Port Curtis Seagrass Seed Bank Density and Viability Studies - final report

Reason, C.L., Rasheed, M.A., Carter, A.B., and Jarvis, J.C. (2017) Port Curtis Seagrass Seed Bank Density and Viability Studies - final report. Report. James Cook University, Cairns, QLD, Australia.

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Abstract

Seagrass seeds and seed banks (seeds stored in sediments) are important in maintaining seagrass populations and their capacity to recover from impacts. Despite their importance, longer-term studies incorporating assessments of seed bank viability are rare and we have little information on how seed banks vary temporally or spatially in their distribution and viability, particularly for tropical and sub-tropical species. This study provides important insights into the seasonal and inter-annual changes in seed bank density and viability, and the implications for local seagrass resilience in Port Curtis and Rodds Bay. The results add substantially to the current knowledge of seagrass seed bank dynamics.

The report details findings from a three year study examining seed bank dynamics for the seagrass Zostera muelleri subsp. capricorni in Port Curtis and Rodds Bay. Results show that a Z. muelleri seed bank was generally present across all sites and times examined, however, temporal trends in seed bank density differed between sites and did not always follow expected seasonal patterns. In addition, viability assessments found that the available seed bank was substantially lower than total seed numbers would suggest, and at times, some sites had no viable seeds present. Viable seeds tended to be located deeper below the sediment surface potentially making them less available for germination and the proportion of the total seed bank that was viable varied considerably between and within sites and over time.

The study highlights the complexity of seed bank dynamics in Port Curtis and Rodds Bay and demonstrates that quantifying resilience requires moving beyond counting densities of seeds to including temporal measurements of seed bank viability. The results provide evidence for the presence of viable seed banks throughout the three year study that are likely to play an important role in conferring resilience to local seagrass meadows. The presence of viable seeds in meadows where no local seed production had been recorded for several years indicates that dispersal of propagules between meadows and sites was likely to be an important process in shaping Port Curtis and Rodds Bay seed banks.

The maintenance of some viable seeds throughout the study meant Port Curtis Z. muelleri meadows were well placed to deal with large-scale impacts and had a pathway to recover from meadow scale losses if these viable seeds were to germinate. However, a substantial decline in viable seeds at the end of the program in 2017 was concerning, particularly if seed banks are not replenished during the 2017 seagrass growing season. This result combined with record lows in area and abundance for the largest Z. muelleri meadow in Port Curtis suggests that at the end of the study, levels of resilience for some Port Curtis and Rodds Bay meadows were reduced.

The results of this study provide a strong case for the inclusion of assessments of the seed bank that incorporate viability assessment as part of routine seagrass monitoring programs. The low and variable proportion of total seed numbers that were actually viable show that total seed counts alone, will not necessarily provide a true understanding of the state of seed banks. Quantifying these seed bank dynamics is particularly important to gain a clear picture of seagrass meadow resilience given that losses of seagrasses at meadow or larger scales will be reliant on seeds for their recovery.

Item ID: 70855
Item Type: Report (Report)
Keywords: seagrass, Gladstone, seed bank, monitoring
Copyright Information: © Gladstone Ports Corporation and James Cook University, 2017.
Funders: Gladstone Ports Corporation Limited Ecosystem Research and Monitoring Program
Date Deposited: 17 Nov 2021 01:16
FoR Codes: 41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410402 Environmental assessment and monitoring @ 100%
SEO Codes: 18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180201 Assessment and management of coastal and estuarine ecosystems @ 100%
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