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PLoS One
2013 Jan 01;89:e73477. doi: 10.1371/journal.pone.0073477.
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Effects of a range-expanding sea urchin on behaviour of commercially fished abalone.
Strain EM
,
Johnson CR
,
Thomson RJ
.
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BACKGROUND: Global climate change has resulted in a southerly range expansion of the habitat modifying sea urchin Centrostephanus rodgersii to the east coast of Tasmania, Australia. Various studies have suggested that this urchin outcompetes black-lipped abalone (Haliotis rubra) for resources, but experiments elucidating the mechanisms are lacking.
METHODOLOGY/PRINCIPAL FINDINGS: We outline a new framework involving experimental manipulations and Markov chain and Pareto modelling to examine the effects of interspecific competition between urchins and abalone and the effect of intraspecific competition in abalone, assessed as effects on behaviour. Manipulations of abalone densities had no detectable effect on urchin behavioural transitions, movement patterns or resightability through time. In contrast, additions of urchins resulted in abalone shifting microhabitats from exposed to sheltered positions, an increase in the proportion of mobile abalone, and declines in abalone resightability through time relative to controls without the urchins. Our results support the hypothesis of asymmetrical competitive interactions between urchins and abalone.
CONCLUSIONS/SIGNIFICANCE: The introduction of urchins to intact algal beds causes abalone to flee and seek shelter in cryptic microhabitat which will negatively impact both their accessibility to such microhabitats, and productivity of the abalone fishery, and will potentially affect their growth and survival, while the presence of the abalone has no detectable effect on the urchin. Our approach involving field-based experiments and modelling could be used to test the effects of other invasive species on native species behaviour.
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24073195
???displayArticle.pmcLink???PMC3779227 ???displayArticle.link???PLoS One
Figure 1. Effect of interspecific competition on the percentage of tagged abalone resighted through time (weeks), in Experiment 2, at Magistrates Point, Maria Island.Data are means (+/−SE) of n = 3 replicate plots. Squares are 0U18A  = 1× ambient density abalone (weeks 1–9) and circles are 18U25A  = 1× ambient density abalone with 1× ambient density urchins (weeks 1–3 were prior to adding urchins, weeks 4–6 with added urchins and weeks 7–9 after the urchins were removed). There were significant differences between 0U25A (weeks 1–3) vs. 18U25A (weeks 4–6), 18U1A (weeks 1–3) vs. 18U25A (weeks 7–9), (see Table 2).
Figure 2. Effects of interspecific competition on abalone behavioural transitions, in Experiment 2 at Magistrates Point, Maria Island.Data are the proportion of tagged abalone observed in each behavioural state the week before (E =  exposed, L =  lost, O =  outside the plot and S =  sheltered) in 3 replicate plots. (a) 0U25A: 1× ambient density abalone, (weeks 1–3 prior to adding urchins and weeks 7–9 after urchins were removed), (b) 18U25A: 1× ambient density urchins, with 1× ambient density abalone, (week 4 with added urchins), (c) 18U25A: 1× ambient density urchins with 1× ambient density abalone, (week 5 with added urchins), and (d) 18U25A: 1× ambient density urchins ×1 ambient density abalone, (week 6 with added urchins). The numbers of abalone in a given behavioural state are summed across all times for the control and given separately at each time for the treatment and are represented as “n = .†inside each circle. Arrows of different thickness are used to show the relative probabilities of abalone transitioning from each behavioural state. The straight arrows show the probabilities of abalone transitioning from one behavioural state to another (e.g. E to S) and the curved arrows show the probabilities of abalone ‘transitioning’ to the same behavioural state (e.g. E to E). These proportions sum to 1 for a given behaviour state (e.g. E-E, E-S, E-L, E-O).
Figure 3. Effect of intraspecific competition on abalone behavioural transitions, in Experiment 2, at Magistrates Point, Maria Island.Data are the proportion of tagged abalone observed in each behavioural state the week before (E =  exposed, L =  lost, O =  outside the plot and S =  sheltered) in n = 3 replicate plots. (a) 0U18A: 1× ambient density abalone, (weeks 1–3 prior to adding extra abalone and weeks 7–9 after the extra abalone were removed combined), (b) 0U50A: 2× ambient density of abalone (week 4 with added extra abalone), (c) 0U50A: 2× ambient density of abalone, (week 5 with added extra abalone), and (d) 0U50A: 2× ambient density of abalone (week 6 with added extra abalone). The numbers of abalone in a given behavioural state are summed across all times for the control and given separately at each time for the treatment and are represented as “n = .†inside each circle. Arrows of different thickness are used to show the relative probabilities of abalone transitioning from each behavioural state. The straight arrows show the probabilities of abalone transitioning from one behavioural state to another (e.g. E to S) and the curved arrows show the probabilities of abalone ‘transitioning’ to the same behavioural (e.g. E to E). These proportions sum to 1 for a given behaviour state (e.g. E-E, E-S, E-L, E-O).
Figure 4. Effect of intra- and interspecific competition on the percentage of sedentary (≤0.4 m) and mobile (>0.4 m) abalone through time (weeks) in Experiment 2 at Magistrates Point, Maria Island.(a) 0U25A: 1× ambient density of abalone with no urchins, (b) 18U25A: 1× ambient density of urchins with 1× ambient density of abalone, and (c) 0U50A: 2× ambient density of abalone with no urchins. Black bars are sedentary abalone (distance moved ≤0.4 m) and white bars are mobile abalone (net distances moved >0.4 m). There were significant differences between 0U18A vs. 0U50A in weeks 5 and 6 and 0U25A vs. 18U25A in weeks 4, 5 and 6 (see Table 3 results).
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