Showing papers in "Marine Ecology Progress Series in 1986"
426 citations
TL;DR: Mechanisms that control the spatial patchiness of eggs and larvae may control early life history survival and thereby influence relative year-class strength of adult fish stocks.
Abstract: Daily instantaneous natural mortality rates of marine pelagic fish eggs and larvae are higher than expected from the trend of mortality rate with dry weight in the sea. The difference between observed mortality rates and those predicted from the trend of mortality with dry weight is directly and positively correlated with the patchiness of their spatial distribution, which suggests that it is caused by the feeding of predators on patches of eggs and larvae. The product of weight-dependent mortality, 5.26 X 10-3 , and 1 + Lloyd's patchiness index predicts mortality rates close to those that have been measured from the field by other workers. Mechanisms that control the spatial patchiness of eggs and larvae may control early life history survival and thereby influence relative year-class strength of adult fish stocks.
407 citations
TL;DR: Results indicate that the decreased water transparency arises from a 40 to 50 % increase in summer values of chlorophyll a and nutrients in the offshore surface water of the Baltic Sea since the 1940's.
Abstract: Although nutrient inputs to the Baltic Sea have increased drastically since the end of the last century, there is still little hard biological evidence of a general eutrophication of the Baltic Sea outside locally polluted areas. A revisit after 40 yr to some well-documented diving stations in the outer archipelago of the h a n d Sea gave us an opportunity to register any changes in benthic vegetation that could be linked to eutrophication, By mapping the vertical distribut~on in coverage of bladder wrack Fucus vesiculosus (L.) at 11 stations we observed that the lower limit of this alga had moved upwards at 10 stations from maximally 11.5 m in 1943/44 to 8.5 m in 1984. Also the depth of maximum development had withdrawn from 5 to 6 m in 1943/44 to 3 to 4 m in 1984, while coverage a t these depths was about the same: 58 % and 51 % respectively. The deepest specimens today at 8.5 m had the same dwarfed appearance as those found at 11.5 m in the 1940's; at that time growth at 8 .5 m was luxuriant During both studies the decrease in F. vesiculosus coverage with depth towards the lower limit could be approximately fitted to an exponentially decreasing light attenuation curve. Since the structure of Baltic hardbottom communities is almost totally governed by abiotic factors, the changes in depth penetration are probably caused by decreased transparency of the water column due to eutrophication. Results indicate that the decreased water transparency arises from a 40 to 50 % increase in summer values of chlorophyll a and nutrients in the offshore surface water of the Baltic Sea since the 1940's.
312 citations
301 citations
TL;DR: The present study shows that the tested oligotrichous ciliates feed in the size range of autotrophic and heterotrophic rnicroflagellates, but that they are incapable of effective ingestion of bacterioplankton.
Abstract: Particle size selection and functional response were studied for 3 marine oligotrichous ciliates. Each species showed a distinct size spectrum of ingested particles. The optimal particle size was 2.1 pm for Strombidiwn vestitum, 7.9 pm for Strombidium reticulatum and 9.7 pn for LohmannielJa spirahs. None of the species could effectively retain 1 particles. The functional response (ingestion rate as function of particle concentration) could be fitted to a hyperbolic function with no apparent feeding threshold at low particle concentrations. Maximum clearing rates for the 3 species ranged from 0.52 to 26 pJ h-'. Video recordings of feedng cihates revealed that particle capture of oligotrichous d a t e s is similar to other investigated polyhymenophorans. S. reticulatum and L. spiralis were isolated from seawater to start laboratory cultures and the numerical response (growth rate as function of food concentration) was studied. Maximum growth rate was 0.036 and 0.044 h' for S. reticulatum and L. spiralis respectively. Yield (gross growth efficiency) was over 40 % (based on volume) for both species. The present study shows that the tested oligotrichous ciliates feed in the size range of autotrophic and heterotrophic rnicroflagellates, but that they are incapable of effective ingestion of bacterioplankton.
273 citations
TL;DR: Observed density-dependent mortality in the Wadden Sea reduced the between-year variation in year-class strength generated in the open sea egg and larval stages from a coefficient of variation of 62 % during larval immigration to 30 % after settling in June.
Abstract: Mortality factors operating in a temporarily isolated 0-group plaice population in the western Wadden Sea have been examined from information on larval immigration, subsequent settlement and changes in demersal densities. Larvae entered the western Wadden Sea every year from the end of February to the beginning of May. In years of strong larval abundance the main perlod of arrival seemed somewhat delayed from March to April. As a result, between-years mean length and density of the settled population showed an inverse relation on June 1. Density-dependent mortality was observed among plaice up to about 35 mm, with instantaneous mortality rates ranging up to 0.06 d-l during and shortly after settling of the larvae. Arguments are given that, although in the coastal zone pelagic predators are present (several coelenterate species), the main dens~ty-dependent mortality processes operate in the demersal phase. The larval data further showed that level of yearclass strength was established early in life, during the planktonic stage in the open sea. Observed density-dependent mortality in the Wadden Sea reduced the between-year variation in year-class strength generated in the open sea egg and larval stages from a coefficient of variation of 62 % during larval immigration to 30 % after settling in June.
270 citations
TL;DR: It is suggested that multiple defenses will be common among seaweeds on coral reefs since herbivore diversity is high and it is unlikely that any single defense will be effective against the many types of herbivores that encounter these plants.
Abstract: The susceptibility of 82 species of tropical seaweeds to grazing by herbivorous fishes was assessed on 8 different coral reefs in the Florida Keys, USA. Most species were simultaneously assayed for the presence or absence of unusual secondary rnetabolites and recorded as having either calcified or uncalcified thalli. Both production of secondary rnetabolites and of a calcified thallus were associated with low susceptibility to herbivory. However, the relative importance of calcification versus chemical deterrents cannot be assessed for the calcified species since almost all these also contained secondary metabolites. Eighty-five % of calcified species, but only 39 % of uncalcified species, produced secondary metabohtes. Secondary metabolites were produced by 71 % of the species least suscephble to herbivory ( t 2 5 % eaten) but by only 20 O/O of the species most susceptible to herbivory (>75 % eaten). Calcified thalh were produced by 50 % of the lowest preference species but by only 9 O/O of the highest preference species. Thus, several common reef seaweeds appear to resist herbivory by relying primarily on chemical deterrents (genera Dictyota, Dilophus, Stypopodium, Lobophora, Avrainvrllea, and some Caulerpa species) but many appear to combine both chemical and morphological defenses (genera Penicillus, Halimeda, Rhipocephalus, Udotea, Amphiroa, and Galaxaura). We suggest that multiple defenses will be common among seaweeds on coral reefs since herbivore diversity is high and it is unlikely that any single defense will be effective against the many types of herbivores that encounter these plants. Thls may account, in part, for the diversity of secondary metabolites produced by some tropical seaweeds.
258 citations
TL;DR: It is concluded that it is possible to obtain reasonable estimates of annual production and its distribution among slze groups in natural benthic comn~unities of eukaryotic organisms using allometric P : B scal~ng.
Abstract: Published data on production of natural populations of benthic organisms were used to derive allometric equations relating annual production per unit biomass (P: B ratio) to mean individual body mass (time and biomass weighted) in the population on which production was measured. Separate equations were derived for meiofauna and macrofauna. Since no published data on production and size-structure in natural bacterial populations were found, P:B ratios for bacteria were calculated by extrapolation from an all-inclusive regression. In situ respiration was then calculated from production assuming the two to be approximately equal over an annual cycle for bacteria and benthc microalgae, and using an empirical relation between annual respiration and production in marine benthic animals for meiofauna and macrofauna. Monthly observations of benthic biomass spectra at Pecks Cove, an intertidal site in the upper Bay of Fundy, were used to estimate production and respiration in bacteria, microalgae, meiofauna, and macrofauna from the allometric equations. These estimates compared well with measured production for Corophjum volutator and Macoma balthjca, the 2 dominant macrofaunal species, and w ~ t h gross primary production by benthic microalgae, but not with total community respiration as measured by sediment oxygen consumption. Calculated values for production by bactena were of an expected magnitude ~f between 1 and 10 O/O of the total biomass was assumed to be active. The contribution of meiofauna and macrofauna to total community production (8 to 19 %, depending on the assumphon for bacterial achvity) was d~sproportionately small compared to their relahve biomass (47 to 52 %, also depending on what proportion of bacterial biomass was considered to be actlve). Estimates of respiration were much higher than measured rates of sediment oxygen consurnphon (2.5 to 5.5 times), although both followed closely sirmlar seasonal trends. Bacterial produchon in nature must be directly measured before the validity of our calculations can be assessed. However, we conclude that it 1s possible to obtain reasonable estimates of annual production and its distribution among slze groups in natural benthic comn~unities of eukaryotic organisms using allometric P : B scal~ng.
230 citations
222 citations
222 citations
TL;DR: A comprehensive explanation of outwelling in North Inlet is proposed which describes this system as an ebb-dominated, bar-built estuary with good flow connection to the sea and with some freshwater input.
Abstract: Extensive measurements of material concentrahons and water velocities at a transect across North Inlet, South C a r o h a (USA) allowed the estimation of net material and water fluxes. Sampling periods were distnbuted seasonally and according to tidal height. Statistical and hydrodynanlic models were used to develop flux estimates for specific tidal cycles. There was a net discharge of water from the marsh-estuanne system to the Atlantic Ocean which is attributed to rainfall runoff and freshwater input from an adjacent estuary. All constitutents were exported seasonally and annually from the system except total semments, imported during fall and winter, and chlorophyll a and zooplankton, imported in summer and fall. ATP, bird biomass and macrodetritus were exported throughout the year. Export of carbon, nitrogen and phosphorus from North Inlet is high compared to other systems studied to date. Large net fluxes of DOC during winter imply coupling with the uplands. The high rates of export of ammonium and orthophosphate along with detritus and microorganisms suggest major decomposition processes are taking place within the system. Export of ammonium and orthophosphate to the coastal ocean also suggest a feedback loop with phytoplankton utilizing these materials, then in turn phytoplankton are imported into the estuary where they are consumed and remineralized. Previous explanations of outwehng and tidal transport are examined and found to be individually lacking. It is proposed that any comprehensive explanahon of the magnitude and direction of transport must include a physical explanation of water motion and the biological and physical mechanisms by which materials are added or removed from tidal waters. A comprehensive explanation of outwelling in North Inlet IS proposed which describes this system as an ebb-dominated, bar-built estuary with good flow connection to the sea and with some freshwater input. It is also a fertile system with high productivity providing materials for export to the coastal ocean and utilization of other imported materials.
TL;DR: Although eukaryotic inhibitors did not prove to be rouhnely useful to estimate protozoan grazing rates on bacterioplankton, they may contribute to understanding qualitahve control mechanisms in the microbial food web.
Abstract: We estimated In si tu grazing rates of heterotrophic nanoplankton (HNAN) on bactenoplankton in a salt marsh estuary using a select~ve metabolic inhibitor technique. Seasonal experiments with prokaryohc inhibitors showed a significant, positive relation between bacterial abundance and HNAN grazing rates. On average, only 40 to 4 5 '/o of bacterioplankton produchon in the estuary appeared to be consumed by phagogrophic Protozoa <20 pm in size. Eukaryotic inhibitor experiments suggested that protozoan grazlng can have a positive feedback effect on bacterioplankton production, and that nitrogen regeneration by Protozoa may be of particular importance to bacterial growth. Although eukaryotic inhibitors did not prove to be rouhnely useful to estimate protozoan grazing rates on bacterioplankton, they may contribute to understanding qualitahve control mechanisms in the microbial food web.
TL;DR: It is suggested that algal clump , postlarval settling behavior, and juvenile interpatch movement and mortality contribute to the highly dispersed distnbution and locally sparse abundances of early benthic juveniles.
Abstract: Clumps of highly-branched red algae Laurencia spp. serve as important settling habitat for postlarval spiny lobsters Panulvus argus and as residence for early benthic-stage juveniles. G ~ v e n choice between the 2 most abundant macrophytes in Florida Bay, Laurenna spp. and the seagrass Thalassia testudinum, postlarval and juvenile lobsters chose Laurencia spp. Postlarvae apparently use intricate algal architecture as a cue for settlement, whereas juveniles use both architecture and food abundance in selecting habitat. In tethering experiments, predation on juve~ule lobsters was very high on open sand, much reduced In algal clumps and seagrass, and lowest in dense algal meadows. Predation rates were s~milar day and night both on open sand and In vegetabon. Most lobsters vacated algal clumps located within continuous algal meadows overnight, at a rate significahtly higher than that from isolated algal clumps. We suggest that algal clump d~s tnbubon , postlarval settling behavior, and juvenile interpatch movement and mortality contribute to the highly dispersed distnbution and locally sparse abundances of early benthic juveniles.
TL;DR: It is concluded that chemical defense IS a major factor in the sumval of marine algae within this order.
Abstract: Forty marine algae of the order Caulerpales were chemically investigated. Virtually all produce toxic secondary metabolites of a unique and unprecedented class. These metabolites are generally Linear terpenoids, but unusual structural features such as aldehydes and bis-enol acetate functional groups make these compounds uruque. The conlpounds are tonc or deterrent toward microorganisms, sea urchin larvae, and herbivous fishes, and when incorporated into diets at naturally occurring concentrations cause mortality in juvenile conch. Concentrations of bioactive metabolites were found to show httle variation in different plant parts such as blades, shpes and holdfasts. Young growlng tips and reproductive structures contained higher concentrahons than mature plant tissues on a dry weight and ash-free dry weight basis. Chemical variation, both qualitahve and quantitative, was observed in different populations of the same species. In the cases examined, algae growing in areas known to have the highest herbivory produced the greatest concentrations and varieties of secondary metabolites. Based upon these observations and pnor feeding preference data, we conclude that chemical defense IS a major factor In the sumval of marine algae within this order.
TL;DR: A comparison of photographs of individually identified humpback whale Megaptera novaeangliae were collected in regions throughout the central and eastern North Pacific during the years 1977 to 1983 as mentioned in this paper.
Abstract: Photographs of individually identified humpback whales Megaptera novaeangliae were collected in regions throughout the central and eastern North Pacific during the years 1977 to 1983. A comparison of these photographs revealed extensive movement between seasonal habitats. Whales found wintering near Hawaii traveled to summer feeding regions throughout the coastal waters of Alaska. Whales wintering near Mexico were found in Alaskan feeding regions and near the Farallon Islands off central California. I-lttle exchange was found between the 2 wintering grounds or among the 5 summering grounds studied. Fidelity to a given feeding region was demonstrated by a high proportion of migratory return. Evidence of fidelity to a given wintering ground was less conclusive. The coloration of humpback whale flukes showed a longitudinal cline across the 5 feeding regions. Flukes of whales from the easternmost feeding regions were, on average, darker than those from the westernmost feeding regions. Whales in Hawaii and Mexico were similar in fluke coloration and the average coloration on both wintering grounds was intermediate between the extremes of the feeding regions. We propose that humpback whales in the eastern and central North Pacific form a single 'structured stock' consisting of several geographically-isolated 'feeding herds' which intermingle on 1 or more wintering grounds. Mark-recapture analyses of resightlng data indicate that the Hawaiian wintering congregation is 4 to 6 times larger than the southeastern Alaska feeding herd. Within a structured stock, sets of whales interact with different probabilities in each seasonal habitat. This, in turn, has important implications for the social organization and management of these whales.
TL;DR: It is concluded that bacterial size distribution in the sea can be affected by size-selective grazing of heterotrophic microflagellates, and it is suggested that this explains the decrease in median bacterial volume during the summer.
Abstract: The effect of rnicroflagellate grazing on the size distribution of bacterial cells was studied using a heterotrophic microflagellate, Ochromonas sp., and mixed seawater bacteria in a 2-stage continuous culture. The flagellate grazed bacteria selectively, preferring cells larger than 0.2 pm3. Median bacterial cell volume was reduced by 47 %, median cell length by 36 O/O and median cell width by 8 % compared to ungrazed control bacteria. An unexpected result was a drastic increase in numbers of bactena in the 3 smallest size classes in the chemostat with flagellates. The size distribution of natural pelagic bacteria in the northern Baltic Sea was studied in spring and summer during 3 consecutive yr, 1982 to 1984. Median bacterial cell volun~e decreased during summer, while phagotrophic microflagellates increased in abundance. We conclude that bacterial size distribution in the sea can be affected by size-selective grazing of heterotrophic microflagellates, and suggest that this explains the decrease in median bacterial volume during the summer.
TL;DR: Reversed sex-roles and parental energy investment in zygotes of two pipefish (Syngnathidae) species are found to be reversed.
Abstract: Reversed sex-roles and parental energy investment in zygotes of two pipefish (Syngnathidae) species
TL;DR: In this article, it was shown that the maximum rates of DFAA uptake would occur in dark conditions in waters depleted of dissolved inorganic nitrogen, where levels of nFA are high and the periods of enforced darkness due to turbidity are likely to induce the development of microalgal amino acid uptake systems.
Abstract: Dissolved free amino acids (DFAA) form a significant proportion of dissolved fixed nitrogen in marine waters and could provide an additional source of nitrogen for the growth of marine microalgae. With the advent of DFAA analysis by HPLC, recent studies of algal physiology, and an increased awareness of potential experimental errors, doubts are cast over the conclusion that marine microalgae are not net users of DFAA. Results obtained by testing the use of a few amino acids cannot be extrapolated; the full range of amino acids should be used in field experiments. A high rate of uptake of any one amino acid is not to be expected. It is more probable that a simultaneous uptake of several amino acids will occur at a lower rate. It is essential that environmental conditions be taken into account in interpretation of results from field experiments. Results from laboratory and field studies suggest that maximum rates of DFAA uptake would occur in dark conditions in waters depleted of dissolved inorganic nitrogen. Turbid estuaries and coastal waters would also be environments likely to induce a significant uptake of amino acids, because levels of nFA.4 i.n. sl~ch WB!P~S S ~ C :~!st;l.~.~!y high and the periods of enforced darkness due to turbidity are likely to induce the development of microalgal amino acid uptake systems.
TL;DR: The macrofauna around a dense intertidal bed of the burrowing ghost shnmp Callianassa californiensis was studied to test the predictions of trophic group amensalism and mobhty mode hypotheses, and distributions are consistent with a mobihty mode of interaction and are in contrast with recent studies of the ghost shrimp's effect on subtidal bivalve populations.
Abstract: Various functional group hypotheses have provided different prehctions for the influence of mobile deposit feeders on the composition of marine soft-sediment communities. Two that have received particular attenhon are the trophic group amensalism and mobhty mode hypotheses. Trophic group amensalism suggests that deposit feeders will primarily affect suspension feeders through resuspension of sediments while a rnobhty mode approach suggests that sediment disruption is the mechanism of interaction, with sedentary organisms being the group most adversely affected. The macrofauna around a dense intertidal bed of the burrowing ghost shnmp Callianassa californiensis (Dana) was studied to test the predictions of these hypotheses. Most sedentary species, including deposit feeders, had much lower numbers withm a dense shrimp bed compared to adjacent areas of low C. cahforniensis numbers. However, there was no change in fauna1 richness. These distributions are consistent with a mobihty mode of interaction and are in contrast with recent studies of the ghost shrimp's effect on subtidal bivalve populations.
TL;DR: The highest treatment mesocosm (32 X) wentbrieny anoxic during the second summer of the experiment during a period when little productivity was occurring in the water column, and with the exception of the 8 x treci\ment, all treatments above 2 X had a greater respiratory demand in theWater column than the benthos.
Abstract: In a 28 mo mesocosm experiment , levels and patterns of productivity and respiration were observed for a range of nutrient additions selected to provide a gradation from conditions in lower Narragansett Bay, Rhode Island , USA. to maximum impact for an urbalJ. t\!ary receiving present day leve1s of sewage effluents. For a 3Z. fold increase in nutrients, system apparent prod.uction increased by only a factor of 3,5. Seasonal patterns of . autotrophy during the winter-spring diatom bloom and , heterolrophy during summer and early fall occurred at all treatment levels. With the exception of the 8 x treci\ment, all treatments above 2 X had a greater respiratory demand in the water column than the benthos. The highest treatment mesocosm (32 X) wentbrieny anoxic during the second summer of the experiment during a period when little productivity was occurring in the water column.
TL;DR: In this article, the authors measured phytoplankton production in the Delaware Estuary (USA) over several seasonal cycles (1980-1985) and found that seasonal variability in daily area1 production (JP; g C m-2 dl ) was closely related to chlorophyll concentrations in the upper estuary, ranging from a maximum of 1.1 g c m-d to a minlmum of d-l.
Abstract: Phytoplankton production in the Delaware Estuary (USA) was measured over several seasonal cycles (1980-1985). Seasonal variability in daily area1 production (JP; g C m-2 dl ) was dlrectly related to chlorophyll concentrations in the upper estuary, ranging from a maximum of 1.1 g C m-' d ' In summer to a minlmum of d-l) dunng summer in the presence of low phytoplankton biomass (2 to 10 kg Chl I ' ) , and in mid-estuary [2.6 g C d-l) during the spring diatom bloom (50 to 60 yg Chll-l). Desplte the occurrence of maximum nutnent concentrations in the freshwater region, highest JP and 90 % of the annual production occurred in the lower estuary, down-stream from the turbidity maximum. The presence of the turbidity maximum immediately downstream from major anthropogenic nutrient sources restricts phytoplankton growth, and limits biomass accumulation below nuisance levels. Annual production for the 1981-1985 period averaged 307 g C and displayed marked inter-annual variability. Llght availability is the predominant regulator of production in the estuary. Although growth was light-limited, neither chlorophyll specific produchon nor the light intensity at which photosynthesis saturates was related to the mean light intensity in the mixed surface-layer. These results suggest that photoadaptive response times are slower than the vertical mlxing rate and that photoadaptation is of mlnor significance to overall production in the system.
TL;DR: The analysis showed that extended aggregations of seabirds are associated with extended aggregatlons of schooling fish and that correlation of these marine carnivores with their prey is scale-dependent.
Abstract: The distribution of piscivorous seabirds relative to schooling f ~ s h was investigated by repeated censusing of 2 intersecting transects in the Avalon Channel, w h c h carries the Labrador Current southward along the east coast of Newfoundland. Murres (primarily common murres Uria aalge), Atlantic puffins Fratercula arctica, and schooling fish (primarily capelin .Mallofus villosus) were highly aggregated at spatial scales ranging from 0.25 to 15 km. Patchiness of murres, puffins and schoohng flsh was scale-dependent, as indicated by significantly higher vc~ridnce-to-mean ratios at large measurement distances than at the minimum distance, 0.25 km Patch scale of puffins ranged from 2.5 to 15 km, of murres from 3 to 8.75 km, and of schoohng flsh from 1.25 CO 15 km. Patch scale of birds and schooling fish was sirmlar m 6 out of 9 con~parisons. Correlahon between seabirds and schooling birds was significant at the minimum measurement distance in b D L I ~ of 12 comparisons. Correlation was scale-dependent, as inlcated by sigruficantly higher coef1i:ients at large measurement &stances than at the minimum distance. Traclung scale, as indicated b) Lhe maxlmum significant correlation between birds and schooling fish, ranged from 2 to 6 km. Our analysis showed that extended aggregations of seabirds are associated with extended aggregatlons of schooling fish and that correlation of these marine carnivores with their prey is scale-dependent.
TL;DR: It is suggested that the maintenance of strong correlations between plant and animal abundances in seagrass meadows requires strong pressures to counterbalance such rapid immigration (e.g. intense predation and/or habitat selection).
Abstract: Are seagrass-associated communities static? In order to measure the ability of seagrassassociated macrofauna to colonize 'empty' habitat patches, we studied the colonization of artificial seagrass, a natural seagrass mimic. In 2 separate experiments, we measured colonization (1) over a time series of 0.5 to 16 d and (2) over a distance series of 0 to 15 m from the source pool of colonists in a seagrass meadow in the Indian River lagoon, Florida. Colonization over time was rapid. Abundance and species richness peaked in 4 to 8 d , while abundances of individual species continued to fluctuate. Colonization was rapid at all distances from the seagrass bed. Although gastropod abundance decreased with increasing distance, abundance of crustaceans increased with distance. At the margin of the seagrass bed, gastropods and crustaceans colonized in approximately equal abundance, whereas 15 m from the bed, crustaceans colonized 6 to 8 times as abundantly as gastropods. Relative to natural densities, the dominant crustacean Cymadusa compta (Amphipoda) colonized 38 times as abundantly as the dominant gastropod, Bittium varium. We attribute this increased crustacean colonization far from grassbeds to the 'nearest refuge' hypothesis, but also suggest an alternative predation hypothesis. Thus, seagrass-associated communities are not static. The short time scale of these experimental colonizations implies that the maintenance of strong correlations between plant and animal abundances in seagrass meadows requires strong pressures to counterbalance such rapid immigration (e.g. intense predation and/or habitat selection).
TL;DR: Community structure of the associated animals of low intertidal patches of Mytilus edulis L. with different age structure was investigated and sediments, shell fragments and byssal threads seemed to play an important role in increasing heterogeneity of environments and thus species diversity.
Abstract: Community structure of the associated animals of low intertidal patches of Mytilus edulis L. with different age structure was investigated at Asamushi, northern Japan. Each patch was composed of similar components i.e. live M. edulis, byssal threads, shell fragments, sediments, algae and associated animals. The amounts of sediments, shell fragments and byssal threads were greater in the periphery (MP) and central part (MC) of adult mussel patches than in patches of young (Y) and old (0) mussels. Total organic matter within sediments increased in the following order: 0, MC, MP and Y. Algal growth was luxuriant in Y and this supported abundant amphipods. Species richness was higher in older patches and species diversity (H') and equitabihty (J') were higher in MP and MC than in Y and 0. Sediments, shell fragments and byssal threads seemed to play an important role in increasing heterogeneity of environments and thus species diversity. Similarities in species compositions among MP, MC and 0 were high, but those between Y and other patches extremely low. This fact is probably caused both by the presence of a large number of epiphytic animals in Y and the difference in the composition of creeping fauna among the patches. Based on these results, the processes controlling community organization of Mytilus islands are discussed.
TL;DR: Pelagic bacteria, heterotrophic and autotrophic nanoflagellates, and ciliates were quantified in the marine shallow-water sound, Limfjorden, Denmark, from March to November 1983, and populations showed pronounced oscillations with time scales of days or weeks.
Abstract: Pelagic bacteria, heterotrophic and autotrophic nanoflagellates, and ciliates were quantified in the marine shallow-water sound, Limfjorden, Denmark, from March to November 1983. During summer the populations showed pronounced oscillations with time scales of days or weeks. Concentrations of bacteria, heterotrophic nanoflagellates and ciliates ranged from 0.5 to 15.2 X 106 ml" (mean: 6.3), 0.2 to 15.2 X 103 ml-' (mean: 2.0), and 1.4 to 162.0 ml-' (mean: 17.1), respectively. Population sizes of bacteria and heterotrophic nanoflagellates were coupled, as were populations of total nanoplankton and ciliates; in contrast there was no direct coupling between bacteria and ciliates. It is estimated that heterotrophic nanoflagellates on average cleared 45 YO (range: 5 to 365 %) of the watercolumn for bactena per day during summer. Ciliates on average cleared 93 % (range: 4 to 352 % ) of the water-column for nanoplankton per day.
TL;DR: The horizontal heterogeneity of the snow-ice cover, whlch is influenced by wind at the air-ice interface, thus provides diversified bottom-ice habitats where irradiance is compatible or not with the physiological limits of the ice microalgals cells, which results in a strong patchiness in distribution of ice-bottom microalgae.
Abstract: Factors controlling the horizontal distribution of sea-ice microalgae were studied in Southeastern Hudson Bay and adjacent Manitounuk Sound (Canadian Arctic). Both large (-30 km) and small (0.3 to 500m) scales of variability were investigated. Results showed that salinity was the most important factor controlling large scale distribution of the ice-microalgal biomass, through its effect on the structure of the ice (surface available for colonization). Variation in the thickness of the snow-ice cover, which determines irradiance at the bottom of the ice, was the factor controlling distribution of the algal biomass at smaller scale (diameter of patches of microalgal biomass ranging between 20 and 90 m). The relation between ice-algal abundance and snow-ice thickness changed however over the season. At the beginning of the growing season (in April when the bottom-ice irradiance was higher than a minimum critical irradiance), maximum algal biomass was observed under areas covered by the smallest snow depths. Towards the end of the season, when light transmitted through the snow-lce cover increased, maximum algal biomass was observed under areas covered by the deepest snow. This suggests that ice algae have both minimum and maximum critical light levels. The minimum level is the irradiance below which there is no photosynthetic activity (Imi, 7.6 CL Einst m-2 S-') and the maximum level corresponds to the inhibiting light intensity, which may vary during the growth season. The horizontal heterogeneity of the snow-ice cover, whlch is influenced by wind at the air-ice interface, thus provides diversified bottom-ice habitats where irradiance is compatible or not with the physiological limits of the ice microalgals cells. This results in a strong patchiness in distribution of ice-bottom microalgae.
TL;DR: In this paper, the effect of nutrient availability on growth was well approximated by a Monod rectangular hyperbola, with growth saturating at ambient nitrate concentrations between 1 and 2 FM.
Abstract: Temporal variations in growth of the giant kelp Macrocystis pyrifera were examined in relation to ambient nutrient availability and chemical composition of mature blades, the primary site of nutrient and carbohydrate storage in M. pyrifera. The effect of nutrient availability on growth was well approximated by a Monod rectangular hyperbola, with growth saturating at ambient nitrate concentrations between 1 and 2 FM. M. pyrlfera was unable to generate nutrient reserves that would last beyond 30 d. Nitrogen reserves were stored as free amino acids, and generally constituted about 10 % of total tissue nitrogen. Total nitrogen content was never more than 2 .5% of dry weight. There was no significant corrc.lation between growth and tissue nitrogen. In contrast, carbohydrate levels were negatively correlated with growth rates, tissue nitrogen content, and ambient nutrient availability. Although concentrations of nitrogen and carbohydrate reserves showed familiar variations described for other kelps, the physical environment in southern California is probably not amenable to M. pyrifera making strategic use of these reserves. Nutrient availability appears to be too low to permit accumulation of more than 30 d reserve of nitrogen, and light levels are probably never low enough to make stored carbohydrate reserves necessary for survival.