leaves, Ipomoea pes-caprae (Conv.).6 The other plants found in this formation also tend to be low, sand-binding herbs, grasses and sedges whose long, deep-rooting stems or stolons spread across or just under the surface of the sand.7 The herbs include the small legume Canavalia, the herb Euphorbia atoto (Euph.), the sedge Cyperus pendunculatum (Cype.) and various grasses. Full lists are given elsewhere (van Steenis 1957; Wong 1978; Soegiarto and Polunin 1980; Whitmore 1984). Most of the species are confined to this habitat type and many are pantropical in their distribution.
The actual composition of the vegetation depends to some extent on the type of sand. There are two main forms on Sulawesi beaches: black, andesitic (volcanic) particles found in the north, and white, calcareous sand from the erosion of coral reefs as found in the southern part of Sulawesi and most of the offshore islands. The black beaches of Minahasa have a poor beach flora probably because the black surfaces absorb more heat and become extremely hot.
Plants are dependent on non-saline soil water but are tolerant of the periodic droughts, salt spray, almost constant winds, low levels of soil nutrients, and high temperatures found in the habitat. The plants also typically have small seeds which are dispersed by water, some even having air sacks around the seeds to assist floating.
The green mat formed by the pes-caprae formation traps leaves and other organic material blown by the wind or tossed up by waves at high tides. Small animals can also take refuge there. As a result, soil conditions improve, nutrients increase and plant succession proceeds (table 2.4).
One of the first large plants to be seen at the landward edge of the pes-caprae formation is the she-oak Casuarina equisitifolia (Casu.), which frequently forms pure stands at the top of the beach. She-oak seedlings are intolerant of shade, but even in open conditions, if there is a carpet of she-oak twigs and litter, the seedlings will not grow. This may indicate the presence of some chemical or allelopathic prevention of regrowth, but this has yet to be proven. Thus, unless the shoreline advances, the belt of she-oak will be replaced by other species.
Barringtotiia Formation
The Barringtonia formation is found behind the pes-caprae formation on sandy soils. It is also found behind on abrading coasts, where sand is either being removed by unhindered ocean waves or where sand has at least ceased to accumulate; in such areas a beach wall about 0.5-1 m tall can be found and the formation is found inland of this. The plants are generally tolerant of salt spray, nutrient-deficient soil and seasonal drought and grow in a belt along the coast, usually between 25 m and 50 m wide, where the lie of the land allows it. The belt will be much narrower where the coast is steep and rocky. Large trees sometimes sprawl across the upper parts of the beach, and as the beach wall is eroded away these eventually fall over, die and become shelters for many small seashore animals.
The larger trees of the Barringtonia association are of three species: Barringtonia asiatica (Lecy.) which has huge 15 cm wide feathery flowers and unusual-shaped fruit (fig. 2.23), Calophyllum inophyllum (Gutt.) which has transparent yellow sap and round fruit of 3 cm diameter, and Terminalia catappa (Comb.) whose large leaves turn red before falling and whose boughs stand out at right-angles to the trunk in a manner similar to kapok trees Ceiba pentandra (Bomb.). Barringtonia itself is not invariably present in the formation which bears its name (van Steenis 1957) and it is sometimes found on sandy ground away from the coast. As with the pes-caprae formation, the plants found in this type of beach vegetation are found in similar locations throughout the Indo-Pacific region and some are typical of sandy shores throughout the tropics. Many of the species are not found outside these formations. In addition to the trees mentioned above, other typical species include the coconut palm Cocos nucifera, the large bush Ardisia elliptica (Myrs.) with its pink young twigs and leaves, Heritiera littoralis with its peculiar boat-shaped floating fruit (fig. 2.23), and other trees such as Excoecaria agallocha (Euph.) with sticky, white sap which may cause temporary blindness (Burkill 1966), pandans Pandanus, the white-flowered and large-leafed Scaevola taccada (Good.) the fruits of which are dispersed by birds (Leenhouts 1957), and two types of hibiscus Hibiscus tiliaceus (Malv.) and Thespesia populnea (Malv.) (van Steenis 1957). Both hibiscus have large, yellow flowers with purple bases, but H. tiliaceus has slightly hairy lower-leaf surfaces, heart-shaped leaves which are as long as they are broad, black-coloured longitudinal glands on the leaf undersur-face near the base, flowers which fall off as soon as they have dried, and smaller fruit. T. populnea has smooth leaves, longer than they are broad with a sharper tip, no black glands on the base of the leaf undersurface, flowers which remain on the plant for some days after they have died and larger fruit (fig. 2.24). Hibiscus tiliaceus is commonly planted in towns and villages.
After L. Clayton pers. comm.
Figure 2.23. Fruits of Barringtonia asiatica (left) and Heritiera littoralis (right). Scale bars indicate 1 cm.
The Calophyllum trees near the mouth of the Lariang River in northern South Sulawesi bear the epiphyte8 Myrmecodia (Witkamp 1940). Myrmecodia and certain other epiphytes are able to grow where there is insufficient organic debris for most epiphytes. This is because Myrmecodia shelters ants within chambers in its swollen stem, and these ants deposit organic matter in the chambers (p. 465). The cycad Cycas rumphii is also sometimes found in the Barringtonia formation. Despite their appearance, cycads are not palms, neither are they ferns, but they are related to the now-extinct seed-ferns that flourished between 280 and 180 million years ago. In addition to the species above, certain species from the pes-caprae association can also be found, particularly near the beach wall.
Figure 2.24. Leaves and fruit of Hibiscus tiliaceus (left) and Thespesia populnea (right). Scale bars indicate 1 cm.
The vegetation on small islands used by seabirds as nesting sites has a peculiar composition, although such islands as Sangisangian (p. 160) have not been investigated in this (or any other) regard. Here the normally basic reaction of the calcareous soil is changed because of the large quantity of uric acid and high phosphate levels in the birds' faeces although the soil pH is about 6.5-8.5 depending on the organic matter content. One tree Pisonia grandis9 with opposite leaves and reddish veins, is confined to such islands and can dominate the vegetation. Islands which lose their populations of seabirds eventually also lose this tree, whose fruit is dispersed by birds, and the more usual Barringtonia formation species take over (Stemmerik 1964). The status of bird islands is discussed below (p. 159).
Rocky Shores
Rocky shores occur where hard, resistant rock faces the sea in such a manner that the products of rock weathering by the waves are swept out to sea rather than deposited to form a beach. Such shores are usually steep with the rocky face often continuing down below the sea surface. There is, however, occasionally a narrow coarse sand or shingle beach. Such steep coasts and cliffs are usually formed of old limestone (e.g., Kaloatoa Island) or volcanic rock (e.g., Lembeh Island).
The vegetation clinging to the upper rock face, above the level of extreme high tides but still affected by sea spray, is similar to that found in the Barringtonia formation.
FAUNA OF SEDIMENT BEACHES
Open Area Communities
Most animals of sediment beaches rarely emerge on the surface and these are known collectively as the 'infauna'. Those that spend some time on the surface such as crabs and snails10 are known as the 'epifauna'. Most of the epifauna are large (macrofauna) but the infauna can be grouped into the microfauna or protozoans, the meiofauna (defined as animals able to pass through a 0.6 mm mesh sieve but retained by a 0.05 mm mesh sieve11),
