The influence of Macomona liliana and Macroclymenella stewartensis on rugosity based on density and distribution within Whangateau Harbour, New Zealand
The influence of Macomona liliana and Macroclymenella stewartensis on rugosity based on density and distribution within Whangateau Harbour, New Zealand
Abstract
This study explores the influence of benthic species on sandflat rugosity across Whangateau Harbour, New Zealand, providing insights into potential ecosystem and environmental changes. The potential drivers of species distribution and densities are explored, considering sediment suitability, food availability, and competition. Macomona liliana, a deposit-feeding bivalve, creates distinctive footprint-like patterns, while Macroclymenella stewartensis modifies the sandflat topography, creating mound-like structures through excrement expulsion. Data via drone mapping collected from 2021 contributes to understanding the relationship between species distribution, densities and surface rugosity. Results reveal that M. liliana exhibits a wider distribution across sandflats than M. stewartensis, with areas of species overlap observed where M. stewartensis is most abundant. Higher counts of M. liliana footprints correlate with increased rugosity, while greater prevalence of M. stewartensis mounds coincides with decreased rugosity, establishing a significant correlation (p-value < 0.05, R² = 0.41). M. liliana's wide dispersal is attributed to various factors, including benthic flux and feeding behaviour. In contrast, M. stewartensis clusters are linked to sediment conditions. The findings underscore the importance of considering these species' roles in shaping environments and highlight potential implications for ecosystem management and conservation.
1. Introduction
The intertidal sandflats of Whangateau Harbour, New Zealand, are rich in biodiversity. Among the benthic species, Macomona liliana and Macroclymenella stewartensis play crucial roles in shaping the ecosystem, particularly influencing surface rugosity. These species create distinctive microstructures, allowing density and distribution estimations without disturbing the sediment. M. liliana, a deposit-feeding bivalve, extends a siphon through the sediment surface, leaving footprint-like patterns (Lelieveld et al., 2004). Conversely, M. stewartensis impacts the sandflat's topography by expelling excrement through the surface, resulting in smooth mounds (Schenone et al., 2019). Understanding the interactions between the abundance, distribution, and behaviour of M. liliana and M. stewartensis on sandflat rugosity provides insights into the potential ecosystem and environmental changes. By creating sediment structures such as holes, mounds, and burrows, these organisms assist in substrate and oxygenated water exchange, enhancing vertical and horizontal transportation of nitrogen and carbon (Wang et al., 2010). On February 2, 2024, students of Marine 305 from the University of Auckland participated in this study, with the hypothesis that sandflat rugosity increased where greater influences of topographic disturbance were present.
2. Methods and Materials
Students utilised two 25x25cm quadrats positioned diagonally to sample the diverse structures across the sandflats. Using video cameras (mobile phones), we recorded footage of the sample area, alongside counting present structures, including mounds, footprints and holes. Using VLC and Meshroom, we extracted frames from the videos and generated high-resolution 3D maps of the sampled areas. These models provided a comprehensive visualisation of the structures and rugosity of the sandflats of Whangateau Harbour.While this report does not discuss the results obtained from these specific samples, data collected from drones employed in 2021 mapping the harbour's topography is analysed. These maps provided an estimation of distribution and densities, identifying mounds and footprints within the sampled areas.3. Results
M. liliana exhibited a greater distribution across the sandflat than M. stewartensis, both laterally and longitudinally (Fig. 1a - b). While M. stewartensis showed less distribution, the areas of abundance appeared denser than those of M. liliana. Species overlap were primarily observed in regions where M. stewartensis showed higher abundance (Fig. 1c).
Where M. liliana displayed higher counts of footprints, M. stewartensis displayed fewer mounds, resulting in increased rugosity (Fig. 2). Conversely, areas with reduced footprints and higher mounds exhibited lower rugosity. A direct correlation emerged between the abundance of M. liliana and increased rugosity, while a higher prevalence of M. stewartensis coincided with decreased rugosity. The p-value of footprints multiplied by mounds (FxM) was <0.05 at 0.0013, while R² = 0.41.
Fig 1. A map of estimated abundance and distribution of M. liliana and M. stewartensis across the sandflat of Whangateau Harbour, New Zealand, in February 2024. A = Recorded footprints by M. liliana, B = Recorded mounds by M. stewartensis, C = Overlap of both. Maps were created using drone images (Schenone & Thrush, 2020).
Fig 2. Interaction analysis and rugosity between M. liliana (footprints) and M. stewartensis (mounds) across the sandflat of Whangateau Harbour, New Zealand. Rugosity ranges from lowest (0-0.05) to highest (0.1-0.15). 4. Discussion
4.1. Abundance, distribution and overlap
With M. liliana exhibiting greater distribution across the sandflat, this could be due to unfavourable conditions such as sediment suitability, food availability, competing species and predators, causing wider dispersal (Lundquist et al., 2004). However, juveniles are restricted to 1cm below the sediment surface, causing dispersal via bedload, which was observed by abundance within bedload traps (Commito et al., 1995). Additionally, dispersal can be attributed to the benthic flux and feeding behaviour of M. liliana, with the release of byssal threads and surface emergence via siphoning, resulting in migration through the water column (Cummings et al., 1993). While our findings do not determine the age of M. liliana we observed, instead focusing on visible microstructures (footprints), it is feasible that wider dispersal patterns are attributed to these behaviours. Furthermore, the low-density areas of M. liliana can be attributed to mud presence, with this species showing reduced densities in muddier sediments (Pratt et al., 2013).
With M. stewartensis showing contrasting dispersal patterns, these denser clusters may be attributed to sediment deposition across the sandflat. Thick deposits (>1cm) have been observed to disrupt habitats, while thinner deposits (<1cm) can modify organism behaviour, potentially leading to changes in dispersal patterns and benthic fluxes (Schenone et al., 2019). It is feasible that in the areas where M. stewartensis density is high, favourable sediment conditions are present.
When we consider instances of species overlap, particularly in regions where M. stewartensis demonstrates higher densities, this questions potential drivers of these species' coexistence. M. liliana may be better equipped to thrive in a broader range of conditions than M. stewartensis, which could be justified by the extensive distribution range. Additionally, M. stewartensis has been observed to have small-scale heterogeneity (Thrush et al., 1989), otherwise characterised as local-level distributors.4.2. Correlation of rugosity, species abundance and distribution
The increased rugosity observed in areas dominated by M. liliana, characterised by higher footprint counts, indicates a correlation between sandflat rugosity and species activity. The footprints made by M. liliana alter the sediment surface, creating rougher topography (Schenone & Thrush, 2020). In contrast, M. stewartensis creates a flatter surface during excretion, hence the lower rugosity in areas where this species is more abundant. These findings can explain the relationship between rugosity and the abundance of M. liliana and M. stewartensis, where rugosity changes based on species densities. Our observations are further supported by the FxM p-value of <0.05, showing the statistical significance of our data and proving our hypothesis. Furthermore, an R² value of 0.41 indicates that 41% of our data can be explained by the independent variable (species densities) and the dependent variable (rugosity).
4.3. Conclusions
The results of this study strongly support the hypothesis that sandflat rugosity is influenced by the abundance and distribution of Macomona liliana and Macroclymenella stewartensis in Whangateau Harbour. With a significant correlation between species’ structures and rugosity, our findings highlight these species' distinct roles in shaping the sandflat topography. Our study emphasises the importance of understanding individual species' roles in shaping environments alongside the observed relationships.References
Commito, J. A., Thrush, S. F., Pridmore, R. D., Hewitt, J. E., & Cummings, V. J. (1995). Dispersal dynamics in a wind‐driven benthic system. Limnology and Oceanography, 40(8), 1513–1518. https://doi.org/10.4319/lo.1995.40.8.1513Cummings, V. J., Pridmore, R. D., Thrush, S. F., & Hewitt, J. E. (1993). Emergence and floating behaviours of post‐settlement juveniles ofMacomona liliana(Bivalvia: Tellinacea). Marine Behaviour and Physiology, 24(1), 25–32. https://doi.org/10.1080/10236249309378875Lelieveld, S. D., Pilditch, C. A., & Green, M. O. (2004). Effects of deposit‐feeding bivalve(macomona liliana)density on intertidal sediment stability. New Zealand Journal of Marine and Freshwater Research, 38(1), 115–128. https://doi.org/10.1080/00288330.2004.9517223Lundquist, C. J., Pilditch, C. A., & Cummings, V. J. (2004). Behaviour controls post-settlement dispersal by the juvenile bivalves Austrovenus stutchburyi and Macomona liliana. Journal of Experimental Marine Biology and Ecology, 306(1), 51–74. https://doi.org/10.1016/j.jembe.2003.12.020Pratt, D. R., Lohrer, A. M., Pilditch, C. A., & Thrush, S. F. (2013). Changes in ecosystem function across sedimentary gradients in estuaries. Ecosystems, 17(1), 182–194. https://doi.org/10.1007/s10021-013-9716-6Schenone, S., O’Meara, T., & Thrush, S. F. (2019). Non-linear effects of macrofauna functional trait interactions on biogeochemical fluxes in marine sediments change with environmental stress. Marine Ecology Progress Series, 624, 13–21. https://doi.org/10.3354/meps13041Schenone, S., & Thrush, S. F. (2020). Unraveling ecosystem functioning in intertidal soft sediments: the role of density-driven interactions. Scientific Reports, 10(1). https://doi.org/10.1038/s41598-020-68869-4Schenone, S., & Thrush, S. F. (2022). Scaling-up ecosystem functions of coastal heterogeneous sediments: testing practices using high resolution data. Landscape Ecology, 37(6), 1603–1614. https://doi.org/10.1007/s10980-022-01447-3Thrush, S. F., Hewitt, J., & Pridmore, R. D. (1989). Patterns in the spatial arrangements of polychaetes and bivalves in intertidal sandflats. Marine Biology, 102(4), 529–535. https://doi.org/10.1007/bf00438355Wang, J. Q., Zhang, X. D., Jiang, L., Bertness, M. D., Fang, C., Chen, J. K., Hara, T., & Li, B. (2010). Bioturbation of burrowing crabs promotes sediment turnover and carbon and nitrogen movements in an estuarine salt marsh. Ecosystems, 13(4), 586–599. https://doi.org/10.1007/s10021-010-9342-5
