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Sci Rep
2015 May 20;5:10349. doi: 10.1038/srep10349.
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The up-scaling of ecosystem functions in a heterogeneous world.
Lohrer AM
,
Thrush SF
,
Hewitt JE
,
Kraan C
.
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Earth is in the midst of a biodiversity crisis that is impacting the functioning of ecosystems and the delivery of valued goods and services. However, the implications of large scale species losses are often inferred from small scale ecosystem functioning experiments with little knowledge of how the dominant drivers of functioning shift across scales. Here, by integrating observational and manipulative experimental field data, we reveal scale-dependent influences on primary productivity in shallow marine habitats, thus demonstrating the scalability of complex ecological relationships contributing to coastal marine ecosystem functioning. Positive effects of key consumers (burrowing urchins, Echinocardium cordatum) on seafloor net primary productivity (NPP) elucidated by short-term, single-site experiments persisted across multiple sites and years. Additional experimentation illustrated how these effects amplified over time, resulting in greater primary producer biomass (sediment chlorophyll a content) in the longer term, depending on climatic context and habitat factors affecting the strengths of mutually reinforcing feedbacks [corrected]. The remarkable coherence of results from small and large scales is evidence of real-world ecosystem function scalability and ecological self-organisation. This discovery provides greater insights into the range of responses to broad-scale anthropogenic stressors in naturally heterogeneous environmental settings.
Figure 1. Net Primary Production (NPP) measured in benthic incubation chambers deployed at 5 sites in the Mahurangi Harbour-Kawau Bay study region. (A) The general positive relationship between Echinocardium density and NPP observed during the first summer of sampling; nâ=â16 replicates from each of 5 sites sampled between Dec 2006 and Feb 2007. (B) Echinocardium vs NPP with all of the data from two consecutive summers of sampling included; open symbols are replicates from the second summer of sampling. (C) Bivariate scatterplot of site averages. The remaining panels show average NPP at a site versus (D) light levels measures at the seabed, (E) the temperature of the bottom water, and (F) the content of Chla in the sediment.
Figure 2. Benthic microalgal standing stock (sediment Chla content) vs Echinocardium density in unmanipulated sediments. (A) All available data. (B) The slopes of relationships during 14 individual sampling occasions from 8 sites. (C) Muddy vs sandy sites, above and below 15% average mud content, respectively. (D) Three parts of Mahurangi Harbour, with turbidity generally increasing between Mouth and Upper. (E-F) Plots of averaged Echinocardium density and Chla values. (G-H) The potential influences of environmental factors on sediment Chla content.
Figure 3. Experimental results from benthic incubation chambers deployed to depths of 17âm (triangles), 11âm (squares) and 5âm (diamonds). (A) Echinocardium vs NPP, which is dissolved oxygen flux in sunlit benthic chambers. (B) Echinocardium vs TOU, which is total oxygen utilization measured at night in dark incubation chambers. (C) Echinocardium vs gross primary production, or GPP, the oxygen produced in the light discounted by the amount of oxygen utilised in the absence of light. (D) The relationship between photosynthetically active radiation (PAR) and sediment Chla content; both variables decreased with depth. (E) Echinocardium density vs Chla. (F) Echinocardium vs GPP/Chla, which is the rate of gross primary production per unit of Chla. The efficiency of the microphytobenthos in producing oxygen increases with decreasing water depth (or factors correlated with depth).
Figure 4. Bivariate plots depicting relationships between Echinocardium density, numbers of macrofauna taxa, and sediment granulometry. (A) Echinocardium vs macrofaunal richness. (B) Echinocardium vs the percentage of sediment particle sizes >250âμm. (C) The percentage of sediment particle sizes >250âμm vs macrofaunal richness. In all panels, significant 90th percentile quantile regression lines (with 95% confidence intervals in grey shading) are drawn.
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