Online Resource 3.A Discussion of Potential Impacts of Nonnative Species Found in British

Online Resource 3.A discussion of potential impacts of nonnative species found in British Columbia’s eelgrass beds.

Most nonnatives sampled in this study were well-established species found in other BC coastal ecosystems with known impacts to seagrass habitats. The clams, Myaareneria and Ruditapesphilippinarum, were introduced in the 1800s for aquaculture and have subsequently invaded intertidal habitats along coastal BC (Newcombe, 1891). Studies suggest the bivalves may inhibit rhizome growth,reducing eelgrass biomass(Reusch & Williams, 1998). Similarly, the Pacific oyster, Crassostreagigas, spread from aquaculture to the natural environment and was found in Nanaimo Estuary and Mud Bay eelgrass beds. Generally Pacific oysters are thought to grow attached to a hard rocky substrate, however C. gigasis an ecosystem engineer that can grow independently in soft-sediment environments, physically altering these habitats(Lejart & Hily, 2011).As a result this species may reduce Z. marina density through competition for space and has the potential to alter species presence within the eelgrass bed with the addition of hard substrate.However, studies on the effects of bivalves on seagrass have suggested that increased water flow from these species can increase eelgrass area by increasing the depth at which eelgrass can grow by improving clarity (Newell & Koch, 2004).

Batillariaattramentariawas the only nonnative gastropod sampled and was only found at Nanaimo Estuary, though other studies have found B. attramentariaat Tsawwassen(Levings & Coustalin, 1975; Swinbanks & Murray, 1981). At Tsawwassen, our samples were collected towards the middle of the large eelgrass-covered mudflat and B. attramentaria are frequently found at the shore-edge of the Z. marina bed;accordingly, our sampling may have missed a present-day population of B. attramentaria(Swinbanks & Murray, 1981; Wonham et al., 2005). The invasion of B. attramentariain eelgrass hasincreased the invasibility of eelgrass beds as it has done in other mudflats in this region (Wonham et al., 2005) by increasing hard substrate in soft-sediment mudflats, grazing, and bioturbating, which may facilitate invasion by the nonnative Japanese eelgrass Z. japonica(a species present at Tsawwassen though not recorded in this study, personal observation; Harrison & Bigley, 1982).

The bamboo worm, Clymenellatorquatawas sampled for the first time in the northern Strait of Georgia during this study. Of the two sites where C. torquata was sampled, highest abundances were found at Tsawwassen, perhaps the result of an initial introduction to Tsawwassen from Boundary Bay (Banse, 1981) followed by a subsequent introduction event to Campbell River. Clymenellatorquata has limited planktonic dispersal, thus northward spread in the Strait of Georgia is likely the result of human-mediated transfer (Mach et al., 2012). In addition the tube-forming polychaete causes sediments to become spongy, this habitat alteration has the potential to deleteriously affect seagrassgrowth and abundance through competition for space and disturbance as has been demonstrated with other infaunalbioturbators(Dumbauld & Wyllie-Echeverria, 2003).

Crustaceans were the most abundant nonnative taxon in this study; the amphipod Amipithoevalida was the most abundant species, and was most abundant in the Nanaimo Estuary, mid-Vancouver Island. There have been no studies on the impacts of this species in its invaded range (Ruiz et al., 2011). Other nonnative crustaceans include the amphipods Monocorphiumacherusicum, M. insidiosum, Melitanitida, Grandidierella japonicaand the tanaid,Sinelobussp. Despite the invasion of these nonnatives on mudflats across the northeast Pacific, the impacts of only two of these crustaceans have been examined (review in Ruiz et al., 2011). M. acherusicum has the potential to alter the native invertebrate community in seagrass beds in BC through predation and competition for resources and space (Barnard, 1958; Onbe, 1966; Talman et al., 1999). In contrast, the effect of G. japonica on estuarine food webs has been studied yet no negative impacts documented (West et al., 2003; Whitcraft et al., 2008). This range of impacts and general lack of understanding makes it difficult to predict how the other nonnative crustacean species might alter eelgrass habitats.

The invasive alga, Sargassummuticum, was identified in Tsawwassen, Stanley Park and Mud Bay eelgrass beds; all sites located in the mid-Strait of Georgia region. This species has a holdfast that requires hard substrate, heavy enough to weigh down a juvenile or adult plant that is buoyed by many air vesicles (White & Orr, 2011). In Tsawwassen, a mud flat comprised of fine sediments, S. muticum was found growing on large Tresuscapaxclamshells, one of the only hard substrates in this eelgrass bed. S. muticum has been shown to shade out Z. marina plants in the NW Atlantic, reducing shoot densities where it invades (denHartog, 1997).

References

Banse K (1981) On some Cossuridae and Maldanidae (Polychaeta) from Washington and British Columbia. Can J Fish Aquat Sci 38:633-637

Barnard JL (1958) Amphipod crustaceans as fouling organisms in Los Angeles-Long Beach Harbors, with reference to the influence of seawater turbidity. California Fish & Game 44:161–170

Carlton JT (eds) In the wrong place - alien marine crustaceans: distribution, biology and impacts. Springer Netherlands, Dordrecht, pp. 215-250

denHartog C (1997) Is Sargassum muticum a threat to eelgrass beds? Aquat Bot 58:37-41

Dumbauld BR, Wyllie-Echeverria S (2003) The influence of burrowing thalassinid shrimps on the distribution of intertidal seagrasses in Willapa Bay, Washington, USA. Aquat Bot 77:27-42

Harrison PG, Bigley RE (1982) The recent introduction of the seagrass Zostera japonica Aschers. & Graebn. to the Pacific coast of North America. Can J Fish Aquat Sci 39:1642-1648

Lejart M, Hily C (2011) Differential response of benthic macrofauna to the formation of novel oyster reefs (Crassostrea gigas, Thunberg) on soft and rocky substrate in the intertidal of the Bay of Brest, France. Journal of Sea Research 65:84-93

Levings CD, Coustalin JB (1975) Zonation of intertidal biomass and related benthic data, Sturgeon and Roberts Banks, Fraser River estuary, British Columbia. Fisheries Marine Service Research Devision Technical Report 468, pp. 138

Mach ME, Levings CD, McDonald PS, et al. (2012) An Atlantic infaunal engineer is established in the Northeast Pacific: Clymenella torquata (Polychaeta: Maldanidae) on the British Columbia and Washington Coasts. Biol Inv 14:503-507

Newcombe CF (1891) Report on the marine shells of British Columbia. Paper Communications of the Natural History Society of B.C. 1:31-72

Newell RIE, Koch EW (2004) Modeling seagrass density and distribution in response to changes in turbidity stemming from bivalve filtration and seagrass sediment stabilization. Estuar Coast 27:793-806

Onbe T (1966) Observations on the tubicolous amphipod, Corophium acherusicum, in Fukuyama harbor area. Journal of the Faculty of Fisheries and Animal Husbandry Hiroshima University 6:323–338

Reusch TBH, Williams SL (1998) Variable responses of native eelgras Zostera marina to non-indigenous bivalve Musculista senhousia. Oecologia 113:428-441

Ruiz G, Fofonoff P, Steves B, et al. (2011a) Chapter 6: Marine crustacean invasions in North America: a synthesis of historical records and documented impacts. In: Galil BS, Clark PF and

Swinbanks DD, Murray JW (1981) Biosedimentological zonation of Boundary Bay tidal flats, Fraser River Delta, British Columbia. Sedimentology 28:201-237

Talman S, Bite SJ, Holloway M, et al. (1999) Impacts of some introduced marine species found in Port Phillip Bay. In: Hewitt CL, Campbell ML, Thresher RE and Martin RB (eds) Marine biological invasions of Port Phillip Bay, Victoria. CRIMP Tech Rep No. 20, CSIRO Marine Research, Hobart, Tasmania, pp. 344

West JM, Williams GD, Madon SP, et al. (2003) Integrating spatial and temporal variability into the analysis of fish food web linkages in Tijuana Estuary. Environmental Biology of Fishes 67:297–309

Whitcraft CR, Levin LA, Talley D, et al. (2008) Utilization of invasive tamarisk by salt marsh consumers. Oecologia 158:259–272

White L, Orr L (2011) Native clams facilitate invasive species in an eelgrass bed. Mar Ecol-Prog Ser 424:87-95

Wonham MJ, O'Connor M, Harley CDG (2005) Positive effects of a dominant invader on introduced and native mudflat species. Mar Ecol-Prog Ser 289:109-116