Daphnia community analysis in shallow Kenyan lakes and ponds using dormant eggs in surface sediments

1. Water fleas of the genus Daphnia are considered rare in tropical regions, and information on species distribution and community ecology is scarce and anecdotal. This study presents the results of a survey of Daphnia species distribution and community composition in 40 standing waterbodies in southern Kenya. The study sites cover a wide range of tropical standing aquatic habitats, from small ephemeral pools to large permanent lakes between approximately 700 and 2800 m a.s.l. Our analysis combines data on Daphnia distribution and abundance from zooplankton samples and dormant eggs in surface sediments. 2. Nearly 70% (27 of 40) of the sampled waterbodies were inhabited by Daphnia. Although their abundance in the active community was often very low, this high incidence shows that Daphnia can be equally widespread in tropical regions as in temperate regions. 3. Analysis of local species assemblages from dormant eggs in surface sediments was more productive than snapshot sampling of zooplankton communities. Surface‐sediment samples yielded eight Daphnia species in total, and allowed the detection of Daphnia in 25 waterbodies; zooplankton samples revealed the presence of only four Daphnia species in 16 waterbodies. 4. Daphnia barbata, D. laevis, and D. pulex were the most frequently recorded and most abundant Daphnia species. Canonical correspondence analysis of species–environment relationships indicates that variation in the Daphnia community composition of Kenyan waters was best explained by fish presence, temperature, macrophyte cover and altitude. Daphnia barbata and D. pulex tended to co‐occur with each other and with fish. Both species tended to occur in relatively large (>10 ha) and deeper (>2 m) alkaline waters (pH 8.5). Daphnia laevis mainly occurred in cool and clear, macrophyte‐dominated lakes at high altitudes.     

Combined effects of local environment and continental biogeography on the distribution of Ostracoda

Summary 1. The relationship between altitudinal gradients on small spatial scales and latitudinal gradients on broader scales has been repeatedly recognised in the biogeography of animals and plants. However, little is known about this topic in the ecology and biogeography of ostracod communities in Mediterranean flowing waters or the factors underlying these spatial patterns. 2. We analysed the ostracod assemblages of near‐natural headwater streams in the Betic and Pre‐Betic Mountains in the southern Iberian Peninsula to decipher the most important environmental gradients structuring ostracod communities on a local scale. In addition, the European altitudinal and latitudinal distributions of the most commonly found species were analysed with GIS and regression models to compare geographical effects from local to continental scales. 3. Forty sampling sites, distributed among six catchments and ranging in altitude between 150 and 1940 m a.s.l., were sampled seasonally. Limnological and geographical information was also recorded for each sample. Seventeen ostracod species were found, two of which were new findings for the Iberian Peninsula: Potamocypris fulva and Cypria reptans. The most common species were Potamocypris zschokkei, Candona neglecta, Herpetocypris brevicaudata, Cyclocypris ovum, Potamocypris villosa and Pseudocandona albicans. The distribution of these species in 918 European locations was analysed to test the hypothesised change in altitudinal distribution with varying latitude. 4. The best subset of logistic and linear regression models, selected by means of the information‐theoretic approach, found that oxygen content and the variables related with substratum and discharge were the most important variables with a negative influence on ostracod presence, abundance and species richness on a local scale. These findings suggest that the negative effect on benthic invertebrates of physical disturbances relates to high flow velocity and turbulences. 5. Multivariate ordination methods show how altitude and water chemistry are the most important variables to explain the distribution of ostracod assemblages on the small spatial scale. On a larger scale, differences in latitudinal distribution throughout Europe were significant for the six most common species found in Granada. In addition, four of these showed significant negative linear relationships between latitude and altitude in Europe, supporting the important effect of climate on local and continental scale distributions. While ostracod biogeographies are still poorly known, our results indicate the influence of Quaternary climate variability on ostracod dynamic colonisation and extinction in Europe in accordance with species‐specific temperature and water chemistry preferences.     

Composition of bryozoan assemblages related to depth in Svalbard fjords and sounds

Svalbard bryozoan communities were investigated along a depth range from the surface to 296 m between the inner glacial fronts and fjord mouths during 2001 and 2002. The main study area was Kongsfjorden (79°N, 12°E). A total of 137 taxa of bryozoans were identified: 108 to species, 24 to genus, 3 to family, 1 to order and 1 to phylum level. Cluster and multidimensional scaling analyses revealed four distinct assemblages of bryozoans: shallow (0–40 m; 68 taxa), deep (40–296 m; 80 taxa), inner fjordic (three taxa) and an assemblage found on small stones in shallow waters (nine taxa). The inner fjordic assemblage was recorded from the front of tidal glaciers extending about 10 km out into the fjord. In terms of abundance, Celleporella hyalina Linnaeus dominated in shallow areas (18%), Hippothoa arctica Kluge (55%) in deep water, Alcyonidium disciforme Smitt (86%) proximate to glaciers fronts and Electra arctica Borg on small stones (98%). The species were classified according to their depth range as a stenobathic-shallow (46 taxa), stenobathic-deep (57 taxa) and eurybathic-generalist (21 taxa). Mean diversity measures did not show any significant differences between the shallow and deep communities. The bryozoan assemblages seem to be structured primarily by processes related to depth and sediment characteristics.     

Veligers of the invasive bivalve Limnoperna fortunei in the diet of indigenous fish larvae in a eutrophic subtropical reservoir

Larval fish development depends largely on their ability to capture and ingest food items, and on food availability. In this context, invasive species, eutrophication and river impoundments have complex impacts on fish larvae. Using samples collected in 2005–2009 in the Salto Grande reservoir (Argentina–Uruguay), periodically affected by cyanobacterial blooms, we studied the impact of the larvae of the exotic bivalve Limnoperna fortunei (Dunker, 1857) (Bivalvia) on larval fish diets. Compared with other nearby waterbodies, the abundance of fish larvae was scarcer in the reservoir, especially during algal bloom periods. Only 20% of the larval fish with gut contents fed on L. fortunei veligers. Seven fish taxa (of a total of 12) consumed veligers of L. fortunei, but only two showed a preference for this prey. Taxonomic changes in the larval fish assemblages due to the river's impoundment, and temporal uncoupling between veliger densities (affected by the toxigenic effects of Microcystis spp.) and ichthyoplankton could account for the comparatively low trophic importance of the invasive bivalve's veligers. These results reflect the complexity of interactions brought about when the same invasive species invades different environments, underscoring that the impacts involved depend as much on the invader, as on the regional and ecological settings of the area invaded.     

Environmental variables associated with the distribution and occupancy of habitat specialist tadpoles in naturally acidic,oligotrophic waterbodies

Environmental factors play an integral role, either directly or indirectly, in structuring faunal assemblages. Water chemistry, predation, hydroperiod and competition influence tadpole assemblages within waterbodies. We surveyed aquatic predators, habitat refugia, water height and water chemistry variables (pH, salinity and turbidity) at 37 waterbodies over an intensive 22‐day field survey to determine which environmental factors influence the relative abundance and occupancy of two habitat specialist anuran tadpole species in naturally acidic, oligotrophic waterbodies within eastern Australian wallum communities. The majority of tadpoles found were of Litoria olongburensis (wallum sedge frog) and Crinia tinnula (wallum froglet) species, both habitat specialists that are associated with wallum waterbodies and listed as Vulnerable under the IUCN Red List. Tadpoles of two other species (Litoria fallax (eastern sedge frog), and Litoria cooloolensis (cooloola sedge frog)) were recorded from two waterbodies. Tadpoles of Litoria gracilenta (graceful treefrog) were recorded from one waterbody. Relative abundance and occupancy of L. olongburensis tadpoles were associated with pH and water depth. Additionally, L. olongburensis tadpole relative abundance was negatively associated with turbidity. Waterbody occupancy by C. tinnula tadpoles was negatively associated with predatory fish and water depth and positively associated with turbidity. Variables associated with relative abundance of C. tinnula tadpoles were inconclusive and further survey work is required to identify these environmental factors. Our results show that the ecology of specialist and non‐specialist tadpole species associated with ‘unique’ (e.g. wallum) waterbodies is complex and species specific, with specialist species likely dominating unique habitats.     

Impact of acidification and eutrophication on the distribution of fish species in shallow and lentic soft waters of The Netherlands: an historical perspective

The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983–1984 Esox lucius, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH≥5) Rutilus rutilus, Scardinius erythrophthalmus, Perca fluviatilis, Ictalurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra pygmaea was extremely acid-tolerant. The percentage of waters which harboured fish as well as the average number offish species per water decreased steeply between pH 6 and 4. The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification, six groups of waters could be distinquished with respect to their fish fauna. The site groups are defined and characterized physico-chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.     

Larger zooplankton in Danish lakes after cold winters: are winter fish kills of importance?

Winter fish kills can be intense under ice in shallow lakes, and have cascading effects on the food web and ultimately on lake water clarity. In maritime Western Europe, winters are usually mild, but occasional colder periods may also have strong effects on lake fish communities. Global warming may have disproportionate effects by delaying freezing and shortening the period of ice coverage. We studied differences in zooplankton (cladocerans, copepods, and rotifers): phytoplankton biomass, zooplankton community structure, and individual body size among 37 Danish lakes of various depths, chemical characteristics, and trophy, by comparing four winters of different severity (mean winter temperatures ranging from −1.19°C in 1996 to +2.9°C in 1995). We found that crustacean mean body sizes were significantly larger in the summer following a severely cold winter. The zooplankton communities in the summer after a cold winter had a significantly larger proportion of larger-bodied species and taxa. Phytoplankton biomass, expressed as chlorophyll-a (chl-a), was lower and zooplankton herbivory (chl-a:TP index), higher, in the summer after the severely cold winter of 1995/1996. All these effects were stronger in shallow lakes than in deep lakes. Changes in zooplankton during summer 1996, compared with other years, were likely caused by fish kills under ice during the preceding severe winter of 1995–1996. Fish kills due to under ice oxygen depletion would be expected to occur earlier and be more complete in the shorter water columns of shallow lakes. With climate change, severe winters are predicted to become less frequent and the winters to be milder and shorter. In general, this is likely to lead to higher winter survival of fish, lower zooplankton grazing of phytoplankton the following summer and more turbid waters, particularly in shallow eutrophic lakes.     

Community assembly of a euryhaline fish microbiome during salinity acclimation

Microbiomes play a critical role in promoting a range of host functions. Microbiome function, in turn, is dependent on its community composition. Yet, how microbiome taxa are assembled from their regional species pool remains unclear. Many possible drivers have been hypothesized, including deterministic processes of competition, stochastic processes of colonization and migration, and physiological ‘host‐effect’ habitat filters. The contribution of each to assembly in nascent or perturbed microbiomes is important for understanding host–microbe interactions and host health. In this study, we characterized the bacterial communities in a euryhaline fish and the surrounding tank water during salinity acclimation. To assess the relative influence of stochastic versus deterministic processes in fish microbiome assembly, we manipulated the bacterial species pool around each fish by changing the salinity of aquarium water. Our results show a complete and repeatable turnover of dominant bacterial taxa in the microbiomes from individuals of the same species after acclimation to the same salinity. We show that changes in fish microbiomes are not correlated with corresponding changes to abundant taxa in tank water communities and that the dominant taxa in fish microbiomes are rare in the aquatic surroundings, and vice versa. Our results suggest that bacterial taxa best able to compete within the unique host environment at a given salinity appropriate the most niche space, independent of their relative abundance in tank water communities. In this experiment, deterministic processes appear to drive fish microbiome assembly, with little evidence for stochastic colonization.     

Why are there so few freshwater fish species in most estuaries?

The freshwater fish assemblage in most estuaries is not as species rich as the marine assemblage in the same systems. Coupled with this differential richness is an apparent inability by most freshwater fish species to penetrate estuarine zones that are mesohaline (salinity: 5·0–17·9), polyhaline (salinity: 18·0–29·9) or euhaline (salinity: 30·0–39·9). The reason why mesohaline waters are avoided by most freshwater fishes is difficult to explain from a physiological perspective as many of these species would be isosmotic within this salinity range. Perhaps, a key to the poor penetration of estuarine waters by freshwater taxa is an inability to develop chloride cells in gill filament epithelia, as well as a lack of other osmoregulatory adaptations present in euryhaline fishes. Only a few freshwater fish species, especially some of those belonging to the family Cichlidae, have become fully euryhaline and have successfully occupied a wide range of estuaries, sometimes even dominating in hyperhaline systems (salinity 40+). Indeed, this review found that there are few fish species that can be termed holohaline (i.e. capable of occupying waters with a salinity range of 0–100+) and, of these taxa, there is a disproportionally high number of freshwater species (e.g. Cyprinodon variegatus, Oreochromis mossambicus and Sarotherodon melanotheron). Factors such as increased competition for food and higher predation rates by piscivorous fishes and birds may also play an important role in the low species richness and abundance of freshwater taxa in estuaries. Added to this is the relatively low species richness of freshwater fishes in river catchments when compared with the normally higher diversity of marine fish species for potential estuarine colonization from the adjacent coastal waters. The almost complete absence of freshwater fish larvae from the estuarine ichthyoplankton further reinforces the poor representation of this guild within these systems. An explanation as to why more freshwater fish species have not become euryhaline and occupied a wide range of estuaries similar to their marine counterparts is probably due to a combination of the above described factors, with physiological restrictions pertaining to limited salinity tolerances probably playing the most important role.     

Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

Long‐term limnological changes in the Ecuadorian páramo: Comparing the ecological responses to climate warming of shallow waterbodies versus deep lakes

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Ostracod distribution in Ulungur Lake (Xinjiang,China) and a reassessed Holocene record

Ostracod shells in surface sediments from Ulungur Lake (Xinjiang, China) belong mainly to Limnocythere inopinata as the dominant species, and Candona neglecta and Darwinula stevensoni as accompanying, less abundant taxa. Shells of an additional nine species were recorded only sporadically. The three most abundant ostracods have wide tolerance ranges in terms of salinity, substrate and water depth. The similarly recorded bivalve Pisidium subtruncatum, and the gastropods Gyraulus chinensis and Radix auricularia belong to the most tolerant representatives of the genera. The bivalve and gastropods, in addition to the ostracod assemblage, reflect the fact that Ulungur Lake has experienced strong lake level and salinity variations due to water withdrawal in the catchment and the counteracting diversion of river waters to the lake in recent decades. The substrate in Ulungur Lake is typically fine-grained, apart from the delta region of the Ulungur River channel, which is marked by relatively coarse-grained detrital sediments barren of ostracod shells. This channel was created 40 years ago to divert water to Ulungur Lake and support its local fisheries and recreational facilities. A reassessed Holocene ostracod record from the lake shows that a significantly higher salinity and lower lake level existed in the early Holocene before 6.0 ka in response to the regional climate. In contrast, a higher lake level and lowest salinity is inferred for the late Holocene period between ca. 3.6 and 1.3 ka before present. Afterwards, the lake level declined and salinity increased in response to regional moisture reduction, although conditions similar to the early Holocene lake status were not re-established. Our surface-sediment-derived data provide a baseline for analysis of future environmental variations due to global climate change and regional water management.     

Ecological influences on larval chironomid communities in shallow lakes: implications for palaeolimnological interpretations

1. To correctly interpret chironomid faunas for palaeoenvironmental reconstruction, it is essential that we improve our understanding of the relative influence of ecosystem variables, biotic as well as physicochemical, on chironomid larvae. To address this, we analysed the surface sediments from 39 shallow lakes (29 Norfolk, U.K., 10 Denmark) for chironomid head capsules, and 70 chironomid taxa (including Chaoborus) were identified. 2. The shallow lakes were selected over large environmental gradients of aquatic macrophytes, total phosphorus (TP) and fish communities. Redundancy analysis (RDA) identified two significant variables that explained chironomid distribution: macrophyte species richness (P < 0.001) and TP (P < 0.005). Generalised linear models (GLM) identified specific taxa that had significant relationships with both these variables. Macrophyte percentage volume infested (PVI) and species richness were significant in classifying the lake types based on chironomid communities under twinspan analysis, although other factors, notably nutrient concentrations and fish communities, were also important, illustrating the complexities of classifying shallow lake ecosystems. Lakes with plant species richness >10 all had relatively diverse (Hill’s N2) chironomid assemblages, and lakes with Hill’s N2 >10 all had TP <250 μg L⁻¹ and total fish densities <2 fish per m². 3. Plant density (PVI), and perhaps more importantly species richness, were primary controls on the distribution of chironomid communities within these lakes. This clearly has implications for palaeoenvironmental reconstructions using zoobenthos remains (i.e. chironomids) and suggests that they could be used to track changes in benthic/pelagic production and could be used as indicators of changing macrophyte habitat. 4. Measuring key biological gradients, in addition to physicochemical gradients, allowed the major controls on chironomid distribution to be assessed more directly, in terms of plant substrate, food availability, competition and predation pressure, rather than implying indirect mechanisms through relationships with nutrients. Many of these variables, notably macrophyte abundance and species richness, are not routinely measured in such studies, despite their importance in determining zoobenthos in temperate shallow lakes. 5. When physical, chemical and ecological gradients are considered, as is often the case with palaeo‐reconstructions rather than training sets chosen to maximise one gradient, complex relationships exist, and attempting to reconstruct a single trophic variable quantitatively may not be appropriate or reliable.     

Invasion of exotic piscivores causes losses of functional diversity and functionally unique species in Japanese lakes

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Diel shifts in the structure and function of nearshore estuarine fish communities

Day–night shifts in the nearshore fish fauna of a temperate microtidal estuary were assessed using a holistic suite of structural and functional community attributes. Mean fish species richness and diversity (taxonomic distinctness) were higher at night across all regions of the estuary and seasons, concurring with the findings of numerous comparable studies reviewed worldwide, while the diel period in which mean abundance was higher varied among seasons. Likewise, species and functional guild compositions (the latter based on feeding modes and habitat use) both differed significantly between day and night, with the extent of the diel shift again varying seasonally. Daytime fish communities were characterized by higher abundances of Atherinidae, Sillaginidae and Mugilidae, while Gobiidae were far more abundant at night. Marked shifts in size composition were also evident, with smaller fishes (<100 mm total length, L_T) being more prevalent during the day and larger fishes (≥200 mm L_T) proportionally more abundant at night. The above diel shifts were feasibly related to a range of predator–prey interactions and feeding‐related movements, namely a nocturnal decrease in top‐order avian piscivory coupled with an increase in invertebrate prey availability, resulting in changes in the presence and catchability of certain fish species in shallow estuarine waters.     

Patagonian ostracods as indicators of climate-related hydrological variables: implications for paleoenvironmental reconstructions in Southern South America

Different precipitation regimes across Patagonia generate an environmental gradient that is expected to reflect upon the solute composition and concentration of lake water through the ensuing differences in water balance. In turn, this hydrochemical gradient could influence the occurrence and distribution of ostracods in the area. A cluster analysis on hydrochemical data of 36 Southern Patagonian waterbodies shows that low salinity, bicarbonate-dominated waters characterize Andean and ecotonal lakes, located in the wetter part of the precipitation gradient, while their steppe counterparts, which receive a much lower precipitation input, are more saline, enriched in all major anions and sodium-dominated. Kruskal–Wallis tests followed by Mann–Whitney pairwise comparisons show statistically significant differences in the ostracod species each water type hosts, with L. patagonica, E. cecryphalium, P. smaragdina and P. incae being found in the more dilute waters characteristic of Andean and ecotonal lakes and Limnocythere rionegroensis in the mesohaline, evaporatively evolved waters typical of steppe lakes. Other species studied do not appear to have such distinct distributions, having been found throughout the range of conditions studied. These findings promote the use of the aforementioned ostracods as semi-quantitative paleohydrological indicators, which could improve paleoclimatic reconstructions in Patagonia.     

Distribution of Cyprideis torosa (Ostracoda) in Quaternary Athalassic Sediments in Germany and its Application for Palaeoecological Reconstructions

Cyprideis torosa (Jones , 1850) is a very common brackish water ostracod of the German coasts, but, despite empty valves are found occasionally in surface sediments of some modern inland waters, C. torosa could not be found living in modern athalassic waters of Germany so far. During interglacial periods, including the Holocene, however, fossils of this species are quite common in Central Germany, at a distance of more than 300 km away from the coasts of the Baltic and North Seas. All 31 Quaternary localities with C. torosa known so far from Germany are documented. C. torosa is an indicator for brackish waters and widely used as index‐fossil in palaeosalinity reconstructions relying on water chemistry bound morphological changes (nodes, sieve‐pores). The comparisons imply a general underestimation of palaeosalinity in oligo‐ to mesohaline athalassic waters if using nodes and sieve‐pores of C. torosa as proxy. A water chemistry (ionic composition) driven morphological response is assumed instead one by salinity only. Palaeosalinity estimations for athalassic waters, relying on morphological variability alone, should therefore be used with caution. Palaeosalinity trends, however, can be detected. Distinguishing thalassic and athalassic sediments with C. torosa is possible by using the associated ostracod fauna as a discriminator. Regarding the ecology and distribution of C. torosa, permanent, brackish, and shallow water bodies under relatively warm conditions are required for its settlement. The source of the salt are brines originating from Zechsteinian or Triassic underground evaporites. Warm and relatively dry climates could enhance the process for such water bodies of becoming salty, a situation present in Holocene Central Germany. The occurrence of C. torosa can therefore be used for palaeoclimatological studies. The most probable migration path of this ostracod species to athalassic waters is by avian transport. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Are mesophotic coral ecosystems distinct communities and can they serve as refugia for shallow reefs?

We analyzed an extensive dataset of over 9000 benthic and suprabenthic species found throughout the Gulf of Mexico (GoMx) to assess whether mesophotic coral ecosystems represent distinct assemblages and evaluate their potential to serve as refugia for shallow reef communities. We assessed community structure of the overall benthic community from 0 to 300 m via non-metric multidimensional scaling (NMDS) of species presence across depth bands. We used the Jaccard index of similarity to calculate the proportion of shared species between adjacent depth bands, measure species turnover with depth, and assess taxonomic overlap between shallow reefs versus progressively deeper depth bands. NMDS ordinations showed that the traditionally defined mesophotic range (30–150 m) as a whole is not a distinct community. In contrast, taxonomically distinct communities, determined by hierarchical clustering, were found at 0–70, 60–120, 110–200, and 190–300 m. Clustering highlighted an important separation in the benthic community at ~60 m, which was especially important for actinopterygian fishes. Species turnover between adjacent depths decreased with depth for all taxa combined and individual taxa, with peaks at ~60, 90–120, and 190–200 m. Fishes showed lower turnover from shallow to upper mesophotic depths (0–50 m) than all taxa combined, a substantial peak at 60 m, followed by a precipitous and continued decline in turnover thereafter. Taxonomic overlap between shallow (0–20 m) and progressively deeper zones declined steadily with depth in all taxa and individual taxa, suggesting that mid- and lower mesophotic habitats have less (but not inconsequential) potential to serve as refugia (60–150 m, 15–25% overlap with shallow habitats) than upper mesophotic zones (30–60 m, 30–45% overlap with shallow habitats) for all taxa combined. We conclude that the traditional mesophotic zone is home to three ecological communities in the GoMx, one that is confluent with shallow reefs, a distinct mesophotic assemblage spanning 60–120 m, and a third that extends onto the outer continental shelf.     

Pleuston communities are buffered from regional flood pulses: the example of ostracods in the Paraná River floodplain, Brazil

1. It is widely acknowledged that sudden, large‐scale flood pulses are drivers of benthic and planktonic biodiversity change in floodplains. The impact of such pulses on pleuston (biotic communities associated with root systems of floating plants) remains to be demonstrated. Here, we investigate the effects of local and regional drivers on seasonal changes in abundance and diversity of ostracod communities in pleuston. 2. Temporal and spatial distribution patterns of species richness, abundance, diversity and evenness of ostracods associated with the floating water hyacinth, Eichhornia crassipes, in a lentic environment from the upper Paraná River floodplain, were investigated in relation to local, as well as regional, environmental factors. Ostracods were sampled monthly over an annual cycle (March 2004–February 2005). Twenty‐seven species were found, representing the families Cyprididae, Candonidae, Limnocytheridae and Darwinulidae. Both diversity and abundance of ostracod communities showed seasonal changes, although species turn‐over during the year was limited. 3. We tested two hypotheses concerning the causality of these fluctuations: seasonal recruitment and influx of allochthonous ostracods during the flood pulse. Our results indicate that seasonal recruitment is more likely to be the driver of fluctuations in relation to the flood pulse. We postulate that pleuston communities are buffered against possible detrimental effects of flood pulses.     

Evolution of Nemertesia hydroids (Cnidaria: Hydrozoa,Plumulariidae) from the shallow and deep waters of the NE Atlantic and western Mediterranean

Moura, C. J., Cunha, M. R., Porteiro, F. M., Yesson, C. & Rogers, A. D. (2011) Evolution of Nemertesia hydroids (Cnidaria: Hydrozoa, Plumulariidae) from the shallow and deep waters of the NE Atlantic and Western Mediterranean. —Zoologica Scripta, 41, 79–96. Hydroid species from the genus Nemertesia develop some of the largest and most complex hydrozoan colonies. These colonies are abundant and ecologically important in both shallow and deep waters worldwide. Here, we analyse the systematics of most Nemertesia species from the NE Atlantic and Mediterranean using morphology and phylogenetic inferences of 16S rRNA haplotype data. Phylogeographical analysis revealed multiple movements of taxa to and from the Mediterranean after the Messinian salinity crisis through shallow and deep waters. The nominal species Nemertesia belini and Nemertesia antennina revealed multiple genetic lineages representing cryptic species diversity. Molecular phylogenetic evidence was supported by consistent phenotypic differences between lineages, and three and seven putative species were resolved within the N. belini and N. antennina complexes, respectively. Three putative species of the N. antennina complex found at different seamounts of Azores grouped in a clade clustered amongst the other four cryptic species present at neighbouring bathyal localities of the Gulf of Cadiz. These cryptic species, mostly from the deep sea, form a clade distantly related to the typical N. antennina from European coastal waters. Depth or environmental correlates of depth seem to influence the reproductive strategies of Nemertesia colonies and ultimately speciation. In particular, speciation of these hydroids must have been influenced by hydrography, habitat heterogeneity, isolation by distance and larval dispersal capacity. The deep sea is shown as an important environment in the generation and accumulation of lineages that may occasionally invade coastal waters in the NE Atlantic. Glacial cycles of cooling, along with changes in sea level, and eradication of some coastal faunas likely facilitated speciation and evolutionary transitions from deep to shallow waters.