Fractal properties of spatial distribution of intertidal benthic communities

Techniques are needed to extend the generality of detailed experimental field studies. Multi-resolution sampling designs nest fine-scale sampling within information about broad-scale processes that may affect finer-scale data. These designs are very appropriate for studies seeking to detect the effects of processes operating over a variety of scales. We tested the utility of a novel, lowintensity/cost, multi-resolution sampling design in an investigation of the relationship between the suspension-feeding pinnid bivalve Atrina zelandica and surrounding benthic macrofauna. Interactions were modelled at different spatial scales, and a variety of covariates were included in the search for the best statistical and most sensible ecological model. We chose our sampling sites to encompass broad-scale gradients in A. zelandica density and size, depth, sediment characteristics and hydrodynamics. We found these gradients helped explain the relationship between A. zelandica and associated benthic macrofauna. Our results suggest that the strength of effects of A. zelandica on benthic macrofauna was dependent on 2 aspects of spatial scale: grain (the area over which A. zelandica measurements were made) and lag (the distance between where the A. zelandica and the macrofauna were sampled). By nesting fine-scale measures of benthic macrofaunal community composition within different spatial arrangements of individual A. zelandica, we were able to determine that the maximum distance between individual A. zelandica, rather than density estimates, better explained effects of A. zelandica on benthic macrofauna. This suggests the value of integrating broad-scale surveys with localised experiments so that organism interactions can be more generally interpreted on the basis of dynamics within landscapes rather than as density-to-density comparisons.

Section: Methodsmentioning

confidence: 99%

Integrating heterogeneity across spatial scales: interactions between Atrina zelandica and benthic macrofauna

Hewitt

Thrush²,

Legendre³

et al. 2002

“…Although this variation occurs at a hierarchy of different scales (Thrush 1991, Underwood & Chapman 1996, Azovsky et al 2000, there is a growing awareness of the relative importance of variation among sites separated by 10s of meters in many benthic marine habitats (e.g. soft sediments: Morrisey et al 1992a, mangroves: Chapman 1998, rocky shores: Olabarria & Chapman 2001).…”

Section: Introductionmentioning

confidence: 99%

Variation in detrital enrichment causes spatio-temporal variation in soft-sediment assemblages

Kelaher¹,

Levinton²

2003

We investigated the importance of algal detritus in determining complex patterns of spatio-temporal variation in annelid assemblages in sites separated by 10s of meters on mudflats on Long Island, New York. We used field sampling to test the hypothesis that spatio-temporal variation in annelid assemblages contributes substantially more to total variation than consistent spatial differences among sites (pure spatial variation). While this pattern was generally shown by dominant surface-feeding annelids (e.g. Paranais litoralis and Streblospio benedicti), this was not the case for the deeper-feeding orbinid polychaete Leitoscolopolos robustus. We enriched the sediment with Ulva rotundata detrius to test the hypothesis that variation in detrital enrichment creates complex spatio-temporal patterns in annelid assemblages. Initially, the diversity and abundance of annelids was lower in enriched sites compared to untouched sites because of anoxic conditions at the sediment -water interface in the manipulated treatment. After about 1 mo, however, populations of opportunistic surface-feeding annelids (e.g. P. litoralis and Capitella capitata) increased in enriched sites to peak significantly higher than those in unmanipulated sediment, indicating resourcelimitation. The annelid assemblages in different treatments then converged in June/July when the excess detrital resources were sufficiently depleted. Overall, we demonstrate the important role that deposition of detritus plays in determining variation in soft-sediment communities. More than just simple spatial variation, however, we show that detritus enrichment can generate the complicated spatio-temporal patterns observed in natural annelid assemblages.

“…Thrush 1991, Azovsky et al 2000. Disturbances cause temporal and spatial heterogeneity by killing, displacing or damaging organisms and by creating opportunities for establishment of others (Dayton 1971, Paine & Levin 1981, Sousa 1984, Pickett et al 1989, Underwood 1989, Valiela & Rietsma 1995, Ford et al 1999.…”

Section: Introductionmentioning

confidence: 99%

Small-scale disturbance and increased nutrients as influences on intertidal macrobenthic assemblages: experimental burial of wrack in different intertidal environments

Rossi¹,

Underwood²

2002

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata causes increased organic content and alters the physical structure of sediments. These effects may influence the types and relative abundances of species in the sediment. Such influences can be expected to vary according to the type and organic content of the sediment. In this study, wrack was buried in 3 mudflats and 2 intertidal sandflats (with coarser sediments) in Botany Bay (New South Wales, Australia). The experiments tested the hypotheses that burial of wrack would (1) increase the content of total nitrogen (N) and organic carbon (OC) of sediments; (2) increase the biomass of micro-algae; and (3) alter the abundances of macrofauna in the sediments. Simulated wrack (equivalent amounts of plastic ribbon, without any organic content) was added to other experimental plots to test the above hypotheses when only physical disturbance, not organic enrichment, occurred. Total OC, N and chlorophyll a (chl a) were sampled every 2 wk for 6 wk and macrofauna were sampled after 6 wk. Some taxa (capitellid, orbinid and nereid worms) increased abundances where wrack was added. Nereidae, however, responded only in muddy sediments. The physical structure associated with wrack also caused an increase in numbers of Oligochaeta and increased patchiness in numbers of the soldier-crab Mictyris longicarpus, but only in sites where they were already abundant. Wrack represents a source of food for some taxa. Physical disturbance due to burial of wrack also adds to patchiness and abundance of taxa on sandy and muddy intertidal shores. The major responses of fauna predicted from other studies did not occur.