Patterns in shallow subtidal marine assemblages along the coast of New South Wales

Mobile animals can be affected by disturbance because of changes to the structure of their habitat. Few studies, however, recognise the potential for the historical configuration of habitat (e.g. density prior to disturbance) to affect the way animals respond to the disturbance. Furthermore, there is a tendency for ecologists to study or manipulate only the most severe disturbances, but such events are less likely to be common. We tested the hypothesis that the density of Ecklonia radiata before disturbance affects the response of assemblages of mobile invertebrates to different severities of disturbance. Differences in the severity of disturbance caused changes in the structure of assemblages, but this response varied depending on the historical configuration of habitat. The magnitude by which assemblage structure differed between undisturbed and disturbed habitats was greater where habitats were historically sparse rather than dense. We emphasise the importance of assessing a range of severities of disturbance and demonstrate the importance of habitat configuration prior to the disturbance, particularly for animals with close association to their habitat.KEY WORDS: Disturbance · Severity · Diversity · Habitat structure · History · Mobile invertebrates · MacroalgaeResale or republication not permitted without written consent of the publisher

Section: Discussionmentioning

confidence: 99%

“…Small-scale variation in the configuration of subtidal, biogenic habitat is considerable in temperate regions of the world (Dayton et al 1984, Underwood et al 1991, Goodsell et al 2004. In Australia, forests of the common kelp Ecklonia radiata provide the major habitat structure for many marine organisms.…”

Section: Introductionmentioning

confidence: 99%

Historical configuration of habitat influences the effects of disturbance on mobile invertebrates

Goodsell

Connell²

2005

“…In general, the 3 locations were situated on rocky reef to a depth of approximately 20 m and the benthic community was dominated by erect sponges. Underwood et al (1991) and Roberts & Davis (1996) have described similar subtidal habitat for coastal waters in New South Wales.…”

Section: Methodsmentioning

confidence: 99%

Rapid changes in encrusting marine assemblages exposed to anthropogenic point-source pollution:a 'Beyond BACI' approach

Roberts¹,

Smith²,

Ajani³

et al. 1998

Cover of and the number of species in encrusting macrobenthic assemblages inhabiting temperate rocky reefs m the vicinity of an ocean outfall changed rapidly following the discharge of secondary treated sewage effluent. Within 3 mo of the commissioning of the outfall, significant reductions in the cover of crustose and foliose algae were apparent when this outfall area was compared to 2 reference locations. The cover of several species of sponge, including Cymbastela concentrica, Geodinella sp. and Spongia sp., also underwent marked declines coincident with the commissioning of the outfall. Only 1 category of cover increased significantly at the outfall; this was a nondescript matrix comprising silt and microorganisms, which doubled its representation to almost 60%. We d~d not detect significant declines in the cover and number of specles of sponges or total fauna, however. A 'Beyond BACI' experimental design was used to deternune the environmental unpact because of the great spatial and temporal variability in these shallow water (-20 m) encrusting communities. Photographic samples were taken in 3 penods, the first pre-commissioning and the other 2 post-commissiorung Multivariate analyses revealed marked shifts in the structure of the assemblage at the outfall relative to the reference locations; these shifts were clearly depicted by a non-metric multi-dimensional scaling (nMDS) plot. A SIMPER analysis confirmed that the overall composition of the community at the outfall changed from one in which algae and sponges were well represented to an assemblage dominated by silt and ascidians.

“…Macroalgal assemblages dominated by densely packed, turf-forming seaweeds are common in tropical and temperate intertidal and subtidal rocky shores (Dahl 1973, Lauret 1974, Hay 1981, Stewart 1982, Adey & Goertmiller 1987, Underwood et al 1991. Despite their abundance, turf-forming algae often are overlooked and the causes of their trend to monopolise space are still poorly known (Sousa et al 1981, Airoldi in press).…”

Section: Introductionmentioning

confidence: 99%

Responses of turf-forming algae to spatial variations in the deposition of sediments

Airoldi¹,

Virgilio²

1998

130

Responses of a turf-forming, filamentous, algal assemblage to spatial variation in the deposition of sediments were investigated from September 1994 to September 1996 on a rocky subtidal reef south of Livorno (Mediterranean Sea) Large-and small-scale spatial differences in the amount and size of sed~ment settling on and accumulating in the turf were investigated over 1 yr in relation to meteorological conditions and to patterns of abundance of the turf. A multifactorial manipulat~on of the deposition of sediment was used to test the hypotheses that (1) different amounts and grain-sizes of settling material affect the cover and biomass of the filamentous algae, (2) any effects of sedimentation are independent of the stage of development of the turf and (3) patterns are consistent at different spatial scales, ranging from a few centimetres to several metres. During the investigation, the reglme of sed~mentation fluctuated greatly over time and among s~t e s The distribution of the turf across diiferent sites was, however, not apparently related to large-scale variations in the deposition of sediment Within sites, accumulation of sediment in the turf was patchy. The results of the experiment indicated that patchiness may affect the local biomass of established turf-forming algae, the abundance of which significantly decreased in quadrats which had higher deposition of sediments. On a scale of centimetres, high accumulation of sediment decreased variability of algal biomass within individual quadrats. The effects of sediment on biomass were also significantly influenced by the stage of development of the turf. No effects were observed on the cover of the filamentous algae. These results suggest that the responses of the turf to variations in the characteristics of the depositional environment may vary with changes in spatial scale and may be dependent on the concomitant action of other physical and biological factors.