Invasive alien aquatic plant species management drives aquatic ecosystem community recovery: An exploration using stable isotope analysis
- Authors: Motitsoe, Samuel N , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423527 , vital:72069 , xlink:href="https://doi.org/10.1016/j.biocontrol.2022.104995"
- Description: The socio-economic and ecological impacts of invasive alien aquatic plant (IAAP) species have been well studied globally. However less is known about ecosystem recovery following the management of IAAP species. This study employed a before-after study design to investigate ecological recovery following the management of Salvinia molesta D.S. Mitchell, at four field sites in South Africa. We hypothesized that the presence of S. molesta would have a negative impact on the ecosystem food web structure, and that following S. molesta control, the systems would show positive ecosystem recovery. Aquatic macroinvertebrate and macrophyte samples collected before and after mechanical or biological control of S. molesta, were analysed for δ13C and δ15N stable isotopes. Salvinia molesta infestations negatively impacted the food web structure, indicated by reduced food chain length, trophic diversity and basal resources. This represented an altered aquatic food web structure, that in some cases, led to the collapse of the aquatic community. In contrast, after either mechanical or biological control, there were increases in food chain length, trophic diversity and abundance of energy resources accessed by consumers, indicating improved food web structure. Although the study showed positive ecosystem recovery following control, we noted that each control method followed a different recovery trajectory. We conclude that S. molesta invasions reduce aquatic biodiversity and alter ecosystem trophic dynamics and related ecosystem processes, necessitating control.
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- Date Issued: 2022
A missing link in the estuarine nitrogen cycle?: coupled nitrification-denitrification mediated by suspended particulate matter
- Authors: Zhu, Weijing , Wang, Cheng , Hill, Jaclyn M , He, Yangyang , Tao, Bangyi , Mao, Zhihua , Wu, Weixiang
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68368 , vital:29244 , https://0-doi.org.wam.seals.ac.za/10.1038/s41598-018-20688-4
- Description: In estuarine and coastal ecosystems, the majority of previous studies have considered coupled nitrification-denitrification (CND) processes to be exclusively sediment based, with little focus onsuspended particulate matter (SPM) in the water column. Here, we present evidence of CND processes in the water column of Hangzhou Bay, one of the largest macrotidal embayments in the world.
- Full Text:
- Date Issued: 2018
Baseline isotopic data for Wolffia spp.: another option for tracing N-loading in freshwater systems?
- Authors: Hill, Jaclyn M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68721 , vital:29308 , https://0-doi.org.wam.seals.ac.za/10.1086/696126
- Description: δ15N values of aquatic plants can reflect anthropogenic N loading. Recent work suggests the duckweed Spirodela spp. effectively maps N loading in freshwater ecosystems, but its use may be complicated by a cyanobacterium–duckweed symbiosis that could reduce its utility in low-nutrient environments. I aimed to evaluate the potential of a 2nd duckweed species Wolffia spp., which lacks a cyanobacterial symbiosis, for use in pollution monitoring in freshwater ecosystems. I used a series of laboratory experiments to investigate δ15N equilibration rates and concentration-level effects of single-source N solutions in plant tissue over 16 d to provide baseline data for sewage-plume mapping with Wolffia spp. I also tested concentration-level effects in multisource solutions to investigate the effects of mixed-source inputs. Wolffia reflected environmental N sources with a 12- to 16-d isotopic equilibration time and showed enriched and depleted δ15N ratios for manure and KNO3 solutions, respectively, but distinguished poorly between lower concentrations of manure. Fractionations at isotopic equilibrium were opposite to expectations and decreased with increasing [N]. Wolffia showed a consistent preference for NH3 in mixed-source treatments, regardless of the proportion or concentration of NH3 or NO3– available, and a capacity for N storage, which may complicate mapping of N-loading in natural environments. Wolffia is likely to be a less useful bioindicator than the previously tested Spirodela. Future research should focus on field applications of Spirodela spp. to test its capacity for sewage-plume mapping of freshwater ecosystems in a natural environment.
- Full Text: false
- Date Issued: 2018
Contrasting responses in the niches of two coral reef herbivores along a gradient of habitat disturbance in the Spermonde Archipelago, Indonesia
- Authors: Plass-Johnson, Jeremiah G , Bednarz, Vanessa N , Hill, Jaclyn M , Jompa, Jamaluddin , Ferse, Sebastian C A , Teichberg, Mirta
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69135 , vital:29398 , hhttps://doi.org/10.3389/fmars.2018.00032
- Description: Habitat modification of coral reefs is becoming increasingly common due to increases in coastal urban populations. Coral reef fish are highly dependent on benthic habitat; however, information on species-specific responses to habitat change, in particular with regard to trophic strategies, remains scarce. This study identifies variation in the trophic niches of two herbivorous coral reef fishes with contrasting trophic strategies, using Stable Isotopes Bayesian Ellipses in R, along a spatial gradient of changing coral reef habitats. In the parrotfish Chlorurus bleekeri, a roving consumer, the range of δ15N and δ13C and their niche area displayed significant relationships with the amount of rubble in the habitat. In contrast, the farming damselfish, Dischistodus prosopotaenia, showed a narrow range of both δ15N and δ13C, displaying little change in niche parameters among sites. This may indicate that parrotfish vary their feeding according to habitat, while the damselfish continue to maintain their turf and invertebrate resources. Assessing isotopic niches may help to better understand the specific trophic responses to change in the environment. Furthermore, the use of isotopic niches underlines the utility of stable isotopes in studying the potential impacts of environmental change on feeding ecology.
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- Date Issued: 2018
Synergies between research organisations and the wider community in enhancing weed biological control in South Africa
- Authors: Martin, Grant D , Hill, Martin P , Coetzee, Julie A , Weaver, Kim N , Hill, Jaclyn M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68452 , vital:29258 , https://doi.org/10.1007/s10526-017-9846-4
- Description: Biological control offers a cost effective and ecologically sustainable tool for the management of invasive alien plants. Its implementation, however, has historically been slow and poorly co-ordinated. In South Africa, as in many other countries, most aspects of biological control programmes were done by researchers, but from 1995 onwards, with the advent of the Working for Water Programme, a more inclusive approach to biological control has been adopted. In this paper, we report on the development of community-based biological control implementation programmes in South Africa, after 1995, and highlight a number of initiatives, including employing persons with disabilities at mass-rearing facilities and in particular, we outline a suite of educational and outreach programmes for the general public and for schools, which have increased capacity, education and employment in the field of weed biological control.
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- Date Issued: 2018
The contributions of biological control to reduced plant size and biomass of water hyacinth populations
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68803 , vital:29326 , https://0-doi.org.wam.seals.ac.za/10.1007/s10750-017-3413-y
- Description: Water hyacinth is invasive in many countries, where it reduces aquatic biodiversity and limits water resource utilisation. Biological control of water hyacinth has been successful in South Africa, but has suffered from a lack of empirical data to prove causation. Insect exclusion trials were conducted to quantify the contribution of Neochetina eichhorniae and N. bruchi to the integrated control of water hyacinth on the Nseleni River, South Africa. Insecticide was not expected to induce phytotoxicity, but would prevent weevil damage in water hyacinth plants; and weevil herbivory was predicted to reduce plant petiole length, and above/below surface biomass. Results showed that insecticide had no phytotoxic effects and excluded weevils for 3 weeks, providing a baseline for field applications. Biological control on the Nseleni River directly affected water hyacinth biomass and petiole length, but did not affect plant cover. Plants subject to weevil herbivory demonstrated reductions in above and below surface biomass and had shorter petioles compared to insect-free plants. Dead biomass was also higher in biological control treatments. Biological control strongly affects plant size, biomass and vigour; however, further integrated control is required to facilitate reduction in mat cover, which is the goalpost for successful control of floating aquatic plants.
- Full Text: false
- Date Issued: 2018
A moderate elevation in [CO 2] results in potential hypervirulence on SABBIErica
- Authors: Gallagher, Sean , Hill, Jaclyn M , Murugan, N , Botha, Christiaan E J
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68835 , vital:29329 , https://doi.org/10.1016/j.sajb.2017.10.010
- Description: The Russian Wheat Aphid (Diuraphis noxia Kurdjumov, 1913) (RWA) is a serious pest of grain crops and is of considerable concern in South Africa, particularly in terms of barley grown specifically for the brewing industry. This paper highlights the effect of a small (50 ppm) increase in [CO2] on the growth rate of the four South African RWA biotypes on the SABBIErica barley cultivar. Controlled environment experiments revealed that the colony growth rate for RWASA4 was significantly lower than SA1 under ambient conditions as well as significantly lower than SA1, SA2 or SA3 under elevated CO2 conditions. The unexpected difference suggested an atypical, non-preferential feeding habit on SABBIErica, for RWASA4. The small RWASA4 colonies inflicted similar morphological damage to the significantly larger RWASA1 – RWASA3 biotype populations — indicative of potential hypervirulence under elevated CO2. The continuous feeding of RWASA biotypes causes damage to the transport system as well as substantial, catastrophic damage to mesophyll chloroplasts as well as mitochondria within the host plant's leaves. The TEM study revealed evidence of sequential/systematic degeneration of chloroplasts and mitochondria with continued aphid feeding, which we suggest is an indication of potential emergent hypervirulence under elevated CO2 conditions.
- Full Text: false
- Date Issued: 2017
Community entomology: insects, science and society
- Authors: Weaver, Kim N , Hill, Jaclyn M , Martin, Grant D , Paterson, Iain D , Coetzee, Julie A , Hill, Martin P
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123343 , vital:35429 , https://hdl.handle.net/10520/EJC-c859bebd5
- Description: Educative outreach programmes have been found to be effective ways in which to raise awareness around basic scientific concepts. The Biological Control Research Group (BCRG) in the Department of Zoology and Entomology at Rhodes University, South Africa, is involved in community engaged initiatives that aim to be interactive and informative around entomology, and more specifically, the use of biological control against invasive alien plants. As a higher education institution, Rhodes University has a civic responsibility to engage with local communities and work with them around local challenges. Three groups of activities undertaken by the BCRG in partnership with local schools and other community partners are described and assessed in this paper as a way of assessing them and exploring future research areas around the aims and outcomes of these programmes.
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- Date Issued: 2017
Comparing the fish assemblages and food web structures of large floodplain rivers
- Authors: Taylor, Geraldine C , Weyl, Olaf L F , Hill, Jaclyn M , Peel, Richard A , Hay, Clinton J
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68961 , vital:29343 , https://doi.org/10.1111/fwb.13032
- Description: The Upper Zambezi, Kavango and Kwando are large floodplain rivers with substantial biodiversity, providing water and ecosystem services to a large tract of southern Africa. These rivers differ in hydrological regime. The Upper Zambezi and Kavango rivers are in flood for 4 months (March, April, May, June) while, in the Kwando River, floods are later and last for 1–2 months in July and August. The Upper Zambezi River has the largest annual flood pulse, followed by the Kavango River, while the Kwando River experiences small and unreliable floods. During years of exceptional flooding of the Upper Zambezi and Kavango rivers, the rivers are interconnected at peak flows and therefore share a common ichthyofauna. This provided a natural experiment to investigate the responses of fish communities comprised of the same species to differing flood regimes by comparing the fish assemblages and food‐web structures between rivers.
- Full Text: false
- Date Issued: 2017
Estimating δ15N fractionation and adjusting the lipid correction equation using Southern African freshwater fishes
- Authors: Taylor, Geraldine C , Hill, Jaclyn M , Jackson, Michelle C , Peel, Richard A , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69124 , vital:29392 , https://0-doi.org.wam.seals.ac.za/10.1371/journal.pone.0178047
- Description: Stable isotope analysis is an important tool for characterising food web structure; however, interpretation of isotope data can often be flawed. For instance, lipid normalisation and trophic fractionation values are often assumed to be constant, but can vary considerably between ecosystems, species and tissues. Here, previously determined lipid normalisation equations and trophic fractionation values were re-evaluated using freshwater fish species from three rivers in the Upper Zambezian floodplain ecoregion in southern Africa. The parameters commonly used in lipid normalisation equations were not correct for the 18 model species (new D and I parameters were estimated as D = 4.46‰ [95% CI: 2.62, 4.85] and constant I = 0 [95% CI: 0, 0.17]). We suggest that future isotopic analyses on freshwater fishes use our new values if the species under consideration do not have a high lipid content in their white muscle tissue. Nitrogen fractionation values varied between species and river basin; however, the average value closely matched that calculated in previous studies on other species (δ15N fractionation factor of 3.37 ± 1.30 ‰). Here we have highlighted the need to treat stable isotope data correctly in food web studies to avoid misinterpretation of the data.
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- Date Issued: 2017
The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River, South Africa
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P , Avery, T S , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69077 , vital:29382 , https://doi.org/10.2989/16085914.2017.1298984
- Description: The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.
- Full Text: false
- Date Issued: 2017
Russian wheat aphids: Breakfast, lunch, and supper. Feasting on small grains in South Africa
- Authors: Botha, Christiaan E J , Sacranie, S , Gallagher, Sean , Hill, Jaclyn M
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69031 , vital:29374 , https://doi.org/10.1016/j.sajb.2016.12.006
- Description: The Russian Wheat Aphid (Diuraphis noxia, RWA) negatively impacts commercially grown barley and wheat in South Africa. Climate change, the attendant rise in [CO2], and the appearance of new RWA biotypes have the potential to induce severe crop yield loss in agriculturally important wheat and barley cultivars. This study presents data showing changes in relative aphid population numbers, concurrently with assessments of plant damage under controlled environmental conditions, under ambient and elevated (450 ppm) [CO2]. Extensive structural damage to the vascular tissue and disruption to the transport systems were revealed using light, fluorescence and electron microscopy. This, coupled with biotype population studies, demonstrated that RWA has the capacity to inflict severe, potentially permanent damage to vegetative small grain plants. Furthermore, some currently ‘resistant’ cultivars may well lose resistance as a direct result of increasing atmospheric [CO2]. A small (50 ppm) increase in atmospheric [CO2] may result in increased aphid population numbers, potentially serious plant damage and, by implication, a potentially negative impact on yield, as increased aphid density per plant leads to an accelerated disruption of the assimilate and transpiration transport pathways. These outcomes pose a direct threat to the commercial small grain industry of South Africa and by extension, to other small grain production areas elsewhere.
- Full Text: false
- Date Issued: 2016
Comparisons of isotopic niche widths of some invasive and indigenous fauna in a South African river
- Authors: Hill, Jaclyn M , Jones, Roy W , Hill, Martin P , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423711 , vital:72088 , xlink:href="https://doi.org/10.1111/fwb.12542"
- Description: Biological invasions threaten ecosystem integrity and bio-diversity, with numerous adverse implications for native flora and fauna. Established populations of two notorious freshwater invaders, the snail Tarebia granifera and the fish Pterygoplichthys disjunctivus, have been reported on three continents and are frequently predicted to be in di-rect competition with native species for dietary resources.
- Full Text:
- Date Issued: 2015
13C pulse-chase labeling comparative assessment of the active methanogenic archaeal community composition in the transgenic and nontransgenic parental rice rhizospheres
- Authors: Zhu, Weijing , Lu, Haohao , Hill, Jaclyn M , Wang, Hailong , Wu, Weixiang
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/122993 , vital:35389 , https://doi.org/10.1111/1574-6941.12261
- Description: Rhabdosargus holubi (Steindachner, 1881) is a small (maximum size = 450 mm total length; Heemstra and Heemstra 2004) sparid that is distributed along the south-east coast of Africa from St Helena Bay, South Africa, to Maputo, Mozambique (Götz and Cowley 2013). Spawning occurs in the nearshore marine environment primarily during winter, specifically May–August in KwaZulu-Natal (KZN) (Wallace 1975) and July–February in the South-Eastern Cape (Whitfield 1998). Individuals reach 50% sexual maturity at approximately 150 mm standard length (SL) in the Eastern Cape (Whitfield 1998). The early life stages are transported by the south-westward-flowing Agulhas Current, and recruit as post-flexion larvae and early juveniles into estuaries during late winter and early summer (Blaber 1974). The warm temperatures and high nutrient levels in estuaries favour fast growth (Blaber 1973a), and fish spend their first year of life in these environments, migrating back out to sea after reaching approximately 120 mm SL. Some individuals remain trapped in closed estuaries, where they may reach sizes greater than 200 mm SL (James et al. 2007a). Rhabdosargus holubi is the dominant estuarine-dependent marine teleost species recorded in permanently open and temporarily open/closed estuaries in the warm-temperate region, which spans the south, south-east and east coast of South Africa (Harrison 2005). The species is also an important component of the linefishery in many SouthAfrican estuaries (10–15.6% by number) (Pradervand and Baird 2002), particularly in Eastern Cape estuaries (Cowley et al. 2003). These figures underestimate the presence of R. holubi, as most individuals making use of estuaries are young, feeding predominately on filamentous macroalgae and diatom flora, and are generally too small to be caught with hook and line (De Wet and Marais 1990). James et al. (2007b) showed that R. holubi made up 34–92% of the annual seine-net catch in the East Kleinemonde Estuary. Rhabdosargus holubi is also important in the KZN shorebased linefishery, representing 4.6% of the total landed catch (Dunlop and Mann 2012)More and more investigations indicate that genetic modification has no significant or persistent effects on microbial community composition in the rice rhizosphere. Very few studies, however, have focused on its impact on functional microorganisms. This study completed a 13C-CO2 pulse-chase labeling experiment comparing the potential effects of cry1Ab gene transformation on 13C tissue distribution and rhizosphere methanogenic archaeal community composition with its parental rice variety (Ck) and a distant parental rice variety (Dp). Results showed that 13C partitioning in aboveground biomass (mainly in stems) and roots of Dp was significantly lower than that of Ck. However, there were no significant differences in 13C partitioning between the Bt transgenic rice line (Bt) and Ck. RNA-stable isotope probing combined with clone library analyses inferred that the group Methanosaetaceae was the predominant methanogenic Archaea in all three rice rhizospheres. The active methanogenic archaeal community in the Bt rhizosphere was dominated by Methanosarcinaceae, Methanosaetaceae, and Methanomicrobiaceae, while there were only two main methanogenic clusters (Methanosaetaceae and Methanomicrobiaceae) in the Ck and Dp rhizospheres. These results indicate that the insertion of cry1Ab gene into the rice genome has the potential to result in the modification of methanogenic community composition in its rhizosphere.
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- Date Issued: 2013
Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production
- Authors: Hill, Jaclyn M , McQuaid, Christopher D , Kaehler, Sven
- Date: 2008
- Language: English
- Type: text , Article
- Identifier: vital:6969 , http://hdl.handle.net/10962/d1012034
- Description: Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.
- Full Text:
- Date Issued: 2008
Biogeographic and nearshore–offshore trends in isotope ratios of intertidal mussels and their food sources around the coast of southern Africa
- Authors: Hill, Jaclyn M , McQuaid, Christopher D , Kaehler, Sven
- Date: 2006
- Language: English
- Type: text , Article
- Identifier: vital:6878 , http://hdl.handle.net/10962/d1011633
- Description: There are broad differences in oceanography and primary production around the southern African coast that are likely to give rise to major differences in trophic pathways. Stable isotope ratios provide integrated information on trophic relationships, yet there has been limited research on geographic variation in isotopic composition of marine consumers and their food. In this study, δ13C and δ15N of suspended particulate matter (SPM), intertidal mussels and common macroalgae along the southern African coastline were explored. Nearshore–offshore isotope trends as well as biogeographic and temporal patterns in isotopic ratios of mussel tissue, macroalgae and SPM were investigated at 12 sites along the coast from Namibia to the Mozambique border. SPM exhibited overall trends of nearshore 13C depletion from south-west to north-east along the coastline and from nearshore (0 km) to offshore (10 km) waters, in both cases suggesting a shift from a nearshore signature strongly influenced by macroalgal detritus to one more representative of oceanic phytoplankton. With one exception it was possible, using discriminant analysis, to categorize mussel populations into 4 geographic groups, on the basis of both carbon and nitrogen signatures: the east coast, the south-east coast, the south-west coast and the west coast. Macroalgae showed no consistent biogeographic trends and need to be examined in greater detail to relate nearshore SPM values to living macroalgal signatures. A linear mixing model indicated that mussels along the entire coastline generally demonstrated more than 50% dependence on nearshore carbon and nitrogen, emphasizing the importance of nearshore primary production to intertidal consumers.
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- Date Issued: 2006