PHLOROTANNINS AS CHEMICAL DEFENSE AGAINST MACROALGAL EPIPHYTES ON ASCOPHYLLUM NODOSUM

Brock, E., Åberg, P., & Pavia, H. Department of Marine Botany, Göteborg University, Box 461, SE 40530 Göteborg, Sweden. Phlorotannins are a group of polyphenolic acids present in brown algae. They have been shown to act as defense against herbivores and UV-B radiation. They have also been suggested to function as a defense against epiphytes. In this study the effect of the presence of macroalgal epiphytes on the phlorotannin content in Ascophyllum nodosum was analysed. Six adult plants of A. nodosum were collected from each of four sites in the archipelago on the west coast of Sweden. Four apical parts from each of the 24 plants were analysed for their phlorotannin content. For each plant, two samples were without any visible macroalgal epiphyte growth and two samples were 50-100% covered by epiphytes, mainly of the orders Ceramiales and Ectocarpales. We were not able to detect any general effect of epiphytes on the phlorotannin content. There was, however, a significant interaction between the two factors algal individual and epiphytes, where apical parts with epiphytes present had either higher or lower levels of phlorotannin than samples without epiphytes. Furthermore, there was a general, significant difference in the phlorotannin content among sites. The results suggest that the relationship between macroalgal epiphytes and phlorotannin production in A. nodosum is complex and influenced by several interacting factors.     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.     

Distribution and development of some Manx epiphyte populations

The success ofElachista fucicola as an epiphyte ofFucus vesiculosus is partly due to its ability to grow on most parts of the host thallus. Its ability to reach reproductive maturity quickly ensures its fitness, even on temporary structures such as receptacles. Epiphyte distribution may also vary with host morphology.Himanthalia elongata is a basiphyte for several tissue-specific epiphytes:Ectocarpus fasciculatus, Elachista scutulata, Herponema velutinum andMyriactula areschougii are exclusive, or almost so, to receptacles. On growing receptacles their specificity extends to conceptacles, which also provide refuges from grazing. Epiphyte abundance in summer is greatest at the upper and lower limits ofHimanthalia distribution, suggesting that basiphytes living under suboptimal conditions are more prone to infestation by epiphytes. 5–10% ofHimanthalia receptacles are thought to persist over winter and so to facilitate the transmission of epiphytes to the following year's crop of receptacles. The distribution ofEctocarpus fasciculatus onLaminaria digitata differs in pattern from that onHimanthalia. The twoEctocarpus populations also differ morphologically, but both have reproductive and developmental, characteristics that are in accord with the ecological cycles of their basiphytes. This characteristic is likely to be an important factor in determining the success of an epiphyte. Success may also be facilitated by epiphyte variability or by possession of a fixed but well-adapted phenotype. The very high incidence of brown algal epiphytes on growingHimanthalia receptacles does not reflect the composition of the surrounding algal vegetation. The possibility that some host-recognition mechanism operates cannot be discounted. Dedicated to Dr. Dr. h. c. Peter Kornmann on the occasion of his eightieth birthday.     

Phlorotannins versus other factors affecting epiphyte abundance on the kelp Ecklonia radiata

We examined factors affecting the abundance and distribution of epiphytes (fouling) on the sublittoral kelp Ecklonia radiata. We first assessed the importance of phlorotannins as chemical defences against epiphytes by (a) correlating epiphyte loads on different parts of the thallus with the phlorotannin content of those tissues, and (b) experimentally testing the effects of variation in phlorotannin concentration against the settlement and growth of gametes of Ulva lactuca, a common epiphyte in the system. Tissue phlorotannin content was, at best, only weakly related to epiphyte loads, with r ² values typically <0.10. Inhibition of Ulva gametes only occurred at concentrations >10 mg l⁻¹, which is 5 orders of magnitude greater than levels of phlorotannins in the water column around beds of E. radiata, and 1–3 orders of magnitude greater than estimated levels in the boundary layer at the surface of the plant. We concluded that phlorotannins have a negligible impact on patterns of epiphytism on E. radiata, and proceeded to investigate other factors influencing the distribution and abundance of epiphytes. In our samples the relative age of different parts of the thallus was strongly correlated with epiphyte abundance, with epiphyte densities greatest on the oldest tissue and least on the youngest. Distal parts of the thalli also had greater epiphyte loads than basal parts. Field experiments in which kelp tissue was suspended at two heights in an E. radiata forest for varying lengths of time confirmed the importance of the length of time that the tissue was in the water, and its height in the water column, to the development of an epiphyte community. Comparison of epiphyte loads on tissue from primary (smooth) and secondary (rough) laminae in these experiments indicated that surface rugosity also affected fouling. Macroherbivores were rare on E. radiata, and abundances of mesofauna and epiphytes were positively related, suggesting that grazers were not important determinants of patterns of epiphyte abundance. Although phlorotannins have been previously suggested to play an important role as defences against epiphytes, we suggest that water-soluble compounds such as phlorotannins are less likely to be effective defences against epiphytes than non-polar metabolites, which can adhere to the surface of the producing organism.     

Defense mechanisms of sargassacean species against the epiphytic red alga Neosiphonia harveyi

Flora diversity and abundance of epiphytes are specific to their basiphyte species and may relate to variations in the defensive abilities of basiphytes. Thus, investigating the interactions between epiphytes and basiphytes is useful for a better understanding of the biological impact of epiphytism and the survival strategies of basiphytes. We examined the epiphyte density on five sargassacean species at six locations between two study sites, which showed that the epiphytic red alga Neosiphonia harveyi was remarkably less abundant on Sargassum siliquastrum at all locations. To assess its defense mechanism against N. harveyi, we performed bioassays of phlorotannins, which are considered effective in deterring fouling, by culturing sargassacean blades with N. harveyi carpospores and observed the process by which sargassacean blades remove epiphytes. When the carpospores were incubated with various concentrations of dissolved phlorotannins, settlement and germination were inhibited only at the highest concentrations (>0.1 g · L^?1), and this effect did not significantly differ among the five sargassacean species. When the carpospores were combined with blades from the five species, many of the spores attached and germinated on every blade. Because N. harveyi penetrated rhizoids into basiphyte tissues, cuticle peeling observed in all five sargassacean species could not remove this epiphyte after germination. However, in S. siliquastrum, the blade tissues around the germlings became swollen and disintegrative, and were removed together with the germlings. The spores normally grew on the dead blades, suggesting that the tissue degradation of S. siliquastrum is triggered by the infection of N. harveyi.     

Effects of territorial damselfish on an algal-dominated coastal coral reef

Territorial damselfish are important herbivores on coral reefs because they can occupy a large proportion of the substratum and modify the benthic community to promote the cover of food algae. However, on coastal coral reefs damselfish occupy habitats that are often dominated by unpalatable macroalgae. The aim of this study was to examine whether damselfish can maintain distinctive algal assemblages on a coastal reef that is seasonally dominated by Sargassum (Magnetic Island, Great Barrier Reef). Here, three abundant species (Pomacentrus tripunctatus, P. wardi and Stegastes apicalis) occupied up to 60% of the reef substrata. All three species promoted the abundance of food algae in their territories. The magnitudes of the effects varied among reef zones, but patterns were relatively stable over time. Damselfish appear to readily co-exist with large unpalatable macroalgae as they can use it as a substratum for promoting the growth of palatable epiphytes. Damselfish territories represent patches of increased epiphyte load on macroalgae, decreased sediment cover, and enhanced cover of palatable algal turf.     

Temporal dynamics of algal epiphytes on Leathesia marina and Colpomenia sinuosa macrothalli (Phaeophyceae)

This is the first study on the temporal dynamics of the epiphyte communities of Leathesia marina and Colpomenia sinuosa, in terms of richness, diversity and abundance, and their relationships between the hosts and the environmental factors. A total of 31 epiphyte taxa were recorded, with the two hosts sharing 64.5% of the epiphytic species found. The red algal epiphytic group had the highest abundance on both hosts and the diatoms presented the highest species richness. The epiphyte species on L. marina showed a progressive increase in abundance during the warm seasons that was related to the end of the macroscopic life stage of the host. They also showed a greater specific richness on L. marina than on C. sinuosa, but a lower diversity and evenness, and a clear dominance of the species Urospora penicilliformis and Erythrotrichia carnea. Low abundance of epiphytes was found on C. sinuosa, without temporal variation, but high diversity and evenness and without any dominant species. In addition, a clear zonation was observed on this host, where epiphytic abundance decreased on the lateral and upper part of the thallus.     

Tropical marine herbivore assimilation of phenolic-rich plants

Phenolics in marine brown algae have been thought to follow a latitudinal gradient with high phenolic species in high latitudes and low phenolic species in low latitudes. However, tropical brown algae from the western Caribbean have been shown to be high in phlorotannin concentration, indicating that latitude alone is not a reasonable predictor of marine plant phenolic concentrations. This study shows that the range of high phenolic phaeophytes is not limited to the western Caribbean but encompasses the western tropical Atlantic, including Bermuda and the Caribbean, where algal phlorotannin concentrations can be as high as 25% dry weight (DW). Assimilation efficiencies (AEs) of phenolic-rich and phenolic-poor plants were examined in three tropical marine herbivores (the parrotfish, Sparisoma radians, and the brachyuran crab, Mithrax sculptus, from Belize and the parrotfish, Sparisoma chrysopterum, from Bermuda). AEs of phenolic-rich food by each of the three herbivore species were uniformly high, suggesting that high plant phenolic concentrations did not affect AEs in these species. This is in contrast to some temperate marine herbivores where phenolic concentrations of 10% DW have been shown to drastically reduce AE. The apparent contradiction is discussed in light of the effects of specific herbivore gut characteristics on successful herbivory of high phenolic brown algae.     

ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)1

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave‐sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species-rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi-deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought-adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization.     

Interaction mechanisms between Gracilaria chilensis (Rhodophyta) and epiphytes

Epiphytes can have a considerable effect on Gracilaria production, and Ulva is one of the commonest algal species identified as an epiphyte, reaching loads of 60% (g of epiphytes per g of Gracilaria) in the intertidal cultures of southern Chile. This study evaluates the relative importance of light reduction, addition of weight to the host thalli and nutrient depletion, as mechanisms determining the interaction effects of Ulva epiphytes on Gracilaria cultivation. Using field experiments undertaken during the main Gracilaria growth season (spring), we evaluate the mechanisms of epiphyte-host algae interaction by manipulating artificial epiphytes. The results indicate that Ulva can significantly depress Gracilaria biomass production and that the addition of weight to the host algae and the consequent dislodgement increase, appear to be the main mechanisms involved in the Ulva-Gracilaria interaction. However, the light reduction caused by the epiphytes can also partially explain the reduction in Gracilaria production. Nutrients depletion would not appear to fully account for the detrimental effects of Ulva over Gracilaria in intertidal farming areas of southern Chile.     

Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds

It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.     

Distribution of α-N-acetylgalactosaminidases among marine bacteria of the phylum <Emphasis Type="Italic">Bacteroidetes</Emphasis>, epiphytes of marine algae of the Seas of Okhotsk and Japan

Occurrence of α-N-acetylgalactosaminidases among 177 strains of marine bacteria of the phylum Bacteroidetes, epiphytes of marine algae growing on the littoral of the Seas of Okhotsk and Japan, was studied. About 36% of the isolates studied contained α-N-acetylgalactosaminidase. All of the bacteria of the genus Arenibacter (species A. latericius, A. certesii, and A. palladensis), irrespective of the source of isolation, synthesized this enzyme. The greatest number of α-N-acetylgalactosaminidase producers was found among the isolates from the algae Neosiphonia japonica, Acrosiphonia sonderi, and Ulva fenestrata sampled in the Cove of Trinity, Posyet Bay, the Sea of Japan. These were mainly bacteria of the genera Zobellia (50%) and Maribacter (58%). Among the epibionts studied, the bacteria Arenibacter latericius KMM 3523, an epiphyte of the brown alga Chorda filum from the Sea of Okhotsk, and Cellulophaga sp. KMM 6488, an epiphyte of the green alga Acrosiphonia sonderi from the Sea of Japan, were marked as the most promising sources of the enzyme. The results of this study showed that aerobic nonpathogenic marine Bacteroidetes, algal associants not requiring special cultivation conditions, are the promising, economical, and ecologically pure sources of unique and biotechnologically significant α-N-acetylgalactosaminidases.     

Influence of light and nitrogen on the phlorotannin content of the brown seaweeds Ascophyllum nodosum and Fucus vesiculosus

Phlorotannins, C-based defence compounds in brown seaweeds, show a high degree of spatial and temporal variation within seaweed species. One important model explaining this variation is the Carbon Nutrient Balance Model (CNBM), which states that the relative supply of carbon and limiting nutrients will determine the level of defence compounds in plants. Nitrogen is often considered to be the limiting nutrient for marine macroalgal growth and the CNBM thus predicts that when the carbon:nitrogen ratio is high, photosynthetically fixed carbon will be allocated to production of phlorotannins. In the present study, we evaluated the effects of light (i.e. carbon) and nitrogen on the phlorotannin content of two intertidal brown seaweeds, Ascophyllum nodosum and Fucus vesiculosus. This was done in an observational field study, as well as in a manipulative experiment where plants from habitats with different light regimes were subjected to different nitrogen and light treatments, and their phlorotannin content was measured after 14 days. The results showed that there was a negative relationship between tissue nitrogen and phlorotannin content in natural populations of F. vesiculosus, but not in A. nodosum. In the short term, the phlorotannin content in both algal species was not affected by changes in nitrogen availability. Exposure to sunlight had a positive effect on the phlorotannin content in natural populations of both algal species but, in the manipulative experiment, only F. vesiculosus showed a rapid response to changes in light intensities. Plants subjected to sunlight contained higher phlorotannin content than shaded plants. In conclusion, the results imply that nitrogen availability explains some of the natural variation in the phlorotannin content of F. vesiculosus, but the light environment has greater importance than nitrogen availability in predicting the phlorotannin content of each species.     

DISTRIBUTION OF ALGAL EPIPHYTES ACROSS ENVIRONMENTAL GRADIENTS AT DIFFERENT SCALES: INTERTIDAL ELEVATION,HOST CANOPIES,AND HOST FRONDS1

Understanding epiphyte distribution in coastal communities is important because these organisms affect many others directly or indirectly. Yet, their distribution has been considerably less studied than that of their hosts and other primary‐space holders. Identifying major sources of variation in epiphyte abundance is thus still a need. Environmental gradients help predict species distribution and are pervasive on marine shores. In this study, we test the notion that environmental gradients across intertidal elevation, throughout host canopies, and along host fronds explain a large variation in the abundance of sympatric epiphytes. Our model system was the assemblage of Ascophyllum nodosum (L.) Le Jol. and its epiphytes Vertebrata lanosa (L.) T. A. Chr. [= Polysiphonia lanosa (L.) Tandy], Elachista fucicola (Velley) Aresch., and Pylaiella littoralis (L.) Kjellm. On the coast of Nova Scotia (Canada), we found evidence of a spatial segregation among these species at almost all scales. While the red epiphyte V. lanosa was more common at high‐ and midintertidal elevations (peaking at midelevations) and on middle segments of host fronds, the brown epiphytes E. fucicola and P. littoralis were more common at low elevations and restricted to distal segments of host fronds. Canopy habitat affected abundance only for V. lanosa, which was more common within the host canopy than on its periphery at midelevations. Since the studied gradients are related to predictable changes in abiotic factors, the identification of likely causes behind the observed patterns was facilitated. Our study ends by proposing abiotic and biotic factors that deserve priority in the experimental testing of the forces structuring this assemblage.     

Epiphyte and herbivore interactions impact recruitment in a marine subtidal system

Marine assemblages are influenced by the rate and timing of species settlement and recruitment. Both abiotic factors and biotic interactions can impact recruitment rates of marine species in a variety of systems. However, the impacts of species which recruit at the same time upon each other are less well understood. We investigated the relationship between the recruitment of Lacuna vincta, a small (<6 mm shell diameter) marine snail, and two species of algal epiphytes, the native Ceramium virgatum and the invasive Neosiphonia harveyi, in the shallow subtidal zone of Narragansett Bay, Rhode Island. All three species exhibit peak recruitment densities during two months in the summer. We found that the presence of algal epiphytes facilitates the recruitment rate of L. vincta, regardless of the epiphyte species composition. We also found a positive relationship between the number of L. vincta present and epiphyte recruitment, which is disproportionately driven by higher recruitment of N. harveyi than C. virgatum. Understanding recruitment dynamics and interactions is vital to effectively mitigate the effects of and adaptations to changes due to the establishment of non-native species.     

Seasonal Occurrences of Epiphytic Algae on the Commercially Cultivated Red Alga Kappaphycus Alvarezii (Solieriaceae, Gigartinales, Rhodophyta)

Common problems faced in farming of the red algal genus Kappaphycus/Eucheuma are “ice-ice disease” and the occurrence of epiphytes. Considerable work has been documented on “ice-ice disease” and it's mode of infection but limited information is available on the emergence of epiphytes. The present study addresses the phenomenon of epiphyte infection, its prevalence in commercially cultivated red alga, Kappaphycus alvarezii, and their variability associated with seasonality. Cultured seaweed became susceptible to epiphytes in the dry seasons (1) between March – June and (2) September – November. Findings revealed Neosiphonia savatieri (Hariot) M. S. Kim et I. K. Lee, as the dominant infecting epiphyte, representing up to 80–85% of the epiphyte present during peak seasons. Besides N. savatieri, Neosiphonia apiculata, Ceramium sp., Acanthophora sp. and Centroceras sp. were observed in smaller quantities. SEM (Scanning Electron Microscope) micrographs revealed the epiphyte's attachment to the host. Further histological study showed the extent of penetration of epiphytes into the host's cortex tissues and condition of its surrounding tissues. The outbreak of epiphytic filamentous red algae also correlated with drastic changes in seawater temperature and salinity during March– June and September – November.     

Latitudinal variation in intertidal algal community structure: the influence of grazing and vegetative propagation

Summary The hypothesis that sea urchin grazing and interactions with turf-forming red algae prevent large brown algae from forming an extensive canopy in the low intertidal zone of southern California was tested with field experiments at two study sites. Experimental removal of sea urchins resulted in rapid algal recruitment. Crustose coralline algae which typically dominate the substratum in areas with dense urchin populations were quickly overgrown by several species of short-lived green, brown and red algae. The removal of urchins also significantly increased the recruitment of two long-lived species of large brown algae (Egregia laevigata and Cystoseira osmundacea at one study site and E. laevigata and Halidrys dioica at the other). The experimental plots at both sites were eventually dominated by perennial red algae.A two-factorial experiment demonstrated that sea urchin grazing and preemption of space by red algae in areas where urchins are less abundant are responsible for the rarity of large brown algae in the low intertidal of southern California. The three dominant perennial red algae, Gigartina canaliculata, Laurencia pacifica and Gastroclonium coulteri, recruit seasonally from settled spores but can rapidly fill open space with vigorous vegetative growth throughout the year. These species encroach laterally into space created by the deaths of large brown algae or by other disturbances. Once extensive turfs of these red algae are established further invasion is inhibited. This interaction of algae which proliferate vegetatively with algae which recruit only from settled spores is analogous to those which occur between solitary and colonial marine invertebrates and between solitary and cloning terrestrial plants.It is suggested that a north-south gradient in the abundance of vegetatively propagating species, in grazing intensity and in the frequency of space-clearing disturbances, may account for latitudinal variation in intertidal algal community structure along the Pacific coast of North America.     

Reti trofiche e flussi di energia nei sistemi a fanerogame marine

Abstract

Food webs and energy flow in seagrass ecosystems. A review on the pathways in the food webs of seagrass ecosystems, both tropical and temperate, with a particular emphasis to Mediterranean Posidonia oceanica meadows is given. Three main pathways of energy transfer from primary producers (host plant and algal epiphytes) were identified: i) the plant itself through photosynthetic tissue; ii) the leaf detritus which in some species forms a litter compartment; iii) the algal epiphytes of leaf blades. The detritus and epiphyte ways are the most common, but they can be differently important according to the season and the spatial patterns of the meadows.     

The biology of an Antarctic aquatic moss community

SUMMARY. Two species of aquatic moss ( Calliergon sarmentosum and Drepanocladus sp.) occur in deep water in Moss Lake, Signy Island (60° 43'S, 45° 38'W). Their elongate stems support a structurally complex community of epiphytic algae and associated invertebrates which has a greater diversity than the surrounding benthic algal communities.
Qualitative differences in the distribution and abundance of the epiphytic algae are described. Two groups of algae present on both mosses are distinguished–'habitual' and 'casual' epiphytes. On Calliergun , algae are most abundant in the leaf axil. The succession of epiphytes down the stem and the progressive deterioration of the moss plant are used to characterize six stem zones.
The invertebrates are benthic and most move actively among the moss. Six species of rotifers are more or less permanently attached and show a preference for the middle stem zones where epiphyte cover is highest. Four species favour the leaf axil, the other two colonize the bare underside of the leaf.
A settlement experiment has shown the importance of wind-induced mixing in summer for the transport of some epiphytic species from shallow parts of the lake. The settlement of sessile rotifers is effected by their larvae.
Photosynthesis declines from the stem apex to the dead old stem. Much of the primary production of the community is algal. The respiration maximum occurs where the highest concentration of epiphytic algae and invertebrates is found.
Interrelationships between the invertebrates and the epiphytic algae are suggested and a comparison is made between these data and other studies.