Abundance Of Epifauna Research Articles

Benthic macrofauna and megafauna assemblages in the Arctic deep-sea Canada Basin

Abstract The benthic component of an interdisciplinary expedition on icebreaker USCG HEALY analyzed box core samples and seafloor photographs to quantify deep-sea assemblages in the Canada Basin and Chukchi Borderland area. Soft bottom metazoan macrofauna (>250 μm) were collected with 33 box cores at 11 stations ranging from 817 to 3961 m water depth in the high-Arctic Canada Basin from 28 June to 25 July 2005. Megabenthic epifauna was quantified with a digital camera platform suspended −2 (89–2722 ind m −2 ) and total biomass ranged from 0.2 to 1.6 g wet weight 0.06 m −2 ( −2 ). Macrofauna diversity numbered between 8 and 55 taxa per station. Abundance, biomass, number of taxa, and diversity indices of macrofauna declined significantly with water depth. Polychaetes, crustaceans and bivalves dominated the macrofaunal densities, biomass and species numbers. The megafauna visible in the seabed photographs was assigned to a total of 67 provisional taxa; the lowest taxon count per station was 11, and the highest was 51 at the pockmark station. Epifauna abundance was also highest in this pockmark (mean 5.8 ind m −2 ) and generally lower at deepest stations (0.1–0.9 ind m −2 ), but was skewed by large numbers of the holothuroid Kolga hyalina . Epifauna observed in the center of the pockmark was significantly different from all other station groups, but did not include known chemosynthetic fauna or bacterial mats. Multivariate analysis indicated that station groupings “Chukchi slope”, “Canada Basin abyss” and the “Chukchi Cap” were significantly different in community composition in the macrofauna box corer samples, but could not be similarly distinguished as such in the epifauna photographs.

Trawl disturbance on benthic communities: chronic effects and experimental predictions

Bottom trawling has widespread impacts on benthic communities and habitats. While the direct impacts of trawl disturbances on benthic communities have been extensively studied, the consequences from long-term chronic disturbances are less well understood. The response of benthic macrofauna to chronic otter-trawl disturbance from a Nephrops norvegicus (Norway lobster) fishery was investigated along a gradient of fishing intensity over a muddy fishing ground in the northeastern Irish Sea. Chronic otter trawling had a significant, negative effect on benthic infauna abundance, biomass, and species richness. Benthic epifauna abundance and species richness also showed a significant, negative response, while no such effect was evident for epibenthic biomass. Furthermore, chronic trawl disturbance led to clear changes in community composition of benthic infauna and epifauna. The results presented indicate that otter-trawl impacts are cumulative and can lead to profound changes in benthic communities, which may have far-reaching implications for the integrity of marine food webs. Studies investigating the short-term effects of fishing manipulations previously concluded that otter trawling on muddy substrates had only modest effects on the benthic biota. Hence, the results presented by this study highlight that data from experimental studies can not be readily extrapolated to an ecosystem level and that subtle cumulative effects may only become apparent when fishing disturbances are examined over larger spatial and temporal scales. Furthermore, this study shows that data on chronic effects of bottom trawling on the benthos will be vital in informing the recently advocated move toward an ecosystem approach in fisheries management. As bottom-trawl fisheries are expanding into ever deeper muddy habitats, the results presented here are an important step toward understanding the global ecosystem effects of bottom trawling.

Mobile ‘reefs’ in the northeastern Gulf of California: aggregations of black murex snails Hexaplex nigritus as habitat for invertebrates

We documented positive interactions created by aggregations of black murex snail Hexaplex nigritus that support an epifaunal community annually. We examined abundance, species richness, and species composition of epifauna associated with aggregations, sampling snails from 12 aggregations and collecting epifauna from snails. We estimated 49 100 organisms (±7400) within a 25 m 2 area of an aggregation, many of which were juvenile invertebrates, and 193 species (95% CI 178-224) representing at least 7 trophic guilds. Epifauna occur on H. nigritus because shell structure provides benthic habitat heterogeneity, although biological characteristics of this foundation species may influence the associated composition of epifauna. To test this hypothesis, we anchored artificial reefs constructed of black murex shells and compared epifaunal communities that developed on them to those on aggregations. Abundance of epifauna was not different between aggregations and artificial reefs (p = 0.4); however, species composition was different (p = 0.005, R = 0.7). Epifaunal communities of aggregations had higher numbers of filter feeders and grazers than artificial reefs. Black murex snails illustrate that mobile benthic organisms can function as a foundation species and that biological characteristics of a foundation species may influence the associated composition of species. This system is ephemeral in nature, and epifauna that occur each spring and summer on snails may vary considerably. Loss of large H. nigritus aggregations has been documented due to overfishing, and declines in black murex populations result in the loss of a benthic substrate.

Species diversity in the soft-bottom intertidal zone: Biogenic structure, sediment, and macrofauna across mussel bed spatial scales

Mussels are important ecosystem engineers that have significant impacts on the ecology of the seafloor. In this study, we attempt to characterize and explain infaunal and epifaunal abundance patterns across scales in a spatially complex, intertidal, soft-bottom habitat: beds of the semi-infaunal mussel, Mytilus edulis. We used univariate and multivariate analyses in a nested sampling design at three locations in eastern Maine to show the relationships between environmental and macrofaunal assemblage variables. The results support the hypotheses that: 1) environmental and macrofaunal assemblage variables vary widely across spatial scales and exhibit maximum variance at different spatial scales; 2) abundance and diversity patterns of macrofauna are linked to spatial variation in environmental variables in the form of biogenic structure (live mussels and mussel shell hash), terrestrially-derived gravel, and, to a lesser degree, the proportion of silt-clay in the sediment; and 3) epifauna are generally positively correlated with hard-substrate features such as live mussels and gravel, and negatively correlated with the silt-clay content of the sediment, although the latter relationships were not strong. On the other hand, the results did not support the hypotheses that: 4) most infauna, specifically those with free-swimming larvae, are negatively correlated with live mussels and silt-clay proportion; instead, they were often positively correlated with live mussels and had weak, insignificant correlations with silt-clay; and 5) infauna without free-swimming larvae are positively correlated with live mussels and silt-clay proportion; instead, they showed some positive correlations with live mussels, but a mix of weak, insignificant correlations with silt-clay. Thus, mussel beds had a variety of scale-dependent relationships, both positive and negative, with each of the macrofaunal groups. The results show that biogenic structure in the form of live mussels and mussel shell hash is important in this system, as is terrestrial gravel, and that these variables are more important than silt-clay content for the macrofaunal assemblage. Mussel beds play an important role in regulating macrofaunal diversity in soft-bottom habitats, and their effects vary across spatial scales.

Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat

Beach-cast wrack is a prominent feature of beaches of south-western Australia. We examined the fauna of these beaches to explore the generalisation [Polis, G.A., Hurd, S.D., 1995. Extraordinarily high spider densities on islands: flow of energy from the marine to terrestrial food webs and the absence of predation. Ecology 92, 4382–4386] that beach-cast wrack from highly productive marine ecosystems subsidises low productivity of terrestrial ecosystems, to establish whether this generalisation is relevant to oligotrophic marine systems. We sampled three beaches with high and three beaches with low volumes of beach-cast wrack to determine if: (1) the presence of wrack influences the abundance of macroinvertebrates; (2) wrack acts as a food source for beach macroinvertebrates; and (3) the influence of wrack varies between zones above the high water mark. We measured wrack volume and composition, sediment characteristics, the abundance of different epibenthic and infaunal macroinvertebrates taxa, and δ 13C and δ 15N of macrophytes and macroinvertebrates. The mean volume of wrack on high-wrack beaches was 0.27–1.07 m 3 wrack m −2 compared to 0.00–0.09 m 3 wrack m −2 on low-wrack beaches. There were no significant differences in sediment grain size, moisture content or loss on ignition between the two types of beaches or zones. Epibenthic fauna and infauna were consistently abundant on high-wrack beaches (20–291 and 0.5–3.5 individuals 0.64 m −2, respectively), but either absent or extremely rare in low-wrack beaches (0–3 and 0–0.1 individuals 0.64 m −2, respectively). Within high-wrack beaches, there were no significant differences in the abundance of epifauna or infauna among beaches or between zones. The δ 13C values of macroinvertebrates at all sites were most similar to red and brown algae, with the exception of beetles from two beaches, which were closest to seagrasses. Mixing model (Isosource) results for mesograzing amphipods and dipteran flies suggested carbon was assimilated mostly from the seagrass Posidonia spp., the dune grass Spinifex longifolia and red algae for amphipods and from brown algae, red algae and dune vegetation for dipteran flies. We conclude that the presence of marine-derived wrack plays a major role in subsidising production of macroinvertebrates on beaches of south-western Australia. We suggest that marine subsidies can play a role in supporting terrestrial production, even in oligotrophic marine environments.

Lack of epifaunal response to the application of salt for managing the noxious green alga Caulerpa taxifolia in a coastal lake

Since the discovery of the green alga Caulerpa taxifolia in Lake Macquarie (New South Wales, Australia) in 2001, the New South Wales Department of Primary Industries (Fisheries) has attempted various control methods, including covering the alga with granulated sea salt to induce osmotic shock and cell lysis. In Lake Macquarie, C. taxifolia often occurs in patches within beds of the native seagrass Zostera capricorni. Although the effects of the salt treatment on blades of Z. capricorni and infauna have been shown to be minimal, there have been no tests of any effects on other native biota, including seagrass epifauna. In this study, we tested the general hypothesis that the abundance and diversity of epifauna would be reduced by salting. We used a ‘Beyond BACI’ experimental design whereby epifaunal invertebrates were sampled 3 months, 6 weeks and 6 days before and then again after salting. Epifaunal abundances at the putatively impacted (salted) location were compared to those at 4 control locations (where no salt was applied). Abundances of most organisms varied significantly among times and locations with no evidence of the consistent effect of salting on diversity or abundance of epifauna. The study represents an example of the use of large-scale managerial action as a scientific experiment.

Seagrass habitat disturbance: how loss and fragmentation of eelgrass Zostera marina influences epifaunal abundance and diversity

Seagrass habitats commonly display evidence of anthropogenic disturbances such as propeller scars, mooring and anchor damage, trampling, and plant harvesting. These physical distur- bances may lead to habitat loss and fragmentation, yet effects of this habitat removal on seagrass epi- faunal communities are not well understood. We investigated how the degree of eelgrass Zostera marina L. loss influenced the abundance, diversity, and community composition of epifauna within experimental seagrass plots in San Diego Bay, California, USA. We established replicate small (4 m 2 ) and large (16 m 2 ) plots within existing eelgrass habitat, and removed all aboveground and below- ground plant material within randomly chosen cells to establish 4 to 6 levels of eelgrass clearing. We then sampled for epifauna up to 8 wk after eelgrass harvesting. We found no correlations between seagrass loss and epifaunal species richness, total epifaunal density or epifaunal diversity in small plots. In large plots, however, plots with 90% habitat removal had significantly lower epifaunal spe- cies richness and total epifaunal density than plots with 0, 10 or 50% habitat removal, suggesting that beyond a threshold level of eelgrass disturbance, species richness and abundance rapidly decline. Multivariate ordinations revealed that the 90% removal plots also had significantly different species composition than plots with less habitat loss. Our results support previous theoretical models predict- ing threshold levels of habitat loss for faunal communities and broaden our understanding of the response of marine epifauna to seagrass habitat degradation.

Interactions between the grass shrimp Palaemonetes pugio and the salt marsh grasses Phragmites australis and Spartina alterniflora

The grass shrimp Palaemonetes pugio, a species common to Spartina alterniflora-dominated marshes, may be sensitive to the invasion of the common reed Phragmites australis in northeastern US salt marshes. We examined two questions: (1) Do grass shrimp have a preference for the native plant over the non-native plant? (2) Are grass shrimp more effective foragers on P. australis? We tested the first hypothesis by comparing the amount of time shrimp spend in physical contact with the plant types over a 1-h period. Shrimp were observed under different arrangements of vegetation to control for differences in conspicuous structural features. Additionally, the amount of time shrimp spent foraging on S. alterniflora and P. australis shoots was compared to determine if shrimp graze more often on S. alterniflora. Shrimp spent significantly more time in contact with S. alterniflora only when plant types were grouped at opposite ends of aquaria, but did not exhibit a foraging preference for this plant type. To address our second question, we investigated the effects of shrimp foraging on stem epifauna, an assemblage of semi-aquatic invertebrates associated with macrophyte shoots. Previous research showed that P. australis supports a lower density of stem-dwelling epifauna relative to S. alterniflora. We hypothesized that the primary grazer of this community, P. pugio, can forage on P. australis stems more effectively due to structural differences between the two plants, causing the lower abundance of epifauna through top-down effects. We exposed individual shoots inhabited by epifauna to shrimp and compared faunal densities on exposed shoots to densities on control shoots after 18 h. The reduction of epifauna by predation was proportional on the two plant types. Therefore, top-down effects can be ruled out as an explanation for the patchy distribution of epifauna observed in P. australis–S. alterniflora marshes.

Estimating the catching efficiency of a 2-m beam trawl for sampling epifauna by removal experiments

Abstract The catching efficiency of a standard 2-m beam trawl for sampling epifauna was estimated by removal experiments at two sites in the southern North Sea. In order to allow repeated sampling of the same area, a rig of three beam trawls one behind the other was constructed, the three being tied together by steel ropes. Catching efficiency was estimated on the basis of the sum of the catches of all three trawls relative to the numbers caught in the first trawl. The catching efficiency of the beam trawl for epifauna ranged from 36% to 44% of total abundance between sites. Efficiency was least for partly buried species (Liocarcinus holsatus, 9% and 18%; Buglossidum luteum, 27%; Arnoglossus laterna, 35%), and slightly better for species living on the surface of the sediment (Asterias rubens, 42% and 46%; Pomatoschistus minutus, 58% and 46%; Pagurus bernhardus, 51%). The abundance of epifauna will be underestimated by a factor of 1.4–11 relative to the abundance in the three trawls. Also, sediment type seems to influence the catching efficiency of the beam trawl, efficiency being less at the sandy study site than at the muddy site for most species.

Depth-related structure and ecological significance of cold-seep communities—a case study from the Sea of Okhotsk

We discovered and investigated several cold-seep sites in four depth zones of the Sea of Okhotsk off Northeast Sakhalin: outer shelf (160–250 m), upper slope (250–450 m), intermediate slope (450–800 m), and Derugin Basin (1450–1600 m). Active seepage of free methane or methane-rich fluids was detected in each zone. However, seabed photography and sampling revealed that the number of chemoautotrophic species decreases dramatically with decreasing water depth. At greatest depths in the Derugin Basin, the seeps were inhabited by bacterial mats and bivalves of the families Vesicomyidae ( Calyptogena aff. pacifica, C. rectimargo, Archivesica sp.), Solemyidae ( Acharax sp.) and Thyasiridae ( Conchocele bisecta). In addition, pogonophoran tubeworms of the family Sclerolinidae were found in barite edifices. At the shallowest sites, on the shelf at 160 m, the seeps lack chemoautotrophic macrofauna; their locations were indicated only by the patchy occurrence of bacterial mats. Typical seep-endemic metazoans with chemosynthetic symbionts were confined to seep sites at depths below 370 m. A comparative analysis of the structure of seep and background communities suggests that differences in predation pressure may be an important determinant of this pattern. The abundance of predators such as carnivorous brachyurans and asteroids, which can invade seeps from adjacent habitats and efficiently prey on sessile seep bivalves, decreased very pronouncedly with depth. We conclude from the obvious correlation with the conspicuous pattern in the distribution of seep assemblages that, on the shelf and at the upper slope, predator pressure may be high enough to effectively impede any successful settlement of viable populations of seep-endemic metazoans. However, there was also evidence that other depth-related factors, such as bottom-water current, sedimentary regimes, oxygen concentrations and the supply of suitable settling substrates, may additionally regulate the distribution of seep fauna in the area. As a consequence of the pronounced pattern in the distribution of seep communities, their ecological significance as food sources of surrounding background fauna increased with water depth. Isotopic analyses suggest that in the Derugin Basin seep colonists feed on chemoautotrophic seep organisms, either directly or by preying on metazoans with chemosynthetic symbionts. In contrast, seep organisms apparently do not contribute to the nutrition of the adjacent background fauna on the shelf and at the slope. In this area, elevated epifaunal abundances at seep sites were caused primarily by the availability of suitable settling substrates rather than by an enrichment of food supply.

Effects of haying on salt-marsh surface invertebrates.

Marsh plants may affect the structure of epibenthic communities in a variety of ways. They might reduce temperature stress on organisms by shading, provide refuge from predators, increase the rate of organic matter accumulation at the sediment surface, and serve as a food source. Thus, salt marsh plants might control the spatial distributions of epibenthic invertebrates within the marsh. An ongoing “experiment” on the impact of the periodic removal of plants has been carried out by New England farmers who have been haying some salt marshes for over 300 years. Earlier research by the Plum Island Estuary Long-Term Ecological Research project (PIE-LTER) has shown that haying causes a short-term increase in the growth of benthic algae (1), causes a shift in the diet of some marsh invertebrates to a greater percentage of algae (2), and results in a change in plant species composition (PIE-LTER, unpubl. results). To determine the shortand long-term effects of haying on the epibenthic community and to identify the principal variables controlling the distribution of epibenthic invertebrates, we carried out two sets of experiments: a marsh-grass-removal experiment to mimic the effects of haying and a survey of invertebrates in areas of the marsh subjected to different haying schedules. Our work was conducted in the Plum Island Sound estuary in Rowley, Massachusetts, from June to August 2002. For our marsh-grass-removal experiment, we clipped and removed the vegetation from three randomly selected circular sites of 3-m radius along a 50-m transect in a marsh that is hayed roughly every other year. Before clipping we counted organisms in four 0.25-m sampling areas, located 1.5 m from the center of the circle and equidistant from each other, within each of the three sites. We sampled the same four areas within each site immediately before clipping, and 1 and 4 days after clipping. Differences in abundances of organisms before and after clipping were evaluated by the Kruskal-Wallis test with time of sampling as treatment. Because differences among circular hayed sites were not significantly different, we pooled replicates from each site before our analysis. For our surveys of invertebrates in areas subjected to different intensities of haying, we examined randomly selected sites in recently hayed and reference marshes along 12 previously established transects for which GPS elevation data were available. We sampled 40 sites between 1 and 3 July, and 40 more between 16 and 18 July. At each site, we visually estimated percent cover of different plant species. A count of organisms was made after clipping all vegetation from 0.25-m plots. A 177-cm plant sample was collected, live biomass was separated from standing dead biomass and weighed separately to determine above-ground biomass. Commonly encountered plants included Spartina patens, Spartina alterniflora, Distichlis spicata, Salicornia europaea, and Juncus gerardi. To evaluate the effect of plant cover on predation rate, we tethered amphipods, Orchestia grillus, to thin-diameter line and deployed 5 per site at most sites for 24 h before clipping. We used stepwise multiple regression to describe the relationship between measured environmental variables and abundance of epifauna for the 16–18 July sampling period (criteria P 0.1 to accept, P 0.25 to reject). Environmental variables used in stepwise multiple regression were haying frequency, elevation, temperature, humidity, dried live plant biomass, dried standing dead, total dried weight, percent live, percent dead, percent bare, percent S. alterniflora, percent S. patens, percent D. spicata, percent S. europaea, percent Atriplex patula, percent Triglochin maritima, percent Iva frutescens, proportion tethered live amphipods, and proportion eaten tethered amphipods. Collinearity among environmental variables was assessed by examining the variance inflation factor for each included variable. All variance inflation factors were less than 2, which indicated that collinearity among independent variables did not significantly affect our results. A few sampling sites were omitted from the regression analysis due to missing data. Analyses were performed using SPSS software.

Plant species diversity and composition: experimental effects on marine epifaunal 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 224:55-67 (2001) - doi:10.3354/meps224055 Plant species diversity and composition: experimental effects on marine epifaunal assemblages John D. Parker*, J. Emmett Duffy, Robert J. Orth College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, PO Box 1346, Gloucester Point, Virginia 23062, USA *Present address: Georgia Institute of Technology, School of Biology, Atlanta, Georgia 30332, USA. E-mail: gte782w@prism.gatech.edu ABSTRACT: Plant diversity is believed to govern animal community structure, yet few studies have tested this relationship. We manipulated plant species diversity and composition (2 seagrasses and 3 seaweeds) and measured the abundance, diversity, and biomass of plant-associated macroinvertebrates in a temperate, estuarine seagrass community. Animal diversity was weakly but positively related to plant diversity (Simpson¹s 1 - λ). Most indices of animal diversity, however, were more strongly related to total plant surface area than to plant diversity. Epifaunal abundance and biomass increased, whereas epifaunal diversity and evenness decreased with total plant surface area. Both food and habitat covary with plant surface area, providing potential mechanistic explanations for these patterns. Plant species composition had strong effects on epifaunal community structure. After statistically controlling for effects of plant surface area, epifaunal abundance and biomass remained higher, and evenness remained lower, among assemblages composed of branched (mostly seaweeds) relative to unbranched (mostly seagrasses) macrophytes. Multiple regression analyses also revealed differential use of particular plant species by epifauna. For example, amphipods responded particularly strongly to the coarsely branched red alga Gracilaria verrucosa. Thus, our experimental results support a strong effect of plant species composition, and little effect of plant diversity per se, on the motile macrofauna that we studied. This conclusion is consistent with results of a concurrent field survey; epifaunal community structure differed among plant species and seasons, with no host-plant specialists. These results support evidence from both terrestrial and aquatic communities; ecosystem structural and functional properties are often more strongly influenced by particular attributes, rather than number of species, in a community. KEY WORDS: Biodiversity · Community structure · Epifauna · Macroalgae · Zostera marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 224. Online publication date: December 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Daily vertical migrations in the epifauna associated with Posidonia oceanica meadows

To estimate the importance of the vertical daily migrations in the structure of the community of the epifauna associated with the leaf stratum of Posidonia oceanica, we compared to the vagil epifauna abundance in respect to the period of the day and the height of the sediment. The study was developed in the P. oceanica meadow of El Campello (Alicante, south-east Spain), during May of 1996, to a depth of 12 m, repeating the samplings in four sites to obtain a correct spatial interpretation. Three main behaviours were detected. Decapods, amphipods, isopods, mysids, ostracods and polychaetes showed a nocturnal increase in the leaf stratum of P. oceanica. By contrast, copepods showed a nocturnal decrease in the leaves and gastropods did not show any temporal change. Chaetognaths and acari did not show statistical differences because of the considerable spatial heterogeneity. These vertical migrations have an extreme importance in the configuration of the structure of the epifauna associated to P. oceanica, in addition to the diverse response of the different taxa.

Spatial and diurnal distribution of invertebrate and fish fauna of a Zostera marina bed and nearby unvegetated sediments in Damariscotta River, Maine (USA)

Fish, epibenthos and macroinfauna were collected in a Zostera marina bed and nearby unvegetated sediments in the estuary of the Damariscotta River, on the mid-coast of Maine. Samples of epibenthic fauna and fish were collected at low tides both during day and night, and samples of infauna at low tides during the day. The mean density of Zostera shoots in the study area was 335 m −2. Abundance and species number of fish were greater at night than during the day and greater in eelgrass beds ( Z. marina) than in unvegetated habitats. Daytime fish collections were dominated by Atlantic silversides ( Medinia medinia), while juvenile winter flounder ( Pseudopleuronectes americanus) dominated night collections. Also Zostera-associated epifaunal abundances and number of species were significantly higher at night than during the day. Mysis stenolepis, Idotea balthica and Littorina obtusata were dominant species in the epifauna samples. Of the total of 37 invertebrate species encountered, only five occurred both in the infaunal and epifaunal samples. Nineteen different taxa were collected from the benthic core samples. The most abundant invertebrate infaunal taxa were sipunculids, the polychaete Nereis virens, and oligochaetes. Infaunal invertebrate abundances and species diversity were significantly higher in eelgrass beds than in unvegetated sediments. The abundance and number of species of benthic invertebrates were also positively correlated to seagrass biomass. Community diversity values ( H′) were relatively low but fit well in the general pattern of decreasing diversity towards northern latitudes.

Abundance of fish and crustacean postlarvae on portable artificial seagrass units: daily sampling provides quantitative estimates of the settlement of new recruits

Artificial collectors and seagrass units have mainly provided qualitative samples of epifaunal abundance or have been difficult and time-consuming to sample. Consequently, they are useful for distinguishing temporal or spatial trends in abundance or they are deployed for several weeks and, as a result, the quantitative samples are cumulative. We developed a portable artificial seagrass unit (ASU) with buoyant plastic artificial seagrass (47 cm long by 15 mm wide strips) that can be retrieved, harvested and re-deployed with 98% catch efficiency in about 5 min by two people from a small boat. They can quickly and easily quantify settlement of crustacean and fish postlarvae over tidal or deil periods. When set for 24 h, postlarvae settled from the plankton during the night and their abundance is the result of a distinct settlement event. When set for longer periods, the numbers of postlarvae may represent several settlement events and post-settlement activities. Crustacean and fish postlarvae and juveniles used ASUs deployed within seagrass in a similar way to natural seagrass. Estimates of juvenile tiger prawn abundance from beam-trawl catches showed similar densities in natural seagrass (2.93 Penaeus semisulcatus de Haan m −2 day) to those in the ASUs (2.40 P. semisulcatus m −2 day −1); their density was significantly lower on bare trays (0.48 P. semisulcatus m −2 day −1). When deployed on bare areas, more epifaunal crustacean postlarvae were collected from the ASUs (e.g. Portunus pelagicus Linnaeus, 1.21 m −2 day −1; caridean shrimp 4.03 m −2 day −1) than from the bare trays (e.g. P. pelagicus, 0.46 m −2 day −1; caridean shrimp 0.78 m −2 day −1). However, greater abundances of the postlarvae of other crustacean taxa were collected from the bare trays than the ASUs (e.g. Sergestes spp. 1.21 and 0.31 m −2 day −1; tiger prawn postlarvae 0.15 and 0.06 m −2 day −1, respectively). Sampling with portable ASUs allows settlement to be assessed temporally (e.g., daily or tidally) or spatially (e.g., distinct areas affected by different current regimes). The strength of settlement can be used to evaluate the productivity of nursery habitat for fishery populations.

The role of fishes in the organization of a Mediterranean sublittoral community: II: Epifaunal communities

Variations in the abundance of epifauna living in sublittoral algal communities were quantified monthly in the Medes Islands Protected Area (Spain, NW Mediterranean) over a year. The relationship between epifaunal biomass and the biomass of algal types was examined. The study was carried out at three sites with marked differences in the abundance of predatory fishes. Changes in epifaunal abundance were linked to changes in the annual standing crop of fleshy erect algae, which exhibited pronounced seasonal variation. However, there were few significant differences in epifaunal abundance levels between sites and, when present, only for short periods. Experimental manipulations of predation intensity (exclusion cages) were employed to examine the effect of fishes on epifaunal abundance. Experimental treatments altered epifaunal abundance: although in some cases epifauna decreased within exclusion cages relative to unmanipulated controls, most epifaunal groups responded to caging by increased abundance. These contradictory results do not allow determination of the role of predation by fishes in regulating the abundance of the epifauna, but they suggest that untested complex interactions (mainly related to algae structure and dynamics) may be responsible for these patterns.

Epifauna living on sublittoral seaweeds around Cyprus

Macroepifauna living on sublittoral seaweeds were counted,identified and compared among six locations in Cyprus. Mollusks,amphipods, and polychaetes were the major taxa represented. Thedominant alga was Cystoseira barbata which was present at 4of 6 stations and ranged in wet weight from 1–2 kg m-2 ofbottom. Percent cover of C. barbata ranged from 25 to 90%.Other dominant algae were Laurencia obtusa, Padinapavonica, and Jania rubens. The distribution of epifaunaabundance, species composition, and species richness varied amonglocations. Total epifauna abundance ranged from 1000 to 2250animals m-2. The abundance of epifauna per gram of plant wassignificantly lower on C. barbata than on the other algalspecies. The total epifauna species richness was more related tolocal algal plant diversity than to plant biomass.

Mixed fractals and anisotropy in subantarctic marine macroalgae from South Georgia:implications for epifaunal biomass and abundance

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 136:245-255 (1996) - doi:10.3354/meps136245 Mixed fractals and anisotropy in subantarctic marine macroalgae from South Georgia: implications for epifaunal biomass and abundance Davenport J, Pugh PJA, McKechnie J Fractal dimensions (D) of image perimeters of 4 macroalgae (Macrocystis pyrifera, Desmarestia menziesii, Schizoseris condensata, Palmaria georgica) collected at South Georgia, Southern Ocean were established over a wide scale range. For 3 species (M. pyrifera, S. condensata, P. georgica)cross-frond D was also estimated. At large scale all species showed complex perimeters (D 1.26 to 1.83, depending on species), but showed reduced complexity (low D) at small scale, and so have mixed fractal characteristics. Cross-frond D was low in the 3 species studied, indicating anisotropy, and was markedly low in P. georgica which has extensive, smooth, flat fronds. Epifaunal community analysis demonstrated that epifaunal abundance and biomass were related more to the scale at which complexity occurs than degree of complexity itself. S.condensata and D. menziesii (particularly complex, high D) show high epifaunal abundance and biomass and a predominance of large animals; M. pyrifera and P. georgica (simpler, lower D) have low abundances and biomasses and the epifauna is dominated by small animals. M. pyrifera is fairly complex (D ca 1.3) at scales above 50 mm; its complexity will impinge on fish, birds and mammals, not epifauna. M. pyrifera beds have a perimeter D (ca 1.4) similar to those of convoluted coastlines. Mixed fractals . Anisotropy . Macroalgae . Epifauna Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 136. Publication date: June 06, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Weight of the Evidence is the Right Approach

Sampling and field experiments were conducted from 1975 to 1990 to test how the structure of marine benthic communities around McMurdo Station, Antarctica varied with levels of anthropogenic contaminants in marine sediments. The structure of communities (e.g., infauna density, species composition, and life history characteristics) in contaminated and uncontaminated areas were compared with the structure of communities influenced by two large‐scale natural disturbances, anchor ice formation and uplift or iceberg scour. Benthic communities changed radically along a steep spatial gradient of anthropogenic hydrocarbon, metal, and PCB contamination around McMurdo Station. The heavily contaminated end of the gradient, Winter Quarters Bay, was low in infaunal and epifaunal abundance and was dominated by a few opportunistic species of polychaete worms, especially Capitella spp., Ophryotrocha claperedii, and Gyptis sp. These are relatively small and motile species. Closely related species live in organically enriched and anthropogenically disturbed sediments throughout temperate latitudes. The edge of the heavily contaminated bay, the transition area, contained several motile polychaete species with less opportunistic life histories, especially Tharyx sp. and Haploscoloplos kerguelensis. Uncontaminated sedimentary habitats harbored dense tube mats of infaunal animals numerically dominated by populations of polychaete worms, crustaceans, and a large suspension feeding bivalve. These species are generally large and relatively sessile, except for several crustacean species living among the tubes. Community patterns along the anthropogenic disturbance gradient were similar to community changes along a natural gradient of anchor ice disturbance. The same motile and opportunistic polychaete worms were most abundant where anchor ice freezing and uplift were most severe. The motile polychaetes, Tharyx sp., Haploscoloplos kerguelensis, and Polygordius sp., were abundant at the edge of the anchor ice disturbance zone. The undisturbed bottom harbored the same dense tube mat community and large bivalve population. Community changes along the anthropogenic disturbance gradient were also similar to colonization patterns into bottom areas gouged by icebergs. The most recent ice gouges along the east side of McMurdo Sound contained large numbers of the motile opportunistic polychaete worms. Ice gouges along the western sound contained more motile species of infauna compared to adjacent undisturbed bottoms with large numbers of tube‐dwelling infauna. Motile species were also the first to colonize experimental sediments placed on the sea floor for 6 yr. Although the community patterns around anthropogenic and natural disturbances were similar, particularly the motile and opportunistic species at heavily disturbed and marginal areas, the natural disturbances cover much greater areas of the sea floor around the entire Antarctic continent. On the other hand, recovery from chemical contamination is likely to take many more decades than recovery from natural disturbances as contaminant degradation is a slow process. This process can be enhanced by ongoing pollution abatement and cleanup operations.

Macrozoobentos da praia do Codó (Ubatuba, SP) e a presença de Halodule wrightii Ascherson

A year's survey conducted at a seagrass (Halodule wrightii Ascherson) bed and an adjacent bare sand area, on Codo Beach, Ubatuba, southern Brazil, showed that the macrobenthic species composition was different at the two habitats. Surface deposit feeder infaunal polychaetes were the dominant species in the Halodule site and omnivorous/carnivorous and filter feeder polychaetes, in the bare sand. These differences could be explained mainly by the characteristics of the sediment and the stability of the bottom and, secondly, by the presence of Halodule. The presence of vegetation has no effect on density of macrobenthos, probably due to the small size of Halodule plants, which do not support an abundant epifauna. Despite that fact, both number and diversity of species were higher in the seagrass area than in the unvegetated site, as was epifaunal abundance. Significant patterns of temporal fluctuations of macrobenthos abundance and species diversity were not observed, but diversity was the highest in Spring at both habitats. The temporal fluctuations of abundance differed in the two habitats. At the unvegetated site instability of the substrate seems to be responsible for the observed fluctuations in densities. At the Halodule site only light fluctuations occurred, though they did not follow those of macrophyte biomass. Macropredator effects are suggested to be one of the controling factors of macrobenthos density at the vegetated habitat.