Showing papers on "Benthic zone published in 1973"

Production of Benthic Foraminifera in Three East Pacific Oxygen Minima

Abstract: Large standing stocks found, characterized by high dominance, low diversity, small thin-shelled specimens, oxygen not limiting ecological factor

Coupling Carbon Flow Through Some Pelagic and Benthic Communities

Abstract: Sediment core oxygen uptake is correlated positively with primary production and inversely with mixed-layer depth in various aquatic ecosystems for which the input of organic matter is predominantly autochthonous. In these areas organic carbon sedimentation is proportional to the ratio of carbon input: mixed-layer depth, which reflects increased mineralization with increased depth of mixing. The ratio of primary production: mixed-layer depth is compared with the carbon equivalent of oxygen uptake by sediments to derive an expression which is used to calculate the amount of photosynthetically fixed carbon respired at the sediment surface.

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. III. Energy transformations by sea urchins

Abstract: An energy budget was constructed for a population of the sea urchin Strongylocentrotus droebachiensis in the nearshore area of St. Margaret's Bay, Nova Scotia, Canada. Of the 6 age classes identified, ages 1+and 2+accounted for about 1/2 the population energy flow. Population production efficiencies were: production/assimilation=0.28, production/consumption=0.04 to 0.13, and production/biomass=0.80. Although S. droebachiensis was the dominant herbivore in the seaweed bed, it utilized only 1 to 7% of seaweed production. As with other populations of sea urchins, however, it had a proportionately greater influence on seaweed biomass, and also presumably production, by clearing seaweed from large areas of substrate and maintaining it clear. Loss of dissolved organic matter, the only term in the energy budget not measured, was estimated by substracting the other terms in the energy budget from consumption. In laboratory individuals, this ranged from 40 to 80% of absorption (consumption-faeces). A critical review of energy budgets for 6 other species of marine benthic grazers also revealed large amounts of energy unaccounted for that might be attributed to loss of dissolved organic matter.

Distribution of coral reefs in the pearl islands (gulf of panama) in relation to thermal conditions1

Abstract: The hypothesis that coral reefs are largely confined to the north and east sides of islands because of favorable thermal conditions was tested and confirmed in the Pearl Islands, Panama. The growth rate of Pocillopom dumicornis, the chief reef-building species, declined markedly or ceased on shores exposed to temperatures in the range 2%21°C when median growth rates dropped to below 1.0 mm month-l and a variety of alien benthic species invaded and overgrew the branch tips of corals. High rates of bedload sedimentation on exposed shores and a high organic matter content of sediments on reefs did not affect coral growth. Differences in coral growth preceding and following upwelling were correlated with seasonal variations in sky cover. Other factors affecting coral growth and reef development include the ability of corals to feed and reproduce at low temperatures, the influence of turbulent conditions, the capacity of a reef structure to modify the surrounding thermal regime, and the effects of attrition due to corallivores.

Redeposition of pollen grains in lake sediment

Abstract: Evidence from sediment traps shows that in dimictic Frains Lake pollen grains and the bottom mud in which they are contained are rcsuspendcd during spring and autumn mixing, while in Saylcs Lake, a nonstratificd lake nearby, similar quantities of pollen-bearing sediment are resuspended at irregular intervals throughout the year. In the nonstratified lake resuspended material is poorly mixed in the lake water, while in the dimictic lake, during the seasons of water mixing, resuspended sediment is similar in amount, perccntagc a5 .h weight, and pollen composition at various lcvcls throughout the water column. Rcsuspension occurs without sorting or diffcrcntial movement of individual pollen grains. The pollen content of rcdepositcd scdimcnt serves as a tracer, showing that sediment is moved from the littoral zone to the deeper basin of the lake. In the littoral zone annual stirring may involve the uppermost 6-12 mm of sediment; even in the dccpcr part of the basin, the uppermost millimeter at least is stirred by this process every year. Redeposition of sediment and pollen has been rcportcd from experiments with scdimcnt traps in Frains Lake, a thermally stratified lake in Michigan (Davis 1968); circulating water stirs and rcsuspends scdimcnt during the spring and fall seasons of water mixing. This process is capable of redistributing scdimcnt within the lake basin (Tutin 1955) and thus affecting the Final distribution of pollen grains in sediment, so it has obvious importance for the interpretation of fossil pollen. Seasonal measurcmcnt of redcposi tion has been cxtcnded to a shallow, nonstratified lake for comparison with Frains Lake. The constrast in timing demonstrates that absence of thermal stratification is csscntial for extcnsivc rcdcposition. To evaluate movcmcnt of the scdimcnt and its effect on pollen distribution, scdimcnt traps wcrc set at various depths in various parts of both lakes. With pollen grains serving as a tracer, thcsc traps dcmonstratc the movcmcnt of scdimcnt from one part of the lake basin to another. They serve further to detect any sorting due to differential movement that may occur within the pollen component of the scdimcnt, a phenomenon that had been suspected from the uneven disL Contribution No. 147 from the Great Lakes Restarch Division, The University of Michigan. tribution of different kinds of pollen within lake basins (Davis et al. 1971). The total amount of pollen deposited in traps at diffcrcnt stations scrvcs to assess the thoroughness of water mixing, In addition to information on the dircction of sediment movement, the amount of movcmcnt, and the distribution of pollen within the suspcndcd sediment, the results of the study provide an estimate of the depth to which sediment in lakes is stirred by the action of water currents. Throughout this paper rcferencc is made to “pollen grains.” In fact the refcrcncc is to the waxy exine of the grains, which is identifiable taxonomically and which is rcsistant to decay. Pollen grains filtered from lake water during the flowering season still retain protoplasm, but a few weeks or months later, only the exine remains. Ccrtdn cxccptional types of pollen arc complctcly destroyed soon after entering the lake by bacteria or fungi (Havinga 1967) or benthic organisms (R. Davis 1969). For example poplar pollen was foulld in traps during the flowering season, but was virtually absent from the sediment on the lake floor. However, pollen is not destroyed after it has been incorporated in sediment; this is cstablishcd by the constancy through time of the ratio of pollen grains to silt and clay in the sediment (Davis 1968). It is for LTMNOLOGY AND OCEANOGRAPIIY 44 JANUARY 1973, V. 18( 1) REDEPOSITION OF POLLEN GRAINS 45 this reason that pollen serves as a useful tracer for suspension, movement, and rcdeposition of the scdimcnt as a whole. I gratefully acknowlcdgc the assistance of J, IM. Bciswengcr and L. B. Brubakcr in the design and cxccution of thcsc cxpcrimcnts. W, R. Solomon kindly made available his data on pollen content in the air at Ann Arbor. The George Rcscrvc, The University of Michigan, pcrmittcd the USC of sediment traps on Sayles Lake in 19651966. The work was supported by National Science Foundation Grants G,B 2377, GB 5320, and GB 7727. DESCRIPTION OF SITES Frains Lake (42”20’N, 83”37’W), 12 km northeast of Ann Arbor, Michigan, is about 200 m wide and 500 m long, sloping gradually to a maximum depth of 10 m in the center. There arc no inflowing or outflowing streams. The surrounding topography is nearly flat, (2uitc unprotcctcd from wind, the lake is surrounded by meadows with a relief of only 3-5 m. ICC about 30 cm thick persists for 3-4 months each winter. In summer the water is strongly stratified, with the top of the thermocline at about 4 m. (For more dctailed information on topography, see Davis ct al. 1971.) Saylcs Lake (42”26’N, 84”4’W), near Pinckncy, Michigan, and 35 km west of Frains Lake, is similar in area and shape to Frains Lake and, like Frains Lake, has no major inflowing or outflowing s trcams. Howcvcr, the lakes do differ in two major ways: 1) Saylcs Lake is less than 1 m deep over most of its area and only rcachcs a maximum depth of 3 m in an area just south of the basin’s ccntcr, and 2) Sayles Lake is surrounded by woods on three sides with a steep ridge 20 m high along the south short. ICC cover is similar to Frains Lake, but Saylcs Lake ncvcr develops thermal stratification.

Growth and Submarine Fossilization of Algal Cup Reefs, Bermuda

Abstract: Small charges of explosives were used to section cup-shaped reefs that occur on the margins of the Bermuda Platform. Study of these artificial outcrops, up to 10 m high, and the samples collected from them show how the reef-building community is rapidly converted to well-lithified reef rock in the marine development. The reefs, known locally as boilers and breakers, occur along the wave-swept south shore of the Bermuda Islands and around the northeast and northwest margins of the Platform. They are cup-shaped, up to 30 m in long dimensions, and rise up to the sea surface as much as 12 m above the surrounding sea floor. The reefs are built by an intergrowth of encrusting organisms, principally crustose coralline algae, an encrusting hydrozoan, Millepora sp., and an attached gastropod, Dendropoma irregulare. The growth framework of these algal cup reefs has extensive voids: large and intermediate-sized growth framework and shelter pores; borings of bivalves and sponges; and both intra- and inter-particle pores. A variety of vagile and sessile organisms (coelobites) inhabit these pores: an encrusting Foraminifera, Homotrema rubrum, is the most abundant attached coelobite; the tests of a variety of benthic Foraminifera and ostracods are common: branched coralline algae, barnacles, bivalves, ahermatypic corals, bryozoans, and burrowing crustaceans occur in varying abundance. Beginning millimetres below the living surface, internal sediments accumulate in the extensive voids. Coarse-grained skeletal sand derived from the surface of the reefs is characteristic of the larger voids; lime mud with the tests of planktonic Foraminifera and planktonic algae occurs generally in the smaller voids. Most specimens from the interior of the reefs show multiple generations of internal sediment that vary in grain size, composition, and colour. The sand-sized sediments are pumped into the voids by the frequent and intense wave action; the lime mud settles out in the smaller, less agitated pores. Cementation of internal sediments and surrounding growth frame begins centimetres below the living surface; it is so pervasive that marble-hard reef rock is developed within 1/2 m or less. The cement is principally high-magnesium calcite of micrite size, and subordinately acicular aragonite, but there are locally wide variations in crystal size and morphology. The occurrence of the cement within the reefs well below sea level, the isotope ratios of the cement crystals, the mineralogy, and the age inferred from radiocarbon age determinations of the growth frame all indicate that the cement is submarine and deposited from water of oceanic composition. The algal cup reefs of Bermuda demonstrate the reef-building ability of a community of encrusting organisms that form only crusts in the intertidal zone of the Mediterranean and Northern Brazil. The cup reefs of the northern margins of the Bermuda Platform are true reefs, not merely veneers covering eroded blocks of Pleistocene limestone. In their composition, location, and early diagenesis, the cup reefs closely resemble the algal or lithothamnion ridge of Pacific atolls. Synsedimentary cementation of internal sediments and growth frame makes a major contribution to the rigidity of these ocean-facing reefs and atoll rims. The assemblage of features that characterize the submarine fossilization of the cup reefs is widespread elsewhere in the modern seas: the floors of the Persian Gulf and parts of the Mediterranean; the margins of Pacific atolls; and the reefs off the north coast of Jamaica. This fossilization is characterized by reiterated generations of coelobites, internal sediments, and synsedimentary cements that can in time replace a major part of the original growth framework. Major variations in the sequence of these generations from pore to pore is the signature of this kind of fossilization. The same features of fossilization are described from reefs in the Devonian, Permian, and Triassic.

Benthic Infauna of Eelgrass, Zostera marina, Beds'

Abstract: The infauna ofZostera beds in the Chesapeake Bay-York River estuary and Chincoteague Bay was sampled in March and July 1970 using a corer. Sediments were fine sand or very fine sand. Sorting of sediments varied from poorly sorted to moderately well-sorted and appeared to be positively correlated with the density ofZostera at the respective stations.

Surface area in ecological analysis: Quantification of benthic coral-reef algae

Abstract: The surface area of organisms and substrata is shown to be a significant ecological parameter because of its functional importance in the system Quantification of surface area can be of particular value in morphologically complex environments such as coral reefs The amount of surface in a reef habitat can be estimated by direct measurements and theoretical approximations, using a surface index (SI) for the amount of surface increase over that of a similarly bounded plane SI values for a section of the British Honduran barrier reef ranged up to 15 in the reef-crest area at scales significant to macro-organisms By combining substrate-area measurements with estimates of percent coverage of the major benthic algal components, a reef transect with a horizontal area of 300 m2 was shown to have over 300 m2 covered by benthic macroalgae The potential for the further development of surface estimation techniques is discussed

Deep-Sea Benthic Community Respiration: An in situ Study at 1850 Meters.

Abstract: The in situ oxygen uptake of sediments at 1850 meters on the continental slope south of New England is two orders of magnitude less than the uptake of sediments from shallow shelf depths After treatment of the sediments with Formalin there was no measurable chemical oxygen uptake, which shows that the total uptake is biological (community respiration)

The acute toxicity of some heavy metal ions toward benthic organisms

Abstract: A great deal of information is being gathered about the acute toxicity of heavy metal ions toward fish and in fact reView articles are available (1,2). It is also important however to attempt to determine the effect of heavy metal ions upon benthic organisms since they may in fact be more sensitive and prove to be good indicator organisms. Warnick has summarized some data pertaining to aquatic insects (6) and the effect of copper upon a variety of benthic organisms bas been studied (7,8).

Studies on a saline lake ecosystem

Abstract: Saline lakes are in many respects simple natural models of ecosystem structure and function. In this regard, a descriptive study was made of a saline crater lake over 3 years (1968-1970). Lake Werowrap is associated with the Red Rock scoria cone, western Victoria. It is small in area (~21 .6 ha), shallow (~1.4 m), and of variable salinity (23-56 g/l.). The local climate is typically cool temperate, but evaporation exceeds precipitation over most of the year. Meteorological data were used to compute the hydrological and analytical energy budgets for 1969 and 1970. The main determinant of variations in lake salinity and volume was the evaporation/rainfall balance, although groundwater seepage also was implicated. The average rate of water renewal was 0.725 times per year. The annual heat budgets of the lake (mean, 1712 g cal/cm² and the lake sediments (mean, 1218 g cal/cm²) were very small fractions of the total energy fluxes within the system. Energy fluxes were governed mainly by incident radiation, evaporation, back-radiation, and sensible heat transfer. Chemically, the lake water is highly alkaline (pH 9. 8), predominantly of sodium "chlorocarbonate" composition, and showed stable ionic proportions despite salinity fluctuations. Inorganic nitrogen and phosphorus concentrations were high and influenced seasonally by a gull population breeding on a small islet in the lake. Partial information on trace elements was obtained. Optical measurements indicated rapid light attenuation due to dissolved organic material and dense plankton populations. The trophic structure of the ecosystem was taxonomically very simple. The blue-green alga Anabaena spiroides predominated in summer and autumn 1969, but subsequently was displaced by the dinoflagellate Gymnodinium aeruginosum and a blue-green alga tentatively identified as Chroococcus. The change in species composition probably was due to a progressive increase in salinity which occurred during the study. G. aeruginosum, unlike the other species, persisted throughout the seasonal cycle, although changes were observed in the size and structure of the species. Summer and autumn generally were the seasons of most intensive photosynthetic activity. The total phytoplankton production in 1970, measured by the carbon-14 method, was 435 g C/m², evidently the highest figure recorded for any unpolluted lake. Carbon-14 and oxygen productivity data showed good correspondence only in summer, due to effects of non-photosynthetic respiration. Changes in cell and pigment concentrations also were monitored. Radiation and temperature appeared to be the most influential factors governing primary productivity. Inorganic nitrogen was the only chemical constituent to show significant depletion, and may also have been important. Considerable bacterial activity was indicated by high rates of "dark" carbon-14 assimilation. Periphytic productivity, although not measured, was likely to have been significant only in spring 1968. Attention was given to the population dynamics of the rotifer Brachionus plicatilis, the dominant zooplankter, which attained peak densities in summer and autumn. Variations in rotifer population parameters were attributed mainly to salinity, temperature, and food supply. Other zooplankton species included the rotifer Hexarthra jenkinae, two ciliates, and larvae of aquatic and terrestrial insects, notably the dytiscid Necterosoma penicillatum, which occurred around the lake margins. The benthic community consisted solely of the chironomid Tanytarsus barbitarsis. Incomplete productivity data suggest that the lake had the most productive benthic community yet recorded. Caloric measurements for some species in the lake are recorded.

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

Abstract: 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.

General Ecology of the Canadian Arctic Benthic Marine Algae

Abstract: The Canadian Arctic marine flora is basically a regional extension of Atlantic species. As the extreme environmental conditions of low temperature, low salinity and long periods of darkness intensify towards the western and northern parts of the Canadian Arctic, there is a marked reduction in the number of species. The protective cover of sea ice, together with the seasonal development of a low salinity layer from ice melt, hinders mixing between water layers, and nutrient replenishment is apparently a critical problem. Communities are generally small and isolated largely because of substrate limitations. A population may be extensive and dense, but this is attributed to the small number of species and the relative ineffectiveness of most of these in competing for the available space. Following seasonal ice melt, the intertidal habitat in colder regions remains unsuitable for algal growth, because of its exposure to a combination of adverse climatic and oceanographic conditions. The decreasing diversity of species, as the physical conditions become more adverse, together with the nearly complete absence of endemics, indicate a low level of adaptation, and the arctic communities are judged to be ecologically immature.

An ecological study of the Ponggol Estuary in Singapore

Abstract: 1. An ecological study of the Ponggol Estuary was conducted from July 1965 to June 1966 and the seasonal data on physical, chemical and biological characteristics were presented. 2. The Ponggol River represents a short, narrow and shallow estuary in Singapore. The river mouth is open throughout the year and water from eastern Johore Straits drains in twice a day at high tide. The upper reach, however, is left exposed at low tide. 3. The Ponggol River was classified as a vertically and laterally homogeneous estuary and was found to exhibit a mesohaline to polyhaline environment. 4. Significant hydrological gradients from the river mouth 10 the upper reach were noted in the river system. Salinity, dissolved oxygen and pH increased towards the mouth of the river and other parameters such as nutrients, dissolved organic matter and turbidity increased towards the source. 5. Although the river received organic pollutants at the upper reach the estuary was able to discharge them fairly rapidly through regular flushing by the tides. The transient rise of organic matter did not appear to impart any serious affect on the biota in the estuary. 6. Over 98% of the phytoplankton consisted of diatoms, most of which were brought into the estuary from eastern Johore Straits. Freshwater forms were relatively few. 7. Phytoplankton biomass was considerably higher than the adjoining waters. and was reduced at the upper reach due to high turbidity of the water. 8. 80% of the zooplankton was composed of dinoflagellates,Difflugia, copepods and bivalve larvae dominating at all sections of the estuary. 9. Percentage composition of the zooplankton showed that dinoflagellates and copepod nauplii predominated at high tide whileDifflugia and bivalve larvae were abundant at low tide. 10. Zooplankton standing crop, in general, was higher towards the source at high tide but the reverse was found at low tide, i.e. standing crop increased towards the river mouth. This was attributed to the process of concentration. 11. Species composition of zooplankton was found to be more or less similar to that of the eastern Johore Straits. 12. The nekton consisted predominantly of small and juvenile fish. Close correlation of fish and copepods was found to be statistically valid and it was concluded that the fish entered the estuary to feed rather than to spawn. 13. The squids formed an important catch of the beach seine unit and were caught throughout the year. 14. The fish population could be grouped into four categories: estuarine components, euryhaline components, marine components and migratory components. 15. Benthic invertebrates were abundant. Commercially important species consisted of prawns,Metapenaeus andPenaeus, and crabs,Neptunus pelagicus andScylla serrata. 16. The river bed was inhabited predominantly by molluscs and the distribution resembled that of the sheltered shore of muddy-sand type.

Studies on the sublittoral free-living nematodes of Liverpool Bay. I. The structure and distribution of the nematode populations

Abstract: Data collected from a survey of the benthic fauna of Liverpool Bay (UK) have been used to study the distribution and structure, in terms of percent age dominance and percent age frequency, of the nematode populations. Cluster analysis of the faunistic data from individual stations has shown that the populations are not sharply delimited. The relative proportions of their characteristic genera are extremely variable, and apparently influenced by small differences in sediment composition. It is, thus, considered more logical to think in terms of a number of different habitats, each with certain characteristic genera, rather than in terms of a series of discrete associations. Six types of habitat are distinguished on the basis of sediment granulometry: (1) mud and sandy mud; (2) very muddy sand; (3) muddy sand; (4) muddy sand-gravel mixtures; (5) clean sand-gravel mixtures; (6) clean sand. Habitats 1, 2 and 3 were dominated by Sabatieria spp., the degree of dominance apparently being related to the percentage of silt-clay. Habitat 4 was dominated by Neochromadora sp. and Sabatieria spp. and Habitats 5 and 6 by Desmodora sp. Both generic and dominance diversity were very much lower for Habitats 1 and 2 than elsewhere.

A Comparison of Benthic Microalgal Production Measured by C14 and Oxygen Methods

Abstract: A comparison of estimates of benthic primary production on a sandy beach measured by in situ oxygen and laboratory C14 methods showed that both methods gave similar measures of the magnitude of production. Sources of error in each method are discussed. Measures of C14 uptake offer sensitivity when production is low, but when undisturbed sediment cores can be obtained, production is most easily measured by following changes in dissolved oxygen.

Surface Area in Ecological Analysis: Quantification of Benthic Coral-Reef Algae

Abstract: The surface area of organisms and s~tbstrata is shown to be a significant ecological parameter because of its functional importance in the system. Quantification of surface area can be of particular value in morphologically complex environments such as coral reefs. The amount of surface in a reef habitat can be estimated by direct measurements and theoretical approximations, using a surface index (SI) for the amount of surface increase over that of a similarly bounded plane. SI values for a section of the British Honduran barrier reef ranged up to 15 in the reef-crest area at scales significant to macro-organisms, tly combining substrate-area measurements with estimates of percent coverage of the major benthic algal components, a reef transect with a horizontal area of 300 m 2 was shown to have over 300 m 2 covered by benthic macroalgae. The potential for the further development of surface estimation techniques is discussed.

An ecological investigation of the Portneuf River, Idaho: a semiarid-land stream subjected to pollution

Abstract: Summary The Portneuf River (mean monthly discharge near mouth 1.4-15.4 m3/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156-km course, during the period 1967-1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil-conservation practices. However, the stream also is affected by wastes from a sewage-treatment plant, phosphate-processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip-net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of reduced habitat.

The ecology and reproduction of a marine bivalve, mysella planulata (erycinacea).

Abstract: Mysella planulata ( Stimpson ) is a small erycinacean bivalve which occurs primarily in muddy sands of the Zostera marina community. The recent distribu tion of M. planulata extends from Nova Scotia to Cape Hatteras on the American Atlantic coast and includes the Texas coast of the Gulf of Mexico. The species also occurs in Pliocene and Pleistocene deposits of Florida and Maine (Dali, 1900) . While M. planulata is not a conspicuous member of the benthos, it may be an abundant and at times even a dominant species. Yet, as with so many other marine invertebrates of no apparent economic importance, virtually nothing is known of its biology. This report presents data on the density, distribution, growth, age-structure and reproduction of a population of M. pianulata from Beebe Cove, at the mouth of the Mystic River, eastern Long Island Sound, Connecticut. Beebe Cove is a small bay, approximately 1500 m long by 305 m wide. The habitat is sublittoral, but water depth does not exceed 2 m ; salinity varies between 29 and 31 %. The sediment is a mixture of fine sand, silt, and clays, the latter components comprising more than 70%. Beds of Zostera marina cover the bottom and contribute large quantities of organic detritus to the benthic ecosystem. Tem perature ranges from —?� 1 to 26°C and an ice cover may be present in winter. Beebe Cove is isolated from the Mystic River by a railroad trestle embankment and exchange occurs only through two narrow channels. Consequently, through most of the cove currents are restricted and sluggish and siltation rates are high. Except for a thin layer at the mud/water interface, the benthic environment is highly reducing. Sampling was restricted to a single station near the center of the cove, marked with a buoy which remained in place throughout the experimental period. Most of the data in this report are based on replicate samples taken at this single station between April 1970 and November 1971, although some information is preseiited for the same station from sampling dates in 1969. Replicate samples were collected using a 0.07 m 2 Peterson grab operated by hand from a small skiff. Samples were washed through a 1 mni mesh stainless steel screen with seawater. For the studies on larval development, animals from the field collections were transferred to finger bowls of seawater. Frequently the act of screening and handling the adults seems to stimulate release of larvae, but a constant supply of newly released veligers was provided by adults maintained in finger bowls con taining sediment from Beebe Cove. Larvae were collected every other day and

Benthic Algal Ecology in a Deep Reef and Sand Habitat off Puerto Rico

Abstract: The algal populations of coral reef and sand habitats at 10—20 m depth off the west coast of Puerto Rico arc dcscribcd on the basis of observations made from an undersea laboratory. Algae were poorly devcloped on the rccf becausc of Sedimentation and heavy grazing pressurc. The sandy plain had extensive algat growth involving a distinctive association between algae and sponges. The transition from reef to algal plain is described, and some aspccts of the dynamics of the System are discussed.