Response of polychaetes to oil spills in natural and defaunated subtropical mangrove sediments from Paranaguá bay (SE Brazil)

A short-term short-scale field manipulation experiment was designed to assess the effects of total or partial defaunation, by sediment drying or diesel oil respectively, on polychaete recolonization rates in mangrove sediments of Paranaguá Bay, SE Brazil. After replacement of defaunated cores in the field, disturbed and adjacent undisturbed control sites were subsequently sampled together with adjacent undisturbed control sites on different dates over a 64-day period. Analyses of variance were carried out to test for differences in polychaete populational densities among experimental treatments and sampling dates. Examination of cores impacted by oil showed that most polychaete species kept rather active, quickly reacting to mechanical or light stimuli or moving rapidly. Polychaete recolonization of local mangroves after small-scale disturbance by oil was a fast process, in contrast to that following total defaunation by sediment drying. Rapid recolonization was largely dependent upon the differing mobility of adults of individual species from unaffected areas nearby, epifaunal crawlers or infaunal predators exhibiting the most rapid recovery rates. Conversely, the slow-paced recolonization of completely defaunated areas was due to the modification of sediment properties by drying and to the absence of larvae or juveniles of local species during the experiment.     

Effects of sediment type on macrobenthic infaunal colonization of laboratory microcosms

We tested the effects of four different sediment types collected from northern Gulf of Mexico estuarine systems on macroinfaunal colonization and community development in our laboratory flow-through microcosm system. Four sediments, types included , a beach sand, two fine-grained muds, but from different locations, and a 50:50 mixture of one of the mud sediments and beach sand. Our hypothesis was that the pattern of colonization would differ among sediment types based on empirical field data and theory but the differences would be expressed most strongly at sediment type extremes (e.g., mud versus sand). A total of 49 taxa colonized the four sediments. Unidentified Actiniaria (sea anemones) numerically dominated densities among all four sediments with densities ranging between 46.5 to 60.5 per microcosm (20 cm side^–1). Average taxa richness per microcosm (N: 10 replicates per sediment treatment) ranged from 10.4 in one of the mud treatments to 14.9 taxa in the sand. These were the only significant differences among sediment types (P0.05) in taxa richness and we detected no significant effects of sediment type on animal densities. Differences in community metrics, although statistically significant, were generally of a relatively small magnitude. Five of 10 microcosms per treatment were randomly selected to test for effects of sediment depth (e.g., top, mid, and bottom). In vertically sectioned microcosms, average taxa richness in sand treatments was significantly greater than those of the other three sediments. A non-parametric multivariate analysis (Primer) revealed that community structure in the vertically sectioned microcosms differed significantly between sand and one of the mud treatments. Mean taxa richness of top sections differed significantly from mid and bottom sections. We detected significantly higher animal densities and taxa richness (p0.05) in vertically sectioned versus non-sectioned microcosms. However, these differences were unexplained based on experimental protocols.     

Benthic invertebrate recolonization of small-scale disturbances in the littoral zone of a subtropical Florida lake

Construction of spawning beds by the exotic cichlid fish, Sarotherodon aurea, produces numerous small-scale disturbances in shallow Florida lakes. Two experimental methods were used to simulate these disturbances (containers filled with defaunated sediment and disturbed natural substratum) and to determine benthic invertebrate recolonization patterns and rates.Recolonization of experimental containers was rapid and densities of macroinvertebrates reached equilibrium with the control habitat by Day 6 following disturbance. However, Chironomidae and miscellaneous taxa usually were more abundant (p < 0.05) in the experimental containers, and Oligochaeta always were more abundant (p < 0.01) in the control. Species of the planktonically dispersed insects either attained equilibrium rapidly or showed significantly higher densities in the experimental containers (i.e. opportunistic species).In the second experimental approach, disturbance of natural substratum removed 91% of the benthic invertebrates. The common species of chironomids reached equilibrium by Day 6 but the two predominant oligochaetes, Limnodrilus and Pristina, reached equilibrium at 9 and 15 days respectively. For the entire community, similarity on Day 6 was 87.1% and over the remainder of the sample period averaged 86.8%. Chironomid instar analyses showed significantly higher proportions of early instars in the disturbed patch indicating that colonization is principally by younger organisms. Thus, small-scale disturbance in freshwater benthic communities may be more important in ordering the biomass or age-group structure than the numerical abundance.     

Development of a meiobenthic nematode community following the intertidal placement of various types of sediment

A field experiment was conducted at an intertidal mudflat in SE England to investigate processes affecting the development of meiobenthic nematode assemblages in response to the placement of different types of sediment, simulating the deposition of fine-grained maintenance dredged material for habitat creation. Natural assemblages were exposed to different types of substrate, including sediment with natural sand and organic content (defaunated control), sediment with elevated sand content (high sand content treatment) and sediment with elevated organic content (high organic content treatment) for a period of 12 months. Differences between colonising assemblages and those from ambient control sediment in terms of total nematode abundance, taxonomic membership (i.e. number of species, species composition) and size (i.e. total biomass, biomass size spectra) were most marked in the plots with elevated organic content. Nematode density, number of species and total biomass in the defaunated control and high sand content treatment came to resemble those in the ambient control sediment after 3 months. In the organically enriched sediment, values only attained background level at the end of the experiment. Multivariate analyses revealed that, although assemblage structure in all treatments, and in particular the defaunated control and the high sand content treatment, became increasingly similar to the ambient sediment over time, recovery to ambient condition had not occurred 1 year after the set-up of the experiment.     

Seasonal variation in benthic invertebrate recolonization of small-scale disturbances in a subtropical Florida lake

Approximately 11.5% of the littoral zone of a hypereutrophic Florida lake is disturbed by the construction of spawning beds by the cichlid fish, Sarotherodon aurea, during a single spawning season. Simulations of these beds were created during three seasons of the year to test for variation in recolonization rates and patterns in the benthic macroinvertebrate community.The seasonal variation in densities of benthic invertebrate populations suggests a direct relationship between reproductive activity and recolonization rate. Recolonization rates of the numerically dominant species, Polypedilum halterale (Diptera: Chironomidae), were much more rapid in the spring and summer than in the winter. In contrast, Hyalella azteca and Glyptotendipes paripes attained peak population densities during the winter season when Polypedilum was present in low densities. These organisms invaded the disturbed area in unusually high abundances and later declined to background levels. The final result was a winter population with densities comparable to the control (undisturbed) area, but the species composition was different.Similarity between disturbed and control communities during the winter season only reached 67% a month after disturbance, while communities during the warmer months attained nearly 90% similarity in less than 15 days. This lack of similarity during the winter indicates that disturbance, at the appropriate time, may play a role in community organization.     

Response of benthic invertebrates to natural versus experimental disturbance in a Swiss prealpine river

1. The crucial point of disturbance experiments in streams is the extent to which they can simulate a natural spate. Ideally, disturbance experiments should proceed side by side with a phenomenological study to allow a direct comparison. In the present study conducted in a prealpine Swiss river, the River Necker, fortuitous events made such a comparison possible. 2. In summer 1994, we took Surber samples one day before and on several sampling dates after a major flood (recurrence interval ≈ 5 years), which was followed by a long period of uniform discharge in a river characterized by frequent spates. Beginning 19 days after this flood, patches of the stream bed (≈ 9 m²) were physically disturbed by kicking and raking. 3. The degrees of reduction in the total number of individuals and the dominant taxa were similar after both types of disturbance, as were the recolonization patterns of Rhithrogena spp., Leuctra spp. and Hydracarina. Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Corynoneura/Thienemanniella spp. showed a distinct lag phase after the flood before recolonization began, whereas there was no such lag phase after the experiment. Therefore, the time needed to recover to pre-flood densities was longer for these taxa. Nevertheless, recolonization rates and patterns after the lag phase were similar to those after the experimental disturbance. 4. Size-class measurements indicated that recruitment from egg hatching may have been more important after the flood than after the experimental disturbance for Rhithrogena spp., but not for Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Leuctra spp. Invertebrate drift was probably the most important pathway of recolonization after both types of disturbance. 5. Our experiment allowed a realistic simulation of several important effects of the large flood on the invertebrate community. Smaller spates that induce substratum movement at a spatial scale similar to our experimental plots are much more common than large floods in the River Necker. For these spates, our experiment should provide an even more realistic simulation of natural disturbance.     

Monitoring of physically restored seagrass meadows reveals a slow rate of recovery for Thalassia testudinum

Physical damage by motor vessels is a widespread problem for seagrass meadows, with hull and propeller strikes accounting for thousands of acres of impaired habitat in Florida, United States, alone. Because the excavations can become topographically unstable, and because recolonization and succession of seagrasses can require decades to reach climax, Thalassia testudinum‐dominated communities, there has been increasing efforts to regrade and stabilize impacted sediments, and to speed succession. A prior project involving eight vessel groundings in two hydrodynamic settings (high and low energy) examined the relative efficacy of capping injuries with sand‐filled fabric tubes or limestone pea rock, followed by planting of fast‐growing seagrass species and nutrient amendment using bird‐roosting stake deployments. Monitoring after 4 years showed recruitment of fast‐growing, subordinate species: Syringodium filiforme or Halodule wrightii, particularly in low‐energy environments; however, T. testudinum had not yet returned to natural densities. The current study extended monitoring an additional 3 years. At 7 years posteffort, T. testudinum recolonization was still incomplete. Of the eight sites, only three had statistically recovered. In low‐energy areas, H. wrightii cover was greater than in reference meadows, and a strong inverse relationship between H. wrightii and T. testudinum was observed. One explanation is that residual nutrients from bird feces switched the competitive outcome. We demonstrate using seagrass tissue N:P that nutrients delivered via bird stakes remained in the sediments of low‐energy environments, and argue that prolonged fertilization resulted in competitive advantages for H. wrightii, depressing T. testudinum recruitment and delaying recovery of the targeted seagrass community.     

THE EFFECTS OF PHYSICAL DISTURBANCE ON AFROPTILUM SUDAFRICANUM (EPHEMEROPTERA: BAETIDAE) POPULATION DENSITIES IN A KENYAN MOUNTAIN STREAM

Summary

The effects of physical disturbance on larval populations of the mayfly Afroptilum sudafricanum Lestage were examined in the Naro Morn River, Kenya. Disturbance was induced by stirring, shifting and relocating streambed substrates by hand. The method aimed to simulate natural physical disturbance. The effects of continuous disturbance were examined by sampling larval populations at minute intervals of up to 14 minutes. The effects of periodic disturbance were examined by sampling larval populations which had been disturbed at intervals of minutes (short-term), hours (medium-term) and days (long-term). About 85% of A. sudafricanum individuals was removed from the streambed within four minutes of continuous physical disturbance. There were higher densities at night than during the day. All densities on the control sites for the medium-term disturbance experiments were significantly higher than those on the disturbed sites. Most of the post-disturbance densities on the medium-term disturbance sites were significantly lower than the pre-disturbance densities (Tukey's honestly significance difference test, α=0.05). There was no distinct density pattern on the sites exposed to long-term disturbances. Sites with the same disturbance regime appeared to react differently, some having dramatic fluctuations in density. Disturbance effects on A. sudafricanum density were multi-faceted with different expressions in time and space. It is concluded that A. sudafricanum is highly mobile and is capable of recolonizing disturbed areas within six hours. Their high mobility enables them to crawl into the deeper sediment layers during floods. However, recovery time depended not only on species mobility but also on how densely the sources of recolonization were populated and the frequency of disturbance. Slight increases, strong declines and negligible disturbance effects on the density of A. sudafricanum were evident. Afroptilum sudafricanum is highly mobile and is capable of rapid recolonization. It is concluded that physical disturbance affects A. sudafricanum populations in the Naro Morn River.     

Drifting Algae as a means of Re-Colonizing Defaunated Sediments in the Baltic Sea. A Short-Term Microcosm Study

We conducted a microcosm experiment to evaluate the capability of fauna inhabiting or being transported by drifting filamentous algae to colonize defaunated sediment. We expected meiofauna would perform a quicker and more effective re-colonization of disturbed areas by means of the algal mats than their macrofaunal counterparts. Similarly, within meiofauna, we expected more mobile taxa such as ostracods and harpacticoids to colonize the sediment more readily than other more sedentary ones such as nematodes. Naturally drifting algae were collected from the field and placed in 1 l aquaria on top of 5 cm of defaunated sediment. After 3 and 6 days, one core sample (5 cm deep) was taken from each aquarium; the first 2 cm were sliced into 2 mm layers, and the remaining fraction into 1 cm layers. The sediment remaining in the aquaria was sieved through a 0.5 mm sieve to collect the re-colonizing macrofauna. The dominant macrofaunal taxa inhabiting the algae were juvenile bivalves and gastropods, with Cerastoderma glaucum accounting for the majority of the bivalves and Hydrobia sp. for most of the gastropods. After 3 and 6 days, the most abundant macrofaunal taxa colonizing the sediment were Cerastoderma glaucum, Hydrobia sp. and gammarid amphipods. Higher abundances were found after 6 days than after 3, though differences were not significant for any of the major taxa. Meiofauna inhabiting the algae were dominated by rotifers, nematodes, ostracods, chironomid larvae and harpacticoid copepods. Contrary to our predictions, nematode and harpacticoid species inhabiting the drifting algae were not driven to sediment re-colonization but remained in the algae. Our results indicate that some benthic animals may indeed benefit from drifting algal mats as a means of dispersal and re-colonization of previously defaunated sediments in relatively short periods of time. Also, they may contribute to explain some of the trends found in other studies, regarding species increase under drifting algae and the recovery patterns found in areas often exposed to algal conglomerates.     

An experimental test of the effects of inorganic sediment addition on benthic macroinvertebrates of a subtropical stream

Inorganic sediments of terrestrial origin may impact stream macroinvertebrate communities. Although input of terrestrial sediments to streams may occur naturally, human-induced activities in the catchment amplify this input greatly. We used an in-stream experiment to investigate whether short-term additions of terrestrial sediments of two size classes affected stream macroinvertebrates. The experiment was designed in blocks to minimize the influence of flow velocity and other environmental variables. Four treatments were employed: (i) addition of fine sand (0–0.24 mm), (ii) coarse sand (0.25–0.8 mm), (iii) fine+coarse sand, and (iv) control (water only). Macroinvertebrates were sampled immediately after the addition of sediments (or water). The experiment consisted of 20 blocks. We analyzed the response of the macroinvertebrate fauna in terms of abundance and species richness. Since species richness is strongly dependent on number of individuals sampled, we also analyzed rarefied species richness. Community structure was evaluated using a distance-based Manova on presence/absence and abundance data. The addition of coarse and fine+coarse sand reduced the abundance and species richness of macroinvertebrates in relation to the control. The response in terms of rarefied species richness in the treatments did not differ from the control, indicating that reduction in species richness was a sampling artifact resulting from decreased sample abundance. The Manova analyses indicated that coarse-sand addition caused changes in both species composition and community structure. Addition of fine and fine+coarse sand affected only slightly species composition and community structure. We concluded that even short-term input of terrestrial sediments causes impacts on benthic macroinvertebrates, and recommend that land-use management of tropical catchments should employ practices that reduce input of terrestrial sediments to streams. Handling editor: K. Martens     

Sustainable control of mosquito larvae in the field by the combined actions of the biological insecticide Bti and natural competitors

Integrated management of mosquitoes is becoming increasingly important, particularly in relation to avoiding recolonization of ponds after larvicide treatment. We conducted for the first time field experiments that involved exposing natural populations of the mosquito species Culex pipiens to: a) application of the biological insecticide Bacillus thuringiensis israelensis (Bti), b) the introduction of natural competitors (a crustacean community composed mainly of Daphnia spp.), or c) a combined treatment that involved both introduction of a crustacean community and the application of Bti. The treatment that involved only the introduction of crustaceans had no significant effect on mosquito larval populations, while treatment with Bti alone caused only a significant reduction in the abundance of mosquito larvae in the short‐term (within 3–10 days after treatment). In contrast, the combined treatment rapidly reduced the abundance of mosquito larvae, which remained low throughout the entire observation period of 28 days. Growth of the introduced crustacean communities was favored by the immediate reduction in the abundance of mosquito larvae following Bti administration, thus preventing recolonization of ponds by mosquito larvae at the late period (days 14–28 after treatment). Both competition and the temporal order of establishment of different species are hence important mechanisms for efficient and sustainable mosquito control.     

Effects of moonlight on the vertical migration patterns of demersal zooplankton

The diel vertical migration patterns of demersal zooplankton, those organisms which habit bottom substrates but periodically emerge to swim freely in the water column, water determined throughout the lunar cycle. Demersal zooplankton were quantitatively sampled on a subtidal sand flat in the Gulf of California every 2 h for 24-h periods at new, full, first, and last-quarter moons, both as they emerged into the water column and as they returned to the benthos. Demersal zooplankton rarely migrated during daylight. Three general patterns of migration were observed. (1) Polychaetes and cumaceans emerged from the benthos at dusk, regardless of the phase of the moon. Polychaetes returned to the benthos throughout the night while cumaceans returned near dawn. (2) Species of amphipods and isopods exhibited significant avoidance of moonlight, delaying emergence until moonset or returning to the benthos at moonrise. (3) Species of copepods, mysids, shrimp, Branchiostoma (cephalochordate), and tanaids emerged into the water column throughout the night. The timing of migration was highly variable and did not correlate with the presence or absence of moonlight. Large zooplankton migrated less frequently into the water column during moonlit periods than small forms, suggesting that nocturnal predation by visually oriented planktivorous fish may be an important selective pressure.Demersal zooplankton emerged into artificially darkened emergence traps in significantly higher numbers during daylight and during full and quarter moons than into undarkened control traps, demonstrating that absence of light is a major cue stimulating migration. Reentry traps resting on the bottom captured higher densities of demersal zooplankton than either emergence traps or reentry traps suspended off the bottom. Thus, many demersal zooplankton remain near the bottom, rarely swimming far into the water column. Some trap avoidance was observed and current methods for collecting demersal zooplankton are evaluated. Since most demersal zooplankton remained in the water column only a short time, dispersal, particularly over short distances, may be a major advantage of migratory behavior. Migration facilitates rapid recolonization of disturbed or defaunated sites, disrupts and mixes bottom sediments, and results in daily variation in the microdistribution, patchiness, and species composition of the benthic fauna.     

Effects of an experimental acid pulse on invertebrates in a high altitude Sierra Nevada stream

The effects of pulsed acidification on invertebrate densities and drift, and water chemistry, in a high altitude Sierra Nevada stream were measured using artificial stream channels. Water was diverted from the Marble Fork of the Kaweah River, California, U.S.A., through twelve replicate channels; however, low flow in the summer of 1985 eliminated all but four of these channels. Channels were stocked with natural substrates and organisms from the Marble Fork of the Kaweah River. After a three week acclimation period, we simulated a low pH rain event by adding acid (H₂SO₄ and HNO₃) to two of the channels, reducing pH to 5.0 for 6 hours. The other two channels acted as controls (pH 6.4). During acid additions, Baetis spp. drift in acidified channels was ca. 7 times higher than in control channels (F = 39.02, p < 0.025; data fourth root transformed, ANOVA), and the percentage of drifting baetids that was dead was significantly higher in acidified than control channels (46% vs. 0%, F = 29.86, p < 0.05; arcsine square root transformed data, ANOVA). Other taxa showed no significant drift responses, and benthic densities of all taxa showed no effects two days after acidification, probably owing to rapid recolonization by invertebrate drift in influent waters. Stream chemistry data are presented; heavy metal concentrations did not significantly increase in the 2 m stream channels.     

High stocking density during larviculture and effect of size and diet on production of juvenile Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

Different stocking densities were investigated in larviculture and feeding of Lophiosilurus alexandri, as well as analyses of the effects on juveniles of two size‐classes and two different commercial formulated diets. The first experiment was two‐phased: (a) larvae stocked at densities of 60, 120, 180, 240, and 300 larvae L⁻¹ fed with Artemia nauplii and reared for 15 days; (b) in phase 2, densities of 5, 10, 15, 30, and 40 juveniles L⁻¹ were evaluated during feed training (20 days). Mean water temperature in both phases was 28°C. In the first phase of experiment 1, the different stocking densities did not affect fish growth or survival. In phase 2, growth was similar in all densities; however, survival was lower at higher densities. The increased density provided a rise in biomass and number of individuals produced in both phases. In the second experiment, two size‐classes of feed‐trained juveniles (30.22 ± 1.84 and 34.66 ± 2.41 mm) were given pellets of two different diameters (1.2 and 2.6 mm) for 20 days. The largest juveniles fed the 1.2 mm inert diet had higher final weights and lengths. Larviculture and feed training of L. alexandri can thus be performed successfully at high stocking densities of 300 larvae L⁻¹ during the first 15 days of feeding, and at densities of up to 40 juveniles L⁻¹ during the 20 days of feed training, respectively.     

Small-scale shifting mosaics of two dominant grassland species: the possible role of soil-borne pathogens

We analyzed the dynamics of dominant plant species in a grazed grassland over 17 years, and investigated whether local shifts in these dominant species, leading to vegetation mosaics, could be attributed to interactions between plants and soil-borne pathogens. We found that Festuca rubra and Carex arenaria locally alternated in abundance, with different sites close together behaving out of phase, resulting in a shifting mosaic. The net effect of killing all soil biota on the growth of these two species was investigated in a greenhouse experiment using gamma radiation, controlling for possible effects of sterilization on soil chemistry. Both plant species showed a strong net positive response to soil sterilization, indicating that pathogens (e.g., nematodes, pathogenic fungi) outweighed the effect of mutualists (e.g., mycorrhizae). This positive growth response towards soil sterilization appeared not be due to effects of sterilization on soil chemistry. Growth of Carex was strongly reduced by soil-borne pathogens (86% reduction relative to its growth on sterilized soil) on soil from a site where this species decreased during the last decade (and Festuca increased), while it was reduced much less (50%) on soil from a nearby site where it increased in abundance during the last decade. Similarly, Festuca was reduced more (67%) on soil from the site where it decreased (and Carex increased) than on soil from the site where it increased (55%, the site where Carex decreased). Plant-feeding nematodes showed high small-scale variation in densities, and we related this variation to the observed growth reductions in both plant species. Carex growth on unsterilized soil was significantly more reduced at higher densities of plant-feeding nematodes, while the growth reduction in Festuca was independent of plant-feeding nematode densities. At high plant-feeding nematode densities, growth of Carex was reduced more than Festuca, while at low nematode densities the opposite was found. Each plant species thus seems to be affected by different (groups of) soil-borne pathogens. The resulting interaction web of plants and soil-borne pathogens is discussed. We hypothesize that soil disturbances by digging ants and rabbits may explain the small-scale variation in nematode densities, by locally providing “fresh” sand. We conclude that soil-borne pathogens may contribute to plant diversity and spatial mosaics of plants in grasslands. Received: 19 January 2000 / Accepted: 11 April 2000     

A bioenergetic study of a benthic nematode,plectus palustris de man 1880, throughout its life cycle

Summary Growth and reproduction of the parthenogenetic freshwater nematode,Plectus palustris, were studied at different controlled levels of food densities at 20° C. A bacteria-sloppy agar mixture was used as substrate and food medium. No growth or reproduction occurred at the lowest food density (8.10⁷ bacterial cells ml^-1). At 8.10⁸ cells ml^-1, the larval duration was 18.5 days, the instantaneous growth rate (g) of young larvae 0.2 d^-1 and the daily fecundity rate during a prolonged period of constant egg production 12.6 eggs·d^-1. At a food density of 8.10⁹ cells ml^-1, the corresponding values are 12.5 days, 0.4 d^-1 and 37.7 eggs d^-1.By including the data on respiration from a previous paper (Klekowski et al., 1979), the energetics of the species at different food densities can be discussed: production processes are apparently more dependent on food supply than respiration. However, prolongation of the larval phase in lower food densities greatly increases the cumulated respiratory costs per unit production. A second point is the ability to produce smaller-sized primiparous females in sub-optimal food which shortens the immature life period and serves to reduce the burden of cumulated metabolic costs for attaining sexual maturity.A comparison of the range of food densities used in the experiments with bacterial densities known from lake sediments of different trophic type suggests that food is likely to be the main factor governing the population dynamics of bacterivorous species under field situations.     

Benthic foraminifera of a Miocene canyon and fan

We present benthic foraminiferal assemblage data from an exhumed Miocene canyon and fan system from the Tabernas Basin (SE Spain). The presence of good indicator taxa and unique assemblages occupying specific environments allows the distinction of slope, canyon and fan environments within the Tabernas Basin by foraminiferal assemblages alone. Five assemblages are defined on the basis of the occurrence of the indicator taxa. Primary control on the distribution of these assemblages is consistent with trends of physical disturbance and consequent defaunation. Barren samples, which are predominantly found in high-energy parts of the proximal canyon, are recognized as representing recently defaunated substrates (i.e. early successional assemblages). High diversity assemblages containing a high abundance of agglutinated taxa are recognised in the undisturbed slope sequences as being the regional equilibrium (“climax”) fauna. Intermediate between these end-members are assemblages with low diversity, dominated by calcareous taxa typically found in the relatively low-energy canyon and fan environments, which are recognized as representing the middle phases of the ecological succession. Two further assemblages, a low diversity assemblage typified by Cassidulina laevigata and Bulimina costata and a very low diversity assemblage dominated (> 10% of all benthic tests) by Globobulimina spp., are restricted to low-energy parts of the canyon and fan, and are absent from the proximal canyon and slope. The composition of these assemblages indicate that nutrient supply/oxygenation is a secondary control on the palaeoecology of the canyon system. A conceptual model for the recolonisation of defaunated substrates in El Buho Canyon is proposed, in which either an oligotrophic climax assemblage or a eutrophic climax assemblage can be achieved at the completion of recolonisation of defaunated substrates, depending on environmental conditions.     

Biocontrol of Fusarium and Verticillium Wilt of Tomato by Penicillium oxalicum under Greenhouse and Field Conditions

Treatments with conidia of Penicillium oxalicum produced in a solid‐state fermentation system were applied at similar densities (6 × 10⁶ spores/g seedbed substrate) to tomato seedbeds in water suspensions (T1: 5 days before sowing, or T2: 7 days before transplanting; 15 days after sowing), or in mixture with the production substrate (T3: 7 days before transplanting; 15 days after sowing). Treatments T2 and T3 significantly (P = 0.05) reduced fusarium wilt of tomato in both greenhouse (artificial inoculation) (33 and 28%, respectively) and field conditions (naturally infested soils) (51 and 72%, respectively), while treatment T1 was efficient only in greenhouse (52%). Verticillium wilt disease reduction was obtained with T3 in two field experiments (56 and 46%, respectively), while T1 and T2 reduced disease only in one field experiment (52% for both T1 and T2). Treatment with conidia of P. oxalicum plus fermentation substrate (T3) resulted in better establishment of a stable and effective population of P. oxalicum in seedbed soil and rhizosphere providing populations of approx. 10⁷ CFU/g soil before transplanting. Results indicate that it will be necessary to apply P. oxalicum at a rate of approx. 10⁶–10⁷ CFU/g in seedbed substrate and rhizosphere before transplanting for effective control of fusarium and verticillium wilt of tomato, and that formulation of P. oxalicum has a substantial influence on its efficacy.     

Macrofaunal recolonization on intertidal mudflats: effect of sediment organic and sand content

Following concerns over how differences in dredged material properties affects recovery following dredged material deposition on mudflats, a field manipulation experiment was conducted to investigate the effects of increased sediment organic content (from 0.9% to 2.8%) and sand content (from 12.0% to 47.0%) on macrofaunal recolonization and sediment properties on an intertidal mudflat, Crouch Estuary, Essex, UK. The manipulated sediments were placed in 1-m² plots, 10 cm deep, in a randomised block design and macrofauna and sediments sampled after 1 week, 1, 3, 6, and 12 months. The results suggested that while increased sand content had no discernible effect on sediment property changes, increased organic content resulted in marked reductions in redox potential at 1-, 2- and 4-cm sediment depths and increased shear strengths. These sediments exhibited a distinct ‘cracking’ appearance on their surfaces. Similarly, while macrofaunal recovery was only affected by increased sand content in the short-term (1 month), total numbers of individuals, number of species and diversity took longer to recover in sediments with increased organic contents. Recolonization proceeded via a gradual increase in the abundance of those taxa present in ambient sediments rather than via a distinct successional sequence. Recovery was species-specific with two species (Hediste diversicolor (Müller) and Hydrobia ulvae (Pennant)) recovering to ambient levels within the first week of the experiment. Multivariate analyses indicated that the community assemblages of the low-organic content treatments had recovered after 12 months while those of the high-organic content treatments were still significantly different to those of the controls at the end of the experiment. We propose that the relatively rapid recovery and lack of successional sequence generally observed in all sediment types of this study can be explained by the opportunistic nature of the ambient assemblage and by the dispersive nature of the dominant species. Reduced sediments and/or increased shear strengths led to a slow recovery in high-organic content treatments. These results indicate that a careful consideration of the organic content of fine-grained dredged material must be made during the licensing process of beneficial use schemes.