Thermal impact of a nuclear power plant in a coastal area in Southeastern Brazil: effects of heating and physical structure on benthic cover and fish communities

The influence of a nuclear power plant’s cooling water and physical structure on benthic cover and fish communities were assessed in a coastal area in Southeastern Brazil. We hypothesised that thermal discharges decrease benthic cover and consequently, change the associated rocky reef fish assemblage structure and that physical structure is directly associated with fish richness and diversity. Twelve sites at different distances (close, near and far) from thermal discharge and types of physical structure (low and high) were sampled by visual census. The average surface temperature at the most impacted sites (close) ranged from 30.5 to 31°C, while at far sites it ranged from 25.5 to 28.5°C. Although thermal influences have decreased benthic cover, and consequently, decreased fish richness and diversity, we found that in near and far sites that had complex habitat structures (physical and benthic cover) fish communities were unaffected. The greatest abundances of Eucinostomus argenteus, Mugil curema and Sphoeroides greeleyi were associated with the highest temperatures at the most impacted sites. In contrast, Abudefduf saxatilis, Chaetodon striatus, Stegastes fuscus, Diplodus argenteus and Malacoctenus delalandii were more abundant at high structured sites far from thermal discharges. Our data support the hypothesis that thermal discharge decreases benthic cover, fish richness and diversity but physical structure, when coupled with high diversity and abundant benthic cover, minimised thermal effects on fish communities.     

黄河三角洲芦苇湿地底栖无脊椎动物与环境因子的关系研究——以石油开采区与淡水补给区为例

分别于2018年5月和8月对黄河三角洲芦苇湿地19(淡水补给区11处,石油开采区8处)处采样点的底栖无脊椎动物和水体理化指标进行调查采样,运用统计方法分析两个区域物种组成、优势种、多样性、群落结构以及与环境因子的关系。结果表明:两季共采集到底栖无脊椎动物54种,主要以水生昆虫、腹足纲和软甲纲为主,淡水补给区和石油开采区各类群组成差异明显。独立样本T检验表明淡水补给区和石油开采区水体理化指标间差异显著(P0.05)。双因子方差分析显示,昆虫纲和腹足纲密度在两区域差异显著(P0.05),软甲纲和腹足纲密度在季节上差异明显(P0.05)。底栖无脊椎动物优势种共10种,淡水补给区指示物种8种,而石油开采区未发现有指示物种。聚类和非参数多维排序(nM DS)显示,底栖无脊椎动物群落结构相似性较低; RDA结果表明:淡水补给区底栖无脊椎动物群落结构主要受Cond,TDS,Sal,pH,Eh,HCO_3~-,SO_4~(2-)等环境因子的影响。石油开采区底栖无脊椎动物群落结构影响较大的环境因子为HCO_3~-、NH_4-N。     

Macrozoobenthos of two Antarctic glacial coves: a comparison with non-disturbed bottom areas

There are only few studies on shallow Antarctic benthic communities associated with habitats affected by intense mineral sedimentation inflow. The analysis of macrofaunal communities associated with two shallow, isolated glacial coves was performed in Admiralty Bay (King George Island) and compared with non-disturbed sites. Multivariate analyses (hierarchical classification, nMDS) clearly separated glacial cove communities (two assemblages) from the sites situated outside both basins (two assemblages). The community influenced by the streamflow of glacial discharge of meltwater situated in the area with sandy–clay–silt sediments had a very low species richness, diversity and abundance. It was dominated by eurytopic, motile deposit feeding polychaetes such as Mesospio moorei, Tharyx cincinnatus and Leitoscoloplos kerguelensis as well as the bivalve Yoldia eightsi. The second glacial community of the area located at a grater distance from the outlet of the stream was characterized by sandy–clay–silt and clay–silt deposits and showed also a low diversity and species richness. The most abundant here were peracarid crustaceans, with the dominant opportunistic feeder Cheirimedon femoratus. Community from the non-disturbed area with silty–clay–sand, and silty–sand sediments had higher species richness and diversity. The assemblage of fauna from the sandy bottom has values of those two indexes similar to those found in the disturbed areas.     

Nearshore macrobenthos of northern Kotzebue Sound,Alaska, with reference to local sewage disposal

Macrobenthos of the shallow (<10 m) nearshore marine waters of northern Kotzebue Sound was examined in 2002–2004 to (1) determine nearshore community structure and (2) assess the influence of sewage disposal. A variable number of benthic stations were sampled during three summers, with extensive effort at the disposal zone in 2003. The benthic community structure is similar to other nearshore Arctic locations, and was similar to a previous benthic study done in 1986–1987. The potential of sewage impact was assessed at the request of the community, because sewage is occasionally discharged into the Sound, in volumes of up to 38 million liters, typically through the ice in early spring. Only minimal effects of disposal on the benthos were evident and the effects could not be separated from the impacts of low salinity and relatively high water pigments. Low diversity (H′) and species richness (d) and high biomass characterized stations in the sewage area. Parameters often associated with extreme sewage pollution, particularly hypoxic and/or anoxic conditions and high abundance of opportunistic taxa, were not observed. Local traditional ecological knowledge was solicited throughout the study, and was used to help define the area potentially affected by sewage disposal.     

太浦河大型底栖动物群落组成及时空分布特征

太浦河连接东太湖和黄浦江,是东太湖向下游行洪的主河道,也是黄浦江上游重要的引水水源。分别于2017年10月、12月和2018年3月、6月在太浦河沿程设置的5个站点开展了大型底栖动物季节频次的取样调研,分析了太浦河大型底栖动物群落的结构特征及其主要影响因子。调查期间共采集到大型底栖动物25种,隶属于3门6纲14科,其中以河蚬（Corbicula fluminea）为代表的双壳类和以铜锈环棱螺（Bellamya aeruginosa）为代表的腹足类处优势地位。太浦河大型底栖动物群落的密度、生物量及多样性特征在不同站点间均存在显著差异（P<0.05）;而在不同季节间均不存在显著差异（P>0.05）。聚类排序分析表明,太浦河大型底栖动物群落在空间上的差异较季节间的变化更为明显。太浦河大型底栖动物群落的物种组成特征与太浦河、东太湖的水文连通格局密切相关;而沿程不同程度人为干扰下的水体营养水平以及底质类型与生境异质性等生境条件对太浦河大型底栖动物群落的分布特征具有重要影响,其综合作用机理有待进一步研究。     

Effects of dredged material disposal on benthic macrofauna near Itajaí Harbour (Santa Catarina,South Brazil)

From July 2006 to November 2007 the effects of sediment disposal on a macrobenthic association were evaluated at the dredged material disposal site, located 3 km northeast of Itajaí Harbour navigation channel. Seven sample sites were chosen, five inside the licensed disposal area and two outside. Five samples were collected from each site with a 0.042 m² Van-Veen grab. Nine sampling campaigns took place, one before, one during, and seven after the disposal operations. Evaluations were carried out through sediment and macrofauna composition analysis. An increase in coarse fractions of sediments was found during the first months, mainly within the licensed disposal area. Sites outside the area kept the same granulometric characteristics. Nested ANOVA showed that abundance, taxa richness and Shannon–Weaver diversity were significantly smaller after the disposal, and recovered the initial mean values after the disposal ends. PERMANOVA showed a high heterogeneity between the sites. It decreased until the fifth month after disposal operations, mainly in the sites inside the licensed area. These sites were characterized by low abundance and high variability among the samples. Eight to 16 months after disposal sites recovered their heterogeneity, indicating less variability among the samples of each site and distinct benthic macrofaunal composition. The high volume and frequency of sediment disposal were the main factors of environmental modifications, since the amount of deposited sediment on the seabed probably exceeded the natural sedimentation rates. The presence of a benthic macrofauna adapted to natural/human disturbances was crucial to the fast recovery verified in the area.     

Gravel dredging alters diversity and structure of riverine fish assemblages

1. Human activities affect fish assemblages in a variety of ways. Large‐scale and long‐term disturbances such as in‐stream dredging and mining alter habitat and hydrodynamic characteristics within rivers which can, in turn, alter fish distribution. Habitat heterogeneity is decreased as the natural riffle–pool–run sequences are lost to continuous pools and, as a consequence, lotic species are displaced by lentic species, while generalist and invasive species displace native habitat specialists. Sediment and organic detritus accumulate in deep, dredged reaches and behind dams, disrupting nutrient flow and destroying critical habitat for habitat specialist species. 2. We used standard ecological metrics such as species richness and diversity, as well as stable isotope analysis of δ¹³C and δ¹⁵N, to quantify the differences in fish assemblages sampled by benthic trawls among dredged and undredged sites in the Allegheny River, Pennsylvania, U.S.A. 3. Using mixed‐effects models, we found that total catch, species richness and diversity were negatively correlated with depth (P < 0.05), while species richness, diversity and proportion of species in lithophilic (‘rock‐loving’) reproductive guilds were lower at dredged than at undredged sites (P < 0.05). 4. Principal components analysis and manova revealed that taxa such as darters in brood hider and substratum chooser reproductive guilds were predominantly associated with undredged sites along principal component axis 1 (PC1 and manova P < 0.05), while nest spawners such as catfish and open substratum spawners including suckers were more associated with dredged sites along PC2 (P < 0.05). 5. Stable isotope analysis of δ¹³C and δ¹⁵N revealed shifts from reliance on shallow water and benthic‐derived nutrients at undredged sites to reliance on phytoplankton and terrestrial detritus at deep‐water dredged sites. Relative trophic positions were also lower at dredged sites for many species; loss of benthic nutrient pathways associated with depth and dredging history is hypothesised. 6. The combination of ecological metrics and stable isotope analysis thus shows how anthropogenic habitat loss caused by gravel dredging can decrease benthic fish abundance and diversity, and that species in substratum‐specific reproductive guilds are at particular risk. The effects of dredging also manifest by altering resource use and nutrient pathways within food webs. Management and conservation decisions should therefore consider the protection of relatively shallow areas with suitable substratum for spawning for the protection of native fishes.     

Assessment of site specific benthic impact of floating cage farming in the eastern Hios island, Eastern Aegean Sea, Greece

The site specific impact on the benthic fauna was assessed within a 4.64 km² area of intensive aquaculture situated on the eastern side of Hios island (Aegean Sea, Greece) at 11 stations seasonally between November 2000 and October 2001. The benthic fauna showed marked changes in species numbers, diversity and faunal abundance between farm and control sites. The polychaetes Nereis diversicolor, Scolelepis fuliginosa and Capitella capitata were the most dominant species at the farm sites (35% of the total abundance), whilst the most dominant species at the control sites were the polychaete Hyalinoecia brementi and the sipunculid Aspidosiphon muelleri (23% of the total abundance). Species richness, diversity and evenness were higher at the control sites whereas numerical abundance was higher at the farm sites. K-dominance curves suggest a minor impact on the benthic community at the farm sites and temporal changes on macrobenthic assemblages.     

三峡库区不同水文类型支流大型底栖动物对蓄水的响应

为探究三峡水库修建对库区不同水文类型支流大型底栖动物的影响,于2015年7月和2016年1月对三峡水库四条支流的大型底栖动物进行调研,分别对周期性受蓄水影响支流的非回水区与回水区和长期受蓄水影响支流的非回水区与回水区大型底栖动物群落结构进行比较研究,结果表明:⑴7月份三峡水库145米低水位时期共采集到底栖动物655头计59种(属),在受蓄水影响河段采集到底栖动物4种共40头,优势种为日本沼虾(占受蓄水影响区域的57.5%); 1月份三峡水库175米蓄水时期共采集到底栖动物1123头计69种(属),在受蓄水影响河段采集到16种238头,优势种为锯齿新米虾(占受蓄水影响区域的14.2%)。⑵周期性受蓄水影响支流的非回水区与回水区底栖动物密度、生物量和多样性指数无显著差异(P0.05);长期受蓄水影响支流的非回水区与回水区之间底栖动物密度和Pielou均匀度指数无显著差异(P0.05),但非回水区底栖动物生物量显著高于回水区(P0.05),底栖动物多样性和丰富度极显著高于回水区(P0.01)。⑶7月份影响底栖动物分布的主要环境因子共6个,分别是水深、流速、硝态氮、溶解氧、水温和电导率; 1月份影响底栖动物分布的主要环境因子共7个,分别是水温、溶解氧、总磷、流速、深度、电导率和透明度。     

Benthic macroinvertebrate assemblages of coastal and continental streams and large rivers of southwestern British Columbia, Canada

In southwestern British Columbia (BC, Canada) and within a relatively small geographic area, lotic environments range from streams in coastal rainforests, to streams in arid continental grasslands, to very large rivers. Little is known about the invertebrate communities in large rivers in general, or in the streams of continental BC. The purpose of this study was to determine whether the benthic invertebrate community structure changes spatially between small coastal and small interior streams; between small streams versus large rivers; and whether changes in the benthic community are related to the environmental conditions. Kicknet samples and environmental data were collected from three coastal streams, three continental streams and two large rivers (discharge of 781 and 3620 m³/s, respectively). The large river sites had low invertebrate abundance, species richness and diversity, relative to the small streams. The coastal streams had the highest species richness and the continental streams had the highest invertebrate abundance. A number of taxa were specific to each class of stream. Invertebrate abundance decreased with river size, and increased with elevation, pH, conductivity, alkalinity, NO₂NO₃-N, total Kejldahl nitrogen and percent carbon in suspended solids.     

Community dynamics of the benthic fauna in a woodland springbrook

Summary The benthic macrofauna of a woodland springbrook, Morgan's Creek, Kentucky, was studied between February 1963 and September 1964 at eight collecting sites. The basic habitat type of the stream is a rubble-riffle complex. Four stations (III, IV, VI, and VII) were located in riffle sections at different points along the stream and additional stations were established at the spring source (I), a cascade area (II), a pool (V), and a reach at the mouth of the stream (VIII).A total of 33 taxa were studied in detail, 30 of which were at the species level. Gammarus minus was the most abundant benthic macroinvertebrate in the stream. It made up 82% of the 224,400 organisms collected during the first 12 months of the study. The next most abundant species were Asellus brevicaudus, 4.4%; Phagocata gracilis, 3.0%; Baetis amplus, 1.6%; Ochrotrichia unio, 1.1%; Epeorus pleuralis, 0.9%: Diplectrona modesta, 0.9% and Baetis herodes, 0.7%.Although the largest number of animals per standard (5-minute) sample was collected at Station I, the greatest density (expressed as numbers per unit area covered by a sample) actually occurred at Station II (32,370 /m²). The remaining stations ranked as follows: I (13,160/m²), IV (11,050/m²), VI (10,820/m²), III (5890/m²), V (1260/m²), VII (490/m²), and VIII (120/m²), for the period 15 February 1963 through 1 February 1964.Information on life histories, based on differences in seasonal abundance and the duration of the life cycle, is summarized for 32 species. Of these, 24 were seasonal in occurrence and had relatively long life cycles. Two-thirds of the seasonal forms were autumn-spring growers, rather than summer growing forms.The community organization of Morgan's Creek was examined from the standpoint of species diversity and total numerical variations at each station. The situation at Stations I and II is typical of communities existing under strongly limiting conditions. The greatest diversity of invertebrates, as well as a relatively abundant number of individuals, was found at Stations III and IV, indicating a probable climax situation in this area. Both species diversity and total numbers of individuals showed marked decreases below Station IV; this was attributed to the removal of forest cover in this region. The most important effect of the removal was the alteration of temperature conditions in the stream. However, since terrestrial leaf detritus was shown to be the most important source of plant material eaten by the herbivores, removal of the riparian vegetation could, under more severe conditions, cause the depletion of primary food supplies essential to the maintenance of the woodland stream community.The environmental factors: water movement, temperature, carbon dioxide, alkalinity, hydrogen ion concentration, and dissolved oxygen were measured throughout the study. The abundance and distribution of the animals are examined in relation to these components and to that of substrate. It is concluded that temperature, substrate, and water movement are among the most important factors in Morgan's Creek.High discharge following a March spate severely devastated the fauna but had little lasting effect on the community. Species with short life cycles were able to recoup their losses quite rapidly and showed an increase in numbers soon after the flood; those with long life cycles were more seriously affected and decreased in numbers or only managed to maintain themselves following resumption of more normal discharge. The nonseasonal fauna showed the greatest decreases in numbers as a result of the spate, but their recovery was faster than for species with long seasonal cycles.A number of closely related species, with the same basic food niche, apparently coexist in Morgan's Creek. Competition between these species is avoided through the interplay of differences in microhabitat preferences and spatial and temporal distribution patterns.Contribution number 101 from the Department of Biology, University of Louisville.     

Impact of abattoir waste on Woji Creek,Port Harcourt,Nigeria, using physicochemistry and macrozoobenthic diversity indices

The impact of waste discharge from Zoo abattoir, Port Harcourt, on the environmental quality of Woji Creek was studied from April 2001 to March 2002 using physicochemistry and diversity of benthic animals as indicators. Priority physicochemical parameters (total suspended solid, dissolved oxygen and biochemical oxygen demand) indicated high organic enrichment, chiefly due to inputs of bloody effluent. The burning of animal skin with discarded car tyres to produce kpomo, a common local soup component, contributes to the creek's quality alterations. Ironically, diversity of zoobenthos was highest at the area receiving the abattoir effluents compared to areas upstream and downstream from that point. Possible explanations are provided for the inverted diversity trend using the Hutcheson Index, which indicated significant diversities in invertebrate species amongst the three sample sites. The inefficiency of ecosystem quality evaluations using isolated single indices is also discussed.     

The occurrence and significance of Cladocera (Crustacea) in some streams of Central Indiana,U.S.A.

Although Cladocera are collected often in large rivers, their importance in streams has been under-estimated. This paper summarizes the results of a preliminary study of the benthic Cladocera in the streams of three watersheds in South Central Indiana. Seventeen sites were sampled with respect to species of benthic Cladocera present, their relative abundance, population size, and population dynamics.Cladocera were present in all streams and sites in the three watersheds. Nineteen species were collected: 13 species from the family Chydoridae, 3 Daphniidae, 2 Macrothricidae, and 1 Bosminidae. Just four species — Alona circumfimbriata, Chydorus brevilabris, Pleuroxus denticulatus, and Macrothrix laticornis — made up 68–96% of the numbers at all sites.Density of Cladocera ranged from 3–5200 m^–2 and they reproduced and maintained populations in the streams sampled. Numbers were generally high in October and early November and decreased to near zero in late December and January. The most important factor appearing to affect population sizes was discharge. Numbers at almost all sites decreased significantly after a rainfall increased discharge.A Principal Components and clustering analysis grouped sites with similar physical parameters in a continuum of low to high order. Sites with low numbers of Cladocera were generally shallow, narrow, and had a loose unconsolidated substrate. Sites with high population numbers were generally deep, wide, and had a stable substrate that accumulated detritus.     

Combined influence of river discharge and wind on littoral nematode communities of a river mouth area of Lake Constance

The littoral nematode community adjacent to a river mouth (River Schussen) on Lake Constance (Germany) was studied from February 1999 to January 2000 in order to determine the influence of stress resulting from fluctuations in river discharge on local nematode assemblages. Additionally, the influence of wind as a second important stress factor was considered. Six sample sites were chosen, reflecting a gradient of river influence within the broader river mouth area. Nematode communities, varying in a mean range from 121 to 165 ind/10 cm², were found to differ significantly in terms of abundance, feeding type composition and species diversity. Deposit feeders were most abundant at all sites followed by chewers. Deposit feeders were affected mainly by wind events, while species diversity and the occurrence of chewers were influenced mainly by river discharge. The impact of both these stress factors was modified by a third variable, water level. Moderate and high levels of combined habitat stress led to significant changes in community structure. Under conditions of calm weather and low discharge, reduced species diversity and an increased predominance of deposit feeders were observed. In most cases, species diversity was found to be higher under moderate stress conditions, an observation that offers support for Connel’s Intermediate Disturbance Hypothesis.     

Mollusc diversity patterns in Central European fens: hotspots and conservation priorities

Aim To assess mollusc species composition and diversity patterns of treeless fen sites and to find simple environmental parameters that characterize diversity hotspots and priority sites for conservation. Location Western Carpathian Mountains, Europe. Methods Mollusc communities were sampled quantitatively from a homogeneous area of 16 m² in the central part of each of 145 treeless fen sites. Water conductivity and pH, geographical coordinates, altitude and habitat size of the sites studied, mean annual rainfall, mean annual temperature and mean January temperature were compiled for each plot. Nestedness in species composition was tested using the binmatnest program to confirm the ‘nested habitat‐quality hypothesis’. Patterns in species diversity were analysed using the regression trees method to isolate the main predictors of species diversity. Results Nested subset patterns of species composition were found along the gradient of mineral richness. Species distribution was highly nested (T_obs = 11.21, P << 0.001) in mineral‐poor sites (with water conductivity < 300 μS cm^?1, n = 42) and was highly correlated with the site’s mineral richness (r_s = 0.76, P << 0.001). By contrast, species distribution and richness of mineral‐rich sites (c.≥ 300 μS cm^?1, n = 103) were not controlled by mineral richness. Variation in species richness was further explained by January temperature, landscape geomorphology, and total habitat area. The southern mineral‐rich low altitude fens were the most species rich, especially those of larger total area (23 species on average). These 24 sites (17% of all sites) harboured 90% of all recorded species, including all highly endangered ones. Mineral‐rich fens in montane valleys were the second most important group because they hosted the majority of populations of two rare glacial relict species (Vertigo geyeri and Pupilla alpicola). Main conclusions The significant nestedness raises the possibility of conserving the whole fen‐mollusc species pool within the most species‐rich sites. Thus, to select the conservation priority sites, easily available site characteristics for the prediction of species richness are needed. This knowledge can help us maintain fen biodiversity, which has become closely dependent on conservation management practices after the cessation of traditional mowing of fens for haymaking.     

Benthic fauna in tropical tidal flats of Hinchinbrook Channel, NE Australia: diversity, abundance and their spatial and temporal variation

A survey of the benthic infauna (macro- and mesofauna) in tidalflats of Hinchinbrook Channel, north-east Australia, was carried out toassess the species diversity and individual abundances as well as theirtemporalvariations. Two sites were surveyed at five occassions from November 1988 toOctober 1991. In addition, spatial distributions over the intertidal gradientwere investigated once in May 1990. During the entire survey, over 200 specieswere recorded, with 53 species found on average at each sampling occassion.Species densities ranged from 4.0 to 8.2 species 177cm^–2 for macrofauna and from 4.1 to 11.8 species10 cm^–2 for mesofauna, but varied little betweensites. The average infaunal diversity (H') was 2.53. Individual abundancesreached median values of 14.0 individuals 177cm^–2for macrofauna and 14.5 individuals 10 cm^–2 formesofauna. Changes in total abundances were not related to season andinconsistent at the two study sites, with significantly higher abundancesoccurring either at site A or B on single sampling dates. Transects sampled inMay 1990 showed varying species compositions and abundances in the upper, midand lower intertidal, but no defined benthic communities were revealed bymultivariate analyses. Temporal variations in the benthic assemblages of thetwotidal flats in Hinchinbrook Channel were higher than variations between sites,with a separation of assemblages before and after 1989. Problems to assess andinterpret temporal changes in species rich tropical benthic communities arediscussed.     

广东鉴江水系底栖硅藻多样性与时空分布特征

为了解广东省鉴江水系底栖硅藻多样性和时空分布特征,对全流域进行了底栖硅藻采样调查。结果表明,从19个采样点4次采样中共检出底栖硅藻10科52属242种,其中舟形藻属(Navicula)、菱形藻属(Nitzschia)和异极藻属(Gomphonema)是优势类群,出现频次和相对丰度较高。硅藻多样性指数(丰富度、真香农多样性指数和真辛普森多样性指数)随河流等级呈现一定的空间分布特征,但它们季节变化不明显。底栖硅藻群落相异性在上游和下游河段较高,从一级到三级河流递减,四级河流又增加。底栖硅藻群落结构空间变化明显,季节变化显著。群落丰富度的稀疏曲线表明,热带河流底栖硅藻群落以400个体计数,不能完整反映底栖硅藻多样性。这些为鉴江水系河流健康监测和水生态保护奠定了基础。     

Antarctic associations: the parasitic relationship between the gastropod <Emphasis Type="Italic">Bathycrinicola tumidula</Emphasis> (Thiele, 1912) (Ptenoglossa: Eulimidae) and the comatulid <Emphasis Type="Italic">Notocrinus virilis</Emphasis> Mortensen, 1917 (Crinoidea: Notocrinidae) in the Ross Sea

The first case of parasitic association between an eulimid mollusc (Gastropoda, Ptenoglossa) and a comatulid (Echinodermata: Crinoidea) is reported for Antarctica. The mollusc involved in the association is Eulima tumidula Thiele, 1912, which has now been ascribed to the genus Bathycrinicola Bouchet & Warén, 1986, never recognized before in Antarctica. This genus is present only in the NE Atlantic Ocean and the Mediterranean Sea, and encompass species which are specific parasites of the sessile stalked crinoids of the family Bathycrinidae. However, in Antarctica, Bathycrinicola tumidula (Thiele, 1912) exploits the endemic vagile comatulid Notocrinus virilis Mortensen, 1917, and attains the largest known dimensions (∼1 cm) for a Bathycrinicola species. The absence of suitable Bathycrinidae host in modern Antarctic benthic assemblages, as well as the long paleontological history of the genus Notocrinus in Antarctica, suggest a possible ‘host-switch’ phenomenon. This event could reasonably have occurred when many species underwent considerable bathymetric shifts, during the dramatic climatic changes that affected Antarctica.     

Diversity and composition of macrobenthic community associated with sandy shoals of the Louisiana continental shelf

Along the Louisiana, USA continental shelf, sandy shoals are shallow, possibly oxygen-rich “islands” surrounded by deeper muddy deposits prone to hypoxia. Shoals also contain significant quantities of fine sand that may be mined in the future for coastal restoration. The ecological role of shoals remains poorly understood and we hypothesized that shoals provide critical habitat for benthic invertebrates. Using Ship Shoal as a model system, we assessed the diversity and structure of macrobenthic assemblages and how community structure varies with season and environmental parameters. High biomass (averaging 26.7 g m⁻²) and high diversity (161 species) of macrobenthos was found in 2006. Polychaetes (45%—72 species) and crustaceans comprised most of the species (28%—46 species); spionids and amphipods dominated the polychaete and crustacean groups respectively, both in terms of number of species and abundances. Sharp decreases in diversity, abundance and biomass occurred from spring to autumn. Species diversity and total abundance significantly increased with decreasing sediment grain size and increasing bottom water dissolved oxygen. Across seasons, mole crabs Albunea paretii and amphioxus Branchiostoma floridae typified the community and contributed most of the biomass. The polychaetes Nephtys simoni, Neanthes micromma, Dispio uncinata, Mediomastus californiensis and Magelona sp. A, the amphipod Acanthohautorius sp. A and the burrowing shrimp Ogyrides alphaerostris also contributed to variation in community composition. Cluster analyses quantified seasonal variation, mainly based on sharp decreases in abundance, as well as spatial differences in species composition oriented along both east–west and north–south gradients. Variation in benthic assemblages was correlated with water depth and sediment characteristics (mean grain size and percentage of gravel-sized shell debris). We conclude that Ship Shoal is an unrecognized biodiversity hotspot and a hypoxia refuge compared to the immediate surrounding area where the benthic community is affected by seasonal hypoxia events and we discuss how sand-mining may influence this community.