M.J. de Kluijver

Localization and ecological significance of oroidin and sceptrin in the Caribbean sponge Agelas conifera

The Caribbean sponge Agelas conifera was found to produce a mixture of previously described bromopyrrole alkaloids of which oroidin (1) and sceptrin (2) were predominant. This sponge harboured large populations of heterotrophic bacteria but no photosynthetic symbionts (cyanobacteria). However, 1 and 2 were not associated with the bacteria but with the sponge cells as shown by their distribution in enriched cell fractions obtained by differential centrifugation and Ficoll density gradients. Spherulous cells, found in great abundance in the sponge ectosome, were assumed to be involved in the production of 1 and 2. The target compounds were detected, although in small amounts, in short-term cultures of sponge cells, validating the possibility of a continuous cell culture source. Laboratory assays showed that organic sponge extracts affected the behaviour of the coral Madracis mirabilis in causing closure and retraction of the polyps at concentrations of the combined compounds 1 and 2 (1:3.3) as low as 0.7 mg/l (0.0125% of the concentration in whole sponges). At higher concentrations (1.4 mg/l) no recovery of the polyps occurred. The extracts, at almost natural concentrations of 1 and 2, deterred feeding by the predatory reef fish Stegastis partitus, supporting other reported research. In field experiments, wounding induced a sharp increase of 1 and 2 in the sponge tissues but prolonged predator exclusion by caging and forced confrontation with coral neighbours did not yield measurable changes in 1 and 2 concentrations. All sponges were found to release measurable amounts of bromopyrrole alkaloids in seawater conditioned for 30 min. Crude and fractionated sponge extracts and pure sceptrin (2) were active against bacteria, yeast and filamentous fungi. Taken together, these results support a role of oroidin (1) and sceptrin (2) in defence mechanisms against predators and possibly against space competitors and invading and fouling organisms.

Changes in the sublittoral hard substrate communities in the Oosterschelde estuary (SW Netherlands), caused by changes in the environmental parameters

In order to assess the effects of the execution of the Delta Project, the sessile sublittoral communities on hard substrates in the Oosterschelde estuary and the environmental parameters were quantitatively investigated from 1985 till 1990. During the construction period of the barrier, three communities were sampled in the photic zone and four in the aphotic zone. The distribution of the communities in the photic zone seemed to be determined by the exposition to water movement and depth, while the communities in the aphotic zone were restricted to geographic areas, with differences in tidal current velocities: the mouth of the estuary, the Hammen, the central part and the Zijpe. Two years after the completion of the enclosure works, the community structure changed rapidly, caused by decreases of tidal current velocities, increases of the amounts of sedimentation, especially of fine sediments, and an increase of the transparency of the water. Changes within the associated vagile animals showed the same tendency as the sessile communities: under less exposed conditions the number of organisms remained the same or increased, while at some locations this increase was nullified by increasing amounts of sedimentation.

Verification of fractal growth models of the sponge Haliclona oculata (Porifera) with transplantation experiments

The growth form of the sponge Haliclona oculata is to a significant extent determined by the environmental conditions in which the form emerges. One of the main environmental parameters affecting the growth form is exposure to water movement. In this study, a morphological growth model is used to simulate the effect on the growth process of a change in exposure to water movement. Predictions based on the model are verified by experiments in which sponges from a sheltered growth site are transplanted to an exposed site, and vice versa. The effect of the transplantation on growth forms is determined by morphological comparisons. By combining the morphological simulation model with interpretation of growth forms, it becomes possible to use the growth form of H. oculata for bio-monitoring purposes. This form reflects the environmental conditions governing the growth process.

Sublittoral hard substrate communities off Helgoland

In the Helgoland region eight sublittoral hard substrate communities occur. These communities were stationary in time during the years 1987–1989. The major governing parameters are the available amount of daylight and the degree of exposure to water movement. In the photic zone, three communities are met with, one of which is widespread and appears to be independent of the exposure to water movement. Under exposed conditions, at the lower border of the photic zone, a second community is observed. A third community is established on erosive muschelkalk substrates. In the aphotic zone also, three communities are found. The distribution of these communities is related to the rate of water movement. One community is divided into three variants, with different preferences regarding the angle of inclination and nature of the substrates. In the artificially constructed harbours, where sedimentation exceeds erosion, two different communities have settled. In the community under moderately sheltered conditions many species are found which also occur in the natural photic zone. Under extremely sheltered conditions a group of species has become dominant which is very rare in the Helgoland region outside the quay-walls but which has been described as being characteristic for sheltered localities elsewhere.

Sublittoral hard-substratum communities off Orkney and St Abbs (Scotland)

During the summer of 1990 the sublittoral communities on hard substrata were investigated at 32 localities off Orkney and St Abbs (Scotland). The environment in both places has an open coast character, with small seasonal fluctuations in temperature and salinity and a high transparency of the water. The major governing environmental factors are the available amount of daylight and the degree of exposure to water movement. For the photic zone two different communities, dominated by foliose algae, are described. Under exposed conditions a widespread community is found, dominated by red algae in the middle structural layer and characterized by a dense canopy of Laminaria hyperborea . Under more sheltered conditions a community occurs in which brown and green algae become more abundant in the middle structural layer, while the top layer is formed by Laminaria saccharina and Saccorhiza polyschides . In the aphotic zone, under exposed conditions, a community is found which consists of a number of variants, with a dominance of the suspension feeders Pomatoceros triqueter and Alcyonium digitatum or bryozoans and hydrozoans. These variants are found in different regions, depths and angles of inclination of the substrata. Comparable variants have also been found off Helgoland (German Bight). Under sheltered conditions the suspension feeders become of minor importance and the community is dominated by encrusting red algae. In a surge tunnel in the photic zone off St Abbs Head, a community dominated by Dendrodoa grossularia and Clathrina coriacea is present.

Preliminary Ecological Studies on Sponges of the Genus Agelas Spp.

The influence of environmental factor, namely depth and sponge-coral interactions as well as the effects of infliction of standardized damages on the production of bromopyrrolic alkaloids isolated from the sponges Agelas dispar and Agelas conifera were analysed.

Preliminary Antifungal Activity of Some Sponges from Indonesia and Oman

80 methanolic extracts from sponges of Indonesia and Oman were screened for antifungal activity against ten strains fungi: Botrytis cinerea, Cladosporium cucumerinum, Fusarium oxysporum, Penicillium expansum, Rhizopus oryzae, Trichoderma harzianum, Aspergillus niger, Mucor pusillus, Absidia corymbifera and Absidia ramosa. The bromopyrrolic alkaloids hymenidin and sceptrin isolated from the sponges Agelas dispar and Agelas conifera, respectively, were also tested against the above fungi.