2020 publications (links to each paper available at Read More)

Environmental controls on the geochemistry of a short-lived bivalve in Southeastern Australian estuaries

Chamberlayne, BK, JJ Tyler, BM Gillanders. 2020. Estuaries and Coasts

Geochemical signals in bivalve carbonate hold the potential to record environmental change over timescales from months to centuries; however, not all bivalves provide reliable proxy records, and modern studies are essential to calibrate these relationships prior to use in palaeo-environmental reconstruction. In this study, 19 shells of the estuarine bivalve Arthritica helmsi, from 14 sites in Southeastern Australia, were obtained from museum collections and analysed for trace elemental (Sr/Ca,Mg/Ca, Sr/Li and Ba/Ca) and stable isotopic ratios (18O/16O and 13C/12C). Mean Sr/Ca and Mg/Ca exhibited significant negative correlations to temperature (R2 = 0.49, p = 0.001; R2 = 0.25, p = 0.02) in agreement with previously published models for trace element partitioning into inorganic aragonite. In addition, the within-shell range of Sr/Ca and Mg/Ca, as measured by laser ablation ICPMS, correlated to the temperature range (R2 = 0.22, p = 0.03; R2 = 0.46, p = 0.002, respectively). Sr/Li ratios were also negatively correlated to temperature (R2 = 0.34, p = 0.008); however, a significant difference in the model coefficients with previous studies

indicates this proxy should be applied with caution. Both oxygen and carbon isotope values exhibited large differences between shells from terrestrial, estuarine and marine waters, suggesting that these stable isotopes hold a potential to record large environmental changes such as sea-level changes or freshening/salinisation in estuarine environments. This study presents the first geochemical study of Arthritica helmsi, highlighting its potential as an environmental tracer.

 

Images: Briony Chamberlayne

Top graphic: Alice Jones; bottom image: Bronwyn Gillanders

Estimating mangrove tree biomass and carbon content: a comparison of forest inventory techniques and drone imagery

Jones, AR, RR Segaran, K Clarke, M Waycott, WSH Goh, BM Gillanders. 2020. Frontiers in Marine Science

Mangroves provide many ecosystem services including a considerable capacity to.sequester and store large amounts of carbon, both in the sediment and in the above-ground biomass. Assessment of mangrove above-ground carbon stock relies on accurate measurement of tree biomass, which traditionally involves collecting direct measurements from trees and relating these to biomass using allometric relationships. We investigated the potential to predict tree biomass using measurements derived from unmanned aerial vehicle (UAV), or drone, imagery. This approach has the potential to dramatically reduce time-consuming fieldwork, providing greater spatial survey coverage and return for effort, and may enable data to be collected in otherwise hazardous or inaccessible areas. We imaged an Avicennia marina (gray mangrove) stand using an RGB camera mounted on a UAV. The imaged trees were subsequently felled, enabling physical measurements to be taken for traditional biomass estimation techniques, as well as direct measurements of biomass and tissue carbon content. UAV image-based tree height measurements were highly accurate (R2 = 0.98). However, the variables that could be measured from the UAV imagery (tree height and canopy area) were poor predictors of tree biomass. Using the physical measurement data, we identified that trunk diameter is a key predictor of A. marina biomass. Unfortunately, trunk diameter cannot be directly measured from the UAV imagery, but it can be predicted (with some error) using models that incorporate other UAV image-based measurements, such as tree height and canopy area. However, reliance on second-order estimates of trunk diameter led to increased uncertainty in the subsequent predictions of A. marina

biomass, compared to using physical measurements of trunk diameter taken directly

from the trees. Our study demonstrates that there is potential to use UAV-based

imagery to measure mangrove A. marina tree structural characteristics and biomass.

Further refinement of the relationship between UAV image-based measurements and tree diameter is needed to reduce error in biomass predictions. UAV image-based estimates can be made far more quickly and over extensive areas when compared to traditional data collection techniques and, with improved accuracy through further model-calibration, have the potential to be a powerful tool for mangrove biomass and carbon storage estimation.

 

Graphic: Kelsey Kingsbury

Range-extending coral reef fishes trade-off growth for maintenance of body condition in cooler waters.

Kingsbury, KM, BM Gillanders, DJ Booth, EOC Coni, I Nagelkerken. 2020. Science of the Total Environment

As ocean waters warm due to climate change, tropical species are shifting their ranges poleward to remain within their preferred thermal niches. As a result, novel communities are emerging in which tropical species interact with local temperate species, competing for similar resources, such as food and habitat. To understand how range-extending coral reef fish species perform along their leading edges when invading temperate ecosystems, we studied proxies of their fitness, including somatic growth (length increase), feeding rates, and body condition, along a 730-km latitudinal gradient situated in one of the global warming hotspots. We also studied co-occurring temperate species to assess how their fitness is affected along their trailing edges under ocean warming. We predicted that tropical fishes would experience reduced performance as they enter novel communities with suboptimal environmental conditions. Our study shows that although tropical fish maintain their body condition (based on three proxies) and stomach fullness across all invaded temperate latitudes, they exhibit decreased in situ growth rates, activity levels, and feeding rates in their novel temperate environment, likely a result of lower metabolic rates in cooler waters. We posit that tropical fishes face a growth–maintenance trade-off under the initial phases of ocean warming (i.e. at their leading edges), allowing them to maintain their body condition in cooler temperate waters but at the cost of slower growth. Temperate fish exhibited no distinct patterns in body

condition and performance along the natural temperature gradient studied. However, in the face of future climate change when metabolism is no longer stymied by low water temperatures, tropical range-extending species are likely to approach their native-range growth rates along their leading edges, ultimately leading to increased

competitive interactions with local species in temperate ecosystems.

 

Graphic: Kelsey Kingsbury

Trophic niche segregation allows range-extending coral reef fishes to co-exist with temperate species under climate change

Kingsbury, KM, BM Gillanders, DJ Booth, I Nagelkerken. 2020. Global Change Biology.

Changing climate is forcing many terrestrial and marine species to extend their ranges poleward to stay within the bounds of their thermal tolerances. However, when such species enter higher latitude ecosystems, they engage in novel interactions with local species, such as altered predator–prey dynamics and competition for food. Here, we evaluate the trophic overlap between range‐extending and local fish species along the east coast of temperate Australia, a hotspot for ocean warming and species range extensions. Stable isotope ratios (δ15N and δ13C) of muscle tissue and stomach content analysis were used to quantify overlap of trophic niche space between vagrant tropical and local temperate fish communities along a 730 km (6°) latitudinal gradient. Our study shows that in recipient temperate ecosystems, sympatric tropical and temperate species do not overlap significantly in their diet—even though they forage on broadly similar prey groups—and are therefore unlikely to compete for trophic niche space. The tropical and temperate species we studied, which are commonly found in shallow‐water coastal environments, exhibited moderately broad niche breadths and local‐scale dietary plasticity, indicating trophic generalism. We posit that because these species are generalists, they can co‐exist under current climate change, facilitating the existence of novel community structures.

 

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