Physically Disturbed Research Articles

Major fine-scale spatial heterogeneity in accumulation of gelatinous carbon fluxes on the deep seabed

Abyssal plain communities rely on the overlying water column for a settling flux of organic matter. The origin and rate of this flux as well as the controls on its fine-scale spatial distribution following seafloor settlement are largely unquantified. This is particularly true across regions where anthropogenically-induced seafloor disturbance has occurred. Here, we observed, quantified and mapped a mass deposition event of gelatinous zooplankton carcasses (pyrosomes) in July-September 2015 across one such physically disturbed region in the Peru Basin polymetallic nodule province (4150 m). Seafloor in this area was disturbed with a plough harrow in 1989 (as part of the DISCOL experiment) causing troughs in the sediment. Other parts were disturbed with an epibenthic sled (EBS) during a cruise in 2015 resulting in steep-walled, U-shaped troughs. We investigated two hypotheses: a) gelatinous food falls contribute significantly to the abyssal plain carbon pump and b) physical seafloor disturbance influences abyssal distribution of organic matter. We combined optical and bathymetric seafloor observations, to analyze pyrosome distribution on seabeds with different levels of disturbance. 2954 pyrosome colonies and associated taxa were detected in > 14,000 seafloor images. The mean regional carbon (C) deposition associated with pyrosome carcasses was significant compared to the flux of particulate organic C (182 to 1543%), and the total respired benthic C flux in the DISCOL Experimental Area (39 to 184%). EBS-disturbed seafloor tracks contained 72 times more pyrosome-associated C than an undisturbed reference site, and up to 4 times more than an area disturbed in 1989. Deposited pyrosomes collected had a higher proportion of labile fatty acids compared to the sediment. We document the temporal and spatial extent of an abyssal food fall event with unprecedented detail and show that physical seafloor disturbance results in the accumulation of detrital material. Such accumulation may reduce oxygen availability and alter benthic community structure. Understanding both the relevance of large food falls and the fine scale topography of the seafloor, is necessary for impact assessment of technologies altering seafloor integrity (e.g. as a result of bottom-trawling or deep seabed mining) and may improve their management on a global scale.

Biological influences on coastal muddy sediment structure following resuspension

AbstractShallow coastal muddy sediments are important for global nutrient cycling and carbon storage and provide a habitat for diverse communities of organisms. Bottom shear stress from physical disturbances such as storms and hurricanes resuspend coastal muds, disrupting their cohesive structure. How biological vs. physical processes affect reconsolidation of physically disturbed natural muds, however, is poorly understood. We compare the recovery of sediment properties related to compaction and cohesion of muds following physical disturbance. We hypothesized that recovery of cohesion would take longer than compaction and that changes in surface and subsurface cohesion would occur on different timescales. We collected muddy sediment cores and resuspended the top 5 cm in the lab to simulate storm disturbance. At several timepoints following resuspension (1–30 d), we measured sediment properties providing metrics of compaction (sediment height, porosity, grain size distribution, sound speed) and of surface and subsurface cohesion (erodibility, fracture behavior, exopolymeric substances [EPS]). Compaction and cohesion increased rapidly over the first 1–2 d after resuspension and continued to slowly increase for 2 weeks. Between 2 and 4 weeks, however, subsurface cohesion increased and turbidity decreased, consistent with sediment restabilization. In contrast, subsurface compaction decreased and eroded mass increased, suggesting destabilization. We attribute this apparent destabilization to delayed activity of small‐bodied infauna. Surprisingly, EPS concentration did not explain cohesion changes. These results highlight the importance of including biological parameters when predicting the recovery of sediment structure following a physical disturbance. This work has implications for understanding coastal sediment transport dynamics in frequently disturbed sediments.

Effects of moisture and physical disturbance on pore-scale oxygen content and anaerobic metabolisms in upland soils.

Soils are the largest dynamic stock of carbon (C) on Earth, and microbial respiration of soil organic C accounts for over 25% of global carbon dioxide (CO2) emissions. Zones of oxygen depletion in upland soils (anaerobic microsites) are increasingly recognized as an important control on soil microbial respiration rates, but the factors governing the volume and distribution of anaerobic microsites are relatively unknown. We measured the dissolved oxygen (DO) content of porewater from incubated soil cores of varying moisture contents (<80% and >80% water saturation) and degrees of disturbance (undisturbed, conventionally tilled, and physically disturbed). Porewater was extracted sequentially from pores constrained by three effective pore diameters, ≥3.0μm, 3.0-1.0μm, and 1.0-0.6μm, from cores incubated for 7, 14, or 28days, using a modified Tempe cell extraction system. We observed a parabolic pattern in mean dissolved oxygen (DO) concentrations across pore sizes, independent of soil moisture and degree of disturbance. Specifically, DO values within the largest and smallest pore domains were relatively depleted (155±10μM and 160±11μM, respectively), while DO values within medium pores were closer to saturation (214±8μM). The observed DO pattern provides insight into the balance of microbial oxygen demand versus oxygen supply across pore domains within upland soils. Additionally, we observed iron and manganese reduction in all soils except samples subjected to disturbance and incubated at <80% water saturation, suggesting that disturbance enhances aeration and diminishes anaerobic metabolisms within upland soils. Our findings highlight the influence of soil moisture and management on soil redox and CO2 efflux rates.

Effects of sediment deposition on the New Zealand cockle, Austrovenus stutchburyi

ABSTRACTNew Zealand estuaries and harbours are subjected to increasing sediment deposition that can smother and bury infaunal communities, yet how coastal species respond to sediment deposition is not well understood. Here, we experimentally examined the effects of native marine sediment deposition on the NZ cockle (Austrovenus stutchburyi). Cockles were found to be highly mobile and capable burrowers, able to resurface within days from beneath 2–25 cm of sediment where no physical disturbance to their natural orientation occurred. Cockles were also resilient to daily (2 cm) reburials. However, following disturbance to their natural orientation, inverted cockles were significantly impeded when buried under 5–10 cm of sediment, with fewer adults resurfacing than sub-adults. Cockle populations are likely to be resilient to native sediment deposition, unless physically disturbed. When disturbed from their natural orientation in the sediment, higher mortality of larger adult-sized cockles would be predicted, with mortality increasing under thicker sediment deposits.

Influence of heavy metals on nematode community structure in deteriorated soil by gold mining activities in Sibutad, southern Philippines

Ore mining is among the most environmentally destructive anthropogenic practices, particularly in developing countries. Correct assessment of its impacts on soil ecosystems requires an understanding of the response of soil food webs. Nematodes, often the most abundant invertebrates in soils, occupy various positions in food webs, and their assemblages are commonly used to reflect soil health. In October 2014, we collected soil samples from five sites of a small-scale mining area in Sibutad, southern Philippines, to assess the influence of mining activities on nematode assemblages. Two sites were considered undisturbed as there were no visible signs of mining, while the other three sites were disturbed. Nematodes were extracted live and identified to genus level using morphology-based identification. We analysed genus composition, genus and trophic diversity, and the life-history based maturity index. We measured soil environmental variables (pH, organic matter, granulometry and several heavy metals), and correlated variation in nematode genus composition to variation in these environmental factors. Small-scale mining activities had variable but generally non-significant impacts on soil properties, altered vegetation and caused increases in concentrations of Hg and Pb, but not consistently so in all impacted sites. The high patchiness in vegetation and heavy metal content were reflected in a high within-site variability of nematode assemblages. Total nematode abundance was significantly lowest in the most physically disturbed site, but not so in the most metal-polluted one, suggesting that abundance is not a good indicator of pollution status. Nematode genus composition significantly differed between disturbed and undisturbed sites. By contrast, only few differences between sites were found for diversity or maturity indices, demonstrating that genus composition was a better indicator of mining-related effects than many common indicator indices and highlighting that detailed assemblage analysis is required for a correct interpretation of moderate pollution effects on soil nematodes. Measured environmental variables together explained 60% of the variation in nematode assemblages in the area; the three ‘single best’ explanatory variables were the concentrations of Pb, Hg and N, but none of these by itself explained more than 8% of the variation in nematode data, while their combination explained 24%. Some genera of predacious and omnivorous nematodes, which are generally expected to be sensitive to both chemical pollution and physical disturbance (e.g., Ironus and Eudorylaimus), were most abundant in sites with elevated heavy metal concentrations, which can have repercussions for the interpretation of nematode-based indices such as the MI.

Response of Posidonia oceanica growth to dredging effects of different magnitude

The response of the seagrass Posidonia oceanica in an area physically disturbed by 2 dredging events was evaluated to understand the recovery time of this species and compared to 2 reference locations. An asymmetrical ‘beyond BACI’ (Before/After, Control/Impact) sampling design was applied in combination with reconstructive techniques to compare vertical rhizome elongation and leaf production in P. oceanica during 4 yr before and 4 yr after each dredging event in 1 disturbed and 2 reference locations. On average, vertical rhizome elongation increased from before to after each dredging event, with higher growth being recorded in the disturbed location compared to the reference locations. This effect appeared to be driven by a combination of the application of different dredging techniques and exposure to prolonged stress, as rhizomes had not completely recovered from the first impact by the time the second, lower magnitude disturbance occurred. No difference in leaf production was found. This work highlights the importance of disturbance history and dredging method in determining the response of P. oceanica to multiple disturbances, and provides insights into the recovery time of the seagrass when repetitive effects to the same meadow occur. This becomes particularly relevant as infrastructure development continues to expand along the world’s coastline and seagrasses are challenged with the exponential increase of physical disturbance.

Evaluation of aboveground and belowground biomass recovery in physically disturbed seagrass beds

Several studies addressed aboveground biomass recovery in tropical and subtropical seagrass systems following physical disturbance. However, there are few studies documenting belowground biomass recovery despite the important functional and ecological role of roots and rhizomes for seagrass ecosystems. In this study, we compared the recovery of biomass (g dry weight m(-2)) as well as the biomass recovery rates in ten severely disturbed multi-species seagrass meadows, after the sediments were excavated and the seagrasses removed. Three sites were located in the tropics (Puerto Rico) and seven in the subtropics (Florida Keys), and all were originally dominated by Thalassia testudinum. Total aboveground biomass reached reference values at four out of ten sites studied, two in the Florida Keys and two in Puerto Rico. Total belowground biomass was lower at the disturbed locations compared to the references at all sites, apart from two sites in the Florida Keys where the compensatory effect of opportunistic species (Syringodium filiforme and Halodule wrightii) was observed. The results revealed large variation among sites in aboveground and belowground biomass for all species, with higher aboveground recovery than belowground for T. testudinum. Recovery rates for T. testudinum were highly variable across sites, but a general trend of faster aboveground than belowground recovery was observed. Equal rates between aboveground and belowground biomass were found for opportunistic species at several sites in the Florida Keys. These results indicate the importance of belowground biomass when assessing seagrass recovery and suggest that the appropriate metric to assess seagrass recovery should address belowground biomass as well as aboveground biomass in order to evaluate the full recovery of ecological services and functions performed by seagrasses. We point out regional differences in species composition and species shifts following severe disturbance events and discuss ecological implications of gap dynamics in multi-species seagrass meadows.

Does physical or acoustical disturbance cause male pickerel frogs, Rana palustris, to vocalize underwater?

AbstractMale pickerel frogs (Rana palustris) vocalize both above water and underwater. Males have a complex vocal repertoire consisting of an advertisement call and two additional call types (i.e., aggressive calls) that can be elicited by the playback of a conspecific advertisement call. Additionally, in a previous study, males in these playbacks often dove and vocalized underwater for a few minutes before returning to the surface. The purpose of this study was to investigate whether physical or acoustical disturbance cause male pickerel frogs to call underwater. Experimental manipulations were performed with resident males that, initially, were calling above water. In the first, 16 males were physically disturbed with the intent to make them dive underwater. Eleven of these began to call underwater within 10 to 95 seconds and continued for up to four minutes before returning to calling above water. The second experiment involved playbacks in which males were disturbed acoustically by two minutes of continuous advertisement calling from either one Bufo americanus or Pseudacris crucifer male. Only one of 15 males dove and then called underwater in response to B. americanus calls even though most subjects emitted aggressive calls during the test period, and no male called underwater in response to P. crucifer calls (n = 13). In conclusion, male pickerel frogs will shift to underwater calling in response to a physical disturbance, but do not shift in response to the sounds of one heterospecific caller.

The Effect of Repeated Physical Disturbance on Soft Tissue Decomposition—Are Taphonomic Studies an Accurate Reflection of Decomposition?*

Although the relationship between decomposition and postmortem interval has been well studied, almost no studies examined the potential effects of physical disturbance occurring as a result of data collection procedures. This study compares physically disturbed rabbit carcasses with a series of undisturbed carcasses to assess the presence and magnitude of any effects resulting from repetitive disturbance. Decomposition was scored using visual assessment of soft tissue changes, and numerical data such as weight loss and carcass temperature were recorded. The effects of disturbance over time on weight loss, carcass temperature, soil pH and decomposition were studied. In addition, this study aimed to validate some of the anecdotal evidence regarding decomposition. Results indicate disturbance significantly inversely affects both weight loss and carcass temperature. No differences were apparent between groups for soil pH change or overall decomposition stage. An insect-mediated mechanism for the disturbance effect is suggested, along with indications as to why this effect may be cancelled when scoring overall decomposition.

Stress elevates corticotropin-releasing factor (CRF) and CRF-binding protein mRNA levels in rainbow trout (Oncorhynchus mykiss)

The objectives of this study were to characterize rainbow trout (Oncorhynchus mykiss) corticotropin-releasing factor (CRF)-binding protein (CRF-BP) cDNA and to examine the variations in CRF-BP and CRF mRNA levels in response to different intensities of stress. Trout were physically disturbed by a single or three consecutive periods of chasing until exhaustion followed by 2 h of recovery. The pituitary CRF-BP and preoptic area CRF1 mRNA contents were significantly increased only after repeated chasing events. Physical disturbance increased plasma cortisol levels with the largest change occurring in the group of trout that were exposed to repeated chasing events. Trout were also individually isolated in 120 l tanks or confined to 1.5 l boxes for 4, 24 or 72 h. CRF-BP mRNA levels in confined fish were greater than those of isolated fish at 72 h although there were no differences compared with the control group. CRF1 mRNA levels in the preoptic area were greater and remained elevated for a longer period in confined compared with isolated trout. Isolation led to a transient increase in plasma cortisol levels, but the higher cortisol values developed in the confined fish suggest that this treatment was more stressful than isolation. These results demonstrate that the intensity and duration of stress are important factors regulating CRF and CRF-BP mRNA levels in rainbow trout. We hypothesize that pituitary CRF-BP is involved in regulating the activity of the stress axis, possibly by reducing access to CRF1 receptors in the corticotropes.

Recovery rates of benthic communities following physical disturbance

Summary Despite numerous studies that have investigated the effects of physical disturbance on marine benthic communities, deducing the ecological significance of such events has been hampered by the specificity of individual studies. Less stable habitats (coarse, clean sands) are thought to recover more quickly than stable (muddy sands and mud) habitats but so far an empirical test of this paradigm has been lacking. We describe a large‐scale field experiment that investigated the response of marine benthic communities within a variety of sediment types (clean sand, silty sand, muddy sand and mud) to physical disturbance. Sites were sampled for macrofauna and habitat characteristics (sediment organic content and water content, depth of water within disturbed pits) following disturbance, in order to examine any relationship between the rate of physical and biological recovery. There were no detectable changes to the measured physical parameters following the disturbance with the exception of the water depth within disturbed areas. It was not possible to derive a linear relationship between the measured habitat characteristics (percentage silt and clay content) and the recovery trajectory of the associated community. However, the rate of sediment infilling of disturbed plots was strongly correlated to the recovery rate of the numbers of individuals within disturbed areas. Clean sand communities had the most rapid recovery rate following disturbance, whereas communities from muddy sand habitats had the slowest physical and biological recovery rates. These findings concur with the predictions of a meta analysis of fishing disturbances for similar habitats. We suggest that physical and biological recovery rates are mediated by a combination of physical, chemical and biological factors that differ in their relative importance in different habitats. Monitoring the infilling rate of physically disturbed patches of sediment has the potential to become a useful tool to predict the recovery rate of associated communities.

Invasion success of exotic plants in natural ecosystems: the role of disturbance, plant attributes and freedom from herbivores

Invasion of natural ecosystems by exotic species is a major threat to biodiversity globally. We assessed two alternative (but not exclusive) hypotheses to explain the success of exotic species in urban bushland on low fertility sandstone-derived soils in Sydney, Australia. These were that success of exotic species is promoted by: (1) plant attributes in particular disturbance types; and (2) freedom from herbivores. We tested these at sites subject to different types of disturbance: nutrient and water enrichment (below stormwater outlets), nutrient enrichment (riparian zones of creeks with an urban catchment) and physical disturbance (tracks), and control sites. At each site we estimated percentage cover of all species and surveyed leaves for damage by herbivores. Species were classified as native, non-invasive exotic or invasive exotic. We found that sites without any disturbance did not support exotic plants. Physically disturbed sites on low fertility soils supported only one exotic species, suggesting that nutrient enrichment is a critical prerequisite for exotic species invasion on low fertility soils. Exotic species cover was highest and native species richness most reduced in areas of highest nutrient enrichment. Both invasive exotic and non-invasive exotic species had significantly lower levels of leaf herbivory than native species, implying that release from pests alone cannot account for the success of invasive species. Specific leaf area of invasive exotic species was consistently higher than specific leaf area of non-invasive exotic and native species, regardless of disturbance type. In physically disturbed sites of higher soil fertility, exotic species were small herbs and grasses of long flowering duration and with small unassisted or wind-dispersed seeds. In sites subject to nutrient-enrichment, exotic species were more likely to be climbers, able to propagate vegetatively, and with seeds dispersed by vertebrates. Thus different plant attributes contribute to exotic species success under different disturbance types. The clearest consistent difference we found between invasive exotic and non-invasive exotic species was in specific leaf area, suggesting that large specific leaf area facilitates invasiveness.

Abyssal nematode assemblages in physically disturbed and adjacent sites of the eastern equatorial Pacific

The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of the eastern equatorial Pacific were investigated 7 years after a physical disturbance. A total of 3048 nematodes belonging to 68 genera and 26 families were identified. The nematode fauna at both disturbed and control sites was dominated by specimens belonging to the genera Acantholaimus, Chromadorita, Thalassomonhystera, Desmoscolex, Halalaimus and Diplopeltula. These genera contribute to about 55% and 50% of total nematode fauna in the disturbed and control sites, respectively. The mean relative abundance of the dominant genus Acantholaimus amounted to about 20%. Generic diversity, evenness and richness at the undisturbed sites do not significantly differ from the corresponding median values at the disturbed sites. Mean k-dominance curves show differences in community structure between treatments. Ordination of square- and fourth-root-transformed family abundances revealed groupings of the disturbed and undisturbed samples (significant at the 5% level), whereas ordination of genus abundances did not. Sample variability was investigated by inspection of the relationship between variance and mean abundance of genera and families in each sample group and by calculating the comparative index of multivariate dispersion (IMD). There is a clear increase in the standard deviation for a given mean of genus or family abundances at the disturbed sites. A higher variability among the disturbed samples, however, does not appear to be true in the multivariate sense.

Impact of large-scale natural physical disturbance on the diversity of deep-sea North Atlantic nematodes

Nematode alpha diversity from 3 physically disturbed sites in the deep North Atlantic was compared with reference sites. Nematode diversity at the HEBBLE benthic storm site was statis- tically, and significantly, lower than at reference sites. Nematode diversity at the Madeira Abyssal Plain site, which was subject to a turbidite dated at 930 BP, also showed a significantly lower diver- sity than reference sites. However, limited data suggest that diversity was not low at a Venezuela Basin turbidite site. The difference in nematode diversity between the 2 turbidite sites is ascribed to a long term change in sediment conditions at the Madeira site. The Venezuela Basin turbidite site has a sedimentation rate greater than the Maderia site by 1 to 2 orders of magnitude, and this was reflected in the sediment profiles. Another possibility is that the Venezuela Basin turbidite is consid- erably older, by at least 1000 yr, than the Madeira turbidite, allowing more time for recolonisation. The data suggest that deep-sea nematode diversity may be affected by physical disturbance but that deep-sea nematodes, like their shallow counterparts, are more robust than macrofauna such as poly- chaetes to such impacts.

Comparative meta-analysis of the impact of offshore marine mining on macrobenthic communities versus organic pollution studies

The phylum-level meta-analysis approach has been proposed as a way of comparing geographically different areas along a common scale of disturbance. However, the training data set which establishes the scale of disturbance and all subsequent studies using the approach have been exposed to some sort of organic or inorganic pollution. Using macrobenthic communities subjected to a short-lived but intense physical disturbance from offshore mining off the west coast of Southern Africa, we tested the applicability of the meta-analysis approach for assessing the severity of disturbance in physically disturbed communities. The positioning of the original data set along a primary axis of disturbance was maintained; however, a second significant separation, along the vertical axis, distinguishes between macrobenthic assemblages from southern Africa and the NE Atlantic Shelf. The southern African samples are characterised by a larger proportion of Crustacea, and in the case of mined samples Mollusca, whereas the NE Atlantic data contain relatively more Echinodermata in the unpolluted samples and are dominated by Annelida in the organically enriched areas. The proportion of annelids decreased by about 50% in mined areas compared to the non-mined areas and the NE Atlantic samples. Conversely, bivalves and gastropods exhibited a notable increase in proportion in the mined patches compared to the adjacent non-mined areas, possibly as a result of their preferential ability to survive the mining process or their better ability to recolonise after mining, or an interplay of both factors. The mining activity may result in the selection of species for their physical robustness and tolerance to mining rather than their resistance to pollution in the conventional sense. The failure of the meta-analysis to ordinate the mined samples along the primary horizontal axis of disturbance, as defined by Warwick & Clarke¹s original study (Mar Ecol Prog Ser 92:221-231), does not reflect a failure of the meta-analysis to detect disturbance, but rather shows that the primary axis is strongly determined by the opportunistic species characteristic of organically enriched areas. It appears that phylum-level meta-analysis is better suited to assessing the impact of organic and chemical pollution on an ocean-basin scale than it is to physical disturbance caused by offshore mining.

Physically disturbed deep-sea macrofauna in the Peru Basin, southeast Pacific, revisited 7 years after the experimental impact

Abstract Long-term disturbance effects of a physical disturbance experiment on the benthic macrofauna (>500 μm), with particular emphasis on the dominant Polychaeta, were investigated in connection with the German ATESEPP joint programme in 4150 m depth in the Peru Basin of the tropical southeast (SE) Pacific. The study site was the 10.8 km 2 experimental field of the dis turbance and re col onization experiment (DISCOL) conducted in early 1989. This programme had the objective to simulate some of the potential disturbance effects of manganese nodule mining on the bottom-dwelling biota with a towed “plough-harrow” disturber, and subsequently to investigate the resultant community responses with three post-impact samplings during a period of 3 years. Seven years after disturbance, in early 1996, the DISCOL site was revisited, and this study focuses on temporal development of the macrofauna over that extended period. Box core samples obtained during all post-impact expeditions from the disturber tracks ( disturbed treatment) were compared with unploughed sediments from the experimental field ( undisturbed treatment) and with samples from unimpacted sites of the surrounding ( reference treatment). The experiment did not cause the disastrous long-term community changes in the sediment dwelling macrofauna that previously were predicted to follow large-scale disturbances. Abundance recoveries of the macrofaunal taxa were largely terminated after 7 years. Major differences in the faunal compositions at the selected taxonomic levels of higher macrofauna taxa, polychaete families and polychaete species between disturbed and control sites were not observed, but certain disturbance effects remained present over the entire 7-year period: Within-treatment data heterogeneity for the higher macrofauna taxa and the polychaete families was greater in the disturber track samples than in undisturbed and reference treatments. Enhanced heterogeneity was expressed by significantly steeper regression slopes of variance-to-mean ratios of faunal abundances ( p E ( S n ) and Shannon's diversity index H ′ calculated in non-standard ways for polychaete species revealed that patterns of diminished “diversity” in the disturbed treatments, which were observed during the later DISCOL period, were still present after 7 years, although the intensity of this signal became weaker. Recent abundance differences between treatments for the Bivalvia, Cumacea and the sigalionid polychaete species Leanira sp. A suggested that unploughed areas from the experimental field possibly were also affected by subtle long-term influences of particle plume settlement caused by the disturber action. A brief comparison with macrofauna abundance data from other ATESEPP sample locations in the Peru Basin revealed highest similarity between the sites located in the manganese nodule province, suggesting that similar disturbance effects can be expected for these areas. Nevertheless, the experimental impact by far did not reach industrial mining impact dimensions and interpretation of the results with regard to commercial mining requires caution.

Sample Number and Colonization Patterns of Benthic Macroinvertebrates and Organic Material on Artificial and Natural Substrata

ABSTRACT We determined differences in colonization by benthic macroinvertebrates among two types of artificial substratum (single rocks and bricks) and natural substratum after it was physically disturbed. We also determined the number of samples required for the same level of precision using the artificial substrata and direct sampling of the natural substratum. The study was conducted in a slow moving riffle-run in the Battle River in Alberta, Canada. All measures of the macroinvertebrate fauna (densities of each taxon, total number of organisms, and total number of taxa) and quantities of organic material were greater on the natural substratum than on artificial substrata Physical disturbance of the natural substratum substantially reduced the macroinvertebrate community and quantity of organic material, and changed the composition and size of the natural substratum. But this disturbance to the substratum did not affect the colonization patterns of the macroinvertebrate fauna and organic material on the substratum types. Artificial substrata, similar those used in our study, are unlikely to give representative samples of macroinvertebrate fauna, especially for densities of zoobenthos taxa, or quantities of organic material on the natural substratum. The artificial substrata, in contrast to the natural substratum, required a larger number of samples for the same level of precision. Using the artificial substrata instead of direct sampling of the natural substratum therefore, does not appear to increase the precision of population estimates of benthic macroinvertebrates or quantities of organic material. Our results suggest that benthic macroinvertebrate communities and organic material in lotic systems might be sampled more efficiently using direct sampling of the natural substratum than the use of artificial substrata.

Survival and Cheliped Loss of Juvenile LobstersHomarus gammarusduring Simulated Out-of-Water Transport

Abstract Juvenile lobsters Homarus gamrnarus reared for stock enhancement programs are frequently packed in Styrofoam boxes between layers of wet newspaper and shellsand and transported out of water from hatcheries to release sites. A single layer of frozen newspaper acts as a cooling element. The physical disturbance experienced by individuals while being transported was simulated under controlled conditions. Juveniles were sent on “journeys” lasting 0, 6, 9, 12, 15, 18, 21, and 24 h and were physically disturbed for 15 min of each hour. Mortality was low (2–7%) within the first 12 h of simulated transport but increased significantly (12–22%) after 15 h of exposure. This increase was primarily a result of high mortality (21–45%) in individuals packed in the layer nearest the cooling element. Air temperature recordings revealed a temperature gradient between layers throughout the test period. In all, 68.5% of all observed mortality occurred within 6 h of juveniles being returned to ambient seawater. Overa...

Use of the abundance/biomass method for comparison of fish communities in regulated and unregulated lowland rivers in Belgium

AbstractThe abundance/biomass comparison (ABC) method, proposed by Warwick (1986) for detecting pollution effects on marine macrobenthic communities, was tested on distribution patterns of numbers and biomass among fish species in regulated and non‐regulated lowland rivers in Belgium. The biomass and abundance of the fish populations were determined by electrofishing. The sample sites represent a range of physically disturbed watercourses, from natural meandering to heavily channelized reaches. Sites upstream and downstream from a polluting discharge were also evaluated. The physical habitat and water quality were measured on each site. Our data show a significant correlation between the qualitatively measured physical habitat and an ABC index, calculated from the ABC graph data. A significant correlation was also found between the pollution level and the ABC index. It is concluded that the ABC method is applicable to the assessment of disturbance in fish communities in rivers, and that the method gives information about both pollution and physical disturbance. The ABC method is a useful instrument to assess the status of a fish community before and after river channel works or natural and human induced river restorations.

Acute correlated changes in plasma T4 and glucose in physically disturbed cannulated rainbow trout, Oncorhynchus mykiss

1. 1. The acute effects (0–7 hr) of physical disturbance on plasma glucose and thyroid hormone concentrations were studied in trout cannulated in the dorsal aorta and starved for 3 days. 2. 2. Deliberate disturbance caused closely correlated significant elevations in plasma lthyroxine (T4) and glucose to a maximum at 3 hr, with no change in plasma 3,5,3'-triiodo-lthyronine or packed cell volume. 3. 3. Since glucose injection alone acutely increases both plasma glucose and T4, the disturbance-induced acute elevation in plasma T4 may be due to the parallel rise in glucose.