Interactions Oetween Arenicola marina and Zostera noltii on a tidal flat in the Wadden Sea

Abstract

On the tidal flats off Terschelling in the Dutch Wadden Sea, the seagrass Zostera noltii Hornem. and adult lugworms Arenicola marina L. show strictly separate distributions with an abrupt border between the 2 communities. Since seagrass and lugworms do not show different limitations regarding sediment type and emersion period, the border must be the result of other environmental factors or plant-animal interactions. Transplantation experiments on the tidal flats showed that the seagrass was quite capable of growing on the lugworm tidal flat when worms were absent However, the seagrass density and biomass were severely influenced in the presence of lugworms, most probably due to the worms' sediment-reworking activities. Lugworms quickly disappeared from the experimental sites on the seagrass tidal flat, irrespective of the actual presence of seagrass. A local survey of the seagrass area showed that funnel formation by lugworms to sufficient depth was restricted by a dense clay layer under the sediment surface, a remnant of a former salt marsh. These results indicate that an increase of lugworm densities in the Dutch Wadden Sea may have contributed to the decrease of the area covered by Z. noltii on the tidal flats off Terschelling over the last 20 yr.

The effects of the polychaete Nereis diversicolor on the distribution and transplanting success of Zostera noltii

“…Experimental additions of shoots of Z. japonica caused temporary decreases in decapod abundance, but established populations of Callianassa eventually destroyed the transplanted seagrasses, usually in the summer when the animals were most active. Philippart (1994) also recorded spatially distinct distributions of Z. noltii and a polychaete, in this case Arenicola marina. Following reciprocal transplant experiments she concluded that the worms restricted colonisation by seagrass, due to their bioturbatory activities.…”

Lugworm (Abarenicola affinis) in seagrass and unvegetated habitats

“…In summary, the present study highlights the negative feedback of seagrass on lugworms, whereas other studies have shown mutual negative effects or have emphasised the negative influence of lugworms on the distribution of seagrass in tidal flats (Phillipart 1994;Valdemarsen et al 2010;Suykerbuyk et al 2012). Where lugworms and seagrasses co-occur, their opposing ways of modifying the sediment may result in the potential of each ecosystem engineer to prevent the establishment of the other type of engineer (van Wesenbeeck et al 2007).…”

“…The present study indicated that such interactions play a role in the variation of lugworm distribution and body size among tidal inlets of southern New Zealand; an established seagrass bed restricted the spatial extent of A. affinis, particularly of large individuals, in an otherwise suitable habitat. Given the potential of lugworms to adversely affect seagrass distribution (Phillipart 1994;Suykerbuyk et al 2012), future research is needed to elucidate factors determining the predominance of either type of organism in joint habitats, as well as factors that may cause shifts in their distributions.…”

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

“…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.…”