Volume 150, Part A, 5 October 2014, Pages 24–35
Special Issue on Sandy Beaches
Edited By Eileen Campbell, Anton McLachlan and Dave Schoeman
Surf zone diatoms: A review of the drivers, patterns and role in sandy beaches food chains
- a Institute of Oceanography, Federal University of Rio Grande, C.P. 474, 96200-970 Rio Grande, Brazil
- b Department of Botany, Coastal and Marine Research Unit, Nelson Mandela Metropolitan University, P O Box 77000, Port Elizabeth 6031, South Africa
- Received 2 February 2013, Accepted 16 July 2013, Available online 25 July 2013
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.
- diatom accumulations;
- geographical distribution;
- abiotic factors;
- trophic relation
The surf zones of several exposed sandy beaches present obvious brownish to greenish water discoloration due to the high abundance of diatoms. The cellular growth of flagellates including dinoflagellates is hampered by the turbulence found in surf zones, whereas diatoms are dependent on high turbulence to optimize their nutrient uptake and light utilization. In addition, some diatoms depend on vertical transport to suspend cells or resting spores from the sediment into the water column after sedimentation during calm periods (Reynolds, 2006).
Among diatoms, a few phylogenetically unrelated species, called surf diatoms, are able to successfully exploit the high wave energy conditions at some sandy beaches. A common feature of surf diatoms is their ability to accumulate in the foam by adhering to air bubbles and, by so doing, form brown patches in the surf zone (Lewin and Schaefer, 1983 and Talbot and Bate, 1988a). There are seven confirmed surf diatom species: the centrics Anaulus australis Drebes et Schulz (Anaulaceae), Attheya armata (West) Crawford (Attheyaceae), Aulacodiscus kittonii Arnott ex Ralfs (Aulacodiscaceae), and the pennates (Fragilariaceae) Asterionellopsis glacialis (Castracane) Round and Asterionellopsis socialis (Lewin and Norris) Crawford and Gardner ( Plate 1). Aulacodiscus africanus Cottam, the first described surf diatom, has not been studied since that early record ( Van Heurck, 1896). Two other species of Aulacodiscus, Aulacodiscus johnsonii Arnott in Pritchard and Aulacodiscus petersii Ehrenberg are regularly subdominants with other surf diatoms in South Africa ( Campbell, 1996) and New Zealand (Campbell, pers. comm.). It appears that surf diatoms thrive exclusively in surf zones, except for Asterionellopsis glacialis, which is also a common component of coastal phytoplankton worldwide ( Campbell, 1996).