Assessment of the seaweed-seagrass resource of Mararison Island,Culasi, Antique,Philippines*

A bimonthly sampling of the seaweed-seagrass resource of Mararison Island, Culasi Antique, was undertaken over 1 year to assess the species composition, similarity of taxa, and biomass (dry weight [d.w.] g m^?2) at seven localities. A total of 45 species was identified: 17 Chlorophyta, seven Phaeophyta, 15 Rhodophyta, one Cyanophyta and five seagrasses. Except for some Rhodophyta and Syringodium isoetifolium (Ascherson) Dandy, the occurrence of species between stations was not significantly different; however, differences in biomass between sampling time (month) were significant. Identical taxa between stations were determined. The highest (40) and lowest (22) number of species collected were in May and July, respectively. The species were most abundant from March to May (dry months) and sparse from July to September (wet months). The most abundant species were: Sargassum polycystum C. Agardh (399 g m^?2) (Phaeophyta), Dictyosphaeria cav-ernosa (Forsskat) Borgesen (43.1 g m^?2) (Chlorophyta), Acanthopeitis japonica Okamura (97.2 gm^?2) (Rhodophyta) and Thalassia hemprichii (Ehrenberg) Ascherson (1370 g m^?2; seagrass). The Phaeophyta were abundant in March, and the Chlorophyta and Rhodophyta in May, while the seagrasses were abundant in September. Some species occurred only during the dry months: two Phaeophyta, nine Chlorophyta and five Rhodophyta. All the seagrasses were found year-round. Almost all of the seaweeds (39/45) were found associated with seagrass. The number of seaweeds in Mararison Island was higher than for seagrasses but the total biomass of the latter was much higher than the combined biomass of the seaweeds.     

海岸不同生态断带植物根叶抗逆生理变化与其Na+含量的关系

以烟台海岸生态断带滨麦(Leymus mollis)和肾叶打碗花(Calystegia soldanella)为材料,在远离高潮线不同位置上取土样和植物材料,通过测定土壤Na+和两植物根叶Na+含量、丙二醛(MDA)含量、抗氧化酶(SOD、POD、CAT)活性和渗透调节物含量,以揭示滨麦和肾叶打碗花根叶中Na+在其适应海岸盐环境中的生理调控机制。结果表明,在高潮线土壤Na+含量最高,滨麦根叶Na+含量较高,两植物根叶中MDA和水分含量、抗氧化酶活力均较低,但渗透调节物含量均较高。随远离高潮线土壤Na+含量下降,滨麦根叶Na+含量下降,而肾叶打碗花根中Na+含量上升,其根叶Na+含量较滨麦分别高637%和319%。同时两植物根叶MDA含量、叶片含水量增加;两植物根中POD和SOD活力增加;两植物根叶可溶性糖和脯氨酸含量下降。但不同生态断带滨麦叶片平均含水量相对较低,MDA含量、POD和CAT和SOD活力、脯氨酸和可溶性糖含量相对较高。在盐土环境中滨麦通过降低Na+的吸收和提高抗氧化酶活力和有机渗透调节物含量维持氧自由基代谢平衡和水分平衡。而肾叶打碗花是泌盐植物,在不同生态断带其叶片Na+含量、平均含水量相对较高,叶MDA含量、POD和CAT活力、脯氨酸和可溶性糖含量均相对较低。泌盐植物的肾叶打碗花依赖根叶中积累的Na+作为无机渗透调节剂维护其离子平衡和水分平衡及正常生长。因此,积累在根叶中的Na+离子既作为无机渗透调节剂维护细胞离子平衡和水分平衡,又引发细胞生理干旱促进有机渗透调节物合成;另外还作为氧自由基诱发剂促使活性氧自由基(ROS)积累,通过积累的ROS激活抗氧化保护酶系统抑制膜脂过氧化、维护氧自由基代谢平衡。海岸沙地土壤中高浓度Na+是海滨滨麦和肾叶打碗花能长期在盐土环境中生存的依靠元素,其对植物的生理调控作用可能是滨麦和肾叶打碗花适应盐土生存的重要生理适应机理。     

Diel dynamics of net phytoplankton in Semyachik Lagoon (Kronotskii Bay, Kamchatka) in August 1982

At three stations in the shallow Semyachik Lagoon, Kronotskii Bay, Kamchatka, 72 species and intraspecific taxa of microalgae were found. Diatoms (55) were the dominant group. In the qualitative and quantitative respects, phytoplankton was mainly represented by casually planktonic (benthic) species of diatoms. The general features of diel dynamics of phytoplankton were similar at the three stations and depended on the fluctuations of the level of tidal currents. The highest biomass (up to 363 mg/m³) and density (up to 66000 cells/I) were observed between 12∶00 and 18∶00 at low tide; these characteristics were an order of magnitude lower than at high tide.     

Diversity assessment of benthic macroinvertebrate communities in Banco National Park (Banco Stream,Côte d'Ivoire)

In the present study, a first inventory of benthic macroinvertebrates in the Banco Stream, Côte d'Ivoire, and the correlations between environmental variables and taxonomic richness were analysed. Seven stations were sampled monthly over a 1‐year period, using a hand net (10 × 10 cm, 250 μm mesh, 50 cm length). One hundred and thirty‐two macroinvertebrate taxa were recorded. These taxa were distributed among 74 families and 15 orders belonging to Insecta (118 taxa; 89% of total richness), Oligochaeta (seven taxa), Crustacea (five taxa) and Mollusca (two taxa). Kruskal–Wallis test revealed significant difference (at least P < 0.05) in macroinvertebrate richness between upstream stations (S1 and S2) and stations S4, S5 and S6. Chironominae and Tanypodinae (Insecta) were the two very frequent taxa in all the stations. Lumbriculidae (Oligochaeta), Desmocaris trispinosa (Crustacea) and Eurymetra sp. (Insecta) were frequently found in the samples. Hierarchical cluster analysis revealed three groups of sampling stations according to taxonomic similarity. Taxonomic richness was significantly and negatively correlated with conductivity, while it was significantly and positively correlated with substrate types (woody debris and gravel). Due to the fact that Banco stream is the locality type of an endemic shrimp species (Macrobrachium thysi), this basin is of high conservation priority.     

Seasonal Variation in Community Structure of Macrobenthic Invertebrates in Sandy Beaches of Jordan Coastline,Gulf of Aqaba,Red Sea

Two Jordanian sandy beaches, one at the northern end and the other at the southern end near the Saudi-Jordanian border, were examined during November 1984 to October 1985. Sediments of the South station were made of coarser sand than the North station. In general, low organic carbon and calcium carbonate levels were found at both stations. A total of 15839 animals representing 45 taxa were collected from both stations. Major differences in community structure were found between the two stations. An average density of 7981/m², 39 taxa. an average diversity value of 1.78 and an evenness of 0.37 were characteristic of the South station. Lower number of taxa (39) and density (818/m²) were found on the North station. However, the average diversity (3.18) and evenness (0.74) were higher. Using the biological index value of MCCLOSKEY (1970), the archiannelid Saccocirrus sp. was the most dominant species at the South station and the bivalve Tellina perna at the North station.     

Meiobenthos in mangrove areas in eastern Africa with emphasis on assemblage structure of free-living marine nematodes

A survey was conducted to examine spatial variations in the population density of major meiofaunal taxa and the assemblage structure of free-living marine nematodes within 5 mangrove areas on the west and east coast of Zanzibar. Meiofauna densities in surface sediments (0–5 cm) ranged from 205 to 5263 ind. 10 cm², being on average 1493 ind. 10 cm². Of the 17 major taxa recorded, nematodes dominated (64–99%) in all samples while harpacticoid copepods were usually second most abundant. Within all areas the numbers of meiofauna were very variable and significant differences among areas were only detected for oligochaetes and turbellarians. Densities of nematodes, harpacticoids, polychaetes and turbellarians were, however, significantly (P<0.001) higher at low water stations compared with mid and high water stations. Harpacticoids were negatively correlated with the numbers of fiddler crab (Uca spp.) burrows. Other correlations between environmental factors (grain size, temperature, salinity, oxygen tension, prop root density, fiddler crab burrows) and major meiofaunal taxa were non-significant. A total of 94 nematode genera were recorded from four mangrove areas. The most abundant and frequent genera were Microlaimus and Spirinia, followed by Desmodora and Metachromadora. Representatives of the genera most common in current study are found all over the globe. There was a high variation in nematode assemblage structure within and between sampling areas indicating the absence of a well defined nematode assemblage confined to mangrove areas. In a hypersaline area diversity was much reduced and where salinity was over 100%. the fauna was restricted to 3 nematode genera, Microlaimus, Theristus and Bathylaimus. Multidimensional scaling ordination (MDS) of the nematode genera separated samples taken from low water stations from other stations, the assemblage structure being significantly different at the low water stations. Numbers of selective deposit feeders were negatively correlated with average grain size and positively correlated with silt content.     

Reproductive allocation and fruit-set pattern in the euhalophyte Suaeda salsa in controlled and field conditions

Reproductive allocation and fruit-set pattern are important characteristics of halophytes, and these characteristics were investigated in euhalophyte Suaeda salsa (S. salsa). The plants comprised of those treated with 1 mM (control) or 500 mM (high salinity) of NaCl for 120 days in a glasshouse and those collected in the field. In controlled conditions, high salinity increased reproductive allocation and the number of fruits and seeds in each node of the branches. In field conditions, reproductive allocation and the number of fruits and brown seeds in S. salsa at the upper tide line were higher than at the lower tide line. There were more fruits and seeds distributed in the central part than those in the base or top of branches in both controlled and field conditions. Soil organic matter, total nitrogen and total phosphorus content at the upper tide line were lower than at the lower tide line. An opposite trend could be observed in the total soluble salt, Na⁺ and Cl^? content in soil. In conclusion, the fruit-set pattern of S. salsa may be affected by both resource constraints and resource allocation. Reproductive allocation and fruit-set pattern may ensure the establishment of S. salsa in high saline and low nutrient environments.     

A comparison of the zooplankton of Lake Kainji and of the Rivers Niger and Swashi

Seventy-nine taxa of periphyton were collected on Plexiglas plates at seven stations in the three streams between March, 1975, and February, 1976. More taxa and lower densities were generally observed at the upstream stations in the creeks than at the downstream stations resulting in greater species diversity values at the upstream stations. Species diversity was generally lower in the river than in the creeks, reflecting the lower numbers of taxa and the presence of several abundant species. Species diversity did not reflect extremes in physiochemical conditions. Although several different species were abundant in the streams during the present study, the most commonly occurring dominants were Gomphonema olivaceum and species belonging to the genera Navicula and Nitzschia. No consistent trend was observed in ash-free weight; however, the concentration of chlorophyll a was generally greater at the downstream stations in the creeks than at the upstream stations.     

The response of macroinvertebrate production to a pollution gradient in a headwater stream

1. This study quantified patterns of macroinvertebrate secondary production and stored benthic organic matter along a gradient of pollution and habitat channelisation over a 3‐km reach of Goosefare Brook, a first‐order stream in southern Maine (U.S.A.). 2. Whole‐community invertebrate production decreased from 26.4 g ash‐free dry mass (AFDM) m⁻² year⁻¹ at the reference station to 1.1 g AFDM m⁻² year⁻¹ at stations with the greatest levels of pollution. Production decreased along the pollution gradient for most taxa, although decreases were partly offset by production increases in tolerant taxa. Biomass turnover rates (P/B) were less affected by the stresses than was production. 3. Differences in functional characteristics of the community were evident at stations with channelised habitat, but overall production declined in a linear pattern that mirrored the pollution gradient. Stored organic matter showed a decline along the gradient, but was also lower at channelised stations. Populations of taxa with documented pollution tolerance were more likely to maintain or increase production and P/B. 4. Decreasing biomass because of decreasing stored organic matter and lethal effects of pollutants resulted in shifts in the pathways of energy flow observed at stations exposed to moderate physical or chemical stress, to the loss of most taxa and an extreme (96%) decrease in production at the stations receiving the highest levels of metal pollution. 5. The shifting prominence of different taxa along a continuum of stress in Goosefare Brook shows that describing the nature of an impairment in a functional context requires consideration of chemical stressors, habitat alterations and food resources.     

High site fidelity and low site connectivity in temperate salt marsh fish populations: a stable isotope approach

Adult and juvenile fish utilise salt marshes for food and shelter at high tide, moving into adjacent sublittoral regions during low tide. Understanding whether there are high levels of site fidelity for different species of coastal fish has important implications for habitat conservation and the design of marine protected areas. We hypothesised that common salt marsh fish species would demonstrate a high site fidelity, resulting in minimal inter-marsh connectivity. Carbon (¹³C) and nitrogen (¹⁵N) stable isotope ratios of larvae and juveniles of five common salt marsh fish (Atherina presbyter, Chelon labrosus, Clupea harengus, Dicentrarchus labrax, Pomatoschistus microps), seven types of primary producer and seven secondary consumer food sources were sampled in five salt marshes within two estuary complexes along the coast of south-east England. Significant differences in ¹³C and ¹⁵N signatures between salt marshes indicated distinct sub-populations utilising the area of estuary around each salt marsh, and limited connectivity, even within the same estuary complex. ¹⁵N ratios were responsible for the majority of inter-marsh differences for each species and showed similar site-specific patterns in ratios in primary producers, secondary consumers and fish. Fish diets (derived from isotope mixing models) varied between species but were mostly consistent between marsh sites, indicating that dietary shifts were not the source of variability of the inter-marsh isotopic signatures within species. These results demonstrate that for some common coastal fish species, high levels of site fidelity result in individual salt marshes operating as discrete habitats for fish assemblages.     

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm⁻² and 903 ind. 10 cm⁻². Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m⁻² to 2 g dwt m⁻² and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm⁻² at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm⁻² and 327 ind. 10 cm⁻². Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.     

Relations among heterotrophic bacteria, chlorophyll-a, total phytoplankton, total zooplankton and physical and chemical features in the Paranoá reservoir, Brasília, Brazil

The plankton community, chlorophyll-a, heterotrophic bacteria and physical and chemical features of the Paranoá Reservoir were studied at monthly intervals at seven stations from March 1988 to March 1989. Thermal structure had a circulation period from May to July and stratification during the other months. The phytoplankton consisted of 76 taxa, was dominated by the cyanophyte Cylindrospermopsis raciborskii and attained concentrations ranging from 7,759,000 up to 98,160,000 org. l^–1. The zooplankton consisted of 36 taxa and was present in densities between 8 and 8,056 org. l^–1. In stations, or seasons with highly eutrophic conditions, there was a decrease in total phytoplankton and an increase in bacteria and total zooplankton. The results had spatial and temporal variations. Spatial variation demonstrated the existence of water quality deterioration at two or three sampling points. Temporal variation showed the influences of water column stability and the dry versus rainy seasons on nutrient concentrations and the planktonic community.     

Meiobenthos of hypersaline tropical mangrove sediment in relation to spring tide inundation

Tropical intertidal sediments often contain porewater of relatively high salinity, especially in areas exposed to longer periods without seawater inundation and high evaporation. Such an area exists on the west coast of Zanzibar: a high intertidal mangrove plateau, flooded only during spring high tides, with sediment porewater salinities commonly exceeding 100 ppt. A field survey was conducted in this area to examine variations in population density of major meiofaunal taxa and the assemblage structure of free-living marine nematodes during spring-neap tidal cycles. Samples were taken on seven occasions for two months, starting from the end of the rainy season. Porewater salinity remained high throughout the sampling period, ranging from 89 to 160 ppt. Neither spring tide inundation nor heavy rains lowered the salinity markedly. The meiofauna consisted only of four taxa, present on all sampling occasions: nematodes, harpacticoid copepods, plathyhelminthes and chironomids. Densities in surface sediments (0–5 cm) were low compared to other mangrove areas, ranging from 271 to 656 animals 10 cm^-2 with nematodes dominant on all sampling occasions (58–87%). Density fluctuations could not be explained by the effects of spring tide inundation, but the meiofauna showed significant correlations with grain size and organic material. Despite the wide range of salinity, only the numbers of chironomids were negatively correlated with increased salinity. Nematode species diversity was low in all samples, although altogether 28 species were recorded in the samples. Four species occurred in more than 50% of the samples (Microlaimus sp. (100%), Metalinhomoeus sp. (76%), Daptonema sp.l (56%), Chromadorina sp. (56%)) while 12 species were found only in one or two samples. Multidimensional scaling ordination (MDS) of the nematode species abundance data indicated little effects of spring tide inundation on the assemblage structure, but rather a successive change from wet to dry season with a reduction in species diversity and increased numbers of the dominant nematode species Microlaimus sp.     

Macrobenthos ofPotamogeton andMyriophyllum beds in the upper reaches of Canal de Mira (Ria de Aveiro,NW Portugal): Community structure and environmental factors

The community structure of the macrobenthic fauna (>0.5 mm) ofPotamogeton andMyriophyllum beds of the upper reaches of Canal de Mira (0.5–2) and of macrofauna density (369, 240 ind m^–2).Potamopyrgus jenkinsi, Corophium multisetosum andLimnodrilus hoffmeisteri are dominant species in the study area. The community of station 1 includes an important set of taxa usually associated to freshwater habitats (oligochaetes, leeches and insect larvae) whilst in station 3 typically estuarine species (Cyathura carinata, Leptocheirus pilosus, Nereis diversicolor, Streblospio shrubsolii) occur. A succession of peak densities of different taxonomic groups during the year indicates seasonal variation in the community structure. The faunal assemblage of the study area is compared with similar ones in NE Atlantic and Mediterranean coastal systems.     

Comparison of spatial scale variability of shoot density and epiphytic leaf assemblages of Halophila stipulacea and Cymodocea nodosa on the Eastern Coast of Tunisia

Abstract

A study was undertaken to compare the patterns of spatial variability, epiphytic percentage cover, and distribution of epiphytic fauna and flora between the two adjacent seagrasses Cymodocea nodosa and the invasive species Halophila stipulucea. Samples were taken at six stations separated by 600?m and exposed to different current conditions. The stations G2 and G5 were affected by a high current tide, while G4 was directly exposed to the northern marine currents. The station G3 was situated in the middle of a Posidonia oceanica bed and was less exposed to hydrodynamism, whereas the other stations were relatively protected. Results indicate that for both H. stipulacea and C. nodosa, shoot density and epiphytic cover biomass decreased when exposed to high levels of hydrodynamic activity. In terms of epiphytic leaf assemblages, our results showed significant differences for the two host plants in their mean cover and for the six stations at the largest and smallest spatial scale. Our observations highlight the dominance of Rhodophyta and the low number of epiphytic species and the epiphytic cover on H. stipulacea compared to C. nodosa. In addition, results indicate the absence of two taxa Hydrozoans and Annelida in the epiphytic assemblage of H. stipulacea leaves.     

The relative influence of hypoxia, anoxia, andassociated environmental factors as determinants ofmacrobenthic community structure in aNorthern Gulf of Mexico estuary

Seasonal patterns (i.e., December 1986, and April and October 1987) in benthic macroinfaunal abundance,distribution, and taxa composition at 19 sites in Perdido Bay, AL/FL, are evaluated to assess the relative importance of environmental factors as determinants of community structure. A total of 46 taxa from five phyla were collected with diver-held bottom corers. Polychaetes were numerically dominant followed by crustaceans. Seventeen taxa co-occurred in samples during all three study periods. Maximum animal densities and taxa richness showed no statistically significant bay-wide seasonal pattern,however, a bay-wide trend was detected where these response parameters tended to be greater in April than December or October. Deeper upper bay stations were depauperate during December and October. Low dissolved oxygen (DO) largely explained the depauperate pattern. Mean taxa richness per core(10 cm dia.) ranged from 0.0 to 5.0, 1.2 to 4.6, and0.0 to 4.4 in December, April and October,respectively. Mean densities ranged from zero to 368,0 to 960, and 0 to 430 individuals per 0.1 m² in December, April, and October, respectively. Results of a three-season statistical regression model indicated that DO deficiency was a primary determinant of taxa richness (partial R ²: 0.27) but was less important in explaining animal densities (partialR ²: 0.16). For December, when additional environmental variables were measured, DO was supplanted by weight loss on ignition (R ²: 0.24)and the sediment C:N ratio (R ²: 0.44) as highest explanatory factors for taxa richness and density,respectively. Application of a benthic index of environmental condition indicated wide-spread ecological stress on the benthic macroinfaunal assemblages. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cyanobacterial blooms and water quality in Greek waterbodies

The cyanobacterial species composition of nine Greek waterbodies of different type and trophic status was examined during the warm period of the year (May–October). Cyanobacterial water blooms were observed in all waterbodies. Forty-six cyanobacterial taxa were identified, 11 of which are known to be toxic. Eighteen species are reported for the first time in these waterbodies, 8 of which are known to produce toxins. Toxin producing species were found in all of the waterbodies and were primarily dominant in bloom formations (e.g., Microcystis aeruginosa, Anabaena flos-aquae, Aphanizomenon flos-aquae and Cylindrospermopsis raciborskii). Cosmopolitan species (e.g., M. aeruginosa), pantropic (e.g., Anabaenopsis tanganyikae) and holarctic species (e.g., Anabaena flos-aquae) were encountered. Shallow, eutrophic waterbodies had blooms dominated by Microcystis species and were characterized by phytoplankton association M. Anabaena and Aphanizomenon species of association H were dominant in waterbodies with low dissolved inorganic nitrogen and thermal stratification in the summer. Total cyanobacterial biovolumes (CBV) ranged from 7 to 9,507 cm³ m⁻³ and were higher than Alert Level 2 and Guidance Level 2 (10 cm³ m⁻³; World Health Organization; WHO) in seven of the waterbodies. Chlorophyll a concentrations ranged from 6 to 90,000 mg m⁻³ and were higher than Alert Level 2 and Guidance Level 2 (50 mg m⁻³; WHO) in eight of the waterbodies. There is also an elevated risk of acute toxicosis (Guidance Level 3; WHO) in five waterbodies. Water of an undesirable quality, hazardous to humans and animals occurs in several Greek waterbodies.     

Amphipod crustaceans as an important component of zoobenthos of the shallow Antarctic sublittoral

Benthic quantitative samples were taken in 1988 in the soft bottom sublittoral of Admiralty Bay (King George Island, South Shetlands) using a Tvärminne-type bottom sampler and SCUBA-diving technique at 7 successive stations situated at depths from 4 to 30 m.Dominant animal groups in terms of abundance were Amphipoda, Polychaeta and Bivalvia, whereas in terms of biomass Echinoidea were also dominant. Amphipod crustaceans clearly dominated the zoobenthos at depths from 10 to 25 m (the numerical share surpaising 60%) with maximal abundance of abt. 17 000 ind m^–2; in terms of biomass at specific depths amphipods occupied the 1st, 2nd or 3rd place with maximal biomass of abt. 100 g m^–2 where the maximal total biomass of zoobenthos reached 260 g m^–2 (10 m).Amphipoda were the most diversified group with some 35 taxa belonging to 14 families. Most species belonged to Eusiridae s.l. and Lysianassidae s.l. Dominant forms were Pontogeneiella brevicornis, Prostebbingia gracilis, Schraderia gracilis, Hippomedon kergueleni, Orchomenella cf. ultima, Cardenio paurodactylus and Paraphoxus rotundifrons.     

The effects of nutrient enrichment on a freshwater meiofaunal assemblage

1. The effects of eutrophication on phytoplankton, zooplankton and fish in lakes are well known. By contrast, little is known about the response of the zoobenthos to nutrient enrichment, while smaller organisms, such as the meiofauna, have for the most part been neglected. 2. In a long‐term (16 months) microcosm experiment, we assessed the effects of five levels of nutrients [total phosphorus (TP), 7–250 μg L^?1; nitrate, 2–8 mg L^?1] on a freshwater meiofaunal assemblage and on nematode diversity in particular. 3. Within the first 8 months, meiofaunal succession was only weakly affected, whereas, during the last 4 months, nutrient addition influenced most of the main taxa, with a concomitant change in the assemblage structure. 4. The density of the numerically dominant nematodes decreased upon nutrient enrichment, whereas ostracods became more numerous. Other taxa, including copepods, reached a maximum at intermediate nutrient levels or, in case of oligochaetes, were almost unaffected by nutrient enrichment. However, the changes in the density of the main taxa were usually insufficient to alter their biomass. Consequently, meiofaunal biomass was remarkably unresponsive to nutrient addition, while meiofaunal density displayed a unimodal relationship, with a peak at a TP concentration of 30 μg L^?1. In addition, nematode species richness decreased significantly with increasing nutrient concentrations. 5. We hypothesise that the response of meiofaunal taxa to nutrients is attributable to the development of primary producers, which shifted with enrichment from low densities of edible diatoms and unicellular green algae to large standing stocks of inedible forms, such as Lemna minor and Cladophora spp.     

Macroinvertebrate communities in Wheeler Reservoir (Alabama) tributaries after prolonged exposure to DDT contamination

Quarterly measurements were conducted of the structure, abundance, and diversity of macroinvertebrates comprising two distinct, but overlapping zoobenthic communities in backwaters to Wheeler Reservoir Alabama. The study area included portions of Huntsville Spring Branch (HSB) and Indian Creek (IC) which contain massive quantities of DDT residues (DDTR = DDT, DDD, DDE). Additionally, sewage effluents entering HSB just upstream from the study area have resulted in nutrient enrichment, especially at the two uppermost stations. Herpobenthos (burrowed in bottom sediments) and haptobenthos (attached to substrates) were collected at seven stations along an east-west gradient including a control site above the DDT contamination, and sites with mean sediment residues ranging from 2,730 ppm DDTR in HSB down to 12 ppm DDTR at the mouth of IC.Fifty taxa were collected from dredge samples of the herpobenthos; Tubificid oligochaetes and chironomid larvae comprised 97% of the herpobenthos. At the two uppermost stations in HSB, the control site and the site with the highest sediment DDTR, oligochaete density averaged twice that of chironomids. Downstream, densities of both groups were similar. Mean density at the upper two stations was 9431 and 10 644 organisms m^–2, respectively, significantly (P < 0.05) higher than downstream stations. Herpobenthos was dominated by detrital-algal feeders in HSB while in IC, predaceous chironomids were more numerous. Taxa diversity was also lowest (P < 0.05) at the two upper sites.Forty-five taxa were collected from artificial substrate (Hester-Dendy multiplate samplers) samples of the haptobenthos. Naidid oligochaetes and chironomids dominated the haptobenthos, although nematodes were occasionaly abundant. Chironomids were more abundant than oligochaetes at all sites except the control station, which received the greatest nutrient enrichment from sewage effluents. Mean haptobenthic density in the middle portion of the study area ranged from 31 163 to 37 310 organisms m^–2 and was diferent (P < 0.05) from upper and lower stations. Taxa diversity was lowest at the upper-most station, but no trends were evident among stations.Nutrient enrichment from sewage effluents apparently had greater impact on zoobenthic communities in the HSB-IC System than did DDT contamination. However, the presence of DDTR undoubtedly contributed, in part, to the few Ephemeroptera, Plecoptera, and Trichoptera collected at contaminated stations. Based on the density of oligochaetes and chironomid larvae at station 2 (highest DDTR), macroinvertebrates in this system are resistant to DDTR.