Sulfate-Reducing Bacteria in Tubes Constructed by the Marine Infaunal Polychaete Diopatra cuprea

Marine infaunal burrows and tubes greatly enhance solute transport between sediments and the overlying water column and are sites of elevated microbial activity. Biotic and abiotic controls of the compositions and activities of burrow and tube microbial communities are poorly understood. The microbial communities in tubes of the marine infaunal polychaete Diopatria cuprea collected from two different sediment habitats were examined. The bacterial communities in the tubes from a sandy sediment differed from those in the tubes from a muddy sediment. The difference in community structure also extended to the sulfate-reducing bacterial (SRB) assemblage, although it was not as pronounced for this functional group of species. PCR-amplified 16S rRNA gene sequences recovered from Diopatra tube SRB by clonal library construction and screening were all related to the family Desulfobacteriaceae. This finding was supported by phospholipid fatty acid analysis and by hybridization of 16S rRNA probes specific for members of the genera Desulfosarcina, Desulfobacter, Desulfobacterium, Desulfobotulus, Desulfococcus, and Desulfovibrio and some members of the genera Desulfomonas, Desulfuromonas, and Desulfomicrobium with 16S rRNA gene sequences resolved by denaturing gradient gel electrophoresis. Two of six SRB clones from the clone library were not detected in tubes from the sandy sediment. The habitat in which the D. cuprea tubes were constructed had a strong influence on the tube bacterial community as a whole, as well as on the SRB assemblage.     

Accurate quantification of the influence of benthic macro- and meio-fauna on the geometric properties of estuarine muds by micro computer tomography

This paper describes the novel application of high resolution micro computer tomography (microCT) to the quantification of the properties of marine biogenic structures. CT scanning has been used to examine sediments in the past but the resolution of most previous techniques has been dependent upon commercial medical CT scanners which only have a slice thickness of ≥ 0.625 mm. In addition adequate software has not previously been available to rapidly quantify all the properties of biogenic structures. The microCT technique developed here used a standard core sample of estuarine sediment and new software was developed to calculate the axial variation of the following burrow parameters: number, diameter, volume, surface area and density. The increased resolution has resulted in the first quantification of meiofaunal burrow structures.A test core has shown, as an example, that the total volume of burrows created by macrofaunal organisms decreased from 827 mm³, within the top 15 mm of the core, to 204.2 mm³ at a depth 60 -75 mm within the core. Total burrow surface area decreased from 1883 mm² to 512 mm², for these depth ranges, respectively and burrow diameter ranged from 2.37-2.58 mm, remaining fairly constant between depths. Meiofaunal burrow structures decreased from 1.3-0.1 mm³ within the top 6 mm of the core with burrow surface area decreasing from 33.52-3.4 mm². Again, burrow diameter remained relatively constant, ranging from 0.23-0.25 mm.Quantification to this resolution is required to identify the impact of infaunal organisms on factors such as oxygen penetration, vertical and horizontal (across burrow walls) gradients in redox conditions and chemical/nutrient speciation and flux. The quantification of these burrow properties will improve the ability to examine the interrelationships between chemical, physical and biological processes and their role in ecological functioning. The present study indicates that there is potential for further development of this software to allow more detailed analysis of burrow structures and surface features including parameters such as burrow length, shape and sediment surface roughness.     

Influences of Infaunal Burrows on the Community Structure and Activity of Ammonia-Oxidizing Bacteria in Intertidal Sediments

Influences of infaunal burrows constructed by the polychaete (Tylorrhynchus heterochaetus) on O₂ concentrations and community structures and abundances of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in intertidal sediments were analyzed by the combined use of a 16S rRNA gene-based molecular approach and microelectrodes. The microelectrode measurements performed in an experimental system developed in an aquarium showed direct evidence of O₂ transport down to a depth of 350 mm of the sediment through a burrow. The 16S rRNA gene-cloning analysis revealed that the betaproteobacterial AOB communities in the sediment surface and the burrow walls were dominated by Nitrosomonas sp. strain Nm143-like sequences, and most of the clones in Nitrospira-like NOB clone libraries of the sediment surface and the burrow walls were related to the Nitrospira marina lineage. Furthermore, we investigated vertical distributions of AOB and NOB in the infaunal burrow walls and the bulk sediments by real-time quantitative PCR (Q-PCR) assay. The AOB and Nitrospira-like NOB-specific 16S rRNA gene copy numbers in the burrow walls were comparable with those in the sediment surfaces. These numbers in the burrow wall at a depth of 50 to 55 mm from the surface were, however, higher than those in the bulk sediment at the same depth. The microelectrode measurements showed higher NH₄⁺ consumption activity at the burrow wall than those at the surrounding sediment. This result was consistent with the results of microcosm experiments showing that the consumption rates of NH₄⁺ and total inorganic nitrogen increased with increasing infaunal density in the sediment. These results clearly demonstrated that the infaunal burrows stimulated O₂ transport into the sediment in which otherwise reducing conditions prevailed, resulting in development of high NH₄⁺ consumption capacity. Consequently, the infaunal burrow became an important site for NH₄⁺ consumption in the intertidal sediment.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.     

Effect of lowered salinity on the survival,condition and reburial of Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae)

Abstract Mass mortalities of fauna are known to occur in estuarine environments during flood events. Specific factors associated with these mortalities have rarely been examined. Therefore, the effect of exposing, to lowered salinities, an infaunal bivalve that is susceptible to mass mortalities during winter flooding in a southern Australian estuary was tested in the present study. In a laboratory experiment, low salinities (≤6 parts per thousand [ppt]), which mimicked those expected during flood events in the Hopkins River estuary, were shown to affect Soletellina alba, both lethally and sublethally. All bivalves died at 1 ppt, while those at 6 ppt took longer to burrow and exhibited a poorer condition than those at 14 and 27 ppt. The limited salinity tolerance of S. alba suggests that lowered salinities are a likely cause of mass mortality for this species during winter flooding.     

New bivalve burrows from the mid-Holocene of northeastern Buenos Aires Province (Argentina): ichnotaxonomy and ethology

Oblongichnus vulpesi n. isp. is herein described as amygdaloid, oval or cleft-shaped burrows with a lining of variable thickness and an oblong to quadrangular elongated shaft from the mid-Holocene of the Destacamento Río Salado Member. Valves of the solenid bivalve species Solen tehuelchus were found within the burrows, indicating that this razor clam is the tracemaker. This new finding corroborates the validity of Oblongichnus and previous interpretation that the burrow was produced by infaunal, filter feeding bivalves with a foot of very limited horizontal movements. We found that the origin of oblong elongate bivalves may be dated back to the Ordovician, while an infaunal radiation likely occurred during late Paleozoic. We interpret that O. vulpesi was made in a moderate energy subtidal marine setting during the last marine highstand.     

Particle size selection in individuals from epifaunal versus infaunal populations of the nereidid polychaete Neanthes succinea(Polychaeta: Nereididae)

Neanthes succinea (Frey & Leuckart, 1847) is a common nereidid polychaete of both epifaunal and infaunal estuarine habitats. The gut contents of individuals collected from two epifaunal and two infaunal habitats are compared. Our a priori expectation was that individuals from epifaunal habitats would be classified as macrophagous with guts indicating carnivory and/or macroalgal herbivory, while individuals from infaunal habitats would be classified as microphagous with guts indicating deposit feeding. At all four locations gut contents indicated deposit feeding with little indication of macrophagous feeding. Average particle sizes for mineral grains did not differ between the four collection sites. For the two infaunal locations mean size of the mineral grains in gut contents was significantly smaller than ambient sediments. In addition to mineral grains, guts contained diatoms, dinoflagellates, macrophytic detritus, protozoan tests, and a variety of metazoans. Our study demonstrates that caution is necessary when inferring feeding type from morphology and that population and habitat specific differences in diet can occur within the same species.     

Firmground crustacean burrow systems (Glossifungites ichnofacies) in marine shelf deposits,Paleocene Clayton Formation,Alabama, USA

The Paleocene (Danian) Clayton Formation of western Alabama, USA, includes multiple marine shelf parasequences, each comprising a relatively thick marl, capped by a thin limestone, the latter variably reflecting marine flooding episodes. The marls host relatively large firmground burrow systems that penetrate 50–60 cm beneath, and are cast by, superjacent limestones. Excavation of two partially exposed burrow systems – one beneath a highstand parasequence-bounding flooding surface and the other beneath an overlying coplanar sequence boundary/transgressive surface (SB/TS) – reveals complex, primarily horizontal, irregularly branching networks. The former, allied with Thalassinoides paradoxicus, lacks wall bioglyphs, whereas the latter, allied with Spongeliomorpha iberica, is characterized by pervasive, mainly rhombohedral wall bioglyphs that reflect a relatively more firm substrate. Contrasts between these burrow systems are consistent with sequence stratigraphical context and inferred differences in the mechanism and magnitude of depositional hiatuses responsible for firmground development. Both excavated burrow systems likely represent cumulative structures produced by multiple organisms over extended periods of time. The cumulative nature and potential taphonomic biases associated with these and comparable burrow systems in the stratigraphical record preclude confident interpretation of tracemakers and their behaviours. The Clayton burrow systems likely were produced by one or more species of decapod crustacean that engaged in suspension-feeding, surface detritus feeding, gardening or some combination thereof.     

atz gene expressions during atrazine degradation in the soil drilosphere

One of the various ecosystemic services sustained by soil is pollutant degradation mediated by adapted soil bacteria. The pathways of atrazine biodegradation have been elucidated but in situ expression of the genes involved in atrazine degradation has yet to be demonstrated in soil. Expression of the atzA and atzD genes involved in atrazine dechlorination and s‐triazine ring cleavage, respectively, was investigated during in situ degradation of atrazine in the soil drilosphere and bulked samples from two agricultural soils that differed in their ability to mineralize atrazine. Interestingly, expression of the atzA gene, although present in both soils, was not detected. Atrazine mineralization was greatest in Epoisses soil, where a larger pool of atzD mRNA was consistently measured 7 days after atrazine treatment, compared with Vezin soil (146 vs. 49 mRNA per 10 ⁶ 16S rRNA, respectively). Expression of the atzD gene varied along the degradation time course and was profoundly modified in soil bioturbated by earthworms. The atzD mRNA pool was the highest in the soil drilosphere (casts and burrow‐linings) and it was significantly different in burrow‐linings compared with bulk soil (e.g. 363 vs. 146 mRNA per 10 ⁶ 16S rRNA, 7 days after atrazine treatment in Epoisses soil). Thus, consistent differences in atrazine mineralization were demonstrated between the soil drilosphere and bulk soil. However, the impact of bioturbation on atrazine mineralization depended on soil type. Mineralization was enhanced in casts, compared with bulk soil, from Epoisses soil but in burrow‐linings from Vezin soil. This study is the first to report the effects of soil bioturbation by earthworms on s‐triazine ring cleavage and its spatial variability in soil.     

Screening of hexavalent chromium biosorbent from marine algae

 A highly chromate-selective biosorbent with high adsorption capacity was found by examining the chromate adsorption capacities of 48 species of red, brown, or green marine algae sampled from the east coast of Korea. As a result of screening, a red marine alga showed excellent adsorption characteristics. It was identified as Pachymeniopsis sp. The timing of the sampling of Pachymeniopsis sp. did not affect the adsorption capacity of the alga but the optimum period for mass collection was April–May. The alga also showed high selectivity for chromate and its adsorption capacity for other heavy metal ions such as cadmium and manganese was relatively low. An investigation of the adsorption isotherm of Pachymeniopsis sp. as a dried powder for chromate adsorption at 25 °C showed Langmuir-type dependence. The maximum chromate adsorption capacity of the selected alga was about 225 mg/g. The desorption of adsorbed chromate from Pachymeniopsis sp. was done by treating samples with 1 N NaOH. It was confirmed that ion exchange type adsorption was observed with anion exchangers but not with cation exchangers. Therefore it is believed that the chromate adsorption is based on the anionic exchange of Pachymeniopsis sp. Received: 6 October 1999 / Received last revision: 19 January 2000 / Accepted: 4 February 2000     

Screening of hexavalent chromium biosorbent from marine algae

A high-chromate-selective biosorbent with high adsorption capacity was sought by examining the chromate adsorption capacities of 48 species of red, brown, or green marine algae sampled from the east coast of Korea. Screening showed a red marine alga to have the most excellent adsorption characteristics among them, and it was identified as Pachymeniopsis sp. The period at which Pachymeniopsis sp. was sampled did not affect the adsorption capacity of the alga, but the optimum period for mass collection was April to May. The alga also showed high selectivity for chromate since its adsorption capacity for other heavy metal ions such as cadmium and manganese ions was relatively low. An investigation of the adsorption isotherm of dried powder of Pachymeniopsis sp. for chromate adsorption at 25 °C showed a Langmuir-type dependence. The maximum chromate adsorption capacity of the selected alga was about 225 mg/g. Desorption of the adsorbed chromate from Pachymeniopsis sp. was done by treating the sample with 1 N NaOH. It was confirmed that ion exchange type adsorption was observed with an anion exchanger but not with a cation exchanger. It is therefore believed that the chromate adsorption is based on anionic exchange of Pachymeniopsis sp. Received: 6 October 1999 / Accepted: 4 February 2000     

Burrow architecture,family composition and habitat characteristics of the largest social African mole-rat: the giant mole-rat constructs really giant burrow systems

Among African mole-rats, the giant mole-rat Fukomys mechowii is the largest social species. Despite several attempts to study a free-living population, information on its biology from natural habitats is very scarce. We mapped two neighbouring burrow systems of the giant mole-rat in a miombo woodland in Zambia. We provide information on the size and kin structure of the respective mole-rat families, architecture of their burrow systems, and characteristics of the food supply and soil around the two mapped and additional ten burrow systems. Both uncovered burrow systems were very large (total lengths, 2,245 and 743 m), making them the largest burrow systems ever mapped. Food resources around the additional ten burrow systems had a clumped distribution (standardized Morisita index of dispersion = 0.526), but a relatively high biomass (298 ± 455 g m⁻²). This, together with favourable soil conditions even in the advanced dry season (cone resistance, 328 ± 50 N m⁻²; soil density, 1.36 ± 0.06 g cm⁻³) indicates relatively hospitable ecological conditions. Both food supply and soil conditions were comparable with the conditions found in a miombo habitat of the solitary silvery mole-rat in Malawi. This suggests that there are no ecological constraints which would preclude the solitary life of a subterranean herbivore from the examined habitat. Microsatellite analysis supported the assumption that giant mole-rats live in monogamous multigenerational families with only one breeding pair of non-related animals and their offspring. The mean family size is consistent with previous findings on this species and comparable to that found in other Fukomys species studied thus far.     

Experimental Measurements of the Adsorption of Bacillus subtilis and Pseudomonas mendocina Onto Fe-Oxyhydroxide-Coated and Uncoated Quartz Grains

In this study, we compared the adsorption of the gram-positive bacterium Bacillus subtilis with adsorption of the gram-negative bacterium Pseudomonas mendocina onto Fe-oxyhydroxide-coated and uncoated quartz grains as a function of pH and bacteria: mineral mass ratio. We studied metabolically-inactive cells in order to focus on the initial bacterial attachment mechanisms. The data show that the presence of Fe-oxyhydroxide-coatings on quartz surfaces significantly enhances the adsorption of bacteria and that in general the extent of adsorption decreases with increasing pH and with decreasing bacteria: mineral mass ratio. B. subtilisadsorbs to a greater extent than does P. mendocina onto the surface of the Fe-coated quartz. The adsorption behavior appears to be controlled by the overall surface charge of both bacterial and mineral surfaces. We model the adsorption data using a semi-empirical chemical equilibrium model that accounts for the site speciation of the adsorbing surfaces. Models describing bacterial adsorption to Fe-oxyhydroxide-coated quartz can account for changes in pH and bacteria: mineral mass ratio using one set of equilibrium constants.     

Bifungites, trace fossils from Devonian-Mississippian rocks of Pennsylvania and Montana,U.S.A

The trace fossil Bifungites Desio 1940, first recognized in Late Devonian rocks of Libya and later in Algeria, is common in Late Devonian rocks of Montana, Pennsylvania, Ohio, and Michigan, and Early Mississippian rocks of Pennsylvania. Its manifestations are given for seven stratigraphic units from forty localities in Pennsylvania, Montana, and Michigan.Bifungites commonly occur on bedding planes and consist of a horizontal shaft with doubly terminating arrow- or dumb-bell-shaped projections. Less apparent are paired vertical cylindrical sediment-filled tubes connected at their base to the bi-arrow or dumb-bell shaft. The combination represents the mud or silt casting of an inverted pi-shaped, μ, infaunal tubular burrow (domichnia). Siltstone slabs have been transversely sectioned to reveal this π-shaped, double-arrow burrow pattern with undisturbed stratification between the vertical tubes.Three new ichnospecies are proposed based on markedly different size and shape of the fossil traces in three stratigraphic zones. A Late Devonian Girard Shale type is the smallest with wide, short arrows on a narrow shaft whose median overall length is 12.5 mm. The latest Devonian Sappington type has well-formed, shortly barbed arrow terminations and median length of 28 mm. An Early Mississippian Meadville type is the largest with median length of 36 mm and prominently barbed broad arrows.The Bifungites organism is unrecognized but it was probably a sedentary, soft-bodied, infaunal suspension-feeding animal inhabiting shallow nearshore marine and brackish water environments. The identified biota directly or indirectly associated with Bifungites is extremely limited to a few brachiopods, clams, and other trace fossils.     

Tithonia oxfordiana,a new irregular echinoid associated with Jurassic seep deposits in south‐east France

Abstract: The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep‐marine middle Oxfordian deposits are exposed in south‐east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chemosynthetic organic matter produced by such bacteria. In view of the fact that T. oxfordiana is the sole species of the Jurassic genus Tithonia known from Oxfordian strata, it is postulated that chemoherms possibly acted as refugia for these peculiar echinoids, which have an episodic record between the Callovian and Valanginian.     

Does invasion of hybrid cordgrass change estuarine food webs?

Studies examining the impacts of introduced species on food webs often focus on the top-down effects of introduced predators. However, marine and estuarine systems have been invaded by plants that have the potential to alter carbon and nitrogen sources available to consumers. In San Francisco Bay, California, USA, hybridized cordgrass Spartina alterniflora × foliosa is adding C₄ carbon biomass to this system. We used natural abundances of stable isotopes of carbon and nitrogen to examine whether infaunal and epifaunal food webs reflected the large detrital input from hybrid Spartina. We compared stable isotope signatures among macrofaunal invertebrate consumers collected in hybrid Spartina, native S. foliosa, or unvegetated mudflats. We found no additional shift towards hybrid Spartina in hybrid areas. Structural changes brought about by an invasive ecosystem engineer, specifically increased biomass and detrital inputs, do not necessarily result in its increased incorporation into the food web.     

Distribution and ecological role of the non-native macroalga Gracilaria vermiculophylla in Virginia salt marshes

Intertidal salt marshes are considered harsh habitats where relatively few stress-resistant species survive. Most studies on non-native species in marshes describe terrestrial angiosperms. We document that a non-native marine macroalga, Gracilaria vermiculophylla, is abundant throughout Virginia’s Atlantic coastline. We sampled eight marshes, characterized by low slopes and by the presence of the tube-building polychaete Diopatra cuprea on adjacent mudflats, which have been shown previously to be associated with G. vermiculophylla. G. vermiculophylla was found in 71% of the sampled quadrats on the border between the mudflat and tall Spartina alterniflora, 51% within the tall S. alterniflora zone, and 12% further inland. We also tagged G. vermiculophylla from two habitats: (1) unattached G. vermiculophylla within marshes and (2) G. vermiculophylla ‘incorporated’ onto D. cuprea tubes on the adjacent mudflats. Of the incorporated thalli, 3–9% ended up in the marsh, demonstrating connectivity between habitats. In addition, 21% of unattached thalli remained for 2 weeks within the marsh, suggesting that entanglement around marsh plants reduces tidal drift. Growth experiments in mesh bags indicate that most of the G. vermiculophylla transferred from the lagoon to the marsh decomposed there, potentially enhancing local nutrient levels. Finally, we document that G. vermiculophylla in marshes had a reduced associated flora and fauna compared to G. vermiculophylla on the adjacent Diopatra mudflats. In conclusion, unattached G. vermiculophylla is abundant along marsh borders in the tall S. alterniflora zone in Virginia, and we hypothesize that this non-native species has significant impacts in terms of marsh habitat complexity, species abundance and diversity, nutrient dynamics, productivity, and trophic interactions.     

Burrowing behavior and burrowing energetics of a bioindicator under human disturbance

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Firm evidence for a post-extinction ichnofauna: earliest Carboniferous Cruziana reticulata assemblage from the Anti-Atlas of Morocco

Cruziana reticulata is an arthropod-related ichnospecies that is characterized by a conspicuous net-like scratch pattern whose initial formation and later preservation require the presence of consolidated substrates in shallow marine fine-grained bottoms. There are two scenarios in which epifaunal to shallow infaunal benthic organisms may access firm siliciclastic substrates: first, by exposure of the compacted bottom after erosion of the upper, water-saturated and usually soft portion of sediment column; and, second, by primary fast substrate stabilization in the absence of biogenic sediment mixing. Whereas the first mode occurs throughout the Phanerozoic, the latter is only prevalent in marine bottoms during the Early Palaeozoic mainly as a consequence of poorly developed infaunal bioturbation. However, by eradicating burrowing organisms, mass extinctions are known (i.e. the end-Permian extinction) to ‘reset’ intensity of ecospace utilization, which entails the return to this anachronistic style of trace fossil preservation in younger times. An earliest Carboniferous ichno-assemblage dominated by Cruziana reticulata from Morocco attests the spread of firm substrates in the aftermath of the Hangenberg Event – a major extinction at the end of the Devonian period. Since evidence for erosion is lacking in accompanying sedimentary rocks and the ichno-assemblage shows characteristics of opportunistic exploitation of the nutritious muddy seabed, we favour the interpretation of this assemblage to represent a post-extinction ichnofauna. It shows that other taxonomically less severe mass extinctions may also exhibit transient but severe ecological effects in open marine ecosystems such as the collapse of vital sediment mixing. Such post-extinction effects may distort the perception of the stratigraphical record as a firmground ichno-assemblage often taken as evidence for submarine erosion and are crucial in highlighting sequence boundaries. We, thus, encourage appreciating macroevolutionary framework of respective ichnofaunas.     

Collection of the clam Anodontia edentula in mangrove habitats in Panay and Guimaras,central Philippines

The mangrove clam Anodontia edentula is highly prized in thePhilippines for its flavor and large size. Because this infaunal species isfound down to one meter deep in mangrove areas, harvesting the clam reportedlydamages mangrove stands. To evaluate such reports, a survey of collectionmethods was undertaken in Panay and Guimaras, central Philippines in August1997–December 1999. Host to chemosynthetic bacterial symbionts thatutilize sulfide as energy source, A. edentula are strategically situated insulfide-rich anoxic substrates but also gain access to oxygenated seawaterthrough a ventilation burrow or tube. By locating the opening of this burrow,collectors can detect the presence of a buried clam and harvest itnondestructively with a blade or bare hands. In contrast, the indiscriminatetilling of wide mangrove areas can damage mangrove plants. Most collectors were40–45 years old with 22–30 years collection experience, married with5–7 children, and had low educational attainment. They sold clams directlyin the local markets or through middlemen (to restaurants and beach resorts);sales provided from 10% to 100% of daily family income. Collectors complained ofdecreasing clam sizes and numbers and the physically strenuous work ofcollecting.