Effects of Disturbance and Initial Settlement on Fouling Community Structure

Anthropogenic structures may play an important role in the marine invasion process by providing novel artificial habitats, often out of the reach of common benthic predators. A survey of piers in northern-central Chile revealed a change in the epibenthic assemblage on pilings at different distances from a rocky shore with abundant grazers and predators. Pilings on soft sediment, away from the rocky shore, were heavily colonized by the invasive bryozoan Bugula neritina. We therefore hypothesized that benthic predators may forage on pilings located on rocky bottom whereas pilings on soft sediment benefit from the absence of generalist benthic predators which do not occur on soft sediment. We examined piling communities using cages directly attached to pilings, where we included or excluded the sea urchin Tetrapygus niger and the rock shrimp Rhyncocinetes typus. Resultant communities differed substantially; a high percentage of bare space occurred in the presence of sea urchins, while turf algae dominated in the presence of shrimp. Both sea urchins and shrimp suppressed the colonization of the invasive B. neritina and, when acting together, totally prevented its recruitment. In contrast, invasive bryozoans colonized 95% of the available substratum in cages where predators were excluded. Our results show the important role of benthic generalist predators in limiting the establishment and spread of non-native species on anthropogenic structures. Further, this study highlights the unprecedented role of shrimp grazing in structuring hard-bottom communities.

Section: Discussionmentioning

confidence: 99%

Anthropogenic structures as a spatial refuge from predation for the invasive bryozoan Bugula neritina

Dumont

Harris²,

Gaymer³

2011

“…Although previous studies have found peaks of diversity at intermediate disturbance levels (Lubchenco 1978, Paine & Levin 1981, Thorp & Cothran 1984, Aronson & Precht 1995, Flöder & Sommer 1999, several other publications do not support the IDH (Mook 1981, Death & Winterbourn 1995, Mackey & Currie 2000, McCabe & Gotelli 2000, reviewed in Mackey & Currie 2001. The IDH depends on a tradeoff between competitive and colonizing abilities, which is suggested to affect the immigration and extinction rates of a patch (Petraitis et al 1989).…”

Section: Introductionmentioning

confidence: 95%

Effects of disturbance on the diversity of hard-bottom macrobenthic communities on the coast of Chile

Valdivia¹,

Heidemann²,

Thiel³

et al. 2005

The intermediate disturbance hypothesis (IDH) predicts maximal diversity at intermediate levels of disturbance, but the validity of this hypothesis is controversially discussed. In this study, results of a field experiment, which was conducted on the northern-central Chilean coast, are presented. Fouling communities on artificial settlement substrata were studied. A total of 7 disturbance frequencies were applied to previously established communities, and a single disturbance event resulted in a removal of ~20% of the biomass. Species cover was estimated at the end of the experimental period, and it was found that diversity was strongly affected by disturbance frequency. With high disturbance frequencies the composition of the community was changed, with a decrease in the solitary ascidian Pyura chilensis (Molina 1782). The decrease of P. chilensis resulted in an increase of the colonial ascidian Diplosoma sp. A unimodal relationship between disturbance frequency and species richness was found, supporting the IDH. The results suggest that disturbance sustains diversity by reducing the abundance of the dominant species (e.g. P. chilensis), preventing competitive exclusion of the subordinate species, thus allowing subordinate species to re-emerge when competition is alleviated by disturbance. The results also suggest that these species show a trade-off between competitive and colonizing abilities, pointing to the existence of a competitive hierarchy. Therefore, the presence of competitive exclusion and disturbance-induced suppression of the dominant species remains a crucial mechanism, permitting species coexistence in the context of the IDH in the system studied.

“…simulating catastrophic, lethal effects) (e.g. Rhoads et al 1978, Mook 1981, Wilson & Tilman 1993, Dudgeon & Petraitis 2001, Lohrer & Whitlatch 2002. However, species differ in their susceptibilities to disturbance, and sub-lethal forms of disturbance may be widespread and frequent.…”

Section: Introductionmentioning

confidence: 99%

Terrestrially derived sediment: response of marine macrobenthic communities to thin terrigenous deposits

Lohrer

Thrush²,

Hewitt³

et al. 2004

Coastal marine habitats adjacent to catchments with encroaching human development are likely to experience increased sediment loadings in ensuing decades. Thus, sedimentary disturbance regimes in which coastal marine benthic communities have evolved may be shifting as depositional events exceeding critical thresholds become more frequent. To understand the threat posed by terrigenous sedimentation in an embayment with increasing urban development, we determined the thickness and frequency at which terrigenous sediment deposits begin to affect the benthos. We performed manipulative experiments involving layers of terrigenous sediment <1 cm thick in a variety of intertidal habitats in the Whitford embayment, North Island, New Zealand. Results of 3 separate experiments performed at 5 sites were largely consistent. While experimental plots were never completely defaunated, as little as 3 mm of the terrigenous material was sufficient to significantly alter macrobenthic community structure (measured after 10 d, relative to 0 mm controls). The direction of change was predominantly negative; the number of individuals and taxa declined as a result of sediment application, as did the densities of nearly every common species. Large bivalves were less affected than smaller ones, and deeper-dwelling species were less affected than ones at the sediment surface. With repeated applications of thin terrigenous layers (3 mm thickness, monthly over a 6 mo period), the sandflat sediments gradually became finer (clay volume % increased), and macrofaunal community composition progressively diverged from controls. To summarise, macrofauna were negatively affected by extremely small amounts of terrigenous sediment, and repeated depositional events did more damage than single ones. With increasing defoliation and excavation of catchment hillsides, the frequency of depositional events of a given intensity is likely to quicken, indicating an enhanced likelihood of macrofaunal disturbance and degradation in estuarine tidal flats. Management decisions that protect coastal catchments may partially ameliorate the threat to the benthos in coastal receiving waters.KEY WORDS: Land-use · Sediment impacts · Terrigenous sediment deposition · Marine benthos · Sandflat · Low intensity · High-frequency disturbance · Self-organized criticality Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 273: [121][122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137][138] 2004 are reacting to and recovering from variously sized disturbances, perhaps of several types and intensities, dating back to various points in time (Connell 1978, Huston 1979, Yodzis 1986, Tokeshi 1999.With so many factors potentially influencing disturbance-recovery dynamics, ecologists have been forced to simplify their models and experimental investigations by focusing on specific circumstances. For example, studies of disturbance-recovery dynamics often begin with the complete defaunation of disturbed pat...