A Comparison of the oxygenating differences of
invasive non-native Lagarosiphon major and native
Ceratophyllum demersum

Rhiann Mitchell-Holland, Nicola Jane Morris and Peter Kenneth McGregor


Native to Southern Africa, Lagarosiphon major is a submerged macrophyte that is recognized as a problematic, invasive
non-native species in many countries including the UK. It is widely sold and promoted through the aquarium and water garden industry as an ‘efficient oxygenator’ for freshwater systems, irrespective of the absence of evidence to support this
statement and evidence of its adverse ecological and economic impacts. A key concern, relating to its rapid growth rate
and high fresh weight density, is that L. major can impose self-shading and limitation of photosynthetic and respiratory
activity, causing it to consume more oxygen than it produces. Low dissolved oxygen (DO) conditions typify diminished
water quality and seriously limit oxygen-dependent organisms. We measured over several months the DO, fresh weight
and associated pond life abundances of L. major and a comparable UK-native macrophyte, Ceratophyllum demersum, established in small-pond conditions to determine which species best maintained a healthy freshwater environment. Both the
time from establishment and species had significant effects on DO concentrations and pond life abundance; L. major produced the least amount of oxygen over time and had significantly less associated pond life compared to the native plant.
L. major also increased significantly in overall fresh weight compared to C. demersum, indicating the higher invasive ability
of the non-native species. In conclusion, our results suggest that L. major is not as good an oxygenator as C. demersum and
that this native species should be promoted through the aquarium and water garden trades as an efficient oxygenator that
improves water quality and habitat conditions over time.

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Valuing Nature: Public Perception of Value
Added by Native and Invasive Non-Native
Species to a Recreational Trail Experience

Peter K. McGregor, Nicola J. Morris, Trevor J. Renals


Aims: To assess the effect of four animal and four plant species on the perceive monetary value of users’ single experience of a recreational trail. To assess the effect on perceived value of identifying to users that four of the species are invasive non-native species (INNS) with adverse impacts on native species.
Study Design: An image-based questionnaire was used to assess perceived monetary value of the species before and immediately after being given information on their INNS status.
Place and Duration of Study: The Camel Trail, North Cornwall UK, used by about ½ million people annually, April and May 2011.
Methodology: Fifty one Camel Trail users completed the questionnaire.
Results: Trail users positively valued all eight species when first shown them. Mean values ranged from £0.066 to £0.104. However, species were valued significantly differently (non-parametric repeated measures ANOVA, H = 55.3, 7 DF, P < .0001). Users showed significant agreement on the rank order of the value of the eight species (Kendall’s coefficient of concordance, W = 0.155, χ2 = 55.3, 7 DF, P < .0001). After the four INNS were identified to users, these INNS were devalued by 115% to 180%. Again there were significant differences between species values (H = 16.9, 3 DF, P = .0007) and significant agreement between users on the rank order value of INNS (W = 0.11 χ2 = 16.9, 7 DF, P = .001).
Conclusion: Using a simple image-based questionnaire to assess perceived monetary value of species can provide evidence to assess the cost of managing INNS.

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