Influence of the mineralogical composition on microbial activities in marine sediments: an experimental approach

We investigated the influence of the mineralogical composition of marine sediments on bacterial activity in experimental microcosms. Calcite and quartz were added to natural marine sediments and microbial response in terms of total bacterial abundance and biomass, β-D-glucosidase exo-enzymatic activity and bacterial incorporation of a radio-labelled (³H-leucine) substrate were investigated for a period of one month. We report here that after 15 days the mineralogical composition of the sediment (calcite vs. quartz) had an impact on bacterial abundance and activity (reduced for ca 15% and 56%, respectively). However, such impact was mitigated or even disappeared in high organic nutrient conditions.     

Microbial reaction rates and bacterial communities in sediment surrounding burrows of two nereidid polychaetes (Nereis diversicolor and N. virens)

The effects of infaunal mode of life on sediment properties, microbial reaction rates, as well as abundance and composition of bacterial communities were studied in sediment surrounding burrows (mucus lining, oxidised wall, ambient anoxic and surface sediment) of two closely related, but behaviourally different, nereidid polychaete worms: the facultative suspension-feeder Nereis (Hediste) diversicolor and the obligate deposit-feeder Nereis (Neanthes) virens. Burrow sediment of the two species was collected from two adjacent (50 m distance) shallow sandy locations (Kertinge Nor, Denmark). The burrow lining and wall of both polychaete species were enriched in organic matter originating from mucous secretions by the inhabitants and phytoplankton trapped through irrigation. This was more evident for N. diversicolor that shows a significantly higher irrigation rate than N. virens. Both the organic matter mineralisation rates (based on anaerobic incubations) and bacterial abundance were higher along the burrow linings and walls. However, accumulation of porewater TCO₂ and dissolved organic carbon in sediments adjacent to burrows increased most rapidly in the presence of N. diversicolor, suggesting higher heterotrophic activity associated with this species. Surprisingly, bacterial abundance was lower around burrows of N. diversicolor than those from N. virens indicating that burrow environments from the first species harbour a more active bacterial community. Molecular fingerprints of the 16S rRNA gene from bacterial communities showed that the composition of the burrow linings and walls resembled the ambient anoxic sediment rather than the oxic sediment surface. On the other hand, the bacterial fingerprints of the sediment surrounding the burrows of the two polychaete species were markedly different suggesting either a site-specific difference in sediment parameters or a significant species-specific impact of the burrow inhabitants.     

Detritus-Bacteria-Meiofauna interactions in a seagrass bed (Posidonia oceanica) of the NW Mediterranean

The biochemical composition of the sediment organic matter, and bacterial and meiofaunal dynamics, were monitored over an annual cycle in aPosidonia oceanica bed of the NW Mediterranean to test the response of the meiofauna assemblage to fluctuations in food availability. Primary production cycles of the seagrass and its epiphytes were responsible for relatively high (compared to other Mediterranean systems) standing stocks of organic carbon in sediments (from 1.98 to 6.16 mg Cg^–1 sediment dry weight). The biopolymeric fraction of the organic matter (measured as lipids, carbohydrates, and proteins) accounted for only a small fraction (18%) of the total sedimentary organic carbon. About 25% of the biopolymeric fraction was of microphytobenthic origin. Sedimentary organic carbon was mostly refractory (56 to 84%) and probably largely not utilizable for benthic consumers. The biopolymeric fraction of the organic matter was characterized by high carbohydrate concentrations (from 0.27 to 5.31 mg g^–1 sediment dry weight in the top 2 cm) and a very low protein content (from 0.07 to 0.80 mg g^–1 sediment dry weight), which may be a limiting factor for heterotrophic metabolism in seagrass sediments. RNA and DNA concentrations of the Sediments varied significantly during the year. High RNA and DNA values occurred during the microphytobenthic bloom and in correspondence with peaks of bacterial abundance. Bacteria accounted for a small fraction of the total organic carbon (0.65%) and of the biopolymeric organic carbon (4.64%), whilst microphytobenthos accounted for 3.79% of total organic carbon and for 25.08% of the biopolymeric carbon. Bacterial abundance (from 0.8 to 5.8 × 10⁸ g^–1 sediment dry weight) responded significantly to seasonal changes of organic matter content and composition and was significantly correlated with carbohydrate concentrations. Bacteria might be, in the seagrass system, an important N storage for higher trophic levels as il accounted for 25% of the easily soluble protein. pool and contributed significantly to the total DNA pool (on average 12%). Total meiofaunal density ranged from 236 to 1858 ind. 10 cm^–2 and was significantly related, with a time lag, to changes in bacterial standing stocks indicating that microbes might represent an important resource. Bacterial abundance and biomass were also significantly related to nematode abundance. These results indicate that bacteria may play a key role in the benthic trophic     

Predator-prey interactions between the larvacean Oikopleura dioica and bacterioplankton in enclosed water columns

The larvacean Oikopleura dioica Fol was fed ³H-labeled natural assemblages of marine bacterioplankton. Grazing rates ranged from <1 to >100 ml day^-1 individual^-1 and were highly dependent onlarvacean body size. These rates were combined with estimates of abundance of O. dioica in large floating enclosures with semi-natural populations (Controlled Ecosystems Populations Experiment, CEPEX) to determine the impact of the larvacean on the bacterial populations and to estimate the amount of bacteria ingested by the larvaceans. Apparently, O. dioica has minimal influence on the population dynamics of the free-living bacteria, although bacteria may form a substantial portion of the larvacean's diet.     

Feeding and bacteriolytic responses of the deposit-feeder Abarenicola pacifica (Polychaeta: Arenicolidae) to changes in temperature and sediment food concentration

Deposit-feeders can respond to seasonal fluctuations in food concentration both functionally (e.g. by adjusting feeding rates) and physiologically (e.g. by changing the concentration of bacteriolytic agents in gut fluids). Laboratory feeding experiments were carried out (11 to 21 July 1997) with the arenicolid polychaete worm Abarenicola pacifica (Healy and Wells). Objectives were to test for separate and interactive effects of sediment food concentration and temperature (6, 11, and 16 °C) on deposit-feeder functional (feeding rates) and physiological (bacteriolytic activity of gut fluids) responses. Food concentration was varied experimentally using sieved (1 mm) natural sediments (Md φ=2.00; 0.6% organic) mixed with combusted (500 °C, 8 h) sediments for final concentrations of 25, 50, and 100% natural sediment. Sediment food quality was measured as: (1) bioavailable amino acids (EHAA), (2) chlorophyll a (chl a), and (3) bacterial abundance. Feeding rates were inferred from egestion rates (ER, g h⁻¹) and analyzed with respect to worm size. Bacteriolytic activity of midgut fluids was assayed turbidimetrically against two bacterial isolates, after worms had fed on experimental sediments for 15 d. Temperature and food concentration both significantly affected feeding rates, with maxima occurring at 50 and 100% natural sediment mixtures, and at high (16 °C) temperature. ER was positively, but not significantly correlated with EHAA and chl a; a positive, significant correlation was detected between ER and sediment bacterial abundance. Overall, functional responses agreed with earlier compensatory intake models for deposit-feeders. However, the size and direction of these responses was temperature-sensitive, suggesting that these models need to be adjusted for changes in absorption rates. No effects of ambient temperature or food concentration on bacteriolytic rates were observed, possibly due to compensatory mechanisms or the presence of multiple bacteriolytic agents in gut fluids. Received: 28 June 1999 / Accepted: 14 March 2000     

Geochemistry and acidity of sulphide-bearing postglacial sediments of western Finland

The geochemistry, mineralogy, acidity and electric conductivity of sulphide-bearing postglacial sediments located on the coastal plains of western Finland were studied. Grain size and mineralogical analysis (eight samples studied) indicated that the sediments are silts dominated by primary minerals (quartz, feldspars), and that the clay fraction (<2µm), which made up less than one-third of the bulk samples, is enriched in phyllosilicates but depleted in quartz and feldspars, relative to bulk samples. As compared to the metal contents of the fine-fraction of glacial till (data of the Geological Survey of Finland), the fine sediments appear to be enriched in sulphur (median = 0.54%) and trace metals such as Ni (31 µg g^–1), Zn (90 µg g^–1), Co (13 µg g^–1), Cr (48 µg g^–1) and V (50 µg g^–1). Statistical analysis indicated that aluminosilicates are the principal carrier phases of trace metals, and that sulphides and organic matter only partially control the distribution of elements other than S and C. A 3-g portion of 232 samples was oxidised in the laboratory by atmospheric oxygen for a period of 1 year. After this period of oxidation, 15 ml of water was added, after which pH and electric conductivity of the suspensions (sediment:water, 1:5) were measured. The quantities of elements mobilised by the oxidation was calculated from the dissolved concentrations found in 3 g of oxidised sediment suspended in 30 ml of deionised water (eight samples studied). The results of the experiment showed that the impact of sulphide oxidation on the pH and conductivity of the sediments is large, and that a high proportion (>13%) of the aqua-regia extractable contents of several elements (Co, Mn, Ca, Ni, Zn, Sr, Na and B) are mobilised at oxidation. Because of the high quantities of acidity and metals liberated at oxidation, it is argued that stream-water quality, which is poor in the study area, will not improve unless artificial draining is restricted in areas of sulphide sediments.     

Antimicrobial activity of extracts of Caribbean gorgonian corals

Extracts of 39 species of Caribbean gorgonians were tested for antimicrobial activity against 15 strains of marine bacteria. The bacteria consisted of three opportunistic pathogens, Vibrio parahaemolyticus, Leucothrix mucor, and Aerococcus viridans, and 12 strains isolated from either healthy or decayed gorgonians. Overall, only 15% (79 out of 544) of the tests resulted in antibacterial activity with 33% (13 out of 39) of the gorgonians inhibiting only one bacterial strain and 23% (9 out of 39) showing no activity. The extracts of four Pseudopterogorgia species showed relatively high levels of activity, inhibiting 43 to 86% of the bacterial strains. The potency of the active Pseudopterogorgia species was variable, however, and three additional Pseudopterogorgia species were inactive against all bacterial strains. With the exception of one sensitive strain, Vibrio species were resistant to gorgonian metabolites. Our results indicate that organic extracts of most Caribbean gorgonians do not possess potent, broad-spectrum antibacterial activity inhibitory to the growth of opportunistic marine pathogens and bacteria associated with healthy and decayed gorgonian surfaces. These findings suggest that the inhibition of bacterial growth is not the primary ecological function of gorgonian secondary metabolites and that bacteria may not be important selective agents in the evolution of gorgonian secondary chemistry.     

Impact of the polychaete Capitella sp. I on microbial activity in an organic-rich marine sediment contaminated with the polycyclic aromatic hydrocarbon fluoranthene

Polychaetes belonging to the genus Capitella are often present in high numbers in organic-rich sediments polluted with, e.g., oil components, and Capitella spp. may have a great impact on the biogeochemistry of these sediments. We examined the influence of Capitella sp. I on microbial activity in an organic-rich marine sediment contaminated with the polycyclic aromatic hydrocarbon, fluoranthene. Capitella sp. I were added to microcosms (10 000 ind m⁻²) and the impact of a pulse-sedimentation of fluoranthene-contaminated sediment (3 mm layer) was studied for a period of 12 d after sedimentation. The sediment oxygen uptake and total sediment metabolism (TCO₂ production) increased in cores with worms (71 to 131%), whereas the anaerobic activity, measured as sulfate reduction rate 12 d after sedimentation, was lower compared to cores without worms. The effect of fluoranthene on sulfate reduction was most pronounced in the presence of worms, with a 34% reduction versus 16% in cores without worms. The reduced sulfur pools in cores with worms were smaller than in cores without worms, suggesting that the reduced anaerobic activity was caused by increased oxidation of the sediment, which may favor O₂ and other electron-acceptors (e.g. NO₃ ⁻, Fe³⁺, Mn⁴⁺) in organic matter decomposition. The sediment oxygen uptake and TCO₂ production did not show significant changes due to fluoranthene treatment, indicating that these parameters were either less sensitive to fluoranthene stress or recovered more rapidly (i.e. within 48 h) than sulfate reduction rates. Bioturbation by Capitella sp. I altered the depth profile of fluoranthene such that fluoranthene was found in deeper sediment layers (down to 2 cm) where diffusional loss and microbial breakdown probably are reduced relative to surface layers. In cores without worms, fluoranthene was found down to 1 cm, with 75% remaining in the upper 5 mm. Received: 5 December 1996 / Accepted: 11 February 1997     

Bacterivory of a mudflat nematode community under different environmental conditions

The fate of the benthic bacterial biomass is a topic of major importance in understanding how soft-bottom environments function. Because of their high abundance, production and nutritional value, benthic bacteria may constitute an important food resource for benthic fauna. The trophic role of bacteria for a nematode community on the Brouage mudflat (Marennes-Oléron-France), dominated by three species: Chromadora macrolaima (64% of the abundance), Daptonema oxycerca (15%) and Ptycholaimellus jacobi (8%), was determined in grazing experiments using ¹⁵N pre-enriched bacteria. On intertidal flats, seasonal, tidal and circadian cycles induce strong variations in environmental conditions. Grazing experiments were performed in order to measure the effects of abiotic (temperature, salinity and luminosity) and biotic (bacterial and algal abundances) factors on assimilation rates of bacteria by nematodes. In order to assess simultaneously bacteria and algal assimilation rates, algal abundances were modified adding ¹³C pre-enriched Navicula phyllepta. Assimilation rate was significantly lower at 5°C; moreover, general trend shows a prominent temperature effect with an optimum around 30°C. Assimilation at salinity 18 was not significantly different from the assimilation at salinity 31. Assimilation was higher under light conditions than in the dark. Above 10⁹ bacteria ml⁻¹, assimilation of bacteria remained unaffected by bacterial abundance. However, assimilation of algae increased with the algal concentration. Nematode kept feeding under conditions of stress, which are typical of the surficial sediment habitat and they appeared to be principally dependent on the algal resource.     

Arylsulfatase activity in marine sediments

Arylsulfatase activity and arylsulfatase-producing bacteria were estimated in sediment samples collected from 3 different biotopes: marine, estuarine, and mangrove. No direct relationship could be established between activity and the number of bacteria at any station. In general, clayey sediments always harboured more arylsulfatase producers than sandy sediments, irrespective of salinity variations. Of the 3 biotopes investigated, the mangrove area exhibited maximum activity. The enzyme showed two pH optima, one at 6.2, the other at 9.0. The optimum substrate concentration was 12x10^-4M. Higher substrate concentrations tended to inhibit arylsulfatase activity. The recovery of added phenolphthalein was maximum only at pH 6.2; KCN, Na₂So₄, and KH₂Po₄ inhibited enzyme activity by 65.5, 46.8 and 37.5%, respectively. More than one type of arylsulfatase may be present in marine sediments; further studies on the role of arylsulfatases are required, since arylsulfatases have been reported to bear on the formation and hardening of exoskeletons in marine forms.     

Distribution and abundance of eggs of Labidocera aestiva (Copepoda: Calanoida) in the bottom sediments of Buzzards Bay,Massachusetts, USA

Grain-size composition of the sea-bed and density of eggs of Labidocera aestiva in bottom sediments in Buzzards Bay were determined at approximately monthly intervals from March 1983 through April 1984. The results of this study, together with those of Marcus (1984), show that during the fall and winter periods of 1982–1984 the proportion of eggs of L. aestiva occurring in the surficial sea-bottom sediments declined and the proportion of eggs in the deeper sediment layers increased. High positive correlations (r ²=0.72 and 0.92) were observed during the early fall 1983 between egg abundance and the proportion of the total sediments represented by the mud fraction. During late fall, winter, and early spring 1983–1984, the coefficients of determination were much lower. Physical criteria (e.g. sedimentation and transport characteristics) can be used to accurately predict the distribution and abundance of recently spawned eggs on the sea-bottom.     

Effects of copper on the faunas of marine soft-sediments: An experimental field study

Although laboratory experimental studies have shown that copper is toxic to marine organisms at concentrations found in contaminated sediments, there is little unequivocal evidence of undesirable ecological effects in the field, other than at extreme concentrations. We describe a study in Botany Bay, New South Wales, Australia, in which the concentrations of copper in marine sediments were experimentally enhanced. Changes in the abundance and taxonomic composition of the fauna of copper-treated sediments relative to those of two control treatments were monitored over a period of six months. Univariate (ANOVA) and multivariate (non-metric multidimensional scaling, MDS) analyses of the changes in the fauna showed that increased concentrations of copper (140 to 1200 g g^-1 compared with background concentrations of 29 to 40 g g^-1) had an impact on the fauna. The nature of the response varied among taxa. For example, in some taxa, numbers of individuals decreased through time relative to controls, whereas the abundance of another taxon remained fairly constant through time in the copper treatment while numbers of control individuals increased. Differences in the changes of the faunas through time among the control and copper treatments were not always consistent among replicate experimental units 5 m apart, nor were they consistent between replicate experimental sites 100 m apart. The magnitudes of the changes in the faunas caused by the copper treatment are considered in the context of the magnitude of previously measured natural temporal variation.     

Chemistry,mineralogy and radioactivity in posidonia oceanica meadows from North-Western Sicily

This paper presents measurements of major, minor, metal trace elements and radionuclides in sediments and in Posidonia oceanica samples from north-western Sicily (Italy). The mineralogical and chemical composition of sediments were determined by X-ray diffraction and X-ray fluorescence techniques, respectively. A flame atomic absorption spectrophotometry was used to measure concentrations of Cu, Zn, Cd and Pb in P. oceanica samples and in sediments. Specific activities of selected radionuclides have been determined by high-resolution gamma spectrometry. Standard statistical analysis was used to assess correlations between different elements and different sample types.     

Selective feeding of littoral harpacticoids on diatom algae: hungry gourmands?

We studied benthic harpacticoid grazing on diatom algae from two sites on the White Sea intertidal sandflat. Diatoms from sediments and from harpacticoid gut contents were sampled in situ, identified and counted, and grazing rates were calculated by two ways: (1) using potential daily ration estimations and (2) from the gut content and gut-residence time data. Paraleptastacus kliei did not contain any diatoms in the guts and presumably fed on other objects (bacteria or flagellates). Two other dominating species studied, Heterolaophonte minuta and Huntemannia jadensis, contained an average of 604 and 222 diatom cells per specimen. Diet composition differed significantly from the natural algal community. Two diatoms of intermediate cell size (Nitzschia palea var. debilis and Navicula sp.) contributed 92–97% of gut content for H. minuta and 58–81% for Hn. jadensis, whereas these diatoms amounted to only about 10% of biomass in native community. Mean consumption rates were estimated as 50–200 μg of wet biomass/day/cm², so the harpacticoids grazed only between 3 and 11% of the total microalgae biomass per day. The grazing impact on the two preferred diatom populations, however, was much more intensive, 10–30% per day for Navicula sp. and 55–228% for N. palea. Therefore, native harpacticoid populations demonstrate highly selective feeding and could be strongly limited by their food in spite of seemingly plentiful total abundance of microphytobenthos. This disproportionally high grazing pressure upon some species apparently could affect the structure of microalgae communities resulting in low relative abundance of mid-sized forms. We hypothesize that a very dynamic spatio-temporal distribution of epibenthic harpacticoids (short-living micropatches) may be the possible adaptation to such local food limitation.     

Complex patterns of change in the macrobenthos of a large sandbank following dredging

The impact of dredging operations on the marine benthos of a large, subtropical, sublittoral sandbank (Middle Banks, Moreton Bay, Queensland, Australia) was investigated during July and August 1982. Statistical comparisons (ANOVA) of species richness, total abundance, Shannon diversity and Shannon equitability were made with extensive predredging data base. Both the dredged and adjacent areas were investigated. Changes in sediments and the distribution and deposition rates of the dredge plumes were also examined. There were significant decreases (P0.025) in the species richness (from 33.0 to 16.6 mean number of species per site), total abundance (from 117.9 to 47.6 mean number of individuals per site) and Shannon diversity (from 4.03 to 3.22 mean diversity per site) within the dredged area. There were significant increases (P0.01) in species richness (from 31.2 to 67.9 mean number of species per site) and total abundance (from 177.7 to 752 mean number of individuals per site) in adjacent benthic areas. The distribution and the predicted deposition rates of the sediment plume correlated precisely with the area of enhancement (P<0.05). The potential causal relationship between deposition and faunal enhancement is discussed. We suggest that the enhanced effect is probably a response of the benthic biota to an increase in available resources.     

Contrasting effects of sulfide and thiosulfate on symbiotic CO2-assimilation of Phallodrilus leukodermatus (Annelida)

Experiments were conducted in order to specify the reductants responsible for the carbon dioxide fixation of the symbiotic sulfur bacteria in the gutless marine oligochaete Phallodrilus leukodermatus (Annelida) from shallow calcareous sediments in Bermuda. Carbon dioxide-uptake rates were suppressed by S⁼ and stimulated by S₂O₃ ⁼. Individuals which hosted bacteria containing reserve energy substances maintained a high short-term CO₂-uptake activity, while bacteria in worm homogenates and in worms treated with an antibiotic (Baypen) did not show any significant metabolic activity. Absolute uptake rates in P. leukodermatus were usually considerably higher than those reported for other animals harbouring prokaryotic sulfuroxidizing symbionts. Utilization of thiosulfate rather than sulfide is compatible with the preferred occurrence of the worms around the redox discontinuity layer and has been confirmed in other thiobiotic animals. Sulfur stored in the symbiotic bacteria appears to be oxidized to sulfate and be excreted when the worms are held under energy-limited conditions. The data emphasize the complexity of the possible metabolic pathways involved in the oxidation of reduced-sulfur compounds by bacterial symbionts in marine invertebrates.     

Study on the marine agarolytic bacterium–infusorium association

Physiological and biochemical properties of a marine agarolytic association of the bacterium Cytophaga diffluens and the infusorium Uronema marinum were investigated. The agarase activity of the association was shown to be higher than that of the pure bacterial culture at all growth stages under identical conditions. Maximum agarase activity of the association, and of the pure bacterial culture, was observed in a medium containing a small amount of organic nitrogen (0.1% yeast extract). Received: 12 October 1998 / Accepted: 11 June 1999     

Impact of canal development on intertidal microalgal productivity: Comparative assessment of Patterson Lakes and Ralphs Bay,South East Australia

We assessed the potential impact of a proposed canal development in an estuarine sandflat at Ralphs Bay, Tasmania on intertidal microalgal productivity and species composition, by comparing it over summer and winter seasons with a well- established (30 year old) canal estate at Patterson Lakes, Victoria. Pulse amplitude modulation (PAM) fluorometry was used to generate a relative measure of photosynthetic performance, which combined with microalgal chlorophyll biomass and irradiance provides an assessment of potential primary productivity. We present a sophisticated mathematical model for calculating benthic microalgal production and the contribution to total primary production, taking into account sediment light attenuation as estimated from sediment grain size. Ralphs Bay had a total productive microalgal biomass of 44 mg chlorophyll a m⁻² which was six times higher than Patterson Lakes, while the relative productivity of Ralphs Bay was four times greater compared to Patterson Lakes where productivity was virtually absent in the subtidal zone of the canal waterway. Ralphs Bay exhibited a more or less homogeneous spatial distribution of microphytobenthos biomass but this was subject to some seasonal variation in species composition, abundance and productivity. By contrast, at Patterson Lakes biomass distribution, diversity and productivity was highly spatially variable in the canal system in both seasons. Patterson Lakes exhibited 60% lower microphytobenthos species richness than Ralphs Bay but little variation in species composition occurred between seasons in the canal estate. This suggests that the dominant diatom species in Patterson Lakes, Pinnularia yarrensis, Gyrosigma balticum and Pleurosigma salinarum, are well adapted to the disturbance regime within the canal estate. The proposed canal development at Ralphs Bay is estimated to cause a decrease in microalgal productivity by both reducing available marine substrate (66% reduction) and replacing productive intertidal phytobenthic habitat with nonproductive canal substrate. These combine to cause a decline in productivity of 92% with significant flow-on effects predicted for higher trophic levels such as migratory wading birds.     

High recovery of culturable bacteria from the surfaces of marine algae

The culturability of heterotrophic marine bacteria obtained from the surfaces of two species of marine algae (Lobophora variegata andHalimeda copiosa) was assessed by comparing total DAPI-stained cell counts to colony-forming bacterial counts on two agar media. The colony-forming bacterial counts on a low-nutrient medium (LN) consisting of seawater and agar were significantly greater for both algal species than counts obtained on a high-nutrient medium (HN) similar in composition to that typically used for the isolation of heterotrophic marine bacteria. On average, 14 and 58%, respectively, of the total bacteria fromL. variegata andH. copiosa were culturable on LN. These recovery rates far exceed those typically reported for marine bacteria. Of 119 LN strains obtained in pure culture, 55% failed to grow on HN. The yeast extract component of HN (1.5 gl^-1) was responsible for the majority of the observed inhibition, suggesting that this nutrient can be highly toxic to marine bacteria. Eighty-nine percent of the strains inhibited by HN were capable of growth when the nutrients in this medium were diluted by a factor of 100 with seawater. Of 66 epiphytic strains, 30 (45%) initially inhibited by HN showed the ability to adapt to this medium after a period of laboratory handling. The initial inability of low-nutrient-adapted bacteria to grow on high-nutrient media may be due to nutrient shock. The results presented here indicate that the culturability of specific populations of marine bacteria can be dramatically improved by the use of low-nutrient media. Further, the importance of developing new medium formulations that eliminate traditional nutrients, some of which are clearly toxic to bacteria, is demonstrated.     

Combined Effects of Levels of Protection and Environmental Variables at Different Spatial Resolutions on Fish Assemblages in a Marine Protected Area

Abstract: The links between species–environment relations and species’ responses to protection are unclear, but the objectives of marine protected areas (MPAs) are most likely to be achieved when those relations are known and inform MPA design. The components of a species’ habitat vary with the spatial resolution of the area considered. We characterized areas at two resolutions: 250 m² (transect) and approximately 30,000 m² (seascape). We considered three categories of environmental variables: substrate type, bottom complexity, and depth. We sought to determine at which resolution habitat characteristics were a better predictor of abundance and species composition of fishes and whether the relations with environmental variables at either resolution affected species’ responses to protection. Habitat features accounted for a larger proportion of spatial variation in species composition and abundances than differences in protection status. This spatial variation was explained best by habitat characteristics at the seascape level than at the transect level. Species’ responses to protected areas were specific to particular seascape characteristics, primarily depth, and bottom complexity. Our method may be useful for prioritizing marine areas for protection, designing MPAs, and monitoring their effectiveness. It identified areas that provided natural shelter, areas acting as buffer zones, and areas where fish species were most responsive to protection. The identification of such areas is necessary for cost‐effective establishment and monitoring of MPAs.