Egg production of the copepodAcartia tonsa in Florida Bay during summer. 1. The roles of food environment and diet

The diet and egg production rate ofAcartia tonsa were measured during the thermally stable period between June and October 1995 at four locations in inner and outer Florida Bay. We sought to characterize the role ofA. tonsa in the bay’s pelagic food web, which has been changing since 1987, when the dominant submerged vegetation began shifting from benthic seagrasses to planktonic algae. At Rankin Lake, a shallow basin on the north side of the inner bay, where extensive seagrass mortality and persistent cyanobacteria blooms have occurred, microplankton biomass was relatively high and dominated by heterotrophic protists and dinoflagellates. Nanoplankton at Rankin, Lake, while numerically abundant, usually contributed only a small portion of the biomass. The ingestion rate ofA. tonsa in Florida Bay varied independently of food concentration (i.e., total microplankton biomass), but rates were higher (mean±SD =3.88 ± 0.73 μg C copepod^?1 d^?1) on the north side of the bay than on the south side (0.78 ±0.11 μg C copepod^?1 d^?1). Microzooplankton and dinoflagellates were important dietary constituents, especially in the vicinity of Rankin Lake. Egg production in this region (mean ± SD = 14.2 ± 7.7 eggs female^?1 d^?1) was considerably high than the baywide mean (5.8±0.81 eggs female^?1d^?1), and principal components analysis revealed associations between egg production and both dietary microzooplankton and dinoflagellate biomass. However, although grazing rates were relatively high in the inner bay,A. tonsa removed only 1–6% of the primary production from the water column during the summer and its egg production rates were low relative to typical rates for the species.     

Effect of discharge on the chlorophylla distribution in the tidally-influenced Potomac River

In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l^?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m³s^?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l^?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m³ s^?1, but sustained discharges greater than 1,100 m³ s^?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.     

Ammonium regeneration and biomass of macrozooplankton and ctenophores in Great South Bay,New York

The rate of zooplankton ammonium regeneration was measured in Great South Bay, Long Island, New York, between July 1982 and May 1984. Ammonium excretion by macrozooplankton (>200 μm) ranged from 7 μg atoms NH₄ ¹⁺?N m^?3 d^?1 in winter to 156 μg-atoms NH₄ ¹⁺?N m^?3 d^?1 in spring. Ammonium excretion by ctenophores was greater than or equivalent to that of macrozooplankton during the period of ctenophore biomass maximum in summer and fall. The temperature coefficient (Q₁₀) for NH₄ ¹⁺ excretion was 1.74 from 2.2 to 27.5°C for macrozooplankton and 1.63 between 17 and 26°C for the ctenophores. Ammonium nitrogen excretion by macrozooplankton and ctenophores combined, accounted for 1 to 3% of phytoplankton nitrogen requirements in summer when primary productivity was high and 39% in the spring. *** DIRECT SUPPORT *** A01BY040 00005     

Long-term Field Observations on Seasonality in Chlorophyll-<Emphasis Type="Italic">a</Emphasis> Concentrations in a Shallow Coastal Marine Ecosystem,the Wadden Sea

Analyses of long-term field observations (1974–2007) on chlorophyll-a concentrations in the western Wadden Sea showed no long-term trends in the timing of the wax and wane of phytoplankton spring blooms. There is weak evidence, however, that the height of the autumn bloom has decreased since the early 1990s. This fading of the autumn bloom may have had consequences for the carbon transfer to higher trophic levels, currently hampering primary consumer species that mostly rely on food supply during late summer. Current and other findings suggest a shortening of the growing season due to the fading of the autumn bloom in the Wadden Sea and a lengthening of the growing season due to an advancement of the spring bloom in the North Sea. These regionally different changes in seasonality may have contributed to the coinciding decrease in bivalve filtering capacity in the western Wadden Sea and the large-scale offshore shift of juvenile plaice from the Wadden Sea to the adjacent North Sea.     

Seasonal Cycle of Phytoplankton Community Composition in the Coastal Upwelling System Off Central Oregon in 2009

Coastal upwelling in the northern California Current varies seasonally, with downwelling in winter and upwelling in summer, resulting in pronounced variability in hydrography, nutrients, phytoplankton biomass, and species composition. Winter was characterized by moderate concentrations of nitrate and silicate (averages of 10 and 18 μM, respectively) and low concentrations of chlorophyll a (Chl a). During the upwelling season, concentrations of the same nutrients ranged from near 0 μM to approximately 27 and 43 μM and Chl a 0.5?<?x?<?15 μg L^?1. During autumn, upwelling weakened and nutrient concentrations were reduced, but large phytoplankton blooms continued to occur. Variations in hydrography, nutrients, and phytoplankton also occurred within the upwelling season due to alternation of the winds between northerly (active upwelling) and southerly (relaxation of upwelling), on a 5- to 10-day time scale. Eleven blooms were observed, most of which occurred near the end of active upwelling events and during relaxation of upwelling. Nonmetric multidimensional scaling ordination of species composition of the microplankton revealed four distinct communities: a winter community, early upwelling and late upwelling season communities, and an autumn community. Diatoms (Asterionellopsis glacialis, Eucampia zodiacus, and several Chaetoceros, Thalassiosira, and Pseudo-nitzschia species) dominated early in the upwelling season, averaging 80 % of the phytoplankton biomass, and dinoflagellates dominated near the end of the upwelling season, averaging 68 % of the phytoplankton biomass. Dinoflagellates formed two monospecific blooms—Prorocentrum gracile in late summer and Akashiwo sanguinea in autumn. Changes in community composition were correlated with bottom temperature and salinity (representing seasonal variability) and sea surface salinity (representing within-season event-scale variability in upwelling).     

Dissolved and particulate organic carbon in Chesapeake Bay

We measured dissolved and particulate organic carbon (DOC and POC) in samples collected along 13 transects of the salinity gradient of Chesapeake Bay. Riverine DOC and POC end-members averaged 232±19 μM and 151±53 μM, respectively, and coastal DOC and POC end-members averaged 172±19 μM and 43±6 μM, respectively. Within the chlorophyll maximum, POC accumulated to concentrations 50–150 μM above those expected from conservative mixing and it was significantly correlated with chlorophylla, indicating phytoplankton origin. POC accumulated primarily in bottom waters in spring, and primarily in surface waters in summer. Net DOC accumulation (60–120 μM) was observed within and downstream of the chlorophyll maximum, primarily during spring and summer in both surface and bottom waters, and it also appeared to be derived from phytoplankton. In the turbidity maximum, there were also net decreases in chlorophylla (?3 μg l^?1 to ?22 μg l^?1) and POC concentrations (?2 μM to ?89 μM) and transient DOC increases (9–88 μM), primarily in summer. These occurred as freshwater plankton blooms mixed with turbid, low salinity seawater, and we attribute the observed POC and DOC changes to lysis and sedimentation of freshwater plankton. DOC accumulation in both regions of Chesapeake Bay was estimated to be greater than atmospheric or terrestrial organic carbon inputs and was equivalent to ≈10% of estuarine primary production.     

Spatial and temporal patterns of factors influencing phytoplankton in a salt wedge estuary, the Swan River, Western Australia

During 1995 the phytoplankton in the Swan River were intensively sampled to assess biomass and species composition. Continuous measurements of fluorescence, salinity, and temperature were made weekly during 40 km sampling trips along the estuary and used to map the seasonal progression of the algal biomass. Weekly measurements of primary production were made and used to model net primary production from the vertical distribution of biomass, irradiance, and phytoplankton species composition. Potential nutrient limitation was assessed with “all but one” nutrient bioassays. The results indicate a complex mixture of potentially limiting factors, which vary in time and space. Although the data sequence is short, it suggests a annual succession pattern of diatoms, chlorophytes, diatoms, and finally dinoflagellates and cryptophytes in late summer-autumn. Peak seasonal biomass was observed during January to April. Mean annual chlorophylla biomass was greatest in upstream stations (5–9), where estimates of net primary production rates averaged 1.55 g C m^?2 d^?1 and gross primary production was 800–1000 g C m^?2 yr^?1. Potential nutrient limitation was most severe from November to May, although not during January 1995. Based on bioassay results, during the period of greatest potential for nutrient limitation, nitrogen was 15 to 30 times more limiting to biomass development than phosphate. Runoff due to consistent rainfall during winter eventually breaks down stratification and flushes the estuary with low-salinity, nutrient-rich water, producing, a light-limited, nutrient-rich aquatic ecosystem. Timing and magnitude of physical forcing events, mainly rainfall, appear critical in determining the susceptibility of this ecosystem to summer and autumn algal blooms.     

Scales of nutrient-limited phytoplankton productivity in Chesapeake Bay

The scales on which phytoplankton biomass vary in response to variable nutrient inputs depend on the nutrient status of the plankton community and on the capacity of consumers to respond to increases in phytoplankton productivity. Overenrichment and associated declines in water quality occur when phytoplankton growth rate becomes nutrient-saturated, the production and consumption of phytoplankton biomass become uncoupled in time and space, and phytoplankton biomass becomes high and varies on scales longer than phytoplankton generation times. In Chesapeake Bay, phytoplankton growth rates appear to be limited by dissolved inorganic phosphorus (DIP) during spring when biomass reaches its annual maximum and by dissolved inorganic nitrogen (DIN) during summer when phytoplankton growth rates are highest. However, despite high inputs of DIN and dissolved silicate (DSi) relative to DIP (molar ratios of N∶P and Si∶P>100), seasonal accumulations of phytoplankton biomass within the salt-intruded-reach of the bay appear to be limited by riverine DIN supply while the magnitude of the spring diatom bloom is governed by DSi supply. Seasonal imbalances between biomass production and consumption lead to massive accumulations of phytoplankton biomass (often>1,000 mg Chl-a m^?2) during spring, to spring-summer oxygen depletion (summer bottom water <20% saturation), and to exceptionally high levels of annual phytoplankton production (>400 g m^?2 yr^?1). Nitrogen-dependent seasonal accumulations of phytoplankton biomass and annual production occur as a consequence of differences in the rates and pathways of nitrogen and phosphorus cycling within the bay and underscore the importance of controlling nitrogen inputs to the mesohaline and lower reaches of the bay.     

Linking phytoplankton community composition with juvenile-phase growth in the Northern QuahogMercenaria mercenaria (L.)

This study examined whetherMercenaria mercenaria (L.) (quahog) growth is influenced by variability in phytoplantkon community composition in the waters of Long Island, New York. Field studies conducted during 1999 and 2000 compared juvenile quahog growth and phytoplankton assemblages between West Sayville (WS), an embayment in Great South Bay along Long Island’s south shore where quahog landings have recently declined, and Oyster Bay (OB), an embayment on Long Island’s north shore where quahog landings are still high. Quahogs grew better at OB than WS during both study years. Centric diatoms were typically the dominant phytoplankton species at OB, and pennate diatoms and dinoflagellates characterized WS. At WS, the phytoplankton community consisted of heterotrophic dinoflagellates during a brown tide in 2000 and pennate diatoms afterward. Nanoflagellates were abundant (10⁵–10⁶ cells ml^?1) at WS throughout the summer of 2000. Multiple regression analysis revealed a significant effect of site and temperature on individual clam biomass during both years, but brown tide was only significant during 2000. Biomass comparisons of dominant phytoplantkon taxa with laboratory physiology studies showed that 0B, with its abundance of centric diatoms, likely represented a more nutritional diet for quahogs than pennate diatoms, which were abundant at WS. Small flagellates, which were common at WS, may also have been important for sustaining growth during some months. Variability in plankton assemblages between OB and WS likely represented two distinct, diets that were critical influences on clam growth.     

Effects of zooplankton grazing on phytoplankton size-structure and biomass in the lower Hudson River estuary

The impact of mesozooplankton (>210 μm, mostly adult copepods and late-stage copepodites) and micrometazoa (64–210 μm, mostly copepod nauplii) on phytoplankton size structure and biomass in the lower Hudson River estuary was investigated using various¹⁴C-labeled algal species as tracers of grazing on natural phytoplankton. During spring and summer, zooplankton grazing pressure, defined as %=mg C ingested m^?2 h^?1/mg C produced m^?2 h^?1 (depth-integrated rates)×100, on total phytoplankton ranged between 0.04% and 1.9% for mesozooplankton and 0.1% and 6.6% for micrometazoa. The greatest grazing impact was measured in fall when 20.2% and 44.6%, respectively, of the total depth-integrated primary production from surface water phytoplankton was grazed. Mesozooplankton exhibited some size-selective grazing on phytoplankton, preferentially grazing the diatomThalassiosira pseudonana over the larger diatomDitylum brightwelli, but this was not found for micrometazoa. Neither zooplankton group grazed on the dinoflagellateAmphidinium sp. We conclude that metazoan zooplankton have a minimal role in controlling total phytoplankton biomass in the lower Hudson River estuary. Differences in the growth coefficients of various phytoplankton size-fractions—not grazing selectivity—may be the predominant factor explaining community size-structure.     

A Decade of Change in the Skidaway River Estuary. III. Plankton

The Skidaway River estuary, GA (USA), a tidally dominated subtropical system surrounded by extensive Spartina salt marshes, is experiencing steady increases in nutrients, chlorophyll, and particulate matter and decline in dissolved oxygen, associated with cultural eutrophication. A long-term study is documenting changes in these parameters: previous papers Verity (Estuaries 25:944–960, 2002a, Estuaries 25:961–975, b) reported on hydrography, nutrients, chlorophyll, and particulate matter during 1986–1996; plankton community responses are reported here. Phytoplankton, bacteria, heterotrophic nanoplankton and dinoflagellates, ciliates, and copepods exhibited strong seasonal cycles in abundance driven by temperature and resource availability, typically with summer maxima and winter minima. However, cultural eutrophication coincided with altered planktonic food webs as autotrophic and heterotrophic communities responded to increasing concentrations and changing ratios of inorganic and organic nutrients, potential prey, and predators. Small (<8 μm) photosynthetic nanoplankton increased in absolute concentration and also relative to larger cells. In contrast, diatoms did not show consistent increases in abundance, despite significant long-term increases in ambient silicate concentrations. Mean annual bacteria concentrations approximately doubled, and eukaryotic organisms in the microbial food web (heterotrophic and mixotrophic flagellates, dinoflagellates, ciliates, and metazoan zooplankton) also increased. All plankton groups except copepods showed trends of increasing annual amplitudes between seasonal high and low values, with higher peak concentrations each year. These observations suggest that the eutrophication signal was gradually becoming uncoupled from regulatory mechanisms. Theory and evidence from other more impacted waters suggest that, if these patterns continue, changes in the structure and function of higher trophic levels will ensue.     

Chemical characteristics of aerosols in MABL of Bay of Bengal and Arabian Sea during spring inter-monsoon: A comparative study

The chemical composition of aerosols in the Marine Atmospheric Boundary Layer (MABL) of Bay of Bengal (BoB) and Arabian Sea (AS) has been studied during the spring and inter-monsoon (March-May 2006) based on the analysis of water soluble constituents (Na⁺, NH ₄ ⁺ , K⁺, Mg²⁺, Ca²⁺, Cl^?, NO ₃ ^? and SO ₄ ^2? ), crustal elements (Al, Fe, and Ca) and carbonaceous species (EC, OC). The total suspended particulates (TSP) ranged from 5.2 to 46.6 μg m^?3 and 8.2 to 46.9 μg m^?3 during the sampling transects in the BoB and AS respectively. The water-soluble species, on average, accounted for 44% and 33% of TSP over BoB and AS respectively, with dominant contribution of SO ₄ ^2? over both the oceanic regions. However, distinct differences with respect to elevated abundances of NH ₄ ⁺ in the MABL of BoB and that of Na⁺ and Ca²⁺ in AS are clearly evident. The non-sea-salt component of SO ₄ ^2? ranging from 82 to 98% over BoB and 35 to 98% over AS; together with nss-Ca²⁺/nss-SO ₄ ^2? equivalent ratios 0.12 to 0.5 and 0.2 to 1.16, respectively, provide evidence for the predominance of anthropogenic constituents and chemical transformation processes occurring within MABL. The concentrations of OC and EC average around 1.9 and 0.4 μg m^?3 in BoB and exhibit a decreasing trend from north to south; however, abundance of these carbonaceous species are not significantly pronounced over AS. The abundance of Al, used as a proxy for mineral aerosols, varied from 0.2 to 1.9 μg m^?3 over BoB and AS, with a distinctly different spatial pattern — decreasing north to south in BoB in contrast to an increasing pattern in the Arabian Sea.     

Secondary production of the amphipod Ampelisca abdita mills and its importance in the diet of juvenile winter flounder (Pleuronectes americanus) in Jamaica Bay,New York

The benthic amphipod Ampelisca abdita dominates mudbottom benthic communities in Jamaica Bay (New York). In this study, we investigated the trophic role of Ampelisca in relation to winter flounder (Pleuronectes americanus) populations—the most frequently trawled fish species in Jamaica Bay. Flounders collected by trawl during summer 1989 were primarily juveniles. Stomach analyses indicated that amphipod crustaceans contributed >99% of prey individuals, with A. abdita making up 88%. Density and size frequency analyses of Ampelisca at three sites indicated two overlapping cohorts: a spring cohort released in June and a summer cohort released in late summer. Most overwintering survivors come from the summer cohort. Secondary production of Ampelisca was estimated at three sites using the cohort summation of biomass method. Estimates of annual production ranged from 25 g DW to 47 g DW m^?2 (mortality + residual biomass); production due to growth ranged from 20 g DW to 26 g DW. Simulations of spring cohort production using a range of plausible growth and mortality schedules suggested that P∶B may be more sensitive to variability in survivorship than growth. Ampelisca secondary production in Jamaica Bay is compared with other amphipod species and with macrobenthic production in other coastal and estuarine systems. We conclude that observed amphipod production is probably more than sufficient to support local winter flounder populations in Jamaica Bay, and we speculate that high nutrient loadings may indirectly stimulate amphipod production. *** DIRECT SUPPORT *** A01BY058 00010     

Determination of some carcinogenic PAHs with toxic equivalency factor along roadside soil within a fast developing northern city of India

The objective of the present study was to ascertain contamination levels, distribution behaviour and PAHs exposure during summer, winter and autumn during 2011–2012 in one of the developing cities of northern India. Average PAHs concentration was found to be 18.17, 4.04 and 16.38 μg g ^?1, whereas, concentration of 16 individual PAHs was found to vary between 0.02 and 200.23, 0.008 and 28.4 μg g ^?1, and 0.01 and 252.55 μg g ^?1 during summer, winter and autumn seasons, respectively. The average concentration of low and high carcinogenic PAHs during summer, winter and autumn was found to be 5.1 and 31.29, 2.1 and 6.4, 4.74 and 35.08 μg g ^?1 at most intercepts. The average ratio of low to high carcinogenic PAHs was found to be 1:6, 1:3, 1:7.6 during summer, winter and autumn, respectively. Five ringed PAHs were found in higher concentration in all seasons. Dib(ah)A and B(a)P were the two individual PAHs found in highest concentration during summer, winter and autumn seasons. Two tailed T-test was applied for authenticity of the results. Toxic equivalency factor of B(a)P and Dib(ah)A was maximum as compared to other PAHs. The study could be of great significance for the planners while considering environmental remedial measures.     

Cell Size-Dependent Effects of Solar UV Radiation on Primary Production in Coastal Waters of the South China Sea

In order to examine the effects of solar ultraviolet radiation (UVR, 280–400 nm) on photosynthesis of differently cell-sized phytoplankton, natural phytoplankton assemblages from the coastal waters of the South China Sea were separated into three groups (>20, 5–20, and <5 μm) and exposed to four different solar UV spectral regimes, i.e., 280–700 nm (PAR?+?UVR), 400–700 nm (PAR), 280–400 nm (UV-A?+?B), and 315–400 nm (UV-A). In situ carbon fixation measurements revealed that microplankton (>20 μm) efficiently utilized UV-A for photosynthetic carbon fixation, with assimilation number of up to 1.01 μg C (μg chl a)^?1?h^?1 under 21.4 W?m^?2 UV-A alone (about half of noontime irradiance at the surface), about 40 % higher than nanoplankton (5–20 μm). UV-B (280–315 nm) of 0.95 W?m^?2 reduced the carbon fixation by approximately 20 and 57 % in microplankton and nanoplankton assemblages, respectively. In contrast, smaller picoplankton (<5 μm) was unable to utilize UV-A for the photosynthetic carbon fixation. In addition, only micro-sized assemblages demonstrated the UV enhancement on their primary productivity in the presence of PAR, by about 8 % under moderate intensities of solar radiation.     

Sterols in interstitial waters of marine sediments

In order to attempt to elucidate the nature of biogeochemical processes occurring at the water-sediment interface, sterols have been analysed in near bottom sea and interstitial waters collected in the eastern and western intertropical Atlantic ocean. Free and esterified sterol concentrations range from 0.2 to 82 μg l^?1 and are much higher than those found in overlying sea water, which range from 0.2 to 1.7 μg l^?1 for the dissolved fraction and from 0.01 to 0.07 μg l^?1 for the particulate fraction. Cholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol are the dominant sterols in sea and interstitial waters. The variability encountered for the relative importance of minor sterols such as 24-methylcholesta-5,24(28)-dien-3β-ol and stanols, 5α-cholest-22(E)-en-3β-ol, 5α-cholestan-3β-ol and 24-ethyl-5α-cholestan-3β-ol in interstitial water and their variation with depth is discussed in terms of diversity of inputs and bacterial activity. For sediments cored off the Mauritanian coast, a productive area characterized by an intense upwelling, the chemical signatures observed in interstitial water through stanol/stenol ratios occur at levels of very high heterotrophic aerobic bacterial biomass estimations. The study of the sterol composition of interstitial water could constitute a valuable tool in appreciating the intensity of chemical and biological processes occurring in the first few metres of recent marine sediments.     

Chlorinated volatile organic compounds found near the water surface of heavily polluted rivers

The objectives of this study were to identify the chlorinated volatile organic compounds near the water surface of two heavily polluted rivers in the south of Taiwan and compare their concentration distributions. Air samples were collected seasonally at the upstream, midstream and downstream water surfaces of each river and the chlorinated volatile organic compounds were analyzed qualitatively and quantitatively by gas chromatography and electron capture detector. Totally, twelve kinds of chlorinated volatile organic compounds were found at the water surfaces of both rivers and many of them were reported to be carcinogenic or probably carcinogenic to human. The results showed that each chlorinated volatile organic compound had its own distribution pattern and no good correlation of chlorinated volatile organic compounds between both rivers was obtained. The chlorinated volatile organic compounds identified at the river water surface of Fong Shan Stream showed much higher concentration than those of Chuen-Tsen River. Several chlorinated volatile organic compounds, including chlorodibromomethane, hexachlorobutadiene, 1,1,2,2-tetrachloroethene and 1,2-dibromo-3-chloropropane were found with much higher concentration (mean concentrations of 124.5 μg/m³, 334.5 μg/m³, 92.2 μg/m³, 268.4 μg/m³, respectively) at the water surface of Fong Shan Stream in some seasons (especially spring and summer, summer and winter, spring and winter, spring and summer, respectively) and they were reported to be possibly carcinogenic to human. Therefore, it may be concluded that the people living close to Fong Shan Stream possibly had higher health risks due to the release of volatile organic compounds from the heavily polluted river.     

Reproduction of the fiddler crabsUca longisignalis andUca spinicarpa in a Gulf of Mexico salt marsh

Monthly field sampling of active animals in a Louisiana coastal salt marsh monitored changes in size class frequency distributions, ovarian development of females, and rates of egg extrusion for two species ofUca endemic to the Gulf of Mexico. Ovigerous females occurred no earlier than February forUca spinicarpa and April forUca longisignalis. Peak percentages of ovigerous females were observed in June 1992 forUca longisignalis (67%) and in March 1993 forUca spinicarpa (85%). Peaks in ash-free dry weight (AFDW, in g) of females coincide with peak periods of ovarian development and subsequent ovigery. Mean biomass as AFDW of males and females combined forUca longisignalis was 0.26 g individual^?1 and forUca spinicarpa was 0.17 g individual^?1. A significant correlation existed between AFDW and carapace width in both species, males and females.U. longisignalis appears to be of warm-temperate lineage, and its reproductive activity is the more seasonally restricted, with later ovarian development, earliest egg laying delayed to late spring, and peak ovigery in summer. In keeping with putative tropical affinities ofUca spinicarpa, ovarian development is episodic over a longer-period from late winter to summer, and eggs are produced earlier in the year. The more striking seasonality in reproductive activity and biomass peaks forUca longisignalis may also reflect some nutritional dependency on temperate, annual marsh plants that characterize its preferred habitats.     

Natural Cycles and Transfer of Mercury Through Pacific Coastal Marsh Vegetation Dominated by Spartina foliosa and Salicornia virginica

The potential for marsh plants to be vectors in the transport of mercury species was studied in the natural, mature, tidal China Camp salt marsh on San Pablo Bay. The fluxes of organic matter, mercury (THg), and monomethylmercury (MeHg) were studied in natural stands of Spartina foliosa and Salicornia virginica. Seasonal fluxes from the sediment into aboveground biomass of live plants and subsequent transfer into the dead plant community by mortality were measured. Loss of THg and MeHg from the dead plant community through fragmentation, leaching, and excretion were calculated and were similar to net uptake. Seasonal data were added up to calculate annual mass balances. In S. foliosa, annual net production was 1,757 g DW m^?2, and the annual net uptakes in the aboveground biomass were 305 μg THg m^?2 and 5.720 μg MeHg m^?2. In S. virginica, annual net production was 2,117 g DW m^?2, and the annual net uptakes in aboveground biomass were 99.120 μg THg m^?2 and 1.990 μg MeHg m^?2. Of both plant species studied, S. foliosa had a slightly lower production rate but greater mercury species uptake and loss rates than S. virginica, and, consequently, it is to be expected that S. foliosa matter may affect the local and possibly the regional food web relatively more than S. virginica. However, the actual effects of the input of mercury-species-containing plant-derived particulate matter into the food webs would depend on trophic level, food preference, seasonal cycle of the consumer, total sediment surface area vegetated, location of the vegetation in the marsh landscape, and estuary bay landscape. Since the levels of mercury species in dead plant material greatly exceed those in live plant material (on a dry weight basis), detritivores would ingest greater mercury species concentrations than herbivores, and consumers of S. foliosa would ingest more than consumers of S. virginica. The greatest THg and MeHg losses of both plant species due to mortality and to fragmentation–leaching–excretion occurred in late spring and early autumn, which corresponds to peak MeHg levels observed in sediments of coastal systems of previous studies, suggesting enhanced THg–MeHg export from the marsh to the nearshore sediment.     

Composition and vertical flux of organic matter in a large Alaskan estuary

Observations of the composition and rate of input of organic matter to the sea floor were made at three locations in lower Cook Inlet, Alaska, during five cruises taken in the spring and summer of 1978. Total particulate, plant pigment, carbon, nitrogen, fecal pellet, and phytoplankton cell fluxes, inferred from sediment trap samples, were related to algal biomass and production in overlying waters. A daily average of 7.5% of the phytoplankton biomass was lost to the bottom. Of this loss, 83% was attributable to zooplankton grazing and fecal pellet production. At the three sampling sites, an average of 39 g C m^?2 (range of 17–60 g C m^?2, was sedimented to the bottom between May and August. This carbon flux represented an average of 12% of the total primary production measured for that time period. Kachemak Bay eastern arm of the inlet, is identified as an extremely productive embayment in which large amounts of organic matter were transferred to the sea floor.