Anton McLachlan

Ecology of sandy shores

1. Introduction. 2. The Physical Environment. Sand. Porosity and permeability. Penetrability. Waves. Types of waves. Wave energy. Refraction. Shoaling and breaking. Wave-driven longshore currents and rip currents. Bound and infragravity waves - surf beat. Edge waves. Tides. Internal waves. Wind. Sand movement. Interaction between beach slope, waves and particle size. Beach types. Circulation cells and mixing. Water filtration by the sand. Exposure rating. Conclusion. 3. Beach and Surf-zone Flora. Benthic microflora. Surf-zone phytoplankton. Conclusions. 4. Sandy-beach Invertebrates, with special reference to the Macrofaunal Genera. Phylum:Porifera. Phylum:Cnidaria. Phylum:Platyhelminths. Phylum:Nemertea. Phylum:Nematoda. Phylum:Rotifera. Phylum:Gastrotricha. Phylum:Kinorhyncha. Phylum:Loricifera. Phylum:Annelida. Phylum:Echiurida. Phylum:Sipunculoidea. Phylum:Brachiopoda. Phylum:Mollusca. Phylum:Tardigrada. Phylum:Arthropoda. Phylum:Ectoprocta. Phylum:Echinodermata. Phylum:Hemichordata. 5. Adaptations to Sandy-beach Life. Locomotion:burrowing. Locomotion:surfing. Rhythms of activity. Sensory responses and orientation. Choice of habitat. Nutrition. Respiration. Environmental tolerances. Reproduction. Aggregations and gregariousness. Responses to and avoidance of predators. Conclusions. 6. The Macrobenthic Communities. Sampling methods. Diversity and abundance. Distribution and zonation. Migrations and spatial and temporal changes. Competition, disturbance and predation. Trophic relationships. Conclusions. 7. Interstitial Ecology. The interstitial climate. The biota. Distribution of the interstitial fauna. Temporal changes. Meiofaunal communities. Trophic relationships. Biological interactions. Conclusions. 8. Surf-zone Fauna. Zooplankton:composition. Adaptations of surf-zone zooplankton. Zooplankton:migrations. Zooplankton:distribution. Zooplankton:biomass and abundance. Food and feeding relationships. Surf-zone fishes. Juveniles and nursery areas. Surf-zone fish communities. Fishes:temporal variability. Ichthyofaunal trophic relationships. Other groups. Conclusions. 9. Birds and other Terrestrial Vertebrates. 10. Sandy Beach Ecosystems. Food sources. Macroscopic food chains. Examples of macroscopic food chains. The interstitial food chain. The microbial loop. Energy flow in beach and surf-zone ecosystems. The sandy beaches of the Eastern Cape. Nutrient cycling. Conclusions. 11. Sandy Beaches and Pollution. Crude oil pollution. Oil dispersants. Sewage and organic enrichment. Factory effluents. Thermal pollution. Indicators of pollution. Toxicity studies. Conclusions. 12. The Dune Ecosystem and Dune/Beach Exchanges. The physical environment - wind and sand transport. Coastal dune formation by vegetation. Dune types. Edaphic features. Water. The gradient across coastal dunefields. Dune vegetation. The fauna. Food chains of the dune ecosystem. Dune/beach exchanges. A case study of dune/beach exchanges. Conclusions. 13. Conservation and Management.

Sandy Beach Ecology — A Review

Sandy beaches dominate most temperate and tropical coastlines where they represent both important recreational assets and buffer zones against the sea. In some areas they are very productive and are exploited commercially. However, they have been regarded as marine deserts by many biologists and were largely neglected until Remane (1933) began studies on the coasts of Germany. The work of Pearse et al (1942) was also pioneering and represented the first qualitative attempt to evaluate a whole beach system. Since then sandy beach ecology has advanced considerably, though it has always lagged behind other aspects of coastal marine ecology in the attention it has enjoyed. During this period biological research on beaches has spread from early taxonomic and qualitative studies through quantitative ecology and physiology of important species towards a more holistic systems approach today.

Global Patterns in Sandy Beach Macrobenthic Communities

Abstract The data from 161 quantitative sandy beach transect surveys from a wide variety of locations were examined to identify trends and relationships between total marine macrofauna species richness, abundance, and biomass and physical variables. Several physical variables were correlated, especially sand particle size and beach face slope, and spring tide range and beach face slope. Higher latitudes experienced larger waves, and flatter beaches had finer sands, larger waves, and larger tides. Strong correlations were found between species richness and beach slope, tide range, and sand particle size, as well as various indices of beach state. Tropical regions harbored significantly more species than other regions. A new Beach index (BI), based on tide range, beach face slope, and sand particle size, correlated well with species richness, explaining 56% of the variability in the data without considering latitude. Abundance and biomass were best correlated with log(1/beach face slope) and tended to be higher in temperate regions. General patterns are discussed; the new index is evaluated; and the roles of sand, tide, slope, and latitude are considered. It is concluded that for regional studies log(1/beach face slope) is the most useful index to compare beaches, whereas for wider comparisons covering areas of differing tide range, BI might be most useful. These patterns have implications for global biodiversity management on sandy beaches.

Sand Beach Energetics: An Ecosystem Approach Towards a High Energy Interface

General results of a study of energetics on open sandy beaches in South Africa are presented. These sand beaches are considered to interact with adjacent terrestrial environments via the sand dune system and with the sea via the surf zone. A food web is given for the macrofauna showing all known interactions from the supply of food material to the beach, mainly from the sea, to the removal of the macrofauna by birds and fishes. An energy circuit diagram is presented quantifying the main energy flows through this system of filter feeders and scavengers. The interstitial biota of these beaches is considered separate from the macrofauna and consists of bacteria, protozoa and meiofauna feeding on dissolved and particulate organics flushed into the beaches by wave and tide action. Interstitial energy flow and nutrient cycling rates are quantified in an energy circuit diagram. It is suggested that nutrients regenerated by this latter system in the intertidal and surf zone, as well as by the activities of the macrofauna, have sufficient residence times in the surf zone to cause blooms of surf zone phytoplankton which in turn are the main food for the intertidal filter feeders. In this respect the beach and surf zone may represent a more closed system than previously thought. A combined energy circuit diagram is given depicting the beach and surf zone as an ecosystem with the surf zone phytoplankton the producers, the macrofauna the consumers and the interstitial fauna the decomposers. Main imports and exports as well as the consequences of this ecosystem approach are discussed.

Adaptations of bivalves to different beach types

Burrowing ability, shape and density of 12 bivalve species from a wide range of beach types were compared as part of a general investigation of the adaptations of bivalves to the swash climates experienced on exposed sandy beaches. The genera used were Donax, Mesodesma, Tivela, Siliqua, Atactodea, Paphies and Donacilla. Burrowing rates varied widely and burrowing ability showed no relation to beach type along the reflective/dissipative beach gradient, i.e. from beaches with low wave energy and coarse sand to beaches with high wave energy and fine sand. Burrowing rate indices (BRIs) ranged from 2 to 17 (rapid to very rapid) and tended to be higher for juveniles of most species. Bivalve species from dissipative beaches varied in shape from almost blade-shaped to almost spherical, whereas those from reflective beaches were more uniform generally wedge-shaped. Species with the most flattened shapes and (greatest height/width ratios) tended to burrow fastest. Striking interspecific differences were found in densities of whole intact bivalves, these ranging from 1.04 g · cm−3 to 2.10 g · cm−3. The highest densities were recorded in bivalves from reflective beaches and the lowest in bivalves from dissipative beaches. Bivalve species typical of intermediate and reflective beaches were successfully separated from those typical of dissipative beaches on the basis of their density, morphology and BRI, particularly their size and density, using discriminant analysis. It is concluded that small species with high density and streamlined shape are best adapted to the dynamic swash conditions that characterise reflective beaches.

The ecology of sandy beaches in southern Africa

The physical features, macrofauna and meiofauna of four exposed sandy beaches along the southern coast of South Africa were quantitatively investigated. All beaches had medium to fine sands with relatively poor to moderate macrofauna and very rich meiofauna. The results are compared with the present knowledge of the southern African coastline. Sandy beaches types around the southern African coastline are summarized according to geomorphology and wave action and three Zoogeographie provinces are recognized. The macrofauna is dominated by crustaceans, mostly scavengers, on the warmer east coast and by molluscs, mostly filterfeeders, on the temperate south coast. Relationships between diversity and abundance of macrofauna, beach slope and particle size are analysed in detail. Intertidal zonation of macrofauna is described and a zonation scheme based on crustaceans proposed. Relationships between meiofauna composition and particle size are described as well as intertidal distribution patterns of the meiofauna...

Composition, Distribution, Abundance and Biomass of the Macrofauna and Meiofauna of Four Sandy Beaches

AbstractThe macrofauna and meiofauna have been investigated quantitatively on four exposed sandy beaches of medium quartz sands. Of the 12 macrofauna species recorded, two bivalves (Donax spp.) and one gastropod (BuUia rhodostoma) made up the bulk of the numbers and biomass values on all beaches. Macrofauna biomass values were 0,01 - 316,46 g/m2 on an ash-free, dry mass basis. Diversity index values for the macrofauna were low and on all beaches decreased from LW to HW irrespective of the distribution of densities. Similarity analysis indicated three fauna assemblages, which were less related to tidal heights than to quantities of available food. High meiofauna numbers were recorded (152 - 7056/10 cm2) and these were made up mainly of crustaceans (48%) and nematodes (44%). Meiofauna ash-free dry biomass values were 0,08-3,36 g/m2. On all beaches the meiofauna tended to be concentrated at those tide levels where a moderate, but not extreme, degree of desiccation of the sand occurred. Biomass values of macr...

Exposed sandy beaches as semi-closed ecosystems

Abstract On the basis of various lines of evidence, mostly coming from exposed sandy beaches in Southern Africa, it is postulated that under certain conditions high energy sandy beaches and their adjacent surf zones may function as viable ecosystems. Where surf zones are reasonably broad and shallow, cellular circulation patterns predominate and these tend to retain nutrients generated by the macrofauna and interstitial fauna of the beach. These nutrients may then cause blooms of surf zone phytoplankton which in turn serve as food for macrofauna filter feeders. With the perimeter of the circulation cells of the surf zone forming its marine boundary, the beach and surf zone may together be considered an ecosystem with surf phytoplankton the primary producers, beach macrofauna the consumers and interstitial fauna the decomposers.

The effect of grain size on the burrowing of two Donax species

Donax serra and Donax sordidus are bivalves inhabiting the intertidal area of sandy beaches in the Eastern Cape, South Africa. This study investigated the effect of grain size on the burrowing performance of these two species in the laboratory to elucidate the influence of grain size on the longshore distribution of Donax populations and, consequently, the importance of particle diameter in swash exclusion. Burial time, burrowing cycles and a burrowing rate index were obtained for both species in nine well-sorted sediments with grain sizes ranging 90–2000 μm. The burial times of both D. serra and D. sordidus were positively correlated with shell length. Burrowing performance of both species was influenced by grain size. Fastest burrowing times were measured in the fine and medium sediments (125–500 μm) but increased towards the very fine (90–125 μm) and coarse extremes (500–2000 μm). Burial time experiments were extended to test how D. serra would behave in sediments with more natural properties and were, therefore, repeated in mixed sands of different sortings. Sediment sorting had a positive influence on the burrowing times of D. serra. Burrowing time was fastest in well-sorted sediments and slowest in moderately sorted sediments, especially those containing fractions of sands >500 μm. Burial times approximating the swash periods on dissipative beaches (∼32 s) were measured for grain sizes <500 μm. It is, therefore, predicted that most D. serra individuals are able to burrow between swashes on dissipative beaches. However, only the smallest individuals (∼15 mm) would be able to burrow between swashes on reflective beaches with swash periods approximating 15 s. The smaller (maximum) size of D. sordidus reduces burial time and should, therefore, enable this slower burrowing species to bury successfully under most dissipative/intermediate conditions.

Aspects of the biology, ecology and seasonal fluctuations in biochemical composition of Donax Serra in the East Cape

Donax serra ROding (Pelecypoda) isalargesand mussel which forms vast populations on some East Cape shores. It is most abundant on exposed beaches where the sand is not too coarse and phytoplankton production is high. Adultsoccupy 1 zonejust above the mean level of spring tide. Spat settle subtidally and move upshore as they grow. Growth is initially rapid, to about 32 mmatoneyearand48 mmattwoyears. Thereafter growth is very slow and most adult productions goesinto reproduction, with a small summerspawning and a large winterspawning each year. Somatic production is low, as large adults totally dominate the population and have low growth and low mortality. Reproductive production is relatively high and P/B values of 0,2 and 0,5 are suggested for growth and reproduction. D. serra was found to be very tolerant of fluctuating salinitiesforupto four days and should be able to penetrate river mouths, but is limited by restricted swash action. Total dry-tissue mass, energy and biochemical constituents showed some...