Macroalgal Recruitment Research Articles

Epilithic Bacterial Assemblages on Subtidal Rocky Reefs: Variation Among Alternative Habitats at Ambient and Enhanced Nutrient Levels.

Temperate rocky reefs often support mosaics of alternative habitats such as macroalgal forests, algal turfs and sea urchin barrens. Although the composition of epilithic microbial biofilms (EMBs) is recognized as a major determinant of macroalgal recruitment, their role in regulating the stability of alternative habitats on temperate rocky reefs remains unexplored. On shallow rocky reefs of the Island of Capraia (NW Mediterranean), we compared EMB structure among canopy stands formed by the fucoid Ericaria brachycarpa, algal turfs, and urchin barrens under ambient versus experimentally enhanced nutrient levels. The three habitats shared a core microbial community consisting of 21.6 and 25.3% of total ASVs under ambient and enhanced nutrient conditions, respectively. Although Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia were the most abundant classes across habitats, multivariate analyses at the ASV level showed marked differences in EMB composition among habitats. Enhancing nutrient level had no significant effect on EMBs, although it increased their similarity between macroalgal canopy and turf habitats. At both ambient and enriched nutrient levels, ASVs mostly belonging to Proteobacteria and Bacteroidetes were more abundant in EMBs from macroalgal canopies than barrens. In contrast, ASVs belonging to the phylum of Proteobacteria and, in particular, to the families of Rhodobacteraceae and Flavobacteriaceae at ambient nutrient levels and of Rhodobacteraceae and Bacteriovoracaceae at enhanced nutrient levels were more abundant in turf than canopy habitats. Our results show that primary surfaces from alternative habitats that form mosaics on shallow rocky reefs in oligotrophic areas host distinct microbial communities that are, to some extent, resistant to moderate nutrient enhancement. Understanding the role of EMBs in generating reinforcing feedback under different nutrient loading regimes appears crucial to advance our understanding of the mechanisms underpinning the stability of habitats alternative to macroalgal forests as well as their role in regulating reverse shifts.

Potential ecosystem regime shift resulting from elevated CO2 and inhibition of macroalgal recruitment by turf algae

Potential ecosystem regime shift resulting from elevated CO2 and inhibition of macroalgal recruitment by turf algae

Ocean acidification increases the impact of typhoons on algal communities

Long-term environmental change, sudden pulses of extreme perturbation, or a combination of both can trigger regime shifts by changing the processes and feedbacks which determine community assembly, structure, and function, altering the state of ecosystems. Our understanding of the mechanisms that stabilise against regime shifts or lock communities into altered states is limited, yet also critical to anticipating future states, preventing regime shifts, and reversing unwanted state change. Ocean acidification contributes to the restructuring and simplification of algal systems, however the mechanisms through which this occurs and whether additional drivers are involved requires further study. Using monthly surveys over three years at a shallow-water volcanic seep we examined how the composition of algal communities change seasonally and following periods of significant physical disturbance by typhoons at three levels of ocean acidification (equivalent to means of contemporary ∼350 and future ∼500 and 900 μatm pCO2). Sites exposed to acidification were increasingly monopolised by structurally simple, fast-growing turf algae, and were clearly different to structurally complex macrophyte-dominated reference sites. The distinct contemporary and acidified community states were stabilised and maintained at their respective sites by different mechanisms following seasonal typhoon disturbance. Macroalgal-dominated sites were resistant to typhoon damage. In contrast, significant losses of algal biomass represented a near total ecosystem reset by typhoons for the turf-dominated communities at the elevated pCO2 sites (i.e. negligible resistance). A combination of disturbance and subsequent turf recovery maintained the same simplified state between years (elevated CO2 levels promote turf growth following algal removal, inhibiting macroalgal recruitment). Thus, ocean acidification may promote shifts in algal systems towards degraded ecosystem states, and short-term disturbances which reset successional trajectories may ‘lock-in’ these alternative states of low structural and functional diversity.

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.

Effects of micro- and mesograzers on intertidal macroalgal recruitment

This study examined the effects of a guild of micrograzing harpacticoid copepods (dominated by two species of Paradactylopodia sp. nov. and one species of Scutellidium sp. nov.) and a mesograzing periwinkle, Afrolittorina praetermissa, on the early recruitment of intertidal macroalgae on a wave-exposed, rocky shore. This is the first study, to our knowledge, to examine the effects of micrograzers (<500 μm) on intertidal macroalgal recruitment. Data showed that microscopic harpacticoid copepods altered the assemblages and reduced the densities of several macroalgal taxa, while A. praetermissa changed the assemblages and reduced both the density and number of macroalgal taxa. Recruitment of encrusting coralline algae was actually higher in copepod inclusions than exclusions, suggesting that copepods may be beneficial to the recruitment of this algal group. These results contribute to the understanding of grazing as a factor causing high mortality of algal recruits, but also highlight the need for more studies that examine the effects of micro- and mesograzers on the distribution and abundance of macroalgae.

Variação temporal do recrutamento e sucessão ecológica de macroalgas em recifes areníticos da Praia de Piedade – PE, Brasil

Two sites, in which Rhodophyta and Chlorophyta were the dominant algae, were selected in the intertidal zone of a sandstone reef at Piedade Beach to evaluate macroalgal recruitment and succession from March 2007 through January 2008. At each site, 2 meter transects were sampled using 20 x 20 cm quadrats in the midlittoral zone of the reefflat. The initial position of the quadrats was randomly chosen. Green algae (filamentousand foliose) showed a bloom at the end of the rainy season (approximately 250 grams of dry weight/m2 on October 2007), as indicated by the differences between the monthly average biomass values observed in the recruitment plots. The biomass measurements of control quadrats and in the succession treatments did not differ statistically during the rainy season for either Chlorophyta or Rhodophyta at Site 1 or during the dry season at Site 2. Green and red algae (filamentous and corticated) exhibited a pattern of alternating oscillations, as shown by the principal component analysis of recruitment, rainfall and air temperature. These results suggested a negative relationship between temperature and the recruitment of red algal biomass. Key words: Macroalgal Biomass, Benthic Ecology, Sandstone Reefs, Ecological Succession, Algal Recruitment.

Partitioning of primary production among giant kelp (Macrocystis pyrifera), understory macroalgae, and phytoplankton on a temperate reef

We experimentally investigated the response of phytoplankton and understory macroalgae to canopies of giant kelp, Macrocystis pyrifera, by following changes in their biomass and net primary production over 17 months in 600‐m2 plots where giant kelp was continually removed or left intact and allowed to vary naturally. Production by phytoplankton was two times greater and understory algae five times greater where Macrocystis was removed relative to the intact forest. Understory biomass, but not phytoplankton biomass, was suppressed inside the forest, leading to a higher magnitude of effect on net primary production (NPP) by understory relative to phytoplankton. Following a natural decline of the Macrocystis canopy by winter storms, understory macroalgae and phytoplankton increased production in the Macrocystis control plot. This response was delayed for both groups, with phytoplankton production increasing in spring and understory increasing later during summer. The longer delay for understory macroalgae was likely due to restrictions in the timing of macroalgal recruitment and their slower growth rates compared with phytoplankton and with increased competition for light resulting from greater light absorption by the spring phytoplankton bloom. Surprisingly, total ecosystem production that included NPP by Macrocystis, phytoplankton, and understory algae did not differ between the Macrocystis control and removal plots for much of the study. NPP by understory algae, which comprised the bulk of the ecosystem NPP in the Macrocystis removal plot, can compensate to varying degrees for the loss of Macrocystis production following its removal by winter storms.

Small-scale disturbance in a stable canopy dominated community: implications for macroalgal recruitment and growth

The long-living species Ascophyllum nodosum dominates the mid-shore of sheltered rocky sites in NW Europe, forming near-monospecific stands. We aimed to determine the effects of small-scale disturbance on such shores, through manipulative experiments over a long period (almost 7 yr). We tested the general hypothesis that small-scale disturbance allows co-existence of Fucus canopy (F. vesiculosus, F. serratus) and promotes recruitment of Ascophyllum itself. Two factorial experiments were established to determine the interactive effects of the Ascophyllum canopy with: (1) the red algal turf which covers approximately 90% of the substratum at the experimental sites, and (2) the dominant grazer, the limpet Patella vulgata, which maintains small patches of open sub- stratum free from turf. Disturbance to plots 25 × 25 cm resulted in significant changes to the under- storey community. Removal of limpets led to high levels of Ascophyllum and Fucus recruitment, irre- spective of the presence of the canopy. In the presence of limpets recruitment of fucoids was negligible. In contrast, removal of turf alone led to high Fucus spp. but not Ascophyllum recruitment. Loss of the canopy and a consequent degradation of the turf was required to promote Ascophyllum recruitment. Despite high recruitment in some treatments beneath an intact canopy, low growth rates in shade prevented development of mature plants. Loss of the overlying Ascophyllum canopy was followed by development of a mixed F. serratus/F. vesiculosus canopy that was still present nearly 7 yr after manipulation. Ascophyllum recruits, while showing enhanced growth in the absence of the canopy, were too slow-growing to form a canopy.

Complex interactions of climatic and ecological controls on macroalgal recruitment

Little is known about the cumulative effects of multiple (.2) environmental controls on species performance and interactions in aquatic ecosystems. We asked how changes in climatic (temperature, ultraviolet radiation) and ecological controls (nutrients, grazing) affect recruitment of the green macroalga Enteromorpha intestinalis, which forms destructive algal blooms in coastal ecosystems worldwide. We designed factorial laboratory experiments to analyze the recruitment response to (1) single and combined effects of nutrient enrichment, grazing pressure, and grazer species composition and (2) the cumulative effects of ultraviolet (UV) radiation, temperature, nutrients, and grazing. Recruitment of E. intestinalis increased exponentially with nutrient enrichment. Grazers could control algal recruitment until a nutrient threshold was reached depending on grazer species composition. Snails (Littorina littorea) had strong negative effects on recruit density, whereas amphipods (Gammarus oceanicus) had weak grazing effects and favored algal recruitment through excretion when nutrient supply was low. Temperature and nutrients both enhanced algal recruitment but also the effects of grazers, which led to a significant three‐way interaction among these factors. Similarly, effects of UV radiation depended on grazer presence and temperature. When grazers were absent, UV radiation reduced recruitment at 11 and 17°C but enhanced recruitment at 5°C. No effects were seen in the presence of grazers. Our results indicate that multiple human influences, such as climate change, eutrophication, and food web alterations, have interdependent effects and the potential for synergistically enhancing the development of macroalgal blooms in coastal ecosystems.

Variable and complementary effects of herbivores on different life stages of bloom-forming macroalgae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 200:167-175 (2000) - doi:10.3354/meps200167 Variable and complementary effects of herbivores on different life stages of bloom-forming macroalgae Heike K. Lotze*, Boris Worm Institut für Meereskunde, Düsternbrooker Weg 20, 24105 Kiel, Germany *Present address: Biology Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada. E-mail: hlotze@is.dal.ca ABSTRACT: Increased nutrient loading favors macroalgal blooms in eutrophied coastal ecosystems. The main counteracting factor on this bottom-up support is top-down control by consumers. We asked (1) whether herbivore control on 2 bloom-forming macroalgae in the Baltic Sea varies between different algal life stages, (2) whether herbivores selectively feed on Enteromorpha spp. (Chlorophyceae) thereby supporting dominance of Pilayella littoralis (Phaeophyceae), and (3) whether various herbivore species differ in their effects. In comparative field and laboratory experiments, we analyzed herbivore pressure and selectivity on germling density and adult thalli of Enteromorpha spp. and P. littoralis. In the field, herbivores reduced macroalgal recruitment by 80% within 14 d indicating strong herbivore control at early life stages. Recruits of Enteromorpha spp. were significantly preferred over P. littoralis Adult thalli of both algae showed similar growth rates, but grazing rates were significantly higher on Enteromorpha spp. In laboratory experiments, Idotea chelipes (Isopoda), Littorina saxatilis (Gastropoda) and Gammarus locusta (Amphipoda) strongly reduced germling density, whereas effects of L. littorea were weak. I. chelipes and L. saxatilis significantly preferred germlings of Enteromorpha spp. over P. littoralis. I. chelipes had strong effects on adult Enteromorpha spp. but not on P. littoralis. The effects of G. locusta and L. littorea on both adult algae were smaller and not selective, and L. saxatilis did not feed on adults at all. Different herbivore feeding modes are discussed. We conclude that strong and selective herbivory on juvenile and adult Enteromorpha spp. favors dominance of P. littoralis in the Baltic. An effective control of macroalgal blooms in eutrophied areas can be supported by sustaining high herbivore density and species richness considering the variable and complementary effects of different herbivore species on different algal life stages. KEY WORDS: Eutrophication · Macroalgal blooms · Species composition · Dominance · Grazing · Selectivity · Diversity · Feeding mode · Enteromorpha · Pilayella · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 200. Publication date: July 14, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Macroalgal recruitment in artificially disturbed areas: interactive effects of temporal and spatial scale

The effect of the surrounding community and spatial extent of disturbance on recruitment was investigated in a mixed stand (dominated by large brown algae of the order Fucales) on a subtidal rocky platform in South Australia. In particular, survival and growth of Cystophora and Sargassum recruits on natural substratum were examined in artificially cleared areas of three sizes (30 × 30 cm, 60 × 60 cm and 100 × 100 cm). Abundance and growth of recruits was monitored for 6 months at both the edge and the centre of the clearances. The influence of clearance size and position within a clearance on the abundance of recruits changes with time. Initially, the size of clearance was most important, with larger clearances supporting denser stands of recruits. However, after 143 days, position within the clearance became important, with greater mortality at the edges than at the centre. The large residual values associated with the analysis were evidence of the variability of the interactions within this community. The results demonstrate the importance of the consideration of spatial and temporal scales, and particularly the position within a disturbed area, in recruitment studies.

Effects of secondarily treated sewage effluent on intertidal macroalgal recruitment processes

Effluent is discharged below the low-water mark at Boags Rocks, Victoria, Australia, at an average rate of 437 × 106 L day–1. Three study sites following a gradient of pollution from high (at Boags Rocks) to intermediate (Cape Schanck) to unpolluted (Cheviot Beach) were chosen for the main experiments. Surveys of the algal assemblages were conducted in spring and summer and showed the absence of the pre-discharge dominant Hormosira banksii at Boags Rocks and an abundance of turf-forming and ephemeral species at the two polluted sites. There was no evidence that the treated sewage detrimentally affected either the availability of propagules (asexual spores, gametes, zygotes or fragments) or macroalgal recruitment to artificial or natural substrata. Opportunistic genera such as UIva and Enteromorpha showed very high recruitment and propagule densities in the water column at polluted sites, apparently benefiting from the increased nutrient loads. Investigation of the number of H. banksii zygotes in water samples from various habitats showed very limited dispersibility for this species. The small dispersal shadow of H. banksii, combined with the environmental pressures placed on establishing zygotes, would severely limit the re-establishment of this species at polluted sites, even if given suitable conditions.