The specific status of the heart‐urchin Echinocardium cordatum (Pennant) around New Zealand is discussed in the context of the suggestion that the New Zealand form of this spatangoid is sufficiently distinct from E. cordatum to be regarded as a separate species, namely E. australe Gray or E. zealandicum Gray. A brief history of the problem is outlined and it is demonstrated that, from the beginning of the present century, specialist opinion has favoured the unitary species concept and been unenthusiastic about the validity of Gray's species. The pattern of variability revealed by a comparative morphological study of E. cordatum from the British Isles and E. australe/zealandicum from New Zealand did not support the specific separation of the Australasian species. Alternatively, it is proposed that the morphological structure of the test in E. cordatum may be considerably influenced by sediment texture and that the distinctiveness of some of the New Zealand specimens is related to their occupation of very fine deposits, which are not commonly exploited by E. cordatum around the British Isles.

The biology of the New Zealand cassiduloid echinoid Apatopygus recens is reviewed in terms of its geographical distribution, sediment relationships, and associations with other echinoids. Observations were also made on the density and size‐frequency distribution of an A. recens population at Croisilles* Harbour, Tasman Bay, and on the burrowing and feeding behaviour of specimens from this locality in an aquarium. A. recens is a rapid and continuous deposit feeder which burrows completely beneath the surface of the coarse sediments with which it is characteristically associated. The construction of a respiratory burrow to the sediment surface was not observed and the species appears to rely entirely on an adequate interstitial water flow for its respiratory requirements. Two 24 mm long specimens each defaecated an average of 0·76 g dry wt of sediment/h which at the Croisilles Harbour habitat was equivalent to a population ingestion rate of about 7·6 g dry wt of sediment/m2/h.

Various test features in six specimens of Echinocardium cordatum collected from South Africa, Trindade Island (South Atlantic), Australia, Japan and Ireland were compared with previously established data relating to British and New Zealand specimens. Morphological variations between the specimens were interpreted as infra‐specific differences and no evidence was detected that the spatangoid conventionally defined as E. cordatum is more than a single species throughout its extensive geographical range.

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Climate change is altering ecosystems in unprecedented ways and necessitates the development of strategies that model ecosystems and allow for the evaluation of environmental impacts of perturbations: including climate events, novel approaches to agronomy or ecosystem management, and impacts of bio-industry and biotechnology innovations. Mesocosms present a platform to model some of the complexity of an ecosystem, while still being controlled and reproducible enough that they can be used to ask targeted questions and systematically assess the impacts of perturbation events. Herein, we established a methodological pipeline to assess the impact of three perturbation events (hydration, nutrification, contamination) upon plant-associated microbial communities using a terrestrial mesocosm. Mesocosms were assessed over a 30-day time-course following environmental perturbations, including modeling contamination with a foreign microbe via the introduction of Saccharomyces cerevisiae. We developed and applied a suite of diagnostic and bioinformatic analyses, including digital droplet PCR, microscopy, and phylogenomic analyses to assess the impacts of a perturbation event in a system that models a terrestrial ecosystem. The resultant data show that our mesocosms are dynamic yet reproducible, and that the analysis pipeline presented here allowed for a longitudinal assessment of microbial population dynamics and abiotic soil characteristics following perturbations, as well as the fate of yeast in the soil. Notably, our data indicate that a single perturbation event can have long-lasting impact upon soil composition and underlying microbial populations. Thus, this approach can be used to ask targeted questions as well as gain insights on broader ecological trends of soil perturbation events.