Data from: The density and spatial arrangement of the invasive oyster Crassostrea gigas determines its impact on settlement of native oyster larvae

Understanding how the density and spatial arrangement of invaders is critical to developing management strategies of pest species. The Pacific oyster, Crassostrea gigas, has been translocated around the world for aquaculture and in many instances has established wild populations. Relative to other species of bivalve, it displays rapid suspension feeding, which may cause mortality of pelagic invertebrate larvae. We compared the effect on settlement of Sydney rock oyster, Saccostrea glomerata, larvae of manipulating the spatial arrangement and density of native S. glomerata, and non-native C. gigas. We hypothesized that while manipulations of dead oysters would reveal the same positive relationship between attachment surface area and S. glomerata settlement between the two species, manipulations of live oysters would reveal differing density-dependent effects between the native and non-native oyster. In the field, whether oysters were live or dead, more larvae settled on C. gigas than S. glomerata when substrate was arranged in monospecific clumps. When, however, the two species were interspersed, there were no differences in larval settlement between them. By contrast, in aquaria simulating a higher effective oyster density, more larvae settled on live S. glomerata than C. gigas. When C. gigas was prevented from suspension feeding, settlement of larvae on C. gigas was enhanced. By contrast, settlement was similar between the two species when dead. While the presently low densities of the invasive oyster C. gigas may enhance S. glomerata larval settlement in east Australian estuaries, future increases in densities could produce negative impacts on native oyster settlement. Synthesis and applications: Our study has shown that both the spatial arrangement and density of invaders can influence their impact. Hence, management strategies aimed at preventing invasive populations reaching damaging sizes should not only consider the threshold density at which impacts exceed some acceptable limit, but also how patch formation modifies this.

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Fig.2. Oyster larval settlement rates on adult oysters in an open estuary, field experiment.Data collected in the field, in an experiment established in an estuary. Excel software was used to create the data file. A)Monospecific Bags: data represent the rate of larval settlement on 9 of each adult oyster: conspecific Sydney rock oysters and native Pacific oysters, deployed in single-species mesh bags. Status indicates oysters that were deployed live or dead. B) Mixed basket: 20 of each Sydney rock oyster and Pacific, live and dead (total 80 oysters) were deployed in one basket. Summary indicates means and standard errors of the means of raw data.Fig.2.xlsxFig.3. Larval settlement rates in response to densities of adult oyster substrate.Data collected in a controlled laboratory experiment, in 8 L replicate buckets. Excel software used to create the data. The number of Sydney rock oyster larvae settled per adult oyster is recorded. Adult oysters used as substrate were either A) Live or B) Dead. Two species of oyster were used; Sydney rock oyster and Pacific oyster. Oysters were placed in buckets in three densities; 1 oyster, 2 oysters and 3 oysters. Summary indicates the mean, and standard error of the mean.Fig.3.xlsxFig.4. Larval settlement rates on adult oysters restricted from feeding.This data was collected in a controlled laboratory experiment, using 8 L replicate buckets. Excel software was used to create this data. The number of larvae settled on individual adult oysters is recorded. Adult oyster substrates were one of two species: conspecific Sydney rock oysters or non native Pacific oysters. Adult oyster were restricted from feeding by banding closed, left to feed normally with no band, or left to feed with a loose band to test effects of the band on larval settlement (band control). Data is summarised as means and standard error of the mean for each treatment.Fig.4.xlsx