Epiphytic Macroalgae Research Articles

Reintroduction of self-facilitating feedbacks could advance subtidal eelgrass (Zostera marina) restoration in the Dutch Wadden Sea

Extensive subtidal eelgrass (Zostera marina) meadows (~150 km2) once grew in the Dutch Wadden Sea, supporting diverse species communities, but disappeared in the 1930s and have been absent ever since. Identifying the most critical bottlenecks for eelgrass survival is a crucial first step for reintroduction through active restoration measures. Seagrasses are ecosystem engineers, inducing self-facilitating feedbacks that ameliorate stressful conditions. Consequently, once seagrass, including its self-facilitating feedbacks, is lost, reintroduction can be challenging. Therefore, we aimed to test whether 1) sediment stabilization and 2) hydrodynamic stress relief would facilitate eelgrass survival in a field experiment replicated at two sites in the Dutch Wadden Sea. We induced feedbacks using biodegradable root-mimicking structures (BESE-elements) and sandbag barriers. Root mimics had a significant positive effect, increasing the chances of short-term survival by +67% compared to controls. Contrary to our expectations, barriers decreased short-term survival probabilities by -26%, likely due to hydrodynamic turbulence created by the barrier edges, leading to high erosion rates (-14 cm). Site selection proved crucial as short-term survival was entirely negated on one of the two study sites after five weeks due to high floating and epiphytic macroalgae loads. No long-term survival occurred, as plants died at the other site two weeks later. Overall, we found that sediment stabilization by root-mimicking structures was promising, whereas manipulating hydrodynamic forces using sandbag barriers had adverse effects. A mechanistic understanding of transplant failures is required before attempting large-scale restoration. Our study indicates that for seagrass restoration in the Wadden Sea, one should carefully consider 1) the reintroduction of positive feedbacks through restoration tools, 2) donor population choice and transplantation timing, and 3) site selection based on local biotic and abiotic conditions. Optimizing these restoration facets might lower additive stress to a degree that allows long-term survival.

Epiphytic macroalgae of maricultured Sargassum and their potential utilizations

Epiphytism commonly occurs in marine benthic macroalgae and seagrass communities under natural conditions and those of mariculture. This can greatly obstruct the cultivation of commercial seaweeds and ultimately impacts the seaweed aquaculture industry negatively. Against a background of climate change and a rapidly increasing market demand, the commercial Sargassum species is experiencing increasing challenges posed by epiphytic macroalgae. Severely reduced growth, lower quality, the emergence of diseases, and the ultimate death of the algae can lead to a commercial loss. Attempts to limit epiphytic macroalgae in aquaculture have so far been inefficient. However, epiphytic macroalgae are also rich in nutritional compounds and their relative biomass could be used as efficiently as the cultivated seaweed. As epiphytes cannot effectively be controlled by the current physical, chemical, and other methods in most cases, the perspective of comprehensive utilization could be an alternative over complete prevention and control by traditional methods. Compared to the existing strategies for controlling the growth and spread of epiphytes in seaweed aquaculture, the integrated and indiscriminate harvest and utilization of epiphytic macroalgae as fertilizer, animal food additive agents, as well as the development of biodegradable materials, might prove to be alternative valorization. However, the implementation of epiphytic macroalgae utilizations still needs to overcome the technical obstacles.

Evaluation of bioprospecting potential of epiphytic Gracilaria edulis harvested from seaweed farm in Seriwe Bay, Lombok, Indonesia

Abstract. Prasedya ES, Fitriani F, Saraswati PBA, Haqiqi N, Qoriasmadillah W, Hikmaturrohmi H, Nurhidayati SZ, Ariati PEP. 2023. Evaluation of bioprospecting potential of epiphytic Gracilaria edulis harvested from seaweed farm in Seriwe Bay, Lombok, Indonesia. Biodiversitas 24: 5343-5351. The seaweed industry is strategically important in Indonesia, comprising over 40% of the nation's aquaculture annual production. Despite the industry's promising growth, various challenges and problems remain, including intense epiphyte infestation. Hence, investigating the economic value of these epiphytes could provide new opportunities for potential industrial applications. Epiphytic algae is commonly found growing on commercial seaweeds which causes decreased biomass and increased risk of crop failure. Information regarding these epiphytic algae remains limited. This study investigates the molecular identification of the abundant epiphytic macroalgae found in one of the largest seaweed farms in, Seriwe Bay, Lombok, Indonesia. In addition, the epiphytic bioactive activity is also evaluated for further industrial potential. Molecular identification with the mitochondrial marker COX1 identifies the epiphytic macroalgae as Gracilaria edulis (S.G.Gmel.) P.C.Silva. The Indonesian G. edulis is closely related to the G. edulis specimens from Malaysia (JQ026083.1), Philippines (KY995636.1 and KY995635.1), and Thailand (JQ026088.1). The outgroup used was the G. edulis specimen from India (KP099563.1) because it shows the most distinct relationship to the other specimens. Extracted agar of Seriwe G. edulis shows moderate yield (21%) and low gel strength (134 g/cm2). The phytochemical content analyses show that G. edulis agar has a TPC value of 3.65 ± 0.52 mg GAE/g and promising antioxidant activity (DPPH IC50 = 797.40 ± 1.50 µg/mL; ABTS IC50 = 558.40 ± 1.44 µg/mL). Further phytochemical profiling with GCMS shows various promising major constituents such as tetradecanoic acid, neophyte diene, pentadecanoic acid, and hexadecanoic acid. Therefore, the findings suggest that G. edulis displays potential applications in the functional food and cosmetic industry.

Biodiversity of epiphytic marine macroalgae in Mexico: composition and current status

Abstract Marine epiphyte studies in Mexico, including macroalgae, are lacking in the published literature. Floristic studies have been mainly focused on identifying the algae growing on rocky substrata, and epiphytic algae have been recorded, but only occasionally. The aim of this work is to establish the current state of knowledge of the epiphytic macroalgae and their hosts on the Mexican coasts. A systematic revision of the literature published from 1950 to 2021 is also reported, the literature information is included, and the composition, species richness, current state of knowledge of the epiphytic marine macroalgae, and their relationship with the various marine Mexican ecoregions are reported. Sixty-one publications since 1950 included at least one record of epiphytic macroalgae. In this study, 615 species of epiphytic macroalgae and 224 species of hosts for Mexico are reported. This checklist will provide a baseline for future taxonomic and biogeographic studies of the epiphytic marine algae in the country.

Differential growth and physiological responses of Sargassum fusiforme and epiphytic Ulva lactuca to culture densities and interspecific competition

The commercial seaweed Sargassum fusiforme is adversely affected by the increasing presence of epiphytic macroalgae, mainly Ulva species, during seawater cultivation, especially at high culture densities. In the present study, comparative studies of S. fusiforme and Ulva lactuca were carry out to examine their physiological responses to densities between monoculture and bi-culture. The results showed that, both species of algae showed significant reduction in growth when the density of the cultures (mono-and bi-culture) was increased, although U. lactuca exhibited stronger growth and photosynthetic rate than S. fusiforme in both cultures. Specifically, for S. fusiforme, its maximum quantum yield of PSII (Fv/Fm), light harvesting efficiency (α), soluble carbohydrate (SC) content, and the ratio of SC/SP were all significantly decreased by high density, whereas its nitrate reductase (NR) activity, chlorophyll a (Chl a) and soluble protein (SP) contents were significantly increased in the monoculture. High density also decreased the photosynthesis and contents of SC and SP of U. lactuca in the monoculture. Moreover, the SC contents and NR activities of both S. fusiforme and U. lactuca significantly increased whereas their SP contents decreased in the bi-culture regardless of the culture densities. U. lactuca was dominant because of its potent neighboring shading and possible allelopathic effects on S. fusiforme. Its nutrients uptake was also more rapid than that of S. fusiforme in bi-culture. The interspecific competition between the two algae became intense with the increasing density. Thus, for the maricultivation of S. fusiforme, a moderate culture density would be preferable because of the higher photosynthetic efficiency and growth rate of S. fusiforme.

Differences of photosynthesis and nutrient utilization in Sargassum fusiforme and its main epiphyte, Ulva lactuca

Sargassum fusiforme is often adversely affected by epiphytic algae during its cultivation. However, the biological differences between S. fusiforme and the epiphytic algae have not yet been elucidated detrimental to the management of S. fusiforme culture. In this study, we sampled S. fusiforme and main epiphytic algae Ulva lactuca in a marine culture cycle and compared their biological characteristics. It indicated that, except during low-temperature months (January and March), the photosynthetic electron activity of U. lactuca were generally higher than S. fusiforme. The nitrogen uptake rates of S. fusiforme and U. lactuca were all significantly higher in the earlier growth stage than other stages. In most cases, the nitrogen uptake and utilization of U. lactuca was higher than those of S. fusiforme. Although S. fusiforme absorbed more trace elements, U. lactuca had relatively strong photosynthesis and nutrient absorption performance; thus, the latter accumulated more soluble carbohydrate and protein and may have stress effect on S. fusiforme. This study will be helpful for understanding the differences in the biological characteristics of economic seaweed and its epiphytic macroalgae and provides a reference for the friendly management and healthy development of seaweed cultivation.

The relative contribution of fleshy epiphytic macroalgae to the production of temperate maerl (rhodolith) beds

Maerl beds are composed of unattached red calcareous coralline algae. When located in shallow ecosystems, these calcareous macroalgae provide substrates for the development of fleshy epiphytic macroalgae, which contribute to the productivity of the maerl beds. To assess the importance of their contribution, we estimated the primary production of the main taxa of fleshy epiphytic macroalgae (Solieria chordalis or Rhodomelaceae), growing in 2 distinct Lithothamnion corallioides maerl beds in the Bay of Brest (Brittany, France), characterized by different depths and incident irradiances. We estimated epiphytic algal photosynthetic parameters derived from photosynthesis-irradiance curves calculated from incubations in photo-respirometry chambers at different irradiances and in the dark. A comparison with results previously obtained in L. corallioides showed that in the 2 studied maerl beds there were no differences between maerl and its fleshy epiphytic macroalgae in terms of photo-acclimation to low irradiances. However, fleshy epiphytic macroalgae had higher photosynthetic efficiencies and photosynthetic rates per unit of biomass or chlorophyll a than the maerl species. Estimations of net primary production per surface area of maerl bed indicated that fleshy epiphytic macroalgae account for 25% of maerl bed productivity. Interactions between L. corallioides and its fleshy epiphytic macroalgae may affect their respective contributions. In the deepest maerl beds, shading by fleshy epiphytic macroalgae may have a detrimental impact on L. corallioides net primary production, whereas in the shallowest maerl beds, fleshy epiphytic macroalgae may protect maerl from photoinhibition under high irradiances.

Distribution of macroalgae epiphytes and host species from the Cuban marine shelf inferred from ecological modelling

Ecological Niche Modelling (ENM) is a tool widely used in ecology to determine environmental conditions and the potential distribution of species. In this article we assess the potential distribution, tolerance limits and similarity niche of macroalgae epiphytes and hosts from the Cuba marine shelf. Using different methods (BIOCLIM, Gower, Maxent and SVM) we have modelled the niche for each species. The final prediction map of distribution was made using the ensemble prediction technique. The similarity of ENMs was quantified by Schoener D and Hellinger I distance. The predictive power of all models was reasonable, since the values of the area under the curve (AUC) were greater than 0.9. The host macroalgae most closely related to the spatial distribution pattern of potential abundance of epiphytic macroalgae are Stypopodium zonale (Kendall correlation, r2 = 0.886) and Digenea simplex (Kendall correlation, r2 = 0.777). Environmental variables that contributed mostly (30 %) to the ecological niche models were: the average maximum salinity per year (35.5−36 PSU); the average minimum flow velocity per year (0.2 m·s−1) and the average minimum light at ground level per year (10−60 E·m−2·yr−1). The results show that epiphytic macroalgae and their most common hosts are generalist species (niche width 0.8) with high overlap in their niche (Schoener D > 0.7; Hellinger I distance = I > 0.6).

When descriptive ecology meets physiology: a study in a South Atlantic rhodolith bed

AbstractThis study presents two years of characterization of a warm temperate rhodolith bed in order to analyse how certain environmental changes influence the community ecology. The biomass of rhodoliths and associated species were analysed during this period andin situexperiments were conducted to evaluate the primary production, calcification and respiration of the dominant species of rhodoliths and epiphytes. The highest total biomass of rhodoliths occurred during austral winter.Lithothamnion crispatumwas the most abundant rhodolith species in austral summer. Epiphytic macroalgae occurred only in January 2015, withPadina gymnosporabeing the most abundant. Considering associated fauna, the biomass of Mollusca increased from February 2015 to February 2016. Population densities of key reef fish species inside and around the rhodolith beds showed significant variations in time. The densities of grouper (carnivores/piscivores) increased in time, especially from 2015 to 2016. On the other hand, grunts (macroinvertebrate feeders) had a modest decrease over time (from 2014 to 2016). Other parameters such as primary production and calcification ofL. crispatumwere higher under enhanced irradiance, yet decreased in the presence ofP. gymnospora. Community structure and physiological responses can be explained by the interaction of abiotic and biotic factors, which are driven by environmental changes over time. Biomass changes can indicate that herbivores play a role in limiting the growth of epiphytes, and this is beneficial to the rhodoliths because it decreases competition for environmental resources with fleshy algae.

Epiphytic macroalgae and hosts of the marine shelf of Cuba: Current status, composition and diversity

The taxonomic composition and diversity of host and epiphytic macroalgal species are important elements in the structure and diversity of marine ecosystems. In this paper, the current state of knowledge and diversity of epiphytic macroalgae and their hosts in Cuba are determined. A systematic review of the scientific literature published from 1900 to 2018 was carried out. The current status of knowledge, main trends, composition, species richness and diversity in the different habitats and areas of the shelf were determined according to the records. We identified 37 publications dealing with the composition and diversity of epiphytism in macroalgae. The studies are grouped into two periods: the first one begins in 1955 addressing only the taxonomy; and the second one begins after 1989 focused on ecology. The flora of Cuban epiphytic macroalgae and hosts is 131 and 130 species, respectively. Habitats with greater structural complexity possess a greater richness of epiphytes, taxonomic structure and alpha diversity. The distribution patterns of epiphytic richness are influenced by both the sampling bias and the limited approach to epiphytism in phycological studies. The average taxonomic distinction (Δ+) expected for the habitats and zones of the Cuban shelf is 82, with 95% confidence limits between 77.21 and 100. Differences in species richness are the component that contributes most significantly to increasing the beta diversity of the epiphytic macroalgae due to the high environmental heterogeneity.

Filamentous calcareous alga provides substrate for coral-competitive macroalgae in the degraded lagoon of Dongsha Atoll, Taiwan.

BackgroundThe chemically-rich seaweed Galaxaura is not only highly competitive with corals, but also provides substrate for other macroalgae. Its ecology and associated epiphytes remain largely unexplored. To fill this knowledge gap, we undertook an ecological assessment to explore the spatial variation, temporal dynamics, and diversity of epiphytic macroalgae of Galaxaura divaricata on patch reefs in the lagoon of Dongsha Atoll, a shallow coral reef ecosystem in the northern South China Sea that has been repeatedly impacted by mass coral bleaching events.MethodsTwelve spatially independent patch reefs in the Dongsha lagoon were first surveyed to assess benthic composition in April 2016, and then revisited to determine G. divaricata cover in September 2017, with one additional Galaxaura-dominated reef (site 9). Four surveys over a period of 17 months were then carried out on a degraded patch reef site to assess the temporal variation in G. divaricata cover. Epiphytic macroalgae associated with G. divaricata were quantified and identified through the aid of DNA barcoding at this degraded site.ResultsPatch reefs in the Dongsha lagoon were degraded, exhibiting relatively low coral cover (5–43%), but high proportions of macroalgae (13–58%) and other substrate (rubble and dead corals; 23–69%). The distribution of G. divaricata was heterogeneous across the lagoon, with highest abundance (16–41%) in the southeast area. Temporal surveys showed consistently high covers (mean ± SD = 16.9 ± 1.21%) of G. divaricata for 17 months. Additional photographic evidence suggested that overgrowth of G. divaricata can persist for 3.5 years. Yet, G. divaricata provides substrate to other macroalgae (e.g., Lobophora sp.) that also limit the growth of corals.ConclusionsOur study demonstrates that an allelopathic seaweed, such as G. divaricata, can overgrow degraded coral reefs for extended periods of time. By providing habitat for other harmful macroalgae, a prolonged Galaxaura overgrowth could further enhance the spread of macroalgae, and strengthen negative feedback loops, decreasing the recovery potential of degraded reefs.

Biodiversity of epiphytic macroalgae (<em>Chlorophyta, Ochrophyta</em>, and <em>Rhodophyta</em>) on leaves of <em>Zostera marina</em> in the northwestern Iberian Peninsula

The composition, abundance, and distribution of epiphytic macroalgae living in meadows of Zostera marina L. in the northwestern Iberian Peninsula are here analyzed. We identified 63 species: 40 red algae, 16 brown algae, and 7 green algae. Most of them are classified as filamentous or filiform functional forms, while Pneophyllum fragile Kütz. was the only encrusting species. In general, the surface covered by epiphytes on the leaves of Zostera marina was low and a 43% of species were only found in juvenile stages. Regarding their frequency, 10 species were collected in the majority of the areas, while others were rare. Most species were found both epiphytic and in other substrata of the meadows, but 9 were exclusively epiphytic. We detected 9 introduced species.

Seasonal change in spatial variability of eelgrass epifaunal community in relation to gradients of abiotic and biotic factors

AbstractSeagrass‐associated macroinvertebrates (epifauna) play important roles as mediators between primary producers and higher consumers in seagrass beds. However, many aspects of the variation in the epifaunal community in seagrass beds remain to be investigated. In this study, we examined how the epifaunal community structure varied seasonally and spatially with abiotic and biotic factors in an eelgrass bed of Akkeshi, northeastern Japan. We predict that abiotic factors are more definitive of the variation in the epifaunal community than biotic factors when the eelgrass bed is less productive in early spring and late autumn, whereas biotic factors including macro‐epibiotic organisms (epiphytic macroalgae and sessile animals on eelgrass blades) are more influential when the eelgrass bed is more productive from late spring to early autumn. The epifaunal community composition varied greatly with season, and its spatial variation was correlated with different sets of abiotic and biotic factors in different seasons. Epibiotic organisms, in addition to other abiotic and biotic factors, explained some of the variation, especially in the productive summer seasons, despite the relatively low biomass of epibiotic organisms compared to that of eelgrass and epiphytic microalgae. Inconsistent with our prediction, abiotic factors were more definitive of the spatial patterns of the epifaunal communities from spring to summer when the productivity of the eelgrass bed was increasing, whereas biotic factors were found to be more important in the autumn when the productivity declined. Our result highlights the importance of epibiotic organisms on eelgrass blades to the epifaunal community, which was underappreciated in previous studies.

A Rapidly Expanding Macroalga Acts as a Foundational Species Providing Trophic Support and Habitat in the South Pacific

Foundation species facilitate associated communities and provide key ecosystem functions, making anthropogenically driven phase-shifts involving these species critically important. One well-documented such phase-shift has been from coral to algal domination on tropical reefs. On South Pacific coral reefs, the macroalga Turbinaria ornata has expanded its range and habitat but, unlike algae that often dominate after phase-shifts, T. ornata is structurally complex and generally unpalatable to herbivores. Therefore, it may serve a foundational role on coral reefs, such as providing habitat structure to more palatable primary producers and corresponding trophic support to fishes. We predicted increasing T. ornata density would facilitate growth of associated algae, resulting in a positive trophic cascade to herbivorous fish. An experiment manipulating T. ornata densities showed a unimodal relationship between T. ornata and growth of understory algae, with optimal growth occurring at the most frequent natural density. Epiphyte cover also increased with density until the same optimum, but remained high with greater T. ornata densities. Foraging by herbivorous fishes increased linearly with T. ornata density. An herbivore exclusion experiment confirmed T. ornata facilitated epiphytes, but resource use of epiphytes by herbivores, though significant, was not affected by T. ornata density. Therefore, T. ornata performs foundational roles because it provides novel habitat to understory and epiphytic macroalgae and trophic support to consumers, though likely this function is at the expense of the original foundational corals.

Biodiversity in canopy-forming algae: Structure and spatial variability of the Mediterranean Cystoseira assemblages

In the Mediterranean Sea, Cystoseira species are the most important canopy-forming algae in shallow rocky bottoms, hosting high biodiverse sessile and mobile communities. A large-scale study has been carried out to investigate the structure of the Cystoseira-dominated assemblages at different spatial scales and to test the hypotheses that alpha and beta diversity of the assemblages, the abundance and the structure of epiphytic macroalgae, epilithic macroalgae, sessile macroinvertebrates and mobile macroinvertebrates associated to Cystoseira beds changed among scales. A hierarchical sampling design in a total of five sites across the Mediterranean Sea (Croatia, Montenegro, Sardinia, Tuscany and Balearic Islands) was used. A total of 597 taxa associated to Cystoseira beds were identified with a mean number per sample ranging between 141.1 ± 6.6 (Tuscany) and 173.9 ± 8.5(Sardinia). A high variability at small (among samples) and large (among sites) scale was generally highlighted, but the studied assemblages showed different patterns of spatial variability. The relative importance of the different scales of spatial variability should be considered to optimize sampling designs and propose monitoring plans of this habitat.

The floating Sargassum (Phaeophyceae) of the South Atlantic Ocean – likely scenarios

:This study represents the efforts of a network of researchers to characterise the large, floating Sargassum (Fucales, Phaeophyceae) biomass that had reached the Brazilian coast in 2014 and 2015. Material collected during these events was identified as Sargassum natans and S. fluitans using morphological characteristics; ITS2 sequences showed low divergence (0%–3%) with sequences of nine other Sargassum species. Several epiphytic macroalgae, invertebrates and fishes were associated with the floating Sargassum. Satellite images did not support the hypothesis of slicks moving south from the Sargasso Sea in the northern Atlantic Ocean. This strengthens the hypothesis that there is a matrix of pelagic Sargassum in the central Atlantic Ocean and that biomass accumulation should be considered a result of the combination of physicochemical seawater conditions and biological interactions. The biomass accumulation of the stranded Sargassum was estimated during four events, peaking in 98 kg m−2 wet weight on a beach on the Amazonian coast. The landing of huge Sargassum biomass represents a potential source of environmental stress, as it can lead to an increase in oxygen demand and eventually synthesise and release chemical compounds with allelopathic properties. On the other hand, these floating islands are a fundamental element of the biogeography and macroecology of tropical environments in the Atlantic Ocean, providing connectivity south/north and east/west among marine biodiversity from Atlantic reef environments. Studies concerning Sargassum effects on local communities are necessary for the proper management of this phenomenon.

Biomass and Habitat Characteristics of Epiphytic Macroalgae in the Sibuti Mangroves, Sarawak, Malaysia.

Mangroves support diverse macroalgal assemblages as epibionts on their roots and tree trunks. These algae provide nutrients to the primary consumers in the aquatic food web and have been reported to be substantial contributors to marine ecosystems. The species diversity, biomass, and habitat characteristics of mangrove macroalgae were investigated at three stations in the Sibuti mangrove estuary, Sarawak, Malaysia, from November 2012 to October 2013. Three groups of macroalgae were recorded and were found to be growing on mangrove prop roots, namely Rhodophyta (Caloglossa ogasawaraensis, Caloglossa adhaerens, Caloglossa stipitata, Bostrychia anomala, and Hypnea sp.), Chlorophyta (Chaetomorpha minima and Chaetomorpha sp.), and Phaeophyta (Dictyota sp.). The biomass of macroalgae was not influenced (p>0.05) by the season in this mangrove forest habitat. The macroalgal species Hypnea sp. contributed the highest biomass at both Station 1 (210.56 mg/cm2) and Station 2 (141.72 mg/cm2), while the highest biomass was contributed by B. anomala (185.89 mg/cm2) at Station 3. This study shows that the species distribution and assemblages of mangrove macroalgae were influenced by environmental parameters such as water nutrients, dissolved solids, and salinity in the estuarine mangrove habitats of Sibuti, Sarawak.

Epiphytic macroalgae mediate the impact of a non-native alga on associated fauna

The introduction of a non-native, habitat-forming macroalga may have impacts on the seaweed-associated faunal community. Codium fragile subsp. fragile is a well-known and widespread algal invader that may compete with native habitat-forming macroalgae and affect ecosystem services. This alga can be abundant at semi-exposed/sheltered sites on the south-west coast of Norway, where its vertical distribution range overlaps with another canopy-forming alga, the native Fucus serratus. Whether these seaweeds support similar or dissimilar associated communities will influence the ecological impact of C. fragile subsp. fragile. Therefore, the richness and composition of fauna associated with these species was assessed by sampling at three localities. While the majority of taxa occurred on both F. serratus and C. fragile subsp. fragile, there were clear differences in community composition between them. Fauna taxa richness and community composition were also related to macroalgal epiphyte abundance, and there were a number of taxa associated to high epiphyte samples. The results suggest that shared macroalgal epiphytes lead to higher similarity between the invertebrate communities associated with C. fragile subsp. fragile and F. serratus, providing correlative evidence that epiphytic macroalgae play a role in shaping the impact of this macroalga on associated fauna.

Structural complexity and species composition of Potrero Grande and Santa Elena mangrove forests in Santa Rosa National Park, North Pacific of Costa Rica

<p>La mayoría de los manglares del Pacífico Norte de Costa Rica son de los más impactados en el país. Además, la información científica sobre la fisiología, ecología, estructura y geoquímica de estos manglares es limitada. Este estudio analizó la complejidad estructural y composición de especies de dos bosques de manglar del Pacífico Norte: Potrero Grande y Santa Elena. Las visitas al campo se realizaron entre mayo y junio del 2012. Se utilizó el método deCuadrantes Centrados en un Punto (PCQM) para estudiar la estructura del bosque. Se anotó las especies de mangle, altura, diámetro a la altura del pecho (DAP) y densidad del dosel en diez puntos a lo largo de cada transecto. Así mismo, se registró la fauna asociada y cobertura de macroalgas epífitas sobre las raíces de mangle. En cada punto se determinó la salinidad de agua intersticial. Se calculó la densidad, área basal, dominancia, valor de importancia e índice de complejidad. <em>Rhizophora racemosa</em> fue la especie con mayor dominancia relativa y valor de importancia para ambos sitios. Santa Elena es el manglar con el mayor índice de complejidad (IC=26.9), lo cual podría deberse a la alta densidad encontrada. Potrero Grande es considerado como uno de los manglares más desarrollados de la costa del Pacífico Norte de Costa Rica, dadas sus características estructurales (árboles con grandes alturas y DAP)y de composición de especies. La distribución conocida de <em>Pelliciera rhizophorae</em> en Costa Rica alcanzaba su límite norte en el manglar de Potrero Grande; sin embargo, este estudio extiende esta distribución más al norte, ya que se encontraron algunos individuos en Santa Elena. A diferencia de Potrero Grande, Santa Elena no cuenta con un sector marino protegido adyacente, esto ha resultado en la extracción de recursos y actividades turísticas incontroladas en la zona. Se recomienda la creación de un área de protección marina en la Bahía de Santa Elena para que sirva de zona de amortiguamiento al manglar.</p>

Red sea urchins (Echinus esculentus) and water flow influence epiphytic macroalgae density

The importance of forests of the kelp Laminaria hyperborea along the Norwegian coast is related to the three-dimensional structure that they create together with the associated macroalgae. Today, kelp forests have recovered in several areas after an extensive overgrazing by green sea urchins (Strongylocentrotus droebachiensis). However, red sea urchins (Echinus esculentus) have been observed grazing on kelp and algae in recently recovered kelp forests. Apart from grazing pressure, the abundance of algae depends on environmental conditions, such as light and water flow. The main aim of this study was to analyse how densities of red sea urchins, wave exposure and current speed influence densities of epiphytic macroalgae associated with kelp stipes. Our results show that the density of red sea urchins had a negative effect on macroalgal densities. In the well-developed kelp forest (i.e. in a late successional stage found in the southern region), macroalgal density decreased with depth and increased with water flow, both in terms of waves and currents. Wave forces had a higher effect than tidal-driven currents. In the recently recovered kelp forests (in the northern region), we found lower densities of epiphytic macroalgae in shallow compared to deep waters, most likely caused by red sea urchin grazing. Our study concludes that water flow is important for the ecological function of the kelp forest through the influence on habitat-forming epiphytic macroalgae, and that grazing by red sea urchins might severely affect kelp forest resilience in recently recovered areas.