Date of Award
2024
Document Type
Thesis
Publisher
Edith Cowan University
Degree Name
Master of Science by Research
School
School of Science
First Supervisor
Professor Glenn Hyndes
Second Supervisor
Professor Paul Lavery
Abstract
Seascapes are connected through the transfer of energy from the movement of fauna, detritus, and nutrients among habitats. This exchange of resources can influence food web dynamics in the recipient system, increasing productivity and biodiversity, thus creating spatial subsidies. Spatial subsidies are usually characterised by the transfer of resources from highly productive donor systems to lower productive recipient systems. However, recent work suggests that recipient systems with comparably high productivity, such as seagrass meadows, may benefit from spatial subsidies. Kelp is regularly eroded from reefs and provides a vector for nutrient and detrital transfer to seagrass meadows, where it can increase nutrient and food availability and potentially increase growth and production of mesograzers. This study investigated the effects of detrital kelp as a subsidy to seagrass-inhabiting mesograzers, and aimed to determine whether any effects of kelp were a result of food and/or habitat provision.
A field experiment was completed to investigate the role of kelp in supporting mesograzers in Posidonia meadows, exploring whether its presence influences mesograzers via food provision and/or habitat availability through the addition of artificial and aged detrital kelp into these seagrass meadows. Results from the experiment demonstrated that the presence of detrital kelp enhanced the densities of gastropods and shrimps, and in addition, identified that some gastropods benefit from kelp as a nutrient source whilst shrimp utilize kelp for its increased habitat complexity as demonstrated by higher densities and biomass in both detrital and artificial kelp treatments. Additionally, the experiment highlighted the significance of kelp-derived nutrients in supporting the recruitment of juvenile gastropods. These results underscore the dual role of detrital kelp as a habitat and food source for mesograzers, thereby acting as an important trophic subsidy in seagrass meadows.
Four field surveys were conducted at three sites to assess the variability in seagrass associated mesograzers in relation to detrital inputs over time in Posidonia meadows. Gastropod assemblages were dominated by a few very abundant species, and were found in all times, with peak densities observed in March and higher biomass observed in September. In comparison, shrimp were not present at all times and were found in much lower densities compared to gastropods. Detrital kelp was identified as a iii transient and patchy resource which may not always be available as a trophic subsidy to mesograzers, however, future studies are required to gain a better understanding of the availability of kelp as a vector in seagrass meadows.
Overall, the results from this study emphasise the role that detrital kelp has as a trophic subsidy in seagrass meadows and imply mesograzer productivity could be significantly impacted as kelp declines globally. Climate change is causing large scale losses of kelp productivity and biomass globally and is predicted to increase over time, which could have negative impacts on food webs and productivity in recipient seagrass meadows. Thus, this study highlights the necessity of understanding trophic connectivity across seascapes for effective management of coastal ecosystems.
DOI
10.25958/xtbn-1r29
Access Note
Access to this thesis is embargoed until 8 December 2025.
Recommended Citation
Billinghurst, J. (2024). The food and habitat effects of detrital kelp as a trophic subsidy to seagrass-inhabiting mesograzers. Edith Cowan University. https://doi.org/10.25958/xtbn-1r29