Non-lethal effects of an invasive species in the marine environment: the importance of early life-history stages

Abstract

26Studies examining the effects of invasive species have traditionally focused on the 27 direct/lethal effects of the invasive on the native community but there is a growing 28 recognition that invasive species may also have non-lethal effects. In terrestrial 29 systems, non-lethal effects of invasive species can disrupt early life-history phases 30 (such as fertilization, dispersal and subsequent establishment) of native species but in 31 the marine environment, most studies focus on adult rather than early life-history 32 stages. Here, we examine the potential for an introduced sessile marine invertebrate 33 (Styela plicata) to exert both lethal and non-lethal effects on a native species 34 (Microcosmus squamiger) across multiple early life-history stages. We determined 35 whether sperm from the invasive species interfered with the fertilisation of eggs from 36 the native species and found no effect. However, we did find strong effects of the 37 invasive species on the post-fertilisation performance of the native species. The 38 invasive species inhibited the settlement of native larvae and, in the field, the presence 39 of the invasive species was associated with a 10-fold increase in the post-settlement 40 mortality of the native species, as well as an initial reduction of growth in the native. 41Our results suggest that the larvae of the native species avoid settling near the 42 invasive species due to reduced post-settlement survival in its presence. Our results 43 also show that invasive species can have complex and pervasive effects (both lethal 44 and non-lethal) across the early life history stages of the native species which are 45 likely to result in its displacement and to facilitate further invasion. 46 47

Early biotic interactions among introduced and native benthic species reveal cryptic predation and shifts in larval behaviour

“…Larvae of both species settled gregariously (Microcosmus squamiger only so at the highest concentration tested), and showed more random settlement in the presence of larvae of the other species. In contrast to our results, Rius et al (2009a) found that the settlement success of M. squamiger in its native Australian range was negatively affected by previously settled recruits of the introduced Styela plicata and vice versa. We expected some kind of interference effect as both species form dense aggregations in nature on artificial man-made substrata, so that competition for space is likely to be strong between them.…”

“…This process did not seem to act in the present work. In previous experiments with the same species used here, Rius et al (2009a) first exposed eggs of M. squamiger in its native range (Australia) to the sperm of introduced S. plicata, then the eggs were washed, and finally exposed to conspecific sperm. That study found no effects of the heterologous sperm on the fertilization process.…”

“…Osman & Whitlatch 1995a,b, Lohrer & Whitlatch 2002, with less attention to species interactions during early lifehistory stages (e.g. Rius et al 2009a). …”

Adaptive paternal effects? Experimental evidence that the paternal environment affects offspring performance

“…Although this may seem to be a short time frame to measure offspring performance, a previous study on Styela plicata at the same field site showed that 99% of all post-settlement mortality occurred within the first two weeks after settlement (Rius et al 2009). Although this may seem to be a short time frame to measure offspring performance, a previous study on Styela plicata at the same field site showed that 99% of all post-settlement mortality occurred within the first two weeks after settlement (Rius et al 2009).…”

Introduced and cryptogenic marine and estuarine species of South Africa

“…It can compete and displace native species (Rius et al 2009b). It is one of the most common harbour ascidian species worldwide (Lambert and Lambert 2003;Rocha and Kremer 2005;Wyatt et al 2005).…”