Hard substrate in the deep ocean: How sediment features influence epibenthic megafauna on the eastern Canadian margin

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 230:159-169 (2002) - doi:10.3354/meps230159 Meiofaunal vertical zonation on hard-bottoms: comparison with soft-bottom meiofauna Roberto Danovaro1,2,*, Simonetta Fraschetti3 1Institute of Marine Science, Faculty of Science, University of Ancona, Via Brecce Bianche, 60131 Ancona, Italy 2DISTeBA, Department of Zoology and Marine Biology, University of Bari, Via Orabona 4, 70125 Bari, Italy 3Laboratory of Zoology and Marine Biology, University of Lecce, 73100 Lecce, Italy *E-mail: danovaro@unian.it ABSTRACT: An annual study on hard-substrate meiofaunal assemblages was carried out at 2 depths (2.5 and 8 m) along a vertical cliff of the Middle Adriatic (Mediterranean Sea) characterised by different macroalgal canopies and structural substrate complexities. The upper sampling area of the rocky cliff was covered by macroalgae, and its upper limit was characterised by the presence of a dense belt of Mytilus galloprovincialis. At 8 m depth, mussels were not present, the algal assemblage was less diversified, and phytal coverage decreased. Dynamics and community structure of meiofauna-inhabiting hard substrates were compared with those of meiofauna collected from soft sediments at the cliff base (9 m depth). Meiofauna of hard and soft substrates displayed significant differences both in terms of density (7-fold higher in soft substrates) and assemblage structure. Meiofauna from rocky substrates were dominated by crustaceans (copepods, nauplii and amphipods), while soft sediments were largely dominated by nematodes (ca 90%). Significant temporal changes of meiofaunal density were observed on both hard and soft substrates, with higher densities in spring to summer and lowest abundance in winter. Despite a completely different algal assemblage and coverage at 2.5 and 8 m depths, hard substrates displayed very similar meiofaunal densities and community structure. Crustacean taxa were correlated with algal coverage. Polychaetes inhabiting hard substrates increased their relevance with depth, whilst amphipods, being significantly correlated with algal biomass, decreased. Nematodes were related with the structural complexity index, calculated on the basis of macroalgal geometric complexity and biomass, whereas copepod and nauplius densities were related with the total structural complexity (as a sum of the algal complexity). The results of the present study indicate that the nature of the substrate (hard vs soft) is the main factor responsible for the differences observed between hard- and soft-bottom meiofauna assemblages, whereas phytal coverage and substrate complexity influenced the structure of hard bottom meiofaunal assemblages. Finally, the analysis of spatial variability of meiofaunal assemblages indicates that hydrodynamic stress also played an important role in meiofaunal structure and distribution on hard substrates, especially at shallow depths. KEY WORDS: Meiofauna · Hard substrates · Soft substrates · Algal coverage · Substrate complexity · Mediterranean Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 230. Online publication date: April 05, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Two populations of Gracilaria pacifica Abbott, that grow on different types of substrates (mud-sand and rochy) and that differ in the type and dominance of reproductive phases, were studied in Estero de Punta Banda, Baja California (Mexico). To determine whether the lack of hard (rocky) substrate, which allows attachment, and the viability of the tetraspores are related to the absence of cystocarpic plants in beds distributed on a soft substrate (mud-sand), the attachment and viability of the tetraspores, on an artificial substrate (concrete slabs), were evaluated in situ and under semicontrolled culture conditions. The fertility and viability of the tetraspores under controlled laboratory conditions were quantified. The tetraspores from both stations germinated under controlled and semicontrolled conditions. Germination in situ occurred only at the station with hard substrate. In the mud-sand environment, growth of plants on the artificial substrates placed among the beds was not observed. It is concluded that the absence of cycstocarpic plants in G. pacifica beds that grow on a mud-sand substrate cannot be attributed to the lack of hard (rocky) substrate or the viability of the tetraspores.

Sediment-dwelling fauna are a ubiquitous component of salt marshes yet we have limited understanding of their roles in marsh functioning and of the environmental conditions that control their distributions and abundances. This paper examines the influence of vegetation (presence, type, density, and biomass) and other environmental variables (marsh age, sediment and porewater properties, elevation, flow, oxygen, and biogenic structures) on salt marsh macrofauna and meiofauna. We review studies from a variety of geographical locations and include new information from systems with adjacent natural and restored sites in southern California. The influence of environmental factors on faunal assemblages varies with marsh system, factor intensity or concentration, taxon studied, and with other interacting factors present. We hypothesize a hierarchy of environmental variables in which abiotic properties such as marsh age, elevation and salinity act over large space and time scales, and are most likely to influence the presence or absence of species. Sediment properties (organic matter and particle size) and vegetation presence or type act on intermediate scales affecting macrofaunal abundance and composition. Plant biomass, culms and biogenic structures generated by fauna are patchy and act on small scales, often interacting with flow, to affect distribution and abundance patterns. Resolution of these processes in salt marshes should improve our understanding of controls on invertebrate communities and will ultimately aid the conservation and restoration of salt marsh habitat.

Marine diversity across the Australian continental shelf is shaped by characteristic benthic habitats which are determined by geomorphic features such as paleoshorelines. In north-western Australia there has been little attention on the fish communities that inhabit an ancient coastline at ~125 m depth (the designated AC125), which is specified as a key ecological feature (KEF) of the region and is thought to comprise hard substrate and support enhanced diversity. We investigated drivers of fish species richness and assemblage composition spanning six degrees of latitude along sections of the ancient coastline, categorised as ‘on’ and ‘off’ the AC125 based on depth, across a range of habitats and seafloor complexity (~60–180 m depth). While some surveyed sections of the AC125 had hard bottom substrate and supported enhanced fish diversity, including over half of the total species observed, species richness and abundance overall were not greater on the AC125 than immediately adjacent to the AC125. Instead, depth, seafloor complexity and habitat type explained patterns in richness and abundance, and structured fish assemblages at both local and broad spatial scales. Fewer fishes were associated with deep sites characterized by negligible complexity and soft-bottom habitats, in contrast to shallower depths that featured benthic biota and pockets of complex substrate. Drivers of abundance of common species were species-specific and primarily related to sampling Areas, depth and substrate. Fishes of the ancient coastline and adjacent habitats are representative of mesophotic fish communities of the region, included species important to fisheries and conservation, and several species were observed deeper than their currently known distribution. This study provides the first assessment of fish biodiversity associated with an ancient coastline feature, improving our understanding of the function it plays in regional spatial patterns in abundance of mesophotic fishes. Management decisions that incorporate the broader variety of depths and habitats surrounding the designated AC125 could enhance the ecological role of this KEF, contributing to effective conservation of fish biodiversity on Australia’s north west shelf.

The densities of alkali fly larvae and pupae were measured in relation to depth and substrate type at six locations around Mono Lake. Samples representing a mixture of different bottom features were taken to a depth of 10 m (33 ft) using SCUBA. This is at or near the depth limit of fly larvae and pupae. The biomass of larvae and pupae on hard substrate were maximum and approximately equal at depths of 0.5 m and 1 m, substantially lower at intermediate depths of 3 m and 5 m, and over an order of magnitude further reduced at 10 m. Densities of flies on hard or rocky substrates (mainly calcareous tufa deposits), were significantly greater than those found on soft substrates such as mud or sand, at all but the greatest depth surveyed.

The effect of substrate heterogeneity on the structure of stream macroinvertebrate assemblages (total abundance, taxon richness, and evenness) is still not clear, but this could be due to the lack of standard methods for quantifying substrate heterogeneity. An accurate quantification of substrate heterogeneity was obtained from photographs of sampled areas (each 225 cm2), which were used to create maps that were subsequently digitized and analyzed using image analysis software. These maps allowed the calculation of multiple metrics quantifying two aspects of substrate heterogeneity: composition and spatial configuration of substrate patches. The diversity of substrate types (calculated as the Shannon diversity index), and the heterogeneity of patch compactness (calculated as the coefficient of variation of the relationship between patch dimensions) were the metrics explaining more biotic variance at the sample scale, but at higher scales there were no relationships between assemblage structure and substrate heterogeneity. Most variation in substrate heterogeneity occurred at the sample scale, while some metrics varied significantly at riffle or segment scales; these patterns of variation match those of macroinvertebrate assemblages, which had been previously studied. The importance of quantifying substrate heterogeneity and considering the spatial scales of its study are discussed.

Patterns of distribution and abundance of benthic megaepifauna demonstrate mesoscale zoogeographic trends across the nearshore Cascadia Abyssal Plain and offshore Tufts Abyssal Plain. Species composition analysis of Holothuroidea and Ophiuroidea (Echinodermata) and Galatheidae (Crustacea: Decapoda) separates the fauna into sediment fan, slope-base, Cascadia Plain, Tufts Plain, Gorda Ridge, and northern California abyssal elements. Faunal distribution and abundance are correlated with distance from the continent and depth of the water column. Gradients in rates of sedimentation and food flux to the seafloor are probable causes. Unlike macrofaunal distribution and abundance patterns, the species composition, abundance, and diversity of megafauna (e.g., Holothuroidea) appear to be more controlled by depth than by distance from the continent.

This is the first study to explore fish community structure and its relations to habitat and topographic complexity in the shallow coastal waters of the Cyclades Archipelago, North-eastern Mediterranean Sea. In situ visual surveys were carried out at 233 sampling sites in 26 islands of the Cyclades Archipelago. Fish community parameters and biomass were estimated across seven substrate types: sand, seagrass, vertical walls, boulders, horizontal/subhorizontal continuous rock, rocky substrate with patches of sand, and rocky substrate with patches of sand and Posidonia oceanica . Topographic complexity and percentage of algal cover were estimated on hard substrate. Substrate type was found to be a determining factor affecting the structure and composition of fish assemblages. Species number, abundance and biomass were significantly lower in sandy areas and always higher on hard substrates, with seagrass habitats presenting intermediate values. Topographic complexity in rocky bottoms did not seem to affect species richness, density or biomass. This study provides a baseline for future evaluation of changes produced by potential management actions such as the creation of marine protected areas in the study region.

This is the first study to explore fish community structure and its relations to habitat and topographic complexity in the shallow coastal waters of the Cyclades Archipelago, North-eastern Mediterranean Sea. In situ visual surveys were carried out at 233 sampling sites in 26 islands of the Cyclades Archipelago. Fish community parameters and biomass were estimated across seven substrate types: sand, seagrass, vertical walls, boulders, horizontal/subhorizontal continuous rock, rocky substrate with patches of sand, and rocky substrate with patches of sand and Posidonia oceanica. Topographic complexity and percentage of algal cover were estimated on hard substrate. Substrate type was found to be a determining factor affecting the structure and composition of fish assemblages. Species number, abundance and biomass were significantly lower in sandy areas and always higher on hard substrates, with seagrass habitats presenting intermediate values. Topographic complexity in rocky bottoms did not seem to affect species richness, density or biomass. This study provides a baseline for future evaluation of changes produced by potential management actions such as the creation of marine protected areas in the study region.

The role of habitat heterogeneity and canyon processes in structuring sediment macrofaunal communities associated with hard substrate habitats in Norfolk Canyon, USA

Landscape configuration modulates carbon storage in seagrass sediments

Understorey vegetation comprises the majority of species diversity and contributes greatly to ecosystem functioning in boreal forests. Although patterns of understorey abundance, species diversity and composition associated with forest stand development are well researched, mechanisms driving these patterns remain largely speculative. We sampled fire‐origin stands of varying stand ages and overstorey compositions on mesic sites of the boreal forest of Canada and used structural equation modelling (SEM) to link time since fire (stand age), light availability and heterogeneity, substrate heterogeneity and soil nitrogen to understorey vegetation cover and species diversity. The most parsimonious model for total understorey cover showed a positive direct effect of stand age (r = .43) and an indirect effect via mean light level (0.18) and shrub cover (−0.11), with a positive total effect (0.50); the per cent broadleaf canopy had a direct negative effect (−0.22) and an indirect effect via shrub cover (−0.11). The model for total understorey species richness showed an indirect effect of stand age via mean light (0.24), light heterogeneity (0.10) and substrate heterogeneity (0.07), with a positive total effect (0.52); per cent broadleaf canopy had an indirect effect via light heterogeneity (0.09), and substrate heterogeneity (−0.10). Soil nitrogen did not significantly influence either understorey cover or species richness. The models for vascular plants followed similar trends to those for total understorey cover and species richness; however, there was an opposite indirect effect of light heterogeneity for both cover and species richness of non‐vascular plants. Shrub cover had positive direct and negative direct and indirect effects on both vascular and non‐vascular cover and species richness. Synthesis. Our findings indicate that understorey cover and species diversity are driven by time since disturbance, light availability as influenced by overstorey and shrub layers, but with important additional effects mediated by light and substrate heterogeneity. Non‐vascular understorey vegetation is more strongly determined by time since disturbance than vascular vegetation, and negatively affected by broadleaf tree abundance. The overall results highlight the importance of colonization, light availability and heterogeneity, substrate specialization and growth dynamics in determining successional patterns of boreal forest understorey vegetation.

This study investigated the spatial and temporal patterns of abundance of four substratum‐associated species of Gobiidae on a heterogeneous reef flat comprised of four distinct habitat zones, and examined microhabitat use within each zone. Asterropteryx semipunctatus had the widest distribution and was the most abundant species in each habitat zone, followed by Amblygobius bynoensis, Valenciennea muralis and Amblygobius phalaena. Significant temporal and spatial differences in mean density were evident. The highest density of A. semipunctatus (312 individuals 10 m–2) was recorded in a habitat zone dominated by algal‐covered rubble, whereas A. bynoensis and V. muralis were most abundant (mean summer density 5·5–5·8 individuals 10 m–2) in habitats containing both sand and hard substrata. In contrast, A. phalaena was uncommon (mean density ≤ 0·4 individuals 10 m–2) in all four habitat zones. Significant seasonal differences in abundance were due to the large influx of recruits in summer. Ontogenetic shifts in habitat use were not evident at either the macrohabitat (i.e. among habitat zones) or microhabitat scale (i.e. substratum use within zones). At the microhabitat scale, V. muralis consistently exhibited a strong positive association with sand and was rarely associated with hard substrata. In contrast, the two Amblygobius species were commonly associated with both sand and hard substrata, but patterns of microhabitat use differed among habitat zones. Substratum composition at the microhabitat scale may influence spatial patterns of abundance at larger spatial scales by providing essential resources and, or influencing carrying capacity and predation risk.

Abstract. We examined the role of playa lakes in promoting regional heterogeneity on the southern High Plains. The goals of this paper were to: (1) describe vegetation types and zonation patterns within playas, (2) evaluate patterns of species distribution and abundance within and among playas, and (3) assess patterns of heterogeneity within and among playas on a portion of the southern High Plains. Perennial grasses were the most abundant species in playa vegetation. Playa vegetation exhibited distinct and repeatable vegetation zones at the majority of sites, but the number of distinct zones varied from site to site. Agropyron smithii, Buchloë dactyloides, and Panicum obtusum were the most important species of playa interior zones, and Bouteloua gracilis, Buchloë dactyloides, and Schedonnardus paniculatus were important upland species outside of playas. Species distribution and abundance were positively correlated at 38 of 40 sites. The distributions of species occurrences among sites were unimodal both locally and regionally. The degree of heterogeneity varied from playa to playa. Local heterogeneity within playas was found to increase regional heterogeneity; therefore, playas increase both local and regional heterogeneity of vegetation. Long‐term monitoring will be necessary to understand the spatial and temporal response of vegetation within and among playas to stochastic climatic factors on the southern High Plains of North America.

In coastal marine ecosystems, predation might affect spatial distribution and population dynamics of benthic assemblages. Here, by means of experimental exclusion of potential predators, we compared the effects of epibenthic predation on metazoan meiofaunal assemblages on soft and rocky substrates. Different patterns of abundance were observed in uncaged versus caged plots, across habitats. In caged soft substrates, the abundance of Nematodes, Copepods and Polychaetes increased by 56, 45, 57%, respectively, in the first 3 months. An increase in the number of meiofaunal taxa was also observed. The exclusion of predators from rocky substrates showed less clear patterns. It did not affect the number of taxa while a decrease in meiofaunal abundance was observed. Our results suggest that the exclusion of epibenthic predators had clear effect on total metazoan meiofaunal abundance and on the number of taxa, only in soft bottoms. The different impact of predation across habitats can be potentially explained by differences in terms of spatial variability and substrate complexity. We estimated that, coarsely, more than 75% of total metazoan meiofaunal production can be channeled to higher trophic levels through predation on soft-bottoms. Among meiofaunal taxa, Polychaetes and Nematodes provided the major contribution to benthic energy transfers. These results suggest the trophic relevance of metazoan meiofauna in coastal food webs and claim for the refinement of further experiments for the quantification of its role in different ecological systems.