Quantitative Ecological Impact Assessments using Natural Abundance Carbon and Nitrogen Stable Isotope Signatures

<p>The use of delta15N and delta13C signatures to infer sources of enrichment in ecological systems relies on predictability in the transfer of delta15N and delta13C ratios. This thesis examines patterns of delta15N and delta13C change as pools of nitrogen and carbon move from a sewage effluent discharge into organisms in an adjacent coastal rocky reef community (Titahi Bay, New Zealand). These changes and their mechanisms are examined in the broader context of current research using carbon and nitrogen stable isotope ratios in marine ecology, with particular reference to impact assessment. Firstly this thesis examines the assimilation of nitrogen and carbon isotopes in Ulva sp. under varying light conditions and nitrogen source (e.g., nitrate or ammonium). In a field study, algae grown at depth and under lower light conditions showed comparatively lighter nitrogen isotope signatures relative to the predicted concentration of available 15N-enriched sewage nitrogen. In a complementary laboratory experiment, results from manipulated light availability and N source (either nitrate or ammonium, in equivalent molar concentrations) suggest that: 1) low-light conditions can produce algae with lighter nitrogen isotope signatures; and 2) this effect was more pronounced for ammonium (3.7 per mil difference between high light and low light treatments) than for nitrate (0.6 per mil difference between high light and low light treatments) sources. Stable carbon isotope ratios (delta13C) of Ulva sp.grown in conditions of low nitrogen availability were shown to be generally lower than those grown in nitrogen rich conditions in both field and laboratory studies. Where nitrogen supply was sufficient for growth, low light conditions also produced generally lower delta13C signatures than high light conditions. Experimental trials with a uniform dissolved inorganic carbon source and altered light and nitrogen enrichment levels produced delta 13C levels in Ulva sp. tissue that spanned the recorded delta13C ranges of many common algal species; -5.99 per mil (high light, with added ammonium and phosphate) to -17.61 per mil (high light without nutrient additions). Chapter 3 of this study examines the growth response of Ulva sp. to surplus nitrate and ammonium (the two most common forms of nitrogen available to plants in seawater), under light limited conditions. Ulva sp. experienced a temporary reduction in growth rate and nitrogen assimilation capacity (shown in tissue nitrogen indices) when grown on nitrate, relative to ammonium. The magnitude and the temporary nature of these results suggest that in natural populations the relative proportion of nitrate or ammonium available is unlikely to significantly affect the growth capacity of Ulva sp. In chapter 4, I use delta13C and delta15N signatures to separately trace the dissolved and particulate fractions of sewage effluent dispersal onto a rocky reef community. Delta15N signatures from tissue of the macroalga Carpophyllum maschalocarpum, and the herbivorous isopod Amphoroidea media tracked the distribution and signature of DIN from a sewage treatment plant that generated heavy delta15N signatures. Delta13C signatures from tissue of the filter-feeding half-crab Petrolisthes elongatus tracked the distribution and signature of suspended sewage particulate organic matter.</p>

Quantitative Ecological Impact Assessments using Natural Abundance Carbon and Nitrogen Stable Isotope Signatures

<p>The use of delta15N and delta13C signatures to infer sources of enrichment in ecological systems relies on predictability in the transfer of delta15N and delta13C ratios. This thesis examines patterns of delta15N and delta13C change as pools of nitrogen and carbon move from a sewage effluent discharge into organisms in an adjacent coastal rocky reef community (Titahi Bay, New Zealand). These changes and their mechanisms are examined in the broader context of current research using carbon and nitrogen stable isotope ratios in marine ecology, with particular reference to impact assessment. Firstly this thesis examines the assimilation of nitrogen and carbon isotopes in Ulva sp. under varying light conditions and nitrogen source (e.g., nitrate or ammonium). In a field study, algae grown at depth and under lower light conditions showed comparatively lighter nitrogen isotope signatures relative to the predicted concentration of available 15N-enriched sewage nitrogen. In a complementary laboratory experiment, results from manipulated light availability and N source (either nitrate or ammonium, in equivalent molar concentrations) suggest that: 1) low-light conditions can produce algae with lighter nitrogen isotope signatures; and 2) this effect was more pronounced for ammonium (3.7 per mil difference between high light and low light treatments) than for nitrate (0.6 per mil difference between high light and low light treatments) sources. Stable carbon isotope ratios (delta13C) of Ulva sp.grown in conditions of low nitrogen availability were shown to be generally lower than those grown in nitrogen rich conditions in both field and laboratory studies. Where nitrogen supply was sufficient for growth, low light conditions also produced generally lower delta13C signatures than high light conditions. Experimental trials with a uniform dissolved inorganic carbon source and altered light and nitrogen enrichment levels produced delta 13C levels in Ulva sp. tissue that spanned the recorded delta13C ranges of many common algal species; -5.99 per mil (high light, with added ammonium and phosphate) to -17.61 per mil (high light without nutrient additions). Chapter 3 of this study examines the growth response of Ulva sp. to surplus nitrate and ammonium (the two most common forms of nitrogen available to plants in seawater), under light limited conditions. Ulva sp. experienced a temporary reduction in growth rate and nitrogen assimilation capacity (shown in tissue nitrogen indices) when grown on nitrate, relative to ammonium. The magnitude and the temporary nature of these results suggest that in natural populations the relative proportion of nitrate or ammonium available is unlikely to significantly affect the growth capacity of Ulva sp. In chapter 4, I use delta13C and delta15N signatures to separately trace the dissolved and particulate fractions of sewage effluent dispersal onto a rocky reef community. Delta15N signatures from tissue of the macroalga Carpophyllum maschalocarpum, and the herbivorous isopod Amphoroidea media tracked the distribution and signature of DIN from a sewage treatment plant that generated heavy delta15N signatures. Delta13C signatures from tissue of the filter-feeding half-crab Petrolisthes elongatus tracked the distribution and signature of suspended sewage particulate organic matter.</p>

Quantitative Ecological Impact Assessments using Natural Abundance Carbon and Nitrogen Stable Isotope Signatures

<p>The use of delta15N and delta13C signatures to infer sources of enrichment in ecological systems relies on predictability in the transfer of delta15N and delta13C ratios. This thesis examines patterns of delta15N and delta13C change as pools of nitrogen and carbon move from a sewage effluent discharge into organisms in an adjacent coastal rocky reef community (Titahi Bay, New Zealand). These changes and their mechanisms are examined in the broader context of current research using carbon and nitrogen stable isotope ratios in marine ecology, with particular reference to impact assessment. Firstly this thesis examines the assimilation of nitrogen and carbon isotopes in Ulva sp. under varying light conditions and nitrogen source (e.g., nitrate or ammonium). In a field study, algae grown at depth and under lower light conditions showed comparatively lighter nitrogen isotope signatures relative to the predicted concentration of available 15N-enriched sewage nitrogen. In a complementary laboratory experiment, results from manipulated light availability and N source (either nitrate or ammonium, in equivalent molar concentrations) suggest that: 1) low-light conditions can produce algae with lighter nitrogen isotope signatures; and 2) this effect was more pronounced for ammonium (3.7 per mil difference between high light and low light treatments) than for nitrate (0.6 per mil difference between high light and low light treatments) sources. Stable carbon isotope ratios (delta13C) of Ulva sp.grown in conditions of low nitrogen availability were shown to be generally lower than those grown in nitrogen rich conditions in both field and laboratory studies. Where nitrogen supply was sufficient for growth, low light conditions also produced generally lower delta13C signatures than high light conditions. Experimental trials with a uniform dissolved inorganic carbon source and altered light and nitrogen enrichment levels produced delta 13C levels in Ulva sp. tissue that spanned the recorded delta13C ranges of many common algal species; -5.99 per mil (high light, with added ammonium and phosphate) to -17.61 per mil (high light without nutrient additions). Chapter 3 of this study examines the growth response of Ulva sp. to surplus nitrate and ammonium (the two most common forms of nitrogen available to plants in seawater), under light limited conditions. Ulva sp. experienced a temporary reduction in growth rate and nitrogen assimilation capacity (shown in tissue nitrogen indices) when grown on nitrate, relative to ammonium. The magnitude and the temporary nature of these results suggest that in natural populations the relative proportion of nitrate or ammonium available is unlikely to significantly affect the growth capacity of Ulva sp. In chapter 4, I use delta13C and delta15N signatures to separately trace the dissolved and particulate fractions of sewage effluent dispersal onto a rocky reef community. Delta15N signatures from tissue of the macroalga Carpophyllum maschalocarpum, and the herbivorous isopod Amphoroidea media tracked the distribution and signature of DIN from a sewage treatment plant that generated heavy delta15N signatures. Delta13C signatures from tissue of the filter-feeding half-crab Petrolisthes elongatus tracked the distribution and signature of suspended sewage particulate organic matter.</p>

Quantitative Ecological Impact Assessments using Natural Abundance Carbon and Nitrogen Stable Isotope Signatures

<p>The use of delta15N and delta13C signatures to infer sources of enrichment in ecological systems relies on predictability in the transfer of delta15N and delta13C ratios. This thesis examines patterns of delta15N and delta13C change as pools of nitrogen and carbon move from a sewage effluent discharge into organisms in an adjacent coastal rocky reef community (Titahi Bay, New Zealand). These changes and their mechanisms are examined in the broader context of current research using carbon and nitrogen stable isotope ratios in marine ecology, with particular reference to impact assessment. Firstly this thesis examines the assimilation of nitrogen and carbon isotopes in Ulva sp. under varying light conditions and nitrogen source (e.g., nitrate or ammonium). In a field study, algae grown at depth and under lower light conditions showed comparatively lighter nitrogen isotope signatures relative to the predicted concentration of available 15N-enriched sewage nitrogen. In a complementary laboratory experiment, results from manipulated light availability and N source (either nitrate or ammonium, in equivalent molar concentrations) suggest that: 1) low-light conditions can produce algae with lighter nitrogen isotope signatures; and 2) this effect was more pronounced for ammonium (3.7 per mil difference between high light and low light treatments) than for nitrate (0.6 per mil difference between high light and low light treatments) sources. Stable carbon isotope ratios (delta13C) of Ulva sp.grown in conditions of low nitrogen availability were shown to be generally lower than those grown in nitrogen rich conditions in both field and laboratory studies. Where nitrogen supply was sufficient for growth, low light conditions also produced generally lower delta13C signatures than high light conditions. Experimental trials with a uniform dissolved inorganic carbon source and altered light and nitrogen enrichment levels produced delta 13C levels in Ulva sp. tissue that spanned the recorded delta13C ranges of many common algal species; -5.99 per mil (high light, with added ammonium and phosphate) to -17.61 per mil (high light without nutrient additions). Chapter 3 of this study examines the growth response of Ulva sp. to surplus nitrate and ammonium (the two most common forms of nitrogen available to plants in seawater), under light limited conditions. Ulva sp. experienced a temporary reduction in growth rate and nitrogen assimilation capacity (shown in tissue nitrogen indices) when grown on nitrate, relative to ammonium. The magnitude and the temporary nature of these results suggest that in natural populations the relative proportion of nitrate or ammonium available is unlikely to significantly affect the growth capacity of Ulva sp. In chapter 4, I use delta13C and delta15N signatures to separately trace the dissolved and particulate fractions of sewage effluent dispersal onto a rocky reef community. Delta15N signatures from tissue of the macroalga Carpophyllum maschalocarpum, and the herbivorous isopod Amphoroidea media tracked the distribution and signature of DIN from a sewage treatment plant that generated heavy delta15N signatures. Delta13C signatures from tissue of the filter-feeding half-crab Petrolisthes elongatus tracked the distribution and signature of suspended sewage particulate organic matter.</p>

Distribution and size variability of Japanese eel leptocephali in their Pacific Ocean spawning area using carbon and nitrogen stable isotope ratio analyses

The diets of larval (leptocephali) anguillid and marine eels are poorly understood, despite studies on their gut contents or stable isotope ratios suggesting marine snow particles represent a food source. Concerns for Japanese eel Anguilla japonica stock conservation necessitate an improved knowledge of their larval ecology to better understand the causes of their recent decline in numbers and fluctuating recruitment into East Asia. To understand the distribution of and variation in size of leptocephali in relation to their feeding, we examine carbon and nitrogen stable isotope ratios of larvae from seven research cruises (2002–2013) in the North Equatorial Current spawning area. Preleptocephali (2–3 days old, ~5 mm total length) isotope ratios reflect maternal ratios, but feeding-stage leptocephali (8–56 mm) tend to have higher ∂15N values with decrease of latitude typically in areas south of a salinity front. Neither ∂15N nor ∂13C ratios are clearly related to longitude or larval size < 30 mm, but ∂13C values of larvae > 40 mm are lower further downstream in the North Equatorial Current and Subtropical Countercurrent. Differences in ∂13C values might be a function of varying spatial baselines in the two currents apart from the spawning area. Although among-year larval isotope ratio differences may reflect temporal baseline variation related to the location of the salinity front, more research with much wider range observations in the spawning season is required because ingested marine snow particles might differ with larval growth and location.