Search

Zostera noltii and Zostera marina var. angustifolia turfs have been transplanted on a pilot trial scale with initial success on sheltered estuarine mudflats in carefully selected areas in Norfolk and Suffolk, Great Britain. Transplanting can be carried out with turfs on suitable mudflats where mud surface changes in level of at least ± 7 cm per year or ± 3 cm per week occur. The results suggest that Z. noltii growth is favoured in areas where a very close balance between the forces of erosion and accretion occures. Field scale transplanting of Z. noltii appears to be feasible in suitable areas approaching 1 ha in size at a cost of about £1 000 per ha (1973 prices). Suitable areas not already colonised by Zostera may be very limited on European coasts and the feasibility and additional costs of creating suitable areas by engineering structures has yet to be explored. Initial results with single turion planting are encouraging. If proved successful, this method could greatly reduce costs of Zostera transplanting.

Ecological studies on the animal communities in eelgrass beds in Japan are briefly reviewed Fish fauna and macro-invertebrate fauna in eelgrass beds have been studied in various localities of Japan. A comparison of fish fauna and mobile epiphytic invertebrate fauna of the various localities indicated a very high similarity between them. Fishes and decapod crustaceans have been classified into several categories according to their residence period in the eelgrass beds. Most of the permanent residents are small in size and have no importance for fisheries, however, the seasonal residents include the juvenile and young subadult stages of some commercial fishes. Trophic relations in eelgrass communities have been examined and seasonal modifications of food-chain relationships described. A faunal change of both fishes and epiphytic invertebrates accompanying the decline of the eelgrass beds has been shown, and the significance of eelgrass beds for conservation of inshore fishery resources has been discussed.

The productivity of eelgrass, Zostera marina L., was measured in relation to light and season using 14C. Net productivity during the summer averaged 56 μg C/g dry weight per langley and on an areal basis 4.8 g C/m2 per day. The total production during the growing season was calculated to be 812 g C/m2 with at least a twofold turnover of the standing stock during this period. The uptake of carbon in relation to light intensity is hyperbolic below 50% light followed by some inhibition at higher intensities. This response is described using Michaelis-Menton kinetic equations. These experiments indicate that light saturation occurs at very low intensity. The half-saturation constant (KLt) was 12.5% of surface light.

In a laboratory sediment model consisting of sand and chopped Zostera marina leaves, the sulfur cycle and the succession and zonation patterns of sulfur bacteria were studied for a period of 7 months. The pool size of different forms of sulfur was quantified, and the rate of sulfate reduction was measured with an in situ radio-tracer technique at regular intervals. From these data, transfer rates of the sulfur cycle in the system could be calculated for different periods. The rate of sulfate reduction was initially 80 nMS·cm3·day-1; this decreased to 25 nMS·cm3·day-1 towards the end of the experiment as the system started to become oxidized. There was a transient accumulation of elemental sulfur in the bacterial plate at the sediment surface. More than 50% of the total mineralization of the organic material was due to sulfate reduction. Comparison with the net oxygen uptake showed that, during the first 2 to 3 months (when the sediment closely resembled a natural, reduced shallow water sediment), SO4- was equally as important as O2 for transporting oxidacion equivalents from the water to the sediment.

The caridean shrimp Hippolyte californiensis Holmes locates its host plant, the eel grass Zostera marina, visually, discriminating it on the basis of its form. Using models of the plant, the form-specific sign stimuli optimally releasing the host-selection response were investigated. Shrimps preferentially approached dark forms presented against a lighter background. The more a form contrasted with the background, the higher was its stimulatory value. Shrimps showed differential responses to solid forms of varying shape, preferring a stripe-like rectangle in a vertical orientation. Rectangular forms 50° (visual angle) or more in height and between 12° and 20° in width were maximally stimulating. Patterns of several vertical stripes had a greater releasing value for the approach response than a solid rectangle form of optimal dimensions. The greater the spatial frequency of a striped pattern, the reater was its attractiveness. Shrimps discriminated patterns of stripes whose elements were as small as 2° wide, giving an estimate of their visual acuity. Along with the relative contrast, the most important stimulus parameters of striped patterns are the continuous, straight form of the edges and their vertical orientation. It is postulated that the scototactic response of H. californiensis to relatively large, dark, solid forms is involved in the distant detection of clumps of eel grass. At closer range, the eel grass plants are then discriminated on the basis of the stripelike pattern of the leaves.

A background, listing the history of transplanting seagrasses is given. There is a need for seagrass field planting methods owing to the extremely high productivity of seagrasses and the perturbations they are subjected to. I have planted vegetative stocks and seeds of Zostera marina L. (eelgrass) across tidal zones, across latitudinal zones (from Alaska into Puget Sound), and into water deeper than indigenous growth. Data from these plantings indicate: (1) varietal distinctions based on leaf dimensions are invalid; (2) the possibility of local physiological race distinction in eelgrass; (3) the depth limit of eelgrass is due to a lack of suitable light deeper than a certain minimum depth; and (4) eelgrass seedlings require a higher light intensity than is present deeper than a certain minimum depth. Thus, transplanting experiments yield much more data concerning seagrass biology than just planting method information.

Rates of uptake and excretion of phosphorus by both roots and leaves of eelgrass (Zostefu mwina L. ) were dependent on the orthophosphate concentration of the medium. In a typical shallow tidal pool dominated by eelgrass, the interstitial reactive phosphorus concentrations of the sediments were as high as 75 pg-atom/liter, while in the water they were ca. 2. The plants absorbed 166 mg P/m2-day from the sediments, assimilated 104 in the production of fresh eelgrass, and excreted 62 into the water. An amount equivalent to about 41% of the reactive phosphorus excreted, or 3 metric tons P/day, was exported from the lagoon into the Bering Sea. These results add a new pathway to the phosphorus cycle for estuaries containing vascular plants.

SUMMARY The red alga Smithora naiadum is normally found only as an epiphyle on the sea grasses Phyllospadix scouleri and Zostera marina. I used 32P and 14CO2 to examine the chemical communication between host and alga. Both 32P and the product of 14CO2 light fixation moved from the host to the alga. Reverse movement between host and epiphyte was also demonstrated. Part of this transfer occurred through the plant and part occurred by leakage from the host into the medium and subsequent uptake by the alga. Although plants were initially labeled in the light, transfer of 14C was light independent. Transfer of 14C-labeled products between host and epiphyte was also shown for Punctaria orbiculata and Z. marina; for Microdadia coulteri on Grateloupia doryphora, and between Gonimophyllum skottsbergii and Botryoglossum ruprechtiana. Epiphyte-host associations do not require a penetrating rhizoid for an exchange of the isotopes tested. By their proximity alone, epiphytic flora are apparently capable l exchanging products before these are diluted by the sea.

In 1923 while the eel grass, Zostera marina, was flourishing in suitable areas around Woods Hole, WV. C. Allee completed a study of the animal communities of the region, and described in some detail the one characteristic of the eel grass areas. In 1931 practically all the Woods Hole eel grass was killed by a mycetozoan parasite, and today it is still very scarce. Interest in the possible changes in the animal community led to a new survey made in early September, 1936. The area which Allee found to show the eel grass community best is a shallow lagoon in the Northwest Gutter, a channel running between Naushon and Uncatena Islands. In 1923 the portion of this lagoon which was always covered by at least 30 centimeters of water was filled with a dense matting of eel grass. In the summer of 1936 the lagoon floor was a vast extent of muck without any plant covering. The eel grass was gone except for one or more small patches about one square meter in area, and the many dead rhizomes still in the mud were the only evidence of its former abundance.

High rates of acetylene reduction were observed in systems containing excised rhizomes of the Caribbean marine angiosperms Thalassia testudinum, Syringodium filiforme and Diplanthera wrightii, and the temperate marine angiosperm Zostera marina. For 4 plant and plant-sediment systems the ratio of acetylene reduced/N2 fixed varied from 2.6 to 4.6. For T. testudinum the estimated rates of nitrogen fixation are in agreement with estimated requirements of the plant for nitrogen. For a typical T. testudinum stand, N2 fixation is estimated to be 100 to 500 kg N/hectare per year. Numbers of N2-fixing bacteria in the rhizosphere sediments were roughly 50 to 300 times more abundant than those in the nonrhizosphere sediments, and in both types of sediments were of the same orders as the estimated numbers of heterotrophic aerobes.

Tests on the through-circulation drying of Zostera marina on a semi-commercial scale have been conducted with a batch dryer to determine the optimum conditions. There was a maximum feasible loading for grasswrack (eel-grass) of approximately 3.8 lb./sq. ft. in each layer. The effects of variations in the rate of air flow, of amount of air recirculated, of air-flow reversal and of temperature (160–220° F) have been studied with particular reference to output and efficiency.

The so-called “MOBA” or “Zostera-zone ” is a place of interest from the view-point of fishery in the inland sea. In Ikawazu-cove Zostera marina and Z. nana make “MOBA”, where the ecological studies on Zosterae has been carried out. In this paper the enviromental factors-hydrographycal and biological-which seem to correlate with the vegetation of Zosterae are reported.

The so-called “MOBA” or “Zostera-zone ” is a place of interest from the view-point of fishery in the inland sea. In Ikawazu-cove Zostera marina and Z. nana make “MOBA”, where the ecological studies on Zosterae has been carried out. In this paper the enviromental factors-hydrographycal and biological-which seem to correlate with the vegetation of Zosterae are reported.

Absorption spectra of acetone-soluble plant pigments were obtained from several sources, including the overlying waters, epibenthic layers and sediments of two New England estuaries, the remains of Zostera marina and its epiphytes, and pure cultures of marine diatoms. Comparisons of the absorption spectra and various absorbance ratios revealed no significant differences in the extracts of pigments sampled from the overlying waters and epibenthic layers; the extracts from both layers differed significantly, however, from the extracts of sedimentary pigments. Unacidified extracts of pigments from healthy diatom cultures and detritus rich in epiphytic diatoms resembled those of the overlying waters and epibenthic layers; acidified extracts from the above two sources and unacidified and acidified extract from non-living detritus resembled those of the sediments. Good correlations between field and laboratory studies are indicated, and the uses of absorbance ratios as ecological indicators are discussed.

1. The plants on the lower and middle beaches of some of the coasts of the Elizabethan Islands and Falmouth are found to have in general definite zonal distribution. 2. The shores may be divided into sea beach and sea cliff types; the latter may be subdivided into cliff types with Zostera marina and those without. 3. The following plants were selected as most representative of the beach type: Ammophila arenaria, Atriplex arenaria, Salsola Kali, Chenopodium rubrum, Arenaria peploides, Cakile edentula, Artemisia Stelleriana, Solidago sempervirens, Euphorbia polygonifolia, Lathyrus maritimus, and Suaeda maritima. Salicornia europaea, Limonium carolinianum, Ligusticum scoticum, Zostera marina, and Spartina glabra pilosa were taken as representatives of the sea cliff type. 4. The upper half of the middle beach is called the transitional zone. 5. When the lower beach is covered most of the time by water, Suaeda maritima, Salicornia europaea, and Limonium carolinianum are found in the order given, from ocean to ...

At the time that this study was begun, mid-summer, 1933, an epidemic, wasting disease had almost entirely destroyed the normally dense beds of the common marine eel-grass, Zostera marina, along the Atlantic coasts of North America and Europe. Since the plant is a prominent member of the shallow water community, sheltering a variety of larval and small sea animals, serving substantially as food for migratory game birds, and checking erosion of the bottom, and because the leaves are used for packing, upholstering, insulating, and other commercial purposes for which they are often peculiarly de sirable, the disappearance of the eel-grass became a problem of prac tical concern. It was recognized, too, that the extensive and persistent wasting of Zostera might indicatephytopathological relationshipsin the sea as significant as the more evident conditions in land vegetation. A further impetus was given this investigation by the popularization of a number of physical and chemical hypotheses for the depletion, of restricted application, and usually of a prejudicial nature. In France,Holland,Denmark, and Canada investigations were already in progress (6), (7), (11), (13), (18). The history of the disease here and abroad, the current condition of the eel-grass beds, and the economic and ecological implications of the wasting have been developed by a number of observers, and comprehensive summaries have been published from time to time by the U. S. Bureau of Bio logical Survey and others (1), (3), (6), (7), (10), (14). This paper is an account of investigations upon the pathology of the diseased eel-grass and upon the specific parasitic nature of an unidentified Labyrinthula, an amoeba-like organism with mycetozoan affinities, found in the leaves of the plant over the entire range @f the epidemic condition. They were begun in the attempt to extend the findings of Messrs. Fischer-Piette, Heim, and Lami of France

Ophiobolus halimus Diehl and Mounce n. sp. is reported on Zostera marina L. from St. Andrews, N.B. It was collected on rhizomes and fertile shoots, and developed in leaves kept in sea water in the laboratory. The fungus is described and illustrated and it is compared with related species.

THE AMERICAN BRANT (Branta bernicla hrota), an important game species on the Eastern Seaboard, suffered great declines in the 1930's. For some time, the brant population has been known to fluctuate considerably from year to year. Presumably arctic storms on the nesting grounds cause declines in some years. Its numbers also have been reduced by encroachment of civilization, increased commercial navigation, oil pollution, over-shooting, and especially by the disappearance of eelgrass (Zostera marina), the bird's staple winter food. Cottam, Lynch, and Nelson (1944) reported that the American Brant population dropped in 1933-1934 to 10 percent of the 19301931 figure as a result of eelgrass destruction. In the Boas River area of Southampton Island, NWT, in the summer of 1953, there existed approximately 700 nesting pairs of brant and 400 yearlings. This indicates a tremendous increase in the last two decades. Manning (1942) reported only two nests in 1934, and Bray (1943) saw eleven in 1936. This increase may have taken place at the expense of another colony, but perhaps comparative studies of other brant colonies in the Eastern Arctic will show a widespread increase in numbers. I was able to study the 1953 brant colony on Southampton Island while accompanying F. Graham Cooch of Cornell University (now of Canadian Wildlife Service), who was studying Blue and Lesser Snow geese (Anser caerulescens). I wish to acknowledge the kindness of the Air Transport Service, RCAF, and the Department of Transport, Canada, for making the air trip possible. The western coast of Southampton Island, facing on the Bay of God's Mercy, is a low, level tidal-plain tundra. The brant colony was centered in the mass of islands in the two-mile-wide delta of the Boas River and thinned out to the east and west for four and one-half miles. This brant concentration was entirely separate from the Blue and Snow geese which nested at least one-fourth mile inland from the high tide line. The area corresponded almost exactly to the brant nesting area described by Bray (1943). The islands, averaging about one foot above high tide, were as small as six feet across and as large as two acres. They were covered with very short thick grass, sphagnum, or limestone gravel. Some were strewn with kelp washed in by fall storms. Weather here was marked by strong and unrelenting winds and

Enchytraeus albidus was fed with Fucus, green algae, Zostera marina and Delesseria. Judging from absorption of food, rate of reproduction and duration of life, the animals preferred the plants in the sequence given above.As the putrefaction of a Fucus substrate advances, more and more enchytraeids leave it. A changing salinity of the substrate also influences the number of emigrating worms, increasing it from 15-45‰, but decreasing it towards 60‰. Fed with Fucus E. albidus tolerates a salinity of 60-70‰ on sand for more than 4 weeks, on filter paper only 50‰ for about one week.Reproduction is possible at salinities up to 40‰. Cocoon production is most frequent at 5‰. The mortality of young worms within the cocoons is lowest at 15‰. The incubation period is significantly shorter at salinities of 0-15‰ than at 30 and 40‰.As a terrestrial immigrant to the seashore Enchytraeus albidus secondarily enlarged its range of poikilosmosis, tolerating a concentration of 72‰ in its coelomic fluid for some time. At low salinities it maintains a remarkable degree of hyperosmosis.

Zostera marina L. was studied at the Izembek Lagoon, Alaska Peninsula. Two morphologically different forms, tidepool and subtidal, can be distinguished. Both show a high tolerance to different salinities and temperatures. The plasmatic resistance was found in a range of distilled H2O up to 3.0 seawater (24 h) and between-6° and 34°C (12 h). Within these resistance limits, the photosynthesis, which has its maximum in normal (1.0) seawater, decreases nearly to zero not only in distilled H2O but even in 2.0 seawater, and increases with the temperature in the tidepool form up to 35°C, but in the subtidal form up to 30°C only. At higher temperatures photosynthesis declines sharply in both forms. Respiration has its minimum in distilled H2O and at 0°C and increases with increasing salinity and temperature.

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x103 kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m2 fresh weight, 0.30 kg/m2 dry weight, 91 g/m2 carbon or 912 kcal/m2. Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.

The marine nematode Rhabditis marina Bastian has been isolated in gnotobiotic culture from collections of Zostera marina made in North Sea Harbor, Southampton, New York. A strain of R. marina has been maintained with three species of bacteria (Pseudomonas sp., Flavobacterium marinum, and Micrococcus sp.) for over 120 generations. A monoxenic strain with Pseudomonas sp. has been maintained for over 25 generations. The life cycle is completed in 5 days under “normal” laboratory growth conditions. Reproduction occurs over a wide (0–80‰) salinity range (the highest salinity tested) and a wide (10–38C) temperature range; optimum growth occurs at 45–55‰ and 25–30C. Normal development is oviparous, but ovoviviparous development is seen in older females. Tracer feeding and synxenic culture experiments have shown that R. marina has rather specific nutritional requirements, which seem to be completely satisfied by a relatively restricted group of microorganisms. Selected species of bacteria comprise the normal diet of this organism. Microscopic observations of intact algae in the digestive tract of the worms and failure of 32P to transfer to the worms from the ingested algae indicate that the worms are not able to digest all ingested potential food organisms. The geographical distribution of the species in relation to its physiological ecology is discussed.

The isopod Idotea resecata (Stimpson) occurs on brown kelp Macrocystis and eelgrass Zostera marina (L.) in bay localities along the Californian coast. It is present in two color varieties, brown and green, which match the colors of its two plant substrata. The overt color of the isopod is a result of the deposition of carotenoids and carotenoproteins in the cuticle. Ten carotenoid pigments were isolated from whole animals. These were: α-carotene, β-carotene, echinenone, monohydroxy-β-carotene, canthaxanthin, 4-hydroxy-4′-keto-β-carotene, lutein, zeaxanthin, flavoxanthin, and violaxanthin. A green carotenoprotein similar to that isolated from other littoral idoteid isopods was also obtained. 14C-labelling was utilized to study the oxidation series from β-carotene to canthaxanthin and the results are related to recent studies on the metabolic pathways for the production of canthaxanthin and astaxanthin from dietary β-carotene in invertebrates. The pigmentation and ecology of this isopod is discussed relative to recent studies on the pigmentation, color change, and ecology of a series of closely related littoral and pelagic idoteid isopods.

A comparison of photographs taken on the eastern shore of Salcombe harbour before and after the disappearance of much of the Zostera marina L. shows that where previously there existed extensive sand banks, stabilized by the growth of this plant, there has been a lowering of ground level of 2 ft. or more, due to the washing away of the sand where the Zostera has died. Much of the ground is more stony than before and has become largely covered with seaweed attached to the stones. The buried fauna is not as rich as it was and some species previously common are rare or have disappeared altogether. A few small patches of Zostera still survive, but the plants are shorter with narrower leaves than before.

Of eelgrass populations sampled from southeast Alaska to Bering Strait, those in Kinzarof and Izembek lagoons on the Alaska Peninsula had the highest standing stocks (mean, 1510 g dry wt/m2) and that in Calder Bay in southeast Alaska had the lowest (65 g dry wt/m2). Caloric content of eelgrass averaged 4211 cal/g in the leaves and 3571 cal/g in the roots and rhizomes. The concentration of chlorophyll a in eelgrass had a mean of 0.513 mg/g fresh wt, with one exception. Population densities were high in Kinzarof and Izembek lagoons (mean, 4576 turions/m2) and low in all other sample areas (599 turions/m2). Flowering plants were 3–4% of the total population. Mean leaf length varied from 13 to 48 cm and width from 2.4 to 5.1 mm. The differences in the eelgrass populations appeared to be related to local conditions rather than a large geographical gradient.

SUMMARY The diatom Cocconeis scutellum (Meunier) colonizes the surface of young plants emerging from the mud in the spring and the usually emersed plant tips as they are knocked over and become immersed in the fall to form a virtually unialgal mat. Broken frustules and detritus adhere to form a crust which then becomes colonized nonselectively by a variety of microorganisms. Removal of the crust shows that the original “cobblestone” surface of the eelgrass is obscured with a layer of deformed cells of C. scutellum which appears to be impressed into the epithelium.

During the summers of 1966 and 1967, 12 field trips were made to stations in North Sea Harbor, Southampton, Long Island (USA). From representative locations, 228 small samples of larger algae and their epiphytes (∼0.2 g dry weight) were taken aseptically. Enteromorpha intestinalis, the most widely distributed aquatic plant, was the most frequently collected. The large standing crop of Zostera marina and Zanichellia palustris was also sampled. Foraminifera were most abundant in epiphytic communities of Enteromorpha in early summer and later spread to Zostera, Zanichellia, Ulva, Polysiphonia, and Ceramium. Foraminifera were rarely found in epiphytic communities of Fucus or Codium. By summers' end Enteromorpha rarely had a standing crop of foraminifera. One of the most abundant foraminiferan species, Protelphidium tisburyensis, was found most frequently on Enteromorpha; Quinqueloculina spp occurring on Enteromorpha, less frequently. Ammonia beccarri and Elphidium spp were abundant in the environment, and showed little substrate preference. Patches of decaying Enteromorpha had the greatest standing crop of foraminifera and low species diversity index (0.581). Young green patches had a much higher species diversity index (0.94). Indices for Zostera, Zanichellia, Polysiphonia, Fucus, Ulva and Codium were, respectively, 0.82, 0.99, 0.86, 0.70, 0.77, and 0.196. No correlation was found between epiphytic community weight and total number of foraminifera recovered. The standing crop of epiphytes/g substrate dry weight was lower at some field stations; possibly explained by stronger current. Of the total samples, 50.4% were positive, with an average of 18 foraminifera/sample, or 40 foraminifera/g substrate plant and epiphytes. Twenty six samples were classified as bloom with 50 or more forams (57 to 425)/sample. Species diversity indices for these blooms ranged from 0.38 to 1.12. Ammonia beccarii was the dominant form in 18 blooms, Allogromia laticollaris and Protelphidium tisburyensis in 3; Elphidium incertum, Quinqueloculina seminulum and Trochammina inflata in 1 each.

Measurement of community metabolism in a coastal pond eelgrass bed gave values of 2.9 g O2 m—2 day —1 for apparent production and 3.6 g O2 m—2 day—1 for night respiration. The excess of consumption over production during a full day in early August is indicative of the declining state of the plants by midsummer. Measurements of upstream—downstream dissolved oxygen in a tidal river eelgrass bed showed unusual transients and occasional high values for production and respiration. These observations may have been related to turbulent tidal transport, to exchanges of oxygen between the water and lacunar spaces within the Zostera, and to higher metabolic rates in faster currents. See full-text article at JSTOR

The absorption of phosphate by eelgrass (Zostera marina L.) was studied using 32P in a partitioned container where leaves were separated from roots and rhizomes. Absorption, which was greatest in the light, occurred through both leaves and roots, and the absorbed phosphorus was transported rapidly to all parts of the plant. It therefore appears that eelgrass can use phosphate from sediments and from water. Phosphate removed from solution by the roots and rhizomes was returned in part to the surrounding water through the leaves, suggesting that in nature seagrass may act either as a sink or as a source for dissolved phosphorus in estuarine waters.

SUMMARY The supposedly obligate epiphyte Smithora naiadum, normally found only on the sea grasses Phyllospadix scouleri and Zostera marina, grew on an artificial substrate under field conditions. This development shows that the alga does not appear to require a chemical factor from its normal host plant for (1) substrate selection and adhesion, (2) growth of basal cushion and young blades, or (3) maturation of thick cushions.

The study was concerned with the horizontal and vertical distributional patterns and the possible summer periodicity of diatoms epiphytic on eelgrass, Zostera marina L., in the vicinity of Gloucester Point, Virginia. Samples were collected in August 1963 and June and July 1964. Horizontal and vertical distributional patterns were demonstrated with respect to the change of total numbers of organisms present. The distributional pattern was, however, more pronounced in the vertical direction. The vertical comparisons generally indicated more pronounced growth of epiphytic diatoms at the blade tip than blade base. Horizontal comparisons generally show more growth in deep than shallow water, but there are exceptions. Two trends were present which suggested periodicity and a shift in generic dominance. Cocconeia and Navicula appeared to reach peak densities on or shortly before June, Whereas, Dimerogramma, Epithemia, and Nitzochia appeared to have reached a peak considerably before the June sampling date. The former two organisms maintained relatively high densities throughout the sampling period, whereas, the latter three did not reach a comparable average density until August. Of the eighteen genera identified, four were chosen for detailed graphical illustration in 1963 and 1964 because of their predominance throughout the sampling period. Cocconeis, Dimerogramma, Epithemia 2 and Navicula were predominant genera in 1963; Epithemia was replaced in abundance by Nitzschia in 1964. Master of Science

Monhystera denticulata Timm, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Zostera marina and established in laboratory culture in order to study the influences of temperature and salinity on its life history. Under experimental conditions, M. denticulata has a generation time (Measured as the time elapsing between the first egg depositions of consecutive generations) of 10-12 days at 25° C and 26‰ S, which represent optimal growth conditions in the laboratory. The organism has a generation time of 20 days at 25° C and 13‰, 17 days at 25° C and 39‰, 18 days at 15° C and 26‰, 36 days at 15° C and 13‰ and 34 days at 15° C and 39‰. As conditions vary from the optimum of 25° C and 26‰ S, a decrease in temperature of 10° C and an increase or decrease in salinity of 13‰ results in a doubling of the generation time. At 5° C the generation time is about 180-197 days.Assuming optimum conditions and average generation time, about 15 generations of M. denticulata could occur in North Sea Harbor during the year. The number of generations occurring in reality is probably less, however, due to the fact that the females deposit their eggs over a period of several days.

THE leaves of seagrasses often harbour dense populations of macroscopic and microscopic algal epiphytes. In many cases seagrasses grow in waters that are extremely low in dissolved inorganic nutrients yet they have high epiphyte standing stocks. These field observations led to direct experiments on the transfer of nitrogen and carbon from the dissolved nutrient pool in the interstitial waters of the sediments into the root system of eelgrass, Zostera marina, and through the plant to the algae on its leaves. Previous studies1,2 on seagrasses have shown that the high productivity of seagrass meadows is largely maintained by the nutrient pool of the sediments. Since the plant system leaks phosphorus and, presumably, other nutrients, it is possible that the production of the leaf epiphytes is indirectly sustained by the nutrients in the sediments. This mechanism has been suggested by several workers for marine and freshwater macrophytes3–7 but definitive experiments are lacking. Here we report the results of experiments designed to test this hypothesis.

Discovery of Its Nutritional Value by the Seri Indians Zostera marina occurs in the northern Gulf of California. The grain of eelgrass is harvested in the spring and formed an important part of traditional Seri diet and culture. This is the only known case of a grain from the sea being used as a human food source. Eelgrass has considerable potential as a general food resource for mankind. Its cultivation would not require fresh water, pesticides, or artificial fertilizer.

IN NATURE of December 30, 1933, a letter appeared on the disease of the eelgrass (Zostera marina) in Danish waters based on investigations which I made in the summer of 1933. I am now able to give further details concerning this disease. The destruction of the leaves was continued during the winter, but young shoots formed in the early spring were generally without infection. Infection of the leaves reappears at the beginning of the summer.

EELGRASS (Zostera marina L.), a marine angiosperm which grows on the Pacific coast of North America from the Gulf of California to the Chukchi Sea1, has been found living under the winter sea ice in Safety Lagoon, an embayment of the Bering Sea near Nome, Alaska. A submarine television system revealed the plants to be in good vegetative condition in the 20 to 30 cm of water between the sediment and the undersurface of the ice (Figs. 1 and 2). The odour of hydrogen sulphide and subsequent tests with an oxygen probe showed this water to be anoxic.

IN a previous note in NATURE1 we pointed out the association of a Labyrinthula-like organism with the wasting disease of the eelgrass along the American Atlantic coast. Since the publication of this announcement, we have performed a number of experiments in the laboratory and in the natural beds themselves, which indicate that this organism is a true parasite of Zostera marina. Communications from other investigators and examinations of specimens submitted from various points show also that this parasite is uniformly present in the infected beds on the Atlantic coasts of both Europe and America.

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.

The interrelations of living things are likely to remain for a long time the least understood of ecological problems. Their study often defies efforts at exactness or completeness, and "laboratory methods" are usually helpless. Yet these complex relations are far reaching and often of decisive importance. Darwin's famous and frequently quoted example of the effect of cats on the clover crop would seem to show that chains of cause and effect have rarely been recorded, and also that their importance is recognized. A series of interrelations of this kind-from man to herons-recently came under my observation. The upper part of Belfast Lough in the North of Ireland is occupied by " the banks," an area of perhaps ten square miles, bare at low water but covered at high tide. This ground used to be very soft with shallow pools and anastomosing streams spreading over the dark oozy ground. At low water it was the feeding place of many birds. Curlews, sandpipers, redshanks, gulls, rooks and others were common; but by far the most conspicuous were the big herons (A4rdea cinerea-closely allied to our A. herodias). These herons were always to be seen in some numbers, often very close to the railroad trains that passed their feeding grounds and to which they had become accustomed. Such was the condition thirty years ago. Within recent years I have several times revisited this ground. Many birds are still there, some in undiminished numbers, but the herons are practically absent. On inquiry the following explanation was given to me and is borne out by my own observations. The only channel through the banks to the port of Belfast used to be through the shallow and meandering river Lagan. The city cut a straight and deep channel, about six miles long, from the port to deep water. Following this, in the course of a few years, the soft mud of the banks was replaced or covered by a firm sand, presumably due to a more direct tidal flow. As a consequence, great stretches of eelgrass (Zostera marina) disappeared, and with it the sand-eels and small fish which found shelter in it. The herons, thus deprived of their food, forsook their old haunts for the neighboring bays and loughs. Thus the chain runs from man through the cutting of the channel, the extensive edaphic change, the eel-grass, the sand-eels to the herons.

IN Dr. Kathleen B. Blackburn's letter on this subject1, the conclusion seems well established, through a study of the chromosomes, that the narrow-leaved form of the eelgrass (grass wrack), which has in many of the diseased areas replaced the larger and broader type of plant, is clearly a form of Z. marina and not a hybrid of Z. marina and Z. nana, as some have believed. Miss Blackburn therefore suggests that the difference in the width of the leaves of varieties of Z. marina may be a purely ecological character. She further remarks that, in the localities examined, the width of the leaf of Z. marina was directly proportional to the depth of the water, and that the very narrow-leaved forms Were those that had been longest exposed by the fall of the tide, while the broader were those that had not been exposed at all.

The invertebrate epifauna occurring onZostera marina L. in the lower York River, Virginia, was sampled with the aid of SCUBA for 14 consecutive months. A collecting station was located at each of three different water depths within a single eelgrass bed. A total of 112 invertebrate species was collected. The five most abundant non-colonial species (Bittium varium, Paracerceis caudata, Crepidula convexa, Ampithoe longimana andErichsonella attenuata) accounted for approximately 59% of the total fauna. These species dominated the epifauna throughout most of the year. Several other species, includingBalanus improvisus, Molgula manhattensis, Polydora ligni and Ercolania fuscata, were abundant for only brief periods. A relatively high average index of affinity (58%) between all synchronous sample pairs indicated a generally homogeneous fauna, although several species were differentially distributed with depth. Exfoliation ofZostera after June caused a steady decline in plant biomass, but the abundance of epifauna continued to increase into the summer and fall. Lowest total numbers and species counts occurred in February and early March. Diversity values (H′) ranged from 1.92 to 3.90 bits/individual and averaged 3.04 bits/individual for all stations. High species numbers in summer were generally counteracted by relatively low equitabilities (e), with H′ showing little seasonal change. The primary sources of nutrition for the epifauna appeared to be 1) plankton and suspended particulate matter, 2) detritus and microorganisms on the plant blades, and 3) epiphytic algae.