Marsh Types Research Articles

Schorre morphology on the south shore of theSaint Lawrence Estuary

The salt marshes are characteristic of a cold-temperature region. Ice is an important morpho-sedimentological agent. A large quantity of boulders and coarse sediments are brought by drift ice which also digs and ploughs the surface of the schorre during winter and spring. Four types of salt marshes are common: The first is characterized by numerous shallow subcircular or irregular shaped pans, the second by an abundance of erratics, mostly crystalline boulders, the third by a rocky platform overlaid by a thin veneer of mud, and the fourth is a muddy schorre similar to common marshes of the Atlantic coast of southeastern Canada. The first three have never been described as such in coastal literature. Schorre is a Dutch word that refers to that part of a salt marsh covered by high tides.

STRUCTURE AND ENERGY FLOW OF A MUSSEL POPULATION IN A GEORGIA SALT MARSH1

Modiolus demissus Dillwyn was studied near Sapelo Island, Georgia. The size distribution of the mussels was bimodal with maximum numbers in the dry weight (body) classes 0–24 mg and 400–599 mg. The total weight of mussels smaller than 200 mg was less than 2% of the total population weight. Random samples gave an estimated population density of 7.8/m2 for the entire inhabited marsh; the estimated organic biomass was 11.5 gm/m2, one third of which was body and two thirds was shell conchiolin. The population was most dense near the heads of small creeks, averaging 32 mussels/m2. The mussels, however, were not only more abundant in some types of marsh than in others, they were also clumped within areas of uniform marsh. Shell growth occurred throughout the year, especially in small and medium‐sized individuals, but it was more rapid during the warm months. The height‐to‐weight ratio changed with the seasons, the mussels being heaviest prior to spawning. Growth and mortality of mussels in flower pots in the marsh indicated a net annual population growth of 445 mg/m2 (dry body weight) and a net annual mortality loss of 1200 mg/m2. Allowance for bias would place the steady state growth‐mortality rate necessary to just maintain the population somewhere between these two estimates. Population growth and gamete production accounted for an energy flux of about 13.9 and 2.8 kg‐cal/m2/yr, respectively. Respiration by the population accounted for approximately 39 kg‐cal/m2/yr, over two thirds of which took place in air during ebb tide. Total assimilation amounted to 56 kg‐cal/m2/yr.

Distribution of Fiddler Crabs in Georgia Salt Marshes

The study of the distribution of animals in nature is especially interesting when several species of one genus occupy the same general area. Along the east coast of the United States there are three species of fiddler crabs of the genus Uca which live in the salt marshes. All three are found in the marshes surrounding Sapelo Island, Georgia, and this paper deals with experiments concerning their distribution in these marshes. I deal with the problem of why the crabs live in certain habitats within their range and not in others, not what determines or has determined their geographical range. The three species of crabs are: Uca mtinax, the largest, generally associated with brackish water; CUca ptigilator, commonly known as the sand fiddler crab, and Uca. pitgnax, found generally throughout the salt marsh. Components of the environment which might be important in determining the distribution of these animals are substratum, food, salinity, exposure or tides, and other animals. The effects of these factors can be evaluated by answering the questions: W~hat is the substratum choice of the animals when other factors are constant? Does the presence of other species of fiddler crabs affect this choice? Can the three species survive in all types of salt marsh or are they restricted to certain types ? What are the salinity and temperature tolerances and salinity preferences of the species ? \Vlhat do the crabs feed on and how is this food distributed in the marsh? Adult animals were used in most of the experiments. It is true that choice of area for settling by the megalops larvae is important in the distribution of the adults; nevertheless, adult fiddler crabs can and do move considerable distances over the marsh and could easily move to an environment different from that chosen by the larvae.

Habits and Economics of the New York Weasel in Michigan

During the autumn, winter and spring of 1939 and 1940, the habits and economics of the New York weasel (Mustela frenata noveboracensis) were studied in Lodi Township, Washtenaw County, near Ann Arbor, Michigan. The area is typical southern Michigan glaciated farm country, with a dispersion of bogs and kettle holes on ground morainal deposits. The cover consisted of interspersed agricultural, woodland, and marsh types in a ratio of about 70, 15 and 15 per cent, respectively.

The Rate of Sedimentation on Salt Marshes on Scolt Head Island, Norfolk

A brief note on this subject was published in the GeologicalMagazine, Vol. LXXII, October, 1935. In September of that year certain more detailed experiments were prepared, whose object was to afford a means of measuring the rate of accretion of tidal silt on different types of marsh in various parts of the island complex. Reference to Text-fig. 1 will show that five lines were prepared. In each case patches of fine and distinctive light brown Lower Greensand were spread over the marsh at measured intervals. Sometimes the patches, each about 2–3 feet in diameter, were put down at regular distances, but, on account of the number of small creeks and salt pans intersected by any straight line across a marsh, it. was usually more convenient to make the intervals between patches irregular. The sand was spread as a fine layer in and on the vegetation, and after it had been covered by one or two big tides, it settled down easily on the true marsh surface under the plant covering. It was then only a matter of time before it was covered by tidal silt. The sand was put down in September, 1935, and the measurements of accretion were made at the end of June, 1937.

Corrosion of water mains

Unvegetated, shallow water habitats adjacent to marshes are an important nursery for juvenile blue crabs, Callinectes sapidus, in Chesapeake Bay. Alteration of the shoreline, either through the replacement of marshes with anthropogenic structures, such as riprap and bulkheads, or through the replacement of the native marsh grass Spartina sp. (Spartina) with the invasive Phragmites australis (Phragmites), may affect the value of this habitat as a nursery. In this study, we compared the effects of four common shoreline types, bulkheads, riprap, Phragmites marshes, and Spartina marshes, on food availability, feeding, growth, and survival of juvenile blue crabs in adjacent subtidal areas, as well as on the abundance and size of predators in the South River, Maryland. Sites with each shoreline type were randomly selected. We used benthic cores to sample macrobenthic prey and performed gut content analysis on caged crabs to examine food availability and feeding. Growth was estimated using caged crabs. Survival was assayed with a tethering experiment and predators were sampled with a seine net. Riprap had a lower abundance of macrofaunal prey, and the macrofaunal community differed from both marsh types in that it had it had smaller an more opportunistic species such as nematodes and small polychaetes compared to more bivalves and larger polychaetes at the marsh sites; however, gut contents and growth did not vary among shoreline types. Predation pressure on juvenile blue crabs was highest at bulkhead sites and lowest at riprap. Predator abundance did not vary among the shoreline types, though piscine predators were smaller in size near Spartina marshes compared to the other shorelines. We conclude that shoreline hardening substantially reduced the value of shoreline habitats for juvenile blue crabs, but that Spartina and Phragmites are functionally equivalent.

Longmans' Wall Pictures Flowers, Butterflies, and Moths Descriptive Notes for Teachers, for use with Longmans' Natural History Wall Pictures Notes on Flowers

THE attractive set of wall pictures published under the above title consist of ten coloured plates, reproduced from water-colour drawings by Mr. A. Thorburn. On each plate, measuring 18 inches by 14 inches—with the cardboard mount, 25 inches by 20 inches—two plants and two butterflies or moths are depicted. The series follows a monthly sequence according to the appearance of the butterflies and the flowering of the plants; one plate is allowed for April and May, and two plates for each month from June to September. So far as the plants are concerned, an ecological basis also exists; thus the April flowers, the primrose and bluebell, are denizens of woodland, the poppy and bluebottle are agrarian, and the purple loosestrife and water-mint are typical marsh plants. The butterflies represented are Fritillaries, Blues, Peacock, Red Admiral, and other common species. The pictures are very effective, as Mr. Thorburn has combined artistic rendering and setting with correct form and colour of the plants; the reproduction, too, is fully satisfactory, so that they form a most decorative series, eminently suitable for display in class or schoolroom.