Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

Summary The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×10⁶ individuals per m² and ash free dry weight of 2.9 g/m² during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 10⁶ individuals per m². This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.     

Inter-annual variability in marine coastal Antarctic bacterioplankton

The dynamics of Antarctic coastal marine bacterioplankton has been studied over a 2-year period. Two field stations were sampled between one and three times a week in 1989 and 1991 in the “Terre Adélie” area. The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic counts, cell volume and frequency of dividing cells estimation) measurements. The results suggest that a strong interannual variability affects the total bacterial abundance, the mean cell volume, the percentage of free living cells and, to a lesser extent. the culturable saprophytic bacterial communities. The observed variability could be partly explained by a large deficit of solar irradiance during the 2nd year of study that may have affected sea ice and seawater primary production.     

Extracellular enzyme activity in anaerobic bacterial cultures: evidence of pullulanase activity among mesophilic marine bacteria.

The extracellular enzymatic activity of a mixed culture of anaerobic marine bacteria enriched on pullulan [alpha(1,6)-linked maltotriose units] was directly assessed with a combination of gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). Hydrolysis products of pullulan were separated by GPC into three fractions with molecular weights of > or = 10,000, approximately 5,000, and < or = 1,200. NMR spectra of these fractions demonstrated that pullulan was rapidly and specifically hydrolyzed at alpha(1,6) linkages by pullulanase enzymes, most likely type II pullulanase. Although isolated pullulanase enzymes have been shown to hydrolyze pullulan completely to maltotriose (S. H. Brown, H. R. Costantino, and R. M. Kelly, Appl. Environ. Microbiol. 56:1985-1991, 1990; M. Klingeberg, H. Hippe, and G. Antranikian, FEMS Microbiol. Lett. 69:145-152, 1990; R. Koch, P. Zablowski, A. Spreinat, and G. Antranikian, FEMS Microbiol. Lett. 71:21-26, 1990), the smallest carbohydrate detected in the bacterial cultures consisted of two maltotriose units linked through one alpha(1,6) linkage. Either the final hydrolysis step was closely linked to substrate uptake, or specialized porins similar to maltoporin might permit direct transport of large oligosaccharides into the bacterial cell. This is the first report of pullulanase activity among mesophilic marine bacteria. The combination of GPC and NMR could easily be used to assess other types of extracellular enzyme activity in bacterial cultures.     

Allee effects may slow the spread of parasites in a coastal marine ecosystem

Allee effects are thought to mediate the dynamics of population colonization, particularly for invasive species. However, Allee effects acting on parasites have rarely been considered in the analogous process of infectious disease establishment and spread. We studied the colonization of uninfected wild juvenile Pacific salmon populations by ectoparasitic salmon lice (Lepeophtheirus salmonis) over a 4-year period. In a data set of 68,376 fish, we observed 85 occurrences of precopular pair formation among 1,259 preadult female and 613 adult male lice. The probability of pair formation was dependent on the local abundance of lice, but this mate limitation is likely offset somewhat by mate-searching dispersal of males among host fish. A mathematical model of macroparasite population dynamics that incorporates the empirical results suggests a high likelihood of a demographic Allee effect, which can cause the colonizing parasite populations to die out. These results may provide the first empirical evidence for Allee effects in a macroparasite. Furthermore, the data give a rare detailed view of Allee effects in colonization dynamics and suggest that Allee effects may dampen the spread of parasites in a coastal marine ecosystem.     

Planktonic ciliated protozoa: their distribution and relationship to environmental variables in a marine coastal ecosystem

The spatial distribution of planktonic ciliated protozoa, physicalvariables and potential food items were measured at northernand southern sites off the west coast of the South Island, NewZealand, to examine which variables were important in structuringthe ciliate community. Ciliates contributed 30% of total zooplanktonbiomass. Ciliate abundance was greatest within 55 km of thecoast on the northern transect, but on the southern transectthe greatest abundance was close inshore and at the stationsoffshore of the continental shelf. The ciliate community wasdominated by small oligotrichs and abundance (114–1139l^–1 was comparable with other oligotrophic marine environments.The depth of the pycnocline had a major influence on the verticaldistribution of ciliates, which were closely correlated withprofiles of phytoplankton biomass and picophytoplankton abundance,but not primary production. The results of this study suggestthat physical factors were more important than biotic factorsin influencing the distribution of protozoan ciliates. The deepmixed layer prevented the formation of deep chlorophyll a orciliate maxima. Few studies of microzooplankton have incorporatedpicophytoplankton distribution, but the importance of smallciliates and picophytoplankton suggests that these groups mayplay a pivotal role in mediating the transfer of organic matterto higher trophic levels in this marine coastal ecosystem.     

Seasonal variations and inherent variability of selenium in marine biota of a tropical wetland ecosystem: implications for bioindicator species

The present study was designed to study the seasonal variations of selenium in marine biota of different trophic levels collected from Sunderban deltaic complex, northeast India. The primary objective of this work is to provide baseline data for a future environmental quality programme. In general, the sequence of Se accumulation observed in biota is as follows: Bivalve>Zooplankton>Macroalgae>Pisces>Seagrass. An elevated level of Se was recorded during monsoon season. The Se level in zooplankton (4 μg/g) was three to four times higher than seagrass. The content of various soft tissues and shell in bivalves molluscs showed an organ-specific pattern in the following order: gill > visceral MASS = mantle > adductor muscle > podium > shell. Fish contain less Se in comparison with macroalgae, zooplankton and bivalves revealing poor or insignificant trophic transfer of Se in the marine food chain. Pelecyora trigona (Bivalve) seems to be reliable indicator of Se contamination because of its high accumulation capacity. An in-depth monitoring program is recommended in order to clarify the present trend and to establish the studied biota as indicator species.     

Extracellular endoglucanase activity by a novel bacterium isolated from marine shipworm

An extracellular enzyme preparation from shipworm bacterium cultures dramatically increased reducing sugar content of carboxymethylcellulose (CMC3), but did not solubilize sugar from particulate cellulose. The preparation degraded cellodextrins larger than cellotriose (G3). Only interior cellodextrin chain linkages were cleaved and the center-most bond of cellohexaose (G6) was preferentially cleaved. Activity maxima were observed at 60 degrees C and between pH 5.0 and 7.0. The activity was resistant to protease treatment and little loss of activity was observed after 14 d at 25 degrees C.     

Seawater DMS in a perturbed coastal ecosystem

Intra- and interspecific niche overlap for two mayfly species with similar life cycle timing, Rhithrogena semicolorata and Ecdyonurus sp. gr. venosus, were investigated. The nymphs were classified into 5 classes according to size and spatial overlaps are measured along a substratum roughness gradient. Substratum roughness selection was investigated by defining utilisation curves, optimum and tolerance values of the nymphs in relation to larval growth. Differences between species and size classes within each species were observed. Ecdyonurus sp. gr. venosus dominated on rough substrates, whereas R. semicolorata was most abundant on smooth substrates. An intermediate value of total interspecific substratum roughness overlap (0.49) was found. Higher intraspecific than interspecific overlap values suggested a spatial niche segregation between the two species. The results suggested that the spatial niches measured, were closer to the `fundamental niches' than could be expected if competition was acting on the two studied populations.     

The importance of physical and biotic scaling to the experimental simulation of a coastal marine ecosystem

A marine microcosm, consisting of a pelagic phase interacting with a benthic phase, is described. Variations in water turnover, turbulence, incident radiation and ratio of pelagic volume to benthic surface area are shown to have significant effects on the behavior of these microcosms. It is argued that the inclusion and accurate simulation of appropriate levels of these variables is important in microcosm studies designed to study the dynamics of natural systems.     

Extracellular enzyme activity associated with suspended matter in the River Rhine

SUMMARY. 1. Spatial and temporal variations in exoenzymatic proteolysis and alkaline phosphatase activity in the River Rhine were measured fluorometrically using L-leucyi (ß-naphthylamide and methylumbelliferyl phosphate (MUFP), respectively, as test substances.
2. Extracellular proteolytic activity measured in the lower 150-km reach of the river during 1988 followed the changes in the concentration of particulate nitrogen associated with the occurrence of phytoplankton blooms. Alkaline phosphatase activity was not related to the concentration of particulate phosphate and correlated weakly with particulate nitrogen and phytoplankton concentrations.
3. Seasonal observations (1989) in the lower River Rhine and transport studies in a 660-km-long reach of the river (1990) indicated that the variations in the exoenzyme activities were unrelated (or not closely related) to fluctuating bacterial numbers. Exoproteolytic activity correlated well with thymidine incorporation and algal density, confirming indications in the literature that the exoenzyme activity is related to the overall metabolic rate of the bacterial populations.
4. The exoproteolytic activities in the Rhine are similar to the highest observed in eutrophic freshwaters, indicating a rapid turnover of proteins in the river. Bacterial phosphatase activities, measured with MUFP, were similar to those in the few marine and inland waters studied so far. However, phosphate-limited algal blooms, such as reported for the plume of the Rhine in the North Sea, are likely to contribute substantially to hydrolysis of natural organic phosphates.     

Warming leads to higher species turnover in a coastal ecosystem

The responses of ecological communities and ecosystems to increased rates of environmental change will be strongly influenced by variation in the diversity of community composition. Yet, our understanding of how diversity is affected by rising temperatures is inconclusive and mainly based on indirect evidence or short‐term experiments. In our study, we analyse the diversity and species turnover of benthic epilithic communities within the thermal flume of a nuclear power plant at the Swedish coast. This flume covers the range of predicted future temperature rises. Species composition was significantly different between control sites and sites with higher temperatures. We found that temperature had little effect on the number of species in three functional groups (macroinvertebrates, benthic diatoms, and macrophytes, which here comprise multicellular algae and macroscopic colonies of unicellular algae and cyanobacteria), neither at single sampling dates nor summed for the entire observation year. However, species turnover significantly increased with increasing temperature for diatoms, macrophytes and invertebrates. Different temperature regimes resulted in significantly different species composition and indicator species. Thus, increasing temperatures in the thermal flume increased temporal beta‐diversity and decreased compositional stability of communities, although observed richness did not change at any point in time. We highlight the need to investigate the consequences of such declines in compositional stability for functional stability of ecosystem processes.     

Transformation and retention of nitrogen in a coastal forest ecosystem

Transformations and fluxes of N were examined in three forested sites located along a gradient of soil texture in the coastal forests of the Waquoit Bay watershed on Cape Cod. Total N leaching losses to ground water were 0.5 kg ha^-1 yr^-1 in the loamy sand site and 1.5 kg ha^-1 yr^-1 in the fine sand site. Leaching loss to groundwater was not measured in the coarse sand site due to the prohibitive depth of the water table but total N leaching loss to 1m depth in the mineral soil was 3.9 kg ha^-1 yr^-1. DON accounted for most of the leaching losses below the rooting zone (77–89%) and through the soil profile to ground water (60%–80%). Differences in DON retention capacity of the mineral soil in the sites along the soil texture gradient were most likely related to changes in mineral soil particle surface area and percolation rates associated with soil texture. Forests of the watershed functioned as a sink for inorganic N deposited on the surface of the watershed in wet and dry deposition but a source of dissolved organic N to ground water and adjoining coastal ecosystems.     

Apparent overdominance of enzyme specific activity in two marine bivalves

Electrophoretic examination of a natural population sample of 332 mussels (Mytilus trossulus) revealed ten active allozyme alleles for the octopine dehydrogenase (Odh) locus and a statistically significant (P<0.005) departure from expected genotypic proportions caused by a deficiency of heterozygous genotypes. In vitro specific activity for octopine dehydrogenase (E.C. 1.5.1.11) was determined for 207 mussels representing 17 different Odh genotypes. Odh heterozygotes had an average specific activity that was 19% greater than that of apparently homozygous genotypes, a significant (P<0.05) difference. Electrophoretic examination of a natural population sample of 209 oysters (Crassostrea virginica) revealed 23 active allozyme alleles for the leucine aminopeptidase-2 (Lap-2) locus and a non-significant (P>0.05) deficiency of heterozygous genotypes. In vitro specific activity for leucine aminopeptidase (E.C. 3.4.-.-) was determined for 89 oysters representing 19 different Lap-2 genotypes. Lap-2 heterozygotes had an average specific activity that was 56% greater than that of homozygous genotypes, a significant (P<0.0001) difference. Possible explanations for the apparent overdominance in enzyme specific activity and the deficiency of heterozygotes include null alleles, molecular imprinting and aneuploidy.     

Single-cell vs. bulk activity properties of coastal bacterioplankton over an annual cycle in a temperate ecosystem

The connections between single-cell activity properties of heterotrophic planktonic bacteria and whole community metabolism are still poorly understood. Here, we show flow cytometry single-cell analysis of membrane-intact (live), high nucleic acid (HNA) content and actively respiring (CTC+) bacteria with samples collected monthly during 2006 in northern Spain coastal waters. Bulk activity was assessed by measuring ³H-Leucine incorporation and specific growth rates. Consistently, different single-cell relative abundances were found, with 60–100% for live, 30–84% for HNA and 0.2–12% for CTC+ cells. Leucine incorporation rates (2–153 pmol L⁻¹ h⁻¹), specific growth rates (0.01–0.29 day⁻¹) and the total and relative abundances of the three single-cell groups showed marked seasonal patterns. Distinct depth distributions during summer stratification and different relations with temperature, chlorophyll and bacterial biovolume suggest the existence of different controlling factors on each single-cell property. Pooled leucine incorporation rates were similarly correlated with the abundance of all physiological groups, while specific growth rates were only substantially explained by the percentage of CTC+ cells. However, the ability to reduce CTC proved notably better than the other two single-cell properties at predicting bacterial bulk rates within seasons, suggesting a tight linkage between bacterial individual respiration and biomass production at the community level.     

Short-term dynamics of bacterial communities in a tidally affected coastal ecosystem

Tidal effects on the composition of free-living (FL) and particle-associated (PA) bacterial communities were studied in a tidal flat ecosystem in the southern North Sea. Denaturing gradient gel electrophoresis targeting the 16S rRNA gene and the 16S rRNA of Bacteria, Bacteroidetes, Alphaproteobacteria and the Roseobacter clade was applied. Despite strong tidal variations in the quantity and, depending on the season, also the quality of suspended matter as well as variations in bacterial activity, the bacterial community composition remained rather stable. FISH showed some variations of the community composition, but these were not related to typical tidal situations. Variations were higher during tidal cycles in May and July compared with November. Bacteroidetes, Alpha- and Gammaproteobacteria constituted the majority of the bacterial communities but relative proportions of the different groups varied considerably. On particles, Betaproteobacteria were also detected to substantial proportions. The Roseobacter clade constituted up to 90% of FL but only 30% of PA Alphaproteobacteria. Banding patterns of the Bacteroidetes-specific amplicons, and in particular those targeting the 16S rRNA, revealed tidally induced effects, as several bands appeared or disappeared at distinct events such as slack water or resuspension. Sequencing of prominent bands revealed predominantly phylotypes reported previously from this ecosystem.     

Experimental confirmation of multiple community states in a marine ecosystem

Small changes in environmental conditions can unexpectedly tip an ecosystem from one community type to another, and these often irreversible shifts have been observed in semi-arid grasslands, freshwater lakes and ponds, coral reefs, and kelp forests. A commonly accepted explanation is that these ecosystems contain multiple stable points, but experimental tests confirming multiple stable states have proven elusive. Here we present a novel approach and show that mussel beds and rockweed stands are multiple stable states on intertidal shores in the Gulf of Maine, USA. Using broad-scale observational data and long-term data from experimental clearings, we show that the removal of rockweed by winter ice scour can tip persistent rockweed stands to mussel beds. The observational data were analyzed with Anderson’s discriminant analysis of principal coordinates, which provided an objective function to separate mussel beds from rockweed stands. The function was then applied to 55 experimental plots, which had been established in rockweed stands in 1996. Based on 2005 data, all uncleared controls and all but one of the small clearings were classified as rockweed stands; 37% of the large clearings were classified as mussel beds. Our results address the establishment of mussels versus rockweeds and complement rather than refute the current paradigm that mussel beds and rockweed stands, once established, are maintained by site-specific differences in strong consumer control. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Multi-level trophic cascades in a heavily exploited open marine ecosystem

Anthropogenic disturbances intertwined with climatic changes can have a large impact on the upper trophic levels of marine ecosystems, which may cascade down the food web. So far it has been difficult to demonstrate multi-level trophic cascades in pelagic marine environments. Using field data collected during a 33-year period, we show for the first time a four-level community-wide trophic cascade in the open Baltic Sea. The dramatic reduction of the cod (Gadus morhua) population directly affected its main prey, the zooplanktivorous sprat (Sprattus sprattus), and indirectly the summer biomass of zooplankton and phytoplankton (top-down processes). Bottom-up processes and climate-hydrological forces had a weaker influence on sprat and zooplankton, whereas phytoplankton variation was explained solely by top-down mechanisms. Our results suggest that in order to dampen the occasionally harmful algal blooms of the Baltic, effort should be addressed not only to control anthropogenic nutrient inputs but also to preserve structure and functioning of higher trophic levels.