Effects of Submerged Aquatic Vegetation on Macrozoobenthos in a Coastal Lagoon of the Southwestern Atlantic

The freshwater‐dominated part of Rocha coastal lagoon recently experienced sudden colonization by submerged aquatic vegetation (SAV). Macrophytes may be beneficial or detrimental for the zoobenthos, and both assemblages may in turn affect the food availability for birds and fishes. With the aim of evaluating the effect of SAV on water conditions and on the composition, abundance and diversity of macrozoobenthos, vegetated areas (V, up to 500 g DW m^–2) were compared with vegetation‐free areas (N). The benthic abundance was higher in V (up to 5000 ind m^–2) than in N (up to 2200 ind m^–2). Species richness and abundance of amphipods, gastropods and chironomids were also higher at V compared with N. Conversely, the abundance of Tanais stanfordi (Crustacea), Erodona mactroides (Bivalvia) and Laeonereis culveri (Polychaeta), and the Shannon diversity were higher at N. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vertical distribution and abundance of mesoplanktonic medusae and siphonophores from the Weddell Sea,Antarctica

The composition, abundance and vertical distribution of mesoplanktonic cnidarians collected along a transect across the Weddell Sea have been analysed. The transect was characterized by a thermocline, approximately between 200 and 100 m, which deepened significantly towards the shelf edges. In total, 10 species of medusae and 18 species of siphonophores were identified. The most abundant medusae were Pantachogon scotti (up to 11,671 specimens/1,000 m³) and Arctapodema ampla (up to 960 specimens/1000 m³). The most abundant siphonophores were Muggiaea bargmannae (up to 1,172 nectophores/1,000 m³) and Dimophyes arctica (up to 230 nectophores/1,000 m³). Five assemblages of planktonic cnidarians were distinguished: (a) epipelagic species located in and above the thermocline; (b) epi- and upper mesopelagic species located in, above and just below the thermocline; (c) epi- and mesopelagic species located in and below the thermocline; (d) mesopelagic species; (e) lower mesopelagic species. Differences in the depth distribution of the various species gave rise to a clear partitioning of the mesoplanktonic cnidarian population throughout the water column. This vertical partitioning was related to the existence of a thermocline, the structure of the water column and the vertical distribution of prey.     

Macroinvertebrate assemblages in Andean Patagonian rivers and streams: environmental relationships

Macroinvertebrate communities from 29 streams and rivers of the mountain and the Andean Patagonian Plateau were analyzed. Samples were collected from six river basins, which were part of four different biozones of the Patagonian Ecoregion. Samples from mountain streams were dominated by Plecoptera, Ephemeroptera, Trichoptera and Diptera, while plateau rivers where mainly Diptera, Oligochaeta and Mollusca. Total invertebrate abundance ranged from 7 to 12249 ind.m^–2. Elmidae, Paratrichocladius, Chironomus, Smicridea annulicornis, Parasericostoma ovale and Meridialaris laminata were the most abundant insect taxa, while Nais communis and Hyalella curvispina were the most abundant non-insect taxa. Species-environmental relationships were examined using Canonical Correspondence Analysis. Current speed, conductivity, substrate size and abundance of aquatic plants, were identified as the major variables structuring faunal assemblages. Regression analyses revealed that species richness was negatively correlated with latitude, and positively correlated with water temperature and altitude. Macroivertebrate abundance increased with conductivity, altitude and water temperature. These results suggest that habitat heterogeneity was the strongest predictor of macroinvertebrate assemblages, but species richness could be predicted at a landscape scale using topographical and climatic features.     

金沙江上段浮游藻类和着生藻类群落格局及其与环境因子的关系比较研究

比较河流浮游藻类和着生藻类群落的时空格局及其与环境因子关系的差异,有助于了解两类藻的区别与联系。然而,目前这方面的研究还不多。基于2019年秋季和2020年夏季金沙江上段干流17个样点藻类及水体理化指标的调查数据,分析了不同季节浮游藻类和着生藻类群落结构及其主要环境驱动因子,比较了两类藻的多样性格局及其与环境关系的异同。结果发现,调查河段的浮游藻类和着生藻类均以硅藻为主,其中浮游藻类以极小曲壳藻(Achnanthes minutissima)、钝脆杆藻(Fragilaria capucina)、适中舟形藻(Navicula accomoda)为主要优势种,着生藻类以极小曲壳藻(Achnanthes minutissima)、扁圆卵形藻(Cocconeis placentula)、橄榄绿色异极藻(Gomphonema olivaceum)为主要优势种。浮游藻类和着生藻类秋季平均密度分别为:2.41×10~5个/L、9.43×10~3个/cm~2,均明显高于夏季的平均密度(4.84×10~4个/L、4.84×10~3个/cm~2)。两类藻的群落格局表现出明显的季节变化,但只有着生藻分类单元...     

Spatial structure of a subtidal macrobenthic community in the Bay of Veys (western Bay of Seine, English Channel)

The spatial distribution of the muddy fine sand community from the Bay of Veys (western English Channel) were investigated during spring and autumn 1997. A grid of 55 and 54 sites was sampled in March and October, respectively, using two replicates per site of a Hamon grab (0.25 m²) for macrofauna collection and an additional one for sediment analysis. A total of 172 species were sampled with a dominance of polychaetes, followed by crustaceans and bivalves. The species richness and abundance show low temporal changes despite higher values in October than in March. In March, the mean abundance was 165 ind. 0.5 m⁻²; in October, the mean abundance was 212 ind. 0.5 m⁻². Four assemblages from the Abra alba-Pectinaria koreni community were identified corresponding to a bathymetric and sedimentary gradient from muddy fine sands with high levels of fine particles in shallow water to fine sands in deeper water. The discussion focuses on factors prevailing on the spatial structure of sandy communities in the English Channel.     

Polychaete community structure of the northwestern coast of Mexico: patterns of abundance and distribution

In August 1998, 72 benthic stations were sampled off the northwestern coast of Mexico. A baseline survey of the polychaete macrofauna was carried out for the southernmost portion of the Southern California Bight (SCB) region. Spatial patterns of polychaete assemblages were characterized to determine evidence of environmental impact from point sources of wastewater discharge near the study area, and to define a standard against which to detect future change. A total of 4231 polychaetous annelids representing 38 families and 210 species were identified, which constituted 53% of the total macrofauna. Families with highest species richness were Spionidae (18 spp.), Onuphidae (15 spp.), and Terebellidae (14 spp.). Species with greatest abundances were Spiophanes duplex (490 ind.), Spiophanes fimbriata (330 ind.), Lanassa sp. D (209 ind.), Pectinaria californiensis (138 ind.), and Euclymeninae sp. A (124 ind.). Based on polychaete assemblages, communities for the southernmost SCB were found to be composed primarily of non-opportunistic species, and no numerically dominant species were found. High values of polychaete diversity (H) indicated the majority of the area of study could be considered an undisturbed environment. Principal Components Analysis (PCA) applied to environmental and faunistic parameters indicated depth, organic carbon, and sediment grain size as the main influences determining the polychaete faunal communities.     

On the distribution patterns and population dynamics of sublittoral and profundal oligochaeta fauna from Lake Banyoles (Catalonia,NE Spain)

Oligochaeta assemblages from Lake Banyoles were composed of one species of Naididae and eight species of Tubificidae, Potamothrix heuscheri (8–1350 ind. m^–2) being the most abundant and widely distributed species, followed by Limnodrilus hoffmeisteri (25–858 ind. m^–2) and Psammoryctides barbatus (12–792 ind. m^–2). The remaining species were Potamothrix hammoniensis, Potamothrix bavaricus, Limnodrilus claparedeanus, Branchiura sowerbyi, Aulodrilus pigueti and Dero digitata, all of which occurred at lower densities and with restricted distributions.Regardless of sampling depth, maximum densities of oligochaetes were found in winter (up to 5,142 ind. m^–2 in December) and secondarily in June. Immature Tubificidae with hair setae and mature P. heuscheri were present and dominant throughout the year. Cestode parasites were recorded infesting L. hoffmeisteri and P. heuscheri populations.Oligochaeta densities increased with depth, but low oxygen concentrations (less than 1 mg l^–1) during a long period (4 months) in some basins of the lake acted as a key factor in reducing the density of worms and the species richness to one species, Potamothrix heuscheri.     

Meso- and bathypelagic distribution and abundance of chaetognaths in the Atlantic sector of the Southern Ocean

We conducted multinet sampling during winter and summer in the Southern Ocean (Atlantic sector) to investigate the effect of water mass, season and water depth on abundance and species composition of meso- and bathypelagic chaetognaths. Eukrohnia hamata (mean 115 ind. 1,000 m⁻³) and Sagitta marri (mean 51 ind. 1,000 m⁻³) were dominant, complemented by E. bathypelagica (mean 19 ind. 1,000 m⁻³) and E. bathyantarctica (mean 19 ind. 1,000 m⁻³) below 1,000 m. A further six species were identified, among them the rare bathypelagic species Heterokrohnia fragilis and the subtropical Eukrohnia macroneura that is new to the Antarctic. Water depth and season were the principal determinants of abundance and species composition patterns, indicating vertical seasonal migration and vertical segregation of species. The life cycles of E. hamata and S. marri were studied additionally. Their maturity stages were vertically segregated and prolonged reproductive periods are suggested for both species.     

Abundance,biomass and spatial distribution pattern of brittle stars (Echinodermata: Ophiuroidea) on the Kolbeinsey Ridge north of Iceland

Species composition, abundance, biomass and spatial distribution pattern of brittle star assemblages of the Kolbeinsey Ridge, north of Iceland, were investigated by analysing seafloor photographs and epibenthic sled catches. Sampling was conducted in July 1992 along a 34 km long cross-ridge transect at 67°55N in depths ranging from 830 to 1100 m. Five brittle star species were found. Only one species, Ophiocten gracilis, occurred with densities of more than 1 ind m^–2. Both ridge slopes were characterized by soft bottom habitats, the ophiuroid distribution, however, revealed differences between slopes. Generally, brittle star densities were significantly higher on the eastern slope. There, the highest mean abundance per station of O. gracilis was 497 ind m^–2. Except for one station, a distinct patchiness on the 100 m-scale was obvious in the spatial distribution of O. gracilis. Small settling stages with disc diameters <1 mm accounted for up to 98% of the population of O. gracilis near the ridge top, but their abundance share decreased with depth to only 6% on the eastern slope foot. Biomasses of O. gracilis were extrapolated by combining abundances estimated from photographic counts with a size-weight relationship and size frequencies established from sled catches. The highest value (120 mg AFDW m^–2) was found on the deep eastern slope where large O. gracilis with disc diameters >4 mm were most abundant. Our findings reflect a cross-ridge gradient in terms of hydrographic regime and, hence, probably pattern of food supply for the benthos.     

大陈岛海域浮游动物群落季节变化及其影响因素

为探究大陈岛海域浮游动物群落的季节变化,于2020年9月（夏季）、11月（秋季）和2021年1月（冬季）、4月（春季）分别对大陈岛海域的浮游动物及环境因子进行了4个航次的调查。结果共鉴定浮游动物90种,包括浮游幼体15类,其中夏季种类数最多（68种）,冬季最少（20种）,常见的优势种有：百陶箭虫（Sagitta bedoti）、微刺哲水蚤（Canthocalanus pauper）、中华哲水蚤（Calanus sinicus）等12种（Y>0.02）。浮游动物的年平均丰度和生物量分别为（153.40±214.73）个/m³、（411.93±561.76） mg/m³,二者存在明显的季节变化,平均丰度为春季（380.17±296.14）个/m³>夏季（135.30±112.59）个/m³>秋季（67.88±90.52）个/m³>冬季（25.30±19.11）个/m³;平均生物量为夏季（895.01±802.54） mg/m³>春季（623.39±358.73） mg/m³>秋季（91.08±82.36） mg/m³>冬季（45.96±84.95） mg/m³。多样性指数（H''）和均匀度指数（J''）的年平均值分别为1.71±0.96和0.53±0.20,均表现出夏秋季较高、冬春季较低的特征。聚类分析结果表明调查海域的浮游动物可划分为夏季类群、秋季类群、冬季类群和春季类群4组类群。Pearson相关性分析和冗余分析（RDA）结果表明,海水温度、盐度、叶绿素a浓度是影响大陈岛海域浮游动物群落特征的重要环境因素。此外,夏季大陈岛海域水母类浮游动物暴发的现象值得关注。研究结果将为大陈岛海域的生物多样性保护及渔业资源可持续开发利用提供可参考的数据资料。     

Sublittoral Macrobenthic Infaunal Assemblages of Two Nearby Embayments from Central Chile

The benthic assemblages in two Central Chile nearby embayments were studied from quantitative samples collected from 15 sites at depths of 8–65 m. The macrobenthic infauna (<0.5 mm) of both bays was greatly dominated by polychaetes. Some 93 taxa were identified, of which 51 were polychaetes. The average macrofaunal abundance for all stations (15,021 ind. m⁻²) is very close to the values reported for the neighboring areas. Numerical classification and ordination (DCA) of sites resulted in three site-groups mostly reflecting differences in the bottom sediments: the muddy-bottom stations of Concepción Bay and the shelf-associated stations, the sandy-bottom stations of San Vicente Bay and an heavily polluted station at San Vicente port. Classification of species showed that the muddy-bottom stations and the sandy-bottom sites had characteristic species assemblages. The macrofaunal assemblages presented high dominance values, which were due to the high numerical abundances of a few species in the collections.     

Summer Weddell sea microplankton: Assemblage structure,distribution and abundance,with special emphasis on the Tintinnina

Summary Silicoflagellates, large thecate dinoflagellates and tintinnids were counted and measured in screened (26 m pore-size) pump-samples retrieved from a depth of ca. 9 m in February-March 1987 along a two-leg north-south transect in the Weddell Sea (approx. 62°S to 78°S). Fourteen tintinnid taxa were identified and their individual abundances and biomasses were estimated. Highest biomass, in terms of organic carbon, was recorded for the Tintinnina, which averaged 4.001 mg C m^-3, with mean cell-numbers of 161 ind. l^-1 (maximum: 859 ind. l^-1); followed by the dinoflagellates (1.018 mg C m^-3, mean: 192 ind. l^-1; max.: 1176 ind. l^-1); and the silicoflagellates (0.391 mg C m^-3, mean: 467 ind. l^-1, max.: 3123 ind. l^-1). Conspicuous abundance and settling volume peaks were recorded at some distance off the edge of the ice-pack (at approx. 69°S to 72°S), and in the ice-covered area south of 74–75°S. This pattern was paralleled by changes in the specific makeup of tintinnid assemblages: in the ice-covered southern area Cymatocylis drygalskii and Laackmanniella prolongata were dominant, while in ice-free waters north of 73°S Codonellopsis gaussi, Cd. glacialis and Cymatocylis affinis/convallaria were the main components of the fauna. Overall tintinnid abundances were higher than those reported for many (but not all) extrapolar areas, and the average size of the species present was considerably larger than elsewhere; tintinnid carbon figures were therefore very high, oscillating around 2 mg C m^-3 in the northern ice-free area, and 20 mg C m^-3 in the southern ice-covered zone.     

黄河口邻近海域浮游动物群落时空变化特征

利用2012年12月—2013年9月4个季度的现场调查资料研究了黄河口邻近海域浮游动物群落的时空分布特征。研究表明,黄河口邻近海域共鉴定出浮游动物70种,包括浮游幼虫19类。浮游动物优势种主要由夜光虫(Noctiluca scintillans)、小拟哲水蚤(Paracalanus parvus)、双刺纺锤水蚤(Acartia bifilosa)、拟长腹剑水蚤(Oithona similis)、强额拟哲水蚤(Paracalanus crassirostris)、近缘大眼剑水蚤(Corycaeus affinis)、强壮箭虫(Sagitta crassa)、双壳类幼体(Bivalvia larvae)、多毛类幼体(Polychaeta larvae)等种类。黄河口邻近海域浮游动物丰度夏季最高(60620个/m~3),春季(31228个/m~3)和秋季(21540个/m~3)次之,冬季最低(7594个/m~3)。不同季节浮游动物丰度的空间分布具有差异性,春季浮游动物丰度呈现出从近岸到外海降低的趋势;夏季浮游动物形成两个高丰度区,分别位于河口邻近海区和河口东部海区;秋季和冬季浮游动物丰度高值区均位于河口东部海区。浮游动物生物多样性指数均呈现从河口到外海升高的趋势,低值区位于黄河口入海口附近海区。相关性分析显示,黄河口邻近海域浮游动物丰度与海水温度显著正相关(r=0.212,P0.05),表明温度为影响黄河口邻近海域浮游动物丰度变化的主要因素。     

Species composition, abundance distribution and diversity of planktonic Ostracoda in the Beibu Gulf, China

Four cruises of survey were carried out in the Beibu Gulf between Feb 1998 and May 1999. A total of 18 species of planktonic Ostracoda were identified, including Cypridina nana, Cypridina dentata, Cypridina acuminata, Cypridina nami, Euconchoecia aculeata, Euconchoecia elongata, Euconchoecia maima, and other taxa. Planktonic Ostracoda in the gulf were divided into three ecological types: (1) a hyposaline and warm-water group, (2) a eurythermal and eurysaline group, and (3) a hyperthermal and hysaline group. The warm water species such as Euconchoecia aculeate and Cypridina acuminate were the dominant Ostracoda species in the gulf, where the overall Ostracoda density ranged from 0.02 ind./m³ to 51.58 ind./m³ and averaged 1.22 ind./m³. The highest average value (2.73 ind./m³) was found in spring. Fuzzy evaluation measures indicated that the diversity in the gulf remained low (level of class I) during all seasons. Diversity appeared to be relatively higher in some regions in which the water mass was strongly influenced by the open sea and had complex structures. This article also discusses how the species composition, abundance and diversity of planktonic Ostracoda are influenced by environmental factors (e.g., aquatic system, water mass, water temperature and salinity) in the Beibu Gulf.     

Species composition, abundance distribution and diversity of planktonic Ostracoda in the Beibu Gulf, China

Four cruises of survey were carried out in the Beibu Gulf between Feb 1998 and May 1999. A total of 18 species of planktonic Ostracoda were identified, including Cypridina nana, Cypridina dentata, Cypridina acuminata, Cypridina nami, Euconchoecia aculeata, Euconchoecia elongata, Euconchoecia maima, and other taxa. Planktonic Ostracoda in the gulf were divided into three ecological types: (1) a hyposaline and warm-water group, (2) a eurythermal and eurysaline group, and (3) a hyperthermal and hysaline group. The warm water species such as Euconchoecia aculeate and Cypridina acuminate were the dominant Ostracoda species in the gulf, where the overall Ostracoda density ranged from 0.02 ind./m³ to 51.58 ind./m³ and averaged 1.22 ind./m³. The highest average value (2.73 ind./m³) was found in spring. Fuzzy evaluation measures indicated that the diversity in the gulf remained low (level of class I) during all seasons. Diversity appeared to be relatively higher in some regions in which the water mass was strongly influenced by the open sea and had complex structures. This article also discusses how the species composition, abundance and diversity of planktonic Ostracoda are influenced by environmental factors (e.g., aquatic system, water mass, water temperature and salinity) in the Beibu Gulf.     

Existing in plenty: abundance, biomass and diversity of ciliates and meiofauna in small streams

1. The ciliate and metazoan meiofaunal assemblages of two contrasting lowland streams in south‐east England were examined over the period of a year, using a high taxonomic resolution. Monthly samples were taken from an oligotrophic, acid stream (Lone Oak) and a circumneutral, nutrient‐rich stream (Pant) between March 2003 and February 2004. 2. We assessed the relative importance of ciliates and rotifers within the small‐sized benthic assemblage with respect to their abundance, biomass and species richness. In addition, we examined the influence of abiotic and biotic parameters and season on the assemblage composition at two levels of taxonomic resolution (species and groups). 3. Ciliates dominated the assemblages numerically, with maximum densities of over 900 000 and 6 000 000 ind. m^?2 in Lone Oak and Pant respectively. Rotifers and nematodes dominated meiofaunal densities, although their contribution to total meiofaunal biomass (maxima of 71.9 mgC m^?2 in Lone Oak and of 646.8 mgC m^?2 in the Pant) was low and rotifer biomass equalled that of ciliates. 4. Although the two streams differed in terms of total abundance of ciliates and meiofauna and shared only 7% of species, the relative proportion of groups was similar. Sediment grain size distribution (the percentile representing the 0.5–1 mm fraction) was correlated with assemblage structure at the species level, revealing the tight coupling between these small organisms and their physical environment. Seasonal changes in the relative abundance of groups followed similar patterns in both streams, and were correlated with the abundance of cyclopoid copepods and temperature. 5. Information on these highly abundant but often overlooked faunal groups is essential for estimates of overall abundance, biomass, species richness and productivity in the benthos, and as such has important implications for several areas of aquatic research, e.g. for those dealing with trophic dynamics.     

Relationship between topographic heterogeneity and vegetation patterns in a Californian salt marsh

Questions: Are species richness and species abundances higher in the presence of tidal creeks? Do species richness and species abundances vary with plot size? Location: Intertidal plain of Volcano Marsh, Bahia de San Quintin, Mexico. Methods: We analysed vegetation patterns in large areas (cells) with tidal creeks (+creek) and without (‐creek). We surveyed vegetation cover, microtopography, habitat type, and distance to creeks in nested plots of five sizes, 0.1, 0.25, 1, 2.5, and 10 m². Results: Species richness, frequency, cover, and assemblages differed between ±creek cells. Richness tended to be higher in +creek cells, and cover and frequency of individual species differed significantly between ±creek cells. We found consistent patterns in vegetation structure across plot sizes. We encountered 13 species that occurred in 188 unique assemblages. The most common assemblage had six species: Batis maritima, Frankenia salina, Salicornia bigelovii, S. virginica, Salicornia spec. and Triglochin concinna. This assemblage occurred in ±creek cells and at all spatial scales. Of the most common assemblages all but one were composed of multiple species (3–9 species/plot). Conclusions: The persistence of vegetation patterns across a 100‐fold range in spatial scale suggests that similar environmental factors operate broadly to determine species establishment and persistence. Differences in assemblage composition result from variation of frequency and cover of marsh plain species, particularly Suaeda esteroa and Monanthochloe littoralis. The recommendation for restoration of Californian salt marshes is to target (and plant) multi‐species assemblages, not monocultures.     

Assemblages of dytiscid predators and culicid prey in relation to environmental factors in natural and clear-cut boreal swamp forest pools

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Culicidae) were studied during 1987–1988 in 40 small, more or less temporary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and clearing pools were warmer than forest pools. Temperature differences between pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pools had 1–13 species. Ten species occurred in both habitats. A few stenotopic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clearing pools. Five of these were found in the forest pools, of which three had no mosquito larvae. Dytiscid assemblages in both habitats and culicid assemblages in clearing pools showed strong nested patterns.Abundance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area >2 m² after that the effects of pool area had been accounted for (MANCOVA). In both habitats, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drought frequency of pools had a negative, less significant effect on the biota. In the clearing, the abiotic correlations with abundance were somewhat weakened chiefly by the relatively low abundance values from the largest pool.Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscids were trapped in the larger (1.6 m²), but not in the smaller (0.07 m²) artificial pools, and the immigration rate was markedly higher on clearings than in forest. Dug pools were colonized faster on clearings than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.     

Distribution and factors influencing on structure of reef fish communities in Nha Trang Bay Marine Protected Area, South-Central Vietnam

Visual censuses of coral reef fishes in Nha Trang Bay Marine Protected Area (MPA) were conducted during September–October 2005. Nha Trang Bay MPA is relatively rich in reef fishes compared to other areas in Vietnam and the Pacific Ocean outside the ‘Coral Triangle,’ consistent with its biogeographic location in the western South China Sea. A total of 266 species of 40 families of coral reef fishes formed five distinct assemblages. Spatial variations in distribution and structure of the assemblages were associated with eight significant biological and physical variables which were cover of living hard corals, encrusting corals, branching corals, Acropora, Millepora, Montipora, depth and distance from the coast of the mainland. The six factors in front are likely related to provision of shelter and nutrition, while the distance factor is likely to represent a gradient in disturbance and impacts from various mainland sources including sedimentation and pollution discharge from nearby rivers. Local species richness ranged from 35 to 70 species 500 m⁻² (mean: 51 ± 2 SE) for reef flat stations and from 23 to 68 species 500 m⁻² (mean: 48 ± 4 SE) for reef slope stations. Total species richness at each site averaged 76 species (±4 SE), ranging from 56 to 110 species, dominated by wrasses, damselfishes, butterflyfishes, parrotfishes, surgeonfishes, groupers and goatfishes. Density of total fishes at each station ranged from 348 to 1,444 individuals 500 m⁻² (mean: 722 ± 302 SE) for the reef flat stations and from 252 to 929 individuals 500 m⁻² (mean: 536 ± 215.7 SE) for the reef slope stations. Overall mean density at each site averaged 628.9 (±238.4 SE) individuals 500 m⁻². The highly protected sites supported higher mean density of fishes per site (ranged: 904.5–1,213 individuals 500 m⁻² for Hon Mun and 1,167.5 individuals 500 m⁻² for Hon Cau) compared to other sites (<800 individuals 500 m⁻²). Of the families included in the census, densities were dominated throughout the MPA by damselfishes and wrasses. Many target species, particularly groupers, snappers and emperors, were rare or absent and the low abundance of big fishes was consistent with over-harvesting. Similarly a low density of butterfly fishes and angelfishes is likely related to the supply for marine aquaria in Vietnam and overseas. This study provides an important baseline against which the success of present and future MPA management initiatives may be assessed.     

Consistent patterns in diatom assemblages and diversity measures across water‐depth gradients from eight Boreal lakes from north‐western Ontario (Canada)

1. Until recently, the distribution of diatom species assemblages and their attributes (e.g. species richness and evenness) in relation to water depth have been identified but not quantified, especially across several lakes in a region. Here, we examined diatom assemblages in the surface sediment across a water‐depth gradient in eight small, boreal lakes in north‐western Ontario, minimally disturbed by human activities. 2. Surface‐sediment diatom assemblages were collected within each lake along a gentle slope from near‐shore to the centre deep basin of the lake, at a resolution of ～1 m water depth. Analysis of sedimentary samples provided an integrated view of assemblages that were living in the lake over several years and enabled a high‐resolution analysis of many lakes. The study lakes ranged in water chemistry, morphology and size and are located along an east–west transect approximately 250 km long in north‐western Ontario (Canada). 3. The majority of diatom species were distributed along a continuum of depth, with those taxa having similar habitat requirements forming distinct, though overlapping, assemblages. Three major zones of diatom assemblages in each lake were consistently identified: (i) a near‐shore assemblage of Achnanthes (sensu lato), Nitzschia, Cymbella (sensu lato) and other benthic species; (ii) a mid‐depth assemblage of small Fragilaria (sensu lato)/small Aulacoseira and various Navicula taxa; and (iii) a deep‐water assemblage of planktonic origin (mainly Discotella spp.). 4. The depth of the transition between assemblage zones varied between the eight lakes. The boundary between the deep‐water planktonic zone and the mid‐depth benthic zone varied according to water chemistry and was probably related to light attenuation. The boundary was deeper in lakes with the lower dissolved organic carbon and total phosphorus (TP) (i.e. less light attenuation) and vice versa. 5. Generally, species richness, species evenness and turnover rate of species as a function of depth were significantly lower in the planktonic assemblage zone in comparison with the two zones nearer the shore. Reproducibility of species and assemblage distributions across the depth gradient of the lakes illustrated that, despite potential for sediment transport, detailed ecological characterisation of diatom species can be gleaned from sedimentary data. Such data are often lacking, particularly for near‐shore benthic species.