The structure of the aquatic insect community associated with intertidal pools on a New Jersey salt marsh

Abstract. 1. Landlocked intertidal pools (potholes) are one of the common aquatic habitats associated with eastern North American salt marshes.
2. Twenty species of insects, of which only eight were common, occurred in the pothole habitat. The harshness of the physical environment incurred in the pothole habitat is largely responsible for this depauperate insect community.
3. Spatial variation in the diversity of the insect community is best explained by differential densities of predaceous fish.
4. Seasonal changes in insect community diversity are attributable to fluctuations in water temperature and accompanying levels of dissolved oxygen.     

GROWTH, SURVIVORSHIP, AND POPULATION SIZE IN THE LAND SNAIL RHAGADA CONVICTA COX, 1870 (PULMONATA: CAMAENIDAE) FROM A SEMIARID ENVIRONMENT IN WESTERN AUSTRALIA

Basic characteristics of a population of the camaenid land snailRhagada convicta were studied in a semiarid environment nearNorth West Cape, in Western Australia. Consistent evidence frommark-recapture studies and analysis of size-frequency distributionindicates an average annual increase in shell diameter of 3.6mm, with an average period of 5 years from hatching to reachadult size. These rates are low, compared with most other landsnails studied, including cama-enids from wetter environments.Estimates of mortality rate and the rate of recruitment intothe adult population indicate that the snails live an averageof approximately 5 years after reaching adult size, which meansthat the period of turnover for this population is approximately10 years. The population density was estimated to be 0.8 adultsper m², with a total population size (± s.e.) of 875± 164. The population is very localised, with an estimateddiameter of the neighbourhood area of only 38 m. (Received 28 August 1990; accepted 12 February 1991)     

The Effect of Ultraviolet Radiation on the Germination of Nosema algerae Vávra and Undeen (Microsporida: Nosematidae) Spores1

Spores of Nosema algerae Vávra and Undeen were subjected to various dosages of 254 nm ultraviolet radiation (UV). Very high dosages of UV were required to block germination. Germination was normal immediately after UV dosages of 0.2 to 1.0 J/cm², followed by a delayed effect in which both percentage germination and the intrasporal concentration of trehalose decreased with time after UV exposure. Although a few spores were germinated, most of them were inactivated (rendered temporarily unable to germinate) by exposure to UV of 1.1 J/cm². Ultraviolet radiation between 1.1 and 3.4 J/cm² stimulated spores to germinate. However, spores were completely unable to germinate immediately after exposure to dosages above 3.8 J/cm². Ammonia had little effect on stimulation by UV but was inhibitory to germination after stimulation had occurred. These results demonstrate that UV behaves like a germination stimulus and are discussed in terms of the hypothesis that germination is initiated by the breakdown of barriers between trehalose and trehalase.     

Perianth Abscission in Montbretia (Crocosmia x crocosmiiflora)

The anatomy, histochemistry, kinetics and hormonal regulationof perianth abscission in Crocosmia x crocosmiiflora (Montbretia)has been investigated. The abscission zone is anatomically welldefined, with cell divisions occurring in this region at anthesis.Abscission is first detectable 3 d after perianth opening, whenthe walls of a group of cells beneath the adaxial epidermisshow reduced staining with polyanion-specific stains, and adecline in penanth break strength also occurs. Abscission isachieved by cell wall breakage in thc abscission zone, whichprogresses eccentrically from the adaxial epidermis throughthe abscission zone, rather than the separation of intact cellsas occurs in flowers of dicotyledons. Experiments on detachedflowers suggest similarities in the hormonal regulation of abscissionin Crocosmia to that of dicotyledons, in that an ethylene promotion,and possibly an auxin inhibition, mechanism may exist in Crocosmia.Ovary expansion occurs throughout the development and senescenceof unpollinated flowers, but does not appear to be the solecause of wall breakage in the abscission zone. It is suggestedthat hormonally regulated wall hydrolases weaken the cell wallsin the abscission zone, and allow wall breakage and subsequentabscission to occur. Cdrocosmia x crocosmiiflora, Montbretia, anatomy, breakstrength, cell wall changes, histochemistry, flowers, monocotyledons, perianth, senescence, ethylene, auxin