Showing papers in "Marine Ecology Progress Series in 1982"
TL;DR: A strategy is presented for analysing marine biological survey data and relating the biotic patterns to environmental data to avoid circular argument, and the 4 major station groups and species groups are related to one another in terms of morphological adaptation to the habitat.
Abstract: A strategy is presented for analysing marine biological survey data and relating the biotic patterns to environmental data. To avoid circular argument, biotic and environmental data are kept separate. The strategy is illustrated by a worked example using data on the distribution of 182 nematode species in 107 samples in the River Exe estuary. Nineteen stations are grouped Into 4 main clusters using complementary classification and multi-dimensional scaling (MDS) ordination techniques. These are both based on root-root transformed abundance data with the Bray-Curtis measure of similarity. Indicator species characterising each group are extracted using information statistics. Inverse analyses give clusters of co-occurring species which are strongly related to the station groups. Relationships of station groups to environmental variables are revealed by superimposing data for one variable at a time on the MDS plot, showing that some station groups differ in sediment granulometry and others in salinity, for example. Some of the other factors plotted show no difference between station groups. Similarly, physiognomic characteristics of the species are superimposed on the MDS plots of the inverse analysis of species groups, revealing differences in setal length and trophic status between the species groups. Finally, the 4 major station groups and species groups are related to one another in terms of morphological adaptation to the habitat.
1,764 citations
TL;DR: It is concluded that a number of the most successful corals are adapted to fragment, and have incorporated fragmentation into their life histories.
Abstract: Production of new colonies by fragmentation of established colonies is shown to be an extremely important mode of reproduction and local distribution anlong major reef-bu~lding corals. This type of reproduction avoids the high mortality rates of larvae and juveniles and spreads the risk of mortality for the genotype Fragmentation by corals wlth high growth rates results In their domination of certain reef zones, rapid growth of reefs on which these corals are abundant, and rapid recovery from disturbances. I conclude that a number of the most successful corals are adapted to fragment, 1.e have incorporated fragmentation into their life histories
678 citations
553 citations
TL;DR: In this article, it was shown that suspension-feeding bivalves are sufficient to filter a volume equivalent to the volume of South Bay at least once daily, and that grazing by benthos is the primary mechanism controlling phytoplankton biomass during summer and fall.
Abstract: South San Francisco Bay, USA, is a shallow coastal embayment that receives large inputs of nutrients (N. P, Si) and small local inputs of freshwater. Phytoplankton dynamics are typically characterized by a spring bloom when surface chlorophyll a increases from 40 mg m-3. The bloom persists for 2 to 4 wk, and then dissipates. Phytoplankton biomass remains low (chlorophyll a < 5 mg m-3) from May through December, although light and nutrient availability are sufficient to sustain growth rates of 1 to 1.5 divisions d-' in the expansive shallows. Transport processes apparently exert a small influence on phytoplankton biomass, and calculated zooplankton grazing accounts for only a small reduction in net rate of phytoplankton population growth in the shallows. However, suspension-feeding bivalves are sufficiently abundant to filter a volume equivalent to the volume of South Bay at least once daily. These observations suggest that grazing by benthos is the primary mechanism controlling phytoplankton biomass during summer and fall.
522 citations
TL;DR: The importance of the benthic filter feeding community as a natural control on eutrophication is considered in this paper, where the important environmental factors favorable for such a control are relatively shallow water depths and a dense benthically filter feeding commmunity of small animals.
Abstract: The importance of the benthic filter feeding community as a natural control on eutrophication is considered. The important environmental factors favorable for such a control are relatively shallow water depths and a dense benthic filter feeding commmunity of small animals. The criteria are summarized in the equivalence of the water recycling time, t, for the benthic community and the time constant, tp, for phytoplankton growth. The criteria are applied specifically to the conditions that exist in South San Francisco bay.
513 citations
508 citations
TL;DR: The existence of a significant positive relation between nitrogen accumulation and the production of humic substances suggests that much of the nitrogen accumulated during detritus decomposition is non-labile humic nitrogen rather than living microbial protein.
Abstract: Studies of the decompositional chemistry of 5 types of estuarine macrophyte detritus were undertaken to examine relations among detrital nitrogen, protein, and other decompositional products. Protein and nitrogen contents of the detritus correlated poorly. Although the total mass of protein in all detritus decreased after 150 d of aging, there was a net increase in the mass of detrital nitrogen in some vascular plant detritus. During decomposition, detritus becomes richer in reactive phenolic and carbohydrate groups which may form condensation products with amino acids, yielding precursors to complex nitrogenous humic geopolymers. The existence of a significant positive relation between nitrogen accumulation and the production of humic substances suggests that much of the nitrogen accumulated during detritus decomposition is non-labile humic nitrogen rather than living microbial protein. The process of nitrogen enrichment often observed in detritus studies is consistent wlth the chemical behavior of nitrogen during humification. Biological availability of this humic nitrogen probably depends upon the extent to which proteinoid subunits are retained in the humic macromolecular structure.
385 citations
234 citations
TL;DR: In the extent of recovery of photosynthesis after desiccation that intertidal brown algae show the clearest correlation with their heights in the zonation pattern on European shores, the photosynthesis rate of each species after full recovery decreased linearly as water loss increased beyond these values.
Abstract: CO2-exchange of emersed plants and 0,-exchange of submersed plants were measured in 5 species of brown algae from different tidal heights on shores in Ireland and Helgoland (southern North Sea). The photosynthesis of emersed fucoids and Laminaria digitata increased as up to 25 % of tissue water was lost, but then declined with further desiccation. The relationship between decrease in photosynthesis and loss of tissue water was similar in 3 species of Fucus, and the photosynthetic apparatus of F. spiralisappeared to be no more resistant to desiccation than that of F. serratus. Recovery from severe desiccation took about 2 h in all species, regardless of their typical position on the shore, but the extent of recovery from a given degree of desiccation was greater in upper shore species. Pelvetia canaliculata and F. spiralis showed complete recovery from 80 to 90% water loss, F. vesiculosus from about 70 %, F. serratus from 60 %, and Laminaria digitata from 55 % water loss. The photosynthetic rate of each species after full recovery decreased linearly as water loss increased beyond these values. It is in the extent of recovery of photosynthesis after desiccation that intertidal brown algae show the clearest correlation with their heights in the zonation pattern on European shores.
223 citations
199 citations
TL;DR: The ability of Palaemon elegans Rathke, 1937 to regulate internal concentrations of copper, zinc and cadmium has been investigated over a wide range of external metal concentrations.
Abstract: The ability of Palaemon elegans Rathke, 1937 to regulate internal concentrations of copper, zinc and cadmium has been investigated over a wide range of external metal concentrations. Total body concentrations of copper and zinc are regulated on exposure to dissolved metal concentrations up to 100 pg 1-' metal. Exposure to higher levels of dissolved copper and zinc produces an increase in the metal concentration of the shrimps. Body concentrations of copper may increase by a factor of at least 5 times but only twice the normal body concentration of zinc could be tolerated by the shrimps. Cadmium concentrations are not regulated, the body concentration of metal being proportional to the external metal concentration.
TL;DR: The potential application of the REMOTS system for efficient monitoring of dredge-spoil activities and as a reconnaissance mapping tool for detecting change in benthic habitats in the region of outer continental shelf drilling fields is discussed.
Abstract: A benthic successional model allows interpretation of structures observed in sediment profile images. From these structures, temporal and spatial changes can be deduced in both benthic habitat and its associated fauna. The instrument used for in situ remote monitoring is the RhoadsCande profile photographic camera or its updated version, the video REMOTS (Remote Ecological Monitoring Of The Seafloor) system. Sediment profile imaging has been used to characterize an estuarine pollution gradient in Narragansett Bay, Rhode Island and to monitor the 'August Effect' on benthic faunal dynamics in New Haven Harbor, Connecticut (USA). The ability of the profile camera to map rapidly patterns of seafloor disturbance and subsequent faunal change is described for a 1.5 mi2 area near the Thimble Islands. Long Island Sound, Connecticut. We discuss the potential application of the REMOTS system for efficient monitoring of dredge-spoil activities and as a reconnaissance mapping tool for detecting change in benthic habitats in the region of outer continental shelf drilling fields.
TL;DR: In this paper, the authors examined the Great Barrier Reef shelf ecosystem for nutrient enrichment from within the seasonal thermocline of the adjacent Coral Sea using moored current and temperature recorders and chemical data from a year of hydrology cruises at 3 to 5 wk intervals.
Abstract: The Great Barrier Reef shelf ecosystem is examined for nutrient enrichment from within the seasonal thermocline of the adjacent Coral Sea using moored current and temperature recorders and chemical data from a year of hydrology cruises at 3 to 5 wk intervals. The East Australian Current is found to pulsate in strength over the continental slope with a period near 90 d and to pump cold, saline, nutrient rich water u p the slope to the shelf break. The nutrients are then pumped inshore in a bottom Ekman layer forced by periodic reversals in the longshore wind component. The period of this cycle is 12 to 25 d in summer (30 d year round average) and the bottom surges have an alternating onshoreoffshore speed up to 10 cm S-'. Upwelling intrusions tend to be confined near the bottom and phytoplankton development quickly takes place inshore of the shelf break. There are return surface flows which preserve the mass budget and carry silicate rich Lagoon water offshore while nitrogen rich shelf break water is carried onshore. Upwelling intrusions penetrate across the entire zone of reefs, but rarely into the Lagoon. Nutrition is del~vered out of the shelf thermocline to the living coral of reefs by localised upwelling induced by the reefs. Bottom chlorophyll concentrations average 0.4 mg m-3 a t the inner reefs and 0.8 mg m-3 near the shelf break while surface concentrations average 0.3 mg m-3; annual top and bottom variances are respectively 0.5 and 1.9 mg m-3 and there is no apparent seasonal cycle. The estimated onshore nitrogen flux in a 10 m thick bottom layer gives an annual nitrogen input of 20 yg at 1-' throughout the water column in a 50 km zone of reefs, an enormous value for tropical waters.
TL;DR: It is apparent that species responses to disturbance were quite variable and no general pattern of recolonization could be applied to Alewife Cove with respect to seasonality and estuarine position.
Abstract: Responses to disturbance of estuarine infauna were studied to test the hypothesis that seasonality, the estuarine environmental gradient and sediment composition would significantly affect recolonization. The study was conducted in a small estuary located in southeastern Connecticut. USA, using controlled disturbance experiments and sampling of the ambient infauna. Species composition in experimental plots and ambient sediments usually did not differ, either on a seasonal or areal basis. Numerically dominant species usually included the polychaetes Streblospio benedicti, Capitella spp. and Polydora ligni, and the oligochaete Peloscolex gabriellae. Other species included the polychaetes Scoloplos fragilis, Hobsonia florida and Nereis virens, the hemichordate Saccoglossus ko waleski, and the amphipods Microdeutopus gryllotalpa and Corophium insidiosum At times, densities of these species exceeded or were equivalent to dominant species densities in ambient sediments and experimental plots. There were usually significant differences in recolonization and ambient population dynamics due to seasonality and estuarine position. The effects of sediment composition on recolonization patterns of the various species were generally not significant. Seasonal trends in ambient and recolonization species densities were similar, with the highest responses to disturbance in the spring and summer. As ambient densities declined during the fall and winter, responses to disturbance did likewise. On an areal basis, the highest responses to disturbance occurred in the middle and upper portions of the estuary. Ambient densities followed a similar pattern, but peak densities in the early spring (May, 1979) were found in the lower portion of the estuary. Based on differences between ambient and recolonization population densities, only 1 species, Polydora ligni, exhibited a regular opportunistic response. Other species exhibited opportunistic responses, but in only 1 or 2 mo during the study. It is apparent, therefore, that species responses to disturbance were quite variable and no general pattern of recolonization could be applied to Alewife Cove with respect to seasonality and estuarine position. Due to this variation, and the historical component involved in recolonization of disturbed habitats, hypotheses correlating species responses to disturbance with life history adaptations may not be generally applicable to estuarine soft-bottom communities.
TL;DR: Using a modification of the log-normal distribution of individuals among species a new method is proposed which can be used to isolate objectively groups of species sensitive to pollution effects.
Abstract: Isolation of groups of species indicative of pollution-induced effects on benthic communities has traditionally been based on subjective ecological expertise. A review of more general methods covering the use of diversity indices, computer based multivariate analyses is glven. The conclusion drawn is that there are many drawbacks with these methods too and their so-called 'objectivity' is questioned. Using a modification of the log-normal distribution of individuals among species a new method is proposed which can be used to isolate objectively groups of species sensitive to pollution effects. An example is drawn from a time-series study on effects of organic enrichment on a soft-sediment community. The method suggested has a sound theoretical base, is simple to plot, utilizes all the data on individuals and species in a community and identifies groups of species that can be used in reduced scale monitoring programmes.
TL;DR: Results indicate that larval herring select prey according to type as well as size and that this behavior is acquired through experience.
Abstract: The hypothesis that larval herring Clupea harenyus select food by type as well as size was tested in laboratory experiments. Herring larvae were reared at 7 to 9'C on wild zooplankton. The percentage of herring larvae with food at day's end increased from 4 % (4 d) to 68 % (9 d) and averaged 83 % for larvae 25 to 74 d old. Larval herring selected particles according to type as well as size; this selectivity varied with larval age and hence size. Copepod nauplii and copepodites were preferred by larvae of all sizes. Among copepodites, Pseudocalanus sp, and Oithona sp. were preferred by smaller and larger larvae, respectively, while Acartia sp. was rarely ingested, even when of acceptable size. Mollusc veligers comprised a significant portion of the diet of young (4 to 24 d) larvae but were actively rejected by older larvae even when perceived and of acceptable size. Particles smaller than the largest acceptable size were consistently preferred, atypical of predation by vertebrates. These results indicate that larval herring select prey according to type as well as size and that this behavior is acquired through experience.
TL;DR: Most grassbed fishes were adapted to extreme seasonal changes in habitat and this adaptation was reflected in observed temporal changes in diet and would explain the difficulty of making direct, linear associations of population distribution with multivariate analyses of specific habitat characteristics.
Abstract: A long-term (8-y) field study was made concerning the trophic relationships of fishes that occupy shallow coastal grassbeds in the northeast Gulf of Mexico. Various populatlons migrate into such areas to nursery during portions of their life histories. Many fishes undergo seasonal progressions of food preferences that follow species-specific, ontogenetic patterns. While the extent of such dietary successions varies considerably among the 14 species examined, many populations follow developmental progressions that may encompass various trophic levels from herbivory to carnivory. Omnivores are relatively common in the grassbed areas and there was a range of trophic specialization among the fishes examined. Generalized food preferences were often associated with early growth stages; as they matured, various populations became more specialized in their feeding habits Through treatment of each developmental stage of trophic preference as an individual entity (or 'ontogenetic trophic unit'), it was possible to identify progressions of feeding organization through time. Varying levels of temporal partitioning of food resources were evident. Periodic interspecific overlap of food resources was noted during periods of high productivity. Most grassbed fishes were adapted to extreme seasonal changes in habitat. This adaptation was reflected in observed temporal changes in diet and would explain the difficulty of making direct, linear associations of population distribution with multivariate analyses of specific habitat characteristics. The use of the 'ontogenetic trophic unit' facilitated the examination of the relationships of complex associations of fishes to a h ~ g h l y variable environment.
TL;DR: The large patches of vegatation in the surf-zone of sandy beaches support densities of A. compressa up to a mean of 110 g-' dry wt vegetation and provide an alternative feeding habitat for these benthic feeders, one of which is restricted to estuaries in other regions of Australia.
Abstract: The feeding ecology and seasonal pattern of occurrence of the 0 + year classes of the fish Aldrichetta forsteri, Cnidoglanis macrocephalus, Sillago bassensis, and Arripis georgianus were investigated to determine relationships between these economically important species and surf-zone accumulations of detached macrophytes along the coast of Western Australia. The main prey of A. forsteri, C. macrocephalus and A. georgjanus and the second most important prey of S. bassensis was the arnphipod Allorchestes cornpressa; the distribution of A. compressa was restricted to detached plants in the surf-zone. The arrival in winter, of 3 of the fish species on the open coast corresponded with the period of greatest deposition of detached plants in the nearshore zone, and there appeared to be sufficient plant material, and associated amphipods, to support fish during summer. The large patches of vegatation in the surf-zone of sandy beaches support densities of A. compressa up to a mean of 110 g-' dry wt vegetation and provide an alternative feeding habitat for these benthic feeders, one of which is restricted to estuaries in other regions of Australia. I t is also likely that this vegetation provides shelter from potential predators such a s diving birds and larger fish.
TL;DR: It is apparent that estuarine succession can be quite varidble and that re-establishment of community structure may occur over various time scales, with classification analysis of similarity between ambient and successional community structure indicated that recovery to ambient conditions occurred rapidly in the lower reach while successional changes in the middle and upper basins continued at least until the end of the winter.
Abstract: Infaunal successional patterns in Alewife Cove, a small estuary in southeastern Connecticut, USA, varied significantly seasonally and along the estuarine environmental gradient. Each study site exhibited different patterns of change in species composition and abundance. However, suites of species found during success~on did not differ greatly from those found in ambient sediments. Species w h ~ c h exhibited the most variable population changes during succession were numerically dominant tubiculous polychaetes (Streblospro benedicti, Capitella spp., Polydora ljgni], and an oligochaete (Peloscolex gabriellae). Other species which exhibited significant activity were the polychaetes Scoloplos fragilis, Hobsonia florida and Nereis virens, the hemichordate Saccoglossus kowaleski, and the amphipods Microdeutopus gryllotalpa and Corophium insidiosum. At certain times, densities of these species exceeded or were equivalent to dominant species densities in ambient sediments and experimental plots. Timing of disturbance greatly influenced succession Succession after an early spring disturbance was characterized by peak species dens~t ies and numbers. Succession following a fall disturbance was abbreviated with few species at low densities, while after a summer disturbance intermediate trends were found. Classification analysis of similarity between ambient and successional community structure indicated that recovery to ambient conditions occurred rapidly in the lower reach (14 to 30 d ) , while successional changes in the middle and upper basins continued at least until the end of the winter. It is apparent that estuarine succession can be quite varidble and that re-establishment of community structure may occur over various time scales w ~ t h no set sera1 stages. The physical and biological processes appearing to be important determinants of estuarine succession include (1) timing of disturbance, (2) habitat in w h ~ c h the disturbance takes place, (3) reproductive periodicity of infauna, (4) ambient population dynamics which generate the pool of recolonizers, (5 ) abiotic and biotic factors (e.g. food and space resources that affect the preceding 4 factors).
TL;DR: The results indicate that the respiratory physiology of C. virginica is highly adapted to life in a fluctuating environment and is well able to regulate VO, when exposed to declining oxygen tensions at all temperature-salinity combinations tested.
Abstract: Acclimated and acute rates of oxygen consumption of the American oyster Crassostrea virginica (Gmelin) were measured under 9 salinity-temperature combinations during declining oxygen tensions. In acclimated and non-acclimated individuals the basal rate of oxygen uptake increased significantly with each 10 C" rise in temperature. Multiple regression equations relating exposure and experimental temperatures and salinities to VO, indicated: (1) as acclimation salinity decreased, the effect of exposure temperature became more pronounced; (2) as acclimation salinity decreased, the effect of exposure salinity decreased; (3) as acclimation temperature increased, the effect of exposure salinity decreased; (4) as acclimation temperature increased, the effect of exposure temperature increased. There is little or no evidence for temperature acclimation even after 3 wk. Q,, values for warm acclimated oysters were generally higher than those of cold adapted oysters with the exception of individuals acclimated at a salinity of 7 %o S and exposed to 28 %O S. At any experimental salinity the highest Q,,, values were observed between 20 and 30°C. C. virginica is well able to regulate VO, when exposed to declining oxygen tensions at all temperature-salinity combinations tested; this capacity decreased considerably at all test temperatures in oysters acclimated tq 7 % S. There is no clear pattern of response between exposure conditions and ability to regulate VO,; the degree of regulation decreases with increasing temperature and/or decreasing salinity. The results indicate that the respiratory physiology of C. virginica is highly adapted to life in a fluctuating environment.
TL;DR: The wide range of toxicity determined for the specimens examined and the fact that approximately 50 % of all specimens were toxic suggests that chemical defences against predation are common in the Alcyonacea of the central region of the Great Barrier Reef.
Abstract: We have tested 136 specimens of soft corals (Coelenterata. Alcyonacea) for toxicity by exposing Gambusia affinis (Vertebrata, Pisces) to aqueous extracts of coral macerate and assessing mortality. Sixty-eight corals were examined in detail utilizing behavioral responses of fish as well as mortality rates to establish relative toxicities among and within coral genera. The responses exhibited by the fish ranged from rapid mortality through slow mortality and varying levels of narcotisation to negligible effects. With respect to individual soft corals, the fish exhibited varying patterns of response through time, and were sorted into 9 distinct groups via multivariate computer analyses according to similarity of these behavioral patterns. Only 2 of the genera tested, Lemnalia and Sarcophyton, were restricted to the most toxic set of groups. A number of genera such as Lobophytum, Sinularia, Nephthea, and Cespitularia had representatives which spanned the entire spectrum of responses from highly toxic to non-toxic. The wide range of toxicity determined for the specimens examined and the fact that approximately 50 % of all specimens were toxic suggests that chemical defences against predation are common in the Alcyonacea of the central region of the Great Barrier Reef. Toxicity, however, occurs significantly less frequently in this group than in those examined from the northern Great Barrier Reef in an earlier study.
TL;DR: This review compares rates of oxygen uptake and intrinsic growth of very small invertebrate species near 20 "C with those of larger invertebrates and unicellular animals by means of the allometric relation (rate a Mb where M = mass).
Abstract: This review compares rates of oxygen uptake and intrinsic growth of very small invertebrate species near 20 "C with those of larger invertebrate and unicellular animals by means of the allometric relation (rate a Mb where M = mass). Respiration rates of small species of major invertebrate taxa are lower than those extrapolated for larger invertebrates but generally higher than those for protozoans of the same mass. Mass-specific rates of small metazoans and protozoans are lowered accordingly; therefore, their total food and oxygen consumption is likely to be small relative to that of large metazoans in average pelagic and benthic communities where most of the biomass is in large animals. The exponent b for each of the major taxa treated here tends to be near 0.75 rather than close to unity. Thus, the respiration of these taxa is about as mass dependent as that of large animals. Metabolic reduction is set in relation to small adult size as such, and previous inferences about the phylogeny of metazoan metabolism do not seem warranted any more. Intrinsic growth rates of benthic rotifers and marine free-living nematodes are not only lower than those extrapolated for larger invertebrates but fall below those for protozoans of the same mass. Among benthic harpacticoid copepods, a slight reduction relative to mass-scaled large invertebrates is indicated. Pelagic freshwater rotifers do not exhibit this reduction. Intrinsic growth rates of pelagic freshwater cladocerans are independent of adult mass and not clearly higher than those of the few pelagic copepods studied. Future research into the physiological reasons for mass dependence of metabolism and growth should focus on unicellular or small multicellular species because of their short generation times
TL;DR: A modified differential filtration was used to measure extracellular release of primary products by natural phytoplankton populations and subsequent incorporation of these products by bacteria as mentioned in this paper.
Abstract: A modified differential filtration was used to measure extracellular release of primary products by natural phytoplankton populations and subsequent incorporation of these products by bacteria. Water samples were incubated with I4C labelled bicarbonate for 6 h and 24 h , respectively. A time course experiment showed that 6 h are sufficient for attaining an approximate isotopic equilibrium between the fractions of inorganic carbon and released organic carbon. Results reveal a strong relationship between primary production and release of organic substances. The highest concentrations of exudates (239 pg C 1-') released by phytoplankton amounts to 27.6 % of the primary production. Percentage of released substances depends on the composition of the algal populations. Skeletonema costaturn released between 5.1 % and 12.5 % of the primary products; nanoflagellates, up to 40 %; Prorocentrurn rnicans, slightly over 20 %; Chaetoceros sp., about 25 %. Up to 90 % of available exudates were utilized by bacteria. Bacterial incorporation of exudates fluctuated during the year. The highest percentage of exudates was incorporated in the presence of dinoflagellates and nanoflagellates. Bacterial utilization of exudates is compared with that of glucose.
TL;DR: The unusual plankton distribution, the predominance of a few species and the ontogenetic segregation of the interzonal species are related to the abnormally high temperature and salinity in the subsurface waters, coupled with a depleted oxygen content in the mesopelagic zone and lack of food in the bathypelagic zones.
Abstract: The vertical distribution of mesozooplankton has been studied in the central Red Sea to determine its relationship to discrete habitat zones defined according to density, oxygen and nutrient concentrations, seston, and phytoplankton profiles. A disproportionately large amount of the 300 pm net plankton occurs both day and night in the epipelagic zone, which occupies the upper water layer above the abrupt thermohalocline at about lOOm In contrast, in the lower bathypelagic zone, a layer between 1,050 and 2 1,850 m, the numerical abundance and biomass of the zooplankton (0.2 specimens and 5 0 . 0 5 m g wet weight m-3) correspond to values encountered in other oligotrophic regions in tropical oceans below a depth of 4,000 to 6,000 m. The subsurface zooplankton maximum is situated in the core of the oxygen minimum layer, which is located in the mesopelagic zone (100 to 750m). Minimum oxygen values at ca. 400 m delimit the upper and lower interzonal (mesopelagic) assemblages. The unusual plankton distribution, the predominance of a few species and the ontogenetic segregation of the interzonal species are related to the abnormally high temperature (2 21.5") and salinity (240 .5% S) in the subsurface waters, coupled with a depleted oxygen content in the mesopelagic zone and lack of food in the bathypelagic zone. Vertical transport of organic matter is achieved by the 'ladder of migrations', involving a few interzonal species that descend into the upper bathypelagic zone but remain above ca 1,100m. Transport of organic debris below this depth by sinking is ineffective because its decay is too rapid.
TL;DR: The kelp community appears to depend primarily on rapid bacterial mineralisation of fragmented kelp and faeces to recycle the minerals necessary to sustain primary production, supplemented by bouts of upwelllng.
Abstract: Primary production by phytoplankton in a Benguela upwelling region off the west coast of the Cape Peninsula, South Africa, is almost equal to that within beds of the kelps Ecklonia maxima and Laminaria pallida. Total primary production of kelps, understorey algae and phytoplankton within an idealised kelp bed of 10 nl average depth is 62,190 kJ yr-l, as compared to 54,037 kJ m-2 yr-' for the phytoplankton community in deeper water nearby. The overall energetic conversion from incident illumination is 1.7% within the kelp bed and 1.5% for phytoplankton in the nearby water column, suggesting that a net production efficiency of 1.5 to 1.7% may approach the maximum attainable by aquatic plants under conditions where nutrients are rarely limiting. The fauna is dominated by filter feeders, which are responsible for 72% of total animal standing stock (B), 77 % of total production (P), 9 4 % of respiration ( R ) , 8 4 % of consumption (C) and 89% of faecal production (F). Independent estimates of primary production and energy requirements of consumers balance to within 8 %, lending confidence to the calculations. Suspended matter, the food of filter feeders, is comprised of macrophyte particles, animal faeces and phytoplankton in roughly equal proportions. Bacteria which utilise dissolved and particulate components of fragmented macrophytes and faeces may produce up to 6,403 kJ m-2 yr-', which is small energetically but belies their importance in protein enrichment of food and in nutrient cycling. The kelp community appears to depend primarily on rapid bacterial mineralisation of fragmented kelp and faeces to recycle the minerals necessary to sustain primary production, supplemented by bouts of upwelllng.
TL;DR: There was no predictable relationship between these quantities and particle size either within or among the 4 sediments, emphasizing the difficulty in attempting to predict nutritional value of sediments from bulk samples.
Abstract: Sieved size fractions of 4 marine sediments were examined for 4 quantities presumably related to nutritional value organic carbon, bacteria, chlorophyll a and C : N ratio of organic matter in order to determine whether they showed a consistent relation with particle size. However, there was no predictable relationship between these quantities and particle size either within or among the 4 sediments. Despite wide variations in organic carbon, bacterial abundance and chlorophyll a content, C : N ratios were similar (near 7) for most of the size fractions from all 4 areas; apparently there was a large, and as yet unidentified, pool of organic carbon in these sediments other than living bacteria or microalgae with a C : N ratio near 7. Variation of microbial abundance between winter and summer was inconsistent, but bacteria always accounted for less than 2 % of the organic carbon in the sediment. This study emphasizes the difficulty in attempting to predict nutritional value of sediments from bulk samples.
TL;DR: The xanthid crabs Panopeus herbstii and Eurypanopeus depressus are a CO-occurring, related species pair that inhabit intertidal oyster reef communities.
Abstract: The xanthid crabs Panopeus herbstii and Eurypanopeus depressus are a CO-occurring, related species pair that inhabit intertidal oyster reef communities. Panopeus herbstij is larger, faster growing, longer lived and more fecund. Eurypanopeus depressus matures earlier, produces more broods per lifetime and has a shorter generation time. These divergent life history patterns appear related to the different ways in which these 2 crabs utilize food and space in the intertidal zone. P. herbstii, which consumes primarily oysters, clams, mussels and barnacles, is prevented by its larger size from entering most of the narrow spaces between living oysters. The narrow spaces are the primary refuge for E. depressus which has a less restricted, more omnivorous diet.
TL;DR: In this article, it was shown that over 90 % of the carbon in these leachates is utilised by bacteria during drainage through a strip of sand 1 m long, 50 cm wide and 12 cm deep, although on an open beach other organisms, e.g. nematodes, may be capable of direct absorption of such organic matter.
Abstract: Primary decon~position of intertidally stranded kelp Ecklonia maxima in a mixed substrate microcosm is effected by bacteria rather than by fungi, which are generally reported to be responsible for the initial decomposition phases of debris in other habitats. Initial colonisation by cocci along the junctions of epidermal cell walls leads to lysis and release of cell contents. Lysed cells are then colonised by bacterial rods. High concentrations of leachates, reaching 5640 mg carbon 1-' subsequently appear beneath the decomposing kelp. Over 90 % of the carbon in these leachates is utilised by bacteria during drainage through a strip of sand 1 m long, 50 cm wide and 12 cm deep, although on an open beach other organisms, e . g. nematodes, may be capable of direct absorption of such organic matter. Calculation of carbon flow via grazing invertebrates and through bacteria shows that 23-27 % of the carbon in kelp is converted to bacterial carbon. This relationship occurs despite wide variations in direct consumption by grazers, since much of the consumed material is returned to the microcosm as faeces. Estimates of the bacterial carbon in equilibrium with the kelp cast up on the strandline suggest that 1648 g of kelp carbon is deposited per metre of strandline each 8 d and that this is capable of supporting a bacterial production of 444.9 g carbon m-' of beach per 8 d cycle; this accords well with recent observations on the biomass of bacteria in the beach itself. The residual 73-77 % of kelp carbon which is not incorporated ~ n t o bacteria is mineralised by the sand beach microbes within 8 d. The microbial community thus occupies a central role in the rapid regeneration of inorganic materials necessary to support the characteristically high primary production of the kelp bed.