Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Connolly, Rod M.; Waltham, Nathan J.

doi:10.1890/es14-00243.1

Cited by 41 publications

(17 citation statements)

References 64 publications

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“…Overall, there is strong evidence that a light-mediated process and CO 2 limitation drive enrichment of M. pyrifera d 13 C. In the field, we observed that depth, position relative to the kelp bed, and upwelling are strong predictors of d 13 C. Resolving these fine spatial and seasonal drivers of d 13 C variation could give us power similar to that of compoundspecific stable isotope analyses, allowing us to relate d 13 C signatures to microhabitats (Finlay et al 1999;Gillies et al 2011;Connolly and Walthan 2015;Mcmahon et al 2015;McPherson et al 2015). There are many species of young fishes and larval/adult invertebrates that exclusively inhabit the kelp forest canopy; conversely, there are also a substantial subset of species that live their adult lives strictly near or on the seafloor (Ebeling et al 1978;Bernstein and Jung 1979;Coyer 1979;Watanabe 1984;Demartini and Roberts 1990;Hartney 1996).…”

Section: Sourcementioning

confidence: 73%

Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera

Drobnitch

Pochron

Miranda

2017

Limnology & Oceanography

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The giant kelp Macrocystis pyrifera is a major primary producer and supports species‐rich and productive marine communities on temperate coastlines. The δ13C signature of M. pyrifera tissue is an important potential tool for understanding species interactions within nearshore trophic networks. However, in macroalgae, δ13C can vary widely, and M. pyrifera can differ up to 6‰ within a single individual, greatly complicating the designation of a primary end member in isotope mixing models. Abiotic factors such as irradiance, dissolved inorganic carbon concentration, water motion, and water temperature can drive δ13C variation, either by altering the supply of total CO2 available to individual tissues, or by inducing facultative carbon concentrating mechanisms. In this study, we combine a controlled laboratory experiment with field sampling to better understand and predict the abiotic drivers of δ13C signatures in M. pyrifera tissues. In the field, data revealed strong correlations between δ13C signatures and depth, as well as season and location within a kelp bed. Experimental data demonstrated that the δ13C of incubated tissue was strongly driven by irradiance but not flow velocity, suggesting that enrichment in M. pyrifera tissue is the result of a light‐induced metabolic process. We also confirmed a physiological δ13C enrichment process associated with photosynthate transport. These results facilitate understanding and prediction of the variation in δ13C observed in the field, and inform interpretations of δ13C signatures in trophic analyses and community interaction studies.

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Section: Sourcementioning

confidence: 73%

Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera

Drobnitch

Pochron

Miranda

2017

Limnology & Oceanography

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“…Although the proportion of epiphytes contributing to food webs did not change, these findings allude to the notion that greater surface area in seagrass meadows leads to higher availability of epiphytes, which in turn could support a larger community of animals. The importance of epiphytes has been demonstrated in seagrass food webs previously (Bologna and Heck , Moncrieff and Sullivan , Connolly and Waltham ), and herbivorous species are known to prefer leaves covered in epiphytes (Marco‐Méndez et al. ).…”

Section: Discussionmentioning

confidence: 91%

Habitat complexity influences the structure of food webs in Great Barrier Reef seagrass meadows

et al. 2019

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Structural habitat complexity is a fundamental attribute influencing ecological food webs. Simplification of complex habitats occurs due to both natural and anthropogenic pressures that can alter productivity of food webs. Relationships between food web structure and habitat complexity may be influenced by multiple mechanisms, and untangling these can be challenging. We investigated whether (1) size spectra vary across a gradient of habitat complexity in seagrass meadows and (2) structural complexity changes the importance of different primary producers supporting the food web (determined using stable isotope analysis) in the Great Barrier Reef World Heritage Area. We found that moderately complex meadows had much steeper size spectra slopes, caused by a higher abundance of smaller animals and fewer larger animals, while meadows on either end of the complexity scale (low and a single meadow with very high complexity) had shallower slopes, indicative of a more balanced distribution of animal sizes across the spectrum. We also found that the importance of epiphytic algae as a food source was high in most meadows, despite the increase in seagrass surface area on which epiphytes could grow. The consistent importance of epiphytic algae suggests that the changes in the availability of different potential food sources did not affect food web structure. Our findings indicate that food web structure may change with variations in structural complexity because of changes in the abundance of smaller and/or larger animals. Food web structure and food sources are important determinants of the dynamic stability of food webs. Size spectra analysis is already used as a monitoring tool for assessing populations of key fisheries species in commercial fishing operations, and thus, we recommend using size spectra as a proxy for assessing the structure of the food webs in different types of seagrass meadows. Size spectra may be a useful indicator of how different meadows provide for ecosystem services such as fisheries.

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“…An additional hypothesis for the discrepancies between our results and previous studies could also be due to limitations in the ability of stable isotope analyses to distinguish among contributing organic matter sources. As discussed, the number of potential sources of OC in Moreton Bay is large with stable isotope values of 13 C and 15 N of seagrass overlapping with other potential sources, such as C4 vegetation and epiphytic algae (Connolly and Waltham ), which can lead to uncertainties and underetimation of seagrass contributions in mixing model solutions (Fry ). The low taxonomic detail in these previous stable isotope models compared to our use of eDNA could be an additional reason why we found significantly higher autochotonous contributions to seagrass sediment organic matter than those using isotopic modelling.…”

Section: Discussionmentioning

confidence: 99%

Using eDNA to determine the source of organic carbon in seagrass meadows

Reef

Atwood

Samper‐Villarreal

et al. 2017

Limnology & Oceanography

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Seagrasses sequester globally significant amounts of carbon (C), which is stored mainly in the sediment. Both C fixation by the seagrass (autochthonous) and the trapping of organic matter that is derived from outside the ecosystem (allochthonous) contribute to seagrass sediment organic C (OC). However, due to limitations in current methods we do not yet fully understand which sources of C are most important to blue C ecosystems. We used environmental-DNA (eDNA) to identify and estimate the contribution of floral sources to seagrass sediment OC sampled from three sites in Moreton Bay, Australia that differ in potential levels of autochthonous and allochthonous OC inputs. Using the plant barcode gene rbcL and a next-generation sequencing platform we identified 150 plant operational taxonomic units in the sediment samples. We found that seagrass DNA composed on average 88% of the eDNA pool in the sediment samples. Allochtonous sources were primarily mangrove, saltmarsh, and freshwater marsh species, but the proportional contribution of other sources varied among meadows. Carbon and nitrogen (N) stable isotope mixing models suggested a lower autochthonous contribution than the eDNA data, but had high ambiguity due to indistinguishable isotopic values among some of the sources. Our study shows that eDNA can be an effective tool for identifying sources to sediment OC in blue C ecosystems and can be used in conjunction with stable isotope analysis to reduce ambiguity. Identifying the sources of OC to the sediments of blue C ecosystems is crucial for building robust and accurate C budgets for these systems.

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Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Cited by 41 publications

References 64 publications

Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera

Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera

Habitat complexity influences the structure of food webs in Great Barrier Reef seagrass meadows

Using eDNA to determine the source of organic carbon in seagrass meadows

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Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Cited by 41 publications

References 64 publications

Patterns and drivers of δ13C variation in the giant kelp, Macrocystis pyrifera

Patterns and drivers of δ13C variation in the giant kelp, Macrocystis pyrifera

Habitat complexity influences the structure of food webs in Great Barrier Reef seagrass meadows

Using eDNA to determine the source of organic carbon in seagrass meadows

Contact Info

Product

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Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera

Patterns and drivers of δ¹³C variation in the giant kelp, Macrocystis pyrifera