Ecological Impact of the Introduction to New Zealand of Asian Date Mussels and Cordgrass—The Foraminiferal, Ostracod and Molluscan Record

Abstract

The ecological impact from the establishment of dense intertidal beds of introduced Asian date mussels (Musculista senhousia) and cordgrass (Spartina alterniflora) in five northern New Zealand estuaries and harbours was documented in 2005–2006, using the fossil record of the shells of foraminifera, ostracods and molluscs in paired sediment cores and surface samples taken from inside and outside selected beds. The most significant changes in faunal composition in all, but the most saline sites, generally occurred in both cores in each pair and could be attributed to the impact of decreased salinity and pH as a result of increased freshwater runoff following clearance of the surrounding forest in the 19th century and urban development in the late 20th century. Establishment of Asian date mussel beds had a greatest impact on the composition of ostracod faunas. At near oceanic salinity, the mussels had completely replaced the native infaunal bivalve fauna, but had little impact on the foraminifera. At more brackish sites, the presence of mussel shells appears to have buffered the calcareous foraminifera from the effects of lowered pH, which had dissolved this component outside the beds. Establishment of cordgrass patches had no impact on ostracod faunas, and little on molluscs except at Kaipara, where introduced Pacific oysters had colonised the cordgrass. Cordgrass had the most impact on the foraminifera. At brackish sites, cordgrass patches had been colonised by agglutinated foraminiferal species different from those that dominate outside. In cordgrass at more saline sites, agglutinated foraminifera have invaded and bloomed at the expense of calcareous Ammonia spp., which dominated outside the patches.

Appendices

APPENDIX: TAXONOMIC REFERENCE LIST

List of Foraminifera, Ostracoda and Mollusca mentioned in this study, together with citations of figured specimens that reflect the taxonomic concept followed here. Foraminiferal species classification largely follows Hayward et al. (1999a). Foraminiferal species abbreviations are those used in Figs. 9 and 10.

Phylum Foraminifera

Order Lituolida Amx = Ammobaculites exiguus Cushman and Brönnimann 1948 in Hayward et al. 1999a, pl. 1, Figs 19–20. Amf = Ammotium fragile Warren 1957 in Hayward et al. 1999a, pl. 1, Figs 21–22.

Hap = Haplophragmoides wilberti Andersen 1953 in Hayward et al. 1999a, pl. 1, Figs 25–26.

Jad = Jadammina macrescens (Brady) = Trochammina inflata var. macrescens Brady 1870 in Hayward et al. 1999a, pl. 1, Figs 27–29.

Mif = Miliammina fusca (Brady) = Quinqueloculina fusca Brady 1870 in Hayward et al. 1999a, pl. 1, Figs 5–6. Scm = Schlerochorella moniliforme (Siddall) = Reophax moniliforme Siddall 1886 in Hayward et al. 1999a, pl. 1, Figs 13–14. Order Trochamminida Portatrochammina sorosa (Parr) = Trochammina sorosa Parr 1950 in Hayward et al. 1999a, pl. 2, Figs 4–5. Tri = Trochammina inflata (Montagu) = Nautilus inflatus Montagu 1808 in Hayward et al. 1999a, pl. 2, Figs 6–8. Trochamminita salsa (Cushman & Bronnimann) = Labrospira salsa Cushman and Bronnimann 1948 in Hayward et al. 1999a, pl. 1, Figs 30–32.

Order Textulariida Txe = Textularia earlandi Parker 1952 in Hayward et al. 1999a, pl. 2, Figs 22–23. Order Miliolida

Qui = Quinqueloculina spp.

Order Buliminida Bol = Bolivina spp.

Order Rotaliida Am = Ammonia spp. Hayward et al. 1999a, pl. 16, Figs 7–12 (as A. parkinsoniana).

Ela = Elphidium advenum (Cushman) s.l. = Polystomella advenum Cushman 1922 in Hayward et al. 1999a, pl. 17, Figs 1–5.

Elc = Elphidium charlottense (Vella) = Elphidiononion charlottense Vella 1957 in Hayward et al. 1999a, pl. 17, Figs 6–8.

Ele = Elphidium excavatum (Terquem) s.l. = Polystomella excavata Terquem 1975 in Hayward et al. 1999a, pl. 17, Figs 11–14. Elphidium gunteri Cole 1931 in Hayward et al. 1999a, pl. 17, Figs 21–22.

Elv = Elphidium vellai Hayward 1997 in Hayward et al. 1999a, pl. 17, Figs 27–28. Hay = Haynesina depressula (Walker & Jacob) = Nautilus depressulus Walker and Jacob 1798 in Hayward et al. 1999a, pl. 15, Figs 10–11. Hel = Helenina anderseni (Warren) = Pseudoeponides anderseni Warren 1957 in Hayward et al. 1999a, pl. 10, Figs 1–3.

Phylum Crustacea

Class Ostracoda

Callistocythere neoplana Swanson 1979, Figs 26a–c.

Keijia demissa (Brady) = Cythere demissa Brady 1880 in Yassini and Jones 1995, Figs. 271–274.

Leptocythere lacustris De Deckker 1981 in Yassini and Jones 1995, Figs 220, 222, 224, 226.

Loxocythere crassa Hornibrook 1952, pl. 2, Figs 26–31.

Macromckenziea aff. porcelanica Whatley and Downing 1983 in Yassini and Jones 1995, Figs 114, 116, 118, 120, 122.

Microcytherura ? hornibrooki (Mckenzie) = Loxocythere hornibrooki McKenzie 1967 in Yassini and Jones 1995, Figs 582, 584.

Munseyella tumida Swanson 1979, Fig. 24.

Procythereis lyttletonensis Hartmann 1982, pl. 5, Fig. 9.

Swansonella novaezealandica (Hartmann) = Tanella novaezealandica Hartmann 1982, pl. 3, Figs 1–14.

Xestoleberis sp. cf. Swanson 1979, Fig. 54.

Phylum Mollusca

Class Bivalvia

Austrovenus stutchburyi (Wood) = Venus stutchburyi Wood 1828 in Powell 1979, pl. 77, Fig. 11 (as Chione).

Crassostrea gigas (Thunberg) = Ostrea gigas Thunberg 1793 in Hayward and Morley 2008, Fig. 17.

Musculista senhousia (Benson) = Modiola senhousia Benson 1842 in Hayward and Morley 2008, fig. 17.