Soft-sediment Systems Research Articles

Dispersal of the estuarine gastropod Pyrazus ebeninus is only weakly influenced by pneumatophore density

Studies on rocky intertidal gastropods indicate habitat complexity and body size to be major determinants of dispersal patterns. Considerations of effects of habitat complexity and body size on soft sediment gastropods are, however, less common. In neither habitat has the interaction between habitat complexity and body size been considered despite the increasing recognition in the general ecological literature that complexity effects are body-size-dependent. We tested independent and interacting effects of habitat complexity and body size on movement of the mud-whelk, Pyrazus ebeninus, by marking large (61–85 mm) and small (31–55 mm) snails in sites with low and high densities of pneumatophores and determining the distance and direction of their dispersal over periods of 1 week, 2 weeks and 1 month. Contrary to our expectation, we found no effect of pneumatophore density on the distance of snail migration over each of the temporal scales; net distance travelled by snails was determined only by body size and idiosynchratic, site-specific factors. The direction of snail movement was, by contrast, influenced on some temporal scales by both pneumatophore density and snail size. Over 1 week, site effects dominated patterns of movement and neither size of snail nor density of pneumatophore produced statistically significant effects. As the temporal scale increased, effects of size and pneumatophore density became increasingly apparent. Over the 1-month period, large snails at all sites and small snails at sites with high pneumatophore density migrated down the shore, while small snails at sites with low pneumatophore displayed non-directional movement. Thus, overall this study provides only weak support for effects of pneumatophore density on snail movement. In combination with other studies, our results suggest that, in comparison to on rocky shores where habitat complexity has strong effects on the distribution, abundance and behaviour of gastropods in soft-sediment systems habitat complexity is a less important structuring agent.

Importance of rock lobster size–structure for trophic interactions: choice of soft-sediment bivalve prey

Ecologists are becoming increasingly interested in how variation in predator demographics influences prey communities. In northeastern New Zealand, the contrasting populations of previously exploited predators in highly protected marine reserves and fished areas have been used to investigate the effects of predation in soft-sediment habitats. However, these experiments have been unable to separate the role of predator size from that of density. This study provides evidence to support the model that foraging by different sizes of the rock lobster Jasus edwardsii affects soft-sediment bivalve populations in different ways. Feeding trials were conducted to investigate whether rock lobsters of different sizes vary in their choice of taxa and size of their bivalve prey. Trials with two morphologically similar species, Dosinia subrosea and Dosinia anus, indicated that lobsters of all sizes choose D. subrosea more frequently than the heavier shelled D. anus. Further results indicated that both large (>130 mm carapace length (CL)) and small ( 40 mm). Patterns in the abundance and size class distributions of these two bivalve species at protected and fished sites supported the feeding choices observed in the laboratory. These results suggest that populations of rock lobsters with large individuals inside reserves are capable of controlling the demography of bivalve populations in adjacent soft-sediment systems.

Episodic disturbance events modify predator–prey interactions in soft sediments

Physical disturbance events are common in shallow soft-sediment habitats and can have significant effects on predator–prey interactions. While several studies have reported on predator aggregations following disturbance events, few studies have investigated the mechanisms and interactive effects of predation and physical disturbance on prey survival in shallow soft-sediment habitats. In this study the interactive effects of sediment resuspension and predation by two contrasting epibenthic predator species were tested on the survival of the amphipod Corophium volutator in a laboratory experiment. The shrimp Crangon crangon and juvenile plaice Pleuronectes platessa were used as predators, both numerical dominants in shallow soft sediments on the Swedish west coast. In addition we quantified epibenthic predator aggregation in the field following small-scale disturbances. In the laboratory, synergistic negative effects of predation and non-lethal disturbance on Corophium survival were found with both predator species, and rapid aggregation of several mobile epibenthic predator species following disturbance was demonstrated in the field. Abundances of C. crangon, the numerically dominant predator in the field, were doubled in disturbed patches within 2 min following disturbance. Our study emphasises the importance of considering episodic small-scale disturbances when interpreting predation effects and trophic interactions in shallow soft-sediment systems.

Differential regulatory roles of crustacean predators in a sub-arctic, soft-sediment system

The role of predation in structuring soft-sediment communities varies as a function of the number and composition of predators that co-occur in a given habitat. In Bonne Bay, Newfoundland, contrasting abundances or predators in different areas of the bay may contribute to different regulatory roles of predators on infauna. To test this hypothesis, results from a field exclusion experiment were compared with 5 laboratory experiments that measured the individual effects of the main crustacean predators of the bay: snow crab, rock crab, and toad crab. In the field experiment, the exclusion of predators generated clear differences in infaunal composition, and 2 species (the polychaete Pholoe tecta and the clam Macoma calcarea) dominated exclusion treatments. Predator exclusion also resulted in a significant increase in density, but only a modest increase in infaunal diversity. In the laboratory, fresh, undisturbed sediment cores were paired with similar cores, protected by mesh and exposed to each crab species in order to test for their potential effects on infaunal communities. Results indicate that snow crab and rock crab have clear effects on species composition and, as was the case with the field experiment, the infaunal species P. tecta and M. calcarea dominated exclusion treatments for both predatory crabs. These predators also reduced total infaunal density, but only rock crab significantly reduced species richness. In contrast, toad crab effects were not significant. Given that snow crab and rock crab are both targeted by commercial fisheries in Atlantic Canada, our results suggest that crab fishery removal may have multiple indirect effects on infaunal communities.

Facilitation of macroalgae by the sedimentary tube forming polychaete Diopatra cuprea

Marine foundation organisms such as seagrasses, corals, and kelps facilitate the distribution of numerous organisms by creating refuges from environmental stressors and by providing food and substrate for settlement and growth. Barren soft-sediment systems often have faunal organisms that facilitate other species by habitat modification. We investigated how an abundant (21 m −2) tube cap forming polychaete, Diopatra cuprea, facilitates macroalgal distribution in Hog Island Bay, a turbid shallow tidal lagoon in Virginia (USA). Seventy percent of the number of mudflat macroalgae were found incorporated into protruding D. cuprea tube caps and field experiments showed that D. cuprea facilitates algal persistence by providing a stable substrate retaining algae against hydrodynamic forces such as tidal flushing and storm surge. If tube caps were removed, simulating storm-induced erosion, they were rebuilt within days and new drift algae incorporated. Also, D. cuprea facilitated the algal assemblage by fragmenting thalli in the attachment process, thereby ensuring a constant fragment supply for vegetative re-growth if storm-induced pruning occurs. On a species-specific level, Gracilaria verrucosa and Ulva curvata benefited more from tube cap construction compared to Fucus vesiculosus, Agardhiella subulata and the alien Codium fragile ssp. tomentosoides. This was partly because G. verrucosa and U. curvata were incorporated and fragmented more readily, and partly because they probably have physiological, morphological and biomechanical traits that enable them to better co-exist with D. cuprea. These results suggest that macroalgal distribution throughout Hog Island Bay to a large extent is linked to the distribution of D. cuprea. The processes of algal attachment, retainment, recovery, re-growth and fragmentation, can have important ecosystem implications because of the sheer abundance of the Diopatra- Gracilaria/Ulva association.

Macrofaunal responses to pit–mound patch dynamics in an intertidal mudflat: local versus patch-type effects

Biogenic structures created via feeding activities have varying effects on soft sediment communities, altering population dynamics, creating a temporal mosaic of successional patches, and ultimately increasing variation at different spatial scales. This study focused on assessing population responses to pits (P) and mounds (M) in an intertidal mudflat (River Plym, England) in order to determine (a) how these structures (max size 1400 cm 2), and their formation, affected infauna and (b) to what extent local variations in ambient communities may have affected infaunal responses. Densities in 0- and 1-week-old pits were significantly lower than in ambient and mound areas for most of the dominant infauna over the study period. Abundances were higher in mounds for some species and responses to both structures differed among juveniles and adults. Recovery to ambient levels in P–M systems took about 3 weeks, although their physical characteristics only lasted about 2 weeks. Correlations among ambient densities and adjacent P–M systems were mixed, but suggested decoupling between local ambient and P–M dynamics for some taxa either in relation to age of the patch and/or size of the individuals. At the community level, local differences appeared to be a significant source of variation in new pits, but differences were swamped out when recruitment was high. Differences were more evident in older P–M systems. These results show that sources of local variation in infaunal dynamics can be attributed to a combination of small-scale disturbance/recovery processes and spatially and temporally changing ambient conditions. Identifying extant spatial and temporal small-scale variation can be a critical component of understanding and interpreting larger-scale dynamics of soft-sediment systems.

Behavioural response of juvenile bivalves to terrestrial sediment deposits: implications for post-disturbance recolonisation

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 278:179-191 (2004) - doi:10.3354/meps278179 Behavioural response of juvenile bivalves to terrestrial sediment deposits: implications for post-disturbance recolonisation V. J. Cummings*, S. F. Thrush National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand *Email: v.cummings@niwa.co.nz ABSTRACT: In soft-sediment systems, terrestrial sediment deposits may result in a marked change in habitat and benthic community composition. We conducted a series of experiments to investigate the behavioural response of juveniles of 2 bivalve species common on New Zealand intertidal sandflats (Paphies australis and Macomona liliana) to terrestrial sediments. Both species are able to actively disperse as juveniles and do so in response to 'unfavourable' conditions. In the laboratory, we investigated the ability of these potential colonists to burrow into thin (0.5, 1.0 cm) surface and submerged terrestrial sediment layers, and their subsequent ability to burrow into natural sediments. Field experiments assessed their response to terrestrial sediments that had been 'aged' in the natural estuarine environment for different lengths of time (up to 1 mo). Exposure to terrestrial sediment treatments negatively affected both species, with fewer individuals burrowing into the terrestrial sediment treatments. In the laboratory, burrowing was slower in the 1 cm-thick surface layers than in the 0.5 cm-thick and submerged layers, and the subsequent burrowing rate in natural sand of individuals recovered from these treatments was similarly affected. This latter effect is important as it suggests that settlement by juvenile bivalves on terrestrial sediment deposits can have a lasting effect even if an individual is able to find a more suitable habitat at a later date. In the field, dispersal of M. liliana away from the terrestrial sediment treatments was reduced, even after the sediment had been Œaged¹ on the sandflat. Depending upon the extent and frequency of disturbance, terrestrial sediments are likely to have important effects on the population and community dynamics of mobile bivalve species, and at a wider scale than that of their immediate impact. KEY WORDS: Sedimentation · Recolonisation · Paphies australis · Macomona liliana · Post-settlement juveniles · New Zealand · Intertidal sandflats Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 278. Online publication date: September 06, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Palatability and defense of some tropical infaunal worms: alkylpyrrole sulfamates as deterrents to fish feeding

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 263:299-306 (2003) - doi:10.3354/meps263299 Palatability and defense of some tropical infaunal worms: alkylpyrrole sulfamates as deterrents to fish feeding Cynthia E. Kicklighter1, Julia Kubanek1,2, Todd Barsby1, Mark E. Hay1,* 1School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA 2School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA *Corresponding author. Email: mark.hay@biology.gatech.edu ABSTRACT: Numerous studies have investigated chemical defenses among sessile species growing on hard substrates, but few have addressed this for mobile species in soft-sediment communities. We investigated the palatability and potential chemical defenses of 11 worm species from soft-sediment systems in southern Florida, USA. Three species were unpalatable to the bluehead wrasse Thalassoma bifasciatum. The polychaete Cirriformia tentaculata and the hemichordate Ptychodera bahamensis were uniformly unpalatable. For the polychaete Eupolymnia crassicornis, the exposed tentacles were unpalatable, but the body, which remains protected in a deeply buried tube, was palatable. These unpalatable worms were chemically defended; extracts of C. tentaculata, P. bahamensis, and the tentacles of E. crassicornis deterred fish feeding. For C. tentaculata, bioassay-guided fractionation demonstrated that a mixture of 3 closely related alkylpyrrole sulfamates deterred fish at naturally occurring concentrations (2-n-hexylpyrrole sulfamate [1.6% of worm dry mass], 2-n-heptylpyrrole sulfamate [3.1% dry mass], and 2-n-octylpyrrole sulfamate [0.8% dry mass]). This appears to be the first documentation of characterized natural products defending a marine worm from consumers. For P. bahamensis and the tentacles of E. crassicornis, deterrent effects of crude extracts decomposed before specific compounds could be identified. KEY WORDS: Chemical defense · Marine worms · Cirriformia tentaculata · Soft-sediment · 2-n-hexylpyrrole · 2-n-heptylpyrrole · 2-n-octylpyrrole Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 263. Online publication date: November 28, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea†

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.

Detection of acoustic class boundaries in soft sediment systems using the seafloor acoustic discrimination system QTC VIEW

Transition zones (or ‘ecotones’) are ecologically important spatial elements of subtidal landscapes that represent a mixture of different habitat elements. We provide a method for identifying such areas in broad-scale surveys of the seafloor using the acoustic discrimination system QTC VIEW. QTC VIEW is an acoustic processing system that assigns sonar ping stacks to clusters of like points, to identify different habitats on the seafloor. Paired QTC VIEW transects (∼20m spacing) were run at intervals of 200m, at two separate sampling locations, to assess the consistency of clustering of individual ping stacks into acoustic classes. Very consistent spatial patterns of class change were found between transect pairs, suggesting high stability in the classification process. QTC VIEW assigns confidence values to each individual record; running averages calculated using a moving window along transects showed drops in confidence values associated with areas of transition in habitat class assignment, but this was not always consistent. The Berger–Parker index, a class dominance statistic, provided a more consistent transition indicator. Class transition ranged from abrupt to gradual, along with areas where a mixture of acoustic classes occurred. However, acoustically detected transition zones did not consistently respond to visual observations of the sea floor.

Fishing disturbance and marine biodiversity: the role of habitat structure in simple soft-sediment systems

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 223:277-286 (2001) - doi:10.3354/meps223277 Fishing disturbance and marine biodiversity: the role of habitat structure in simple soft-sediment systems Simon F. Thrush1,*, Judi E. Hewitt1, Greig A. Funnell1, Vonda J. Cummings1, Joanne Ellis1, Diane Schultz1, Drew Talley2, Alf Norkko1 1National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand 2Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0201, USA *E-mail: s.thrush@niwa.cri.nz ABSTRACT: Broad-scale anthropogenic disturbances that reduce the density of epifauna and homogenise surficial sediments can have important consequences for seafloor biodiversity. We investigated the habitat structure and macrofaunal diversity of relatively simple soft-sediment habitats over a number of spatial scales (cm to km) to identify the role of habitat structure in influencing macrobenthic diversity and to assess the validity of using habitat structure as a surrogate measure for biodiversity. We sampled 10 locations with differences in habitat structure using a sampling design that nested macrobenthic core samples within videoed transects of the seafloor. This allowed us to determine relationships between observable habitat structure and macrobenthic diversity at a number of spatial scales. We characterised elements of habitat structure based on direct counts of surficial sediment characteristics and the presence of other immobile features, many of which were biogenic in origin. We also used multivariate measures (the relative multivariate dispersion, the mean and range of the Bray-Curtis dissimilarity along the transects) to characterise habitat structure at the transect scale. We developed regression models based on measures of habitat structure that explained 74 to 86% of the variance in macrobenthic diversity. This result suggests that removal of habitat structure in relatively low-structure soft-sediment systems will significantly decrease their biodiversity, and consequently that of the wider marine ecosystem. Erratum KEY WORDS: Biodiversity · Soft-sediments · Habitat structure · Habitat heterogeneity · Habitat complexity · Habitat disturbance · Fishing impacts · Nested multi-resolution sampling · Kawau Bay · New Zealand Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 223. Online publication date: November 28, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Fishing disturbance and marine biodiversity: role of habitat structure in simple soft-sediment systems

Broad-scale anthropogenic disturbances that reduce the density of epifauna and homogenise surficial sediments can have important consequences for seafloor biodiversity. We inves- tigated the habitat structure and macrofaunal diversity of relatively simple soft-sediment habitats over a number of spatial scales (cm to km) to identify the role of habitat structure in influencing mac- robenthic diversity and to assess the validity of using habitat structure as a surrogate measure for bio- diversity. We sampled 10 locations with differences in habitat structure using a sampling design that nested macrobenthic core samples within videoed transects of the seafloor. This allowed us to deter- mine relationships between observable habitat structure and macrobenthic diversity at a number of spatial scales. We characterised elements of habitat structure based on direct counts of surficial sedi- ment characteristics and the presence of other immobile features, many of which were biogenic in origin. We also used multivariate measures (the relative multivariate dispersion, the mean and range of the Bray-Curtis dissimilarity along the transects) to characterise habitat structure at the transect scale. We developed regression models based on measures of habitat structure that explained 74 to 86% of the variance in macrobenthic diversity. This result suggests that removal of habitat structure in relatively low-structure soft-sediment systems will significantly decrease their biodiversity, and consequently that of the wider marine ecosystem.

Effects on the ecological integrity of a soft-bottom habitat from a trawling disturbance

The effects of trawling disturbance on a soft-sediment system were investigated with a manipulative field experiment in an area that had been closed to shrimp trawling activities for 20 years. The area was also chosen for its weak natural physical agents i.e. no scouring of sediments by storm events or tidal flow, allowing a quantitative assessment of the effects of trawling on the benthic fauna and geochemical properties of the soft substrate.

Incorporation of soft-sediment systems into a model of marine benthic community regulation

This review (1) describes important regulating forces in soft-sediment systems, (2) outlines existing models of community regulation, and (3) revises a model of community regulation to incorporate soft-sediment systems. The Menge and Sutherland (MS) model of community regulation and its refinements were developed for hard-bottom habitats, but can be modified for soft-sediment systems. This ‘consumer stress model’ posits that mobile consumers feed ineffectively in harsh environments, and that the relative importance of physical disturbance, interspecific competition and predation varies predictably with the magnitude of recruitment, environmental conditions, productivity and trophic position. The MS model predicts that interspecific competition for a resource depends directly upon the level of recruitment, though it does not explicitly address the joint effects of recruitment and resource availability, which are important in soft-sediment communities. The model is here revised to incorporate hard-bottom and soft-sediment systems by changing the recruitment axis to a ‘recruitment:resource ratio’, whereby the effect of a given level of recruitment depends on resource availability. The potential utility of the revised model is illustrated in a hypothetical contrast of the effect of recruitment:resource ratios on community regulation for a mussel-dominated assemblage in hard-bottom habitats and an infaunal clam-dominated system in soft sediments.

Refuges from predation and the persistence of estuarine clam populations

Densities of adult infaunal clams Macoma balthica and Mya arenaria in mesohaline sections of Pamlico Sound, North Carolina, USA, declined rapidly between April and June 1991 and 1992, except in places where there was abundant shell material on the sediment or large densities of the mactrid bivalve Rangia cuneata. Survivorship of M. balthica and M. arenaria was examined experimentally in 1 M2 plots containing different types of habitat: widgeon grass Ruppia maritima, live R. cuneata, 'artificial' R. cuneata, shell valves of R. cuneata and clean sediments to determine whether these structures provided a refuge from predation for the clams. M. balthica and M arenaria obtained a substantial refuge from predation by crabs when living in patches containing R. cuneata. Neither species obtained a refuge from predation when in beds of widgeon grass. There were 2 surprising results in these experiments. First, survivorship of the clams was significantly reduced in patches containing both seagrass and R. cuneata compared with patches of only R. cuneata. Second, survivorship was significantly less in patches of live R. cuneata than in patches of 'sham' (artificial) clams or equal numbers of shell valves. Two alternative, but not necessarily exclusive, explanations are offered for these results. (1) Subsurface rhizomes of widgeon grass may reduce the depth to which clams are able to burrow into the substratum leaving them more susceptible to predation by digging crabs. (2) Increased availability of alternative prey in patches of widgeon grass causes predators to spend more time foraging in these patches and, by chance alone, they capture more clams. Alternatively, predators spend more time in the patches with widgeon grass because they obtain a partial refuge from their own predators. The occurrence of a refuge from predation for M arenaria and M balthica living with R. cuneata is a striking example of an associational defense between potentially competing species. Associational defenses such as this may be a common structuring force in soft-sediment systems and future work may help in producing a more synthetic understanding of their importance in aquatic systems.

Oil pollution studies of the Solbergstrand mesocosms

Two medium-scale ecosystems (mesocosms) were built on the Oslofjord: one a hard-bottom intertidal system and the other a subtidal soft-sediment system. The hard-bottom mesocosm consists of four basins, two controls and two which were dosed with diesel-oil (129 μg 1-1a high oil (HO) dose and 29 μg 1-1a low oil (LO) dose). Both oil doses caused high mortality ofMytilus edulisand growth was reduced in the macroalgaeAscophyllum nodosumandLaminaria digitata. Recruitment ofLittorina littoreawas also affected by oil so that populations declined over time. Subtidal benthic communities have been established in the mesocosm and show variations in sediment chemistry within the range found in the field. Although recruitment of benthic macrofauna is reduced, dominant species and species structure remain closely similar to that in the field over six months. Bioturbation effects studied in the mesocosm have shown the important influence of large, rare species in structuring benthic communities, a finding which would not be possible in nature by diving or by the use ofsubmersibles. Preliminary results from a community taken from 200 m depth and established in the mesocosm suggest that it is now possible to do detailed manipulation experiments on communities simulating the whole continental shelf.

Larval settlement into marine soft-sediment systems: Interactions with the meiofauna

The distribution and abundance of organisms exhibiting complex life cycles, like marine invertebrates, reflect ecological processes operating at all stages in the life history. Few studies have yet considered the mortality patterns of larvae and juveniles. To test whether the permanent meiofauna play a role in macrofaunal larval site-selection, and/or if permanent meiofaunal predators or competitors and disturbers are a significant source of mortality for newly settled macrofaunal juveniles, a series of manipulations of meiofauna were performed. Densities of (1) predatory turbellarians alone, and (2) other meiofauna, were increased in small boxes placed on a holding table in a shallow subtidal habitat. Natural settlement into meiofauna manipulations was examined approximately monthly for a year. Other experiments were conducted to examine the relative importance of site-selection and post-settlement mortality and to determine if settlement was density-dependent or density-independent. Densities of spionid, cirratulid, terebellid, capitellid, and maldanid polychaetes, oligochaetes, bivalves, and amphipods were all reduced by high densities of turbellarians, and sometimes by other meiofauna. Turbellarian predation was responsible for significant post-settlement mortality, but spionids, cirratulids, terebellids, and maldanids also appeared to avoid dense turbellarian treatments. Bivalve densities were reduced by high densities of other meiofauna, probably due to their sedimentary disturbance. Syllid polychaete densities were higher in turbellarian treatments, suggesting that they select for areas with high densities of their prey (small turbellarians). The effects of meiofauna on settlement and survival were greatest in spring and summer. The results of these experiments suggest larval settlement patterns and early juvenile survival should be considered in developing general models of life history and community structure for soft-sediment systems.

An adaptive correlator for underwater measurements. : Wolf, Alfred A. and J. H. Dietz 1962. Marine Instrumentation, Inst. Soc. Amer. Plenum Press, N.Y. 1: 347–354.

Marine foundation organisms such as seagrasses, corals, and kelps facilitate the distribution of numerous organisms by creating refuges from environmental stressors and by providing food and substrate for settlement and growth. Barren soft-sediment systems often have faunal organisms that facilitate other species by habitat modification. We investigated how an abundant (21 m−2) tube cap forming polychaete, Diopatra cuprea, facilitates macroalgal distribution in Hog Island Bay, a turbid shallow tidal lagoon in Virginia (USA). Seventy percent of the number of mudflat macroalgae were found incorporated into protruding D. cuprea tube caps and field experiments showed that D. cuprea facilitates algal persistence by providing a stable substrate retaining algae against hydrodynamic forces such as tidal flushing and storm surge. If tube caps were removed, simulating storm-induced erosion, they were rebuilt within days and new drift algae incorporated. Also, D. cuprea facilitated the algal assemblage by fragmenting thalli in the attachment process, thereby ensuring a constant fragment supply for vegetative re-growth if storm-induced pruning occurs. On a species-specific level, Gracilaria verrucosa and Ulva curvata benefited more from tube cap construction compared to Fucus vesiculosus, Agardhiella subulata and the alien Codium fragile ssp. tomentosoides. This was partly because G. verrucosa and U. curvata were incorporated and fragmented more readily, and partly because they probably have physiological, morphological and biomechanical traits that enable them to better co-exist with D. cuprea. These results suggest that macroalgal distribution throughout Hog Island Bay to a large extent is linked to the distribution of D. cuprea. The processes of algal attachment, retainment, recovery, re-growth and fragmentation, can have important ecosystem implications because of the sheer abundance of the Diopatra-Gracilaria/Ulva association.