Development of an epiphyte indicator of nutrient enrichment: Threshold values for seagrass epiphyte load

Metrics of epiphyte load on macrophytes were evaluated for use as quantitative biological indicators for nutrient impacts in estuarine waters, based on review and analysis of the literature on epiphytes and macrophytes, primarily seagrasses, but including some brackish and freshwater rooted macrophyte species. An approach is presented that empirically derives threshold epiphyte loads which are likely to cause specified levels of decrease in macrophyte response metrics such as biomass, shoot density, percent cover, production and growth. Data from 36 studies of 10 macrophyte species were pooled to derive relationships between epiphyte load and −25 and −50% seagrass response levels, which are proposed as the primary basis for establishment of critical threshold values. Given multiple sources of variability in the response data, threshold ranges based on the range of values falling between the median and the 75th quantiles of observations at a given seagrass response level are proposed rather than single, critical point values. Four epiphyte load threshold categories − low, moderate, high, very high, are proposed. Comparison of values of epiphyte loads associated with 25 and 50% reductions in light to macrophytes suggest that the threshold ranges are realistic both in terms of the principle mechanism of impact to macrophytes and in terms of the magnitude of resultant impacts expressed by the macrophytes. Some variability in response levels was observed among climate regions, and additional data collected with a standardized approach could help in the development of regionalized threshold ranges for the epiphyte load indicator.     

Effect of nutrient availability, grazer assemblage and seagrass source population on the interaction between Thalassia testudinum (turtle grass) and its algal epiphytes

Seagrass leaves are often densely covered by epiphytic algae which can suppress seagrass productivity and has been implicated in declines of seagrass meadows worldwide. The net effect of epiphytes on seagrass growth and morphology depends on the independent and interactive effects of a variety of factors, including nutrient availability and the intensity of grazing on epiphytes. Here I report the results of a mesocosm experiment designed to test the effects of nutrient addition and within-functional group variation (grazer species composition and the source population of seagrass) on the strength of the interactions among grazers, epiphytes, and turtle grass (Thalassia testudinum). Turtle grass ramets from two sites in the northern Gulf of Mexico were cleared of epiphytes and transplanted into common-garden mesocosms. Replicate ramets were grown in a split-split plot design with two levels of dissolved nutrients and four different grazer species combinations (Tozeuma carolinense alone, Pagurus maclaughlinae alone, both species together, and no grazers present). As expected, grazers had a significant negative effect on epiphyte biomass/leaf area and a significant positive effect on turtle grass growth in the mesocosms. The two species were more similar in their direct effects on epiphyte biomass than in their indirect effects on turtle grass growth; this may reflect differences in epiphyte community composition under different grazer treatments. The effect of nutrient addition on turtle grass growth depended critically on the intensity of grazing: in the presence of grazers, turtle grass tended to produce a greater biomass of new leaf tissue in the tanks with nutrients added than in the control tanks. However, when grazers were absent, the direction of the effect was reversed, and plants with nutrients added grew less than the control plants. The two source populations of turtle grass differed significantly in epiphyte biomass/leaf area accrued in the mesocosms as well as in the strength of the effect of grazers on turtle grass growth. This suggests that population differentiation in seagrass interactions with epiphytes, as well as spatial and temporal variation in resources and grazer community composition, can greatly effect the role of epiphytes in limiting seagrass productivity.     

Top-down and bottom-up control in an eelgrass–epiphyte system

Nutrient supply and the presence of grazers can control primary producers in aquatic ecosystems, but the relative importance of bottom-up and top-down effects remains inconclusive. We conducted a mesocosm experiment and a field study to investigate the independent and interactive effects of nutrient enrichment and grazing on primary producers in an eelgrass bed Zostera marina . Nutrient treatments consisted of ambient or enriched (2× and 4× ambient) concentrations of inorganic nitrogen and phosphate. Grazer treatments consisted of presence or absence of field densities of the common isopod Idotea baltica . We found strong and interacting effects of nutrients and grazing on epiphytes. Epiphyte biomass and productivity were enhanced by nutrient enrichment and decreased in the presence of grazers. The absolute amount of epiphyte biomass consumed by grazers increased under high nutrient supply, and thus, nutrient effects were stronger in the absence of grazing. The effects of grazers and fertilisation on epiphyte composition were antagonistic: chain-forming diatoms and filamentous algae profited from nutrient enrichment, but their proportions were reduced by grazing. Eelgrass growth was positively affected by grazing and by nutrient enrichment at moderate nutrient concentrations. High nutrient supply reduced eelgrass productivity compared to moderate nutrient conditions. The monthly measured field data showed a nitrogen limitation for epiphytes and eelgrass in summer, which may explain the positive effect of nutrient enrichment on both primary producers. Generally, the field data suggested the possibility of seasonally varying importance of bottom-up and top-down control on primary producers in this eelgrass system.     

Relative effects of nutrient enrichment and grazing on epiphyte-macrophyte (Zostera marina L.) dynamics

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m^–2 d^–1) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon.     

Development of a diverse epiphyte community in response to phosphorus fertilization

The role of terrestrial soil nutrient supply in determining the composition and productivity of epiphyte communities has been little investigated. In a montane Hawaiian rainforest, we documented dramatic increases in the abundance and species richness of canopy epiphytes in a forest that had been fertilized annually with phosphorus (P) for 15 years; there was no response in forest that had been fertilized with nitrogen (N) or other nutrients. The response of N-fixing lichens to P fertilization was particularly strong, although mosses and non-N-fixing lichens also increased in abundance and diversity. We show that enhancement of canopy P availability is the most likely factor driving the bloom in epiphytes. These results provide strong evidence that terrestrial soil fertility may structure epiphyte communities, and in particular that the abundance of N-fixing lichens – a functionally important epiphyte group – may be particularly sensitive to ecosystem P availability.     

Response of seagrass epiphyte loading to field manipulations of fertilization, gastropod grazing and leaf turnover rates

This study evaluates the bottom-up and top-down controls on epiphyte loads under low nutrient additions. Nutrients and gastropod grazers were manipulated in a field experiment conducted within a Thalassia testudinum meadow in Florida Bay, FL, USA. The effect of seagrass leaf turnover rate on epiphyte loading was also evaluated using novel seagrass short-shoot mimics that “grow,” allowing for the manipulation of leaf turnover rates. During the summer growing season and over the course of one seagrass leaf turnover period, low-level water column nutrient additions increased total epiphyte load, epiphyte chlorophyll a, and epiphyte autotrophic index. T. testudinum leaf nutrients (N and P) and leaf productivity also increased. Epiphyte loading and T. testudinum shoot biomass and productivity did not respond to a 60% mean increase in gastropod abundance. Manipulations of seagrass leaf turnover rates at minimum wintertime and maximum summertime rates resulted in a 20% difference in epiphyte loading. Despite elevated grazer abundances and increased leaf turnover rates, epiphyte loads increased with nutrient addition. These results emphasize the sensitivity of T. testudinum and associated epiphytes to low-level nutrient addition in a nutrient-limited environment such as Florida Bay.     

Nutrient induced changes in the species composition of epiphytes on Cladophora glomerata Kütz. (Chlorophyta)

Cladophora glomerata is a widely distributed filamentous freshwater alga that hosts a complex microalgal epiphyte assemblage. We manipulated nutrients and epiphyte abundances to access their effects on epiphyte biomass, epiphyte species composition, and C. glomerata growth. C. glomerata did not grow in response to these manipulations. Similarly, nutrient and epiphyte removal treatments did not alter epiphyte biovolume. Epiphyte species composition, however, changed dramatically with nutrient enrichment. The epiphyte assemblage on unenriched C. glomerata was dominated by Epithemia sorex and Epithemia adnata, whereas the assemblage on enriched C. glomerata was dominated by Achnanthidium minutissimum, Nitzschia palea and Synedra spp. These results indicate that nutrients strongly structure epiphyte species composition. Interactions between C. glomerata and its epiphytes were not affected by epiphyte species composition in our experiment but may be when C. glomerata is actively growing.     

Factors affecting the initiation and growth of aboveground adventitious roots in a tropical cloud forest tree: an experimental approach

Some of the proximate factors that would induce aboveground stems to produce adventitious roots were investigated experimentally on Senecio cooperi, a tropical cloud forest tree. Stem segments were air-layered with different treatments to promote root formation, and the number of roots initiated and rates of root growth were monitored for 20 weeks. Treatments were the application of wet epiphytes or dry epiphytes plus associated humus, sponges wetted with either water or nutrient solutions, or dry sponges. Controls (stem segments with nothing applied) were also monitored. Numbers of adventitious roots formed and rates of subsequent root growth differed among treatments. Wet epiphyte/humus and nutrient solutions were most effective in producing roots, which suggests that epiphytes and the nutrients they intercept and retain within the canopy may cue adjacent host tissue to exploit this resource.     

Non‐consumptive effects of avian predators on fish behavior and cascading indirect interactions in seagrasses

Top–down impacts of avian predators are often overlooked in marine environments despite evidence from other systems that birds significantly impact animal distribution and behavior; instead, birds are typically recognized for the impacts of their nutrient rich guano. This is especially true in shallow seagrass meadows where restoration methods utilize bird perches or stakes to attract birds as a passive fertilizer delivery system that promotes the regrowth of damaged seagrasses. However, this method also increases the local density of avian piscivores that may have multiple unexplored non‐consumptive effects on fish behavior and indirect impacts to seagrass communities. We utilized laboratory and field experiments to investigate whether visual cues of avian predators impacted the behavior of the dominant demersal fish in seagrass habitats, the pinfish Lagodon rhomboides, and promoted cascading interactions on seagrass‐associated fauna and epiphytes. In laboratory mesocosms, pinfish displayed species specific responses to models of avian predators, with herons inducing the greatest avoidance behaviors. Avoidance patterns were confirmed in field seagrass meadows where heron models significantly reduced the number of fish caught in traps. In a long term field experiment, we investigated whether avian predators caused indirect non‐consumptive effects on seagrass communities by monitoring fish abundances, invertebrate epiphyte grazers, and the seagrass epiphytes in response to heron models, bird exclusions, and bird stakes. On average, more fish were recovered under bird exclusions and fewer fish under heron models. However, we found no evidence of cascading effects on invertebrate grazers or epiphytes. Bird stake treatments only displayed a simple nutrient effect where higher bird abundances resulted in higher epiphyte biomass. Our results indicate that although birds and their visual cues can affect fish and epiphyte abundance through non‐consumptive effects and nutrient enrichment, these impacts do not propagate beyond one trophic level, most likely because of dampening by omnivory and larger scale processes.     

Ecological stoichiometry of the epiphyte community in a subtropical forest canopy

Epiphytes in tree canopies make a considerable contribution to the species diversity, aboveground biomass, and nutrient pools in forest ecosystems. However, the nutrient status of epiphytes and their possible adaptations to nutrient deficiencies in the forest canopy remain unclear. Therefore, we analyzed the stoichiometry of five macroelements (C, N, P, K, and Ca) in four taxonomic groups (lichens, bryophytes, ferns, and spermatophytes) to investigate this issue in a subtropical montane moist evergreen broad‐leaved forest in Southwest China. We found that the interspecific variations in element concentrations and mass ratios were generally greater than the intraspecific variations. And there were significant stoichiometric differences among functional groups. Allometric relationships between N and P across the epiphyte community indicated that P might be in greater demand than N with an increase in nutrients. Although canopy nutrients were deficient, most epiphytes could still maintain high N and P concentrations and low N:P ratios. Moreover, ferns and spermatophytes allocated more limited nutrients to leaves than to stems and roots. To alleviate frequent drought stress in the forest canopy, vascular epiphytes maintained several times higher K concentrations in their leaves than in the tissues of lichens and bryophytes. Our results suggest that epiphytes may have evolved specific nutrient characteristics and adaptations, so that they can distribute in heterogeneous canopy habitats and maintain the stability of nutrient metabolism.     

Does structural parasitism by epiphytes exist? A case study between Tillandsia recurvata and Parkinsonia praecox

The effects that epiphytes have on their hosts have been poorly explored in an experimentally. Correlational evidence suggests that epiphytes may be either mutualists or structural parasites, as has been proposed for Tillandsia recurvata on Parkinsonia praecox. To test the effect of T. recurvata upon P. praecox, the epiphyte load on branches of P. praecox was measured and two 1‐year experiments were performed to detect the effect of transplantation/removal of epiphytes and shade (0%, 35%. 50% and 80%) on shoot dynamics. If T. recurvata represents a selective pressure for P. praecox, then the frequency of branches carrying large epiphyte loads will be high, and host shoot survival will decrease in the presence of T. recurvata and with increased shade. A weak inverse relationship between epiphyte load and percentage of dead shoots in the host was detected. Shoot survival was independent of epiphyte presence. Shade decreased shoot survival by 35–72%. Results suggest that at the study site, T. recurvata is a commensalist of P. praecox. An alternative hypothesis to explain the correlation between high epiphyte load and branch/tree decay is that older branches carry more epiphytes, receive more shade from neighbouring branches and could be undergoing a natural decline process.     

The physiological ecology of vascular epiphytes: current knowledge, open questions

The current knowledge of the physiological ecology of vascular epiphytes is reviewed here with an emphasis on the most recent literature. It is argued that by far the most relevant abiotic constraint for growth and vegetative function of vascular epiphytes is water shortage, while other factors such as nutrient availability or irradiation, are generally of inferior importance. However, it is shown that the present understanding of epiphyte biology is still highly biased, both taxonomically and ecologically, and it is concluded that any generalizations are still preliminary. Future studies should include a much wider range of taxa and growing sites within the canopy to reach a better understanding how abiotic factors are limiting epiphyte growth and survival which, in turn, should affect epiphyte community composition. Finally, a more integrative approach to epiphyte biology is encouraged: physiological investigations should be balanced by studies of other possible constraints, for example, substrate instability, dispersal limitation, competition or herbivory.     

Interactions between epiphytes during canopy soil formation: an experiment in a lower montane cloud forest of southeast Mexico

• In several montane forests around the world, epiphytes coexist in mats, sharing the rhizosphere and forming histosol-type soils rich in nutrients. The role of these epiphytes in the formation of canopy soil and the fitness costs that epiphytes face when cohabiting in these mats are unknown.
• In a lower montane cloud forest in central Veracruz, Mexico, a 2-year factorial experiment was carried out with the presence/absence of ramets of Phlebodium areolatum (Polypodiaceae), Tillandsia kirchhoffiana, T. multicaulis and T. punctulata (Bromeliaceae). We examined (i) which epiphyte species contribute to the formation of canopy soil, (ii) the role of epiphyte composition in the soil nutrient composition, and (iii) the fitness costs faced by epiphytes when cohabiting.
• Canopy soil formation highest when P. areolatum is present. Soil nutrient content does not change with epiphyte composition, is influenced by the microbiota, and P content decreases with the presence of epiphytes. The fitness costs show that the species compete, decreasing their survival and growth, but the competitive capacity differs between the species.
• We conclude that P. areolatum is an ecosystem engineer that promotes the creation of canopy soil but is a poor competitor. The results coincide with the model of succession by facilitation. Canopy soil is a slow-created component whose nutrient content does not depend on the epiphytic flora. In epiphyte mats, the dominant interactions are competitive, but there is also facilitation.

     

Responses of growth and phlorotannins in <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> to nutrient enrichment and herbivory

Discharge from anthropogenic sources may modify both macroalgal growth patterns and resource allocation to carbon based secondary compounds, thereby affecting their susceptibility for herbivory. We tested the effect of eutrophication in terms of nutrient enhancement on growth and phlorotannin concentration of Fucus vesiculosus by conducting manipulative experiments in the field and mesocosms. In the field experiment we utilised fish farms as nutrient sources and in the mesocosm-experiment we manipulated ambient nutrient levels and occurrence of the herbivorous isopod Idotea baltica. Vicinity of a fish farm affected neither growth nor the phlorotannin concentration of Fucus but increased the amount of epiphytes growing on Fucus. Other organisms such as epiphytic filamentous algae and periphyton, which are more capable of quickly utilizing excess nutrients, may restrain the direct effects of nutrient enhancement on Fucus. In a manipulative mesocosm experiment, neither nutrient enrichment nor occurrence of herbivores affected phlorotannin concentration implying lack of induced defences, at least in terms of increasing phlorotannin concentration. Feeding of thallus decreased the growth rate of algae, but the number of reproductive organs, receptacles, was not affected by herbivory. The negative effect of herbivory on the amount of apical tips tended to be stronger under nutrient enriched conditions. We conclude that eutrophication processes, in terms of nutrient enrichment, does not have strong direct effect on growth or phlorotannin production of F. vesiculosus. However, there may be important indirect consequences. First, herbivory may be targeted more to apical parts of the thallus under eutrophicated conditions. Second, the result that Fucus growing close to nutrient sources were smaller than those in control areas may reflect differences in mortality schedules of algae between eutrophicated and control areas.     

Vascular epiphyte populations with higher leaf nutrient concentrations showed weaker resilience to an extreme drought in a montane cloud forest

• Leaf stoichiometry can characterize plant ecological strategies and correlate with plant responses to climate change. The role of vascular epiphytes in the ecosystem processes of tropical and subtropical forest ecosystems cannot be ignored. Vascular epiphytes are very vulnerable to climate change, however, the relationship between the response of epiphytes to climate change and leaf stoichiometry is not well understood.
• We present data for 19 vascular epiphyte species that were collected during four consecutive censuses (in 2005, 2010, 2015, and 2020) over 15 years in a subtropical montane cloud forest. We assessed the relationships between the population dynamics and leaf stoichiometry of these vascular epiphytes.
• Experiencing an extreme drought, 14 of the 19 epiphyte species showed an obvious decrease in the number of individuals, and all species showed negative growth in the number of populations. Subsequently, the total number of individuals gradually recovered, increasing from 7,195 in 2010 to 10,121 in 2015, then to 13,667 in 2020. The increase in the number of vascular epiphyte individuals from 2010 to 2015 was significantly negatively correlated with leaf nitrogen and phosphorus concentration, and was significantly positively correlated with the leaf carbon-nitrogen ratio.
• Vascular epiphyte populations with higher leaf nutrient concentrations exhibited weaker resilience to the extreme drought, which demonstrated that a resource-conservative strategy was advantageous for the recovery of epiphyte populations. Our findings suggest that ecological stoichiometry can be a useful framework for forecasting the dynamics of vascular epiphyte populations in response to climate change.

     

Epiphyte host preferences and host traits: mechanisms for species-specific interactions

We investigated species-specific relationships among two species of vascular epiphytes and ten host tree species in a coastal plain forest in the southeastern United States. The epiphytes Tillandsia usneoides and Polypodium polypodioides were highly associated with particular host species in the field, but host traits that favored colonization were inadequate to fully explain the epiphyte-host associations for either epiphyte. Field transplant experiments that bypassed epiphyte colonization demonstrated that the growth of epiphytes was significantly higher on host tree species that naturally bore high epiphyte loads than on host species with few or no epiphytes. These species-specific relationships were highly correlated with the water-holding capacity of the host tree's bark. Positive and negative effects of throughfall, light attenuation by the canopy, and bark stability did not explain the overall patterns of host specificity, but did correlate with some epiphyte-host species relationships. The relative importance of particular host traits differed between the "atmospheric epiphyte" Tillandsia, and the fern Polypodium, which roots in the bark of its hosts. Species-specific interactions among plants, such as those described here, suggest that communities are more than individualistic assemblages of co-occurring species.     

云南哀牢山山地湿性常绿阔叶林附生植物的多样性和分布

附生植物对山地森林生态系统的物种多样性形成及其维持机制、生态系统的水分和养分循环等有重要作用。作者调查分析了云南哀牢山原生山地湿性常绿阔叶林 80株不同种类、不同径级乔木上附生植物种类、数量及空间分布特征,结果表明该区森林附生植物种类较为丰富。共收集到附生植物 69种,分属 33科 49属,其中维管束植物32种,苔藓植物 37种。附生维管束植物的Shannon Wiener指数和Simpson指数分别为 2. 93和 0. 91,附生苔藓植物分别为 3. 31和 0. 95。附生维管束植物中蕨类较为丰富,以棕鳞瓦韦 (Lepisorusscolopendrium)、拟书带蕨 (Vittariaflexuosoides)、柔毛水龙骨(Polypodiodesamoenavar. pilosa)等为主;附生种子植物以黄杨叶芒毛苣苔 (Aeschynanthusbuxifolius)、长叶粗筒苣苔(Briggsialongifolia)、白花树萝卜 (Agapetesmannii)等为主。该地区全年气候潮湿、温凉,使得附生苔藓植物非常丰富,主要优势种类包括东亚鞭苔 (Bazzaniapraerupta)、小叶鞭苔 (B. ovistipula)、齿边广萼苔(Chandonanthushirtellus)、树平藓 (Homaliodendronflabellatum)、刺果藓 (Symphyodonperrottetii)、青毛藓 (Dicran odontiumdenudatum)、小蔓藓(Meteoriellasoluta)、尖喙藓(Kindbergiapraelonga)等。从空间分布特点上看,     

Agent‐based modeling of the effects of forest dynamics,selective logging,and fragment size on epiphyte communities

1. Forest canopies play a crucial role in structuring communities of vascular epiphytes by providing substrate for colonization, by locally varying microclimate, and by causing epiphyte mortality due to branch or tree fall. However, as field studies in the three‐dimensional habitat of epiphytes are generally challenging, our understanding of how forest structure and dynamics influence the structure and dynamics of epiphyte communities is scarce.
2. Mechanistic models can improve our understanding of epiphyte community dynamics. We present such a model that couples dispersal, growth, and mortality of individual epiphytes with substrate dynamics, obtained from a three‐dimensional functional–structural forest model, allowing the study of forest–epiphyte interactions. After validating the epiphyte model with independent field data, we performed several theoretical simulation experiments to assess how (a) differences in natural forest dynamics, (b) selective logging, and (c) forest fragmentation could influence the long‐term dynamics of epiphyte communities.
3. The proportion of arboreal substrate occupied by epiphytes (i.e., saturation level) was tightly linked with forest dynamics and increased with decreasing forest turnover rates. While species richness was, in general, negatively correlated with forest turnover rates, low species numbers in forests with very‐low‐turnover rates were due to competitive exclusion when epiphyte communities became saturated. Logging had a negative impact on epiphyte communities, potentially leading to a near‐complete extirpation of epiphytes when the simulated target diameters fell below a threshold. Fragment size had no effect on epiphyte abundance and saturation level but correlated positively with species numbers.
4. Synthesis: The presented model is a first step toward studying the dynamic forest–epiphyte interactions in an agent‐based modeling framework. Our study suggests forest dynamics as key factor in controlling epiphyte communities. Thus, both natural and human‐induced changes in forest dynamics, for example, increased mortality rates or the loss of large trees, pose challenges for epiphyte conservation.

     

Diversity of phlorotannin profiles among sargassasacean species affecting variation and abundance of epiphytes

In general, epiphytes have detrimental effects on the growth of their basiphytes due to competition for light and nutrients. Therefore, basiphyte species must expend energy suppressing epiphytes. Some studies suggest that phlorotannins, i.e. brown algal polyphenols, prevent colonization by epiphytes, whereas others question their allelopathic function because there is not necessarily a negative correlation between epiphyte abundance and the phlorotannin content of the basiphyte algae. Various phlorotannin components are found in brown algal species, thus we hypothesized that the antifouling activities of polyphenolic compounds may differ and that the analysis of phlorotannin profiles could be useful for estimating their ecological functions. We surveyed the epiphyte richness in the apical portions of 373 thalli from 15 sargassacean species, demonstrating that the variation and abundance of epiphyte species differed remarkably among the basiphyte species. However, there was a weak negative correlation between the density and total phlorotannin content of the basiphyte algae in only one of the 18 epiphyte species. The interspecific differences in the phlorotannin profile were characterized by quantitative ¹H nuclear magnetic resonance spectroscopy (qNMR), and four major groups were categorized based on cluster and principal component analyses of polyphenolic signals in the qNMR spectra. The epiphyte Neosiphonia harveyi was more abundant on Sargassum hemiphyllum, S. patens and S. piluliferum than on other basiphyte species, and these three species were similar according to the cluster analysis. These results suggest that some phlorotannin components may be more effective for antifouling; thus interspecific differences in the phlorotannin profile could affect the variation and abundance of epiphytes.     

Nutrient limitation in relation to phytoplankton carotenoid/chiorophyll a ratios in freshwater mesocosms

The 480/665 nm absorption ratio for pigment extracts was evaluatedas an indicator of nutrient limitation using freshwater planktoncommunities and a mesocosm approach. The mesocosm design wasused to create various nutrient regimes for the phytoplanktoncommunities, and nutrient limitation was detected by means ofgrowth response assays (¹⁴ fixation and pigment increase followingaddition of nutrients) and the 480/665 ratio. Results from fourperiods in 1993 and one period in 1994 showed that high 480/665ratios (indicative of nutrient limitation) were only found atchlorophyll a concentrations <20 µg I^–1, wherenutrient limitation was not detected. Periods with potentialnutrient limitation exhibited low 480/665 ratios. Consequently,the absolute values of the 480/665 ratio could not be used topredict nutrient limitation. However, when nutrients were addedto nutrient- limited phytoplankton communities in growth responseassays, the ratio decreased, indicating that the 480/665 ratiocan be used as a relative index to detect nutrient limitationin bioassays.