Effects of graveling on the primary productivity,respiration and nutrient flux of two estuarine tidal flats

This study was conducted in Puget Sound, USA, and investigated the effect of graveling intertidal mud and sandflats to enhance clam production on the benthic assemblage structure, primary productivity, respiration, and nutrient flux. The study was conducted between spring and autumn (1991), the period of greatest productivity and plant standing stock in Puget Sound. Graveled and control plots were established in the low intertidal zone on a mud flat in a protected embayment (Chapman Cove) and an exposed sandflat (Semiahmoo Bay). Gravel altered benthic assemblage structure, respiration, and nutrient flux rates. Graveled plots contained more surface coverage of sessile animals and seaweeds. Net productivity (NP), which differed relatively little between graveled and control plots, was negative for all but one sampling at the protected embayment plots. In contrast, NP was always positive at the exposed sandflat plots. The respiration rate was 13 to 57% greater in the graveled plot at Chapman Cove than in the adjacent control plot, and 7 to 54% greater in the gravel plot than the control plots at Semiahmoo Bay. Heterotrophy was greater in the graveled plots, as reflected by a lower net productivity to respiration ratio. Effects of graveling on water quality parameters such as dissolved oxygen and inorganic nitrogen concentrations were not detected. Graveling sandy and mud beaches increases secondary productivity, which is associated with increased rates of remineralization and release of dissolved nutrients to the water column.     

Evidence for multiple recruitment-cohorts of Puget Sound Dungeness crab,Cancer magister

While sampling intertidally in Puget Sound, Washington, USA, for juvenile Dungeness crab (Cancer magister) in 1984, we found evidence of two distinct cohorts of the same year-class based on sizes of first-instar juveniles (J1) and the spatial/temporal patterns of settlement. In 1988, three distinct cohorts were observed to settle in Puget Sound and its approaches. Settlement of one cohort occurred during May in the Strait of Juan de Fuca and in those areas of Puget Sound closest to the Strait. J1 individuals of this cohort were large (x=7.4 mm carapace width, CW) and comparable in both size and timing of settlement to populations along the Washington coast (e.g. Grays Harbor and Willapa Bay). Initial settlement density of the May cohort was as high as 215 crabs/m² in intertidal eelgrass beds along the Strait of Juan de Fuca and decreased to <2 crabs/m² within Puget Sound and the Strait of Georgia. A second cohort apparently originated in Hood Canal (a deep inland fjord), its size upon settlement in June was significantly smaller (J1 x= 5.3 mm CW) than the May cohort, and it was limited to Hood Canal and areas of Puget Sound close to the mouth of Hood Canal. A third cohort, which settled in late July and August, was the smallest of the three cohorts (J1 x= 4.8 mm CW), and was widely distributed around Puget Sound from Seattle in the south to the USA/Canadian border in the north. We hypothesize that most juvenile recruitment in Hood Canal and Puget Sound originates from parental stocks endemic to their respective basins (Hood Canal and Puget Sound cohorts), but that, on occasion, oceanographic conditions allow substantial influx of Pacific Ocean Dungeness crab larvae (oceanic cohort) through the Strait of Juan de Fuca into Puget Sound. Tracking of spatial/temporal settlement patterns and comparison of J1 sizes proved useful for estimating the probable sources and dispersion of Dungeness crab larvae. Differences in size and time of settlement between various larval cohorts of C. magister may prove useful as biomarkers for tracing circulation patterns within and between inland waters of Washington and the Pacific Ocean. Causes of smaller size and later settlement of the Puget Sound cohort relative to oceanic conspecifics of the same year-class are discussed.Contribution No. 856, School of Fisheries, University of Washington, Seattle     

Two populations of the marine fish Porichthys notatus,one lacking in luciferin essential for bioluminescence

Porichthys notatus is a common benthic fish found along the Pacific coast of North America. It possesses more than 700 small dermal photophores on its head and trunk. When P. notatus collected in Monterey Bay, California, is injected subcutaneously with norepinephrine, the photophores emit a long-lasting luminescence that is readily visible to the dark-adapted eye. The light emission is due to the oxidation of luciferin (substrate) by molecular oxygen, catalyzed by luciferase. In contrast, P. notatus collected in Puget Sound, Washington, is nonluminous, even though the photophores do not differ ultrastructurally from those of the California fish. The inability of the Puget Sound fish to luminesce is due to lack of luciferin in its photophores. Luminescence capability, however, may be induced in the Puget Sound fish by the oral or intraperitoneal administration of a small amount of luciferin from the tiny luminescent marine ostracod crustacean, Vargula hilgendorfii, suggesting that the origin of luciferin in P. notatus may be from the diet. In this study, specimens of P. notatus were collected over the entire known range of the species, between November 1981 and September 1987, and the presence of luciferin in the photophores determined. The results indicate that there are two populations of P. notatus: a luciferin-deficient, nonluminescent population located north of northern California and a luciferin-containing, luminescent population extending south of Cape Mendocino, California, to Baja California, Mexico. At the northern end of the southern population, a mixture of luminescent and nonluminescent P. notatus was found.     

Short-term changes in feeding and digestion by the copepodCalanus pacificus

The planktonic marine copepodCalanus pacificus exhibits an enhanced feeding rate, or hunger response, when exposed to food following short periods of starvation. In a scries of laboratory experiments with copepods collected from the main basin of Puget Sound, Washington, during 1982 and 1984, we measured maximum ingestion rate, assimilation efficiency, and digestive enzyme activity to determine the time scales over which the feeding behavior ofC. pacificus responds to increases in food. These laboratory results were then compared to field studies of diel fluctuations in digestive enzymes and gut fluorescence ofC. pacificus in Dabod Bay, a fjord of Puget Sound, during September, 1980, and the closely relatedC. marshallae off the Washington coast, in August, 1981. Laboratory experiments demonstrated that the hunger response ofC. pacificus lasts approximately 6 h before ingestion rate returns to a steady state level of about one-half maximum. On the order of 12h of starvation were required to induce the maximum ingestion rate of the hunger response. Digestive enzyme activities did not change over these time scales. Assimilation efficiency peaked within a few hours of the onset of feeding, with low initial rates possibly related to the period of starvation prior to feeding. These results were consistent with diel patterns observed in the field. The hunger response ofC. pacificus appears to be controlled by processes within the gut, and our results are discussed in relation to recent studies of the digestive processes of calanoid copepods.Contribution No. 1772 from the School of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Differences in morphology and habitat use among the native mussel <Emphasis Type="Italic">Mytilus trossulus</Emphasis>, the non-native <Emphasis Type="Italic">M. galloprovincialis,</Emphasis> and their hybrids in Puget Sound,Washington

Mytilus galloprovincialis (Mg), the Mediterranean blue mussel, is sympatric with the native M. trossulus (Mt) throughout much of the north Pacific, likely as the result of human introduction. We investigated the distribution of the two species and their hybrids (Mgt) in Puget Sound, Washington, to determine whether differences occur in habitat preference between the two species and hybrids. In addition, we investigated whether there were consistent size and shape differences between the native and introduced mussels and hybrids. Measurements of over 6,000 mussels from 30 sites, of which 1,460 were genotyped for a species-specific genetic marker, revealed that Mg and Mgt can be found throughout Puget Sound. Mg and Mgt were larger and exhibited a greater height:length ratio than Mt. Frequencies of Mg and Mgt were higher in subtidal habitats, such as docks, than on intertidal rocks, walls or pilings. Within intertidal habitats, Mg and Mgt were more frequent than Mt in the lower reaches of the intertidal. At slightly more than half the sites the frequency of the three genotypes accorded with random mating expectations suggesting no consistent barriers to gene flow between species. The standardized random sampling methods and simple morphometric identification techniques described here can be used to test whether the frequency of invasive mussels changes over time and space in Puget Sound.     

Population interconnectivity and implications for recovery of a species of concern, the Pacific hake of Georgia Basin

To aid the recovery of a species, understanding the extent to which populations are connected is useful for targeting conservation efforts. Pacific hake within waters of Puget Sound, Washington State, USA, and Georgia Strait, British Columbia, Canada are listed as a species of concern under the U.S. Endangered Species Act due to dramatic declines in the Puget Sound population. To assess the role of dispersal in the recovery of Pacific hake, we sought to quantify patterns of connectivity between populations in Puget Sound and Georgia Strait. Using natural chemical markers from otoliths of fish sampled from these two populations, we linked natal signatures of fish to signatures of individuals from known spawning grounds. Results indicated that 82 % of individuals collected from Puget Sound (n = 78) were estimated to have originated there, while 40 and 92 % of the individuals collected from two cohorts within Georgia Strait (n = 9 and 24, respectively) had originated from Puget Sound. A trend of “population abandonment” of fish from Puget Sound suggests that recovery of this Pacific hake population will depend on local management practices.     

Latitudinal trends in size-dependence of bioluminescence in the midshipman fish Porichthys notatus

The bioluminescent fish Porichthys notatus (plainfin midshipman), has a discontinuous distribution along the Pacific coast of North America. The fish is present from Cape Mendocino southward to Baja California, Mexico, absent off the coast of Oregon, USA, and abundant, northward, in Puget Sound, Washington. Interestingly, the population in Puget Sound lacks the substrate (luciferin) necessary for the luminescence reaction and, despite possessing an otherwise fully functional photophore system, is nonluminescent. The California population of P. notatus is uniformly luminescent south of Monterey Bay, but 15% of the speciments tested from San Francisco Bay and the Gulf of the Farallons have been reported to be nonluminescent. Explanations for nonluminescent midshipman in both Puget Sound and the San Francisco Bay area have focussed on a dietary requirement for luciferin. To gain further insight into reasons for nonluminescence in the San Francisco Bay region, the distribution of bioluminescence in P. notatus was studied from Monterey Bay to Cape Mendocino during 1985. A complex pattern of bioluminescence was found, in which nonluminescent individuals reflected neither a local anomaly in the San Francisco Bay region nor a simple gradient of decreasing luminescence towards the northern end of the range of the California population. Instead, a distinct size-dependent component in luminescence capability of the fish was observed. Aspects of the life history of P. notatus and related factors which might influence the bioluminescence characteristics of this population are discussed.Please address all correspondence to Dr. F.I. Tsuji at the Osaka Bioscience Institute     

Larval development of the crabCancer magister in temperature regimes simulating outer-coast and inland-water habitats

Postlarval megalopae of the Dungeness crabCancer magister inhabiting offshore coastal waters along the west toast of North America are larger and settle earlier than do those occupying the inland waters of the Puget Sound basin (Washington, USA, and British Columbia, Canada). The Puget Sound habitat is characterized by low initial temperatures that steadily increase during the course of zoeal development, while offshore temperatures are more moderate and stable. Larvae were raised in the laboratory from hatching to megalopa in three temperature treatments: (1) constant 10 °C (CO), (2) a regime that temporally simulated temperatures found off the central California coast during the larval season (CA); and (3) a regime simulating temperatures found within the Puget Sound basin (PS). Zoeal duration was 44% longer in the PS treatment than in the other two, at least partially accounting for observed differentes between outer-toast and inland-water settlement times. Although differentes were measured in megalopal weights and carapace lengths among treatments, results do not explain differences in megalopal size observed between outer-toast and inland-water individuals. Survival to megalopa was highest in the PS treatment, with the difference due to significantly lower mortality than in CO and CA treatments during the terminal zoeal stage. Daily instantaneous mortality rates were lower in the PS than in CO or CA treatments, indicating Chat extended larval duration will not necessarily result in reduced settlement success.     

Population genetics and systematics of theLeptasterias hexactis (Echinodermata: Asteroidea) species complex

Morphological characters and 14 enzyme loci were examined for 1 040 sea stars, currently recognized as forms ofLeptasterias hexactis, from Lynn Canal, Alaska, and Puget Sound, Washington, USA, between March 1988 and April 1989. Three morphologically and two genetically distinctLeptasterias forms were identified. The most common form found at both localities wasL. epichlora (Brandt)sensu Verrill.L. hexactis (Stimpson)sensu Verrill co-occurred withL. epichlora at all study sites and apparently hybridizes extensively withL. epichlora in the Puget Sound region, but rarely, if at all, in Alaska. The presumptive product of this hybridization morphologically resembledL. aequalis (Stimpson)sensu Fisher, and was conspicuously absent from Alaskan samples. Considerable genetic distance existed betweenL. epichlora andL. hexactis (Nei'sD=0.19±0.01) and moderate genetic differentiation occurred between populations of each species from Alaska and Washington (Weir and Cockerham'sF _RT =0.29±0.04 forL. epichlora and 0.21±0.15 forL. hexactis). A significant (p<0.05) deficiency in the proportion of heterozygous individuals was found compared to Hardy-Weinberg expectations (Wright's fixation index,F _ID=0.12±0.04 and 0.31±0.08 forL. epichlora andL. hexactis, respectively). However, mean observed heterozygosity for each species (0.09±0.03, 0.14±0.04 and 0.14±0.04 forL. epichlora, L. hexactis andL. aequalis, respectively) fell within the range of reported values for other asteroid species (ca. 0.04 to 0.37). The results of this study indicate that considerable genetic integrity is maintained betweenL. epichlora andL. hexactis, which warrants their recognition as distinct species despite their apparent hybridization in the Puget Sound region.     

Disruptive counterillumination and its anti-predatory value in the plainfish midshipman Porichthys notatus

The plainfin midshipman Porichthys notatus Girard occurs in nearshore waters off the western coast of North America. We found that the ventrally directed photophores of juvenile laboratory-grown P. notatus function in counterillumination. Their bioluminescence matched downwelling light to obscure the silhouette as viewed from below. P. notatus did not obligatorily counterilluminate at all times in appropriate light. A hydrodynamic stimulus, in addition to appropriate downwelling light, was required to induce counterillumination. This is perhaps an adaptation to conserve its Vargula-type luciferin, which is obtained from its diet. The angular distribution of light produced by P. notatus approximated that typical of downwelling light in the ocean. There was a direct relationship between downwelling irradiance and the maximum intensity of P. notatus luminescence. Insufficient light was produced to replace the light blocked by the fish under lighting conditions typical of the natural environment. The luminescence was, however, effective in eliminating the silhouette of P. notatus as observed with an image-intensifying camera and by dark-adapted human observers. Consequently, the effectiveness of counterillumination probably originates in part from the disruptive pattern of the luminous photophores. P. notatus from the Puget Sound population, which lacks a luciferin source and is non-luminous, displayed counterillumination behavior when its luminescent system was activated by force-feeding the fish with dried Vargula hilgendorfi. Experiments using adult P. notatus as predators on a mixed population of non-luminous (Puget Sound) and luminous (Santa Barbara Channel) juvenile P. notatus revealed that under conditions of dim overhead illumination non-luminous P. notatus were preyed upon at twice the rate of luminous individuals. This is the first experimental evidence suggesting that counterillumination is effective as an anti-predatory strategy. Received: 25 August 1998 / Accepted: 25 March 1999     

Eutrophication and trophic structure in response to the presence of the eelgrass <Emphasis Type="Italic">Zostera noltii</Emphasis>

In estuaries, eelgrass meadows contribute to fundamental ecosystem functions of estuaries, providing food to several predators and buffering the negative effects of eutrophication. We asked whether the presence of the eelgrass Zostera noltii decreased the nitrogen concentration in the overlying water, affected the sources of nitrogen sequestrated by primary producers and changed the benthic and pelagic food web structures. We also studied the importance of these food webs in providing food to fish. We compared bare sediment to sediment covered by a Z. noltii meadow, and examined nutrient concentrations in the water column and δ¹⁵N in primary producers as indicators of anthropogenic inputs of nutrients. We then measured both δ¹³C and δ¹⁵N in the tissues of plants and consumers to establish food web structures. There were no differences in the concentrations and sources of nitrogen between sites. Rather, δ¹⁵N values indicated anthropogenic inputs of N (e.g. sewage discharges, agriculture) in both sites. There were no major differences in the structure of the planktonic food web, which was in part sustained by particulate organic matter and supported most predator fish, and in the structure of the benthic food web. Nonetheless, there were differences in the sources of food for omnivore consumers and for the detritivore Scrobicularia plana. Overall, the benthic food web did not use food derived from the eelgrass or macroalgae deposited on the substratum. Suspension feeders used particulate and sediment organic matter, whereas the δ¹³C and δ¹⁵N values of the other consumers indicated a likely contribution of benthic microalgae. Furthermore, in both habitats we found large variability in the isotope signatures of benthic macrofauna consumers, which did not allow distinguishing clearly different trophic groups and indicated a high level of omnivory and a mixed diet opportunistically making use of the availability of food in the surroundings.     

Production dynamics of the eelgrass, <Emphasis Type="Italic">Zostera marina</Emphasis> in two bay systems on the south coast of the Korean peninsula

Production dynamics of eelgrass, Zostera marina was examined in two bay systems (Koje Bay and Kosung Bay) on the south coast of the Korean peninsula, where few seagrass studies have been conducted. Dramatically reduced eelgrass biomass and growth have been observed during summer period on the coast of Korea, and we hypothesized that the summer growth reduction is due to increased water temperature and/or reduced light and nutrient availabilities. Shoot density, biomass, morphological characteristics, leaf productivities, and tissue nutrient content of eelgrass were measured monthly from June 2001 to April 2003. Water column and sediment nutrient concentrations were also measured monthly, and water temperature and underwater irradiance were monitored continuously at seagrass canopy level. Eelgrass shoot density, biomass, and leaf productivities exhibited clear seasonal variations, which were strongly correlated with water temperature. Optimal water temperature for eelgrass growth in the present study sites was about 15–20°C during spring period, and eelgrass growths were inhibited at the water temperature above 20°C during summer. Daily maximum underwater photon flux density in the study sites was usually much higher than the light saturation point of Z. marina previously reported. Densities of each terminal, lateral, and reproductive shoot showed their unique seasonal peak. Seasonal trends of shoot densities suggest that new eelgrass shoots were created through formation of lateral shoots during spring and a part of the vegetative shoots was transformed into flowering shoots from March. Senescent reproductive shoots were detached around June, and contributed to reductions of shoot density and biomass during summer period. Ambient nutrient level appeared to provide an adequate reserve of nutrient for eelgrass growth throughout the experimental period. The relationships between eelgrass growth and water temperature suggested that rapid reductions of eelgrass biomass and growth during summer period on the south coast of the Korean peninsula were caused by high temperature inhibition effects on eelgrass growth during this season.     

Long-term variability in the structure of subtidal benthic communities in Puget Sound,Washington, USA

Data on benthic infauna from 4 permanent stations in Puget Sound off Seattle, USA, collected during 1963–1964, 1967, and 1969, revealed considerable stability in numbers of species and specimens and in diversity within stations among sampling dates. The species composition of the faunal assemblages also remained rather constant during the period of investigation, but the relative dominance among the numerically important species varied somewhat. Biomass data did not differ significantly in 1964 and 1969, but the 1967 data were considerably lower at all stations.     

Distribution and structure of benthic assemblages in Puget Sound,Washington, USA

Benthic infauna was collected with a 0.2 m² van Veen grab at 48 stations in Puget Sound, Washington, USA during February–March 1969. All the crustaceans, lamellibranchs, and echinoderms were identified and counted. Particle size distributions and nitrogen contents of the sediments, depths, and temperature and salinity of the bottom water were determined at all stations. The first three factors of a factor analysis applied to between-stations measures of affinity, explained 41.26% of the total variance. The first factor had representative stations on shallow-water mud bottoms, the second factor on bottoms dominated by coarse sediments, and the third factor had representative stations on deep-water mud bottoms. The multiple correlation coefficients for each of the three factors with depth and mean particle size of the sediments were 0.752, 0.897, and 0.706, respectively. The factor analysis did not result in clusters of stations that could be interpreted as discrete benthic communities. The number of species per 0.6 m² ranged from 8 to 55 species, with a mean of 26.4 species. The frequency distribution of specimens among the species was in good agreement with a log-normal distribution. The number of specimens per 0.6 m² ranged from 57 to 1733 specimens, with a mean of 584.0 specimens. The species diversity ranged from 0.34 bits/individual to 4.35 bits/individual, and there was a weak trend of increasing diversity towards coarser sediments. The first three factors applied to the matrix of between-species correlation coefficients explained 43.72% of the total variance. With each factor there was one group of species with high positive loadings and one group with high negative loadings. Each group of species could be identified with particular environments. The standing crop, measured as ash-free dry weight, ranged from 0.490 to 54.093 g/m², with a mean of 13.752 g/m². Only about 24% of the variability in standing crop could be attributed to variability in sediment types, nitrogen content in the sediments, salinity of the bottom water, and depth.     

Adenosine triphosphate and adenylate energy charge in marine sediments

The determination of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) concentrations in sediments from both Puget Sound and the Washington State continental shelf (USA) has been investigated. Major losses during the extraction procedure included sediment sorption, coprecipitation, and unreactivity of the soluble adenylates presumably through irreversible binding to solubilized sediment organics. Addition of phosphoric acid and the non-ionic detergent Triton X-100 to cold sulfuric acid significantly increased the extraction efficiency and sensitivity over that of sulfuric acid alone, although both methods yielded similar results when corrected for losses. Vertical profiles of ATP, total adenylates (A_T), and adenylate energy charge (EC) in sediments from both areas are presented. Profiles of A_T are similar in both areas, but EC values in the shelf sediments are significantly lower, which suggests a depressed physiological condition in the shelf population relative to that in Puget Sound.Contribution No. 513 from the University of Washington's College of Fisheries, and Contribution No. 1135 from the University of Washington's Department of Oceanography     

13C label identifies eelgrass (Zostera marina) Carbon in an Alaskan estuarine food web

The food web of Izembek Lagoon, Alaska draws most of its carbon from eelgrass (Zostera marina) and phytoplankton. The¹³C:¹²C ratios of these primary producers are sufficiently different to enable their contributions to consumers to be estimated from consumer¹³C:¹²C ratios. Although the technique is conceptually simple, carbon inputs from other sources and isotope fractionations occurring in the food web limit its precision. Isotopic data nevertheless helps to establish the major carbon fluxes through the community and to assess the importance of eelgrass carbon to individual animals. It is particularly useful when dealing with detritus food chains, where direct observations of animal feeding habits are difficult to make. The Izembek community draws much of its carbon from eelgrass. Detritus food chains provide the major pathway for assimilation of eelgrass carbon by the community, but grazers are also important. Eelgrass carbon is more important to benthic animals than to the eelgrass epibiota and the fishes, which depend mainly on phytoplankton carbon.Publication No. 381 of the Institute of Marine Science, University of Alaska.     

Grazing by 35 to 202 μm micro-zooplankton in Long Island Sound

Micro-zooplankton abundance in Long Island Sound varied from 10³ to 10⁴ animals l^-1 at the station studied and consisted almost entirely of tintinnids. The micro-zooplankton were found to sometimes remove a significant portion of the chlorophyll a standing stock, with an upper limit of 41% of the standing stock being ingested per day. Observed ingestion rates ranged from 0.001 to 0.17 ng chlorophyll a removed animal^-1 h^-1 and from 0.06 to 87 cells removed animal^-1 h^-1, depending on season and type of cell being ingested. Filtering rates varied from 1.03 to 84.7 l animal^-1 h^-1. As a community, the micro-zooplankton exhibited the same order of magnitude ingestion and filtering rates as those noted for copepods.Contribution No. 259 of the Marine Sciences Center     

The dynamics of phytoplankton blooms in puget sound a fjord in the Northwestern United States

This paper describes a quantitative investigation of relationships between the growth of phytoplankton, and climatic and hydrodynamci conditions in temperate fjords with marked tides, as exemplified by Puget Sound, Washington (USA). Algal growth in the open waters of the central basin of the Sound is dominated by a number of intense blooms beginning in late April or May and recurring throughout the summer. Rarely, and only briefly, does nitrate become exhausted. The phytoplankton production rate in the central basin of Puget Sound is about 465 g C m^-2 year^-1. During the springs of 1966 and 1967, oceanographic measurements were carried out at a mid-channel station with sufficient frequency to allow investigation of physical and biological processes with time scales of the order of a day. The principal investigative tool is a numerical model in which the hydrodynamical conditions are represented by an approximate analysis of the gravitational convection mode of circulation. Algal concentration is represented as a continous function of space and time in the model which ascribes changes in phytoplankton density to variations in photosynthetic and respiratory activity, algal sinking, grazing by herbivores, and to mixing and advection. Computations adequately reproduce the principal features of phytoplankton concentrations observed during 75 days and 35 days in the springs of 1966 and 1967, respectively. Numerical experiments assess the relative importance of various processes which govern the level of primary production in Puget Sound. It is concluded that phytoplankton growth is limited by a combination of factors, including vertical advection and turbulence, modulation of underwater light intensity by self-shading and inorganic particulates, sinking of algal cells, and occasional rapid horizontal advection of the population from the area by sustained winds. The high primary productivity of the Sound is due to intensive upward transport of nitrate by the estuarine mechanism. These results should be generally applicable to other temperate fjords because of the largely conventional choice of the biological functions.     

Sea level rise and eelgrass (Zostera marina) production: A spatially explicit relative elevation model for Padilla Bay, WA

The dynamics that govern the elevation of a coastal wetland relative to sea level are complex, involving non-linear feedbacks among opposing processes. Changes in the balance between these processes can result in significant alterations to vegetation communities that are adapted to a specific range of water levels. Given that current sedimentation rates in Padilla Bay, Washington are likely less than historical levels and that eustatic sea level rise is accelerating, the extensive Zostera marina (eelgrass) meadows in the bay may be at risk of eventual submergence. We developed a spatially explicit relative elevation model and used it to project changes in the productivity and distribution of eelgrass in Padilla Bay over the next century. The model is mechanistic and incorporates many of the processes and feedbacks that govern coastal wetland elevation change. Accretion estimates made using ²¹⁰Pb dating of sediment cores, sediment characteristics measured within cores, and eelgrass productivity and decomposition data were used to initialize and calibrate the model. Validation was performed using an elevation change rate measured with a network of surface elevation tables. Both the field data and model simulations revealed a net accretion deficit for the bay. Simulations using current rates of sea level rise indicated an overall expansion of eelgrass within Padilla Bay over the next century as it migrates from the center of the bay shoreward.     

Seasonal changes of benthic bacteria in a seagrass bed (Posidonia oceanica) of the Ligurian Sea in relation to origin,composition and fate of the sediment organic matter

Variations in number and biomass of benthic bacteria were examined in the surface sediments of a Mediterranean seagrass bed [Posidonia oceanica (L.) Delile] in the Gulf of Marconi (northwestern Mediterranean Sea) from 1990 to 1991. The annual dynamics of benthic bacterial density and biomass were compared to changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter, as well as to microphytobenthic biomass, dissolved inorganic nutrients and ATP. Bacterial densities exhibited marked seasonal variations (5.12 to 322.7x10⁸ cells g^-1 sediment dry wt) with highest values in late spring. Bacterial standing stocks (15.8 to 882.33 g C g^-1 of sediment dry wt) were high. Bacterial biomass did not correlate with organic C, total N or to specific biochemical components, but correlated significantly with chlorophyll a, ATP and porewater phosphate concentrations. There is evidence that benthic bacteria were responding to variations of algal biomass. Bacterial biomass accounted, on average, for 30% of total living carbon (calculated on the basis of the ATP concentrations) and 8.4% of total organic carbon.