Colony development and formation in halysitid corals

Lee, D.-J. & Noble, J. P. A. 1990 04 15: Colony development and formation in halysitid corals. Lethaia , Vol. 23. pp. 179–193. Oslo. ISSN 0024–1164.
Modes of colony formation and their relationship with colony morphology, size and substrate characteristics in species of halysitid corals have been studied. Two distinctive modes of colony formation in halysitids are proposed. In the monoplanulate mode. represented by Catenipora snnplex . the colony is developed from a single protocorallite and colony formation is achieved by a combination of asexual increase and intracolony fusions. In contrast, the polyplanulatc mode is demonstrated by C. escharoides . in which the early colony formation is achieved primarily by fusions of many 'incipicnt colonies' of more than a single planulate origin and of different generations. The latter mode has not previously been described in tabulates and has significant implications for coloniality, reproductive and life history characteristics, histo-compatibility and adaptative ecology. The colony size and morphology. and The distribution of halysitid species were primarily determined by the modes of colony formation and the substrate characteristics. Colonies of the monoplanulate mode. when developed on soft substrates, exhibit a small and spherical morphology with isolated distribution patterns, while those developed on hard substrates are tabular and variable in size. depending on the availability of substrate. In colonies of the polyplanulate mode, on the other hand. the size of the colony is largely dependent on The frequency and timing of allograft fusion. They are characteristically found on soft substrates. often as dense mono specific thickets. The mode of colony formation in halysitids is probably species-specific and results in the adaptation to substrates. * Colony development, halysitid corals, Anticosti Island. Gotland .     

Interactions between seedlings of Chrysanthemoides monilifera and Acacia longifolia

Displacement of Acacia longifolia on coastal dunes in New South Wales by the invasive species Chrysanthemoides monilifera may be linked to the greater competitiveness by the latter in the seedling stage, as demonstrated in pot experiments. This occurs despite a lower chlorophyll concentration in shoots of C. monilifera which leads to a lower assimilation rate per unit leaf area and lower carbohydrate concentrations. However, this assimilate is spread over a greater total leaf area. Such a strategy associated with‘quantity’may thus be more important than leaf‘quality’in terms of competitiveness. In A. longifolia, the production of higher quality‘leaves’but of lower total area may be well-suited in the often sparse native populations found in sand dunes, but appears disadvantageous when seedlings of C. monilifera also co-exist. The competitive advantage of C. monilifera over A. longifolia is reduced but not reversed under water stress. Under severe stress, mortality of C. monilifera is greater than that of A. longifolia in monocultures but mortality of both species is similar in mixtures. The reason appears to be that C. monilifera transpires more water per plant even though its rate of transpiration per unit leaf area is reduced under water stress because of early stomatal closure. In mixtures, faster root growth of C. monilifera ensures faster uptake of the available soil water, thus minimizing the inherent advantage in A. longifolia of its lower water use and greater efficiency.     

The biology and autecology of Nitraria L. in Australia. I. Distribution,morphology and potential utilization

Nitraria billardieri occurs in all mainland states of Australia and on several adjacent islands south of the Tropic of Capricorn between Lat. 25° and 38°S and Long. 113° and 147°E. Other species of Nitraria are found in North Africa, the Middle East and Eurasia. The probability that Nitraria is a very old genus, having its origins in central Asia, is discussed. The wide disjunction between N. billardieri in Australia and the closely related N. schoberi in eastern Europe and Asia is difficult to explain. Observations on various populations grown under nursery conditions at Deniliquin, combined with those undertaken during field traverses across Australia, clearly indicate that considerable inter-population variability occurs. Whether these different forms are ecotypes in which particular characters have become genetically fixed in specific habitats, is uncertain; but the form growing along the Indian Ocean coast of Western Australia shows marked contrasts to the other forms and may ultimately be described as a distinct species. Possible uses for N. billardieri in arid and semi-arid zones of Australia are discussed. Particular reference is made to the abundance of N. billardieri in low shrubland communities which were dominated by chenopods prior to the introduction of domestic livestock. The marked increase in N. billardieri on overgrazed saltbush (Atriplex vesicaria) communities of the Riverine Plain suggests that it may serve as an indicator species in range condition assessment of these communities.     

The biology and autecology of Nitraria L. in Australia. II. Seed germination,seedling establishment and response to salinity

Detailed investigations were undertaken to determine the requirements for optimal germination and establishment of Nitraria billardieri. Germination of N. billardieri on the Riverine Plain is aided considerably by prior ingestion of the fruit by the emu (Dromaius novaehollandiae). Experiments suggested that the increase in germination of emu-ingested seed is largely a response to the removal of the saline outer pericarp during digestion. In one experiment, 62% of emu-ingested seed germinated after 24 days compared with 6% of the hand-picked seed. Studies of field populations of N. billardieri seedlings indicated that they are susceptible to competition from cool season annual species. A competition experiment in sand boxes between seedlings of N. billardieri and Atriplex vesicaria showed N. billardieri to have a slower growth rate and to be susceptible to competition by the seedlings of the perennial A. vesicaria. Studies of the root extension of N. billardieri and Atriplex nummularia in root observation boxes demonstrated the poor performance by the Nitraria roots which grew only 53 cm in 7 weeks whereas the Atriplex roots grew 160 cm in 4 weeks. These data suggest that N. billardieri establishes and successfully competes in the field only with severely weakened saltbush stands. Other important factors are the availability of 'safe sites’ and the degree of competition from annual species. Glasshouse experiments using sand culture indicated that both Nitraria and Atriplex vesicaria could survive in salinities of 0.9 M NaCl and both responded in terms of dry matter production to low salt inputs (e.g. 0.3M NaCl) although growth of Nitraria decreased more rapidly as salinity increased.     

The Recent Terebratulina Community in the rocky subtidal zone of the Bay of Fundy, Canada

A distinctive rocky subtidal benthic community (the Terebratulina Community) is described from the Bay of Fundy, Canada. It is shown to consist of three closely intcrspersed sub-communities: a cavity sub-community, characterised by chitons, coelenterates, brachiopods, bryozoans, chordates and annelids; a rock-face subcommunity, similar in composition but enriched in brachiopods and sponges; and an upper-surface subcommunity, dominated by algae, chitons, bivalves and echinoids.
Comparison with recently described Jurassic, Cretaceous and Recent (Mediterranean) hard-ground communities suggests a relative constancy in composition, in terms of higher taxa, since the Mesozoic. Development of these (sub-)communities occurs wherever crevice or cavity systems on hard substrates lead to microenvironments differentiated mainly on the basis of water energy and light.
The composition and trophic structure of the community and the life habits of Terebratulina septentrionalis (Couthouy) are related to aspects of the environment. Marked differences in composition between the living cavity sub-community and the death assemblage in the sediments are shown to be due to differential preservation, fragmentation, population dynamics and limited local transportation.