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Diversity estimates play a key role in ecological assessments. Species richness and abundance are commonly used to generate complex diversity indices that are dependent on the quality of these estimates. As such, there is a long-standing interest in the development of monitoring techniques, their ability to adequately assess species diversity, and the implications for generated indices. To determine the ability of substratum community assessment methods to capture species diversity, we evaluated four methods: photo quadrat, point intercept, random subsampling, and full quadrat assessments. Species density, abundance, richness, Shannon diversity, and Simpson diversity were then calculated for each method. We then conducted a method validation at a subset of locations to serve as an indication for how well each method captured the totality of the diversity present. Density, richness, Shannon diversity, and Simpson diversity estimates varied between methods, despite assessments occurring at the same locations, with photo quadrats detecting the lowest estimates and full quadrat assessments the highest. Abundance estimates were consistent among methods. Sample-based rarefaction and extrapolation curves indicated that differences between Hill numbers (richness, Shannon diversity, and Simpson diversity) were significant in the majority of cases, and coverage-based rarefaction and extrapolation curves confirmed that these dissimilarities were due to differences between the methods, not the sample completeness. Method validation highlighted the inability of the tested methods to capture the totality of the diversity present, while further supporting the notion of extrapolating abundances. Our results highlight the need for consistency across research methods, the advantages of utilizing multiple diversity indices, and potential concerns and considerations when comparing data from multiple sources. [ABSTRACT FROM AUTHOR]

Past tests of settlement by marine invertebrate larvae on different colours were not designed to distinguish between responses to substrate colour and substrate brightness. Using colour vision testing methods, the design of this study provided a true test for responses to colour by including both coloured and grayscale settlement plates. The dominant fouling taxa at the test sites (the solitary ascidian, Ciona intestinalis ; the colonial ascidians Botryllus schlosseri or Botrylloides violaceous ; and a bryozoan Bugula sp.) showed no significant differences in settlement between blue, red or green plates. In contrast, the ascidians responded to substrate brightness with significantly lower settlement on lighter plates, while the bryozoans showed no significant preference relative to substrate brightness. The methods used here are a model for future tests of responses to colour during settlement. In addition, the contrasting responses to brightness are at odds with previous laboratory experiments that showed larvae of both ascidians and bryozoans are negatively phototactic at settlement. These results suggest that other cues must supersede any phototactic responses in the bryozoans, or alternatively that the range of light intensities near darker and lighter substrata were not part of the tests in the earlier reports. [ABSTRACT FROM AUTHOR]

Abstract: Anthropogenic marine habitats, such as marinas and breakwaters, are frequently colonized by nonindigenous species (NIS). Comparative studies show that few sessile NIS are found in nearby natural habitats, but little is known about the processes affecting the spread of NIS into these habitats. In southern British Columbia, the invasive colonial ascidian Botrylloides violaceus is widespread, but is far more common on man-made structures at marinas and aquaculture facilities than adjacent natural rocky reefs. To determine whether predation by native species, one element of biotic resistance, influences the successful infiltration of B. violaceus into natural benthic habitats, we conducted a series of predator exclusion experiments. Established adult colonies and newly settled juvenile B. violaceus were transplanted onto replicate PVC panels and deployed at marina pilings and adjacent natural rocky reefs at two locations. Panels were assigned to caged, uncaged, and procedural control treatments to test whether predator exclusion changed survivorship. Both juvenile and adult ascidian survival was significantly lower in uncaged treatments, suggesting that predation can limit the abundance and distribution of this species. Results were similar between piling and rocky reef habitats regardless of life stage and our results suggest that adult and juvenile B. violaceus are vulnerable to predation in both habitats studied. If B. violaceus propagules can disperse from dock floats and infiltrate adjacent natural rock, biotic resistance, through predation by native species, may diminish the likelihood of successful colonization in these habitats. Ensuring that natural habitats and native benthic communities remain healthy and intact may reduce the likelihood that invasive ascidians will spread beyond anthropogenic introduction sites where they can dominate the fouling community. [Copyright &y& Elsevier]