Surveys of the distribution, abundance and size of the ctenophore Mnemiopsis leidyi were carried out in Narragansett Bay, R.I. over a 5-year period, 1975–1979. Yearly variations were observed in time of initiation of the ctenophore increase and maximum abundance. Biomass maxima ranged from 0·2 to 3 g dry weight m−3 at Station 2 in lower Narragansett Bay while maximum abundance varied from 20 to 100 animals m−3. Ctenophores less than 1 cm in length generally composed up to 50% of the biomass and 95% of the numerical abundance during the peak of the M. leidyi pulse. During the 1978 maxima and the declining stages of the pulse each year, 100% of the population was composed of small animals. M. leidyi populations increased earlier, reached greater maximum abundances, and were more highly dominated by small animals in the upper bay than toward the mouth of the bay. The averageclearance rate of M. leidyi larvae feeding on A. tonsa at 22°C was 0·36 l mg−1 dry weight day−1, with apparent selection for nauplii relative to copepodites. Predation and excretion rates applied to ctenophore biomass estimated for Narragansett Bay indicated that M. leidyi excretion is minor but predation removed a bay-wide mean of 20% of the zooplankton standing stock daily during August of 1975 and 1976. Variation in M. leidyi predation at Station 2 was inversely related to mean zooplankton biomass during August and September, which increased 4-fold during the 5-year period.
Seasonal and short term variations in phytoplankton biomass were examinedin the Penzé estuary (Northern Brittany) from June 1975 to July 1976. A simple model is proposed to characterize the seasonal variation of chlorophyll a concentration from June 1975 to June 1976. The tidal cycle seems to induce diurnal variations which may be very important in summer in the upper part of the ria. Chlorophyll a concentration increases towards low tide, and correlates with salinity and water level.
The pollen of alien weeds and ornamentals is used to determine sedimentation rates in four California coastal salt marshes. The results indicate that during the present century sedimentation rates have been ca. 50 cm/100 years in southern California and 10 cm/100 years in central California. We interpret this regional contrast to be primarily the result of differences in land use history, although 'natural' environmental differences are apparently also involved. Radiocarbon dates indicate that pre-European sedimentation rates were ca. 10 cm/100 years in southern California and ca. 5 cm/100 years in central California.
Periodic surveys have been made of Holm Sand, a Holocene deposit incorporating One Fathom Bank and part of Mackenzie Shoal in the Bristol Channel (British Admiralty Chart, 1182). The deposit is worked for seadredged aggregate, primarily building and concereting sands, although the latter are becoming depleted. The surveys show that the deposit lies on irregular pre-Holocene substrate and is incorporated as two suites of sand waves: large, mainly asymmetrical, outer sand waves and smaller, symmetriclaly-variable, inner sand waves. Sediments are classified into seven types (A-G), outer sand waves being formed in gravelly sands and sandy gravels (types C-F) and inner sand waves in unimodal medium sands (types A and B). It is suggested that sand wave scale is related to transport mode: transport of inner waveform sediments is mainly as suspended load, whereas outer waveform sediments are transported part as bed load, part as suspendes load. A progressive sequence of profiles is evident in outer sand waves and their alignment and mobility indicate that Holm Sand sediments are derived from channels to the northwest and southeast. This sequence, together with a progressive fining in mean sizes towards the deposit axis, suggests that the structure could have evolved during the (Holocene) Sub-Atlantic period.
Monthly cruises were conducted for one year to examine temporal and spatial variability in nutrients, chlorophyll, and the relative rate of photosynthesis of the <10 μm and total size fraction along a cross-shelf transect off Savannah, Georgia. Additionally, an upwelling event on the outer shelf was examined in some detail to determine its effect on primary production, phytoplankton species composition, nutrient and chlorophyll concentrations. Our results show that chlorophyll concentrations are always high (1.9–8.0 μ l−1) close to shore with little cruise-to-cruise variability. At offshore stations (>20–30 km) nutrients and chlorophyll concentrations were generally low (nitrate <0.1 μm, chlorophyll <1.0 μg l−1). The outer shelf (c. 100 km offshore), however, exhibited considerable variability. When we found upwelling at the shelf break, chorophyll a concentrations at the surface were as high as 6.0 μg l−1. At other times surface chlorophyll at the same locations averaged 0.1–0.2 μg l−1 with nitrate concentrations <0.1 μm. Phytoplankton >10 μm dominated the near shore stations. The <10 μm fraction dominated the phytoplankton of the mid and outer shelf, except during upwelling when diatoms such as Skeletonema costatum and Asterionella japonica were found in high abundance. Our study shows that phytoplankton abundance exhibits little seasonal variability in the Georgia Bight, but that upwelling events induce high frequency (days to weeks) variability on the outer shelf.
A new genus and a new species of a psammobiotic, sphaeromatid isopod, Tholozodium ocellatum, is described from the west coast of India (Goa). It is found on fine sediment beaches (Mdo = 2·72-2·47) located in the vicinity of estuaries which receive large inputs of organic matter. The species is mainly distributed at the upper reaches of the beach and occurs in densities ranging from a few individuals to over 4700 m−2. The existing evidence indicates that this herbivorous/omnivorous species has a fossorial existence without the occurrence of a free-swimming phase and with little interaction with the rest of the fauna. Moreover T. ocellatum in common with some other platybranch genera does not fit into any of the sub-divisions of this group as proposed by Hansen (1905). This suggests that with more information becoming available an extensive revision of this group of sphaeromatids is needed.
Cold bottom water is found during the summer months in a region extending from the shelf break to the nearshore zone in the area of the New York Bight. This cold bottom water, some of which is in the temperature range of the cold cell (8 °C or less), is observed to move onshore in response to upwelling events initiated by a strong wind stress from the south. Surf temperatures, nearshore temperature sections off Monterey Beach, N.J., wind velocities and offshore temperature sections are combined to document the cold cell's formation during 1974 and to demonstrate that the shoreward boundary of the cold bottom water and possibly cold cell water can move into the surf zone causing rapid decreases in surf temperature. In addition, under upwelling conditions, such onshore movements may have significant biological impacts, such as were observed during the summer of 1976 when anoxic conditions prevailed in much of this region.
The concentrations of 32 metals in sediment cores collected from the Continental Shelf off the south-eastern United States are generally uniform with depth. These sediments are predominantly sand with very low organic carbon throughout the core length. The metal concentrations are low compared to those found in average sandstone and to average crustal abundances, and small variations correlate with variations in texture, and in amount of calcium carbonate and organic carbon. No evidence of accumulation of anthropogenic metals was found in these sediments. The data presented are the first compilation of trace metal concentrations in sediment cores of this area and provide a basis for determining the magnitude of future trace metal deposition in these sediments.
Particulate material from the Susquehanna River is enriched in Fe (5–7%),allowing it to be distinguished from other sources of particles in surface waters of the Chesapeake Bay. Although the turbidity maximum removes most of the river-borne detritus, chemical composition of particles (SPM) indicates that Susquehanna River materials dominate the inorganic suspended matter in surface waters of the Bay at least 20–40 km further. Fe concentrations, Fe/Ti, and Fe/Zn ratios in surface water SPM still farther down the Bay indicate that those particles are a mixture of river derived and biological material and that shore erosion is not normally a source of surface water suspended sediments as far as the mouth of the Potomac. Seasonal variations1 of elemental ratios such as Fe/Zn can also be used to demonstrate scavenging of soluble trace elements by particles during summer conditions.
The application of differential pulse polarography to the estimation of manganese (II) in estuarine waters is described. The method is assessed and used in the concentration range 10–300 μg 1−1. Polarographic manganese measurements on samples obtained from the Tamar Estuary (SW England) are compared with colorimetric measurements of total dissolved manganese, and it is shown that polarographically determined manganese (II) can very widely from 100% to <10% of the total dissolved manganese. It is suggested that the manganese not measured by the polarographic method is in colloidal form.
Tide-induced fluctuations in biological oxygen demand (BOD) on two medium to fine sandy beaches were recorded over two separate 24-h periods in February (summer) 1979. Fluctuations in BOD of over two orders of magnitude were found with the highest occurring at or just after high tide and the lowest at low tide. Greatest fluctuations occurred at the higher tidal levels as well as near the surface of the substratum. Significant correlations between BOD and the degree of water saturation of the sand were found, although no such correlations with either bacterial or protozoan numbers or temperature occurred. It appears that in areas of the beach where the water content decreases to 30% or less, BOD is greatly reduced and increases again only upon re-wetting by the incoming tide. Measurements of BOD made during low tide in such areas may underestimate oxygen consumption by as much as 300%. Conversely, measurements made on saturated sediments only may be overestimates of a similar magnitude.
The population ecology of Echinoderes coulli (Kinorhyncha) in a South Carolina, U.S.A., Spartina alterniflora salt marsh was studied at two nearby intertidal sites. Seasonal cycles in population density, spatial dispersion, age structure, size distribution, sex-ratio and gonad condition were determined. Abundance peaked in midsummer and again during fall months at both sites. Density declined during February and abundance minima were recorded during spring. Overall, density ranged from 0·4 to 72·0 × 10 cm −2 . Based on ANOVA, significant (at the 0·05 level) seasonal variations in adult/juvenile ratio and frequency of occurrence of mature gonads in both sexes were demonstrated. Juveniles were fewest in the population during the late fall, winter and spring. Except for males in March, sexually mature individuals were present the entire year with maxima in spring and early fall. The mean length of adults fluctuated seasonally, the minimum occurred in February. Reproduction and the frequency of juveniles were greatest from March to September when an intrinsic rate of natural increase of 0·018 day −1 was achieved. Two distinct female morphotypes, one with long and one with short lateral terminal spines, are present in E. coulli . Two-way ANOVA revealed that the two morphotypes reacted similarly to seasons as no difference across seasons or interaction with seasons in the relative frequency of occurrence of each morphotype or the occurrence of eggs in each morphotype could be identified.
The heavy minerals in recent bottom sediments of the Bristol Channel have distribution patterns which reflect their predominantly uniform source area and the extent of their response to the superimposition of the Channel hydrodynamics. Factor analysis has identified three major factors, which relate to five hydrodynamically fractionated mineral groups and a source-controlled mineralogical province (in the Barnstaple Bay region). This analysis accounts for 77.1% of the total variation in the heavy mineral distributions. The fractionated grouping is related to an increasing hydraulic inequivalence (with the heavy minerals being smaller than predicted) which, in turn, is directly proportional to the shallowing of the main Channel. The hydraulic inequivalence is considered to be result of differential entrainment of heavy minerals; the accompanying mineral-suite changes are a reflection of the size restriction inherent in certain minerals from source.
The origins of intertidal indentations and undercuts (nips and notches) in calcareous shores has long been disputed. In recent years this dispute has centered on the efficacy of solution by seawater vs the erosional effects of marine organisms. Little attention has been given to solution by fresh groundwater even though it is a proven solvent of calcareous rocks whereas seawater is not. The solutional effects of groundwater—either floating as a surface layer on seawater or seeping through porous rocks at the shoreline—would be strictly confined to the intertidal zone and most intense at midtide level. Just such a distribution of erosional effect is required for the formation of nips and notches, yet such a distribution of effect has yet to be demonstrated either for seawater or for most erosional marine organisms. On purely theoretical grounds, then, solution by groundwater deserves consideration as a major factor in the origin of coastal undercuts. In Greece, notches in calcareous rocks occur only in proximity to coastalsprings, where surface seawaters are locally diluted by freshwater. Per cent saturation of these waters with respect to calcium carbonate is not known, but the one-to-one correspondence of notches with springs is by itself persuasive circumstantial evidence that solution by groundwater is the chief factor in the origin of the notches.
Macroinfaunal benthos off the South Texas Coast of the Gulf of Mexicoformed different assemblages distributed according to depth: shallow (22 m), mid-depth (36 to 49 m) and deep water (78 to 131 m). Species composition of shallower stations were less diverse, composed of eurytopic and opportunistic species adapted to a fluctuating environment. The deep water benthos, in a more stable environment, had a higher diversity. Sediment composition (high proportions of silt) at the mid-depth stations resulted in dominance of deposit feeders. The environmental gradient was related to a species continuum which changed from polychaete dominated groups in shallow water, to deposit feeding molluscs and crustaceans, to a deep water diverse fauna not dominated by any particular group. Environmental heterogeneity, including climatic variability, may be most important in controlling shallow water benthos. In deeper more stable shelf habitats where diversities are higher and species equilibrium is the case, species interactions may determine community structure.
During 1973–74 biweekly collections of zooplankton in Jobos Bay, Puerto Rico revealed that major differences in the abundance and variety of several populations were related to water circulation, seasonal rainfall, and diel behavior. Total densities of zooplankton ranged from 225 to 9050/m3 for night and 30 to 4700/m3 for day samples. Abundance levels increased about twofold from coastal to isolated regions of the bay but at least twice as many species occurred in the coastal areas. Rapid, short-term changes in abundance, pulses of about one order of magnitude, occurred shortly before and during the wet season. Diel differences in density, most notable among the copepod, Acartia tonsa, coincided with a seasonal increase in abundance. The size and composition of the zooplankton communities in Jobos Bay were similar to those found in one polluted, tropical embayment (Guayanilla Bay, Puerto Rico) but differed greatly from those described in another (Kingston Harbour, Jamaica).
In order to evaluate the influence of the ocean dumping of sewage sludge upon the organic carbon fraction of sediments of the New York Bight, a study of carbon isotopic variations in surface sediments from the area has been completed. On the basis of our 13C/12C measurements, it appears that: (1) sewage is depleted in 13C as compared to average marine organic sedimentary carbon, and (2) δ13C values from sediments of the New York Bight show systematic variations which are a direct consequence of the sludge disposal. Based on assumptions regarding inputs of sedimentary carbon to the sea floor in this area, we have modeled these 13C/12C variations in terms of progressive dilution of normal marine carbon with carbon derived from the ocean dumping of wastewater sludges. The isotopic composition of carbon in sediments from the New York Bight may serve as a quantitative tracer of sewage sludge components.
Variation of chromium concentrations with grain size in estuarine sediments comples use of a sediment textural indicator in examination of pollutant chromium distribution. Sediment specific surface area is shown to be superior to measurements of the proportion of fine-grained sediment in defining regional variations of chromium concentration with sediment texture in three relatively unpolluted estuaries. Mineralogy is the prime control on chromium levels in these estuaries. The application of a textural normalization technique using specific surface areas in an estuary receiving a chromium-rich effluent allows differentiation of polluted from nonpolluted sediments. Accumulation of effluent chromium occurs within the estuary, not in adjacent coastal sediments, and concentration occurs in intertidal rather than subtidal zones.
