Community-Wide Effects of Nonindigenous Species on Temperate Rocky Reefs

Abstract

Ecological interactions among invading species are common and may often be important in facilitating invasions. Indeed, the presence of one nonindigenous species can act as an agent of disturbance that facilitates the invasion of a second species. However, most studies of nonindigenous species are anecdotal and do not provide substantive evidence that interactions among nonindigenous species have any community-level effects. Here, using a combination of field experiments and observations we examine interactions among introduced species in New England kelp forests and ask whether these interactions have altered paradigms describing subtidal communities in the Gulf of Maine. The green alga Codium fragile was observed at the Isles of Shoals, Maine, USA, in 1983 and has since replaced the native kelp as the dominant seaweed on leeward shores. Experiments manipulating kelp and Codium reveal that Codium does not directly inhibit growth or survival of kelp. Codium does, however, successfully recruit to gaps in the kelp bed and, once established, inhibits recruitment of kelp. A second nonindigenous species, Membranipora membranacea, grows epiphytically on kelp, and experiments reveal that the presence of Membranipora reduces growth and survival of kelp, resulting in defoliation of kelp plants and gap formation in kelp beds. In the absence of Codium, kelp recolonizes these gaps, but when present, Codium colonizes and prevents kelp recolonization. Manipulations of herbivores demonstrate that herbivory will reinforce Codium dominance. Thus, the demise of New England kelp beds appears to result from one invasive species facilitating the spread of a second nonindigenous species.

Does the invasion ofCaulerpa racemosavar.cylindraceaaffect the feeding habits of amphipods (Crustacea: Amphipoda)?

“…Our results are similar to those found on other invasive seaweeds where amphipods and other herbivores and omnivores fed very little on the invasive species, and therefore the spread of introduced seaweeds is not under herbivore control (Trowbridge, 1995;Levin et al, 2002;Britton-Simmons, 2004;Chavanich & Harris, 2004;Conklin & Smith, 2005;Davis et al, 2005;Sumi & Scheibling, 2005;Gollan & Wright, 2006;Box et al, 2009). 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 caulerpa racemosa---feeding habits---amphipodsLow herbivore diversity and abundance, combined with very little feeding on and weak habitat preference for invasive algae result in limited grazing pressure, as has been reported for the amphipod Cymadusa setosa on C. taxifolia (Gollan & Wright, 2006).…”

Positive effects of a dominant invader on introduced and native mudflat species

“…Crooks 2002) or other invaders (Simberloff & Von Holle 1999, Richardson et al 2000, Ricciardi 2001). Positive interactions, namely mutualisms (+/+) and 1 side of both commensal (+/0) and exploitative (+/-) relationships, have thus far only rarely been reported between marine invaders (Crooks 2002, Levin et al 2002, Wonham 2003. As the prevalence and ecological importance of positive interactions are increasingly recognized in marine systems (Peterson & Heck 2001, Stachowicz 2001, Bruno et al 2003, Mouritsen 2004, we anticipate an increase in reports of facilitative interactions with invaders as well.…”

Variation in Herbivore-Mediated Indirect Effects of an Invasive Plant on a Native Plant

“…Invasive exotic species, such as musk thistle (Carduus nutans) and the flower head weevil (R. conicus), represent a significant threat to biodiversity; yet, the mechanisms by which invaders affect native species and communities remain poorly understood (Parker et al 1999, Levin et al 2002. A mechanistic understanding of invasive species effects on native species is essential to predicting their impacts if they invade new communities (Louda et al 2003a(Louda et al ,b, 2005.…”