Biomechanical warfare in ecology; negative interactions between species by habitat modification

Abstract

Since the introduction of the term ecosystem engineering by Jones et al. many studies have focused on positive, facilitative interactions caused by ecosystem engineering. Much less emphasis has been placed on the role of ecosystem engineering in causing negative interactions between species. Here, we report on negative interactions between two well known ecosystem engineers occurring at the interface of salt marsh and intertidal flat (i.e. common cordgrass Spartina anglica and lugworms Arenicola marina ), via modification of their joint habitat. A field survey indicated that, although both species share a common habitat, they rarely co-occur on small spatial scales ( B/1 m). Experiments in the field and in mesocosms reveal that establishment of small Spartina plants is inhibited in Arenicola -dominated patches because of low sediment stability induced by the lugworms. In turn, Arenicola establishment in Spartina -dominated patches is limited by high silt content, compactness and dense rooting of the sediment caused by Spartina presence. Our results show that negative interactions by modification of the environment can result in rapid mutual exclusion, particularly if adverse effects of habitat modification are strong and if both species exhibit positive feedbacks. This illustrates the potential for negative interactions via the environment to affect community composition.

Distribution and abundance ofAbarenicola affinis(Arenicolidae, Polychaeta) in tidal inlets of Otago, New Zealand

“…Arenicola marina, van Wesenbeeck et al 2007;Ekloef et al 2011). Overall, faecal cast counts underestimated lugworm abundance by 9%, which is close to findings for Arenicola marina documenting underestimations of 6% Flach & Beukema 1994).…”

“…In contrast, in Papanui Inlet and at Harwood low lugworm abundance in mid and low intertidal zones coincided with widely distributed seagrass (Mills & Berkenbusch 2009). The cooccurrence of seagrass, stabilising and binding the sediment, may inhibit the distribution of large burrowers such as lugworms due to cohesive and dense root and rhizome matrices, which are difficult to penetrate for burrowing infauna and thus limit their spatial expansion (Brenchley 1982;Reise 1985;van Houte-Howes et al 2004;Siebert & Branch 2005;Berkenbusch et al 2007;van Wesenbeeck et al 2007). The feedback between counteracting ecosystem engineers such as seagrass (sediment stabiliser) and lugworm (sediment destabiliser) in Otago inlets may be temporally dynamic and coupled with abiotic factors (Phillipart 1994;Eriksson et al 2010), and needs further research to elucidate mechanisms that contribute to the distribution of lugworm populations in these inlets.…”

Comparing biodiversity effects among ecosystem engineers of contrasting strength: macrofauna diversity in Zostera noltii and Spartina anglica vegetations

“…The much higher root mass and sediment compaction in Spartina sites may physically hamper establishment and survival of endobenthic species (e.g., Brusati and Grosholz 2006). For example, sediment compaction and fine grain size distribution hampers settlement of A. marina in Spartina patches (van Wesenbeeck et al 2007). Although we observed Arenicola in both the Zostera meadow and the small Spartina patches, this species was completely absent in the Spartina marsh.…”

“…Spartina anglica is characterized by much taller and stiffer shoots and a larger above-ground biomass. Positive habitat complexity effects of Spartina on benthic assemblages may be counteracted by its effect on sediment properties, as Spartina forms well-defined dome-shaped tussocks (Castellanos et al 1994;Bouma et al 2007;van Hulzen et al 2007) with a relatively compact, densely rooted, well aerated, dry sediment (Van Wesenbeeck et al 2007). This effect on sediment properties may be expected to be more pronounced in mature Spartina marshes than in more recently established Spartina tussocks, as the latter will contain a lower shoot and root density.…”

Lugworm (Abarenicola affinis) in seagrass and unvegetated habitats

“…Both seagrasses and lugworms modify habitats to their own benefit and have the potential to inhibit the distribution and functioning of each other, when co-existing on tidal flats (van der Heide et al 2007;van Wesenbeeck et al 2007;Bouma et al 2009;Ekloef et al 2011). Sediment processing by lugworms can lead to burial of seagrass seeds and plants, whereas, in turn, established root systems of seagrasses consolidate the sediment, inhibiting reworking and burrowing activities of lugworms (Brenchley 1982;van Wesenbeeck et al 2007;Valdemarsen et al 2010;Ekloef et al 2011).…”