Date of Award

Summer 8-17-2023

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Nathalie Reyns

Committee Member

Michel Boudrias

Committee Member

Jeff Crooks

Abstract

Non-indigenous species (NIS) are often thought to have negative consequences on ecosystems. However, some NIS are ecosystem engineers, organisms that modify and/or create habitats by changing physical structure (either biogenic or abiotic), such as Amathia verticillata (previously Zoobotryon verticillatum [delle Chiaje, 1822]), a non-indigenous bryozoan with a global distribution. The role of NIS as ecosystem engineers can be complicated due to the mix of impacts that they may have on the ecosystem. Thus, the role of A. verticillata as an ecosystem engineer may shift our understanding about its ecological role on anthropogenic structures, such as docks through an urbanized area, Mission Bay, San Diego, California. A yearlong study, examining weekly A. verticillata percent cover and YSI handheld abiotic point measurements at 6 stations throughout the bay, was conducted to evaluate the spatial and temporal distribution of A. verticillata colonies and environmental conditions from July 2021 to July 2022. Bimonthly and weekly A. verticillata samples were collected to identify the associated marine invertebrate community. In addition, a one-month experiment was conducted in the bay to further explore how structure impacts the development of the marine invertebrate community assemblages within A. verticillata. To isolate the structural component of A. verticillata from other possible living organism effects, mimics of A. verticillata were constructed from clear silicone tubing and glue. Two morphotypes (compact: denser, bushy morphotype, less than 25 cm; elongated: longer, wispy morphotype, longer than 25 cm) were created based on field observations of A. verticillata colonies in Mission Bay. We compared these mimics to live A. verticillata colonies collected during the same sample period. In general, the western region of Mission Bay near the inlet experienced more stable abiotic conditions, less A. verticillata percent cover, and a more diverse invertebrate community compared to the eastern region. The eastern region had higher temperatures, salinity, and A. verticillata percent cover. Overall, A. verticillata housed an abundant and diverse group of marine invertebrates with a total of 25 different identified families. There were 15 organisms identified to species, with more native isopods found in the eastern region, and more non-indigenous amphipods in the western region; however, there was no significant difference between the invertebrate community associated with A. verticillata in the western and eastern regions. All history life stages, including females with eggs, were found residing in A. verticillata. The mimics showed similar patterns with invertebrate counts, but the composition of the community differed between mimics and live colonies. Additionally, we examined how invertebrate community diversity varied based on A. verticillata morphotype and structural complexity (defined by the colony dry weight: low < 0.5 g, medium > 0.5-5 g, and high > 5 g) by comparing their Shannon-Weiner indices. The invertebrate abundance and diversity increased with structural complexity, which suggests that A. verticillata structure is important. Furthermore, our results suggest that this bryozoan may be acting as a nursery habitat for other organisms, but additional research is needed to better understand if it disproportionately supports other NIS or native species.

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