Search USGS⌕ Search

SEARCH · Search USGS

Results for “Marine Ecology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
USGS2005

Grazing by the intertidal gastropod Melampus coffeus greatly increases mangrove leaf litter degradation rates

Melampus coffeus , a pulmonate gastropod, forages for mangrove leaf litter at low tide and climbs tree trunks to avoid inundation during high tide. Unlike many grazers, these snails can assimilate mangrove leaf material. At Boca Ceiga Bay, Florida, densities of adult snails were high (>100 snails m –2 ) throughout a 130 m wide intertidal zone. A mark–recapture study indicated that over the course of 1 mo 48.6 ± 6.1% of snails returned to their initial tree during high tides, while those that did relocate moved 6.66 ± 0.60 m and were recorded from 33 new trees at high tide. A field experiment comparing tethered leaves with small and large litter bags showed that snail grazing greatly increased the rate of red ( Rhizophora mangle ) and black ( Avicennia germinans ) leaf litter breakdown. Grazing by M. coffeus resulted in 90% weight loss in <4 wk ( A. germinans ) and 7 wk ( R. mangle ), compared to slower breakdown in litter bags (12 to 26 wk, A. germinans ; >26 wk, R. mangle ). Another experiment showed greater leaf litter accumulation on the forest floor in plots where M. coffeus was excluded. The decomposition coefficient ( k ) was 10× greater when M. coffeus grazing was allowed than k for any studies that enclosed leaves in litterbags. During our experiment, M. coffeus consumed an estimated 40.5% of mangrove leaf fall, and 19.8% of leaf litter was exported as particulate or dissolved material. This M. coffeus population can produce an estimated 3 × 10 6 larvae m –2 yr –1 , which suggests that the larval pathway is an important conduit of mangrove leaf resources to the estuarine food web.

Florida↗
USGS2005

Salt tolerance underlies the cryptic invasion of North American salt marshes by an introduced haplotype of the common reed Phragmites australis (Poaceae)

A distinct, non-native haplotype of the common reed Phragmites australis has become invasive in Atlantic coastal Spartina marshes. We compared the salt tolerance and other growth characteristics of the invasive M haplotype with 2 native haplotypes (F and AC) in greenhouse experiments. The M haplotype retained 50% of its growth potential up to 0.4 M NaCl, whereas the F and AC haplotypes did not grow above 0.1 M NaCl. The M haplotype produced more shoots per gram of rhizome tissue and had higher relative growth rates than the native haplotypes on both freshwater and saline water treatments. The M haplotype also differed from the native haplotypes in shoot water content and the biometrics of shoots and rhizomes. The results offer an explanation for how the M haplotype is able to spread in coastal salt marshes and support the conclusion of DNA analyses that the M haplotype is a distinct ecotype of P. australis .

Marine Ecology Progress Series↗
USGS2005

Effects of physical processes on structure and transport of thin zooplankton layers in the coastal ocean

Thin layers of plankton are recurrent features in a variety of coastal systems. These layers range in thickness from a few centimeters to a few meters. They can extend horizontally for kilometers and have been observed to persist for days. Densities of organisms found within thin layers are far greater than those above or below the layer, and as a result, thin layers may play an important role in the marine ecosystem. The paramount objective of this study was to understand the physical processes that govern the dynamics of thin layers of zooplankton in the coastal ocean. We deployed instruments to measure physical processes and zooplankton distribution in northern Monterey Bay; during an 11 d period of persistent upwelling-favorable winds, 7 thin zooplankton layers were observed. These zooplankton layers persisted throughout daylight hours, but were observed to dissipate during evening hours. These layers had an average vertical thickness of 1.01 m. No layers were found in regions where the Richardson number was <0.25. In general, when the Richardson number is <0.25 the water column is unstable, and incapable of supporting thin layers. Thin zooplankton layers were also located in regions of reduced flow. In addition, our observations show that the vertical depth distribution of thin zooplankton layers is modulated by high-frequency internal waves, with periods of 18 to 20 min. Results from this study clearly show an association between physical structure, physical processes and the presence of thin zooplankton layers in Monterey Bay. With this new understanding we may identify other coastal regions that have a high probability of supporting thin layers.

Marine Ecology Progress Series↗
USGS2006

Permanent 'phase shifts' or reversible declines in coral cover? Lack of recovery of two coral reefs in St. John, U.S. Virgin Islands

Caribbean coral reefs have changed dramatically in the last 3 to 4 decades, with significant loss of coral cover and increases in algae. Here we present trends in benthic cover from 1989 to 2003 at 2 reefs (Lameshur Reef and Newfound Reef) off St. John, US Virgin Islands (USVI). Coral cover has declined in the fore-reef zones at both sites, and no recovery is evident. At Lameshur Reef, Hurricane Hugo (1989) caused significant physical damage and loss of coral. We suggest that macroalgae rapidly colonized new substrate made available by this storm and have hindered or prevented growth of adult corals, as well as settlement and survival of new coral recruits. Overfishing of herbivorous fishes in the USVI and loss of shelter for these fishes because of major storms has presumably reduced the levels of herbivory that formerly controlled algal abundance. Coral cover declined at Newfound Reef from 1999 to 2000, most likely because of coral diseases. The trends that we have documented, loss of coral followed by no evidence of recovery, appear similar to findings from other studies in the Caribbean. We need to focus on functional shifts in the resilience of coral reefs that result in their inability to recover from natural and human-caused stressors.

U.S. Virgin Islands↗
USGS2006

Trophic transfer of trace metals: Subcellular compartmentalization in a polychaete and assimilation by a decapod crustacean

The chemical form of accumulated trace metal in prey is important in controlling the bioavailability of dietary metal to a predator. This study investigated the trophic transfer of radiolabelled Ag, Cd and Zn from the polychaete worm Nereis diversicolor to the decapod crustacean Palaemonetes varians . We used 2 populations of worms with different proportions of accumulated metals in different subcellular fractions as prey, and loaded the worms with radiolabelled metals either from sediment or from solution. Accumulated radiolabelled metals were fractionated into 5 components:metal-rich granules (MRG), cellular debris, organelles, metallothionein-like proteins (MTLP), and other (heat-sensitive) proteins (HSP). Assimilation efficiencies (AE) of the metals by P. varians were measured from the 4 categories of prey (i.e. 2 populations, radiolabelled from sediment or solution). There were significant differences for each metal between the AEs from the different prey categories, confirming that origin of prey and route of uptake of accumulated trace metal will cause intraspecific differences in subsequent metal assimilation. Correlations were sought between AEs and selected fractions or combinations of fractions of metals in the prey-MRG, Trophically Available Metal (TAM = MTLP + HSP + organelles) and total protein (MTLP + HSP). TAM explained 28% of the variance in AEs for Ag, but no consistent relationships emerged between AEs and TAM or total protein when the metals were considered separately. AEs did, however, show significant positive regressions with both TAM and total protein when the 3 metals were considered together, explaining only about 21% of the variance in each case. A significant negative relationship was observed between MRG and AE for all metals combined. The predator ( P. varians ) can assimilate dietary metal from a range of the fractions binding metals in the prey ( N. diversicolor ), with different assimilation efficiencies summated across these fractions. TAM and/or total protein may represent an approximate minimum for trophic availability but neither of these alone is a fully accurate predictor.

Marine Ecology Progress Series↗
USGS2006

Differential response in chick survival to diet in least and crested auklets

Least auklets Aethia pusilla and crested auklets A. cristatella are abundant planktivorous seabirds found throughout the Bering Sea and are inextricably linked to the secondary productivity of this northern marine ecosystem. We assessed the relationship between productivity and diet in least and crested auklets by examining breeding chronology, daily survival rates (DSR) of chicks, and nestling diet composition at 2 mixed colonies on St. Lawrence Island in the northern Bering Sea during the 2000 to 2002 breeding seasons. Nestlings of both least and crested auklets hatched earlier, had higher survival rates, and were fed more of the large, oceanic copepod Neocalanus cristatus in 2002 compared to the 2 yr of lower chick survival. In contrast, during the year of lowest DSR for both auklet species (2001), the small copepod Calanus marshallae was more prevalent in the diet of least auklets and the mid-sized copepod N. flemingeri was more prevalent in the diet of crested auklets compared to the other 2 yr. The prevalence of oceanic copepods in meals fed to chicks explained much of the annual variation in DSR in least auklets. Interannual differences in timing of nest initiation, nest survival, and diet of least and crested auklets may be associated with the strength of the cold, nutrient-rich Anadyr Current, which passes in close proximity to St. Lawrence Island and has important influences on zooplankton productivity and distribution. Auklet productivity and diet composition may serve as key indicators in the overall effort to monitor the impact of climate change on the productivity of the Bering Sea.

Marine Ecology Progress Series↗
USGS2006

Genetic structure of eelgrass Zostera marina meadows in an embayment with restricted water flow

Genetic structure of the seagrass Zostera marina in a coastal lagoon with restricted water flow, and with heterogeneous water residence times and oceanographic characteristics, was assessed using 8 polymorphic microsatellite loci. Analyses of genetic differentiation (θ) and Bayesian clustering suggested that the Z. marina population in San Quintin Bay (SQB) is genetically substructured, with at least 4 genetically different groups: (1) West Head, (2) Mouth, (3) East Arm, and (4) East Head. The greatest θ value was observed between the most distant sites (θ = 0.095). The lowest values were found among sites closest to the mouth of the coastal lagoon (θ = 0.000 to 0.009). The maximum likelihood approach showed that the sites at the mouth have a mixed pattern of gene flow without a unidirectional pattern. In contrast, there was a clear pattern of asymmetrical gene flow from the mouth towards the West Head. These results suggested that the restriction of water flow at the heads, current pattern, and the distance between sites can reduce genetic flow and promote genetic differences within Z. marina meadows in small water embayments such as SQB. Though the population is genetically substructured and a 14% decline in cover has been detected, this study did not show evidence of a recent genetic bottleneck. In contrast, mouth sites have experienced a recent expansion in their population size, and also perhaps a recent influx of rare alleles from genetically distinct immigrants

Marine Ecology Progress Series↗
USGS2006

Northern Florida reef tract benthic metabolism scaled by remote sensing

Holistic rates of excess organic carbon production (E) and calcification for a 0.5 km 2 segment of the backreef platform of the northern Florida reef tract (NFRT) were estimated by combining biotope mapping using remote sensing with community metabolic rates determined with a benthic incubation system. The use of ASTER multispectral satellite imaging for the spatial scaling of benthic metabolic processes resulted in errors in E and net calcification (G) of 48 and 431% respectively, relative to estimates obtained using AISA hyperspectral airborne scanning. At 19 and 125%, the E and G errors relative to the AISA-based estimates were less pronounced for an analysis that used IKONOS multispectral satellite imagery to spatially extrapolate the chamber process measurements. Our scaling analysis indicates that the holistic calcification rate of the backreef platform of the northern Florida reef tract is negligible at 0.07 g CaCO 3 m -2 d -1 . All of the mapped biotopes in this reef zone are net heterotrophic, resulting in an estimated holistic excess production rate of -0.56 g C m -2 d -1 , and an overall gross primary production to respiration ratio of 0.85. Based on our finding of ubiquitous heterotrophy, we infer that the backreef platform of the NFRT is a sink for external inputs of suspended particulate organic matter. Further, our results suggest that the inward advection of inorganic nutrients is not a dominant forcing mechanism for benthic biogeochemical function in the NFRT. We suggest that the degradation of the northern Florida reef tract may parallel the community phase shifts documented within other reef systems polluted by organic detritus.

Florida↗
USGS2006

Seasonal migration and environmental conditions of Pacific halibut Hippoglossus stenolepis , elucidated from pop-up archival transmitting (PAT) tags

Pop-up archival transmitting (PAT) tags were used to study the fall migration of halibut in the Gulf of Alaska (GOA). We tagged 6 Pacific halibut Hippoglossus stenolepis on summer feeding grounds in the eastern GOA and another 6 in the western GOA from June 13 to August 6, 2002. The tags were programed to be released from the fish on January 15, 2003, at the height of the winter spawning season: 10 tags successfully detached, transmitted archived environmental data (depth and temperature), and generated accurate latitude–longitude coordinates shortly after pop-up; 2 tags deployed off SE Alaska were lost. The tags revealed that 6 fish had moved a considerable distance (>200 km) between tagging and pop-up, and all of these had moved northward to some extent. The longest of the observed migrations was from the southern Alaska Peninsula to Yakutat Bay, a linear displacement of 1153 km; 4 fish showed little evidence of geographic displacement, exhibiting migrations that ranged only from 30 to 69 km. Although 2 fish had moved inshore by the end of the tagging period, all other fish had moved offshore regardless of their overall migration distance. The precise timing of offshore movements varied, beginning as early as August and as late as January. These observations generally corroborate conventional tagging, indicating migration of halibut toward winter spawning grounds in the northern GOA, and movement of fish to deep water in fall. However, no single stereotypic migration behavior was apparent, and a variety of vertical movement patterns and temperature profiles were observed. Halibut spent most time in waters of 5 to 7°C, but experienced temperatures ranging from 2.6 to 11.6°C. Depth observations ranged from 0 to 736 m, with summertime activity concentrated in depths from 0 to 400 m, and halibut that exhibited offshore movement were typically observed at 300 to 700 m by mid-winter. Vertical movement (short-period changes in depth) varied among fish and over time, with some fish displaying little vertical activity, others displaying short periods of activity, and still others displaying considerable activity throughout their time at liberty.

Marine Ecology Progress Series↗
USGS2006

Inhibition of coral recruitment by macroalgae and cyanobacteria

Coral recruitment is a key process in the maintenance and recovery of coral reef ecosystems. While intense competition between coral and algae is often assumed on reefs that have undergone phase shifts from coral to algal dominance, data examining the competitive interactions involved, particularly during the larval and immediate post-settlement stage, are scarce. Using a series of field and outdoor seawater table experiments, we tested the hypothesis that common species of macroalgae and cyanobacteria inhibit coral recruitment. We examined the effects of Lyngbya spp., Dictyota spp., Lobophora variegata (J. V. Lamouroux) Womersley, and Chondrophycus poiteaui (J. V. Lamouroux) Nam (formerly Laurencia poiteaui) on the recruitment success of Porites astreoides larvae. All species but C. poiteaui caused either recruitment inhibition or avoidance behavior in P. astreoides larvae, while L. confervoides and D. menstrualis significantly increased mortality rates of P. astreoides recruits. We also tested the effect of some of these macrophytes on larvae of the gorgonian octocoral Briareum asbestinum. Exposure to Lyngbya majuscula reduced survival and recruitment in the octocoral larvae. Our results provide evidence that algae and cyanobacteria use tactics beyond space occupation to inhibit coral recruitment. On reefs experiencing phase shifts or temporary algal blooms, the restocking of adult coral populations may be slowed due to recruitment inhibition, thereby perpetuating reduced coral cover and limiting coral community recovery. ?? Inter-Research 2006.

Marine Ecology Progress Series↗
USGS2006

Fate of fish production in a seasonally flooded saltmarsh

Although saltmarshes are thought to enhance the productivity of open estuarine waters, the mechanism by which energy transfer occurs has been debated for decades. One possible mechanism is the transfer of saltmarsh production to estuarine waters by vagile fishes and invertebrates. Monthly estimates of fish standing stock, net fish ingress, and predation were used to develop a biomass budget to estimate annual production of fishes and the relative yield to predatory fish, birds, and direct migration to the estuary. Annual production of saltmarsh fishes was estimated to be 31.0 g m-2 saltmarsh, which falls within the range of previously reported values for estuarine fish communities. The relative yields were 12 to 20% to piscivorous fishes, 8 to 13% to piscivorous birds, and 18 to 29% to export. Annual export of fish biomass was 5.6 g fish m-2 saltmarsh, representing about 1 to 2% of saltmarsh primary production. Saltmarsh fishes convert marsh production to high-quality vagile biomass (fishes concentrate energy, protein, and nutrients as body mass) and move this readily useable production to the estuary, providing an efficient link between saltmarshes and estuarine predators. ?? Inter-Research 2006.

Marine Ecology Progress Series↗
USGS2007

Effects of predation by sea ducks on clam abundance in soft-bottom intertidal habitats

Recent studies have documented strong, top-down predation effects of sea ducks on mussel populations in rocky intertidal communities. However, the impact of these gregarious predators in soft-bottom communities has been largely unexplored. We evaluated effects of predation by wintering surf scoters Melanitta perspicillata and white-winged scoters M. fusca on clam populations in soft-bottom intertidal habitats of the Strait of Georgia, British Columbia. Specifically, we documented spatial and temporal variation in clam density (clams m &ndash;2 ), scoter diet composition, and the consequences of scoter predation on clam abundance. Of the 3 most numerous clams, Manila clams Venerupis philippinarum and varnish clams Nuttallia obscurata were the primary prey items of both scoter species, while clams of the genus Macoma were rarely consumed by scoters. Between scoter arrival in the fall and departure in the spring, Manila clams decreased in density at most sample sites, while varnish clam densities did not change or declined slightly. Our estimates of numbers of clams consumed by scoters accounted for most of the observed declines in combined abundance of Manila and varnish clams, despite the presence of numerous other vertebrate and invertebrate species known to consume clams. For Macoma spp., we detected an over-winter increase in density, presumably due to growth of clams too small to be retained by our sieve (<5 mm) during fall sampling, in addition to the lack of predation pressure by scoters. These results illustrate the strong predation potential of scoters in soft-bottom intertidal habitats, as well as their potentially important role in shaping community structure.

British Columbia↗
USGS2000

Limited effects of a keystone species: Trends of sea otters and kelp forests at the Semichi Islands, Alaska

Sea otters are well known as a keystone species because of their ability to transform sea urchin-dominated communities into kelp-dominated communities by preying on sea urchins and thus reducing the intensity of herbivory. After being locally extinct for more than a century, sea otters re-colonized the Semichi Islands in the Aleutian Archipelago, Alaska in the early 1990s. Here, otter populations increased to about 400 individuals by 1994, but rapidly declined to about 100 by 1997. Roughly 7 yr after initial otter re-colonization, there were only marginal changes in sea urchin biomass, mean maximum test size, and kelp density. These small changes may be the first steps in the cascading effects on community structure typically found with the invasion of a keystone species. However, no wholesale change in community structure occurred following re-colonization and growth of the sea otter population. Instead, this study describes a transition state and identifies factors such as keystone species density and residence time that can be important in dictating the degree to which otter effects are manifested.

Alaska↗
USGS2006

Modeling habitat distribution from organism occurrences and environmental data: Case study using anemonefishes and their sea anemone hosts

We demonstrate the KGSMapper (Kansas Geological Survey Mapper), a straightforward, web-based biogeographic tool that uses environmental conditions of places where members of a taxon are known to occur to find other places containing suitable habitat for them. Using occurrence data for anemonefishes or their host sea anemones, and data for environmental parameters, we generated maps of suitable habitat for the organisms. The fact that the fishes are obligate symbionts of the anemones allowed us to validate the KGSMapper output: we were able to compare the inferred occurrence of the organism to that of the actual occurrence of its symbiont. Characterizing suitable habitat for these organisms in the Indo-West Pacific, the region where they naturally occur, can be used to guide conservation efforts, field work, etc.; defining suitable habitat for them in the Atlantic and eastern Pacific is relevant to identifying areas vulnerable to biological invasions. We advocate distinguishing between these 2 sorts of model output, terming the former maps of realized habitat and the latter maps of potential habitat. Creation of a niche model requires adding biotic data to the environmental data used for habitat maps: we included data on fish occurrences to infer anemone distribution and vice versa. Altering the selection of environmental variables allowed us to investigate which variables may exert the most influence on organism distribution. Adding variables does not necessarily improve precision of the model output. KGSMapper output distinguishes areas that fall within 1 standard deviation (SD) of the mean environmental variable values for places where members of the taxon occur, within 2 SD, and within the entire range of values; eliminating outliers or data known to be imprecise or inaccurate improved output precision mainly in the 2 SD range and beyond. Thus, KGSMapper is robust in the face of questionable data, offering the user a way to recognize and clean such data. It also functions well with sparse datasets. These features make it useful for biogeographic meta-analyses with the diverse, distributed datasets that are typical for marine organisms lacking direct commercial value. ?? Inter-Research 2006.

Marine Ecology Progress Series↗
USGS2006

Potential inhibitors to recovery of Acropora palmata populations in St. John, US Virgin Islands

Populations of Acropora palmata in the Caribbean were decimated in the 1970s and 1980s, with little apparent signs of recovery until the late 1990s. Here, we document an increase in A. palmata colonies between 2001 and 2003 at 8 of 11 monitoring sites in waters adjacent to the island of St. John, US Virgin Islands. The shallow waters along the NW coast of the island exhibited the greatest increase in colony abundance, perhaps due to greater larval supply and/or conditions that favor settlement and subsequent survivorship. Of concern, however, is the lack of survival of large colonies (at all sites), which are most frequently affected by stressors (e.g. Coralliophila abbreviata, damselfishes, active disease) and are most likely to be remnants (colonies with discontinuous, living coral-tissue over an existing coral framework). Predation by C. abbreviata and active coral disease may directly contribute to the development of these remnant colonies. In addition, we recorded damage to colonies attributed to damselfishes and raise the possibility that these territorial reef-inhabitants act as vectors in the transmission of coral disease. While the incidence of disease around St. John is generally low, it may persist as a ubiquitous, chronic stress. Finally, because stressors are more prevalent on large colonies and in high-density stands, they have the potential to inhibit the recovery of A. palmata populations to their historic condition. ?? Inter-Research 2006.

Marine Ecology Progress Series↗
USGS2006

Genetic structure of natural and restored shoalgrass Halodule wrightii populations in the NW Gulf of Mexico

The decline of seagrass communities worldwide has sparked an urgent need for effective restoration strategies, which require a working knowledge of population genetic structure. Halodule wrighti is a common seagrass of the Caribbean region that is being restored to areas of the Gulf of Mexico, yet little is known of its population genetics. This study provides an assessment of individual, clonal and population effects on the genetic structure of 4 natural H. wrightii populations occupying 170 km of coastline in and around Galveston Bay, Texas, for comparison with 7 restored populations ranging in age from 2 to 7 yr. By using molecular markers, in the form of amplified fragment length polymorphisms (AFLPs), we found considerable variation in clonal richness at the population scale (from 0.54 to 0.82), with the restored populations occupying an intermediate to high position within this range. Replicate sampling within individual seagrass beds of 3 to 5m diameter generally revealed higher levels of clonal richness, elevated by 4 to 22% over that at the population scale, suggesting that seed recruitment is more important at the local scale than at distances of >10 m. Genetic diversity was 2 to 3 times less than that expected for a widespread, outcrossing species like H. wrightii, although a 170% increase in the frequency of variable markers relative to the mean for all other populations was noted for a volunteer population that had recruited from a mixture of donor materials planted at a nearby restoration site. Within the spatial extent of this study, natural populations adhered to a model of isolation-by-distance, whereas donor materials from these same natural populations were undergoing a rapid genetic convergence within a restored site where they had been planted together.

Texas↗
USGS1988

Phytoplankton growth rates in a light-limited environment, San Francisco Bay

Phytoplankton cells reside in a turbulent medium partitioned into an upper photic zone that sustains photosynthesis, and a lower aphotic zone that does not. In estuaries, vertical mixing rates between these 2 zones can be rapid (< 1 generation time) because of tidal stirring and because the mixing depth is generally shallow. Moreover, the photic depth is characteristically shallow in estuaries because of the high seston concentrations that typify these systems (e.g. Cloern 1987). Hence the mean light exposure of phytoplankton cells, and their rates of photosynthesis and growth in estuaries, should be related to the ratio of photic depth Z p to mixing Z m , (defined as either the water column depth, or the surface layer depth in a stratified estuary). Grobbelar (1985) has measured phytoplankton production in turbid waters and used the ratio Z p :Z m as a simple index to quantify the degree of light limitation. Harris and his colleagues have examined in detail the importance of the Z p :Z m ratio in lakes for influencing variability of phytoplankton production and photosynthetic parameters (Harris et al. 1980), and variability of species composition both temporally (Harris & Piccinin 1980) and spatially (Haffner et al. 1980). Phytoplankton growth rates have only rarely been measured in estuaries (Malone 1977, Furnas 1982, Harding et al. 1986) where cycling rates between the photic and aphotic zones can be much faster than in lakes or the open ocean. This study was motivated by the need for quantitative measures of phytoplankton population growth rate in an estuarine environment, and was designed around the presumption that growth rates can be related empirically to light exposure. We conducted the study in San Francisco Bay (California, USA), which has large horizontal gradients in light availability (Z p :Z m ) typical of many coastal plain estuaries, and nutrient concentrations that often exceed those presumed to limit phytoplankton growth (Cloern et al. 1985). We tested the hypothesis that light availability is the primary control of phytoplankton growth, and that previous estimates of growth rate based on the ratio of productivity to biomass (Cloern et al. 1985) are realistic. Specifically, we wanted to verify that growth rate varies spatially along horizontal gradients of light availability indexed as Z p :Z m , such that phytoplankton turnover rate is rapid in shallow clear areas (high Z p :Z m ) and slow in deep turbid areas (low Z p :Z m ). We used an in situ incubation technique which simulated vertical mixing, and measured both changes in cell number and carbon production as independent estimates of growth rate across a range of Z p :Z m ratios.

California↗
USGS1986

Effect of seasonally changing tissue weight on trace metal concentrations in the bivalve Macoma balthica in San Francisco Bay

The influence of seasonal changes in the weight of soft tissues on temporal fluctuations in tissue concentrations of Cu and Zn was examined in 4 populations of the clam Macoma balthica sampled in San Francisco Bay for a period of 2 to 5 yr. Fluctuations in metal concentration expected from changes in tissue weight between sampling dates were estimated by assuming that whole body metal burden was constant during the sampling interval. Comparison of estimated and actual metal concentrations showed that the degree to which fluctuations in trace metal concentrations were driven by weight changes differed considerably among stations, among years at a single station, and between metals.

California↗