Biogeographical Patterns of Marine Benthic Macroinvertebrates Along the Atlantic Coast of the Northeastern USA

The biogeography of marine benthic macroinvertebrates of US Atlantic estuaries and inshore coastal areas from Delaware Bay north to Passamaquoddy Bay was studied to compare recent data with historical biogeographic studies, define physical–chemical factors affecting species’ distributions, and provide information for calibrating benthic indices of environmental condition. Five years (2000–2004) of data from 614 non-polluted, soft-bottom stations from the National Coastal Assessment were analyzed. Multi-dimensional scaling done on Bray-Curtis similarity matrices of species’ relative abundance (547 species) suggested seven subregions: two based on salinity (oligohaline, mesohaline) and five based on latitude. Species’ distribution patterns for stations with salinities ≥18 (n = 558) were strongly influenced by latitude; Cape Cod was a clear faunal transition zone (R = 0.92, p < 0.001). Conversely, for stations with salinities <18 (n = 56), salinity was the more important factor. An ordination of abiotic variables (temperature, salinity, sediment percent silt-clay, depth) correlated well with the ordination of species’ relative abundance data (R = 0.77, p < 0.001). The first split of a multivariate regression tree was by a summer bottom temperature of 20°C at Cape Cod. Salinity and percent silt-clay led to further splits. These results support the existence of Virginian and Transhatteran biogeographic provinces. They constitute a baseline for addressing broad-scale and long-term issues such as global climate change, species invasions, and conservation planning.     

Indirect Effects of Salinity and Temperature on Kuwait’s Shrimp Stocks

Discharge of the Shatt Al-Arab is believed to be a dominating component of the northern Arabian Gulf’s ecology and largely responsible for productivity of Kuwait’s fisheries. With major construction of dams on the Tigris and Euphrates Rivers in Turkey, river discharge has been substantially reduced, and flooding essentially eliminated. We attempted to relate river flow and shrimp landings indirectly by correlating 19 years of salinity and temperature data from Kuwait’s waters with corresponding annual shrimp landings. For green tiger prawns (Penaeus semisulcatus), the combination of October salinities and January temperatures provided the best correlation (r = 0.67) with landings in the following shrimping season. For the combined landings of jinga and kiddi shrimps (Metapenaeus affinis and Parapenaeopsis stylifera, respectively), December salinity during season and May temperature prior to season resulted in the best correlation (r = 0.87). Landings of these two species also correlated well with spring and summer temperatures. Under normal conditions, late winter or early spring temperatures prior to fishing season influence recruitment of the green tiger prawn, whereas December salinities during harvest season influence the abundance of jinga–kiddi shrimps. With further reductions in the Shatt Al-Arab discharge and the elimination of flood events, Kuwait’s shrimp landings will most likely decrease over time.     

Seasonal variations in biomass and species composition of seaweeds along the northern coasts of Persian Gulf (Bushehr Province)

This study was carried out to evaluate the seasonal variations of seaweed biomass and species composition at six different sites along the coastal areas in Bushehr Province. Sampling depths varied among sites, from 0.3 to 2.0 m below mean sea level. A total of 37 (i.e., 10 Chlorophyta, 12 Phaeophyta and 15 Rhodophyta) seaweed species were collected. Studies were conducted for quantifying the seaweeds during four seasons from October 2008 until July 2009. During present research, Ulva intestinalis and Cladophora nitellopsis of green, Polycladia myrica, Sirophysalia trinodis and Sargassum angustifolium of brown and Gracilaria canaliculata and Hypnea cervicornis of red seaweeds showed highest biomass in coastal areas of Bushehr Province. The Cheney‘s ratio of 2.1 indicated a temperate algal flora to this area. All sites exhibited more than 50% similarity of algal species, indicating a relatively homogenous algal distribution. Total biomass showed the highest value of 3280.7 ± 537.8 g dry wt m^− 2 during summer and lowest value of 856.9 ± 92.0 g dry wt m^− 2 during winter. During this study, the highest and lowest seaweed biomass were recorded on the site 2 (2473.7 ± 311.0 g dry wt m^− 2) and site 5 (856.7 ± 96.8 g dry wt m^− 2), respectively.     

Interactions of Salinity,Marsh Fragmentation and Submerged Aquatic Vegetation on Resident Nekton Assemblages of Coastal Marsh Ponds

Increases in relative sea level are fragmenting the emergent vegetation of Louisiana’s coastal marshes. Nekton abundance is likely impacted by salinity and whether emergent vegetation is replaced by submerged aquatic vegetation (SAV) or open water. To assess these effects, we sampled nekton densities along a salinity gradient (categorized as freshwater, intermediate, and brackish marsh) in fragmented and non-fragmented areas. Total nekton density increased strongly with SAV in brackish marsh but only weakly in freshwater marsh (F _2,238 = 10.03, p < 0.0001). Freshwater and intermediate marshes had higher nekton densities when fragmented than when non-fragmented; this relationship was reversed in brackish marsh (F _2,238 = 8.89, p = 0.0002). Fragmentation, SAV, and salinity interacted to affect the densities of Gambusia affinis, Poecilia latipinna, Cyprinodon variegates, and Lucania parva. Our results suggest that the presence of both emergent vegetation and SAV was necessary for maintaining high nekton densities, with this combination being especially important in brackish marshes.     

Oyster and Macroalgae Bioindicators Detect Elevated δ<Superscript>15</Superscript>N in Maryland’s Coastal Bays

Nitrogen loading from anthropogenic sources, including fertilizer, manure, and sewage effluents, has been linked with declining water quality in coastal lagoons worldwide. Freshwater inputs to mid-Atlantic coastal lagoons of the USA are from terrestrially influenced sources: groundwater and overland flow via streams and agricultural ditches, with occasional precipitation events. Stable nitrogen isotopes ratios (δ¹⁵N) in bioindicator species combined with conventional water quality monitoring were used to assess nitrogen sources and provide insights into their origins. Water quality data revealed that nutrients derived from terrestrial sources increased after precipitation events. Tissues from two bioindicator species, a macroalgae (Gracilaria sp.) and the eastern oyster (Crassostrea virginica) were analyzed for δ¹⁵N to determine spatial and temporal patterns of nitrogen sources. A broad-scale survey assessment of deployed macroalgae (June 2004) detected regions of elevated δ¹⁵N. Macroalgal δ¹⁵N (7.33 ± 1.15‰ in May 2006 and 6.76 ± 1.15‰ in July 2006) responded quickly to sustained June 2006 nutrient pulse, but did not detect spatial patterns at the fine scale. Oyster δ¹⁵N (8.51 ± 0.89‰) responded slowly over longer time periods and exhibited a slight gradient at the finer spatial scale. Overall, elevated δ¹⁵N values in macroalgae and oysters were used to infer that human and animal wastes were important nitrogen sources in some areas of Maryland’s coastal bays. Different nitrogen integration periods across multiple organisms may be used to indicate nitrogen sources at various spatial and temporal scales, which will help focus nutrient management.     

Cryptic Blooms: Are Thin Layers the Missing Connection?

Harmful algal blooms (HABs) are common in Monterey Bay, CA, and have resulted in repeated closures of shellfish fisheries and the poisoning and death of marine mammals. In the majority of instances, HAB events in this region are first detected by the presence of sick or dying animals. The phrase “cryptic blooms” was adopted to denote the appearance of poisoning at higher trophic levels with no prior evidence of a large phytoplankton bloom. We hypothesize that the onset of many HAB events goes undetected because the bloom is initially concentrated in discrete thin subsurface layers in the water column that are easily missed by conventional sampling and monitoring methods. In this paper, we report on the detection and monitoring of a subsurface layer of phytoplankton in northern Monterey Bay, CA, using a high-resolution, autonomous profiler. This ‘thin layer,’ which measured from 10 cm to 3 m in thickness (85% < 2 m; 54% < 1 m), persisted over a 7-day period near the base of the pycnocline. The phytoplankton assemblage in the layer was primarily composed of a multi-species assemblage of Pseudo-nitzschia including the toxin-producing species Pseudo-nitzschia australis. Concentrations of toxic phytoplankton (P. australis), cyanobacteria, and bacteria in the layer were significantly higher than outside the layer (P < 0.05). Counts of total Pseudo-nitzschia spp. showed similar levels of enrichment in the layer compared to outside the layer. Our findings indicate that, when monitoring for HABs, it is critical to sample at scales appropriate to resolve thin layers. Thin layers have been identified as a common recurrent feature in a variety of coastal systems, suggesting that the use of autonomous high-resolution vertical profilers coupled with targeted sampling, could allow more timely detection of HABs in many coastal environments.     

Factors Affecting <Emphasis Type="Italic">Pisidium amnicum</Emphasis> (Müller, 1774; Bivalvia: Sphaeriidae) Distribution in the River Minho Estuary: Consequences for its Conservation

The bivalve Pisidium amnicum (Müller 1774) is a common species in several European freshwater ecosystems. However, few Iberian watersheds are colonized by this species, and the River Minho estuary is possibly the Iberian aquatic ecosystem with the larger population. In October 2004–2007, investigations on spatial and temporal variations in P. amnicum abundance and biomass were carried out at 16 sites along the River Minho tidal freshwater wetlands. Mean abundance and biomass per site ranged from 0 to 750 ind m⁻² and 0 to 7.42 g AFDW m⁻², respectively. A clear decrease in the spatial distribution, abundance, and biomass was observed during the 4-year assessment. Furthermore, a stepwise multiple regression model showed that organic matter and conductivity explained 50.2% of the variation in P. amnicum abundance (R ² = 0.502, F _{[2, 15]} = 7.569, p = 0.005). Ecological knowledge is essential to the implementation of future conservation plans for P. amnicum, and the results of this study are of paramount importance to identify habitats that should be protected in order to preserve this species and provide scientific reference that may be useful in the development of management and/or restoration plans.     

Spatial Heterogeneity Created by Burrowing Crabs Affects Human Impact on Migratory Shorebirds

We show that, as previously described, there are conflicts between areas used by people and shorebirds. However, we propose that burrowing organisms add complexity to the shorebird–human interaction that should be taken into account for management and conservation. This is because SW Atlantic mudflats are dominated by high densities (up to 60 crabs m⁻²) of a strong bioturbator, the burrowing crab Neohelice granulata (=Chasmagnathus granulatus). These crabs affect the habitat use and foraging performance of shorebird species. The two-banded plover Charadrius falklandicus feed more in burrow areas whereas the yellowlegs Tringa spp. and the white-rumped sandpiper Calidris fuscicollis tend to avoid burrow areas. We evaluated the effect of human recreational activities on shorebirds, taking into account shorebird–crab interaction, during shorebird migratory periods (November to April) of 2001, 2002, and 2003. This study was performed at the Mar Chiquita coastal lagoon (37° 40′ S, Argentina). Results showed that people only rarely used the extensive soft bottom intertidals dominated by burrowing assemblages of N. granulata because the soft sediments make walking difficult. Therefore, human impact is reduced for the two-banded plover. However, for several migratory shorebirds that also avoid burrow areas, these areas act as suboptimal alternative areas when human impact is important in their preferred habitats. When human activity is low, shorebirds remain foraging in the area but they decrease their feeding intakes. The extensions of burrow areas differ among estuaries and are likely to generate between-estuaries differences as stopover sites for shorebirds. Also, other species that form large burrowing assemblages can have a similar impact on shorebird–human interactions.     

Food Web Structure of the Alaskan Nearshore Shelf and Estuarine Lagoons of the Beaufort Sea

The eastern Alaska Beaufort Sea coast is characterized by numerous shallow (2–5 m) estuarine lagoons, fed by streams and small rivers that drain northward from the Brooks Range through the arctic coastal plain, and bounded seaward by barrier islands and shoals. Millions of birds from six continents nest and forage during the summer period in this region using the river deltas, lagoons, and shoreline along with several species of anadromous and marine fish. We examined biogeochemical processes linking the benthic community to the overall food web structure of these poorly studied but pristine estuaries, which are largely covered by 1.8 m of ice for 10 months annually. In summer, these lagoons are relatively warm with brackish salinities (5–10°C, S = 10–25) compared to more open coastal waters (0–5°C, S > 27). The stable isotopic composition of organic materials in sediments (i.e., benthic particulate organic matter) and water column suspended particulate organic matter from both streams and lagoons are largely indistinguishable and reflect strong terrestrial contributions, based upon δ¹³C and δ¹⁵N values (−25.6‰ to −27.4‰ and 1.4‰ to 3.3‰, respectively). By comparison, shifts toward more heavy isotope-enriched organic materials reflecting marine influence are observed on the adjacent coastal shelf (−24.8‰ to −25.4‰ and 3.4‰ to 5.3‰, respectively). The isotopic composition of lagoon fauna is consistent with a food web dominated by omnivorous detritovores strongly dependent on microbial processing of terrestrial sources of carbon. Biomagnification of ¹⁵N in benthic organisms indicate that the benthic food web in lagoons support up to four trophic levels, with carnivorous gastropod predators and benthic fishes (δ¹⁵N values up to 14.4‰) at the apex.     

Distribution of Diatoms and Development of Diatom-Based Models for Inferring Salinity and Nutrient Concentrations in Florida Bay and Adjacent Coastal Wetlands of South Florida (USA)

The composition and distribution of diatom algae inhabiting estuaries and coasts of the subtropical Americas are poorly documented, especially relative to the central role diatoms play in coastal food webs and to their potential utility as sentinels of environmental change in these threatened ecosystems. Here, we document the distribution of diatoms among the diverse habitat types and long environmental gradients represented by the shallow topographic relief of the South Florida, USA, coastline. A total of 592 species were encountered from 38 freshwater, mangrove, and marine locations in the Everglades wetland and Florida Bay during two seasonal collections, with the highest diversity occurring at sites of high salinity and low water column organic carbon concentration (WTOC). Freshwater, mangrove, and estuarine assemblages were compositionally distinct, but seasonal differences were only detected in mangrove and estuarine sites where solute concentration differed greatly between wet and dry seasons. Epiphytic, planktonic, and sediment assemblages were compositionally similar, implying a high degree of mixing along the shallow, tidal, and storm-prone coast. The relationships between diatom taxa and salinity, water total phosphorus (WTP), water total nitrogen (WTN), and WTOC concentrations were determined and incorporated into weighted averaging partial least squares regression models. Salinity was the most influential variable, resulting in a highly predictive model (r _apparent² = 0.97, r _jackknife² = 0.95) that can be used in the future to infer changes in coastal freshwater delivery or sea-level rise in South Florida and compositionally similar environments. Models predicting WTN (r _apparent² = 0.75, r _jackknife² = 0.46), WTP (r _apparent² = 0.75, r _jackknife² = 0.49), and WTOC (r _apparent² = 0.79, r _jackknife² = 0.57) were also strong, suggesting that diatoms can provide reliable inferences of changes in solute delivery to the coastal ecosystem.     

Ingress of Brachyuran Crab Post-larvae to the Newport River Estuary

Planktonic larvae of estuarine species often develop in the coastal ocean and return to estuaries using favorable currents. This study investigated spatial distributions of brachyuran crab post-larvae during ingress to the Newport River estuary, North Carolina, USA (34°41′ N, 76°40′ W). Nearshore plankton tows were conducted across the inlet to the estuary. Settlement on passive ‘hog’s hair’ collectors was simultaneously monitored in each of four estuarine channels. Callinectes sapidus density was highest east of the inlet, whereas relative estuarine abundance was higher in western channels. In separate sampling with collectors at coastal and estuarine locations, spatial distributions of post-larvae were consistent through time but differed for C. sapidus, Uca spp., and Pachygrapsus transversus. The diel timing of C. sapidus settlement on collectors was determined at the coast and compared to previous studies of settlement in the estuary. Behavioral responses to environmental cues may alter transport pathways from those predicted by hydrodynamic models.     

Foraging by Two Estuarine Fishes, <Emphasis Type="Italic">Fundulus heteroclitus</Emphasis> and <Emphasis Type="Italic">Fundulus majalis</Emphasis>, on Juvenile Asian Shore Crabs (<Emphasis Type="Italic">Hemigrapsus sanguineus</Emphasis>) in Western Long Island Sound

The Asian shore crab, Hemigrapsus sanguineus, is a recent and particularly successful introduction to the east coast of the USA. Little research has been done on the utilization of Asian shore crabs for food by native species, a potential form of biocontrol. Over a 4-year period, we examined the gut contents of cogeners, Fundulus heteroclitus and Fundulus majalis, collected from two embayments in western Long Island Sound for the presence of juvenile H. sanguineus. Frequency (percent) of occurrence of food items in the guts of both species varied over year and study site. Asian shore crabs were consumed more often by F. heteroclitus than by F. majalis, but predation pressure by both species was low. Only 13% of F. heteroclitus and 7.7% of F. majalis found with food in their guts had ingested Asian shore crab remains. Of those, 1/3 had consumed whole crabs; the rest had only autotomized appendages in their guts. The mean carapace width of juvenile Asian shore crabs ingested by F. heteroclitus was 3.59 ± 2.22 mm (N = 33). Results of our study on killifish predation support the hypothesis that H. sanguienus abundance is partly explained by reduced impact of native predators (i.e., the “enemy release hypothesis”). Predation pressure of other potential enemies on both planktonic and benthic stages of the Asian shore crab must be investigated, however, to understand the full impact of predation on H. sanguineus population dynamics.     

Kristiansenite, a new calcium–scandium–tin sorosilicate from granite pegmatite in Tørdal, Telemark, Norway

Summary Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, T?rdal, Telemark, Norway. Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition Ca₂ScSn(Si₂O₇)(Si₂O₆OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) ?, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) ?³ (Z = 4). It has a monoclinic cell within ∼ 0.1 ? and is polysynthetically twinned on {010} by metric merohedry. The strongest reflections in the X-ray powder pattern are [d in ?, (I _obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’ hardness is 5?–6; D_calc. = 3.64 g/cm³; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal chemistry of scandium are briefly discussed. Received April 30, 2001; accepted July 28, 2001     

Long-term declines in two apex predators,bull sharks (<Emphasis Type="Italic">Carcharhinus leucas</Emphasis>) and alligator gar (<Emphasis Type="Italic">Atractosteus spatula</Emphasis>), in Lake Pontchartrain,an oligohaline estuary in southeastern Louisiana

We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks (Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005), we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9% (95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%) in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could seriously affect efforts to restore this degraded estuarine ecosystem.     

Effects of Life History Strategy on Fish Distribution and Use of Estuarine Salt Marsh and Shallow-Water Flat Habitats

To assess the potential for habitat isolation effects on estuarine nekton, we used two species with different dispersal abilities and life history strategies, mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides) to examine: (1) distribution trends among estuarine shallow-water flat and various intertidal salt marsh habitats and (2) the influence of salt marsh habitat size and isolation. Collections were conducted using baited minnow traps set within nonisolated interior marshes (interior), nonisolated fringing marshes (nonisolated), isolated island marshes (isolated), and shallow-water flat habitats (flat) that were adjacent to isolated and nonisolated marshes. Size range of individuals collected included juvenile and adult F. heteroclitus (20–82-mm standard length) and L. rhomboides (22–151-mm standard length). During high tide, F. heteroclitus exclusively used marsh habitats, particularly high marsh, whereas L. rhomboides used marshes and flats. F. heteroclitus abundance followed an interior > nonisolated > isolated pattern. L. rhomboides abundance patterns were less consistent but followed a nonisolated > isolated > interior pattern. A size-dependent water depth relationship was observed for both species and suggests size class partitioning of marsh and flat habitats during high tide. Minimum water depth (~31 cm) restricted L. rhomboides populations in marshes, while maximum water depth (~69 cm) restricted F. heteroclitus population use of marshes and movement between marsh habitats. Disparities in F. heteroclitus young of year contribution between isolated compared to nonisolated and interior marsh types suggests isolated marshes acted as population sinks and were dependent on adult emigrants. Resident and transient salt marsh nekton species utilize estuarine habitats in different ways and these fundamental differences can translate into how estuarine landscape might affect nekton.     

The Role of Zooplankton Grazing and Nutrient Loading in the Occurrence of Harmful Cyanobacterial Blooms in Florida Bay,USA

Florida Bay is Florida’s (USA) largest estuary and has experienced harmful picocyanobacteria blooms for nearly two decades. While nutrient loading is the most commonly cited cause of algal blooms in Florida Bay, the role of zooplankton grazing pressure in bloom occurrence has not been considered. For this study, the spatial and temporal dynamics of cyanobacteria blooms, the microbial food web, microzooplankton and mesozooplankton grazing rates of picoplankton, and the effects of nutrients on plankton groups in Florida Bay were quantified. During the study, cyanobacteria blooms (>3 × 10⁵ cells mL⁻¹) persisted in the eastern and central regions of Florida Bay for more than a year. Locations with elevated abundance of cyanobacteria hosted microzooplankton grazing rates on cyanobacteria that were significantly lower (p < 0.001) and less frequently detectable compared to sites without blooms. Consistent with this observation, cyanobacteria abundances were significantly correlated with ciliates and heterotrophic nanoflagellates at low cyanobacteria densities (p < 0.001) but were not correlated during bloom events. The experimental enrichment of mesozooplankton abundance during blooms yielded a significant decrease in the net growth rate of picoplankton but had the opposite effect when blooms were absent, suggesting that the cascading effect of mesozooplankton grazing on the microbial food web was also altered during blooms. While inorganic nutrient enrichment significantly increased the net growth rates of eukaryotic phytoplankton and heterotrophic bacteria, such nutrient loading had no effect on the net growth rates of cyanobacteria. Hence, this study demonstrates that low rates of zooplankton grazing and low rates of inorganic nutrient loading contribute to the persistence of cyanobacteria blooms in Florida Bay.     

Fine-scale responses of phytoplankton to freshwater influx in a tropical monsoonal estuary following the onset of southwest monsoon

In May of 2007, a study was initiated by the National Institute of Oceanography (NIO), Goa, India, to investigate the influence of monsoonal rainfall on hydrographic conditions in the Mandovi River of India. The study was undertaken at a location ∼2 km upstream of the mouth of this estuary. During the premonsoon (PreM) in May, when circulation in the estuary was dominated by tidal activity, phytoplankton communities in the high saline (35–37 psu) waters at the study site were largely made up of the coastal neritic species Fragilaria oceanica, Ditylum brightwellii and Trichodesmium erythraeum. During the later part of the intermonsoon (InterM) phase, an abrupt decline in salinity led to a surge in phytoplankton biomass (Chlorophyll a ∼14 mg m^− 3), of a population that was dominated by Thalassiosira eccentricus. As the southwest monsoon (SWM) progressed and the estuary freshened salinity and Chlorophyll a (Chl a) concentrations decreased during the MoN, Skeletonema costatum established itself as the dominant form. Despite the low biomass (Chl a <2 mg m^− 3), the phytoplankton community of the MoN was the most diverse of the entire study. During the postmonsoon (PostM), the increase in salinity was marked by a surge in dinoflagellate populations comprising of Ceratium furca, Akashiwo sanguinea, and Pyrophacus horologium.     

Zooplankton In An Australian Tropical Estuary

The composition of the zooplankton community in a macrotidal (8 m tidal range), tropical estuarine system (Darwin Harbour, Australia; 12^o28′ S, 130^o50′ E) was studied over a 2 year period with the goal of describing biodiversity and determining the environmental factors that have the greatest impact on community structure. Most (82–84%) of the >73 μm plankton was composed of copepod nauplii and copepodites, and plankton samples taken with larger, coarser meshed (150 and 350 μm) nets did not contain significant numbers of larger (non-copepod) organisms. In all, 32 copepod species were recorded, with small euryhaline marine copepod species such as Parvocalanus crassirostris, Bestiolina similis and Oithona aruensis dominating the zooplankton. Plankton abundances ranged between 30,000 and 110,000 m⁻³, and there were significant year (2003 > 2004), season (wet > dry) and site differences (inner harbour sites > outer harbour sites), but negligible diurnal differences. Multivariate analyses identified three sample groups: (1) middle and outer harbour sites, (2) inner harbour and river sites and (3) the river site during the wet seasons. Middle and outer harbour stations were characterised by a diverse mixture of coastal copepods, whereas inner harbour and river sites were dominated by P. crassirostris and O. aruensis. During the wet season, there was a distinct copepod community within the Blackmore River, dominated by Acartia sinjiensis, Oithona nishidai and Pseudodiaptomus spp. Environmental variables (nutrients and chlorophyll a) were correlated with salinity, which had the strongest influence on community structure. There was a significant drop in species richness from harbour to river sites. Small copepods of the families Paracalanidae and Oithonidae dominate tide-dominated Australian tropical estuaries, whereas copepods belonging to the family Centropagidae (such as Gladioferens spp.) appear to be characteristic of wave-dominated estuaries in southern Australia.     

An experimental investigation on diffusion of water in haplogranitic melts

  The diffusivity of water has been investigated for a haplogranitic melt of anhydrous composition Qz₂₈Ab₃₈Or₃₄ (in wt %) at temperatures of 800–1200°C and at pressures of 0.5–5.0 kbar using the diffusion couple technique. Water contents of the starting glass pairs varied between 0 and 9 wt %. Concentration-distance profiles for the different water species (molecular water and hydroxyl groups) were determined by near-infrared microspectroscopy. Because the water speciation of the melt is not quenchable (Nowak 1995; Nowak and Behrens 1995; Shen and Keppler 1995), the diffusivities of the individual species can not be evaluated directly from these profiles. Therefore, apparent chemical diffusion coefficients of water (D _water) were determined from the total water profiles using a modified Boltzmann-Matano analysis. The diffusivity of water increases linearly with water content <3 wt % but exponentially at higher water contents. The activation energy decreases from 64 ± 10 kJ/mole for 0.5 wt % water to 46 ± 5 kJ/mole for 4 wt % water but remains constant at higher water contents. A small but systematic decrease of D _water with pressure indicates an average activation volume of about 9 cm³/mole. The diffusivity (in cm²/s) can be calculated for given water content (in wt %), T (in K) and P (in kbar) by

Long-Term Effects of Tidal Exclusion on Salt Marsh Plain Species at Estero de Punta Banda,Baja California

Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion. Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals, short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries.