Surf Diatoms Research Articles

Surf-diatoms from sandy beaches on the Eastern Coast of South America (Brazil): the identification ofAnaulusEhrenberg andAsterionellopsisRound

Abstract“Surf diatoms” can form high biomass in the surf zone of sandy beaches around the world,AsterionellopsisandAnaulusbeing the main genera of this group in Brazil.Asterionellopsis glacialiswas considered a cosmopolitan species, and taxonomic studies using molecular and morphological tools showed thatA. glacialisis a complex with cryptic and semicryptic species. So, it would be plausible to suppose thatAnaulus australis, another surf zone patch-forming diatom with wide latitudinal occurrence could also be part of a species complex. We collected and identifiedAnaulusandAsterionellopsisstrains from tropical, subtropical and warm temperate sandy beaches on the east coast of South America (Brazil) based on genetic divergence, phylogeny, single-locus automated species delimitation methods (both genera), and frustule ultrastructure (Anaulus).AnaulusandAsterionellopsisshowed contrasting diversity patterns and spatial distribution: a single species ofAnaulus australiswas registered in tropical and subtropical beaches, while at least three species ofAsterionellopsis:A. tropicalis,A. thurstoniiandA. guyunusaewere observed at different latitudes, indicating thatAsterionellopsisspecies have distinct ecological requirements.Asterionellopsis thurstoniiwas previously reported in Europe and it is documented here for the first time in the Southern Hemisphere. The different diversity patterns between these two surf diatom genera suggest that they are likely to have distinct ages, and dispersion and/or speciation processes.

Association of early stage fishes with surf diatom Anaulus australis accumulations in a warm temperate surf zone, South Africa

Surf zones are recognised as important nursery habitats for early stage fishes worldwide, but microhabitat opportunities for feeding and refuge are not well studied. Surf diatoms accumulate in high densities, discolouring the water and offering potential refuge and feeding opportunities. The aim of this study was to investigate the association of early stage fishes with surf diatom Anaulus australis accumulations in the Sundays Beach surf zone on the South African southeast coast. Early stage fishes were sampled within and outside of visible A. australis accumulations using a 4.5 × 1.5 m larval fish seine net with 500 μm mesh. Over 22 sampling trips, 338 replicate samples were collected. Species diversity, the overall catch per unit effort (CPUE) and that of the dominant species Chelon richardsonii, Diplodus capensis, Rhabdosargus globiceps and R. holubi, were significantly higher within accumulations compared to outside. Postflexion larvae and early juveniles occurred in significantly higher numbers within accumulations, indicating that fishes were actively selecting A. australis accumulations. Generalized linear models revealed that temperature, dissolved oxygen (mg l−1), turbidity and A. australis biomass (μg Chl a l−1) were the most significant variables correlated with the overall CPUE and that of dominant species. Since A. australis accumulations have a patchy distribution in the surf zone, it is suggested that early stage fishes are opportunistically using this resource when and where it occurs as both a feeding and refuge area. Understanding the role of microhabitats for early stage fishes is essential for understanding survival and life history strategies within the mosaic of coastal nursery areas.

Ecophysiological and biochemical variation of the surf zone diatom asterionellopsis glacialis sensu lato from Santa Catarina, Southern Brazil

Abstract Patches formed by dense accumulations of diatoms in the surf zone (surf diatoms) are common on sandy beaches with intermediate to dissipative morphodynamic states. Their appearances are correlated with environmental factors such as the passage of cold fronts when onshore winds increase beach hydrodynamics, resuspending epibenthic stocks and accumulating them through the inner surf zone. In Santa Catarina state, Southern Brazil, two beaches are known to have frequent occurrence of accumulations of the surf diatom Asterionellopsis glacialis sensu lato: Rincão Beach (28°50' S) and Navegantes Beach (26°52' S). The high biomass of this alga and its central importance in the trophic structure of the coastal ecosystems suggest studies about its potential applications. In the present study, strains of A. glacialis were isolated, cultured under different conditions and evaluated for ecophysiological aspects: growth rate under different conditions, potential biological activities of exudates, biomass and lipid content, and fatty acid profile. A. glacialis cells in culture showed deformation, which were ameliorated by using agitation and silicon and phosphorus enriched culture media. Exudates of the strains showed no allelopathic effects, although previous studies have indicated activity. Lipid content showed variation depending on the strain and culture media. Values ranged from 9% to 13.6% by dry weight. In all strains saturated fatty acids and polyunsaturated fatty acids were identified. Some hypotheses were proposed to explain the variation of the lipid contents, fatty acid profiles and physiological features between strains of the same species. We believe that the fatty acids profile of this primary producer has important consequences in the sandy beach ecology.

Trophic niche shifts driven by phytoplankton in sandy beach ecosystems

Stable isotopes (δ13C and δ15N) together with chlorophyll a and densities of surf diatoms were used to analyze changes in trophic niches of species in two sandy beaches of Uruguay with contrasting morphodynamics (i.e. dissipative vs. reflective). Consumers and food sources were collected over four seasons, including sediment organic matter (SOM), suspended particulate organic matter (POM) and the surf zone diatom Asterionellopsis guyunusae. Circular statistics and a Bayesian isotope mixing model were used to quantify food web differences between beaches. Consumers changed their trophic niche between beaches in the same direction of the food web space towards higher reliance on surf diatoms in the dissipative beach. Mixing models indicated that A. guyunusae was the primary nutrition source for suspension feeders in the dissipative beach, explaining their change in dietary niche compared to the reflective beach where the proportional contribution of surf diatoms was low. The high C/N ratios in A. guyunusae indicated its high nutritional value and N content, and may help to explain the high assimilation by suspension feeders at the dissipative beach. Furthermore, density of A. guyunusae was higher in the dissipative than in the reflective beach, and cell density was positively correlated with chlorophyll a only in the dissipative beach. Therefore, surf diatoms are important drivers in the dynamics of sandy beach food webs, determining the trophic niche space and productivity. Our study provides valuable insights on shifting foraging behavior by beach fauna in response to changes in resource availability.

Surf zone diatoms: A review of the drivers, patterns and role in sandy beaches food chains

The accumulation of high biomass of diatoms in the surf zone is a characteristic feature of some sandy beaches where the wave energy is sufficiently high. A few species of diatoms, called surf diatoms, thrive in this harsh environment. The main processes driving the spatial and temporal distribution of surf diatoms as well as their standing biomass and growth were described twenty to thirty years ago based on studies conducted on the western coast of the United States of America and South African beaches. Since then, over fifty locations around the world have been reported to have surf diatom accumulations with most (three-quarters) of these being in the southern hemisphere. Their occurrence is controlled by physical and chemical factors, including wave energy, beach slope and length, water circulation patterns in the surf zone and the availability of nutrients to sustain the high biomass. The main forces driving the patterns of temporal variability of surf diatom accumulations are meteorological. In the short term (hours), the action of wind stress and wave energy controls the diatom accumulation. In the intermediate time scale (weeks to months), seasonal onshore winds of sufficient strength, as well as storm events are important. Furthermore, anthropogenic disturbances that influence the beach ecosystem as well as large-scale events, such as the El Niño Southern Oscillation, may lead to significant changes in surf diatom populations in the long term (inter-annual). Surf diatoms form the base of a short and very productive food chain in the inshore of the sandy beaches where they occur. However, the role of surf diatoms in the microbial food web is not clear and deserves further studies.

A low-latitude bloom of the surf-zone diatom, Anaulus australis (Centrales, Bacillariophyta) on the coast of Southern Queensland (Australia)

A novel bloom of the surf diatom Anaulus australis Drebes et Schultz was observed in subtropical waters off Surfers' Paradise, Queensland, Australia (27 degrees 55'S; 153 degrees 23'E) in early May 2000. This is the lowest latitude in which an Anaulus australis surf diatom bloom has been reported. Nitrogen stable isotope analysis of surf diatoms may indicate anthropogenic nutrient inputs in this environment.

Surf Diatoms of the Lagos Lagoon Beach, Nigeria

Investigations into the dry season surf diatoms of the Lagos lagoon along the University of Lagos beach were carried out for six months (Dec. 1989 – May 1990). Forty-two diatom taxa belonging to 23 genera were recorded. The diatoms recorded, showed euryhaline tendencies. On the whole the more frequent species were Navicula expansa, Achanthes coaractata, Cymbella minuta, Nitzschia irresoluta, Nitzschia closterium, Gyrosigma tenuissimum, Amphora ovalis and Hantzschia amphioxys. The importance of these diatom to the shore–line sandy habitat fauna was highlighted. Journal of Aquatic Sciences Volume 16, April 2001, pp. 35-38 KEY WORDS: Surf, diatoms, Lagos lagoon, Nigeria

Bioenergetics of fishes in a high-energy surf-zone

Energy budgets are proposed for four teleost and two elasmobranch species as well as for the main icthyofauna groups for a surf-zone ecosystem. The ecology of surf-zone fishes of eastern Cape beaches, Algoa Bay South Africa, is reviewed. Using the equationC=F+U+R d +R R +ΔB, the following general energy budgets were derived for fishes: teleosts − 100=10+4+21+23+42; elasmobranchs − 100=11+2+16+24+48; whereC: food consumption;F: faeces;U: nonfaecal excretion;R d : apparent specific dynamic action;R R : routine metabolism;ΔB: growth. These show that most of the energy consumed is used in metabolism (R d +R R ) and growth (ΔB) whereas excretion (U) only accounts for a small portion. The energy budgets developed are within ranges recorded for other species. The main feeding groups of surf-zone icthyofauna are the southern mulletLiza richardsonii, the sandsharkRhinobatos annulatus, benthic feeders, zooplankton feeders, omnivorous and piscivorous fish with biomass values of 1000, 1000, 3000, 2400, 400 and 400 kJ m−1, respectively; and annual consumption budgets of 22107, 13725, 65710, 65476, 9758 and 8517 kJ m−1 yr−1, respectively.L. richardsonii feeds mainly on surf diatoms, consuming 0.5% of total diatom production. Zooplankton production supplies 91%, and macrobenthic production 9%, of the energy needs of other non-piscivorous carnivorous fishes. Piscivorous fishes consume 30% of the available fish production. Nonfaecal-energy production (8229 kJ m−1 yr−1) is utilised by surf diatoms, and faecal-energy production (30 341 kJ m−1 yr−1), is returned to the detritus pool to be utilised by the microbial loop in surf-waters. Our current knowledge of surf-zone energetics indicates that fishes are important predators. This study confirms the concept that the ecosystem generates adequate food for the fish assemblage. Fishes recycle energy, as excretory products, via the detritus pool and surf-diatoms, while fishes moving across the outer boundary of the surf-zone export energy from the system. Data presented, therefore, also support the general concept of a self-sustaining beach/surf-zone ecosystem.

The use of false buoyancies by the surf diatom Anaulus birostratus in the formation and decay of cell patches

We describe a shift in our understanding of cell patch dynamics in the surf diatom Anaulus birostratus (Grunow) Grunow as a result of recent findings concerning their vertical distribution. An extension of previous investigations to include the psammic or sediment habitat of the surfzone has shown this surf diatom to alternate from a planktonic and neustonic life mode during the day to epipsammic at night. The pattern and magnitude of this shift are discussed in the light of existing hypotheses, and form the basis of a new approach to the question of patch formation and decay by surf diatoms. Briefly, cells acquire a positive buoyancy during the day, enabling them to occupy the air/water interface despite their high specific gravity. This positioning allows for the build-up of a concentration gradient in the inner surfzone in spite of the excessive offshore drainage brought about by rip activity. The resultant concentration of cells at the surface is a major causal factor involved in patch formation. Evidence is provided to show that during the late afternoon cells switch adherence from air bubbles to sediment particles in order to enter the sediment. In this way the patch disappears but the cells are retained within the inner surfzone. The cycle is repeated when the epipsammic cells elute out of the sand in the early morning. In the absence of cell patches there is still a resident sediment population, although cell numbers are two orders of magnitude lower. We also observed that under these circumstances the elution process in the early morning was suppressed. Preliminary data obtained for other surf diatoms at the Sundays River Beach, South Africa, suggest the dynamics described above for A. birostratus to be common to this group of marine phytoplankton.

Photosynthetic Rates and Photoinhibition of Surf Diatoms in Fluctuating Light

Photosynthetic Rates and Photoinhibition of Surf Diatoms in Fluctuating Light

Rip current charactersitics and their role in the exchange of water and surf diatoms between the surf zone and nearshore

Photogrammetric measurements of dye dispersion in a high-energy surf zone provided semi-quantitative measurements of the pattern and flux of water exchange between the surf zone and nearshore. The intensity of current flow, the rip morphology and its position within the surf zone have important ecological implications for the surf zone and nearshore biota. A variety of water-movement patterns was found, ranging from currents which remained confined to the beach terrace to those which involved substantial exchange across the breaker line. In considering rips as exchange mechanisms, two rip types are recognized. Depending on the exchange of water across the breaker line, a rip may be classified as ‘exchange’ or ‘non-exchange’. The ecological significance of these current types is discussed and a classification scheme for rip currents is proposed. Offshore fluxes across the breaker line by rip currents ranged from negligible to 80 m 3s −1 rip −1. The estimated maximum flux per running meter of the Sundays River Beach was calculated as 0·0.32m 3 s −1. The half-residence period of surf-zone water ranged from as little as 22 min t0 5 days, averaging 3·6 h. A dichotomy of current patterns found between the water column and surface layers is used to explain the build up of a concentration gradient in cell numbers of the surf diatom Anaulus birostratus within the surf zone despite extensive flushing by surf circulation.

Mullet grazing on surf diatom accumulations

Grazing by southern mullet, Liza richardsoni (Smith), on surf diatoms occurring in bloom concentrations off an ocean‐exposed East Cape beach, South Africa, was investigated. Field observations and stomach content analysis demonstrated that surf diatoms taken from the air‐water interface were a principal source of food. A qualitative examination of stomach contents revealed a feeding transition from planktonic carnivore in juveniles to a diet consisting entirely of surf diatoms in larger fishes. This change in diet commonly occurred at a standard length of 50–135 mm. Fish larger than 135 mm fed entirely on surf diatoms which were ingested together with large quantities of beach sediment. Grazing on surf diatoms only took place during daylight hours. Energy, ash, protein, fat and carbohydrate content determinations indicate a high food quality of surf diatoms. It is concluded that surf diatom accumulations form a richly concentrated and reliable food source of high nutritional quality for these fish. Possible widespread grazing on surf diatoms by mullets is considered.

Persistent blooms of surf diatoms (Bacillariophyceae) along the Pacific coast, USA. III. Relationships between diatom populations and environmental variables along Oregon and Washington beaches (1977 and 1978)

The surf diatom populations and environmental conditions at 13 beaches along the Oregon and Washington coasts were studied from June 1977 through August 1978. Spearman rank correlation coefficients were calculated for 14 environmental variables and seven species. Cell numbers of four of the species (Chaeloceros armalum, ASlerionella socialis, Biddulphia aurita, and Aulacodiscus kittonil) were positively correlated with rainfall and river discharge and negatively correlated with air temperature, water temperature, salinity, upwelling, daylength, and nitrogen (nitrate and ammonium) concentrations. These four species are stable members of the surf ecosystem. The remaining three species (Thalassiosira pacifica, Skeletonema costatum, and Asterionella glacialis) exhibited weaker correlations that were consistently opposite in direction to the correlation coefficients calculated for the surf diatoms, above.

Persistent blooms of surf diatoms (Bacillariophyceae) along the Pacific coast, U.S.A. II. Patterns of distribution of diatom species along Oregon and Washington beaches (1977 and 1978)

Diatom populations in the surf along thirteen exposed sandy beaches of the Oregon and Washington coast were sampled from June 1977 through August 1978. The dominant species, Chaetoceros armatum, and the secondary dominant, Asterionella socialis, are both recognized as ‘true’ surf diatoms. These two species predominated along coastal beaches, but both were less frequently observed and less abundant along three of the intermediate Oregon beaches (Cannon Beach, Ocean-side and Gleneden). Aulacodiscus killonii and Biddulphia aurita were similarly less frequently observed along these same beaches. A. killonii, the major component of surf blooms along these beaches fifty years ago, was observed on 42 occasions in low concentrations at eight beaches along the Oregon coast but was not present along the Washington coast. Asterionella glacialis was more frequently observed in surf samples from the northern beaches and decreased in frequency and abundance toward the south. It never reached the high densities reported from other coastlines of the world, where it occurs as a major component of surf blooms. Other ecologically important diatom species (Skeletonema costatum and Thalassiosira pacifica) occurred at certain times along some of the beaches, more frequently toward the south, and are considered as transients in the surf habitat, affected by increased upwelling and onshore winds.

Persistent blooms of surf diatoms along the pacific coast, U.S.A.: I. Physical characteristics of the coastal region in relation to the distribution and abundance of the species

The surf diatom populations at thirteen beaches along the Oregon and Washington coast were studied from June 1977 through August 1978. Chaetoceros armatum T. West and Asterionella socialis Lewin & Norris, the two species responsible for the blooms, were present in the surf along beaches between Point Grenville, Washington, and Cape Blanco, Oregon. On the basis of the cell densities of these two species, the beaches were arranged into four distinct groups. Discriminant analysis showed that the four groups could also be completely separated by three discriminant functions composed of four physical variables: offshore bottom slope, per cent chlorite, per cent montmorillonite and beach length. The absence of surf diatoms at two beaches south of Cape Blanco can probably be explained by the unsuitable physical conditions along the coast south of the Cape.

Concentrations and temporal variations of 210Po, 210Pb, and Al in the surf zone ecosystem of Copalis Beach, Washington

Surf diatoms monitored during a 21-month period at Copalis Beach, Washington, contained elevated concentrations of Al, 210Pb, and supported 210Po compared to net phytoplankton from Washington coastal waters and Puget Sound. Aluminum concentrations of several per cent dry weight found in the surf diatoms were not a reflection of contamination by discrete inorganic particulate matter but were the result of a natural coating of clay-sized particles on Chaetoceros armatum, the predominant diatom in the surf blooms. A high correlation between Al and 210Pb in the surf diatoms suggests 210Pb and supported 210Po were also associated with the clay-sized particles. During fall through spring, the unsupported 210Po concentrations in the surf diatoms were correlated with the input of 210Po by precipitation. A summer maximum in unsupported 210Po concentrations in the surf diatoms may reflect upwelling that causes higher dissolved 210Po concentrations in the summer surf relative to those of late spring and early fall. The consumers of the surf diatoms exhibited larger 210Po-activity-to- 210Pb-activity ratios than their food, indicating 210Po was preferentially accumulated in the higher trophic level.

Blooms of surf-zone diatoms along the coast of the Olympic Peninsula, Washington: IX. Factors controlling the seasonal cycle of nitrate in the surf at Copalis Beach (1971 through 1975)

Nitrate depletion in the upper water layers beyond the breaker zone at Copalis Beach, Washington, takes place in April of each year due to spring phytoplankton blooms. In 1974, Thalassiosira pacifica was the species responsible for almost all of the nitrate depletion over a considerable ocean area beyond the region of the breakers. This same nitrate-depleted water was also characteristic of the surf zone in April of each year (1971 through 1975). Between mid-April and mid-October, reintroduction of nitrate into the surf region depends on encroachment of upwelled oceanic deep water high in nitrate; in 1971, when there was only weak upwelling, nitrate in the surf remained depleted over an extended period (6 months). Upwelling can be masked by the presence of freshwater discharge from rivers and streams (as in 1971, 1972 and 1974). In the summer of 1973, when the rate of river discharge was at an all-time record low, nitrate concentrations in surf samples were higher than in any of the other summers during our study period. Cell concentrations of both surf diatom species were reduced in summer; Asterionella socialis disappeared completely in mid or late summer, and Chaetoceros armatum showed symptoms of physiological stress. The annual cycles of abundance of each species seemed to be repeated in more or less the same fashion from year to year, in spite of the very different patterns observed in nitrate concentrations from summer to summer. This points to the importance of ammonia as an alternate nitrogen source for surf diatoms, particularly during summer months.

Blooms of surf-zone diatoms along the coast of the Olympic Peninsula, Washington: V. Environmental conditions associated with the blooms (1971 and 1972)

Populations of surf diatoms at Copalis Beach, Washington, were monitored over a two-year period, along with associated environmental parameters (temperature, salinity, nutrient concentrations). In spite of widely fluctuating environmental conditions, the diatom populations remained at relatively dense concentrations throughout the year. Chaetoceros armatum was present at all times; Asterionella socialis disappeared for a time in late summer and autumn of 1972, coincident with a period of upwelling of oceanic water. Biddulphia aurita, a species of minor importance in the blooms, was present in late winter and spring. Nitrate became undetectable in the surf zone in April of both years. During the summer of 1971 there was very weak upwelling of oceanic deep water so that nitrate remained scarcely detectable for a period of six months. During 1972, upwelling was stronger and nitrate remained undetectable over a three-month period. During those times when nitrate was absent, the nitrogen source for algal growth was probably supplied by ammonium, which was always present in surf samples in appreciably high concentrations.