Soft-bottom Systems Research Articles

The seafloor from a trait perspective. A comprehensive life history dataset of soft sediment macrozoobenthos

Biological trait analysis (BTA) is a valuable tool for evaluating changes in community diversity and its link to ecosystem processes as well as environmental and anthropogenic perturbations. Trait-based analytical techniques like BTA rely on standardised datasets of species traits. However, there are currently only a limited number of datasets available for marine macrobenthos that contain trait data across multiple taxonomic groups. Here, we present an open-access dataset of 16 traits for 235 macrozoobenthic species recorded throughout multiple sampling campaigns of the Dutch Wadden Sea; a dynamic soft bottom system where humans have long played a substantial role in shaping the coastal environment. The trait categories included in this dataset cover a variety of life history strategies that are tightly linked to ecosystem functioning and the resilience of communities to (anthropogenic) perturbations and can advance our understanding of environmental changes and human impacts on the functioning of soft bottom systems.

Structure of the Community of Dominant Fish Species Associated to Soft-Bottoms in the Lagoon of La Paz, B.C.S., México

The study of fish communities from coastal lagoons allows a better understanding of role of these organisms in these systems, and the effect of anthropogenic impact. The aim of the present study was to determine the community structure, in particular dominance of fish species associated to soft bottoms in the lagoon of La Paz. Six bimonthly samplings were carried out in seven localities from November 2016 to September 2017 and physicochemical parameters were recorded. Analysis of temperature showed differences between two marked seasons, warm and cold. Species richness showed differences between months and localities. Shannon-Weaver index and Pielou’s evenness showed significant differences only between months. Simpson’s index suggests a high diversity. According to the BVI, 15 species from the families Haemulidae, Sciaenidae and Gerreidae, were the most biologically important. Zoogeographic affinity analysis showed that 58% of the species prefer the Province of Cortez. Dominant species recorded in this study play a key role in soft-bottom systems like the lagoon of La Paz.

What happens after mussels die? Biogenic legacy effects on community structure and ecosystem processes

Mussels are well-known ecosystem engineers in soft-bottom systems. Mytilus edulis beds have myriad effects on sediment, benthic organisms, and ecosystem processes such as hydrodynamic transport of sediment and animals. When mussels die, they may leave behind massive amounts of whole (empty) and fragmented shells. The legacy effects of this long-lasting biogenic material (i.e., shell hash) on benthic systems are poorly understood. We measured percent cover values of 4 bottom cover types, i.e., live mussels, whole shells, fragmented shells, and bare sediment, at the mussel bed in Carrying Place Cove, Harrington, Maine, USA, and examined their effects on sediment characteristics, community structure of macrofauna and meiofauna, and ecosystem processes of sediment flux and dispersal of postlarval macrofauna and meiofauna. We predicted that live mussels are the cover type with the greatest effects compared to bare sediment, followed by fragmented shells and then whole shells. We discovered mostly bare sediment, substantial cover of whole and fragmented shells, and almost no live mussels in what had in past years been a robust bed. We found significant univariate and multivariate differences in sediment and animals across cover types, especially for meiofauna. Fragmented shell material in particular may be an important driver in this system. Our results are the first to quantify the 4 mussel bed cover types and demonstrate their effects. Mussel beds in the Gulf of Maine have experienced severe declines in the past two decades, attributed primarily to climate change and the invasive green crab, Carcinus maenas. Our results may be useful in predicting the responses of soft-bottom systems as intact mussel beds die off, leaving large areas of bare sediment and shell hash.

An ecological quality status assessment procedure for soft-sediment benthic habitats: Weighing alternative approaches

An assessment procedure for determining the ecological quality status of soft-sediment benthic habitats requires the following aspects: (1) habitat assignation of the samples (habitat approach), (2) reference or target conditions for the benthic parameters (reference approach), and (3) the selection of indicator tools to assess the relative quality status (indicator approach). For all these aspects, different approaches exist, and the indicator selection and reference approaches are largely documented. The aspect of the habitat approach is sometimes neglected, but is essential in determining the reference conditions per habitat type. Benthic habitats differ in structure and function, and as such will show wide variations in statistics or measures between habitats. A major problem, mainly in coastal soft-bottom systems, is to track the deviation lines within data of the different benthic habitat types. This study shows that both a classical community analysis and the use of habitat suitability maps seem to be appropriate tools, but further fine-tuning is necessary. For the second assessment step, an objective assessment of reference conditions is a challenge in areas lacking pristine or minimally disturbed sites, and areas of which historic data are not available. This can be remedied by using a dataset of the area with a good spatial and temporal coverage of the benthic data, thereby avoiding data originating from highly impacted areas. For the third aspect in the assessment procedure, we recommend the use of different indicators with different properties (parameters, algorithms) since it indicates their weaknesses and strengths in the local region.In general, this study showed us that it is valuable to test different existing approaches for EcoQ assessment in a local area, revealing strengths, weaknesses and shortcomings within the assessment regarding data, habitat identification, monitoring strategy, reference settings and indicator use. All these aspects need to be taken into account within an ecological quality status assessment of an area in order to improve its confidence.

Tube-forming polychaetes enhance invertebrate diversity and abundance in sandy sediments of Mozambique, Africa

In marine soft-bottom systems, polychaetes can increase habitat complexity by constructing rigid tubes (e.g. several onuphid species) that contrast with surrounding topographically flat sediments. These structures can provide predation refuges and increase larval settlement and thereby increase the richness and abundance of fauna. We collected invertebrate samples from an intertidal flat with low onuphid tube density (2.7 m–2) in Mozambique and document that more organisms (70 times higher mollusc abundances) and more species (15 times more mollusc species) were found associated with solitary tubes of an onuphid polychaete compared with surrounding sand habitats. These results are in agreement with tube versus sand comparisons from soft-bottom systems in the North Atlantic where polychaete tube densities are often much higher.

Broad-scale patterns of abundance of non-indigenous soft-bottom invertebrates in Denmark

Quantifying the broad-scale distribution and abundance of non-indigenous species (NIS) is necessary to provide accurate estimations on impacts of invasions, to prioritize research, and to guide national management. Sediment grab-sampling is a standardized method for monitoring marine benthos. In Denmark, ~45,000 grab-samples were collected from 1970 to 2005. Using these samples, we compared densities of NIS and native species among 27 broad spatio-temporal groupings. Eight known NIS and one ‘cryptogenic species’ (the polychaete Neanthes succinea) were found in the samples. Most were present in low abundance, but the bivalve Mya arenaria, likely introduced by the vikings from North America, was particularly abundant. M. arenaria was found in ca. 20% of all samples and was among the 10 most common species in all of Denmark. M. arenaria’s high abundance, high filtration capacity and importance in food-web interactions, suggest that this species has dramatically impacted shallow coastal ecosystems in Denmark. The polychaete Marenzelleria viridis, the gastropod Potamopyrgus antipodarum and N. succinea were also widespread and abundant, and they too are likely to have had broad-scale impacts. In conclusion, 28% of grab-samples collected in Denmark over 35 years were affected by some degree of NIS or cryptogenic species, suggesting that centuries of human-mediated transfer of organisms has had a profound impact on the ecology of soft-bottom systems in Denmark.

Predation in subtropical soft-bottom systems: spiny lobster and molluscs in Florida Bay

Predation in subtropical soft-bottom systems: spiny lobster and molluscs in Florida Bay

Fractal characterization of Mytilus edulis L. spatial structure in intertidal landscapes using GIS methods

The blue mussel, Mytilus edulis L., forms dense and variable patch mosaics composed of aggregates of mussel individuals. Knowledge of mussel bed spatial pattern at multiple scales is important for understanding the form and function of intertidal systems where mussels are prominent features. This study extends prior work demonstrating fractal patterns of mussel boundaries in soft-bottom systems at the quadrat-scale by investigating fractal structure using GIS methods at both the quadrat- and bed-scales. The study pursues three goals for mussel beds in eastern Maine: (1) to compare quadrat-scale fractal dimensions obtained using manual methods with those obtained using digital imagery and techniques, (2) to determine if fractal patterns identified at the quadrat-scale are also present at the bed-scale, (3) and to evaluate the effectiveness of aerial photography and image analysis techniques. Photographs of randomly located quadrats (2500 cm2 each) were scan digitized and classified into mussel presence/absence classes. Fractal dimensions of mussel/non-mussel boundaries were calculated using the box-counting method and compared with results obtained using analog photographs and methods. Digital aerial photographs at low tide were acquired for beds at two sites and classified using image processing techniques, and bed-scale fractal dimensions were calculated. At the quadrat-scale, fractal dimensions and their relationship with percent cover differed consistently in absolute value from results using manual methods but agreed in demonstrating fractal patterns for all quadrats and a parabolic trend with percent cover very similar to the one revealed manually. At the bed-scale, both sites were shown to be fractal, with higher dimension value for the bed that subjectively appeared more fragmented and highly dissected. Because mussels are important soft-bottom ecosystem engineers, i.e., foundation species that regulate species composition and abundances, the fractal spatial distribution identified in this study suggests that the species affected by them also exhibit fractal patterns. These results indicate the effectiveness of archive imagery and GIS methods for characterizing intertidal systems and point to the feasibility of future image acquisition.

Effects of point-source nutrient addition and mussel removal on epibiotic assemblages in Perumytilus purpuratus beds

The objective of this study was to evaluate the effects of point-source nutrient addition and mussel removal on species diversity of the epibenthic assemblage of the purple mussel Perumytilus purpuratus. It was hypothesised that mussels cushion the effects of disturbance on the associated organisms and thereby favour species diversity in patches with added nutrients. In order to test this hypothesis, a two-factorial field experiment was conducted at an exposed rocky shore of northern-central Chile in which nutrient addition and mussel removal were manipulated with two levels. Experimental units consisted of 100-cm 2 mussel plots that were sampled after two months of experimental manipulations. Local nutrient addition was done with coated slow-release fertilisers. Mussel removal treatments consisted in three destructive events applied throughout the experimental phase, and each event consisted in the removal of 20% of the mussel biomass from each plot. While point-source nutrient addition had only minor effects on diversity, mussel removal had significant and negative effects on faunal species richness and the abundance of suspension-feeders and sessile organisms. The abundance of predators/scavengers significantly decreased with mussel removal in the presence of nutrient addition. Grazers and mobile organisms were very abundant in the mussel assemblage but their abundance remained unaffected by treatments. Finally, species richness and total abundance of algae were also not affected by the treatments. Although the duration of our experiment was relatively short, we suggest that the effects of local nutrient addition are of minor importance at the study site in comparison to the effects of mussel removal. Based on our results and previous studies conducted in soft-bottom systems, we suggest that physical and biological stress acting on exposed hard-bottom communities overshadows the potential effects of local nutrient addition.

Effects of chronic trawling disturbance on the production of infaunal communities

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 243:251-260 (2002) - doi:10.3354/meps243251 Effects of chronic trawling disturbance on the production of infaunal communities Simon Jennings1,*, Mike D. Nicholson1, Tracy A. Dinmore1, John E. Lancaster2 1Centre for Environment, Fisheries & Aquaculture Science, Lowestoft Laboratory, Lowestoft NR33 0HT, United Kingdom 2School of Biological Sciences, University of Wales, Swansea SA2 8PP, United Kingdom *Email: s.jennings@cefas.co.uk ABSTRACT: Trawling causes widespread physical disturbance in shallow shelf seas. While the impacts of trawling on the biomass and community structure of benthic fauna are well known, no existing studies have quantified the effects of trawling disturbance on the absolute production of small benthic infauna. We investigated the effects of beam trawling disturbance on the production of small benthic infauna (AFDM > 0.78 to 62.5 mg) at 9 sites that were subject to a 17.5-fold range in annual trawling disturbance, using a size-based approach that could be applied to other soft-bottom systems. We developed a generalised additive model to test for relationships between trawling disturbance and infaunal production and size structure, after accounting for differences in sediment characteristics and depth. The statistical power of our analyses to detect linear and non-linear relationships between production and disturbance, including increased production at intermediate levels of disturbance, was high (>90% probability of detecting a 50% change in production across the range of disturbance). The analyses showed that trawling frequencies of 0.35 to 6.14 times yr-1 did not have a significant effect on the production of small infauna or polychaetes. This result contrasts with order of magnitude decreases in the production of large infauna, and shows that small polychaetes with fast life histories are less vulnerable to trawling disturbance. Since small infaunal polychaetes are a key source of food for flatfishes, we conclude that beam trawling disturbance does not have a positive or negative effect on their food supply. KEY WORDS: Fishing effects · Size spectra · Production · Infauna · Disturbance · Power analysis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 243. Online publication date: November 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Differential dispersal rates in an intertidal meiofauna assemblage

Meiofaunal nematodes and copepods disperse passively with sediment bedload, and copepods also display active emergence and reentry behavior. Epigrowth-feeders may be the nematode feeding group most susceptible to passive transport because they live closest to the sediment surface. We used bottom traps at a nematode-dominated intertidal mudflat in Maine, USA, to test the hypotheses that (1) meiofauna taxa disperse in relative proportions different from those of the ambient community; (2) copepods have the highest relative dispersal rate (number of individuals trap −1 day −1 ambient individual −1) and are not as tightly linked as other taxa to sediment flux; and (3) epigrowth-feeders have the highest nematode relative dispersal rate. Results supported all three hypotheses. Nematodes accounted for 95.8% of the individuals in cores, but only 38.9% of the individuals in traps. Copepods accounted for 1.5% of the individuals in cores, but 56.7% of the individuals in traps. Less common taxa also had different relative proportions in cores and traps, as did nematode feeding groups and individual species. The relative dispersal rate was far higher for copepods than for any other taxonomic group, and the absolute (number of individuals trap −1 day −1) and bulk (number of individuals g sediment −1 trap −1 day −1) dispersal rates for copepods were equal to those of the 65-fold more abundant nematodes and higher than those for all other taxa. The non-selective deposit-feeders were the most abundant nematode feeding group in the ambient community, but the epigrowth-feeders as a group and as individual species had the highest absolute, relative, and bulk dispersal rates. Non-metric multidimensional scaling (MDS) using analysis of similarity (ANOSIM) and species similarity percentages (SIMPER) reflected these differences between ambient and dispersing nematode assemblages. Significant positive regression relationships between sediment weight and the number of individuals captured in traps for nematodes and some other taxa indicated that they moved passively in the bedload. Lack of a significant regression relationship for copepods suggested an active behavioral component to dispersal. Meiofauna populations in this soft-bottom community were highly dynamic, demonstrating that the role of dispersal must be included in any consideration of the ecology of soft-bottom systems at local and regional spatial scales.

Seasonal effects of intraspecific density and predator exclusion along a shore-level gradient on survival and growth of juveniles of the soft-shell clam, Mya arenaria L., in Maine, USA

The relative roles that predation and competition play in regulating populations of infaunal marine bivalves in soft-bottom systems are strikingly different. Exploitative competition for food typically occurs at elevated densities, but crowding rarely results in mortality and competitive exclusion. Predation by decapods, gastropods, and, sometimes asteroids, is more important in controlling patterns of distribution and abundance. Most field tests leading to this synthesis have been conducted between 35°N and 35°S and/or with bivalves in the families Veneridae and Tellinidae. To test the robustness of these ecological processes at another geographic setting (45°N) using a species from another family within the suspension-feeding guild (Myidae), we performed a short-term field manipulation at an intertidal mud flat in eastern Maine, USA. We followed survival and growth of 10,080 juveniles (12.4-mm shell length (SL)) of the soft-shell clam, Mya arenaria L., in field enclosures with and without predator-deterrent netting at three densities (330, 660 and 1320 m −2) along a tidal gradient over four sampling intervals from April to December 1996. We used a generalized completely randomized block design to assess variation in these dependent variables within a given tidal height (high, mid, and low) on a particular date. Mortality varied seasonally, peaking (13.6%) between August and September when seawater temperatures were warmest. No significant mortality occurred after September, when mean (±95% CI) percent survival pooled over all treatments was 72.9±8.5%. Netting (6.4-mm aperture) effectively excluded predators along the tidal gradient as overall mean clam survival, independent of tidal position, was 88.7±4.1% in protected units (plastic plant pots with area=181 cm 2), but decreased from upper and mid tide levels (82.9±6.1%) to lower on the shore (66.3±9.7%) in unprotected units. Density-dependent mortality resulted in reduced survival (−4.6%) in clams stocked at the two highest levels ( P<0.001); however, numbers of dead clams with undamaged valves provided little evidence that this effect was due to starvation. Incremental growth also varied seasonally with greatest amounts of shell added during June–August at all tidal levels. Shell growth stopped or slowed significantly after September at all tidal positions. Mean SL increased with decreasing tidal height (December sizes: high=20.6±2.9 mm, mid=24.1±1.0 mm; low=28.2±1.2 mm); however, submergence time alone failed to explain completely these differences. Density-dependent growth was detected once (August–September). Animals at the two highest densities experienced a growth depression of ca. 7%. We conclude predation, rather than competition, is more important in regulating populations of soft-shell clams in this intertidal location.

Epibenthic Predators and Marine Meiofauna: Separating Predation, Disturbance, and Hydrodynamic Effects

In many marine soft—bottom systems, natant predators disturb the bottom while foraging for infaunal prey. This study was designed to determine if the predatory fish Leiostomus xanthurus exerts its effect on meiofaunal prey primarily via predation (consumption) or via disturbance and if flow modifies this effect. Experiments were conducted in a laboratory flume that allowed for both the addition and removal of fish and the mimicking of predator—induced disturbance, while controlling flow. Prey species differed with respect to the relative effects of predation and predator—induced disturbance. Disturbance accounted for 30—55% of the predator—associated decreases in copepods and foraminiferans, while disturbance accounted for virtually all of the nematode mortality. The latter was significant only when flow was absent. For other prey taxa, mortality was not influenced by flow; however, predator—induced drift (down—stream transport) of all meiofauna was significantly increased when flow was present. If experimental sites are not in equilibrium between upstream and downstream transport, then ignoring this drift could result in an overestimation of fish consumption on meiofauna by as much as 50%. Thus, the mechanisms by which fish predators influence meiofauna prey included direct consumption, disturbance—induced mortality, and enhanced water—column transport.

Importance of predation by infaunal polychaetes in controlling the structure of a soft-bottom community in Maine, USA

Field manipulations in a Maine, USA intertidal mud flat showed that Nereis virens adults were an important factor in regulating the abundance of Corophium volutator, an amphipod which comprised 63% of the total number of individuals in the benthic community. Removal of N. virens adults resulted in an increase in C. volutator abundance, while addition of N. virens adults led to a decrease. There was a significant negative correlation between the abundance of N. virens adults and that of C. volutator. C. volutator was also negatively correlated with the density of all the other infaunal species combined. These results suggest that there is at least a 3-level interactive system (N. virens —C. volutator — other infaunal species) within the infauna in Maine; N. virens is a factor in controlling the abundance of C. volutator, and C. volutator may play a role in regulating the densities of other infaunal species. Models of generalized “cropping” in soft-bottom systems may be too simple if they ignore complex trophic relationships within the infauna.