The distribution and abundance of barnacles in a mangrove forest

Abstract The grey mangrove tree, Avicennia marina, forms a hard substratum in an area otherwise dominated by soft-sediment. Various intertidal organisms attach to and move about on the trees. The abundant barnacles Elminius covenus, Hexaminius popeiana and Hexaminius foliorum live on a variety of substrata in mangrove forests. Their patterns of distribution and abundance were recorded and models proposed to explain these patterns. Densities of barnacles on bark, leaves and twigs of A. marina were estimated in a locality near Sydney. Elminius covenus were more abundant on bark than on leaves or twigs of A. marina. Hexaminius popeiana, although less abundant on bark than E. covenus, were not found on twigs or leaves. In contrast, H. foliorum were more abundant on twigs than leaves and were not found on the bark of A. marina. Densities of barnacles were greater in the seaward than in landward parts of the forest. Elminius covenus were the most abundant barnacles, H. foliorum were less abundant and H. popeiana were virtually absent in the landward zone. Barnacles in the seaward zone were most abundant at mid-tidal levels, less at high and low tidal levels of trunks and more abundant on lower than upper surfaces of trunks and leaves. The densities of barnacles differed according to the orientation of the bark or leaf. Models are proposed to explain the patterns of distribution and abundance of these barnacles. Each involves larval supply, settlement and post-settlement mortality. It is concluded that similar processes determining patterns of distribution and abundance for sessile organisms living on rock platforms may be applicable to sessile organisms living in the very different habitats of mangrove forests.     

Morphology and Life History of Colpoda maupasi, Bensonhurst Strain

Strains of Colpoda maupasi previously reported were found to produce only octogenic reproductive cysts and monogenic wrinkled resting cysts. The present form of C. maupasi (Bensonhurst strain), isolated by the senior author in 1949, was found to produce, in addition to the above, quadrigenic reproductive cysts, digenic corrugated (wrinkled) resting cysts, and smooth thick-walled monogenic, digenic and quadrigenic resting cysts. Some of the factors leading to the development of these cysts in the Bensonhurst strain are believed to be related to nutrition, age and size of the trophic forms. The cytological changes in encystment and excystment were followed with particular attention to aging monogenic resting cysts. The latter were observed for over 4 years.     

The savanna ecology of Kidepo Valley National Park: The effects of burning and browsing on the vegetation

Between 1947 and 1967 tree frequency was reduced by 30% in the Narus valley, Kidepo Valley National Park. Between 1967 and 1972 a further 50% reduction took place on experimental plots. Elephants were largely responsible. Despite a regeneration potential of c. 200 young trees per ha, very little tree regeneration was observed. Experimental fire treatments and animal–free exclosures revealed that annual burning and the current browsing pressure were independently capable of preventing tree regeneration. Fire effects were significant in the herb composition of the animal exclosures but less so on the grazed areas. This was attributed to trampling of litter on the grazed areas, which assisted termites in litter removal. Untrampled litter accumulation suppressed Themeda triandra to the benefit of Panicum maximum. Fire effects on the soil were small and impermanent.     

Oysters as habitat for limpets in a temperate mangrove forest

In temperate mangrove forests in New South Wales, Australia, the limpet Patelloida mimula Iredale lives on the oyster Saccostrea commercialis Iredale and Roughley, which, along with mangrove trees, provide the only hard substrata in a habitat otherwise dominated by soft-sediment. The objective of this study was to ascertain the degree of association between the limpet and the oyster by examining their patterns of co-occurrence in the forest and the relationship between individual pairs of limpets and oysters. Sampling of the distribution and abundance of limpets and oysters throughout the mangrove forest revealed that limpets were rarely present on substrata other than oysters. Patterns of abundance of limpets were, however, not directly related to the amount of habitat provided by the oysters. For example, there was a dramatic decline in the abundance of oysters from seaward to landward in the mangrove forest which was not reflected in the densities of limpets. Consequently, oysters appear to set the limits of distribution of limpets, but other factors modify their broad-scale patterns of distribution and abundance within these bounds. Limpets leave scars on oysters which might be home sites. About 98% of oysters with limpets had only one limpet per surface of oyster, and the distribution of limpets was overdispersed or repulsed. Moreover, in some areas of the forest, the lengths of limpets were directly related to lengths of oysters. Tracking of individual limpets for 13 days revealed that > 70% remained on the same scar of an oyster. This evidence suggests that for some limpets there is a strong association with particular oysters. Factors determining the distribution, abundance, and sizes of oysters are likely to be important sources of variation to the structure of populations of P. mimula in temperate mangrove forests.     

THE EFFECTS OF MECHANICAL DISTURBANCES ON THE BEHAVIOUR OF INACTIVE TERRESTRIAL SNAILS

Based on comparison to controls, inactive Otala lactea (Mull.)respond to mechanical disturbances such as shaking, percussion,transmitted vibrations, and rotation. Responses in a 15-minperiod include motion of large portions of the mantle, openingof the pneumostome and protrusion of the posterior part of thefoot through the mantle collar. Responses reflect preliminarystages of arousal. It is suggested that an incomplete arousalto a potentially valuable, but environmentally ambiguous stimulus,may be of adaptive value. (Received 30 January 1978;