gradients and primary and secondary productivity. The influence of these factors over different spatial scales (80 to 640 nautical miles) was examined, and the importance of food resources in determining sperm whale distribution was assessed. The data were collected during a survey around the South Pacific. Principal component analyses were used to assess the relationship between the environmental measures recorded and to relate them to sperm whale density. The first principal component was considered as an index of secondary productivity, the second as an index of underwater topography, and the third as a contrast between deep and surface productivity. Sperm whale density was correlated with the first and the second principal components over spatial scales equal to or greater than 320 n miles. This result indicates that sperm whales are generally distributed within large areas which are characterized by high secondary productivity and steep underwater topography. The size of these areas may reflect the distances over which the groups of whales move in search of food. The absence of correlation over smaller spatial scales suggests that factors other than the distribution of food resources also influence sperm whale distribution over these scales. Sperm whale . Distribution . Spatial scale . Temporal scale . Principal component analyses . Chlorophyll concentration . Sub-surface biomass . Underwater topography Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 135. Publication date: May 17, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Changes in fish populations affected by the construction of the La Grande complex (Phase I), James Bay region, Quebec

Catches per unit of effort (CPUE) with experimental gill nets, recruitment, growth, and condition were monitored between 1977 and 1992 to evaluate the impact of impoundment on the main fish species of La Grande 2, Opinaca, and Caniapiscau reservoirs and the Boyd–Sakami diversion. CPUE and recruitment of northern pike (Esox lucius) and lake whitefish (Coregonus clupeaformis) increased markedly at most stations after impoundment and decreased at the end of the series. The lake whitefish and cisco (Coregonus artedii) showed their most striking rise in CPUE at two bay stations of La Grande 2 and Opinaca reservoirs. CPUE and recruitment of the longnose sucker (Catostomus catostomus), white sucker (Catostomus commersoni), and lake trout (Salvelinus namaycush) (Caniapiscau) showed a general decrease following impoundment. CPUE for the walleye (Stizostedion vitreum) also decreased at several stations; however, the two most southerly stations in La Grande 2 reservoir and the Boyd–Sakami station showed high CPUE during the series. Concentration–redistribution phenomena explain part of the observed variations in CPUE. Correlation analyses showed that walleyes and white suckers were attracted to the warmer, more turbid stations, and that the high primary and secondary productivity of bay stations attracted the coregonines. Growth and condition of the main species increased during variable time intervals after impoundment and decreased at the end of the series.

Atrazine Impacts on Shortgrass Prairie Microcosms

Alterations in shortgrass ecosystem structure and function following long-term use of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3, 5-triazine,2,4-diamine] for increased secondary productivity raised concerns about sustainability of the practice. A microcosm approach was designed to 1) model the direction and temporal features of blue grama [Bouteloua gracilis H.B.K.) Lag. ex Steud.] biomass accumulation and tissue N, nitrate reductase activity, chlorophyll, total nonstructural carbohydrate, and phosphorus (P) levels following atrazine applications of 0.84 and 2.24 kg ha-1 and hydroxyatrazine (6-hydroxy-N-ethyl-N'-(1-methylethyl)-1,3, 5-triazine,2,4,-diamine) at 1.12 kg ha-1, and 2) to relate plant growth and metabolism changes to possible short- and long-term modifications of soil microbial abundance and activities associated with C and N transformations. Atrazine applied to dormant plant-soil microcosms reduced below-ground (crown plus root) biomass and shoot total nonstructural carbohydrate levels during regrowth. Atrazine application increased shoot chlorophyll content, N levels, and nitrate reductase activity, but not total plant N content. Decreased below-ground biomass accumulation, and increased shoot N and nitrate reductase activity levels were linked to decreased total nonstructural carbohydrate availability. Total plant P levels were highest at the intermediate atrazine rate. Differences in soil microbial biomass and activities, and chemical properties resulted primarily from presence of blue grama and duration of plant regrowth. Soil nitrifying activity was depressed in soil previously exposed to atrazine whether or not blue grama was present. Hydroxyatrazine was not identified as an important factor in observed plant or soil changes. Atrazine may alter shortgrass system structure and function by immediate impacts on primary producers and long-term impacts on soil microbial processes.

The South Channel Ocean Productivity EXperiment

The South Channel Ocean Productivity EXperiment (SCOPEX) was a multidisciplinary study of a whale-zooplankton predator-prey system in the southwestern Gulf of Maine, focusing on the oceanographic factors responsible for the development of dense patches of the copepod Calanus finmarchicus, which comprise the major prey resource for right whales ( Eubalaena glacialis). Three non-mutually exclusive hypotheses underlay the study: patch development is due to (1) extremely high in situ primary and secondary productivity; (2) large numbers of Calanus advected into the region and concentrated by hydrographic processes; and/or (3) a behavioral tendency of the copepods themselves to aggregate. The results confirmed the cooccurrence of right whales with high density Calanus patches, and also demonstrated that right whales fed on patches with higher proportions of larger lifestages. The physical oceanographic studies supported the advection hypothesis, possibly augmented by a tendency of Calanus to aggregate, but there was little evidence to support the productivity hypothesis.

Desertification of subtropical thicket in the Eastern Cape, South Africa: Are there alternatives?

The Eastern Cape Subtropical Thicket (ECST) froms the transition between forest, semiarid karroid shrublands, and grassland in the Eastern Cape, South Africa. Undegraded ECST forms an impenetrable, spiny thicket up to 3 m high consisting of a wealth of growth forms, including evergreen plants, succulent and deciduous shrubs, lianas, grasses, and geophytes. The thicket dynamics are not well understood, but elephants may have been important browsers and patch disturbance agents. These semiarid thickets have been subjected to intensive grazing by domestic ungulates, which have largely replaced indigenous herbivores over the last 2 centuries. Overgrazing has extensively degraded vegetation, resulting in the loss of phytomass and plant species and the replacement of perennials by annuals. Coupled with these changes are alterations of soil structure and secondary productivity. This rangeland degradation has largely been attributed to pastoralism with domestic herbivores. The impact of indigenous herbivores differs in scale, intensity, and nature from that of domestic ungulates. Further degradation of the ECST may be limited by alternative management strategies, including the use of wildlife for meat production and ecotourism. Producing meat from wildlife earns less income than from domestic herbivores but is ecologically sustainable. The financial benefits of game use can be improved by developing expertise, technology, and marketing. Ecotourism is not well developed in the Eastern Cape although the Addo Elephant National Park is a financial success and provides considerable employment benefits within an ecologically sustainable system. The density of black rhinoceros and elephant in these thickets is among the highest in Africa, with high population growth and the lowest poaching risk. The financial and ecological viability of ecotourism and the conservation status of these two species warrant expanding ecotourism in the Eastern Cape, thereby reducing the probability of further degradation of ECST.

Discrimination and open unemployment in a segmented labour market

Jobs in the primary sector require firm-specific training, with wages determined as a result of bargaining. Firms pay for the training and since they are imperfectly informed about worker productivity, they test workers before hiring them. The secondary sector is competitive. Taking a job in the secondary sector signals low productivity, and therefore workers in the secondary sector are unable to get jobs in the primary sector. Open unemployment coexists with unfilled vacancies for low wage jobs.

Ecomethodology for organoosmotrophs: Prokaryotic unicellular versus eukaryotic mycelial

Although they are very unlikely to play large direct roles in water-column microbial loops, eukaryotic mycelial decomposers (the mycelial true fungi, eumycotes, and zoosporic "fungi," oomycotes) have the potential to be important secondary producers in decaying plant material in shallow aquatic systems. Their secondary productivity may lead to important exchanges of material with microbial loops: output of ascospores, conidia, zoosporic flagellates, leaked lysates, and particles of decayed plants containing mycelium; input of dissolved organics and inorganic nutrients. Development of methods for ecological study of the aquatic mycelial eukaryotic decomposers has not advanced as rapidly as that for the prokaryotes of microbial loops, probably because (1) there are fewer aquatic microbial ecologists with mycological training and inclination than with prokaryotic leanings; and (2) the mycelial decomposers are difficult to work with, because they produce their mycelial mass virtually entirely within opaque solid substrates. Direct microscopic methods have emerged as prime tools for the measurement of prokaryotic mass, whereas an index-chemical assay (ergosterol) is currently the most efficient way to measure the mass of eumycotes. For measuring productivity of prokaryotes of microbial loops, microbial ecologists may choose from several (>10) published and field-tested methods, involving direct microscopy or monitoring of radiotracers. Extensive reviews of distribution and dynamics of aquatic bacterial mass and productivity have appeared. For measuring productivity of eukaryotic mycelial decomposers, one has only two published methods from which to choose, a direct-microscopic and a radiotracer method, neither of which has had adequate field testing. We are, furthermore, much less well equipped to obtain mass and productivity information for the poorly known mycelial oomycotes than we are for the eumycotes. Application of productivity techniques and nucleic-acid technology, may within the next decade allow knowledge of ecology of aquatic eukaryotic mycelial decomposers to advance to levels approaching that for the prokaryotes of microbial loops.

Effects of graveling on the primary productivity, respiration and nutrient flux of two estuarine tidal flats

This study was conducted in Puget Sound, USA, and investigated the effect of graveling intertidal mud and sandflats to enhance clam production on the benthic assemblage structure, primary productivity, respiration, and nutrient flux. The study was conducted between spring and autumn (1991), the period of greatest productivity and plant standing stock in Puget Sound. Graveled and control plots were established in the low intertidal zone on a mud flat in a protected embayment (Chapman Cove) and an exposed sandflat (Semiahmoo Bay). Gravel altered benthic assemblage structure, respiration, and nutrient flux rates. Graveled plots contained more surface coverage of sessile animals and seaweeds. Net productivity (NP), which differed relatively little between graveled and control plots, was negative for all but one sampling at the protected embayment plots. In contrast, NP was always positive at the exposed sandflat plots. The respiration rate was 13 to 57% greater in the graveled plot at Chapman Cove than in the adjacent control plot, and 7 to 54% greater in the gravel plot than the control plots at Semiahmoo Bay. Heterotrophy was greater in the graveled plots, as reflected by a lower net productivity to respiration ratio. Effects of graveling on water quality parameters such as dissolved oxygen and inorganic nitrogen concentrations were not detected. Graveling sandy and mud beaches increases secondary productivity, which is associated with increased rates of remineralization and release of dissolved nutrients to the water column.

Isotopic tracers of nitrogen from atmospheric deposition to coastal waters

Nitrogen deposition to global oceans from the atmosphere can be about two times that of natural riverine input [see Duce et al. (1991) for recent comprehensive review]. Even accounting for the increased loading of riverine nitrogen by anthropogenic inputs, total atmospheric deposition (AD) is essentially equal to that of riverine sources. Among growth-limiting nutrients, nitrogen plays a key role in regulating primary and secondary productivity both on regional and global scales (e.g., Ryther and Dunstan, 1971; Nixon et al., 1986). As such, proper identification and characterization of nitrogen sources and their impacts on nutrient flux and trophic utilization is of prime concern in understanding biogeochemical responses in coastal ecosystems (Eppley and Peterson, 1979; Paerl, 1985; Legendre and Gosselin, 1989). AD represents a quantitatively-important, but poorly assessed, nitrogen source in these ecosystems (Paerl, 1985; Fisher et al., 1988; Prado-Fiedler, 1990; Loye-Pilot et al., 1990). Current estimates indicate that from 20% to as much as 50% of annual nitrogen loading is attributable to AD alone in geographically-diverse coastal regions, including those along the U.S. Eastern Seaboard (Fisher et al., 1988 ). Even among large bodies of water such as the Baltic and Mediterranean Seas, AD constitutes a highly-significant N source (PradoFiedler, 1990; Loye-Pilot et al., 1990). In North Carolina's adjacent coastal Atlantic waters, AD is a major source (35-80%) of new nitrogen. Assumptions for this type of calculation include the following: ( 1 ) advective input of N from Gulf Stream is very low; ( 2 ) no upwelling is occurring; and (3) N2 fixation accounts for no more than 10% of new N inputs. Here, AD has been shown to significantly stimulate primary production by as much as 50-200% at natural input levels (Paerl, 1985; Paerl et al., 1990). The need to have a more detailed understanding of the impacts of AD of nitrogen in coastal waters is pressing, because previouslypristine segments of the coastal oceans are now exhibiting both incipient and advanced stages of eutrophication. Nitrogen from AD may be a unique nutrient source in the coastal zone for two reasons. Firstly, direct surface water deposition, as wet and dryfall, frequently occurs downstream of oligoand mesohaline estuarine nutrient stripping regions that assimilate a majority ofterrigenous N inputs (Boynton et al., 1982; Sharp et al., 1984). In shallow coastal areas, such as those present along the mid-Atlantic states, dilution of AD is minimized, which amplifies its importance as a new nitrogen source. Secondly, AD is highly dynamic in terms of the magnitudes of dissolved inorganic nitrogen (DIN) and dissolved organic nitro-

Ecology of macrobenthos in the shallow coastal areas of Tewalit (Massawa), Ethiopia

The ecology of the macrobenthos was investigated around the shallow coastal area of Tewalit (Massawa), at three sites from October 1986 to April 1987. A total of 43 taxa and 8 major groups were encountered. Polychaetes were most abundant. Depth, sediment grain size and sediment organic matter content influenced the abundance, distribution and composition of the benthos. Temperature had no effect. The macrobenthos had high species diversity, high biomass diversity and high equatability but no dominance. Quantitatively, seven general associations of macrofauna were identified. Benthic assemblages were not similar between study sites. Faunal biomass was relatively higher than secondary production. Estimated total biomaass over all the study area, was 56.69 g m −2 (dry wt.) and total production was 3.56 g m −2 0.5 year −1. Turnover rate was 0.82. Generally, the Tewalit coastal area is characterized by low secondary productivity.

Interspecific Competition and the Geographical Distribution of Red and Arctic Foxes Vulpes Vulpes and Alopex lagopus

The geographical distribution of red and arctic foxes differ. The hypothesis that this difference results directly from their relative adaptations to extreme cold is evaluated and dismissed. An alternative hypothesis is developed from considerations of body size and biogeographic effects on productivity. This suggests that the northern limit of the red fox's geographic range is determined directly by resource availability (and thus ultimately by climate), whereas the southern limit of the arctic fox's range is determined, through interspecific competition, by the distribution and abundance of the red fox. Predictions from this hypothesis are fulfilled, particularly by data on fur harvests. The argument is extended to other pairs of similar canid species, with the conclusion that equivalent interactions between body size, secondary productivity and direct competition have general relevance to their geographical distributions.