Year

2023

Degree Name

Bachelor of Science (Honours)

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Marian Wong

Abstract

Biogenic ecosystem engineers play significant roles in providing habitat for other organisms through their own physical structures. In marine ecosystems, benthic organisms are well known to provide sheltered-mediated benefits to a range of taxa. However, mobile benthic organisms like echinoids (Phylum Echinodermata) are rarely studied relative to other sedentary taxa like anemones and corals (Phylum Cnidaria). Considering the previous reports of Australian sea urchin species and their contribution to rocky reef habitats, they provide a perfect opportunity to investigate potential associative relationships with other invertebrates and fish. The long-spined sea urchin Centrostephanus rodgersii is a native species in New South Wales that is ecologically important due to their ability to modify habitats. Other ecological purposes, like symbiotic associations with other organisms are possible but remain unknown. To examine this hypothesis, our study provided a comprehensive investigation of individual C. rodgersii using observational and experimental approaches to assess the potential of symbiont-mediated sheltering by fish and invertebrates within and adjacent to the structures of C. rodgersii. We sampled C. rodgersii individuals at a site that is primarily an urchin-dominated barren, Bass point, NSW. The presence of an ‘associate’ (i.e. an organism associating with an urchin) was quantified through ten 10 m transect snorkel surveys. In addition, possible symbionts were investigated through deployment of remote underwater videos (RUV) of 32 C. rodgersii individuals for 35 min. Finally, a subset of RUV-sampled C. rodgersii were subjected to an experimental removal and artificial-urchin substitutions protocol, to decern the causal relationship between urchin presence and associates. We found a large guild of associative fauna including reef fish (primarily Lepidoblennius haplodactylos and Aspasmogaster costata), decapod crustaceans (Rhynchocinetes serratus and Pagurus lacertosus), gastropod molluscs (Astraea tentoriiformis and Turbo torquatus) and various other echinoderm species (Ophicomella spp., Phyllacanthus parvispinus and Ptilometa australis). However, the hypothesised drivers of symbiont-associative behaviour (i.e. C. rodgersii test diameter) were not significant predictors in this study. In addition, the experimental manipulation of urchin 3 presence did not influence close associations of individuals with C. rodgersii. Findings suggest that behaviours exhibited from associating individuals seem to be species dependent. Our study is novel in investigating associative behaviours of both invertebrates and fishes as symbionts of C. rodgersii, and provides strong evidence of a variety of relationships of different degrees with sea urchins. However, the nature and predictors of these relationships, as well as the specific benefits received from host and symbiont remain unclear. These findings provide a foundation to understand C. rodgersii as a biogenic ecosystem engineer and indicate the ecological importance of sea urchins beyond habitat modification.

FoR codes (2020)

310301 Behavioural ecology, 310305 Marine and estuarine ecology (incl. marine ichthyology)

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.