Infaunal Predators Research Articles

Mollusc shell detritus affects benthic subtidal community dynamics in the Northern Wadden Sea

A shallow subtidal area in the northern Wadden Sea was monitored over 17 years (from 2003 to 2019) for sediment parameters and macrobenthic fauna. Due to the sheltered position of the study area, sediment composition remained rather stable with only minor annual and seasonal variations in sediment granulometry. An intermittend storm (‘Kyrill’) had no significant effect on sediment composition parameters; the construction of an artificial dune along the southern border of the study area had minor transient but no lasting effects on sediment composition. Faunal species richness and total abundance showed the typical seasonality with minimum abundance in late winter and a peak after recruitment in summer. Variations between years in autumn (post-recruitment) abundances were best explained by the number of days with a seawater temperature <1°C during the preceding winter. Temperature during other seasons, salinity, chlorophyll concentration and NAO showed no significant correlations with total abundance, nor did storm (‘Kyrill’) or construction of the artificial dune. Within-site faunal variability was best explained by water depth and velocity of the tidal currents while sediment granulometry was of minor importance. However, the amount of bivalve shell detritus mixed with the sandy sediment proved to be the strongest covariant of species numbers, total abundance, and species-specific abundances. At the sediment surface, shells provide the only anchorage for epibenthic species which in turn attract associated fauna. Shells inside the sediment hamper movement of infaunal predators and epibenthic predators are handicapped in rooting about for prey. Thus, shell material is a highly significant structural factor for the macrozoobenthos in these shallow waters. In a future with increasing ocean acidification, the availability of benthos as a food source for higher trophic levels will depend on the balance between pH-driven shell destruction and the compensatory power of shell-building species.

You Are What You Eat: Stable Isotopic Evidence Indicates That the Naticid Gastropod Neverita duplicata Is an Omnivore

Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for one year. The median N fractionation factor derived from the experimental moon snails was 3.58 ‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4 ‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiments. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the ecological implications of potential naticid omnivory.

Trophic ecology of deep-sea Asteroidea (Echinodermata) from eastern Canada

Asteroids (sea stars) can be important predators in benthic communities and are often present in ecologically important and vulnerable deep-sea coral and sponge habitats. However, explicit studies on the trophic ecology of deep-sea asteroids are rare. We investigated the diets of seven species of deep-sea asteroid from the bathyal zone of Newfoundland and Labrador, eastern Canada. A multifaceted approach including live animal observations, stomach content analysis, and stable isotope analysis revealed the asteroids to be either top predators of megafauna or secondary consumers (mud ingesters, infaunal predators, and suspension feeders). The stable isotope signatures of Ceramaster granularis, Hippasteria phrygiana, and Mediaster bairdi are characteristic of high-level predators, having δ15N values 4.4‰ (more than one trophic level) above Ctenodiscus crispatus, Leptychaster arcticus, Novodinia americana, and Zoroaster fulgens. We present strong evidence that corals and sponges are common food items for two of the predatory species, C. granularis and H. phrygiana. During laboratory feeding trials, live H. phrygiana fed on several species of soft coral and C. granularis fed on sponges. Stomach content analysis of wild-caught individuals revealed sclerites from sea pens (e.g. Pennatula sp.) in the stomachs of both asteroid species; H. phrygiana also contained sclerites from at least two other species of octocoral and siliceous sponge spicules were present in the stomachs of C. granularis. The stomach contents of the secondary consumers contained a range of invertebrate material. Leptychaster arcticus and Ctenodiscus crispatus feed infaunally on bulk sediment and molluscs, Zoroaster fulgens is a generalist infaunal predator, and the brisingid Novodinia americana is a specialist suspension feeder on benthopelagic crustaceans. This study provides a foundation for understanding the ecological roles of bathyal asteroids, and suggests that some species may have the potential to be important modulators of deep-sea benthic communities.

Comparison of diet and feeding activity of two polychaetes, Nephtys caeca (Fabricius) and Nereis virens (Sars), in an estuarine intertidal environment in Québec, Canada

It is crucial to study how food resources are allocated in order to understand how invertebrate species of soft-bottomed benthic communities can live in the same environment, especially when belonging to the same trophic level. On the southern shore of the Lower St. Lawrence Estuary, the polychaetes Nereis virens (Nereidae) and Nephtys caeca (Nephtyidae) represent the main infaunal predators and are known to regulate (by predation) other populations within their community. For these animal populations, there is a high degree of spatial overlap in the horizontal dimension as well as vertically in the sediment column. The purpose of this study was to describe and compare the feeding activity of N. virens and N. caeca in relation to several environmental factors. The feeding activity of N. caeca was further studied under natural and experimental conditions and a feeding experiment was carried out to evaluate how the food resource is subdivided in conditions of high spatial overlap. Finally, the prospecting activity of N. virens was described under natural conditions. N. virens and N. caeca exhibited a high degree of dietary overlap, particularly at the adult stage. This food resource overlap can easily influence the regulation of these species, even though they display different feeding responses to environmental stimuli. Tides and storm events can also influence the feeding behaviour. We conclude that different behavioural feeding responses likely favour the occurrence of these two species in the same trophic environment.

The influence of structure and dynamics of infaunal predator populations on predatory activity: the example of Nephtys hombergii

In an attempt to associate population structure of infaunal predators with the effect of predation in structuring benthic communities, an extensive study was conducted focusing on a population of the predatory polychaete Nephtys hombergii in the Rance estuary (western English Channel). Sampling was designed to study both spatial distributions in abundance and weight throughout the whole estuary (1995), and temporal variations of the predator population on a sublittoral mudflat (1995–1997). The results reveal that large individuals are significantly distributed on intertidal mudflats, while juveniles (G0 and G1 classes) inhabit the whole sublittoral area. Juveniles are dominant throughout the year (>90% of individuals), but are characterized by high mortality rates (70–80%), which are directly responsible for changes in population abundance. Before investigating the effect of predation, the population structure and the spatial distribution of predators must be known, an important step when considering that prey mortality induced by a 1-year-old N. hombergii was about 20% higher than rates observed with adults. Based on the example of N. hombergii, the results underline the necessity of considering the age, the weight structure and the dynamics of the predator population to understand the dynamics of marine communities in a better way.

Long‐term observations on the dynamics of three species of polychaetes living on tidal flats of the Wadden Sea: the role of weather and predator–prey interactions

Summary 1. On the tidal flats of the Wadden Sea, the predatory polychaete Nephtys hombergii (Sav.) is sensitive to low winter temperatures, whereas its main prey, the smaller polychaetes Scoloplos armiger (O.F.M.) and Heteromastus filiformis (Clap.) are not. 2. Monitoring macrofauna dynamics during the last three decades (1970–97) in two distant Wadden Sea areas revealed that Nephtys abundance was severely reduced in all eight coldest winters (generally to an average of &lt; 0·1 g ash‐free dry weight m–2), whereas its biomass reached mean values around 1 g AFDW m–2 during periods with mild winters (≤ 5 days with an air temperature remaining below 0°C all day). Over‐winter changes in Nephtys abundance were strongly related to temperature and 70% of the variability in late winter abundance of this species could be explained by temperature characteristics of the foregoing winter. 3. Biomass values of Nephtys observed in late winter predicted to a high degree (90%) the generally somewhat higher values in the subsequent summer. This seasonal change of predator abundance was generally not related to prey density. Only locally (in an exposed low‐biomass area) and rarely (one‐tenth of the years of observation) did low prey supply (if it was lower than simultaneous predator biomass) coincide with a decline, rather than the usual seasonal increase in Nephtys biomass. 4. A negative influence of predator abundance on prey biomass was observed in both prey species over the entire range of observed predator biomass values. The usual seasonal (winter to summer) increase of prey biomass was significantly smaller at high than at low Nephtys biomass and was even reduced to nil at the highest predator density observed. Scoloplos biomass was about four times higher after years with low (&lt; 0·1 g m–2) than after years with high (&gt; 1·0 g m–2) Nephtys biomass. Similar differences were observed in biomass of Heteromastus. 5. It is concluded that winter temperatures act as an important structuring factor in the Wadden Sea zoobenthic community by directly governing the densities of an important infaunal predator and indirectly affecting the abundance of at least two important prey species. Cold winters intervene by starting a new cycle of predator–prey interaction on average once per 3 or 4 years. 6. Predator abundance was more frequently determined by weather conditions than by food supply. Prey abundance was primarily governed by predator abundance and food supply and was only indirectly (via predator abundance) affected by the incidence of cold winters.

Predation by polychaete worms on larval and post-settlement abalone Haliotis iris (Mollusca:Gastropoda)

Predation on post-settlement abalone ( Haliotis iris) by polychaete worms inhabiting the crusts of non-geniculate coralline algae was examined experimentally. In the subtidal habitat of H. iris, the warty Mesophyllum printzianum supported dense assemblages (> 0.5 cm −1) of the cirratulid Dodecaceria berkeleyi and the spionid Boccardia chilensis, but few polychaetes were found in the encrusting Spongites yendoi. Survival rates for inocula of hatchery-reared larvae of H. iris ( n = 10) on experimental substrata ( M. printzianum) were 29.0 + 9.2% with D. berkeleyi, and 52.4 + 10% with B. chilensis after a 24 h trial. There was no significant density effect (1–4 individuals per 10 cm 2 vs. 6–10 individuals per 10 cm 2) for either species of polychaete. The results indicate that refugia from water currents and piscivorous predators offered by coralline surfaces are offset by the biological hazards associated with resident infaunal predators. This interaction will determine levels of recruitment of abalone and other benthic invertebrates to coralline surfaces.

Effects of sediment disturbance on the structure of benthic fauna in a subtropical tidal creek of southeastern Brazil

An experimental analysis of benthic response to sediment disturbance by the blue crab Callinectes danae was carried out in an unvegetated flat adjacent to a salt marsh of the tidal Perequ& Creek (Paranagua Bay, SE Brazil). In order to mimic the natural pits dug by C. danae, we made randomly arranged holes, which were subsequently sampled together with undisturbed control sites on 6 different sampling dates, up to 18 d after disturbance. Analyses of variance were performed to determine if significant differences in macrobenthic population densities and abiotic parameters existed at different sampling times, and between control and disturbed areas. Apart from water content, physical variables did not differ significantly between disturbed and control areas, suggesting that adaptive strategies of the organisms themselves were the maln structuring factor of the recolonization process. We provide evidence that active immigration, together with passlve deposition, is a major colonization vector for the fauna of local low-energy tidal flats. Recolonization rates of the local fauna paralleled the mobility degrees of individual species or taxa. The numerically dominant surface crawler Heleobia australis and the burrower Lumbrineris tetraura, which are the more mobile species of local macrofauna, also exhibited the more rapid recolonization. There was no evidence that the catchment action of pits actually concentrated food resources, since sediment organic content was essentially similar between disturbed and control sites. Evidence for passive deposition was shown for the sedentariate species Laeonereis acuta, Capitella capitata and an unidentified nematode, whose recolonization rates were moderate and followed the sediment infill of pits. The only species to exhibit evidence of exploiting conditions created by pit simulation was the suspension-feeding bivalve Anomalocardia brasiliana that exhibited fast recolonization rates and higher abundance at disturbed sites. The infaunal predator Sigambra grubji was the only species present at significantly lower densities in pits throughout the experiment, probably due to the removal of its putative food source. Disturbances made by blue crabs, though short-lived, are abundant and frequent enough actually to maintain high densities of species that are otherwise scarce in similar tidal habitats. Such biogenic disturbances can be considered as a mechanism that allows for the persistence and numerical dominance of opportunistic species in tidal flats of local tidal creeks.

Are Infaunal Predators Important in Structuring Marine Soft-Bottom Communities?

The role of infaunal predators in structuring marine soft-bottom communities was evaluated according to these predators': 1) effects on prey density based on manipulative field experiments, 2) feeding rates, 3) effects on prey distribution, 4) effects on species diversity, and 5) interactions with their prey. Estimates of feeding rates indicate that many predatory taxa have the potential to reduce the size of prey populations and suggest that nemerteans are likely to have a larger impact on infaunal abundances than polychaetes. Infaunal predators have been demonstrated to have a significant effect on infaunal densities and to affect the spatial and temporal distribution of their prey. The effects of these predators on species diversity apparently depend on the predator and the diversity of the system. These conclusions may not be applicable to all soft-bottom habitats or all groups of infaunal predators because they are based on studies of very few taxa conducted almost exclusively in intertidal, unvegetated, mud habitats. Additional studies are needed on the effects of predation by infauna on infaunal population dynamics and on the mechanisms of interactions between predator and prey. Further investigation will probably reveal that different groups of infaunal predators play different roles in structuring soft-bottom communities.

Complex Predator‐Prey Interactions within an Estuarine Benthic Community

Indirect predator—prey interactions have been suggested to be important in a variety of communities. However, we still understand little about the factors determining the relative importance of indirect and direct effects of predation or what forms indirect predator—prey interactions may take. We examined the direct effects of predation by an omnivorous grass shrimp. Palaemonetes pugio, and the indirect effects for prey species of interactions between this shrimp and other predators in an estuarine benthic community. Direct and indirect effects of predation were examined in the field using a combination of large— and small—scale enclosure/exclosure experiments. Specific interactions and mechanisms of effects were examined in laboratory predation studies, utilizing both two—species and multi—species systems. Grass shrimp predation reduced the densities of a variety of benthic fauna, but the effects varied seasonally and with prey size. Interactions between grass shrimp and other predators took two forms: reduction of an infaunal predator by shrimp predation and predation on grass shrimp by fish. Both types of interactions had a mixed effect on lower trophic levels, with enhancement of certain benthic prey and no effect on other species. Interactions between grass shrimp and their fish predators resulted in changes in shrimp distribution independent of changes in shrimp abundance, creating spatial refungia for shrimp prey. The dynamics of indirect interactions in this community are strongly affected by the omnivorous nature of the major predators. Our results emphasize the general importance of omnivory in regulating predator—prey interactions and in predicting the relative importance of indirect predator effects.

The effect of a biologically produced structure on the benthic copepods of a deep-sea site

In deep-sea soft bottoms, a variety of organisms produce structures that persist for long periods, even after the structures are vacated. It has been hypothesized that these structures are a major source of patchiness in these communities and are important in maintaining the high diversities that characterize the deep sea. Although several studies have shown species' abundances to be correlated with structures, the mechanisms underlying the associations are not known. We attempted to discover these mechanisms, focusing on the responses of benthic copepods to mudballs made by the polychaete Tharyx luticastellus at a site at 1050 m depth in San Diego Trough (32° 52.4′N, 117°45.5′W). It was found that seven out of 40 species responded. Four were more abundant around the structure only when the worm was in residence. These species apparently benefit from some consequences of the worm's presence. Given that bacterial abundance is higher about occupied Tharyx mudballs than nearby controls, it may be that the attractiveness occupied Tharyx mudballs arises from the provision of food. Three species responded to unoccupied mudballs. We measured responses to various types of mudball mimics to determine whether responses were to a habitat provided by the mudball, to a refuge from predation in its vicinity, or to hydrodynamically mediated increases in local food availability. Two of the species appeared to use the mudball as a habitat, the third as a refuge from infaunal predators. The results indicate that biologically produced structures can persist long enough to be viewed as habitat heterogeneity by other species in the community and that this source of patchiness is important to deep-sea species.

Guild structure and foraging impact of blue crabs and epibenthic fish in a sub-estuary of Chesapeake Bay

Structure and impact of the guild of epibenthic predators foraging on infaunal communities were measured in the Rhode River, a small mesohaline subestuary of Chesapeake Bay. Measures of long-term variation in guild structure (species composition, abundance, and size), patterns of prey utilization (stomach contents), and predator exclusion experiments assessed the interaction of guild structure and function. Monthly otter trawls from 1981 to 1988 caught 38 species, w hich utilized the subestuary on a markedly seasonal cycle with peak abundances during summer months. Species composition was significantly consistent among years, with the blue crab Callinectes sapidus, a sciaenid fish Leiostomus xanthurus or, in one year, Micropogonias undulatus, and the sole Trinectes maculatus comprising the dominant members of the guild. However, abundances of all 4 dominant species fluctuated significantly among years and, except for M. undulatus, among stations. Seasonally consistent patterns of population size structure showed that: L. xanthurus was composed of only 1 yearclass recruiting in May; M. undulatus had 1 year-class with recruitment in November; T. maculatus was composed of 3 year-classes with recruitment in October; and C. sapidus Iiad a 2 year-class population with recruitment in late fall and spring. Despite marked juvenile growth over the season, ontogenetic changes in diets of the 4 species occur at sizes smaller than those comprising the populations. All predators consumed a diversity of infaunal prey early in the summer, but their diets varied significantly during the season as prey availability changed. L. xanthurus and T. maculatus consumed mainly amphipods and polychaetes early in the season, and took increasing frequencies of clam siphons later; while M. undulatus primarily consumed amphipods. C. sapidus consumed mainly whole clams, other blue crabs and fish, but shifted from amphipods early in the season to increased frequencies of clams late in the season. Dietary breadth and overlap within the guild reflected the generalized, overlapping diets of the 4 species, although dietary breadth varied with predator species and season. For all species stomach contents did not vary with sediment type. Natural densities of Macoma balthica, a major dietary component for C. sapidus, responded to annual fluctuations in crab abundance as well as to variation in clam recruitment. Experimental exclusion of predators from clams (M. balthica) placed in buckets in the subestuary significantly increased clam survival. Experimental exclusion of epibenthic predators at 5 stations in the subestuary resulted in significantly higher densities for 12 of 16 infaunal species as well as for total infaunal organisms and higher ratios of infaunal predators to prey. However, most infaunal species exhibited significant variation among stations, reflecting spatial variation in both predation intensity and prey abundances . Experimental exclusion of the epibenthic predators from plots of dyed sand showed that the guild caused major sedimentary disturbance to sediment depths of 10 cm, while low infaunal densities of subsurface deposit feeders caused comparatively little bioturbation. These experiments indicate that the guild's foraging activity not only has strong direct effects . on infaunal community structure, but that the guild also has significant indirect effects on infaunal community organization and patch dynamics which are highly variable in space and time.

The marine invertebrate fauna of a British coastal salt marsh

There are few accounts in the literature of the marine fauna of European salt marshes. The marine invertebrate populations of a coastal salt marsh in eastern England were studied for two years. A total of 32 marine species were recorded. The community was composed of a subset of species from adjacent intertidal sand and mud flats, along with a brackish water component. This gave the marsh a characteristic fauna, which was dominated by infaunal and surface‐living deposit feeders. The community showed a seasonal minimum in winter, and the infauna showed an additional summer decrease. This is attributed to increased interstitial salinities. Principal component analysis revealed the importance of the tidal gradient and the structure of the habitat in determining the community. The abundance of both epibenthic and infaunal predators were negatively correlated with the abundance of some prey. Also a small number of other pairwise negative interactions were revealed, but overall there was no strong evidence of interspecific competition exerting much influence on the community. The role of habitat heterogeneity and variation in the lateral movement of adult benthos and larval recruitment as promoters of diversity are discussed.

The role of epibenthic predators in structuring the marine invertebrate community of a British coastal salt marsh

The marine fauna of salt marshes are subjected to predation by birds, tidally feeding flatfish, crabs, prawns and small gobiid fish. The role of these epibenthic predators in structuring the community was investigated using cages to exclude predators. A range of designs of cages and partial cages was employed to control for artefacts due to caging, and sufficient cages were employed so that each cage was only sampled once to prevent the compounding of disturbance due to predation and sampling. Two mesh sizes were employed, a fine mesh excluding epibenthic predators and a coarse mesh allowing access by small crabs, prawns and gobiid fish but excluding birds and larger fish. The exclusion was maintained for 2 years. The presence of any experimental structure had a significant effect on the sedimentary regime within the cage. Epibentic predator exclusion let to an increase in infaunal predator density, but had no significant effect on the infaunal deposit feeders. There was some evidence that predators limit the surface deposit feeding gastropood Hydrobia ulvae during the winter. The gastropod Littorina littorea responded positively to the presence of any caging structure; this may be the result of changes in the availability of food, as the sides of a cage support a diatom flora which this species can exploit. The lack of a response from the infaunal deposit feeders is attributed to their horizontal mobility within the sediment. The possible interactions between epibenthic and infaunal predators are discussed.

Influence of the predatory polychaete Nephtys hombergii on the abundance of other polychaetes

Negative relations between abundance of the predatory polychaete Nephtys hombergii and values for biornass and rate of increase in 2 of its prey species, the polychaetes Scoloplos armiger and Heteromastusfiliformis, are evident in long-term (18 yr) data from tidal flats in the westernmost part of the Wadden Sea. Values for prey biornass tended to decline at high N. hombergii biomass (above ca 0.3 g m-' AFDW), whereas they tended to increase at lower levels of N. hombergii biomass. These results corroborate Schubert & Reise's (Mar. Ecol. Prog. Ser. 34: 117-124, 1986) conclusion, based on short-term enclosure experiments, that N. hornbergl~ is an important infaunal predator in the Wadden Sea.

Infaunal or semi‐infaunal bellerophont gastropods: analysis of Euphemites and functionally related taxa

Burrowing and plowing gastropods may have existed prior to the Mesozoic, contrary to the conservative tendency of categorizing Paleozoic archaeogastropods as herbivorous hardground dwellers. We propose that Euphemites and other bellerophontiform molluscs such as Praematuratroph and Beyrichidiscus make functional and paleoecological sense only if reconstructed with an internal shell adapted to an infaunal mode of life. Attributes diagnostic of a probable infaunal mode of life in fossil bellerophontiform molluscs include: (1) lack of apertural flare; (2) restricted aperture; (3) low rate of whorl expansion; (4) semi-radial aperture; (5) extensive secondary shell deposits; (6) absence of extensive collabral ornament; (7) dorsolateral or umbilical furrows; (8) color patterns indicative of mantle extension and retraction capabilities; (9) absence of shell breakage and repair; and (10) associated lithologies indicative of penetrable substrates such as mudstones. Niche diversity in the bellerophontacean molluscs was probably much greater than previously suspected. This is entirely consistent with their long geologic range. Most bellerophontaceans, particularly the Late Paleozoic forms, were probably either ‘nestling’ or semi-infaunal with the apertural margins enwrapped by mantle or mantle and foot. As such they may have been particularly susceptible to predation during the postulated Mesozoic increase in number of infaunal predators- a factor which may have been contributory to the bellerophontacean demise.

Production due to regeneration by Euclymene oerstedi (Claparède) (Polychaeta: Maldanidae) in the maritime basin of the Rance (Northern Britanny)

The polychaete species Euclymene oerstedi (Claparède) forms one of the dominant populations of the muddy fine sand community in the maritime basin of the Ranee (Northern Britanny). Analyses of regular samples of this species indicated that regeneration was an important process within the population. Of the individuals examined 22% were found to be regenerating the anterior and 41% the posterior regions of the body. The distribution of the incision sites demonstrated a distinct preference for the body sections extending from both extremities to segment 3 or 18 inclusive, with the mean recovery times being 1.5 and 1 month respectively. Biomass production from regeneration within the population is estimated as 2 g·m −2·yr −1. From a comparison between the total amounts regenerated by individuals protected by cages and those in the surrounding environment, it is suggested that posterior regeneration is essentially linked to epibenthic predation, while regrowth of the anterior region may also be a result of the activities of infaunal predators. The occurrence of these phenomena may be related to the behaviour of E. oerstedi within its tube.