Algal Functional Groups Research Articles

Harnessing Desmochloris edaphica Strain CCAP 6006/5 for the Eco-Friendly Synthesis of Silver Nanoparticles: Insights into the Anticancer and Antibacterial Efficacy.

Microalgae-mediated nanoparticle (NP) biosynthesis is a promising green synthesis method that overcomes the challenges of conventional synthesis methods. The novel Desmochloris edaphica strain CCAP 6006/5 was isolated, purified, and characterized morphologically and genetically. GC-MS analysis of the algal biomass (DBio) phytochemicals showed the abundance for elaidic acid (18.36%) and monoolein (17.37%). UV-VIS spectroscopy helped analyze the effects of the AgNO3 concentration, algal/silver nitrate ratio, temperature, reaction time, illumination, and pH on AgNP synthesis. DBio extract or cell-free medium (DSup) of D. edaphica successfully biosynthesized small silver NPs (AgNPs), namely, DBio@AgNPs and DSup@AgNPs, under optimum reaction conditions. TEM and SEM showed a quasi-spherical shape, with average diameters of 15.0 ± 1.0 nm and 12.0 ± 0.8 nm, respectively. EDx and mapping analyses revealed that silver was the main element, the NP hydrodynamic diameters were 77.9 and 62.7 nm, and the potential charges were -24.4 and -25.8 mV, respectively. FTIR spectroscopy revealed that the DBio@AgNPs, and DSup@AgNPs were coated with algal functional groups, probably derived from algal proteins, fatty acids, or polysaccharides, representing reductant and stabilizer molecules from the synthesis process. They showed significant anticancer activity against breast cancer cells (MCF-7), low toxicity against normal kidney cells (Vero), and potent inhibitory activity against Staphylococcus aureus, Bacillus subtilis, and Shigella flexneri. D. edaphica is a novel biomachine for synthesizing small, stable and potent therapeutic AgNPs.

Testing effects of bottom-up factors, grazing, and competition on New Zealand rocky intertidal algal communities.

Top-down and bottom-up factors and their interaction highlight the interdependence of resources and consumer impacts on food webs and ecosystems. Variation in the strength of upwelling-mediated ecological controls (i.e., light availability and herbivory) between early and late succession stages is less well understood from the standpoint of influencing algal functional group composition. We experimentally tested the effect of light, grazing, and disturbance on rocky intertidal turf-forming algal communities. Studies were conducted on the South Island of New Zealand at Raramai on the east coast (a persistent downwelling region) and Twelve Mile Beach on the west coast (an intermittent upwelling region). Herbivory, light availability, and algal cover were manipulated and percent cover of major macroalgal functional groups and sessile invertebrates were measured monthly from October 2017 to March 2018. By distinguishing between algal functional groups and including different starting conditions in our design, we found that the mosaic-like pattern of bare rock intermingled with diverse turf-forming algae at Twelve Mile Beach was driven by a complex array of species interactions, including grazing, predation, preemptive competition and interference competition, colonization rates, and these interactions were modulated by light availability and other environmental conditions. Raramai results contrasted with those at Twelve Mile Beach in showing stronger effects of grazing and relatively weak effects of other interactions, low colonization rates of invertebrates, and light effects limited to crustose algae. Our study highlights the potential importance of an upwelling-mediated 3-way interaction among herbivory, light availability, and preemption in structuring contrasting low rocky intertidal macroalgal communities.

Patterns of Phytoplankton and Microphytobenthos Development in Channel Ecotones in the Goryn River

Studies of phytoplankton and microphytobenthos of the Goryn' River demonstrated discrete-continual character of these communities' development, which reflects occurrence of ecotones in the channel and flood land system of the river. In ecotones, upstream and downstream them the species composition, dominant complexes and quantitative parameters changed, owing to specific features and hydrological conditions of the flow forming. The algal functional groups diagnostic technique was tested to assess state of the algal communities and revelation of their development specificity in the Goryn River, which enabled to reveal mechanisms of the algal communities' modifications in terms of the functional groups within the ecotones: pool, riffle, contact zone of the river channel and ameliorated flood land.

Trends in Dominican Republic Coral Reef Biodiversity 2015–2022

In 2015, we initiated a country-wide coral reef ecosystem-monitoring program in the Dominican Republic (DR) to establish biodiversity baselines against which trends in the most important components of coral reef ecosystem’s structure and function could be tracked. Replicate transects were set at a 10 m depth at each of the 12 coral reef sites within 6 DR regions in 2015, 2017, 2019, and 2022. We quantified the species-level abundances of adult and juvenile corals, reef fishes, sea urchins, lionfishes, and algal functional groups. Country-wide, coral cover and reef fishes have declined. The steepest declines occurred for reefs that had been among the best in the Caribbean in 2015. However, by 2022, adult and juvenile coral, parrotfish, and other herbivores had declined, and macroalgae had increased. The declines in north-shore coral abundance corresponded with the observed disturbances from coral bleaching, hurricanes, and disease. The capacity of reefs to recover from such disturbances has been compromised by abundant and increasing macroalgae that have likely contributed to north-shore declines in juvenile corals. Country-wide, the abundance of all reef fish species has declined below those of other regions of the Caribbean. Improved management of fishing pressure on coral reefs would likely yield positive results.

Distribution, population structure and settlement preference of Tubastraea spp. (Cnidaria: Scleractinia) on rocky shores of the Cagarras Islands Natural Monument and surroundings, Rio de Janeiro, Brazil

Tubastraea coccinea and T. tagusensis are invasive corals that have well-established populations along the broad Brazilian coasta. Over a decade of field surveys (2010–2021) in the Cagarras Islands Natural Monument, a no-take Marine Protected Area (MPA), and surroundings in Rio de Janeiro metropolitan region, the colonization processes of Tubastraea spp. has been followed up. In 2019, Tubastraea spp. population structures were determined by photoquadrats on Comprida (CO) and Cagarra (CA) islands, where patches with the highest coral densities had been detected. In laboratory, Tubastraea spp. planulation was recorded and settlement bioassays were conducted on live crustose coralline algae Lithophyllum spp. (Rhodophyta) compared to respective controls (i.e. dead Lithophyllum spp. fragments). A total of 1908 colonies of Tubastraea spp. were recorded in the photoquadrats, of which T. tagusensis represented practically all colonies (T. coccinea had a single record); thus, the analyses considered the data set for the former. The mean colonies density was 636.0 ± ind.m−2, composed mainly by founder polyps, and the mean cover was similar for CO (9.3%) and CA (13.9%) islands. Most of the founder polyps settled on crustose coralline algae — CCA (63.0%), followed by CCA/Turf (24.4%). Higher incidence of founder polyps on CCA (Lithophyllum spp.) indicates the importance of this algal functional group for the recruitment and colonization of T. tagusensis. Planulation was similar for both species and planulae preferred to settle and metamorphose on live Lithophyllum spp. These results on coral–algae interactions will contribute to enhance control/ management actions of Tubastraea spp. on Brazilian rocky shores.

Recyclable self-floating A-GUN-coated foam as effective visible-light-driven photocatalyst for inactivation of Microcystis aeruginosa

In this work, a recyclable self-floating A-GUN-coated (Ag/AgCl@g-C3N4@UIO-66(NH2)-coated) foam was fabricated for effective inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. The floating photocatalyst was able to inactivate 98% of M. aeruginosa within 180 min under the visible-light irrigation, and the floating photocatalyst exhibited a stable performance in various conditions. Moreover, the inactivation efficiency can still maintain nearly 92% after five times recycle experiments, showing excellent photocatalytic stability. Furthermore, effects of A-GUN/SMF floating catalyst on the physiological properties, cellular organics, and algal functional groups of M. aeruginosa were studied. The floating photocatalyst can not only make full use of excellent photocatalytic activities of A-GUN nanocomposite, but also promote contact between catalyst and algae, and realize the effective recovery of the photocatalyst. Finally, possible photocatalytic inactivation mechanisms of algae were obtained, which provides references for removing cyanobacteria blooms in real water bodies.

In situ prepared algae-supported iron sulfide to remove hexavalent chromium.

The effects of algae on the removal of contaminant by iron sulfide (FeS) are still unknown. Chlorella vulgaris (CV), a remarkable algal specie, was used to prepare the CV-supported FeS (CV-FeS) and to investigate the role that CV plays in the removal of a heavy metal (i.e., hexavalent chromium (Cr(VI)) by FeS. The stabilized effect from algal extracellular polymeric substance (EPS) enhanced the reactivity of FeS due to the decrease of FeS aggregation, thus increasing Cr(VI) removal rate from 0.21 min-1 to 0.79 min-1. Furthermore, the strong buffering induced by the algal functional groups could effectively prevent the solution pH from increasing, which improved Cr(VI) removal because acidic solution facilitated Cr(VI) reduction by FeS. However, the complexing capacity from algal EPS made Fe(II) unavailable for Cr(VI) reduction, which led to 35% decrease of Cr(VI) removal. The Fe(II) was oxidized to α-FeOOH by Cr(VI) in the absence of CV, while the unreacted Fe(II) was detected as in the form of Fe(OH)2 in CV-FeS. Cr(VI) was reduced to Cr(III) and S(-II) was oxidized to elemental sulfur (S8) regardless of the CV. This work showed the different roles of algae in the removal of Cr(VI) by FeS and provided value information for the application of FeS in the polluted algae-containing water system.

Timing of disturbance, top‐down, and bottom‐up driving on early algal succession patterns in a tropical intertidal community

SUMMARYHerbivory and nutrient enrichment are major drivers of the dynamics of algal communities. However, their effects on algal abundance are under the influence of seasons. This study investigated the effects of herbivory and nutrient enrichment on early algal succession patterns using cages (uncaged and fully caged treatments) and two nutrient levels (ambient and enriched concentrations). To determine seasonal influences, experiment plots on dead coral patches were cleared during both dry and rainy season. Of the 17 algal species recruited in the experiment plots, three were dominant: Ulva paradoxa C. Agardh, Padina in the Vaughaniella stage, and Polysiphonia sphaerocarpa Børgesen. In this succession process, U. paradoxa was the earliest colonizer and occupied the cleared plots within the first month after clearing with the highest percentage of 83.33 ± 1.67% to 88.33 ± 9.28%. Then, it was replaced by the late successional algae, Padina in the Vaughaniella stage, and P. sphaerocarpa. The effects of herbivory and nutrient enrichment on algal abundance varied across algal functional groups and seasons. During the dry season, neither herbivory nor nutrient enrichment affected Ulva cover but during the rainy season, Ulva cover was influenced by nutrient enrichment. However, the abundance of algae in this early stage was not apparently affected by either herbivory or nutrient enrichment. Our results indicated that the timing of disturbance strongly influenced the algal abundance and successional patterns in this tropical intertidal community.

Functional diversity among herbivorous sea urchins on a coral reef: grazing rate, dietary preference, and metabolism

Herbivores influence the structure and function of ecosystems, especially in the marine environment where ecosystems can be rapidly transformed due to the presence or absence of a single important grazer or grazing community. Intra-guild variation in the ecological functions of herbivores, however, likely determines their ultimate effects on benthic dynamics. For example, echinoids (sea urchins) can facilitate the growth of stony corals by consuming fleshy algal competitors, yet our understanding of taxonomic variation in their grazing behaviors remains limited. Here, we examined the trophic functions of 5 herbivorous echinoids on a coral reef in Maui, Hawaii. We conducted field-based assays to compare grazing rates and consumption profiles using several key algal functional groups and contrasted the results with reported differences in echinoid metabolism. Grazing rates varied among species by up to 10-fold, with taxonomic differences explaining 77-85% of the variation among individual urchins and metabolic rate explaining 81-98% of the taxonomic variation in mean biomass and energy ingestion rates. Though all species consumed several algae, they also exhibited distinct grazing behaviors. Species with lower metabolic rates exhibited the largest intraspecific variation in diets and showed no clear algal preferences. In contrast, species with higher metabolic rates consistently consumed or avoided specific macroalgae, indicating a positive relationship between metabolic rate and diet specificity. This phylogenetic variation in grazing and metabolism aligns with classic metabolic and foraging theory and suggests that species identity, community structure, and complementarity are likely key to understanding the functional roles of herbivorous echinoid communities on coral reefs.

Groups of small lakes maintain larger microalgal diversity than large ones

The question of whether one large, continuous area or many smaller habitats maintain more species is one of the most relevant questions in conservation ecology, and it is referred to as the SLOSS (Single Large Or Several Small) dilemma in the literature. This question has not yet been raised in the case of microscopic organisms, therefore we investigated whether or not the SLOSS dilemma could apply to phytoplankton and benthic diatom metacommunities. Benthic diatom and phytoplankton diversity in pools and ponds of different sizes (ranging between 10−2–107 m2) was studied. Species richness of water bodies belonging to neighbouring size categories was compared step by step across the whole size gradient. With the exception of the 104–105 m2 and 105–106 m2 size categories, where phytoplankton and benthic diatom richness values of the SL water bodies were higher than that of the SS ones, findings showed that the diversity of several smaller (SS) sized waters was higher than that in single large water bodies (SL) throughout the whole studied size range. The proportion of the various functional groups of algae, including both the benthic diatoms and phytoplankton, showed remarkable changes from the smaller water bodies to large sized ones.

Spatiotemporal Succession Characteristics of Algal Functional Groups and Its Impact Factors for a Typical Channel-Type Reservoir in a Southwest Mountainous Area

In order to explore the spatial and temporal variations of algal functional groups in the Zipingpu reservoir, a typical channel-type reservoir in the southwest mountainous area of China, water samples were collected from eight sections of the Zipingpu reservoir from April 2016 to March 2017.A total of 21 algal functional groups were identified as B, C, D, F, G, H1, J, L0, LM, MP, N, P, S2, T, W1, W2, X1, X2, X3, Y, and Z. Based on the analysis of the dominant degree (y > 0.02), the algal functional groups were dominated by W2, Y, L0, W1, MP, and B. The C-R-S strategy of algal growth in the Zipingpu reservoir showed that R-type was a more dominant type than the S- and C-type for the majority of the time. Peridinium (group L0, type S) was the significant algae in the Zipingpu reservoir algal bloom event in June 2016.Redundancy analysis (RDA) was used to explore the relationship between algal functional groups and environmental factors. The results showed that algal density, chlorophyll a, water temperature, and biochemical oxygen demand were the major factors influencing the spatiotemporal succession of algal functional groups across the eight sampling sections, with water temperature having the highest influence.

Biodiversity influences invasion success of a facultative epiphytic seaweed in a marine forest

The biotic resistance hypothesis predicts that more diverse communities should have greater resistance to invasions than species-poor communities. However for facultative and obligate epiphytic invaders a high native species richness, abundance and community complexity might provide more resources for the invader to thrive to. We conducted surveys across space and time to test for the influence of native algal species abundance and richness on the abundance of the invasive facultative epiphytic filamentous alga Lophocladia lallemandii in a Mediterranean Cystoseira balearica seaweed forest. By removing different functional groups of algae, we also tested whether these relationships were dependent on the complexity and abundance of the native algal community. When invasion was first detected, Lophocladia abundance was positively related to species richness, but the correlation became negative after two years of invasion. Similarly, a negative relationship was also observed across sites. The removal experiment revealed that more complex native communities were more heavily invaded, where also a positive relationship was found between native algal richness and Lophocladia, independently of the native algal abundance. Our observational and experimental data show that, at early stages of invasion, species-rich seaweed forests are not more resistant to invasion than species-poor communities. Higher richness of native algal species may increase resource availability (i.e. substrate) for invader establishment, thus facilitating invasion. After the initial invasion stage, native species richness decreases with time since invasion, suggesting negative impacts of invasive species on native biodiversity.

Interactive effects of three pervasive marine stressors in a post-disturbance coral reef

Ecosystems are commonly affected by natural, episodic disturbances that can abruptly and drastically alter communities. Although it has been shown that resilient ecosystems can eventually recover to pre-disturbed states, the extent to which communities in early stages of recovery could be affected by multiple anthropogenic stressors is poorly understood. Pervasive and rising anthropogenic stressors in coastal marine systems that could interactively affect the recovery of these systems following natural disturbances include high sedimentation, nutrient enrichment, and overfishing. Using a 6-month field experiment, we examined the effects of all combinations of these three stressors on key functional groups in the benthic community growing on simulated, post-disturbance reef patches within a system recovering from large-scale natural disturbances (corallivorous seastar outbreak and cyclone). Our study revealed that sedimentation, nutrient enrichment, and overfishing (simulated using exclusion cages) interactively affected coral survival and algal growth, with taxon-specific effects at multiple scales. First, our treatments affected corals and algae differently, with sedimentation being more detrimental to macroalgal growth but less detrimental to coral (Porites rus) survival in caged plots, driving significant interactions between sedimentation and caging for both taxa. We also observed distinct responses between coral species and between algal functional groups, with the most extensive responses from algal turf biomass, for which sedimentation suppressed the synergistic (positive) combined effect of nutrient enrichment and caging. Our findings suggest that different combinations of ubiquitous anthropogenic stressors, related to either sea- or land-based activities, interactively influence community recovery from disturbance and may alter species compositions in the resulting community. Our findings further suggest that anthropogenic stressors could promote further degradation of coral reefs following natural disturbances by inhibiting recovery to coral-dominated states that provide vital ecosystem services to coastal populations worldwide.

Grazer diversity interacts with biogenic habitat heterogeneity to accelerate intertidal algal succession.

Environmental heterogeneity contributes to coexistence by allowing species with different traits to persist when different species perform best at different times or places. This interaction between niche differences and environmental variability may also help explain relationships between biodiversity and ecosystem functioning, but few data are available to rigorously evaluate this hypothesis. We assessed how a biologically relevant aspect of environmental heterogeneity interacts with species diversity to determine ecosystem processes in a natural rocky intertidal community. We used field removals to factorially manipulate biogenic habitat heterogeneity (barnacles, bare rock, and plots that were 50/50 mixes of the two habitat types) and gastropod grazer species richness and then tracked algal community succession and recovery over the course of 1yr. We found that herbivore diversity, substrate heterogeneity, and their interaction played unique roles in the peak abundance and timing of occurrence of different algal functional groups. Early successional microalgae were most heavily grazed in diverse herbivore assemblages and those with barnacles present, which was likely due to complementary feeding strategies among all three grazers. In contrast, late successional macroalgae were strongly influenced by the presence of a habitat generalist limpet. In this herbivore's absence, heterogeneous habitats (i.e., mixtures of bare rock and barnacles) experienced the greatest algal accumulation, which was partly a result of complementary habitat use by the remaining herbivores. The complex way habitat identity and heterogeneity altered grazer-algal interactions in our study suggests species' differences and environmental heterogeneity both separately and interactively contribute to the relationship between biodiversity and ecosystem functions.

Abiotic versus biotic drivers of ocean pH variation under fast sea ice in McMurdo Sound, Antarctica.

Ocean acidification is expected to have a major effect on the marine carbonate system over the next century, particularly in high latitude seas. Less appreciated is natural environmental variation within these systems, particularly in terms of pH, and how this natural variation may inform laboratory experiments. In this study, we deployed sensor-equipped moorings at 20 m depths at three locations in McMurdo Sound, comprising deep (bottom depth>200 m: Hut Point Peninsula) and shallow environments (bottom depth ∼25 m: Cape Evans and New Harbor). Our sensors recorded high-frequency variation in pH (Hut Point and Cape Evans only), tide (Cape Evans and New Harbor), and water mass properties (temperature and salinity) during spring and early summer 2011. These collective observations showed that (1) pH differed spatially both in terms of mean pH (Cape Evans: 8.009±0.015; Hut Point: 8.020±0.007) and range of pH (Cape Evans: 0.090; Hut Point: 0.036), and (2) pH was not related to the mixing of two water masses, suggesting that the observed pH variation is likely not driven by this abiotic process. Given the large daily fluctuation in pH at Cape Evans, we developed a simple mechanistic model to explore the potential for biotic processes – in this case algal photosynthesis – to increase pH by fixing carbon from the water column. For this model, we incorporated published photosynthetic parameters for the three dominant algal functional groups found at Cape Evans (benthic fleshy red macroalgae, crustose coralline algae, and sea ice algal communities) to estimate oxygen produced/carbon fixed from the water column underneath fast sea ice and the resulting pH change. These results suggest that biotic processes may be a primary driver of pH variation observed under fast sea ice at Cape Evans and potentially at other shallow sites in McMurdo Sound.

Use of fuzzy logic models for prediction of taste and odor compounds in algal bloom-affected inland water bodies

Mechanistic modeling of how algal species produce metabolites (e.g., taste and odor compounds geosmin and 2-methyl isoborneol (2-MIB)) as a biological response is currently not well understood. However, water managers and water utilities using these reservoirs often need methods for predicting metabolite production, so that appropriate water treatment procedures can be implemented. In this research, a heuristic approach using Adaptive Network-based Fuzzy Inference System (ANFIS) was developed to determine the underlying nonlinear and uncertain quantitative relationship between observed cyanobacterial metabolites (2-MIB and geosmin), various algal species, and physical and chemical variables. The model is proposed to be used in conjunction with numerical water quality models that can predict spatial-temporal distribution of flows, velocities, water quality parameters, and algal functional groups. The coupling of the proposed metabolite model with the numerical water quality models would assist various utilities which use mechanistic water quality models to also be able to predict distribution of taste and odor metabolites, especially when monitoring of metabolites is limited. The proposed metabolite model was developed and tested for the Eagle Creek Reservoir in Indiana (USA) using observations over a 3-year period (2008-2010). Results show that the developed models performed well for geosmin (R (2) = 0.83 for all training data and R (2) = 0.78 for validation of all 10 data points in the validation dataset) and reasonably well for the 2-MIB (R (2) = 0.82 for all training data and R (2) = 0.70 for 7 out of 10 data points in the validation dataset).

Space competition between coral and algae — effect of two functional groups of algae on juvenile Acropora corals

Space competition between coral and algae — effect of two functional groups of algae on juvenile <i>Acropora corals</i>

Dietary habits of grazers influence their suitability as biological controls of fouling macroalgae inex situmariculture

The dietary habits of the sea urchin Salmacis sphaeroides and the gastropod Trochus maculatus in ex situ mariculture were examined. Fouling algal assemblages on terracotta tiles were exposed to the grazers and compared. Except for Day 0, the assemblages on Days 2, 13 and 27 differed significantly across treatments. S. sphaeroides rapidly consumed most algae, leaving an assemblage dominated by turf algae and bare tile. T. maculatus primarily fed on green filamentous algae, resulting in an even distribution of other algal functional groups, while control tiles were dominated by green filamentous algae. Using three representative fouling algae species (Bryopsis corymbosa, Hypnea spinella and Lobophora variegata), the consumption rates of both grazers and dietary preferences of S. sphaeroides were examined through a single-diet and a choice experiment respectively. The single-diet experiment revealed differential algal consumption rates for S. sphaeroides (H. spinella = B. corymbosa > L. variegata) and T. maculatus (B. corymbosa > H. spinella = L. variegata). The choice experiment showed that S. sphaeroides preferred H. spinella over the other two species. These experiments highlighted the importance of understanding the dietary habits of grazers as this has direct implications on their effectiveness as biological controls of fouling macroalgae in mariculture.

Contrasting resource limitations of marine primary producers: implications for competitive interactions under enriched CO2 and nutrient regimes.

Primary producers rarely exist under their ideal conditions, with key processes often limited by resource availability. As human activities modify environmental conditions, and therefore resource availability, some species may be released from these limitations while others are not, potentially disrupting community structure. In order to examine the limitations experienced by algal functional groups that characterise alternate community structures (i.e. turf-forming algae and canopy-forming kelp), we exposed these groups to contemporary and enriched levels of carbon dioxide (CO2) and nutrients. Turfs responded to the individual enrichment of both CO2 and nutrients, with the greatest shift in the biomass and carbon:nitrogen (C:N) ratios observed under their combined enrichment. In contrast, kelp responded to enriched nutrients, but not enriched CO2. We hypothesise that the differing limitations reflect the contrasting physiologies of these functional groups, specifically their methods of C acquisition, such as the possession and/or efficiency of a carbon concentrating mechanism (CCM). Importantly, our results reveal that these functional groups, whose interactions structure entire communities, experience distinct resource limitations, with some potentially limited by a single type of resource (i.e. kelp by nutrients), while others may be co-limited (i.e. turf by CO2 and nutrients). Consequently, the identification of how alternate conditions modify resource availability and limitations may facilitate anticipation of the future sustainability of major ecosystem components and the communities they support.

Detecting spatial heterogeneity in intertidal algal functional groups, grazers and their co-variation among shore levels and sites

Few studies have examined the nature of spatial structure in intertidal systems, especially that of macroalgae and grazers, and it is not clear how consistent spatial heterogeneity is among sites and levels on the shore. Here we studied the consistency of spatial heterogeneity in several algal functional groups and in grazer biomass between two sites and across the shore using a combination of semivariograms and fractal analysis of data collected from transects. Additionally, we tested for consistency in spatial co-variation between algae and grazers using cross-semivariograms. The study was conducted at two sites in South Africa and across a gradient of physiological stress at three levels on the shore (low, mid and high shore). We observed spatial heterogeneity in macroalgal functional groups and in the biomass of grazers at one of the sites and at different levels of environmental harshness (i.e. heights on the shore), while the other site showed consistently random patterns. In terms of alga–grazer co-variation, most transects showed significant co-variation, but with more differences in the sign and the number of lags between sites than among levels on the same shore, suggesting stronger differences in spatial patterns between sites. Also we observed differences in co-variation between macro and mesograzers on the midshore. Variability in spatial patterns among levels on the shore and between sites is not explained by topographic complexity, but may be a product of several biotic factors interacting at small scales (cm–m). Differences in spatial patterns among shore levels and between shores also appear to reflect the indirect effects of an upshore reduction in algal biomass (due to heat and desiccation stress) and human harvesting of grazers at one of the sites, respectively. The results show that spatial heterogeneity of particular organisms (algal groups and grazers) and co-variation between them can emerge at small spatial lags, and reduction in spatial heterogeneity in the intertidal can be induced by a cascading effect driven by disturbance.