Ecosystem Engineering Effects of <Emphasis Type="Italic">Aster tripolium</Emphasis> and <Emphasis Type="Italic">Salicornia procumbens</Emphasis> Salt Marsh on Macrofaunal Community Structure

This paper examines how perennial Aster tripolium and annual Salicornia procumbens salt marshes alter the biomass, density, taxon diversity, and community structure of benthic macrofauna, and also examines the role of elevation, sediment grain size, plant cover, and marsh age. Core samples were collected on a fixed grid on an intertidal flat in the Westerschelde estuary (51.4° N, 4.1° E) over 5 years (2004–2008) of salt marsh development. In unvegetated areas, macrobenthic biomass, density, and taxon diversity were highest when elevation was highest, benthic diatoms were most abundant, and sediment median grain size was smallest. In contrast, in salt marsh areas, macrobenthic biomass and taxon diversity increased with median grain size, while the effects of elevation and diatom abundance on macrobenthic biomass, density, and diversity were not significant. In fine sediments, macrofaunal community structure in the salt marsh was particularly affected; common polychaetes such as Nereis diversicolor, Heteromastus filiformis, and Pygospio elegans had low abundance and oligochaetes had high abundance. Marsh age had a negative influence on the density of macrofauna, and A. tripolium stands had lower macrofaunal densities than the younger S. procumbens stands. There were no significant effects of marsh age, plant cover, and vegetation type on macrobenthic biomass, taxon diversity, and community structure. The results highlight that ecosystem engineering effects of salt marsh plants on macrofauna are conditional. Organic enrichment of the sediment and mechanical hindering of macrofaunal activity by plant roots are proposed as plausible mechanisms for the influence of the salt marsh plants on macrofauna.     

Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada

Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment. A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada, with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88 species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m⁻² (ranged from 4,371 to 19,930 ind. m⁻²), 23.4 species grab⁻¹ and 3.29 grab⁻¹, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth (1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting (σ_I). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay fraction, σ_I and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction as the single best-correlated variable.     

Effects of Shoreline Modifications on Supratidal Macroinvertebrate Fauna on Puget Sound,Washington Beaches

In coastal environments, the supratidal zone bridges marine and terrestrial ecosystems and is important for energy exchange. However, it is also subject to extensive anthropogenic disturbance, such as armoring of shorelines. Shoreline armoring is extensive along many coasts, but the impacts on biota are comparatively unknown. Between 2000 and 2002, paired and synoptic sampling regimes were employed to assess armoring effects on insects and benthic macroinvertebrates in the supratidal zone of Puget Sound beaches. Paired sampling showed natural beach sites had significantly more deposited wrack. Infauna was dominated by oligochaetes and nematodes; talitrid amphipods, insects, and collembolans were significantly more numerous at natural beaches, and crustaceans were more abundant at altered beaches. Insect assemblages were diverse, with taxon richness higher at natural beach sites. In the synoptic sampling, where sites with higher elevation modifications were used, there were fewer differences in invertebrate assemblages between armored and nonarmored sites. The results show that, where shoreline armoring lowers the land–sea interface, benthic infauna and insect assemblages are disrupted. Widespread shoreline modifications may decrease the availability of prey resources for fish and wildlife and decrease the contribution of organic material entering the nearshore ecosystem.     

Axial zonation patterns of subtidal macrozoobenthos in the Gamtoos estuary,South Africa

The distribution of macroinfauna was quantified in subtidal, soft-bottom habitats, extending from the estuarine mouth to the tidal head of the Gamtoos—a small, shallow, temperate estuary situated on the south coast of South Africa. Sampling covered the full salinity gradient from fresh to marine waters, and all sediment types from marine sands to fluvial silts. A total of 35 taxa was recorded, of which 22 occurred throughout the year. Species richness and diversity declined from the seawater-dominated mouth region toward the fresh water section at the tidal head of the estuary. Sediment type generally bore no clear relation to biotic diversity. A marked drop in salinity between winter and summer sample series (Δ 0.2‰ to 24‰) coincided with a reduction of mean macrofaunal density by 70%, a more seaward relocation, and a compression of axial ranges of most taxa. Numerical classification and ordination of faunistically similar regions and of co-occurring species delineated four habitat zones along the longitudinal axis of the estuary which harbour four distinct macrofaunal assemblages: 1) A tidal inlet area with salinities close to seawater; clean, coarse, marine sands, rich in CaCO₃ harbour a stenohaline fauna normally found on adjacent, marine sandy beaches. 2) In the lower reaches, where fine, fluvial silts of high organic content prevail, euryhaline polychaetes dominate the macrozoobenthic community; bottom salinities in this zone seldom dropped below 25‰ 3) The middle reaches, characterized by oligohaline- to polyhaline waters, stretch over sandy sediments of intermediate carbonate, silt, and organic fractions; the fauna comprises typical estuarine forms, which occurred throughout most of the estuary except at its seaward and landward limits. 4) The upper reaches encompass the limnetic waters near the tidal head of the estuary with sediments in this zone being composed mostly of coarse, clean sands, low in CaCO₃; the macrobenthos in this region is dominated by taxa of freshwater origin, which generally do not penetrate seaward beyond the oligohaline waters, and by exceptionally euryhaline estuarine species. Salinity appears as the main factor in controlling faunal assemblages at both extremes of the estuarine gradient (i.e., tidal inlet and head), whereas sediment type delineates between communities in the mesohaline to polyhaline reaches. Axial (i.e., from tidal inlet to tidal head of the estuary) zonation patterns of macroinfauna broadly matched those of mesozooplankton and fishes, supporting the notion of a general structure underlying species distribution patterns in the Gamtoos estuary.     

Determination of Trophic Transfer at a Created Intertidal Oyster (<Emphasis Type="Italic">Crassostrea ariakensis</Emphasis>) Reef in the Yangtze River Estuary Using Stable Isotope Analyses

Oysters can create reefs that provide habitat for associated species resulting in elevated resident abundances, lower mortality rates, and increased growth and survivorship compared to other estuarine habitats. However, there is a need to quantify trophic relationships and transfer at created oyster reefs to provide a better understanding of their potential in creating suitable nekton habitat. Stable isotope analyses (δ¹³C and δ¹⁵N) were conducted to examine the organic matter sources and potential energy flow pathways at a created intertidal oyster (Crassostrea ariakensis; hereinafter, oyster) reef and adjacent salt marsh in the Yangtze River estuary, China. The δ¹³C values of most reef-associated species (22 of 37) were intermediate between those of suspended particle organic matter (POM) and benthic microalgae (BMI), indicating that both POM and BMI are the major organic matter sources at the created oyster reef. The sessile and motile macrofauna colonizing the reef make up the main prey of transient nekton (e.g., spotted sea bass, Asian paddle crab, and green mud crab), thus suggesting that the associated community was most important in supporting higher trophic levels as opposed to the direct dietary subsidy of oysters. The created oyster reef consistently supported higher trophic levels than the adjacent salt marsh habitat due to the dominance of secondary consumers. These results indicate that through the provision of habitat for associated species, created oyster reefs provide suitable habitat and support a higher average trophic level than adjacent salt marsh in the Yangtze River estuary.     

Composition of macrobenthos from the Central Indian Ocean Basin

The deep sea is well known for its high faunal diversity. But the current interest in its abundant polymetallic nodules, poses a threat to the little known benthic organisms surviving in this unique environment. The present study is the first attempt to document the Indian Ocean abyssal benthic diversity of macroinvertebrates and to investigate its relation to the surface primary production (chl-a), sediment labile organic matter, organic carbon and texture. The present study is based on 87 individuals. Altogether 39 macroinvertebrate genera were obtained from water depths of 4500–5500 m from 23 box cores. Reduction in macrobenthic density was seen towards the southern latitudes. The area was dominated by deposit feeding macrobenthos. Vertically, the fauna was distributed down to 30 cm depth, with the highest faunal density in the top 2–5 cm sediment section. The values for population density were strongly correlated with surface water chl-a and sediment protein, indicating supply of fresh organic matter as a critical factor for maintaining the deep sea benthic diversity and abundance.     

Progradational Holocene carbonate tidal flats of Crooked Island,south‐east Bahamas: An alternative to the humid channelled belt model

The stratigraphic record of many cratonic carbonate sequences includes thick successions of stacked peritidal deposits. Representing accumulation at or near sea‐level, these deposits have provided insights into past palaeoenvironments, sea‐level and climate change. To expand understanding of carbonate peritidal systems, this study describes the geomorphology, sedimentology and stratigraphy of the tidal flats on the Crooked‐Acklins Platform, south‐east Bahamas. The Crooked Island tidal flats extend continuously for ca 18 km on the platformward flank of Crooked Island, reaching up to 2 km across. Tidal flats include four environmental zones with specific faunal and floral associations and depositional characteristics: (i) supratidal (continuous supratidal crust and pavement); (ii) upper intertidal, with the mangrove Avicennia germinans and the cyanobacteria Scytonema; (iii) lower intertidal (with the mangrove Rhizophora mangal) and (iv) non‐vegetated, heavily burrowed subtidal (submarine). These zones have gradational boundaries but follow shore‐parallel belts. Coring reveals that the thickness of this mud‐dominated sediment package generally is <2 m, with depth to Pleistocene bedrock gradually shallowing landward. The facies succession under much of the tidal flat includes a basal compacted, organic‐rich skeletal‐lithoclast lag above the bedrock contact (suggesting initial flooding). This unit grades upward into rhizoturbated skeletal sandy mud (subtidal) overlain by coarsening‐upward peloid‐foraminifera‐gastropod muddy sand (reflecting shallowing to intertidal elevations). Cores from landward positions include stacked thin indurated layers with autoclastic breccia, root tubules and fenestrae (interpreted as supratidal conditions). Collectively, the data reveal an offlapping pattern on this prograding low‐energy shoreline, and these Holocene tidal flats may represent an actualistic analogue for ancient humid progradational tidal flats. Nonetheless, their vertical facies succession is akin to that present beneath channelled belt examples, suggesting that facies successions alone may not provide unambiguous criteria for prediction of the palaeogeomorphology, lateral facies changes and heterogeneity in stratigraphic analogues.     

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian,SE France) evidenced by calcareous nannofossils

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.     

Post-settlement alteration of spatial patterns of soft shell clam (<Emphasis Type="Italic">Mya arenaria</Emphasis>) recruits

To examine the roles of settlement and early post-settlement processes in patterns of recruitment of the soft shell clamMya arenaria, abundance of juvenileMya at three intertidal sites in Barnstable Harbor, Massachusetts, was monitored over two settlement seasons. Two peaks of settlement occurred in 1998 (July and September) and one peak was recorded in June 1999, indicating that a late season settlement event is not a consistent feature at this site. Abundance of recent settlers (i.e., early recruits, < 1 week past settlement) varied significantly among the tidal flats (sites) that were separated by hundreds of meters to kilometers, but not among plots meters apart. Differences in abundance of settlers likely resulted in these differences in early-recruit abundance among sites. Settlement was greatest at the site with the greatest variability in flow speed. Sites also differed to some extent in their sediment characteristics and macrofaunal assemblages, which may influence larval substrate choice. Between-site differences in abundance ofMya decreased after settlement. The rate of decline of abundance varied among cohorts and sites. Comparison of abundance of recent settlers (up to 145,000 m⁻²) to that of juveniles > 3-mm shell length at the end of the settlement season (up to 60 m⁻²) indicated large losses of individuals during the early post-settlement period. This study demonstrates that spatial patterns inMya abundance can change substantially during the early post-settlement period, and that high mortality rates can result in cohorts contributing little to the population size even when rates of settlement are high.     

Recolonization of Intertidal Infauna in Relation to Organic Deposition at an Oyster Farm in Atlantic Canada—A Field Experiment

A field experiment was carried out to investigate the patterns of macrobenthic recolonization and to determine the effects of biodeposition on benthic communities at an intertidal oyster culture site in New Brunswick, Canada. Total organic deposition in azoic organic-free sediment trays was generally higher within the farm compared to reference sites. Two weeks after deployment of trays, total organic content had reached 1.1%. The abundance, species number, and diversity of the macrobenthic community were positively correlated with the total organic content in the experimental trays, but the correlations between community parameters and organic content were negative in the ambient sediment. The results suggest that organic matter in sediment may have positive effects on macrobenthic infauna at low levels as an additional food source but may be harmful to benthic animals at high levels. This study also indicates that location in the intertidal zone is a major parameter affecting the community structure of macrobenthic colonization.     

An assessment of the utility of regional diatom‐based tidal‐level transfer functions

In order to understand natural sea‐level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom‐based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom‐based tidal‐level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site‐specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal‐level transfer functions, may be more appropriate. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative assessment of benthic food resources for juvenile Gulf sturgeon,Acipenser oxyrinchus desotoi in the Suwannee River estuary, Florida, USA

Gulf sturgeon,Acipenser oxyrinchus desotoi, forage extensively in the Suwannee River estuary following emigration out of the Suwannee River, Florida. While in the estuary, juvenile Gulf sturgeon primarily feed on benthic infauna. In June–July 2002 and February–April 2003, random sites within the estuary were sampled for benthic macrofauna (2002 n = 156; 2003 n = 103). A mean abundance of 2,562 ind m⁻² (SE ± 204) was found in the summer, with significantly reduced macrofaunal abundance in the winter (mean density of 1,044 ind m⁻², SE ± 117). Benthic biomass was significantly higher in the summer with an average summer sample dry weight of 5.92 g m⁻² (SE ± 0.82) compared to 3.91 g m⁻² (SE ± 0.67) in the winter. Amphipods and polychaetes were the dominant taxa collected during both sampling periods. Three different estimates of food availability were examined taking into account principal food item information and biomass estimates. All three estimates provided a slightly different view of potential resources but were consistent in indicating that food resource values for juvenile Gulf sturgeon are spatially heterogeneous within the Suwannee River estuary.     

The effect of freshwater inflow on meiofaunal and macrofaunal populations in the Guadalupe and Nueces Estuaries,Texas

Two estuaries with very different inflow characteristics were compared to test the hypothesis that benthic standing crops are enhanced by freshwater inflow. Assuming predation pressure is similar in both estuaries, this would imply that freshwater inflow enhances secondary production. The Guadalupe Estuary had 79 times more freshwater inflow than the Nueces Estuary, and a third of the salinity. The Guadalupe had higher macrofaunal densities and biomass than the Nueces, and both parameters increased with decreasing salinity within the Guadalupe Estuary. Macrofauna density increased with increasing salinity in the Nueces Estuary, due to invasion by marine species. However, meiofauna population size responds differently than macrofauna. Meiofaunal densities were higher in the low-inflow Nueces Estuary, and increased with increasing salinity in both estuaries. Macrofauna diversity increased with salinity, both within and between estuaries. The macrofauna response supports the hypothesis that increased freshwater inflow stimulates secondary production. A review of past benthic studies in these estuaries and the historical climatic patterns indicate that wet years with high inflow result in increased macrofaunal productivity. Since, macrofaunal diversity decreased with lower salinity both within and between the estuaries, the enhanced productivity is due to increases by freshwater and estuarine species that can tolerate low salinities. Increased macrofaunal densities are associated with decreasing meiofaunal densities. The latter result could be due to either increased macrofaunal competition with or predation on meiofauna, or a lack of low-salinity tolerance by meiofauna.     

Natural Disturbance Shapes Benthic Intertidal Macroinvertebrate Communities of High Latitude River Deltas

Unlike lower latitude coastlines, the estuarine nearshore zones of the Alaskan Beaufort Sea are icebound and frozen up to 9 months annually. This annual freezing event represents a dramatic physical disturbance to fauna living within intertidal sediments. The main objectives of this study were to describe the benthic communities of Beaufort Sea deltas, including temporal changes and trophic structure. Understanding benthic invertebrate communities provided a baseline for concurrent research on shorebird foraging ecology at these sites. We found that despite continuous year-to-year episodes of annual freezing, these estuarine deltas are populated by a range of invertebrates that represent both marine and freshwater assemblages. Freshwater organisms like Diptera and Oligochaeta not only survive this extreme event, but a marine invasion of infaunal organisms such as Amphipoda and Polychaeta rapidly recolonizes the delta mudflats following ice ablation. These delta sediments of sand, silt, and clay are fine in structure compared to sediments of other Beaufort Sea coastal intertidal habitats. The relatively depauperate invertebrate community that ultimately develops is composed of marine and freshwater benthic invertebrates. The composition of the infauna also reflects two strategies that make life on Beaufort Sea deltas possible: a migration of marine organisms from deeper lagoons to the intertidal and freshwater biota that survive the 9-month ice-covered period in frozen sediments. Stable isotopic analyses reveal that both infaunal assemblages assimilate marine and terrestrial sources of organic carbon. These results provide some of the first quantitative information on the infaunal food resources of shallow arctic estuarine systems and the long-term persistence of these invertebrate assemblages. Our data help explain the presence of large numbers of shorebirds in these habitats during the brief summer open-water period and their trophic importance to migrating waterfowl and nearshore populations of estuarine fishes that are the basis of subsistence lifestyles by native inhabitants of the Beaufort Sea coast.     

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.     

Links Between Bottom-Water Anoxia,the Polychaete <Emphasis Type="Italic">Nereis diversicolor</Emphasis>, and the Growth of Green-Algal Mats

Sediment–water incubations were used to study effects of episodic anoxia on filamentous Ulva sp. Treatments included undisturbed sediment with (AnoxSed) and without (NatSed) exposure to 5 days of anoxia, and cores with only the top 0.5 cm of sediment (SurfSed; no macrofauna, restricted pore-water nutrient pool). All three treatments contained Ulva propagules. An Ulva mat developed in the SurfSed, and after the anoxic period in the AnoxSed cores. No growth was observed in the NatSed treatment. In the AnoxSed, Ulva was progressively removed upon reoxygenation through grazing by Nereis. The results suggest that episodic anoxia stimulates the growth of macroalgal mats not only by increasing the availability of nutrients from the sediment, but also by reducing macrofaunal grazing pressure. Infauna (grazing and bioturbation), benthic microalgae (nutrient competition and retention), and pore-water nutrients appear key components in a biogeochemical network with complex feedbacks controlling the growth of green-algal mats in shallow-water systems.     

Microphytobenthos: The ecological role of the “secret garden” of unvegetated,shallow-water marine habitats. II. role in sediment stability and shallow-water food webs

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroalgae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat characteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic infauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic microalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man’s activities. *** DIRECT SUPPORT *** A01BY074 00005     

Reappraisal of early Paleogene CCD curves: foraminiferal assemblages and stable carbon isotopes across the carbonate facies of Perth Abyssal Plain

Bulk carbonate content, planktic and benthic foraminiferal assemblages, stable isotope compositions of bulk carbonate and Nuttallides truempyi (benthic foraminifera), and non-carbonate mineralogy were examined across ∼30 m of carbonate-rich Paleogene sediment at Deep Sea Drilling Project (DSDP) Site 259, on Perth Abyssal Plain off Western Australia. Carbonate content, mostly reflecting nannofossil abundance, ranges from 3 to 80% and generally exceeds 50% between 35 and 57 mbsf. A clay-rich horizon with a carbonate content of about 37% occurs between 55.17 and 55.37 mbsf. The carbonate-rich interval spans planktic foraminiferal zones P4c to P6b (∼57–52 Ma), with the clay-rich horizon near the base of our Zone P5 (upper)—P6b. Throughout the studied interval, benthic species dominate foraminiferal assemblages, with scarce planktic foraminifera usually of poor preservation and limited species diversity. A prominent Benthic Foraminiferal Extinction Event (BFEE) occurs across the clay-rich horizon, with an influx of large Acarinina immediately above. The δ¹³C records of bulk carbonate and N. truempyi exhibit trends similar to those observed in upper Paleocene–lower Eocene (∼57–52 Ma) sediment from other locations. Two successive decreases in bulk carbonate and N. truempyi δ¹³C of 0.5 and 1.0‰ characterize the interval at and immediately above the BFEE. Despite major changes in carbonate content, foraminiferal assemblages and carbon isotopes, the mineralogy of the non-carbonate fraction consistently comprises expanding clay, heulandite (zeolite), quartz, feldspar (sodic or calcic), minor mica, and pyrolusite (MnO₂). The uniformity of this mineral assemblage suggests that Site 259 received similar non-carbonate sediment before, during and after pelagic carbonate deposition. The carbonate plug at Site 259 probably represents a drop in the CCD from ∼57 to 52–51 Ma, as also recognized at other locations.     

Palaeoceanographic implications of abundance and mean proloculus diameter of benthic foraminiferal speciesEpistominella exigua in sub-surface sediments from distal Bay of Bengal fan

Temporal variation in abundance and mean proloculus diameter of the benthic foraminiferal speciesEpistominella exigua has been reconstructed over the last ∼ 50,000 yr BP, from a core collected from the distal Bay of Bengal fan, to assess its potential application in palaeoceanographic reconstruction studies. The down-core variation shows significant change in abundance ofE. exigua during the last ∼ 50,000 yr BP. In view of the present day abundance of this species from areas with strong seasonal organic matter supply, we conclude that at ∼ 7, ∼ 22, ∼ 33 and ∼ 46kyr BP, strong seasonality prevailed in the distal Bay of Bengal fan, probably indicating either strong or prolonged north-east monsoon or weakened south-west monsoon. For the first time, a strong correlation is observed in abundance and mean proloculus diameter ofE. exigua. Based on coherent variation in mean proloculus diameter and abundance, it is postulated that mean proloculus diameter can also be used to infer increased seasonality in organic matter production, thus variation in strength or duration of monsoon. Thus, this study establishes that the down-core variation in the abundance and mean proloculus diameter ofEpistominella exigua can be used to infer past climatic variations from the distal Bay of Bengal fan.     

Optimal benthic macrofaunal sampling protocol for detecting differences among four habitats in Willapa Bay,Washington, USA

As part of an effort to estimate estuarine habitat values with respect to ecological indicators of benthic macrofaunal community condition, an optimal (effective and least costly) sampling protocol (sample unit size [area x depth], sieve mesh size, and sample number [n]) was determined. The goal was to use four ecological indicators (number of species, abundance, biomass, and fish and crab prey abundance) to detect differences among four intertidal habitats in Willapa Bay, Washington, United States. The four habitats were eelgrass (Zostera marina), Atlantic cordgrass (Spartina alterniflora), mud shrimp (Upogebia pugettensis), and ghost shrimp (Neotrypaea californiensis). Four sample unit areas (0.005, 0.010, 0.015, and 0.020 m²), two sample unit depths (0–5 and 0–10 cm), and two sieve mesh sizes (1.0 and 0.5 mm) were evaluated. The optimal sampling protocol was defined as the least costly protocol capable of reliably (statistical power, 1?β≥0.80) detecting significant (α=0.05) differences among ≥4 of the 6 pairwise habitat contrasts by ANOVA on all four ecological indicators. The relative cost of each sampling protocol was estimated as a direct function of the sample unit size and number and the cost-in-processing-time ratios of 1 (5 cm deep):1.7 (10 cm deep) and 1 (≥1.0 mm macrofauna size fraction); 2.5 (≥0.5 mm macrofauna size fraction), which were taken from previous studies. The optimal sampling protocol was 15–20, 0.01-m²×5-cm deep, 0.5-mm mesh samples per habitat.