coast. (R. Steene)
FAUNAL COMPOSITION
Most of the region’s reef and shore fishes can be broadly described as being of Indo-Pacific origin. In other words, they belong to the overall reef fish community that ranges across the vast reaches of the tropical Indian and Pacific oceans. Although individual species, and particularly the mixture of species present, vary greatly from one locality to the next in this huge region, there is a general faunal theme that pervades. Nearly all families and many genera are widely distributed throughout the region. Also the dominant (i.e., most speciose) families tend to be the same regardless of locality. Dominant groups across this region usually include such families as gobies, wrasses, damselfishes, gropers, moray eels, cardinalfishes, and surgeonfishes.
The reason for the region’s relative homogeneity in faunal composition is at least partly explained by examining the life cycle of reef fishes. With few exceptions most species have a pelagic larval stage which is transported by ocean currents for variable distances depending on hydrological conditions and duration of the larval period. Until recently the length of larval life for most fishes was an unknown factor, but thanks to otolith aging techniques our knowledge in this area is rapidly expanding. Essentially this technique consists of counting daily microscopic growth rings that appear on the bones of the inner ear (otoliths). We now know that the larval duration is highly variable, ranging from just a few days up to nearly two months, with an average length of about 3-4 weeks. Although the adults of most reef fishes are highly home-ranging or territorial, a homogeneous gene-pool is maintained over a broad area by the dispersal capabilities of the larval stage.
Many Indo-Australian reef fishes are distributed widely across the Indian and West and Central Pacific oceans. Species such as the Racoon Butterflyfish (Plate 55-13) and Pacific Gregory (Pl. 66-12) range from the shores of eastern Africa to the Hawaiian Islands and a few others such as the Moorish Idol (Pl. 92-9) and Longnose Hawkfish (Pl. 67-18) extend even farther, to the coast of the Americas. Indeed, throughout the Indo-Pacific region a significant segment of the fauna consists of similar widespread species. Another important component of the fauna consists of species that have more limited regional distributions. A number of species such as the Honey-Head Damsel (Pl. 61-8) and Rainbow Monocle Bream (Pl. 51-12) are mainly confined to what biogeographers refer to as the Indo-Australian Archipelago, which encompasses the Malay Peninsula, Indonesia, Philippines, northern Australia, and Melanesia. At the bottom end of the scale, a few species such as the Banggai Cardinalfish (Pl. 34-7) have an extremely limited range. It is only found among a small group of islands off central-east Sulawesi. This fish, and others that are similarly restricted, usually lack a pelagic larval stage, which prevents their dispersal.
BIOLOGY OF
REEF FISHES
The region’s tremendous diversity of inshore fishes is reflected in a wide variety of reproductive habits and life history strategies. The following discussion is intended to give an overview of the most common patterns. More detailed information is available in the scientific literature or semi-popular works such as Thresher’s (1984) Reproduction in Reef Fishes. The majority of reef fishes are egg layers that employ external fertilisation. Relatively few species bear live young that are prepared to fend for themselves at birth. Included in the latter category are sharks, rays, and cusk eels. Basically two patterns of oviparous or egg-laying reproduction is evident in most reef species. Females of many fishes, including the highly visible wrasses and parrotfishes, scatter relatively large numbers of small, positively buoyant eggs into open water where they are summarily fertilised by the male. The spawning event is typically preceded by nuptial chasing, temporary colour changes, and courtship display in which fins are erected. This behaviour is generally concentrated into a short period, often at sundown or shortly afterwards. This pattern is seen in diverse groups such as lizardfishes, angelfishes, wrasses, parrotfishes, and boxfishes. Typically either pair or group spawning occurs in which the participants make a rapid dash towards the surface, releasing their gonadal products at the apex of the ascent.
The fertilised eggs float near the surface and are dispersed by waves, winds, and currents. Hatching occurs within a few days and the young larvae are similarly at the mercy of the elements. Recent studies of the daily growth rings found on the ear bones (otoliths) of reef fishes indicate that the larval stage generally varies from about 1-8 weeks depending on the species involved. The extended larval period no doubt accounts for the wide dispersal of many reef species. For example, many fishes that occur in our region have geographic ranges that extend from East Africa to Polynesia.
A second reproductive pattern involves species that lay their eggs on the bottom, frequently in rocky crevices, empty shells, sandy depressions, or on the surface of invertebrates such as sponges, corals, or gorgonians. Among the best known fishes in this category are the damselfishes, gobies, and triggerfishes. These fishes often prepare the surface prior to egg deposition by cleaning away detritus and algal growth. Bottom spawners also exhibit elaborate courtship rituals which involve much aggressive chasing and displaying. This behaviour has probably been best studied amongst the damselfishes. In addition, one or both parents may exhibit a certain degree of nest-guarding behaviour in which the eggs are kept free of debris and guarded from potential egg feeders such as wrasses and butterflyfishes. A very specialised mode of parental care is seen in cardinalfishes, in which the male broods the egg mass in its mouth. Similarly, male pipefishes and seahorses brood their eggs on a highly vascularised region of the belly or underside of the tail. As a rule the eggs of benthic nesting fishes are more numerous, larger, have a longer incubation period, and are at a more advanced developmental stage when hatched, compared to the eggs and larvae of pelagic spawning fishes. Hatching may require up to one week (in anemonefishes for example) and the larvae then lead a pelagic existence for up to several weeks before settling on the bottom in a suitable reef habitat.
There is very little information on the longevity of most reef fishes. Perhaps one of the longest life spans is that of the Lemon Shark which may reach 50 years or more. Most of the larger reef sharks probably live at least to an age of 20-30 years. In general the larger reef fishes such as gropers, snappers, and emperors tend to live longer than smaller species. Otolith aging techniques indicate that large gropers may live at least 25 years and some snappers approximately 20 years. Most of our knowledge of smaller reef fishes has resulted from aquarium studies. The values obtained from captive fishes may exceed the natural longevity due to lack of predation and the protective nature of the artificial environment. Batfishes (Platax) are known to survive for 20 years and even small species such as damselfishes and angelfishes may reach an age of 10 years or more.
Many-spotted Sweetlips and small reef fishes (mainly Anthias) are typical reef inhabitants throughout the region. (R. Steene)
ECOLOGY OF
REEF FISHES
The majority of fishes included in this book are generally considered to be inhabitants of coral reefs. However, reefs are highly complex systems, consisting of numerous microhabitats. In general, coral reef fishes are finely synchronised to their environment.
Each species exhibits very precise habitat preferences that are dictated by a combination of factors including the availability of food and shelter, and various physical parameters such as depth, water clarity, currents, and wave action. The huge number of species found on coral reefs is a direct reflection of the high number of habitat opportunities afforded by this environment.
Coral reef fishes generally exhibit a higher degree of habitat partitioning than do fishes from cooler seas. A good example of the fine scale on which this principle operates is the Urchin Clingfish (Pl. 12-6). It is usually found amongst the spines of Diadema sea urchins or nearby branching corals and feeds primarily on the tube feet of its host
