Macroalgal Community Structure Research Articles

Life between tides: Spatial and temporal variations of an intertidal macroalgal community at Potter Peninsula, South Shetland Islands, Antarctica

Intertidal zones are one of the most studied habitats in the world. However, in Antarctica, further studies are needed for a more complete understanding of these systems. When conspicuous Antarctic intertidal communities occur, macroalgae are a key component. Given that intertidal communities have a fast response to variations in environmental conditions and could reflect climate fluctuations, we conducted a non-destructive study with photographic transects in an intertidal zone at Potter Peninsula, Isla 25 de Mayo/King George Island, over four years and during five months of the warm season. We tested the general hypothesis that macroalgal intertidal communities are mainly structured by the vertical stress gradient and that changes in temperature between seasons and between years have a great influence in the macroalgal community structure. Spatial, seasonal and inter-annual variations were studied using GLM, quantile regression and NMDS ordinations. The vertical stress gradient was the main factor that explained macroalgal cover. The Low and the Middle level shared similarities, but the latter was more variable. The High level had the lowest cover, richness and diversity. The dominant species here was the endemic red alga Pyropia endiviifolia, which is strongly adapted to extreme conditions. At the Middle level, there was a significant increase in macroalgal cover during spring months, and it stabilized in summer. Inter-annual variations showed that there is a strong variation in the total macroalgal cover and community structure over the studied years. Environmental conditions have a significant effect in shaping the studied intertidal community, which is very sensitive to climate oscillations. An increase in temperature produced a decrease of annual ice foot cover, number of snow days and - as a result - an increase in macroalgal cover. In a global climate-change scenario, a shift in species composition could also occur. Species with wide physiological tolerance that grow in warmer conditions, like Palmaria decipiens, could benefit, while other species will be discriminated. More detailed studies are necessary to predict future changes in Antarctic intertidal communities.

Seasonal regulation of herbivory and nutrient effects on macroalgal recruitment and succession in a Florida coral reef.

Herbivory and nutrient enrichment are drivers of benthic dynamics of coral reef macroalgae; however, their impact may vary seasonally. In this study we evaluated the effects of herbivore pressure, nutrient availability and potential propagule supply on seasonal recruitment and succession of macroalgal communities on a Florida coral reef. Recruitment tiles, replaced every three months, and succession tiles, kept in the field for nine months, were established in an ongoing factorial nutrient enrichment-herbivore exclusion experiment. The ongoing experiment had already created very different algal communities across the different herbivory and nutrient treatments. We tracked algal recruitment, species richness, and species abundance through time. Our results show seasonal variation in the effect of herbivory and nutrient availability on recruitment of coral reef macroalgae. In the spring, when there was higher macroalgal species richness and abundance of recruits, herbivory appeared to have more control on macroalgal community structure than did nutrients. In contrast, there was no effect of either herbivory or nutrient enrichment on macroalgal communities on recruitment tiles in cooler seasons. The abundance of recruits on tiles was positively correlated with the abundance of algal in the ongoing, established experiment, suggesting that propagule abundance is likely a strong influence on algal recruitment and early succession. Results of the present study suggest that abundant herbivorous fishes control recruitment and succession of macroalgae, particularly in the warm season when macroalgal growth is higher. However, herbivory appears less impactful on algal recruitment and community dynamics in cooler seasons. Ultimately, our data suggest that the timing of coral mortality (e.g., summer vs. winter mortality) and freeing of benthic space may strongly influence the dynamics of algae that colonize open space.

The influence of habitat structure, at different spatial scales, on the ecological distribution of macroalgal communities in streams

Habitat heterogeneity influences the composition and structure of macroalgal communities in lotic environments. However, depending on the spatial scale, different environmental characteristics may exert more or less influence. This study aimed to evaluate, at different spatial scales of observation, the influences of local and regional environmental variables on ecological distribution of macroalgae in stream ecosystems. The field work was conducted during the months of June and July 2007 in streams of two river basins located in southern Brazil. The spatial scales used were drainage basin, shading, mesohabitat, and microhabitat. According to the results, there are few differences regarding abiotic variables between spatial scales, however, suggesting that sunlight and, consequently, the shading scale have a strong impact on the distribution pattern of stream macroalgae. The mesohabitat scale at the current velocity proved to be an important factor in structuring communities of macroalgae. Finally, microenvironmental factors (e.g., substrate, current velocity, and light availability) appear to exert their direct influence on the spatial distribution of stream macroalgae, generating particular features in each spatial scale of observation, although regional abiotic parameters (e.g., temperature, pH, and conductivity) should also be considered for the structural characterization of these organisms.

Spring Macroalgal Flora and Community Structure in Subtidal Zone around Coasts of Jeju Island, Korea

Spring Macroalgal Flora and Community Structure in Subtidal Zone around Coasts of Jeju Island, Korea

Implementation of a new index to assess intertidal seaweed communities as bioindicators for the European Water Framework Directory

An index CCO (cover, characteristic species, opportunistic species) has been developed for the implementation of the European Water Framework Directory (WFD) in coastal waters, using intertidal macroalgal communities as bio-indicator (Biological Quality Element). CCO is based on the calculation of three metrics corresponding to the global cover of macroalgal communities (metric 1), the number of characteristic species per topographic level/seaweed community (metric 2) and the cover of opportunistic species (metric 3). The final rating is obtained by pooling the scores of the three metrics. Results are given for 32 sites in 29 water bodies, grouped into four biogeographic regions along the Channel–Atlantic coasts of France. Over the six-year study, most of sites were sampled twice each (every three years). CCO index revealed that 25 coastal water bodies of both the Channel and the Bay of Biscay were in good or high ecological quality status (EQS), whereas only 4 of them were moderate and none in poor to bad status. However, significant differences have been found between sites and between geographic regions, water bodies located in Brittany obtaining the best EQS. No significant change occurred between the three-year sampling sets. A significant correlation has been established between a three-component anthropogenic pressure index and CCO ratings, showing the accuracy of CCO to evaluate the impact of anthropic activities on the structure and development of macroalgal communities as indicator of the ecological quality of coastal water bodies.

한국 남서해안 진도군 금갑의 해조상 및 군집구조의 계절 변화

Seasonal variation in marine macroalgal community structure was examined at the intertidal zones of Geumgap, Jindo, Korea, from October 2013 to August 2014. In total, 56 macroalgal species were identified, including 9 green, 12 brown, and 35 red algae. Annual seaweed biomass was 548.96 g wet wt. /<TEX>$m^2$</TEX> with seasonal range between 371.08 g wet wt. /<TEX>$m^2$</TEX> at summer and 32.91 g wet wt. /<TEX>$m^2$</TEX> at winter. The dominant seaweed in terms of biomass was Sargassum thunbergii and subdominant species were Gelidium elegans, Sargassum fusiforme, and Ishige okamurae. The vertical distribution of seaweeds from the upper to lower intertidal zones was Gloiopeltis spp., Ulva spp.- S. thunbergii, S. fusiforme, Ishige okamurae - S. thunbergii, S. fusiforme, G. elegans. Annual seaweed coverage, richness index (R), evenness index (J'), and diversity index (H') values were 27.95%, 6.10, 0.38, and 1.38, respectively. Coarsely branched form was the most dominant functional group in terms of species number and biomass among benthic macroalgal species.

변산반도 해조류 군집구조의 계절적 변동

We examined seasonal variation in the structure of marine macroalgal communities at five sites around the Byeonsan Peninsula, Korea, from January to October 2011. Sixty eight species were identified, including 11 green, 17 brown and 40 red algae. Species richness was highest at Gyeokpo (51 species) followed by Sambal (47), Gosapo (34), Byeonsan (33), and Habgoo (18). Seaweed biomass ranged from 12.98 to 145.33 g dry <TEX>$wt/m^2$</TEX>, with maximum and minimum biomasses at Gyeokpo and Habgoo, respectively. Sargassum thunbergii was the representative alga species occupying 47.89% of the total biomass. The dominant seaweeds were S. thunbergii, Corallina pilulifera, Ulva spp, Gracilaria vermiculophylla, and Carpopeltis affinis. No distinctive vertical distribution of seaweeds was found because S. thunbergii, Ulva spp, and G. vermiculophylla were all distributed from high to low shore. Community indices were as follows: dominance index (DI), 0.44-0.61; richness index (R), 6.27-10.35; evenness index (J'), 0.38-0.59; and diversity index (H'), 1.48-1.71. Gyeokpo had the most biomass and highest species richness, and the lowest percentage of Ulva species. However, species richness declined at Gyeokpo, from 78 to 51 species within 10 years, implying that eutrophication and sedimentation from Mankyeong and Dongjin rivers have reduced the stability of seaweed communities.

The roles of environmental conditions and spatial factors in controlling stream macroalgal communities

In the last three decades, several studies have suggested that the structure of stream macroalgal communities is shaped by local environmental variables, but some recent papers have shown that the relevance of the environment on these communities may be overestimated. Using Partial Redundancy Analysis (pRDA), we analyzed macroalgal communities (considering all macroalgae and Phyla Chlorophyta, Cyanobacteria, and Rhodophyta individually) from 105 streams in southern Brazil to test the hypothesis that the relative contributions of the environment and space on the taxonomic composition of these communities is mainly determined by the biological traits and dispersal mechanisms typical for each group. The pRDA showed that the taxonomic composition of the entire community and green algae were explained by both space and environment, whereas for cyanobacteria, only the environment was significant, and for red algae, only space was significant. These divergences in the relative contribution among algal phyla were consistent with our initial hypothesis and can be ascribed to the differences in the ecological features of each group. Our results also support the idea that the community structure of organisms with low dispersal is influenced more significantly by spatial processes, whereas for organisms with high dispersal the local environmental variables are more influential.

The non-native turf-forming alga Caulacanthus ustulatus displaces space-occupants but increases diversity

Non-indigenous seaweeds can be found in coastal habitats worldwide yet the ecological effects of only ~6 % of macroalgal introductions have been studied. The turf-forming red alga Caulacanthus ustulatus, a putative introduction from Asia, was discovered in southern California in 1999, yet has received very little attention despite being common in rocky intertidal habitats in the region. The purpose of this study was to evaluate the potential effects of Caulacanthus on native invertebrate and seaweed community composition. Macrofaunal, meiofaunal, and macroalgal community structure and diversity were compared between patches with (non-native) and without Caulacanthus (native) in the upper intertidal zone at 5 locations in southern California. Caulacanthus appears to displace macro invertebrates, such as barnacles, limpets, and periwinkles, while facilitating a more diverse array of meiofauna and macroalgae. This is likely due to the formation of a novel turf habitat in the upper zone where turfs are uncommon in this region naturally; algal turfs can increase habitat complexity, trap sediment, and maintain moisture during low tide which likely benefits meiofauna and seaweeds by providing food, habitat, or refuge from desiccation stress. Subsequent comparisons of invertebrate and seaweed assemblages were conducted in native and non-native patches at one site in the upper intertidal zone as well as in the middle intertidal zone where a native turf zone exists. Despite differences in community composition in the upper intertidal zone, no differences were observed in the middle zone, providing support that the novel turf created by Caulacanthus in the upper zone drives community differences.

Development of a quality index to evaluate the structure of macroalgal communities

A quality index Ics (= index of community structure) has been developed as a single numeric descriptor to assess the structural state of macroalgal communities and to evaluate their relative development on rocky shores. Coverage of seaweed species were sampled on the field and treated by taxonomic groups, size classes and structural – functional groups (SFG), giving sub-indices It (= taxonomic index), Is (= stratification index) and Io (= organization index), respectively. Six macroalgal communities corresponding to canopies (belts) distributed vertically on the shore have been investigated for several years in 14 sites of Brittany (France). Communities developing at high topographic levels could be distinguished from those occurring at mid-tide to low levels by Ics values. Communities were globally stable over the sampling period, with few geographical discrepancies. Seasonal or sub-community variations could be tracked by sub-index values. The value of Ics to demonstrate the potential evolution of seaweed communities is discussed by comparison to other quality indices and in the perspective of ecological perturbations.

한국 남서해안 흑산도와 홍도의 조간대 해조류 생물량과 군집구조의 계절적 변동

Seasonal variation in marine macroalgal community structure was examined at the intertidal zones of Heuksando and Hongdo, Shinan, Korea, from July 2008 to May 2009. In total, 86 macroalgal species were identified, including 12 green, 19 brown, and 55 red algae; 67 species at Heuksando and 70 species at Hongdo, were observed. Annual seaweed biomass was 252.44 g dry <TEX>$wt/m^2$</TEX> at Heuksando and 217.67 g dry <TEX>$wt/m^2$</TEX> at Hongdo. The dominant seaweed in importance value (IV > 15) differed between the sites: Sargassum thunbergii at Heuksando and Corallina pilulifera at Hongdo. The vertical distribution pattern of seaweeds from the upper to lower intertidal zones at Heuksando was Gloiopeltis spp., Ulva spp. - S. thunbergii, S. fusiforme, Hildenbrandia rubra - S. thunbergii, C. pilulifera. On the rocky shore of Hongdo, seaweed zonation was distinct: Porphyra yezoensis, Gloiopeltis spp., Ulva spp. - C. pilulifera, S. fusiforme, Myelophycus simplex - Chondrus ocellatus, C. pilulifera, and Carpopeltis affinis. Annual seaweed coverage, richness index (R), evenness index (J'), and diversity index (H') values were greater at Hongdo (41.35%, 12.82, 0.59, and 2.50 respectively) than at Heuksando (31.54%, 11.93, 0.44, and 1.87 respectively), which may indicate that the seaweed community at Hongdo is more stable relative to the one at Heuksando.

Usefulness of tissue nitrogen content and macroalgal community structure as indicators of water eutrophication

We tested the hypothesis that the community structure and biochemical composition of macroalgae reflect the degree of nutrient concentrations in the water column. Benthic community structure and tissue nitrogen (N) content of macroalgae on intertidal rocky shores at three sites were investigated in relation to sewage effluents on Mireuk Island, Tongyeong city, on the southern coast of Korea. Ulva australis clearly dominated at site 1, which was close to a sewage treatment plant, where higher dissolved inorganic N and dissolved inorganic phosphate concentrations were observed. U. australis-dominated communities also appeared at site 2 (intermediate levels of nutrient enrichment). The macroalgal assemblage at site 3 (unimpacted site) was significantly different from those at sites 1 and 2. Five species (U. australis, Sargassum fusiforme, Grateloupia elliptica, Gelidium amansii, and Sargassum horneri) were dominant at site 3, representing 87 % of the total coverage throughout the study period. Species richness (d), evenness (J'), and diversity index (H') were highest at site 3, intermediate at site 2, and lowest at site 1, showing a negative relationship with nutrient levels. These results indicate that macroalgal community structure can be used as a bioindicator in water quality assessment. The tissue N content of green and red algae was responsive to nutrient availability, while the tissue N content of brown algae was relatively unchanged among the sites. This suggests that tissue N content as a bioindicator for detecting the influence of sewage effluent should be considered to reflect the N storage capacity of macroalgae.

啃食性端足类强壮藻钩虾对筼筜湖三种大型海藻的摄食选择性

Marine algae vary considerably in their nutritional,chemical,and structural composition,thus providing a heterogeneous and variable food resource for marine herbivores. However,Due to seasonal fluctuation in species composition and abundance of marine algae,herbivores usually encounter the environments with little tasty,highly nutritional food. Because herbivores eat foods that are much lower in nutrients than their own tissues,they display a diversity of behavioral and physiological adaptations to cope with the low nutritional value of their foods. Selective feeding on more nutritious plants,increasing consumption of lower quality foods( compensatory feeding) have all been proposed as important behaviors allowing herbivores to obtain adequate nourishment.Amphipods were common benthic species in macroalgal-based communities. They may regulate the macroalgal community structure by their selective feeding behavior. This study investigated the feeding of amphipod Ampithoe valida on three dominant macroalgae( Ulva lactuca,Gracilaria tenuistipitata var. liui and Rhizoclonium sp.) of Yundang Lagoon, and analyzed how the nutritional quality in terms of dry mass / wet mass( DM / FM),total organic carbon( TOC),total nitrogen( TN),C / N ratio and protein level may affect the food selectivity in the amphipod. The results showed that there was negative correlation between the feeding rates and the DM / FM,or TOC / FM of the macroalgae when macroalgae was separately offered to A. valida,indicating compensatory feeding behavior in the amphipod,that is,A. valida can use quantity to compensate quality when nutritional value of macroalgae was low. A. valida preferentially fed on U. lactuca and Rhizoclonium sp.,and their feeding rates negatively correlated to the TOC concentrations or protein levels in the macroalgae. However,no relationship was found between the feeding rates and TN. These results suggest there are no predictable effects of the nutritional quality on the feeding selectivity of amphipods. However,although A. valida have strong preference to green algae,Yundang Lagoon doesn' t structure a macroalgal community dominated by red algae G. tenuistipitata var. liui.

동해안 3개 해역의 조하대 해조상 및 군집구조

Abstract The purpose of this study is to analyze seasonal variations of seaweed community structure according to ocean environment at three areas in the east coast of Korea. Mean water temperatures of Gosung, Samchuk, and Gyeongju were 8.3 ℃ , 11.2 ℃ , and 13.1 ℃ , respectively, during the growing winter season of 2011. Subtidal benthic macroalgal flora and community structure were investigated at the sites between February to November 2011. The numbers of seaweed species at the areas were 38, 12, and 15, respectively. The amounts of biomass were 7.35 kg m -2 , 1.80 kg m -2 , and 0.84 kg m -2 , respectively, during the period. The values of C/P, R/P, and (R+C)/P representing flora characteristics at Sokcho area were 0.1, 1.1, and 1.2, respectively. The values of flora characteristics at Samchuk were 0.3, 0.6, and 1.0, respectively. The values of flora characteristics at Gyeongju were 0.4, 4.0, and 1.2, respectively. Key Words : Algal flora, Water temperature, Community, Seaweed species

Green sea urchins structure invertebrate and macroalgal communities in the Magellan Strait, southern Chile

Although sea urchins play a central role in determining the structure and functioning of macroalgal communities in many parts of the world, past research in southern Chile has failed to identify strong effects of urchin grazing, despite the prevalence of coralline-dominated commu- nities and abundant urchins, which indicate a likely structuring role for urchins. Here, we con- ducted experimental removals of the most common urchin, the green sea urchin Arbacia dufres- nii, on a single bedrock wall in the Magellan Strait, Chile. We monitored the responses of invertebrate and macroalgal communities relative to a control wall 6 times over 64 wk. The struc- ture of macroalgal communities on each wall remained similar until more than 40 wk after urchin removal, at which time the community structure diverged, with significantly more macroalgae present on the urchin removal wall. These changes coincided with the onset of early summer and were likely driven by greater settlement, recruitment and growth of algae in the absence of urchins. After 64 wk, the abundance of chitons, bryozoans, mussels and the small bivalve Hiatella solida was also significantly greater on the urchin removal wall. Herbivory by A. dufresnii on these high latitude rocky reefs appears to have a potential structuring effect on benthic assem- blages, although further replicated field experiments are required to document where and when these effects may occur.

Macroalgal Community Structure on the Rocky Shores of Ongdo, Jusamdo, and Woejodo Islands of the Yellow Sea, Korea

The benthic algal community structures of the seaweed biomass, vertical distribution of dominant seaweeds, and species composition were examined on the rocky shores of Ongdo, Jusamdo, and Woejodo Islands, Korea, in August 2006. A total of 68 seaweeds were identified, comprising 5 green, 11 brown, and 52 red algae from the three study sites. The number of species at Ongdo (32 species) was less than that at Jusamdo (45 species) and Woejodo (44 species). Jusamdo exhibited the maximum seaweed biomass (73.99 g dry <TEX>$wt/m^2$</TEX>), while the minimum value was found at Woejodo (36.90 g dry <TEX>$wt/m^2$</TEX>). On the three islands, coarsely branched forms were the most dominant functional group in terms of species number and biomass among benthic algal species. The dominant species were Gelidium amansii, Chondrus ocellatus, and Chrysymenia wrightii at Ongdo, Sargasum thunbergii, Ulva pertusa, and Sargassum fusiformis at Jusamdo, and U. pertusa, Undaria pinnatifida, and Corallina pilulifera at Woejodo. Perennial seaweeds were abundant at Ongdo (G. amansii and C. ocellatus) and Jusamdo (S. thunbergii and S. fusiformis), whereas the sheet form of U. pertusa was relatively abundant at Woejodo Island.

Effects of the alien algae Undaria pinnatifida (Phaeophyceae, Laminariales) on the diversity and abundance of benthic macrofauna in Golfo Nuevo (Patagonia, Argentina): potential implications for local food webs

Changes in macroalgal community structure caused by invasive seaweeds have strong impacts on the associated macrofauna due to the role of macroalgae as autogenic ecosystem engineers. This study investigates the effect of Undaria pinnatifida on the abundance and diversity of benthic macrofauna in Golfo Nuevo, northern Patagonia, using a manipulative experiment involving the systematic removal of Undaria microthalli from strips of hard bottom during its eighth-month growing period. Species richness and diversity were higher in plots covered by Undaria than when Undaria was removed. Also, the abundance of two species of crustaceans, one species of sea urchin, one species of nemertina and several species of polychaetes was higher. We attribute these effects to the provision of new habitat structure by Undaria, a larger and structurally more complex species than the local native seaweeds. These results support the hypothesis that complex habitats enhance abundance and species richness, by offering different shelter and foraging opportunities compared to morphologically simpler habitats. Based on a review of diet studies in the region, we speculate that Undaria could potentially produce a bottom-up effect on local food chains by increasing abundance of prey for a wide variety of predators, from invertebrates to marine mammals. While our study has a narrow temporal and spatial scale, we expect similar effects of Undaria on the macrofauna in other sites of the Argentine coast, especially those dominated by small native macroalgae.

Temporal and spatial distribution of macroalgal communities of mountain streams in Valle de Bravo Basin, central Mexico

The stream macroalgal community is controlled by heterogeneous physical, chemical, and biological factors related with multiple spatial and temporal scales; however, the mechanisms that explain diversity and distribution are scarcely known. The present investigation was conducted to characterize the macroalgal community structure and spatial and temporal distribution and to recognize biogeographic affinities with mountain streams from other regions. Habitat characteristics, abundance, and diversity were investigated in four mountain streams of Valle de Bravo Basin, central Mexico, during two annual cycles. Sampling of visible benthic growths was collected in the most contrasting parts of the year. Physicochemical parameters were recorded in situ at each site and the main ions and nutriments were evaluated for every collection. Statistical analysis between dates was assessed with one-way analysis of variance (ANOVA) and Canonical Correspondence Analysis (CCA). Observed richness average was four species per site and the high abundance of Phormidium interruptum, Nostoc parmelioides, Paralemanea mexicana, Batrachospermum gelatinosum, Sirodotia suecica, Cladophora glomerata, and Prasiola mexicana correlated with cold dry season, high current velocity, and a major size substrate. Valle de Bravo streams can be viewed as a habitat subjected to moderated disturbance, mainly due to the effects of seasonal changes in rainfall contrary to torrents expected of tropical regions. The seasonal patterns of macroalgal communities in Valle de Bravo basin were typically characterized by two distinct periods essentially determined by the rainfall regime and related to temperature, and can be viewed as habitats subjected to moderate disturbance according to intermediate disturbance hypothesis. The distribution species pattern registered suggests a group of temperate species frequently found in mountain regions of the Mexican Volcanic Belt and temperate eastern region of North America and may indicate a possible biogeographic connection with the Neartic region with similar environmental requirements.

통영 지역의 암반 조간대에서 배출수 유입으로 인한 해조 군집 구조와 엽체 내 질소 함량의 변화

Enrichment in nutrients coming from urban sewage outfalls can lead to eutrophication in coastal areas, which can also change the species composition and community structure of macro algal communities. We investigated the structure of the macro algal community within three rocky shores in order to assess any possible differences in their characteristics. Site 1 was located near Tongyeong city's sewage outfall, Site 2 was located near a public beach area, and Site 3 faced open channel of the Ocean. All three sites were located within the same stretch of the coast, where Site 2 was located between sites 1 and 3. We measured the nutrient concentration in water and the tissue nitrogen content in macro algae samples. Nutrients in the water column surrounding site 1 were high in ammonium (<TEX>$30.2\pm1.8{\mu}M$</TEX>), nitrate (<TEX>$26.2{\pm}0.1{\mu}M$</TEX>), and phosphate (<TEX>$2.7{\pm}0.1{\mu}M$</TEX>) content, and were characterized by low numbers of macroalgal species and species and a low species diversity index. In contrast, site 3 exhibited relatively low nutrient concentration levels and a high number of macroalgal species and a high species diversity index. Comparative analysis showed that the tissue nitrogen content of macroalgae were significantly (P<0.05) affected by the nutrient concentration in the water column. The tissue nitrogen content of green algae within site 1 was higher than the others sites. However, the tissue nitrogen content of brown algae was similar at all three sites. Thus, the tissue nitrogen content of macro algae and the macro algal community structure of intertidal rocky shores were dependent on location and the performance of macroalgal communities was dependent on water quality.

Top–down and bottom–up regulation of macroalgal community structure on a Kenyan reef

Top–down and bottom–up regulation in the form of grazing by herbivores and nutrient availability are important factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenic activities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, are altering the interaction of these two structuring forces. The present study was conducted in Kenya and investigates the relative importance of herbivory and nutrient loading on macroalgal community dynamics, by looking at alterations in macroalgal functional groups, species diversity ( H′) and biomass within experimental quadrats. The experiment was conducted in situ for 42 days during the dry season. Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition was conducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory is generally low and nutrient levels are relatively high for the region. Nutrient addition increased tissue nutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivore exclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticated forms. These results are in accordance with similar studies in other regions, but are unique in that they indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure is relatively low, continued anthropogenic disturbance results in further ecological responses and increased reef degradation.