Macrofaunal Production Research Articles

Benthic macrofaunal production for a typical shelf–slope–basin region in the western Arctic Ocean

Secondary production by macrofaunal communities in the western Arctic Ocean were quantified during the 4th and 5th Chinese Arctic Scientific Expeditions. The total production and P/B ratio for each sector ranged from 3.8 (±7.9) to 615.6 (±635.5)kJm−2yr−1 and 0.5 (± 0.2) to 0.7 (± 0.2) yr−1, respectively. The shallow shelves in the western Arctic Ocean exhibited particularly high production (178.7–615.6kJm−2yr−1), particularly in the two “hotspots” – the southern and northeastern (around Barrow Canyon) Chukchi Sea. Benthic macrofaunal production decreased sharply with depth and latitude along a shelf–slope–basin transect, with values of 17.0–269.8kJm−2yr−1 in slope regions and 3.8–10.1kJm−2yr−1 in basins. Redundancy analysis indicated that hydrological characteristics (depth, bottom temperature and salinity) and granulometric parameters (mean particle size, % sand and % clay) show significant positive/negative correlations with total production. These correlations revealed that the dominant factors influencing benthic production are the habitat type and food supply from the overlying water column. In the Arctic, the extreme environmental conditions and low temperature constrain macrofaunal metabolic processes, such that food and energy are primarily used to increase body mass rather than for reproduction. Hence, energy turnover is relatively low at high latitudes. These data further our understanding of benthic production processes and ecosystem dynamics in the context of rapid climate change in the western Arctic Ocean.

Macrofaunal production and biological traits: Spatial relationships along the UK continental shelf

Biological trait analysis (BTA) is increasingly being employed to improve our understanding of the ecological functioning of marine benthic invertebrate communities. However, changes in trait composition are seldomly compared with concomitant changes in metrics of ecological function. Consequently, inferences regarding the functional implications of any changes are often anecdotal; we currently have a limited understanding of the functional significance of the traits commonly used. In this study, we quantify the relationship between benthic invertebrate trait composition and secondary production estimates using data spanning almost the breadth of the UK continental shelf.Communities described by their composition of 10 traits representing life history, morphology and behaviour showed strong relationships with variations in total secondary production. A much weaker relationship was observed for community productivity (or P:B), a measure of rate of energy turnover. Furthermore, the relationship between total production and multivariate taxonomic community composition was far weaker than that for trait composition. Indeed, the similarities between communities as defined by taxonomy were very different from those depicted by their trait composition. That is, as many studies have demonstrated, taxonomically different communities may display similar trait compositions, and vice versa. Finally, we found that descriptions of community trait composition vary greatly depending on whether abundance or biomass is used as the enumeration weighting method during BTA, and trait assessments based on biomass produced better relations with secondary production than those based on abundance. We discuss the significance of these findings with respect to BTA using marine benthic invertebrates.

Pattern of benthic biomass size spectra from shallow waters in the East China Seas

Benthic biomass size spectra (BSS) and normalized biomass size spectra were constructed, and benthic secondary production was estimated by a size spectrum equation in the shallow waters in the East China Sea, ranging latitudinally from 40°N to 29°N. The BSS patterns were bimodal, two biomass peaks corresponding to meiofauna and macrofauna, respectively, separated by a trough of low biomass at 8–256 μg individual dry weight which varied in position with median sediment particle size. The BSS also displayed bimodality within meiofauna size ranges, which in most stations was due to the relative proportions of nematodes and other meiofauna taxa. Re-analysis of data from sites in the UK, South Africa, and Antarctic showed a similar bimodality in the adult species body size distribution within the meiofauna size range. Macrofaunal production estimated by the size spectrum equation was very similar to the results of Brey90 empirical equation. However, these production values were much lower than those calculated by Brey01. Different individual dry-to-wet conversion ratios, temperature deviation, and macrofauna taxonomic composition might be responsible for the between-model differences. The macrofaunal P/B ratios calculated by this equation ranged from 0.3 to 3.4 which were in accordance with values from Northern Hemisphere mid-latitudes. Meiofaunal production estimates will need further empirical support.

Brazilian sandy beach macrofauna production: a review

The state of the art of the studies on the production of Brazilian sandy beach macrofauna was analyzed on the basis of the data available in the literature. For this purpose, the representativeness of the production dataset was examined by latitudinal distribution, degree of exposure and morphodynamic state of beaches, taxonomic groups, and methods employed. A descriptive analysis was, further, made to investigate the trends in production of the more representative taxonomic groups and species of sandy beach macrofauna. A total of 69 macrofauna annual production estimates were obtained for 38 populations from 25 studies carried out between 22º56'S and 32º20'S. Production estimates were restricted to populations on beaches located on the southern and southeastern Brazilian coast. Most of the populations in the dataset inhabit exposed dissipative sandy beaches and are mainly represented by mollusks and crustaceans, with a smaller number of polychaetes. The trends in production among taxonomic groups follow a similar pattern to that observed on beaches throughout the world, with high values for bivalves and decapods. The high turnover rate (P/B ratio) of the latter was due to the presence of several populations of the mole crab Emerita brasiliensis, which can attain high values of productivity, in the dataset. Most of the studies focus on the comparison of production and, especially, of P/B ratio according to life history traits in populations of the same species/taxonomic group. Despite the importance of life history-production studies, other approaches, such as the effect of man-induce disturbances on the macrofauna, should be undertaken in these threatened environments.

Secondary production of sandy beach macrofauna: An evaluation of predictive models

During the last three decades, several predictive models have been developed to estimate the somatic production of macroinvertebrates. Although the models have been evaluated for their ability to assess the production of macrobenthos in different marine ecosystems, these approaches have not been applied specifically to sandy beach macrofauna and may not be directly applicable to this transitional environment. Hence, in this study, a broad literature review of sandy beach macrofauna production was conducted and estimates obtained with cohort-based and size-based methods were collected. The performance of nine models in estimating the production of individual populations from the sandy beach environment, evaluated for all taxonomic groups combined and for individual groups separately, was assessed, comparing the production predicted by the models to the estimates obtained from the literature (observed production). Most of the models overestimated population production compared to observed production estimates, whether for all populations combined or more specific taxonomic groups. However, estimates by two models developed by Cusson and Bourget provided best fits to measured production, and thus represent the best alternatives to the cohort-based and size-based methods in this habitat. The consistent performance of one of these Cusson and Bourget models, which was developed for the macrobenthos of sandy substrate habitats (C&BSS), shows that the performance of a model does not depend on whether it was developed for a specific taxonomic group. Moreover, since some widely used models (e.g., the Robertson model) show very different responses when applied to the macrofauna of different marine environments (e.g., sandy beaches and estuaries), prior evaluation of these models is essential.

Estimates of autumntime benthic secondary production in Laizhou Bay and adjacent Bohai Sea waters

The whole metazoan community inhabiting Laizhou Bay and adjacent Bohai Sea waters were sampled in late autumn, 2006. Secondary production estimates for macrofauna and meiofauna were made separately. Total benthic secondary production was as high as 8.38 ± 4.08 g ash-free dry weight (AFDW) m−2 a−1, which represented the autumn production level. In general, macrofaunal secondary production in Laizhou Bay was much lower than that in adjacent Bohai Sea areas. In contrast, meiofaunal secondary production in Laizhou Bay was higher than that in adjacent Bohai Sea areas. Macrofauna contributed 61% to benthic secondary production (5.09 ± 3.26 g AFDW m−2 a−1), lower than the value in previous studies in Bohai Sea. Sediment granulometric characteristics and bottom-water salinity could explain the substantial variability in the macrofauna biomass and production. Meiofaunal production was an important component of benthic production and exceeded macrofauna production under exceptional conditions, e.g. in Laizhou Bay, where macrofauna was restricted. Chlorophyll pigments (Chl-a) concentrations in sediment explained the general meiofaunal biomass and production distribution here.

Macrofaunal production along the UK continental shelf

Estimates of secondary production ( P/ B ratio and total production) by macrobenthic communities across the UK continental shelf are presented. Values for individual sampling stations varied from 0.21 to 4.1 y − 1 for community P/ B and 3.1 to 897.2 kJ m − 2 y − 1 for total production. Such data fills an important gap pertaining to our understanding of the spatial variation in production estimates for this region. Benthic production estimates varied primarily at small (inter-station) scales (24 nm), although larger-scale differences were observed. In general, the highest production estimates were exhibited by benthic communities in Cardigan Bay (Irish Sea) and East English Channel, while the lowest estimates were observed for the mid- and northern North Sea areas. The former were typified by shallow, gravelly areas of seabed which exhibit high bed tidal stress and do not thermally stratify during the summer months. On average, annelids contribute an overwhelming majority of the total production with different regions varying in the relative contributions from other phyla such as molluscs, crustaceans and echinoderms. Spatial heterogeneity of sediment granulometric variables occurred primarily between stations while those of other variables (e.g., depth, stratification, and tidal bed stress) were more regional. Although a large proportion of the spatial variation in secondary production estimates was not explained by environmental characteristics, the data indicate that such relationships are scale-dependent. Average bed temperature was a significant factor in creating some of the observed differences at large spatial scales. The possible reasons why a larger proportion of the variation in production estimates was not explained by the present study are presented.

Effects of chronic trawling disturbance on the secondary production of suprabenthic and infaunal crustacean communities in the Adriatic Sea (NW Mediterranean)

Towing gears are known to produce several kinds of effects on benthic ecosystems. As small organisms and benthic species with faster growth rates and shorter life histories can withstand the fishing mortality and benefit from reduced competition or predation, trawl fishing can enhance their proliferation. Thus, trawl fishing can lead to biomass loss and production increase, since smaller specimens are more productive than bigger ones. In the present study we evaluate the effects, if any, of trawling on benthic crustacean macrofaunal production rates. Sampling was carried out in two neighbouring sites in the central Adriatic Sea (central Mediterranean), one affected by fishing activity and one not. Production and production/biomass (P/B) ratio of 13 species of peracarid and eucarid crustaceans were estimated using the Hynes size-frequency method. Estimates measured at both sites were compared in order to test the hypothesis that higher production and P/B values should occur in the fished area rather than in the unfished one. Our results indicated that the effects on the species are more complex than expected in regard to this hypothesis, and that they depend on the ecological and behavioural characteristics of the selected species.

Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France)

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 344:39-48 (2007) - DOI: https://doi.org/10.3354/meps06947 Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France) Cédric Hubas1,2,*, Luis Felipe Artigas1, Dominique Davoult2 1FRE 2816 ELICO, Université du Littoral Côte d'Opale, Maison de la Recherche en Environnement Naturel, 32 av. Foch, Wimereux 62930, France 2UMR 7144 AD2M, Université Pierre et Marie Curie-Paris 6, Station Biologique de Roscoff, BP 74, Roscoff 29680, France *Email: hubas@sb-roscoff.fr ABSTRACT: The role of the bacterial community in the annual benthic metabolism of Roscoff Aber Bay, France, was estimated during low tide at 2 sampling sites of different trophic status, located at either end of a strong environmental gradient. The benthic gross primary production (GPP) and community respiration (BCR) were assessed in situ over 1 yr with a benthic chamber; simultaneously, bacterial production (BP) was estimated by radiotracer incorporation in slurries. BP appeared to be significantly controlled by temperature during low tide. On an annual scale, microphytobenthos gross primary production (GPPa), bacterial production (BPa), meiofauna production (MePa), macrofauna production (MaPa) and benthic community respiration (BCRa) were estimated. While the estimated annual processes were generally higher at the muddy station, our results indicated that (1) the contribution of BPa to the annual benthic community production (CPa = BPa + MePa + MaPa) increased with increasing grain size, and (2) the bacterial community can modulate its growth efficiency (BGEa) when exposed to an environmental gradient: in intertidal sediments, the production of new cells is enhanced when the organic matter concentration is lower, sustaining the development of the community on the annual scale. This behaviour was inferred to be the predominant factor affecting the trophic state of the system. KEY WORDS: Intertidal sediments · Benthic bacterial growth efficiency · Gross primary production · Community respiration Full text in pdf format PreviousNextCite this article as: Hubas C, Artigas LF, Davoult D (2007) Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France). Mar Ecol Prog Ser 344:39-48. https://doi.org/10.3354/meps06947 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 344. Online publication date: August 23, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Bacterial production in the carbon flow of a central European stream, the Breitenbach

Summary1. Over the last 30 years, many investigations have been performed on the dynamics of bacteria and organic matter in the Breitenbach, a first‐order stream in central Germany. The data now available allow a synthesis of the role of bacteria in the carbon budget, as an example of the general importance of bacteria in stream ecosystems.2. Comparing measured and estimated inputs and outputs to the ecosystem, the organic matter budget of the Breitenbach is fairly balanced: 1.84 kg C m−2 year−1 (sum of inputs) versus 1.88 kg C m−2 year−1 (sum of outputs). No major missing link remains.3. The basis of the food web in the Breitenbach is mainly allochthonous organic matter (dissolved and particulate 1.02 and 0.42 kg C m−2 year−1, respectively). Autochthonous gross primary production is 0.4 kg C m−2 year−1. Most of the organic matter leaves the stream via transport to the River Fulda (dissolved and particulate 0.74 and 0.34 kg C m−2 year−1, respectively), the rest by respiration (0.80 kg C m−2 year−1 or 43% of total outputs).4. Bacteria constitute an important part (36%) of heterotrophic biomass (average: 0.004 kg m−2 bacterial C of 0.011 kg m−2 total heterotrophic C). Bacteria also account for the major fraction (71%) of heterotrophic production: 0.20 of 0.28 kg C m−2 year−1 total heterotrophic production. Bacterial production in the Breitenbach is similar in magnitude to the estimate of photoautotrophic net primary production: both approximately 0.20 kg C m−2 year−1.5. Protozoa, the main consumers of bacteria in the Breitenbach, consume approximately one‐third of bacterial production (0.07 kg C m−2 year−1). Small metazoa (meiofauna, <0.5 mm) play a lesser role in the consumption of bacteria, consuming <0.01 kg bacterial C m−2 year−1. Larger metazoa (macrofauna, >0.5 mm) consume approximately 10% of bacterial production. Although this is a considerable amount of the carbon resources needed by the macrofauna (0.02 kg C m−2 year−1 of bacterial production versus 0.06 kg C m−2 year−1 macrofauna production plus respiration), the carbon demand of the macrofaunal community is met to a larger extent by particulate organic matter than by bacteria.6. Bacteria are the main decomposers in the Breitenbach. They account for 78% of heterotrophic respiration (0.47 of 0.60 kg C m−2 year−1) and 59% of total respiration (0.47 of 0.80 kg C m−2 year−1).

Numerical analysis of the food web of an intertidal mudflat ecosystem on the Atlantic coast of France

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 246:17-37 (2003) - doi:10.3354/meps246017 Numerical analysis of the food web of an intertidal mudflat ecosystem on the Atlantic coast of France Delphine Leguerrier1, Nathalie Niquil1,*, Nicolas Boileau2, Jadwiga Rzeznik1,3,4, Pierre-Guy Sauriau5, Olivier Le Moine6, Cédric Bacher5 1Laboratoire de Biologie et Environnement Marins, EA 3168, Université de La Rochelle, Pôle Sciences et Technologie, avenue Michel Crépeau, 17042 La Rochelle Cedex 1, France 2Ligue pour la Protection des Oiseaux (LPO), Réserve Naturelle de Moëze-Oléron, Plaisance, 17708 Saint-Froult, France 3ESA 8044 CNRS-BIM, Muséum National d¹Histoire Naturelle, 57 rue Cuvier 75231 Paris, France 4University of Gdansk, Institute of Oceanography, Marine Biology and Ecology Department, Al. Pilsudskiego 46, 81-378 Gdynia, Poland 5Centre de Recherche sur les Ecosystèmes Marins et Aquacoles (CREMA/UMR10 CNRS-IFREMER), BP 5, 17137 L¹Houmeau, France 6Laboratoire Conchylicole Poitou-Charentes (LCPC), IFREMER, BP 133, 17390 La Tremblade, France *Corresponding author. Email: nniquil@univ-lr.fr ABSTRACT: Food web modelling is an ideal way to describe ecosystems, because it accounts for the totality of the relationships between its various components. One difficulty of such an approach, however, lies in the lack of data and information about some ecological relationships, resulting in underdefined systems. Inverse analysis can serve to complete steady-state food webs where the number of direct flow measurements is insufficient relative to the actual number of flows. We applied this method to the intertidal mudflat ecosystem of Brouage (eastern Marennes-Oléron Bay, SW France) and estimated the annual average carbon flows between the compartments of a coupled benthic and pelagic trophic food web from primary producers (microphytobenthos and phytoplankton) to top predators (fish and birds). The resulting network was very sensitive to the primary production of the microphytobenthos which was the most important flow in the system. Sensitivity analyses demonstrated the need for additional data on the nekton, pelagic protozoa, and bacterial compartments. The resulting network showed high bacterial activity, but indices resulting from network analysis showed low cycling in comparison with other ecosystems. The meiofauna had a small biomass, but constituted a very active compartment compared to the macrofauna. Bird production was limited by macrofaunal production. Macrofaunal production reached the maximum allowed by the analysis. The intertidal mudflat ecosystem at Brouage is dominated by benthic production (including benthic primary producers, secondary producers, and predators) with an input of phytoplankton primary production. KEY WORDS: Carbon flow · Inverse analysis · Food web · Network analysis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 246. Online publication date: January 16, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Macrofaunal secondary production in a lagoon of the Po River Delta: An evaluation of estimation methods

The utility of calculating macrobenthic secondary production with estimation methods that have less rigorous data requirements than most classical techniques was investigated at three subtidal sites located in the Sacca di Goro, a brackish lagoon in the Po Delta area (Upper Adriatic Sea). Of the four estimation methods used, two that were based solely on biomass and individual body weight gave the lowest production estimates, while the two that also accounted for population or environmental parameters yield ed higher values. Production estimates ranged from 16.6 to 107.4 g ash free dry weight m‐2 yr‐1 over the period studied. The sec ondary production of the few taxa for which growth and life‐his tory had been formerly estimated in the Po Delta area, was calcu lated by means of a classical technique and compared with fig ures obtained with such empirical models. Average error varied from 13.5% to 75.6%, depending on the method used. Although they may be not preferable to classical techniques, empirical methods can provide a reliable and practical means of estimating secondary production in studies where logistical or economical constraints are operating.

Benthic activity in sediments of the northwestern Adriatic Sea: sediment oxygen consumption, macro- and meiofauna dynamics

Benthic activity was examined at three stations (18 m water depth) in the northwestern Adriatic Sea. Carbon mineralisation rates, as based on sediment oxygen consumption rates, ranged from 54 to 89 g C m −2 y −1. The relatively high carbon mineralisation rates, large macrofaunal biomass (9 to 16 g C m −2) and macrofaunal production (11 to 19 g C m −2 y −1) provide evidence of high organic-matter input and intense benthic–pelagic coupling. This is further supported by the high dominance of the suspension-feeding bivalve Corbula gibba, which accounts for 52 to 63% of the total annual macrofaunal biomass production. Although the infaunal distribution of total macrofauna showed a sharp decline in densities and biomass with depth into the sediment, different patterns within the dominant taxa were observed. Whilst the bivalve Corbula gibba and the amphipod Ampelisca sp. were restricted to the surface layer, other species such as the dominant bivalve Mysella sp. and the gastropod Hyala sp. were not confined to a specific depth level and the majority of the populations occurred deeper than 5 cm into the sediment. Bioturbation, based on the occurrence of macrofauna, extended to at least 20 cm. Nematodes and foraminifera together formed 80 to 90% of the meiofaunal community in the upper 5 cm of the sediment. Annual mean densities ranged from 3.40 to 6.07×10 6 ind. m −2. Maximum abundance of meiofauna was not encountered at the station where maximum macrofaunal activity was recorded, and this could reflect the negative effect of biological interaction on meiofaunal densities in areas that have a high food supply.

The production and trophic ecology of shallow-water fish assemblages in southern Australia III. General relationships between sediments, seagrasses, invertebrates and fishes

Fishes and benthic invertebrates were sampled in seagrass and unvegetated habitats at 14 localities across southern Australia in order to determine any consistent relationships between animal production, fish consumption and environmental parameters over a large spatial scale. Most of the features identified in a related study at Western Port were confirmed over the extended geographic range; however, an exception was that the production of fishes in the smallest size-classes (i.e. <1 g wet weight) was not consistently greater in seagrass habitat than unvegetated habitat. The more important characteristics of seagrass and unvegetated habitat types identified in the extended study were (1) more fish species were associated with seagrass habitat than unvegetated habitat, (2) the majority of small-fish species in both habitat types fed on crustaceans, with relatively few species capable of utilising algae and virtually no species utilising seagrass, (3) the few species that did ingest algae often occurred in high abundance, (4) the size of prey eaten by fishes increased consistently with fish size, with prey length averaging ≈6% of fish length, (5) abundant large fish species generally consumed smaller prey than rarer large fish species at the same body size, (6) greater benthic invertebrate and demersal fish production occurred in seagrass habitat than in unvegetated habitat, (7) most of the production of crustaceans >1-mm sieve size was ingested by fish predators while only a small proportion of non-crustacean benthic production was consumed. Fish production was highly correlated with crustacean production and seagrass biomass, and was negatively correlated with wave exposure (measured as fetch) across the range of sites. The estimated production of crustaceans was highly correlated with the biomass of seagrass material and also with the proportion of particles <63 μm in the sediments. The overall relationships between macrofaunal production ( M; mg · m −2 · day −1), macrocrustacean production ( C; mg · m −2 · day −1), demersal fish production ( D; mg · m −2 · day −1), fetch ( F; km), seagrass biomass ( L; g · m −2), proportion of particles <63 μm ( S;%) and temperature ( T; °C) were: ln M = 1.41 + 0.088 ln ( L + 1) + 0.38 ln S + 0.89 ln T, ln C = −0.93 + 0.27 ln ( L + 1) + 0.22 ln S + 0.89 ln T, ln D = −1.23 − 0.62 ln F + 0.36 ln ( L + 1) + 1.04 ln T. These regression equations can be used as models to predict the production of macrofauna, crustaceans and small fishes at unexamined sites. When predictions were compared with estimates of annual production at the eight sites previously examined in Western Port, most predictions lay between 50 and 200% of measured values. Additional work in Australia and overseas should allow these models to be refined.

Composition, Abundance, Biomass, and Production of Macrofauna in a New England Estuary: Comparisons among Eelgrass Meadows and Other Nursery Habitats

Quantitative suction sampling was used to characterize and compare the species composition, abundance, biomass, and secondary production of macrofauna inhabiting intertidal mud-flat and sand-flat, eelgrass meadow, and salt-marsh-pool habitats in the Nauset Marsh complex, Cape Cod, Massachusetts (USA). Species richness and abundance were often greatest in eelgrass habitat, as was macroinvertebrate biomass and production. Most striking was the five to fifteen times greater rate of annual macrofaunal production in eelgrass habitat than elsewhere, with values ranging from approximately 23–139 g AFDW m2 yr−1. The marsh pool containing widgeon grass (Ruppia maritima) supported surprisingly low numbers of macroinvertebrates, probably due to stressfully low dissolved oxygen levels at night during the summer. Two species of macroinvertebrates, blue mussels (Mytilus edulis) and to a lesser extent bay scallops (Argopecten irradians), used eelgrass as “nursery habitat.” Calculations showed that macroinvertebrate production is proportionally much greater than the amount of primary production attributable to eelgrass in the Nauset Marsh system, and that dramatic changes at all trophic levels could be expected if large changes in seagrass abundance should occur. This work further underscores the extraordinarily large impact that seagrass can have on both the structure and function of estuarine ecosystems. *** DIRECT SUPPORT *** A01BY070 00006

Resource limitation and fish predation: their importance to mobile epifauna associated with JapaneseSargassum.

The possibility that resource limits constrain the growth of mobile epifaunal populations associated withSargassum patens plants was investigated by placing plants and associated animals into field microcosms which excluded fish predators, and then comparing faunal abundance and size-structure changes in different microcosm treatments with field populations. Four different micrososm treatments were set up: two treatments containing defaunated plants inoculated with caprellid amphipods, and two control treatments with natural faunas. The estimated secondary production of faunas enclosed in all microcosm treatments rapidly settled on a constant value (5 mg/day) which was similar to that determined in experiments conducted in Western Australia using the same microcosms but for faunas associated with a seagrass rather than a macroalga. These results support the hypothesis that the secondary production of epifaunal communities associated with macrophytes is constrained by quantifiable food resource ceilings. Predation by the most common fish species in the area, the wrasseHalichoeres tenuispinis, did not appear to alter macrofaunal production in theS. patens bed; however, it did greatly affect the faunal size-structure by eliminating most of the larger animals. The majority of epifaunal animals ≥ 2.0 mm sieve-size were consumed byH. tenuispinis, while negligible numbers of 0.5-mm sieve-size animals were captured. We postulate that food resource ceilings and predatory size-selectivity are widespread phenomena, affecting epifaunal populations at a variety of locations. Predation is predicted to generally increase rather than decrease faunal abundance because the consumption of each large invertebrate by a predator frees sufficient resources to feed several smaller individuals.

Effects of Disturbance on Benthic Functional Structure and Production in Mountain Streams

To assess the role of macrofauna consumers in organic matter dynamics of headwater streams, we applied seasonal insecticide treatments to a southern Appalachian Mountain stream and compared benthic community structure between this and two other streams. Production was estimated in the two major habitats: mixed cobble-gravel-sand substrate and bedrock outcrop. Using the proportional availability of the habitats in each stream, production over the entire stream was measured. Annual habitat-weighted production in the untreated streams during the two study years ranged from 8.9 to 14.0 g AFDM m^-2 yr^-1, 81 to 86% of which was attributed to insects. Habitat-weighted production was distributed rather evenly among the collector-gatherer (32-41%), shredder (23-31%), and predator (28-33%) functional groups. Collector-filterer and scraper groups accounted for less than 9% of total habitat-weighted production in all three streams. Insecticide applications resulted in dramatic changes in the macrofaunal community. Annual habitat-weighted production (4.4 g m^-2 yr^-1) in the treated stream decreased by 62% from Yr 1 to Yr 2, with insects contributing only 45% to total production. Oligochaetes, several Diptera, dragonflies, and copepods composed most of the production during treatment. Although habitat-weighted production of all functional groups was lower in the treatment year than in the pre-treatment year, collector-gatherer production decreased the least (21% reduction) and dominated overall production during treatment. Production of the other functional groups decreased by 71-94% between the two years. The changes in macrofaunal community structure and production observed in the insecticide treated stream were much greater than between-year changes in the reference stream, despite the occurrence of a record drought in Yr 2. The effect of the two different disturbances on overall production differed not only in magnitude but also in direction, with production in the reference stream increasing (12% over Yr 1) during the drought year. Resource ingestion was estimated using values of functional group production. Estimates of ingestion suggested that the major functional groups were ingesting a fairly large portion of available resources in the untreated streams. Collector-gatherers consumed 34-64% of total annual habitat-weighted fine particulate organic matter. Shredders consumed an estimated 28-47% of average annual standing crop of leaves, and predators ingested 67-79% of total macrofaunal production. Insecticide treatments resulted in much lower levels of resource ingestion: 26%, 4%, and 50% for collector-gatherers, shredders, and predators, respectively. Our results show the importance of using estimates of production when assessing disturbance effects on macrofaunal communities, since abundances greatly underestimated the impact of insecticide treatments. Biomass estimates, though providing better measures of disturbance than abundances, tended to overestimate overall macrofaunal losses because of the disproportionate influence of large, slow growing taxa such as crayfish.

Trophic relationships in tidal flat areas: To what extent are tidal flats dependent on imported food?

In four intertidal areas of ‘Königshafen’ (island of Sylt, FRG), biomass and production of macrozoobenthos were measured monthly in 1980 and 1984. The areas were characterized by different macrofauna assemblages ( Nereis-Corophium belt, seagrass bed, Arenicola flat and mussel bed). Biomass and production of macrofauna were partitioned with regard to food preference of single species as well as to the food availability within their habitat. In the Nereis-Corophium belt, seagrass bed and the Arenicola flat, most of the secondary production of the macrofauna was formed by grazing animals. Secondary production of mussel beds was nearly 10 times higher than in the other three assemblages. The suspension feeder assemblage depended on planktonic food imported from outside the bay. Considering the secondary production of the total tidal flat area, suspension feeders dominated the other trophic groups, indicating a key position of this group relative to the other macrofaunal assemblages. Mussel beds regulate the seston input to other communities situated further landward. Because of this dominance of the suspension feeder group, the energy and material flow of the total tidal flat is strongly dependent on the seston input from the coastal waters of the North Sea or from other parts of the Wadden Sea.

The influence of plant structure on the species richness, biomass and secondary production of macrofaunal assemblages associated with Western Australian seagrass beds

Considerable differences were found in the species of macrofauna present at Cliff Head and Seven Mile Beach, two coastal seagrass-dominated sites with differing wave exposure in Western Australia. The differences in the faunas between sites were generally much greater than differences between the various habitats within each site. The species richnesses of the faunal assemblages in different seagrass habitats nevertheless followed consistent patterns at both sites, with rankings of habitats from species richest to poorest as: turf, Amphibolis frond, Posidonia, Halophila/Heterozostera, Amphibolis rhizome, detached macrophyte and unvegetated sediments. The faunas associated with artificial seagrass clumps placed in three habitats at each site showed similar patterns of species richness, with significant differences between habitats and between sites but with no site—habitat interaction. Only one environmental factor, the diversity of food resources, was found to correspond with these patterns of faunal species richness. Macrofaunal abundance, biomass and production were all much greater in vegetated than unvegetated habitats. These faunal parameters nevertheless varied greatly between habitats and between sites. Amongst the vegetated habitats, estimated annual secondary production was highest in the Amphibolis rhizome (47.2 g AFDW · m −2 · yr −1) and least in the Halophila/Heterozoslera (24.3 g AFDW · m −2 · yr −1) habitats at Cliff Head. The converse situation was found at Seven Mile Beach, with the Halophila/Heterozostera habitat (42.2 g AFDW · m −2 · yr −1) having nearly four times the estimated macrofaunal production of the Amphibolis rhizome habitat (11.7 g AFDW · m −2 · yr −1). These differences between sites are explained by reference to the distribution of plant debris bound at the sediment surface. Similar relationships between secondary production, the biomass of debris and the biomass of live plant material were independently formulated for the two sites, with the general equation for both sites being P = 13.8 + 0.22 · D + 0.039 · S ( n = 12, r 2 = 0.61) where P is annual macrofaunal production (g · m −2 · yr −1), D is the mean biomass of debris (g· m −2) and S is the mean biomass of live plant material (g · m −1). Neither the biomass of seagrass rhizomes nor the biomass of drifting debris were significantly correlated with secondary production.

Benthic Macrofaunal Production of Browns Bank, Northwest Atlantic

Benthic macrofauna of the coarse sediments of Browns Bank, off southwest Nova Scotia, Canada were sampled with a modified 0.5-m2 Van Veen grab; 29 stations from 1983 to 1985. Production was estimated from alcohol-stored biomass by multiplying by the annual turnover ratio, P:B, of each species. The latter was determined from an empirically derived relationship using known or estimated lifespans. Benthic macrofaunal production averaged 64 g wet weight∙m−2∙yr−1 on Browns Bank, markedly lower than the 193 g wet weight∙m−2∙yr−1 in the mixed and finer sediments of the Bay of Fundy. Other community characteristics, such as the number of polychaete and amphipod species for the two areas were similar, which we attribute to the similar geological ages of the sediments. Prey consumed by juvenile age 0 haddock (Melannogrammus aeglefinus) consist mostly of deposit-feeding macroinfauna which produce ~1.8 × 104 t wet biomass per year, representing ~8% of the total production of Browns Bank. Two linked hypotheses are proposed to account for the suitability of Banks as juvenile gadid feeding grounds: rapid rates of suspension of macrofauna by strong tidal currents; and drifting animals are of a suitable size and kind for juvenile haddock feeding.