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.     

Dynamics of benthic vegetation standing-stock,irradiance, and water properties in central Puget Sound

The standing stock of benthic macroalgae, sediment-associated microalgae and eelgrass (Zostera marina L.) was sampled in conjunction with irradiance and water properties from June 1982 through March 1984 to examine the relationship between the dynamics of benthic primary producers and environmental factors in central Puget Sound, Washington, USA. Sediment-associated microalgal standing stock (measured by chlorophylla) peaked in April and August. The seaweed assemblage, dominated by bladed green algae (e.g.Ulva fenestrata) and eelgrass exhibited maximum standing stocks in August. Although water temperature correlated best with changes in standing stock of all vegetation types, solar irradiance appeared to trigger the onset of biomass buildup and autumn die-back by the plants. Seasonal variations in dissolved oxygen reflected the buildup and loss of plant standing-stock. Nutrient concentrations, with the exception of ammonia, exhibited seasonal trends. Most nutrients were in greatest concentration in winter and reached minimum concentration in late spring-summer. Regeneration of nutrients in autumn followed shortly after the autumn dieback of the benthic vegetation. We concluded that irradiance was the primary controlling factor in the system. Nutrient limitation (primarily nitrate) may control standing-stock accumulations from the period May–October when light is not limiting. In contrast to phytoplankton systems in deep portions of Puget Sound, shallow nearshore systems may be more susceptible to the effects of increased inorganic nutrient-loadings from anthropogenic sources.Contribution No. 808, School of Fisheries, University of Washington     

Distribution,movement and diet of the snailSearlesia dira in the intertidal community of San Juan Island,Puget Sound,Washington

Searlesia dira Reeve is a locally abundant, carnivorous gastropod that occurs from Alaska to central California. I studied populations of this snail at a variety of sites on San Juan Island in order to provide information on their distribution and abundance and to analyze their community role, i.e., their potential impact on their prey populations and their dietary overlap with co-occurring invertebrate predators. I established permanent transects, both random and in crevices, at three areas of differing exposure to wave action. On these transects I recorded the number and size ofS. dira, activity, distance to nearest neighbor, other organisms present, and tidal height on four phases of the mixed semi-diurnal tidal cycle. The results are (1) an increase in density with increase in substrate relief, (2) an occurrence of highest densities in moderately exposed and exposed sites rather than in protected ones, (3) an increase in mean size with increase in depth along the intertidal gradient, (4) an increase in both total activity and feeding success on the high water immediately following an extreme minus low tide occurring during the daytime in the summer, (5) a relative restriction of feeding success to that high tide, and (6) a similarity of the diet to the relative abundance of the main observed prey for most areas. The main exceptions are chitons and one lower intertidal limpet, all of which are taken in excess of their apparent abundance and especially in the middle intertidal. The upward extension of some lower intertidal prey populations, such as chitons, may be limited by the increased susceptibility of individuals at the upper margin of the population to predators such asS. dira; susceptibility appears to be increased after periods with a higher probability of increased physiological stress, such as extreme low tides on summer days.     

Feeding mechanisms and possible resource partitioning of the caprellidae (Crustacea: Amphipoda) from Puget Sound,USA

Caprellid amphipods feed by browsing, filter-feeding, predation, scavenging, and scraping. Food acquisition is related to the presence or absence of plumose setae on the second antenna; those species with such setae obtain a significant amount of their diet from filtering and scraping periphyton while those species without such setae usually rely on predation. Two primary predators and 8 primary filter-feeders and scrapers were investigated. Substrates inhabited by the predators did not overlap, but some filter-feeders were found together. Feeding overlap has been decreased among filter-feeders that occur together, as they either feed on different sized particles or they filter at different heights from the substrate. Species filtering the same sized particles at the same heights that were found together utilized alternate feeding mechanisms, e.g. browsing on algal filaments.     

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     

Relationship between depth, sediment, latitude, and the structure of benthic infaunal assemblages on the mainland shelf of southern California

A regional benthic survey was conducted in 1994, and the data were used to assess the relationship among three habitat factors (depth, sediment grain size, and latitude) and the distribution of benthic infaunal assemblages on the southern California coastal shelf. Benthic samples were collected with a 0.1 m² Van Veen grab from 251 sites on the continental shelf (10–200 m deep) from Point Conception, California, to the United States–Mexico international border. The relationship between habitat and assemblages was investigated by conducting a Q-mode cluster analysis to define groups of stations with similar species composition and then examining whether differences were present in physical habitat attributes among those groups of stations. Analysis of data from 175 uncontaminated sites yielded four habitat-related benthic infaunal assemblages along the southern California coastal shelf: a shallow-water assemblage from 10–32 m, a mid-depth assemblage between 32 and 115 m, and two deep-water (115–200 m) assemblages, one in fine and one in coarse sediments. These empirically defined points in the depth and sediment grain size gradients can be used to define reference habitats for the development of biocriteria. Benthic abundance and diversity were greatest in the mid-depth assemblage, conforming to predictions for benthic assemblages in regions of upwelling. Within the 500 km of coastline examined, latitude was not an important factor in defining assemblages. Received: 3 December 1999 / Accepted: 9 October 2000     

Benthic polychaete assemblages and their relationship to the sediment in Port Madison,Washington

Two indices of community association and a 3 dimensional ordination of stations were used to elucidate the relationship between small-scale changes in species, composition of polychaete assemblages and changes in the physical character of the sediment, at 9 stations along a 1.5 km subtidal transect. There were no faunal or physical discontinuities that might have been used to delineate boundaries of polychaete communities, except at a very shallow station where the effects of extreme fluctuations of temperature and salinity were evident. The degree of similarity between assemblages was related to the similarity of the sediments at the different stations. In particular, the changes in species composition appeared to correspond most clearly to differences in the clay content of the sediment.     

Seasonal abundance, philopatry and demographic structure of Caribbean reef shark (Carcharhinus perezi) assemblages in the north-east Exuma Sound, The Bahamas

The Caribbean reef shark (Carcharhinus perezi), an abundant coral-reef-associated apex predator, is one of the most economically and ecologically important, yet least studied species of large shark in the greater Caribbean region. The relative abundance and population structure of C. perezi off Cape Eleuthera, The Bahamas, was surveyed by standardised longline surveys from May 2008 to October 2011, which resulted in the capture of 331 sharks. Abundance peaked in the summer and was lowest during the winter. Females were 1.6 times more abundant than males and the assemblage was dominated by immature female sharks (45.5 %). The abundance of mature male and female sharks peaked a month apart in June and August, respectively. All 331 sharks were tagged and released with 15.4 % being recaptured after periods at liberty between 5 and 1,159 days (Mean = 333.4 ± 42.7 SE). The mean distance between tagging and recapture was 1.77 km for recaptures in excess of 6 months, indicating seasonally stratified philopatry in this species. C. perezi inhabiting Bahamian waters have developed complex habitat use patterns that are both spatiotemporally and demographically segregated, most probably in response to the large and diverse habitat mosaic available on the Bahamas Banks compared to contemporary study sites. This study represents an important step in understanding the spatiotemporal population structure of C. perezi and illustrates the potential for studies examining behavioural plasticity in response to environmental variation and anthropogenic disturbance.     

Quantitative characterization of shallow marine benthic assemblages at Ryder Bay,Adelaide Island,Antarctica

Non-destructive photographic techniques are valuable for surveying benthic epifauna in sensitive areas. Inherent in these techniques, however, are selectivity biases related to the scale at which surveys are conducted. Such biases have not been addressed for surveys of marine benthos. The present study surveyed epifaunal assemblages at two depths (8 m and 20 m) and three locations close to Rothera Point, Adelaide Island, Antarctica. Two scales of photographic sampling were employed in order to encompass a broad range of taxon sizes and distributions, and their parallel use allowed qualitative and quantitative comparisons to be made between results from each scale. An additional physical sampling element was incorporated to assess sessile cryptic assemblages. A total of 79 faunal taxa from 10 phyla, together with 6 algal taxa, were recorded in the survey. Echinoderms were the most speciose group at both photographic scales, whereas cryptic assemblages were dominated by bryozoans. There were clear resolution-related differences between scales but all three methods revealed pronounced differences in assemblages by depth and location. Assemblages at both depths were notable for consistently high densities (~100 individuals m^–2) of the regular echinoid Sterechinus neumayeri, and at 8 m for high densities (~100 individuals m^–2) of the limpet Nacella concinna. The results emphasise the general requirement for sampling methodologies to be matched to the size spectra of the organisms under study and, more specifically, highlight the need for studies to assess the relative importance of biotic and physical factors in structuring the Antarctic benthos.Communicated by J.P. Thorpe, Port Erin     

A seasonal study of arsenic in groundwater,Snohomish County,Washington, USA

A series of arsenic poisonings near Granite Falls in Snohomish County, Washington, were identified during 1985–87. An initial investigation revealed the source of arsenic exposure to be high levels of arsenic in well water. A large number of wells in eastern Snohomish County were tested, residents were interviewed and sources of contamination, both natural and man-made, were investigated. More than 70 private drinking-water wells were found to contain elevated levels of arsenic . One well contained 33 mg As L^–1. The finding of elevated arsenic levels in a previously approved drinking-water well for a restaurant, plus suggestions of symptoms consistent with arsenic poisoning among people with wells with no detectable arsenic, raised concern over possible temporal variation in arsenic levels. To evaluate this temporal variation, a 12-month study of arsenic in groundwater was conducted in selected wells near Granite Falls. The 12-month study of 26 wells, conducted between February 1988 and January 1989, found arsenic levels for individual wells to vary from one to 19 fold over time. Because of this variability, four out of the eight wells with arsenic levels close to the Maximum Contamination Level (MCL) of 0.050 mg As L^–1 would have been considered safe on the basis of a single sample, but would have exceeded the MCL at another time of the year.In areas with a high occurrence of arsenic contaminated drinking water, approval of well water prior to the sale of a house or issuance of a building permit which is based on a single arsenic test may result in later findings of unacceptable drinking water. When the arsenic is near the MCL, it may be prudent to follow well-water arsenic concentrations over time to assure that the arsenic level remains within acceptable bounds. If lower arsenic standards are adopted for drinking water, the issue of temporal variation around the standard will become a matter of more widespread concern.To whom correspondence should be addressed. The contents of this paper do not necessarily reflect the views and policies of the US Environmental Protection Agency.     

Lionfish alter benthic invertebrate assemblages in patch habitats of a subtropical estuary

Invasive lionfish (primarily Pterois volitans) have spread throughout the Caribbean region, Gulf of Mexico, and the Southeast US coast, and resulting impacts on reef fish populations have been well documented. We examined whether lionfish can likewise affect benthic invertebrate communities, using an in situ caging experiment, in the Loxahatchee Estuary, Florida, USA. We found that lionfish caused significant declines in the three most abundant benthic invertebrate species, driving an overall shift in assemblage composition. For example, grass shrimp (Palaemonidae) abundance was reduced by nearly 90 % in the presence of lionfish. Species richness of benthic organisms was significantly higher when lionfish were present, suggesting potentially complex emergent effects of lionfish predation on benthic assemblages. Despite the fact that this experiment was conducted in just a single location using relatively small experimental units, we show altered benthic invertebrate communities could well be an additional outcome of the lionfish invasion.     

Distribution of euphausiid assemblages in the Mediterranean Sea

Eleven species of euphausiids from 24 Isaac-Kidd Midwater Trawl (IKMT) night collections taken at stations throughout the Mediterranean Sea were counted. The frequency of occurrence and dominance of individual species and percent similarity faunal analysis of the euphausiid community were used to describe changes in faunal composition between geographical areas and differences in vertical distribution. Although most species were widespread, three distinct patterns of abundance were apparent: Euphausia krohnii, Nematoscelis megalops, Meganyctiphanes norvegica, and Stylocheiron abbreviatum predominated in western basin areas west of the Tyrrhenian Sea; Euphausia hemigibba, Thysanopoda aequalis, and Stylocheiron longicorne predominated in the Tyrrhenian Sea and eastern Mediterranean Sea; Euphausia brevis and Stylocheiron suhmii predominated in the eastern Mediterranean Sea. Percent similarity analysis of data from the IKMT samples and data from Ruud (1936) indicates the Tyrrhenian Sea fauna at the time of the collections was more similar to eastern Mediterranean areas than to most other areas in the western basin, although the degree of similarity was dependent, to some extent, on the depth at which the samples were collected. The composition of euphausiids living above 150 m at night in this area was more similar to eastern basin areas, while the composition of deeper living forms was more similar to those of the rest of the western basin. Comparison of euphausiids collected at three points over a 60 year time-span in the Balearic Sea shows the similarity in composition to be greater within the area over time than between adjacent areas in the western Mediterranean Sea.Contribution No. 2732 from the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA. This research was supported by the Atomic Energy Commission Contract AT (30-1)-3862, ref. NYO-3862-49, National Science Foundation Grant GA 29303 and Office of Naval Research Contract N00014-71-C-0284.     

Molecular population structure of the marine benthic copepod Microarthridion littorale along the southeastern and Gulf coasts of the USA

Relationships among populations (southeast Atlantic and northern Gulf coast, USA) of a ubiquitous, estuarine, harpacticoid copepod (Microarthridion littorale Poppe) were estimated using sequence data from two loci: one mitochondrial [cytochrome b (Cyt b)] and one nuclear [first internal transcribed spacer of ribosomal DNA (ITS-1)]. Copepods were collected from seven estuaries in 1997/98. Allelic phylogenies based on both genes were generally concordant, and suggested that M. littorale populations are structured over large geographic scales (hundreds of kilometers). Three well-supported groups were found in both gene trees comprising clades of alleles sampled from South Carolina, Florida, and Louisiana. Alleles from the Savannah, Georgia sample formed a monophyletic group using the Cyt b data, but this clade was not distinguishable with comparable ITS-1 data. A single specimen from Louisiana was classified in different clades depending on the locus assayed. Received: 11 June 1998 / Accepted: 29 April 1999     

Environmental stresses and intertidal assemblages on hard substrates in the port of Long Beach,California, USA

Nine intertidal stations within the Port of Long Beach, California, USA, were sampled during September and October 1975 using the random point method and the scraping technique. A total of 96,168 individuals belonging to 55 taxa were recorded in the quantitative survey; qualitative scrapings included 136 taxa. The protected outer coast intertidal assemblages were found at all but three stations along the shoreline. The shoreline, being situated in between the more environmentally stressed inner harbor and the less stressed open ocean, supported assemblages characterized by an instability in species composition. The upper midlittoral zone was typically dominated by Chthamalus dalli, C. fissus and Balanus glandula. The lower midlittoral was colonized either by Anthopleura elegantissima-Prionotis lanceolata facies along the outer breakwater or by A. elegantissima-Tetraclita squamosa rubescens facies along the inner breakwater. The mussel bed, which is the characteristic assemblage of the Californian lower midlittoral zone was obscured by the competitors P. lanceolata, T. squamosa rubescens and A. elegantissima, and was thinned out by predators, of which Pisaster ochraceus was the most voracious. Suspension feeders were dominant in the upper midlittoral and producers and grazers in the lower midlittoral. Predators were few in number and restricted to levels below mean lower low water. There was a gradual increase in numbers of intertidal species and individual abundance from level +5 ft (1.5 m) to level +1 ft (0.3 m) and from shoreline to outer breakwater. This may be attributable to the decrease in environmental stresses in the lower water levels and the improvement in water quality from the inner to outer harbor area.     

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound,Marlborough Sounds,New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m^-2 at the mussel farm and 6.1 to 8.9 mol m^-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm^-3 (surface) to 149 nmol cm^-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm^-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m^-2 d^-1 at the mussel farm and from 8.5 to 25.0 mmol m^-2 d^-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m^-2 d^-1 at the mussel farm and 0.1 to 0.9 mmol m^-2 d^-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m^-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m^-2 at the reference site and 137 mg m^-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.     

Seasonal variations in the utilization of ammonium and nitrate by photoplankton in Vineyard Sound,Massachusetts, USA

The nitrogenous nutrition of the phytoplankton in Vineyeard Sound, Massachusetts, USA was investigated over a 15-month period. Highest rates of ammonium uptake were observed immediately prior to, or during, the diatom bloom periods, and with one exception were found in the <10 m size class. The saturating rate of ammonium uptake correlated well with temperature and gave Q₁₀ values of 2.6–3.2; correlations with ambient solar irradiation were not nearly so clear. Uptake rates of ammonium exceeded those of nitrate except during the winter bloom of the diatom Rhizosolenia delicatula; yet calculation of the f ratio revealed that nitrate was relatively important in the nitrogenous nutrition of the phytoplankton throughout the year.Contribution no. 5096 from the Woods Hole Oceanographic Institution     

Gene flow among population of a teleost (painted greenling,Oxylebius pictus) from Puget Sound to southern California

Net photosynthetic oxygen evolution in Amphiroa anceps (Lamarck) Decaisne is inhibited at high oxygen concentrations. Photosynthesis is highest between pH 6.5 and 7.5. At pH 9 to 10 there is still a significant photosynthetic rate, suggesting that this alga can use HCO _- ³ as a substrate for photosynthesis. At pH 7.0 to 8.5, the photosynthetic rate saturates at a total inorganic carbon concentration (C_i) greater than 3 mM. At pH 8.5 and 8.8, calcification rate continues to increase with increasing concentration of C_i. Between pH 7 and 9, the calcification rate in the light in A. foliacea Lamouroux is proportional to the photosynthetic rate, whereas at higher pH where the photosynthetic rate is very low, the calcification rate is stimulated by the higher concentration of CO _2- ³ ion. At all pH values examined, the calcification rate of living plants in the dark and of dead plants is directly proportional to the CO _2- ³ ion concentration, suggesting little metabolic involvement in calcification processes in the dark, whereas calcification in live A. foliacea in the light is influenced both by the photosynthetic rate and the CO _2- ³ ion concentration in the medium.     

Effect of Hurricane Eloise on the benthic fauna of Panama City Beach,Florida, USA

The effect of Hurricane Eloise in September, 1975 on the benthic fauna inhabiting the swash zone on Panama City Beach, Florida, USA is described. Damage by the storm to the beach and property was considerable. The effect of the storm on the benthic invertebrates was not adverse, as the number of individuals occurring in the swash zone was about the same after the storm as before. The number of species increased after the storm, but later decreased to approximate numbers before the storm. The increase in the number of species was mainly due to the influx of species that norusually accompanies a hurricane was probably a factor enabling benthic organisms that normally live in high salinities to survive.     

Seasonal fluctuations of benthic macrofauna in the apalachicola estuary,Florida, USA: The role of predation

Long-term monitoring studies revealed a negative correlation between the abundance of bottom-feeding fishes (Leiostomus xanthurus and Micropogonias undulatus) and benthic macrofaunal density, suggesting a causal relationship. To test this hypothesis, large (3x3 m) topless predator-exclusion cages (mesh opening=6 mm) of a design that produced minimal physical artifacts were constructed at two shallow mud-bottom oligohaline stations. Two-sided control cages and uncaged control areas were also sampled Experiments coincided with maximum abundances of bottom-feeding fishes in the spring and motile macroinvertebrates (penaeid shrimp) in the fall. During short-term (two-month) exclusion experiments in the spring and fall of 1980, large predators (those excluded by 6-mm mesh) were not a major factor in regulating the densities of most macrofaunal species. Predation may be important during other seasons, although this possibility was not tested. Densities of Leiostomus xanthurus and Penaeus setiferus during 1980 were lower than in previous years. Despite the reduced abundance of bottom-feeding fishes, macrofaunal densities still declined during late winter/early spring. It is postulated that increased river flow and lowered salinities during the late winter/early spring may contribute to the decline of macrofaunal densities by reducing larval recruitment.