Unvegetated Habitats Research Articles

Photosynthetic activity of seagrasses and macroalgae in temperate shallow waters can alter seawater pH and total inorganic carbon content at the scale of a coastal embayment

Many studies have reported fluctuations in pH and the concentration of dissolved inorganic carbon (DIC) in shallow coastal waters as a result of photosynthetic activity; however, little is known about how these fluctuations vary with degree of exposure among habitats, and at different scales. In the present study, diel variation in seawater pH was apparent in aquaria experiments with Zostera marina and Ruppia maritima. These pH variations were affected by light regime, biomass level and plant species. Subsequently, the natural variability in seawater pH and the concentration of DIC was assessed in six shallow embayments (three sheltered and three exposed) during sunny days. From the outer part towards the interior part of each bay, the following four habitats were identified and studied: the bay-mouth open water, seagrass beds, mixed macrophyte belts and unvegetated bottoms. The two vegetated habitats and unvegetated bottoms were characterised by higher pH and a lower concentration of DIC than in the bay-mouth water. The mixed macrophytes habitat showed slightly higher pH and a lower concentration of DIC than the seagrass and unvegetated habitats. No significant effect of exposure was detected. Our findings clearly showed that the photosynthetic activity of marine macrophytes can alter the coastal pH and the concentration of DIC and that the effects can be observed at the scale of a whole bay.

California spiny lobster (Panulirus interruptus) movement behaviour and habitat use: implications for the effectiveness of marine protected areas

The effectiveness of conservation efforts, including marine protected areas (MPAs), hinges on adequate knowledge of movement patterns, habitat associations and habitat-specific survival rates of mobile organisms. California spiny lobsters (Panulirus interruptus) support commercial and recreational fishing in southern California; however, we lack basic information to determine whether MPAs planned for the region will enhance abundance. Working within and outside a small southern California MPA, we (1) quantified the movement patterns and home ranges of the lobster over two time scales, (2) determined lobster day and night habitat associations and (3) determined habitat-specific predation risk. Lobsters exhibited high site fidelity and small home ranges (geometric mean of 651 m2 and 5912 m2 per week, on the basis of 50% and 95% kernel utilisation distributions, respectively). Lobsters were associated with rocky habitat during the day and with the red algae Plocamium cartilagineum while feeding at night. Relative survival rates of lobsters were high across vegetated and unvegetated habitats at night, and were highest in surfgrass (Phyllopsadix torreyi) habitat during the day. Our results highlight the need to consider how movement patterns vary over short and long time scales, and how habitat use may vary from day to night for nocturnally active species such as lobsters, when planning MPAs.

Elevated habitat quality reduces variance in fish community composition

Understanding the intrinsic variability of habitat-specific faunal communities is important to species conservation and ecosystem management. Community variability is driven by many environmental factors, including density-dependent habitat selection. Extensions of MacCall's Basin Model of density dependent habitat selection indicate that variance of a species' density is generally expected to be independent of habitat quality while variance in community composition is expected to decrease with habitat quality. We used these expectations to investigate variability of nearshore fish communities. Fish collections were conducted biweekly in eelgrass (high quality) and unvegetated (low quality) habitats from early summer to late autumn from 1996 to 2009. Higher fish density and biomass, taxa richness, and elevated variability of these measures were associated with the higher quality habitat. Seasonality explained the greatest variance in the fish community followed by habitat quality and year. Consistent with expectation, variability in community composition was less in the high quality habitat. In addition to differences in variability, cyclical seasonal transitions were less predictable and directional multi-year shifts in community structure were more pronounced in the low quality habitat. Our results show that community variability is associated with suboptimal or degraded habitats; a finding of significance given the increased prevalence of anthropogenic disturbance in ecosystems globally.

Exotic macroalga Gracilaria vermiculophylla provides superior nursery habitat for native blue crab in Chesapeake Bay

ABSTRACT: Exotic species often reduce the abundance or diversity of species in marine ecosys-tems, but some exotics may benefit native species, such as when habitat is enhanced. In Chesa-peake Bay, the exotic macroalga Gracilaria vermiculophylla (Rhodophyta) has flourished and dis-persed widely, yet the consequences for native species diversity and abundance are not wellknown. We experimentally examined the capacity of the structurally complex G. vermiculophylla to provide nursery habitat for the blue crab Callinectes sapidus in Chesapeake Bay, where nativeeelgrass nursery habitat has dwindled. We also examined ontogenetic shifts in survival acrossalternative nursery habitats. In field surveys, juvenile density was similar in macroalgae and eel-grass, but lower in unvegetated mud habitat. In field experiments, juvenile survival was positivelyrelated to crab size in mud but negatively in eelgrass, confirming the paradigm of a predation-induced ontogenetic shift from seagrass to unvegetated habitat. In contrast, irrespective of crabsize, survival was higher in macroalgae than in either native habitat. Thus, exotic habitat-formingmacroalgae can compensate for severe declines in seagrass nurseries, and facilitate the emer-gence of a novel ecosystem.KEY WORDS: Exotic species · Ontogenetic habitat shift · Predation · Prey size refuge · Novelecosystem · Emerging ecosystem · Macroalgae · Seagrass

Seasonal dynamics of prey size mediate complementary functions of mussel beds and seagrass habitats for an avian predator

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 467:219-232 (2012) - DOI: https://doi.org/10.3354/meps09943 Seasonal dynamics of prey size mediate complementary functions of mussel beds and seagrass habitats for an avian predator Eric M. Anderson1,2,*, James R. Lovvorn1,3 1Department of Zoology and Physiology, University of Wyoming, 1000 E. University Avenue, Laramie, Wyoming 82071, USA 2Present address: Department of Renewable Resources, British Columbia Institute of Technology, 3700 Willingdon Avenue, Burnaby, British Columbia V5G 3H2, Canada 3Present address: Department of Zoology and Center for Ecology, Southern Illinois University, Carbondale, Illinois 62901, USA *Email: eric_anderson@sfu.ca ABSTRACT: Foraging profitability can be strongly affected by the size structure of different prey, so that predator distributions are not a simple function of total prey biomass. For a bottom-feeding avian predator, the surf scoter Melanitta perspicillata, we assessed effects of prey size and other prey attributes on seasonal shifts in scoter use of 2 major foraging habitats in Puget Sound, Washington, USA. During early winter, many thousands of scoters fed at an unvegetated site where profitable prey appeared limited to mussels Mytilus trossulus of smaller sizes (2 to 30 mm) despite their much lower biomass relative to larger mussels and several other prey types. Accordingly, scoter numbers decreased at that site as small mussels declined over winter. During pre-migratory fattening in spring and feather molt in summer, >8000 surf scoters aggregated at a seagrass site where they fed mainly on epifaunal crustaceans (50 to 73%) and gastropods (12 to 27%). Body sizes of most crustacean prey had increased substantially since winter. Thus, prey size had opposite effects on the profitability of unvegetated habitats that provide mainly mussels (smaller items likely reduce shell processing costs) versus seagrass crustaceans (larger items are likely more visible and yield greater energy per prey item, although relative mobility of prey can alter their value). Total prey biomass, and prey distributions relative to water and sediment depths, appeared less important than prey size to shifts in scoter diets and numbers. Our synthesis of past studies indicates that biomass and production of mussel beds are typically an order of magnitude greater than for entire assemblages of seagrass macroinvertebrates. However, because of seasonal shifts in prey size structure, seagrass sites can be an important complement to mussel beds when the narrow size fraction of mussels that are profitable to scoters declines. KEY WORDS: Epifauna · Foraging profitability · Marine habitat · Melanitta perspicillata · Prey biomass · Size selection of prey · Surf scoter Full text in pdf format PreviousNextCite this article as: Anderson EM, Lovvorn JR (2012) Seasonal dynamics of prey size mediate complementary functions of mussel beds and seagrass habitats for an avian predator. Mar Ecol Prog Ser 467:219-232. https://doi.org/10.3354/meps09943 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 467. Online publication date: October 25, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Habitat connectivity and spatial complexity differentially affect mangrove and salt marsh fish assemblages

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 466:177-192 (2012) - DOI: https://doi.org/10.3354/meps09791 Habitat connectivity and spatial complexity differentially affect mangrove and salt marsh fish assemblages Benjamin C. Green1,2, David J. Smith1,*, Graham J. C. Underwood1 1School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK 2Present address: Marine Monitoring Service, Environment Agency, Kingfisher House, Goldhay Way, Orton Goldhay, Peterborough PE2 5ZR, UK *Corresponding author. Email: djsmitc@essex.ac.uk ABSTRACT: Coastal salt marshes and mangroves are both intertidal habitats that, relative to unvegetated habitat, provide increased food, shelter and a nursery function to fish. Patch structural complexity and connectivity can influence assemblage structure across multiple spatial scales, and should be taken into account when assessing the effectiveness of marine reserves. We tested the hypothesis that fish assemblage density and species richness of the 2 habitats would be strongly associated with similar patch complexity-, connectivity- and physically-based variables (37 variables assessed) in a replicated investigation of 10 Indonesian mangrove and 9 European salt marsh habitats. Salt marsh and mangrove fish assemblage density and species richness (4.95 and 111.5 ind. 100 m−2; 13 and 64 species for salt marshes and mangroves, respectively) showed significant variation between patches, and were influenced by different spatial variables. Patch shape (increased circularity) was the most highly influential variable in both habitats associated with enhanced fish species richness and density. Prop root density and number of mangrove patches within 1 km radial extent were strongly positively correlated with mangrove fish species richness, and patch isolation was negatively correlated with density. Salt marsh fish assemblage structure was negatively correlated with intertidal mudflat extent, patch seaward edge length and patch depth. The role of habitat mosaics was less important in structuring salt marsh fish than mangrove fish assemblages. Different spatial factors must be integrated when considering the role of coastal fringing habitats as fish nursery sites, and to maximize their conservation value, salt marsh and mangrove habitats may require different management approaches. KEY WORDS: Salt marsh . Mangrove . Fish . Connectivity . Habitat loss · Habitat mosaic · Estuary · Spatial ecology Full text in pdf format Supplementary material PreviousNextCite this article as: Green BC, Smith DJ, Underwood GJC (2012) Habitat connectivity and spatial complexity differentially affect mangrove and salt marsh fish assemblages. Mar Ecol Prog Ser 466:177-192. https://doi.org/10.3354/meps09791 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 466. Online publication date: October 15, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Invasive ecosystem engineer selects for different phenotypes of an associated native species

Invasive habitat-forming ecosystem engineers modify the abiotic environment and thus represent a major perturbation to many ecosystems. Because native species often persist in these invaded habitats but have no shared history with the ecosystem engineer, the engineer may impose novel selective pressure on native species. In this study, we used a phenotypic selection framework to determine whether an invasive habitat-forming ecosystem engineer (the seaweed Caulerpa taxifolia) selects for different phenotypes of a common co-occurring native species (the bivalve Anadara trapezia). Compared to unvegetated habitat, Caulerpa habitat has lower water flow, lower dissolved oxygen, and sediments are more silty and anoxic. We determined the performance consequences of variation in key functional traits that may be affected by these abiotic changes (shell morphology, gill mass, and palp mass) for Anadara transplanted into Caulerpa and unvegetated habitat. Both linear and nonlinear performance gradients in Anadara differed between habitats, and these gradients were stronger in Caulerpa compared to unvegetated sediment. Moreover, in Caulerpa alternate phenotypes performed well, and these phenotypes were different from the dominant phenotype in unvegetated sediment. By demonstrating that phenotype-performance gradients differ between habitats, we have highlighted a role for Caulerpa as an agent of selection on native species.

Habitat Affects Survival of Translocated Bay Scallops, Argopecten irradians concentricus (Say 1822), in Lower Chesapeake Bay

Bay scallop (Argopecten irradians) populations existed in Chesapeake Bay until 1933, when they declined dramatically due to a loss of seagrass habitat. Since then, there have been no documented populations within the Bay. However, some anecdotal observations of live bay scallops within the lower Bay suggest that restoration of the bay scallop is feasible. We therefore tested whether translocated adults of the southern bay scallop, Argopecten irradians concentricus, could survive during the reproductive season in vegetated and unvegetated habitats of the Lynnhaven River sub-estuary of lower Chesapeake Bay in the absence of predation. Manipulative field experiments evaluated survival of translocated, caged adult scallops in eelgrass Zostera marina, macroalgae Gracilaria spp., oyster shell, and rubble plots at three locations. After a 3-week experimental period, scallop survival was high in vegetated habitats, ranging from 98% in their preferred habitat, Z. marina, to 90% in Gracilaria spp. Survival in Z. marina was significantly higher than that in rubble (76%) and oyster shell (78%). These findings indicate that reproductive individuals can survive in vegetated habitats of lower Chesapeake Bay when protected from predators and that establishment of bay scallop populations within Chesapeake Bay may be viable.

Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season

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 446:259-273 (2012) - DOI: https://doi.org/10.3354/meps09455 Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season Joaquim Ribeiro*, Gonçalo M. Carvalho, Jorge M. S. Gonçalves, Karim Erzini Centro de Ciências do Mar (CCMAR), Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal *Email: jmnribeiro@sapo.pt ABSTRACT: Fish assemblages in seagrass and unvegetated habitats located in shallow intertidal creeks within the saltmarsh area of the Ria Formosa coastal lagoon were sampled with a Riley push net at 3 sites on a monthly basis over a 1 yr period. The objective was to test if both habitats support similar fish assemblages in terms of abundance, diversity, assemblage structure, and size distribution, and to investigate how site and season affect the assemblages. Fish assemblages associated with these habitats were significantly different in terms of diversity, abundance, and assemblage structure. Seagrass supported a larger number of species and greater diversity, while unvegetated habitat supported greater fish numbers but only of a few species. The habitats were dominated by different groups of resident species that were responsible for major differences in fish assemblage structure between habitats. Pomatoschistus microps and young-of-the-year (YOY) Atherina presbyter dominated the unvegetated habitat, while seagrass was dominated by a diverse group of species, in particular syngnathids and small labrids, revealing different habitat preferences. Site and season were determinant factors conditioning the role of habitat in structuring fish assemblages. Distance between habitats, site elevation, and the amount of marsh drained affected fish assemblages in both habitats. Seasonal fluctuations in the presence and abundance of YOY from marine migrant and resident species were responsible for comparable changes in fish assemblage structure in both habitats. Both habitats provide a distinctive nursery area for different species, while common species reveal ontogenic distributional changes between habitats, where smaller fish appear first in unvegetated creeks. KEY WORDS: Fish fauna · Coastal lagoon · Saltmarsh · Intertidal habitats · Seasonal variations · Habitat association · Ria Formosa · South Portugal Full text in pdf format PreviousNextCite this article as: Ribeiro J, Carvalho GM, Gonçalves JMS, Erzini K (2012) Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season. Mar Ecol Prog Ser 446:259-273. https://doi.org/10.3354/meps09455 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 446. Online publication date: February 02, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Impact of sampling depth and plant species on local environmental conditions, microbiological parameters and bacterial composition in a mercury contaminated salt marsh

We compare the environmental characteristics and bacterial communities associated with two rushes, Juncus maritimus and Bolboschoenus maritimus, and adjacent unvegetated habitat in a salt marsh subjected to historical mercury pollution. Mercury content was higher in vegetated than unvegetated habitat and increased with sampling depth. There was also a significant relationship between mercury concentration and bacterial composition. Habitat (Juncus, Bolboschoenus or unvegetated), sample depth, and the interaction between both, however, explained most of the variation in composition (∼70%). Variation in composition with depth was most prominent for the unvegetated habitat, followed by Juncus, but more constrained for Bolboschoenus habitat. This constraint may be indicative of a strong plant–microbe ecophysiological adaptation. Vegetated habitat contained distinct bacterial communities associated with higher potential activity of aminopeptidase, β-glucosidase and arylsulphatase and incorporation rates of 14C-glucose and 14C-acetate. Communities in unvegetated habitat were, in contrast, associated with both higher pH and proportion of sulphate reducing bacteria.

Differences in anti-predator traits of a native bivalve following invasion by a habitat-forming seaweed

Invasive habitat-forming species cause large changes to the abiotic environment, which may lead to lethal and sublethal effects on native fauna. In this study, we tested whether morphological anti-predator traits of an infaunal bivalve, Anadara trapezia, differed between areas invaded by the habitat-forming seaweed Caulerpa taxifolia and uninvaded habitats in estuaries in New South Wales, Australia. Caulerpa changes the abiotic environment in ways that may affect traits of native species. In particular, there is lower water flow, lower dissolved oxygen in the water and sediments are more silty and anoxic than in unvegetated habitat. To test our hypotheses, we collected Anadara from Caulerpa and uninvaded habitats and measured shell thickness, shell strength and resistance to opening of valves. We found that all three traits were reduced in Anadara from Caulerpa habitat compared with Anadara from uninvaded habitats. These findings are consistent with the idea that trait modifications in native fauna in response to invasive habitat-forming species can potentially increase susceptibility to predation.

Assessment of fish assemblages in coastal lagoon habitats: Effect of sampling method

The structure of fish assemblages accounted for by different sampling methods (namely fyke net, seine nets, visual census) applied to vegetated and unvegetated lagoon habitats was investigated in terms of species composition, functional groups (ecological and trophic guilds), and fish size distribution. Significant differences were detected among methods, even among similar ones (seine nets). Visual census and fyke net detected more easily pelagic species, allowing the sampling of larger fish, whereas seine nets targeted more efficiently benthic-demersal species, with a dominance of 2–10 cm size classes in the fish catches. Differences were detected also among habitats, reflecting the different fish assemblages associated to vegetated and unvegetated habitats in coastal lagoons and transitional waters. However a different ability of discriminating between habitat-associated fish assemblages was recorded for the sampling methods. The different selectivity and functioning of the tested sampling methods confirm the importance of considering the targeted scale at which the research is being carried out, as well as the method that will be used to assess the ecological status of lagoon fish assemblages when choosing the most appropriate sampling method. A cross-validation of fish sampling methodologies in transitional waters is necessary to cope with the mandatory of the Water Framework Directive of standardization and comparability of monitoring methods.

Feeding ecology of King George whiting Sillaginodes punctatus (Perciformes) recruits in seagrass and unvegetated habitats. Does diet reflect habitat utilization?

This study investigated the feeding ecology of King George whiting Sillaginodes punctatus recruits to determine how diet composition varies between habitat types (seagrass and unvegetated habitats), and between sites separated by distance. Broad-scale sampling of seagrass and unvegetated habitats at nine sites in Port Phillip Bay (Australia) indicated the diet composition varied more by distance into the bay than by habitat. Near the entrance to the bay the diet was dominated by harpacticoids and gammarid amphipods, in the middle reaches of the bay the diet was completely dominated by harpacticoids, while at sites furthest into the bay, mysids and crab zoea were also important. Abundances of prey in guts was significantly higher between 1000 and 2200 hours compared with other times, indicating diurnal feeding. Laboratory determined gut evacuation rate (based on an exponential model) was estimated to be -0·54. Daily rations were highly variable among sites and habitat types. Sillaginodes punctatus recruits consumed much higher quantities of prey on unvegetated habitat than seagrass habitat at some middle reach sites; with prey consumption of harpacticoid copepods on unvegetated habitat approaching 3000 individuals per day at one site. The results of this study provide insight into why habitat associations of S. punctatus recruits within mosaics of seagrass and unvegetated habitat show high spatial variation.

Monitoring acoustically tagged king prawns Penaeus (Melicertus) plebejus in an estuarine lagoon

Fine-scale movement patterns in penaeid prawns are rarely observed in situ, but are essential in understanding habitat use, foraging, and anti-predator behaviour. Acoustic telemetry was applied to examine the activity, space utilization, and habitat use of the eastern king prawn Penaeus (Melicertus) plebejus, at small temporal and spatial scales. Tracking of sub-adult P. plebejus (n = 9) in Wallagoot Lake (36.789°S, 149.959°E; 23 April–12 May 2009) and calculation of a minimum activity index (MAI) revealed high variation in activity rates across diel periods and in different habitats. Elevated activity rates and movement indicated foraging in unvegetated habitats during the night. Areas within the 95 and 50% space utilization contours averaged 2,654.1 ± 502.0 and 379.9 ± 103.9 m2, respectively, and there was a significant negative relationship between these areas and prawn activity rates in unvegetated habitats. This study provides the first estimates of prawn activity rates and space utilization in the field. Application of acoustic telemetry can increase knowledge of prawn movements and their interactions with other marine species in different habitats.

Small-scale effect of intertidal seagrass (Zostera muelleri) on meiofaunal abundance, biomass, and nematode community structure

Seagrass beds are common features of coastal ecosystems worldwide, and their associated infauna are often more productive and diverse than in unvegetated habitats. Little is known, however, about the ecology of meiofaunal communities living in seagrass sediments. We compared the abundance and biomass of sediment meiofauna inside and outside an intertidalZostera muelleribed in southern New Zealand to assess the impact of seagrass cover on meiofaunal distribution. Nematode community structure, diversity, and feeding groups were also compared between habitats and sediment depths (0–2, 2–5 and 5–10 cm) to evaluate the effect of seagrass on nematode communities. Meiofaunal biomass was significantly higher inside than outside theZ. muelleribed, but secondary productivity inside the bed is likely to have been limited by the availability of labile organic matter. There were significant differences in nematode community structure between unvegetated, sparsely vegetated, and densely vegetated sites (102 m scale), as well as between sediment depths (cm scale). No significant differences were found in depth-integrated (0–10 cm) nematode diversity between sites, but vertical gradients in diversity differed between vegetated and unvegetated sites. Epistrate feeders were the most common feeding group in unvegetated sediments whereas most feeding groups were common inside the seagrass bed. Findings from this study indicate that seagrass beds can have a marked impact on infaunal structure and function over small spatial scales through their effect on sediment characteristics and organic matter input. Some unexpected trends observed in the present study, i.e. low meiofaunal biomass at the vegetated sites, and lower abundance of copepods inside than outside the seagrass bed, suggest that the nature of seagrass–invertebrate interactions may depend on habitat characteristics and the identity and ecology of species considered.

A multi-method approach for identifying meiofaunal trophic connections

Meiofauna can play an important role in the energetics of benthic communities, but determining their diet remains problematic due to their small size. In this study, the contribution of primary producers to the diet of meiofauna and to bulk and fine (<125 µm) sediment organic matter (SOM) was investigated in Papanui Inlet, southern New Zealand, using stable isotopes (δ 13 C and δ 15 N) and fatty acid analyses in the field and in a microcosm experiment. Seston did not contribute significantly to SOM of vegetated (seagrass Zostera muelleri) and unvegetated habitats, suggesting limited bentho-pelagic coupling. The contribution of different benthic primary producers to SOM and meiofaunal diet could not be determined accurately based on isotopic signatures alone due to over- lapping isotopic signatures. The high content of highly unsaturated fatty acids (HUFAs) of harpacti- coid copepods from vegetated and unvegetated sites suggested that their main food item was micro- phytobenthos (MPB), although bacterial biomarkers were twice as abundant in copepods sampled from the seagrass bed than in copepods sampled from unvegetated sediments. Isotopic and fatty acid analyses showed that the uptake of 13 C-labeled macroalgal (Enteromorpha sp.) detritus by harpacti- coid copepods in the microcosm experiment was minimal. Nematode diet could not be assessed with certainty, but seagrass detritus and MPB are likely to represent significant food sources at the vege- tated and unvegetated sites, respectively, based on the fatty-acid profile of fine SOM. This combined approach (i.e. isotopic and fatty acid analyses, field sampling and microcosms), and analysis of bulk SOM, fine SOM, and aged seagrass detritus helped circumvent limitations associated with the indi- vidual methods. The combination of approaches was still insufficient to quantify the contribution of different primary producers to meiofaunal diet, however, highlighting the difficulties associated with the study of meiofaunal trophic connections in coastal systems.

Comparison of two methods for estimating the abundance, diversity and habitat preference of fluvial macroinvertebrates in contrasting habitats

In this research we evaluate the effects of the method used for estimating the potential surface available for benthic macroinvertebrates in macrophyte and unvegetated habitats on several metrics and habitat preference of aquatic macroinvertebrates in the upper catchment of the Henares River (Guadalajara, Central Spain). Three sampling sites were selected: a well-preserved stream (site A), a stream with no wood riparian vegetation (site B), and a straightened and deforested reach (site C). Two habitats were selected in each site: unvegetated habitat (i.e., substrata without macrophytes) and macrophyte habitat (i.e., substrata covered by macrophytes). In each habitat, six macroinvertebrate samples (including all macrophytes or mineral particles) were collected using a Hess sampler. Diversity and density of major families were referred to the surface of the Hess sampler (=Hess surface method) and to the actual surface of either mineral particles or macrophytes (=actual surface method). In general, for the actual surface method, biomass, richness, dominance, and diversity metrics were higher in the mineral habitat than in the macrophyte habitat. This trend was different for the Hess surface method. In general, densities turned out to be higher in the unvegetated habitat than in the macrophyte habitat when using the actual surface method, but the reverse occurred when using the Hess surface method. This fact is relevant for river biomonitoring, especially when reaches with different dominant substrates (macrophytes vs mineral) are compared using just one of the methods. It is concluded that the macrobenthic metrics and density values are influenced by the method used to estimate the potential available surface for aquatic macroinvertebrates.

Population dynamics, life-history traits of and habitat use by two sympatric nothobranchiid fishes in a tropical stream, Kainji Lake Basin, Nigeria

Population dynamics and life-history traits of two sympatric nothobranchiid killifishes, Epiplatys bifasciatus and E. spilargyreius, were studied for 24 months in an intermittent stream in the Kainji Lake Basin, Nigeria. Epiplatys bifasciatus was more abundant throughout the study period, but monthly abundance of both species followed the same pattern. For both species, growth parameters and life-history strategies are characterised by small size, high growth rate, early maturity, high reproductive effort through daily spawning, short generation time, short life span and high mortality rate. Both species reproduce throughout the year, with peak periods of recruitment during the February to April and October to November periods. The population structures showed a preponderance of females over males, while males attained a larger total length than females. Three habitat types (vegetated pool, vegetated riffle, and marsh) were preferred by both species, whilst unvegetated habitats were avoided. Epiplatys spilargyreius was fairly specific in its habitat preference, with a significant positive correlation (r = 0.65, p < 0.05) to marshy habitat, whereas E. bifasciatus showed some habitat-use plasticity.

Habitat preference of three common fishes for seagrass, Caulerpa taxifolia, and unvegetated substrate in Moreton Bay, Australia

A decrease in seagrass cover and a commensurate increase in Caulerpa taxifolia distribution in Moreton Bay have prompted concern for the impact that habitat change may have on faunal communities. Therefore, it is important to understand the patterns of habitat use. We examined habitat selection of three common seagrass species: double-ended pipefish (Syngnathoides biaculeatus), eastern trumpeter (Pelates quadrilineatus), and fan-bellied leatherjacket (Monacanthus chinensis) using a mesocosm experiment. Fish were given three possible habitat pairings (1) seagrass and C. taxifolia, (2) seagrass and unvegetated, and (3) C. taxifolia and unvegetated. Observation trials were conducted during the day and night over two days. In all trials, fish preferred vegetated habitat (seagrass or C. taxifolia) over unvegetated habitat (sand). In seagrass and C. taxifolia trials, all species preferred seagrass significantly over C. taxifolia. Habitat use patterns did not differ between day and night trials. Caulerpa taxifolia provides a valuable structured habitat in the absence of seagrass; however, it is unclear if C. taxifolia meadows provide other resource benefits to fishes beyond that of shelter.

Influence of seagrass meadows on predator–prey habitat segregation in an Adriatic lagoon

Seagrass meadows have been hypothesized to protect mobile macrofauna from preda- tion by providing structural complexity that interferes with predator movement and vision. However, if ambush predators are common in seagrass, they may exclude many prey species, resulting in lower total abundance and diversity in seagrass relative to neighboring bare substrates, and segregation of predators and their prey into different habitats. We tested these abundance and diversity predictions using visual censuses of fish and invertebrates employing georeferenced videography to quantify habitat and pinpoint every observation, and using bait stations and drop nets over 38 km of scuba transects in all 4 seasons and by day and night in an enclosed estuary of the northeast Adriatic (Novi- grad Sea, Croatia). The primary fish predators at our study site were the ambush or stalk-attack predators, grass goby Zosterisessor ophiocephalus and European eel Anguilla anguilla, and we found that these species strongly preferred seagrass habitat. In contrast, most other fish, including small juveniles, avoided seagrass and preferred bare sediment to vegetated habitats. Species strongly pre- ferring seagrass were primarily sessile invertebrates not preyed on by the goby or eel. Both total macrofaunal density and total taxon richness were greatest on bare sediment and lowest in dense seagrass habitats. The 3-dimensional aspect of habitat structure was as important in delineating the communities as the presence or absence of habitat structure. These results are consistent with the hypothesis that ambush predators reduce the value of seagrass habitat for their prey relative to neighboring bare sediment or rock; that structured habitat might carry a higher mortality risk for many prey species, and that neighboring unvegetated habitat, including bare sediment, can be at least as important as seagrass in harboring biodiversity.