Food and feeding of small fish in the Rakaia River,New Zealand

Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12‐month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.     

Evaluating ecosystem-based management options: Effects of trawling in Torres Strait,Australia

A suite of management options for a prawn trawl fishery in Torres Strait, Australia was assessed for impacts on the benthic fauna using a dynamic management strategy evaluation approach. The specification of the management options was gained through consultation with stakeholders. Data for the model was drawn from several sources: the fleet data from fishery logbooks and satellite vessel monitoring systems, benthic depletion rates from trawl-down experiments, benthic recovery rates from post-experiment recovery monitoring studies, and benthic distribution from large-scale benthic surveys. Although there were large uncertainties in the resulting indicators, robust measures relevant to management were obtained by taking ratios relative to the status quo. The management control with the biggest effect was total effort; reducing trawl effort always led to increases in benthic faunal density of up to 10%. Spatial closures had a smaller benefit of up to 2%. The effect of closing a set of buffer zones around reefs to trawling was indistinguishable from the status quo option. Closing a larger area, however, was largely beneficial especially for sea cucumbers. When the spatial distributions of fauna prior to fishing were accounted for, fauna with distributions positively correlated with effort improved relative to those negatively correlated. The reduction in prawn catch under effort reduction scenarios could be ameliorated by introducing temporal closures over the full-moon period.     

Size of anal papillae in chironomids: Does it indicate their salinity stress?

Salinity of inland waters is affected by a range of human activities and is regarded as a major environmental contaminant in many parts of the world. Changes in salinity are well known to be associated with changes in macroinvertebrate communities of flowing waters. However, as many environmental factors co-vary with salinity, it is not known whether, and if so how, salinity causes communities to change. Being able to measure the osmoregulatory stress that individual stream macroinvertebrates are experiencing would be useful to understand if and how salinity affects their populations and thus communities. Additionally, inferring salinity stress in individual invertebrates could provide a valuable biomonitoring tool to detect the initial effects of salinity before major ecological changes have occurred. Osmoregulation in larval Chironomidae (Diptera) takes place in the anal papillae and their size is believed to be associated with osmoregulatory stress. In two laboratory experiments and a field survey in southern Victoria, Australia, we determine if the size of the anal papillae of larva chironomids is a useful biomarker of salinity stress. Experiments with Chironomus oppositus showed that the surface area of the anal papillae was similar in larva hatched across 5 egg masses collected from 3 sites but were affected by salinity treatments. Furthermore, the (transformed) ratio of this surface area to the body length of the larva was independent of the size of C. oppositus. However, for Chironomus cloacalis, this surface area differed between larva hatched from egg masses collected from the same site. The expected trend in surface area of the anal papillae relative to the size of larva (Chironomu alternans, C. cloacalis, Dicrotendipes sp., Criptochironomus sp. and Tanypodinae) was not duplicated in the field survey. It would appear that unknown factors, other than salinity, are affecting the size of the anal papillae of chironomids in southern Victoria.     

Biostratigraphic Analysis of the Top Layer of Sediment Cores from the Reference and Test Sites of the INDEX Area

Abstract

Radiolarian fossil study in the sediment cores collected during the pre- and postdisturbance cruises of the Environmental Impact Assessment (EIA) Indian Ocean Experiment (INDEX) program of deep sea mining in the Central Indian Ocean Basin suggests a pronounced directional deposition of fossil radiolarians exhumed during the deep sea benthic disturbance experiment. The relative occurrences of the Stylatractus universus species that became extinct ～0.425 million years before present were mostly confined to the older and deeper strata of the sediment of the disturbance tract in the southwestern direction. This pattern is remarkable and suggests that the disturbance plume has been preferentially redeposited in the southwestern direction. This observation is in concurrence with the prevailing southwestern abyssal current during the disturbance experiment in the Central Indian Basin.     

冲绳海槽北段表层沉积物中底栖有孔虫分布的研究

对1992年5月取自冲绳海槽北段（水深113-1156m，东经126°58.71'-129°9.06’，北纬28°41.75'-31°40.56'）92个表层沉积物中的底栖有孔虫数据进行R型因子分析。分析表明，黑潮流系有4个不同垂直水团的底栖有孔虫群落组合。其中Pseudorotaliaindopacifica,Bolovinarobusta,Cibicidesmargaritiferus,Textulariasaggitula,Cibicideslobatulus和Quinqueloculinaspp.代表黑潮流系的表层水;Hyalineabalthica，Caribeanelladepressa,Cibicidespraecinctus，Planulinawuellerstorfi和Melonisaffinis代表黑潮流系的次表层水;Globobuliminapacifica,Globocassidulinasubglobosa和Trifarinaspp.代表黑潮流系的中层水;Oridorsalistener,Martionottiellaokinawaensis,Pulleniaquinqueloba和Uvigerinadirupta代表黑潮流系的深层水。     

Geotechnical Properties of Surface Sediments in the INDEX Area

As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0-10 cm) have a shear strength of 0-1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312-577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm 3 . Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer.     

Sedimentary labile organic carbon and pore water redox control on species distribution of benthic foraminifera: A case study from Lisbon-Setúbal Canyon (southern Portugal)

Rose Bengal stained benthic foraminifera were studied from 11 cores collected along two depth transects off southern Portugal: one in the Lisbon-Setúbal Canyon and the other along the canyon edge. The total standing stocks and distribution of foraminifera were investigated in relation to sediment and pore water geochemistry. Nitrate was used as a redox indicator, sedimentary chlorophyll a and CPE (chloroplastic pigment equivalents) contents as a measure of labile organic matter, and total organic carbon as a measure of bulk organic matter availability.The canyon sediments were enriched in organic carbon and phytopigments at all water depths in comparison with the canyon edge. Water depth seemed to control sedimentary phytopigment content, but not total organic carbon. No significant correlation was seen between pigment and total organic carbon content.The abundance of calcareous foraminifera correlated with the phytodetritus content, whereas a weaker correlation was observed for the agglutinated taxa. Therefore, calcareous foraminifera appear to require a fresher food input than agglutinated taxa. The foraminiferal species composition also varied with pigment content and nitrate penetration depth in the sediment, in line with the TROX concept. Phytopigment-rich (surficial CPE content >20 μg/cm³) sediments with a shallow nitrate penetration depth (∼1 cm depth) were inhabited by generally infaunal species such as Chilostomella oolina, Melonis barleeanus and Globobulimina spp. As the nitrate penetration increased to ∼2 cm depth in sediment and the pigment content remained relatively high (>15 μg/cm³), Uvigerina mediterranea and Uvigerina elongatastriata became dominant species. With declining CPE content and increasing nitrate penetration depth, the foraminiferal assemblages changed from the mesotrophic Cibicides kullenbergi-Uvigerina peregrina assemblage to the oligotrophic abyssal assemblage, mainly consisting of agglutinated taxa.     

Small macro‐benthic invertebrates influence the survival,growth and behaviour of juvenile green sea urchins Strongylocentrotus droebachiensis in the laboratory

Recent settlers of many marine benthic invertebrates are cryptic, which exposes them to a suite of animals that differs from those they may experience as adults, potentially resulting in interactions causing mortality and/or reducing growth. Previous field experiments have indicated that such is the case with small juvenile green sea urchins Strongylocentrotus droebachiensis but which taxa are responsible for the mortality and reduced growth was not determined. A laboratory study was conducted to examine the effects of small macro‐benthic invertebrates, specifically chitons, scaleworms and larger juvenile conspecifics, as well as the full suite of cobble‐dwelling organisms, on the mortality, growth and behaviour of small (<3 mm) juvenile sea urchins. The likelihood of survival of small juvenile sea urchins was lower in the presence of larger juvenile sea urchins or with the full suite of cobble‐dwelling organisms than in the absence of animals. The small juvenile sea urchins survived and grew the best when they were with chitons and scaleworms. The behaviour of small sea urchins with the full suite of cobble‐dwelling organisms was more cryptic than the behaviour of urchins with scaleworms. This study indicates that interactions with the suite of small organisms living amongst cobbles can affect survival, growth and behaviour of small juvenile sea urchins, and that larger juvenile sea urchins can be a source of mortality for smaller conspecifics.     

Incidence of marine debris and its relationships with benthic features in Gray's Reef National Marine Sanctuary, Southeast USA

Gray's Reef National Marine Sanctuary (GRNMS) is an increasingly popular site for recreational fishing and diving in the South Atlantic Bight (SAB). As a result, there has been heightened concern about potential accumulation of marine debris and its consequent effects on sanctuary resources. Field surveys were conducted at GRNMS in 2004 and 2005 to provide a spatially comprehensive characterization of benthic communities and to quantify the distribution and abundance of marine debris in relation to bottom features. The spatial distribution of debris was concentrated in the center of the sanctuary and was most frequently associated with ledges rather than other bottom types. On ledges, the presence and abundance of debris was significantly related to observed boating activity and physiographic features including ledge height, ledge area, and percent cover of benthic organisms. The results from this study will aid managers in optimizing cleanup efforts and long-term monitoring of debris accumulation patterns at GRNMS and other hard bottom areas in the SAB.     

Environmental drivers of megafaunal assemblage composition and biomass distribution over mainland and insular slopes of the Balearic Basin (Western Mediterranean)

The influence of mesoscale physical and trophic variables on deep-sea megafauna, a scale of variation often neglected in deep-sea studies, is crucial for understanding their role in the ecosystem. Drivers of megafaunal assemblage composition and biomass distribution have been investigated in two contrasting areas of the Balearic basin in the NW Mediterranean: on the mainland slope (Catalonian coasts) and on the insular slope (North of Mallorca, Balearic Islands). An experimental bottom trawl survey was carried out during summer 2010, at stations in both sub-areas located between 450 and 2200 m water depth. Environmental data were collected simultaneously: near-bottom physical parameters, and the elemental and isotopic composition of sediments. Initially, data were analysed along the whole depth gradient, and then assemblages from the two areas were compared. Analysis of the trawls showed the existence of one group associated with the upper slope (US=450–690 m), another with the middle slope (MS=1000–1300 m) and a third with the lower slope (LS=1400–2200 m). Also, significant differences in the assemblage composition were found between mainland and insular slopes at MS. Dominance by different species was evident when the two areas were compared by SIMPER analysis. The greatest fish biomass was recorded in both areas at 1000–1300 m, a zone linked to minimum temperature and maximum O₂ concentration on the bottom. Near the mainland, fish assemblages were best explained (43% of total variance, DISTLM analysis) by prey availability (gelatinous zooplankton biomass). On the insular slope, trophic webs seemed less complex and were based on vertical input of surface primary production. Decapods, which reached their highest biomass values on the upper slope, were correlated with salinity and temperature in both the areas. However, while hydrographic conditions (temperature and salinity) seemed to be the most important variables over the insular slope, resource availability (gelatinous zooplankton and Calocaris macandreae) predominated and explained 59% of decapod assemblage variation over the mainland slope. Both fish and decapods were linked to net primary production recorded over the mainland 3 months before sampling, while the delay between the input of food from the surface and fish abundance was only 1 month on the insular slope. Our results suggest that trophic relationships over insular slopes probably involve a shorter food chain than over mainland slopes and one that is likely more efficient in terms of energy transfer.