REEF PROCESSES 



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seven major groups of fishes: algal feeders, detritus 

 feeders, scavengers, plankton feeders, carnivores, coral 

 polyp feeders, and omnivores. Their algal feeders were 

 divided into four categories: (1) those which subsist on uni- 

 cellular algae (mullets and some blennies); (2) grazers, 

 which crop very closely to substratum and ingest some of 

 it along with the algae (surgeonfishes, damselfishes, gobies, 

 blennies, triggerfishes); (3) browsers, which use cutting 

 teeth for biting off algal fronds or filaments above the sub- 

 stratum and do not take in any of the nonalgal material 

 (surgeonfishes, damselfishes, triggerfishes); and (4) 

 incidental algal feeders, which feed primarily on other 

 materials (butterflyfishes, wrasses, parrotfishes, gobies, 

 puffers). The detritus feeders are represented by relatively 

 few species (mullets, gobies, blennies). The scavengers 

 included only the nurse shark In addition to the manta 

 ray, the plankton feeders included some round herrings, 

 halfbeaks, silversides, damselfish, and wrasses. The car- 

 nivores included a large number and variety of fishes fall- 

 ing into five groups: (1) those feeding on fossorial fauna, 

 (2) those feeding on benthonic fauna, (3) those feeding on 

 mid-water fauna, (4) resident roving carnivores, and (5) 

 transient roving species. The coral polyp feeders included 

 browsers, grazers, and feeders on branching coral tips. 

 Both facultative and incidental omnivores were recognized. 

 Colin, in chapter 7 of this volume, considers the feeding 

 relationships of fishes in greater detail. 



Hiatt and Strasburg (1960) raised several points of 

 interest in understanding trophic relationships of the fishes. 

 These points have perhaps not been pursued sufficiently in 

 subsequent research. They regarded benthic invertebrates 

 as the chief organisms for converting particulate and col- 

 loidal organic material to animal protoplasm, with the 

 energy and materials then reaching the fishes through 

 predators on the invertebrates. Hence, they stated that an 

 understanding of the primary producers and the trophic 

 relationships of the higher organisms (i.e., fishes) is rela- 

 tively well advanced in the reef ecosystem, "but there still 

 remains to be known the role of the myriads of inver- 

 tebrates which inhabit the reef." 



Subsequent studies have continued to focus on the pri- 

 mary producer level and on the fishes, and the role of 

 invertebrates is still relatively unknown. Hiatt and Stras- 

 burg pointed out that herbivorous species dominate the 

 fish fauna of Marshallese reefs; this is a generalization 

 which apparently applies to most reefs. Moreover, "It is 

 still an enigma why the biomass of herbivorous fishes is so 

 proportionately great on tropical reefs where the large 

 seaweeds are not abundantly available, and so propor- 

 tionately small along coastal shores in the temperate and 

 arctic seas." This may be less an enigma than Hiatt and 

 Strasburg thought, considering that algal productivity is 

 high in reef ecosystems and that the rate of energy 

 transfer through these producers can be high even with a 

 small biomass. It is probable, however, that the role of 

 algal turfs has been insufficiently appreciated and that 

 these multispecies assemblages, which are visually 

 unimpressive but are apparently subjected to heavy grazing 



pressure, have high rates of productivity even with their 

 low-standing crops, (See Marsh, 1976, for further develop- 

 ment of this point.) 



Hiatt and Strasburg further pointed out that, among 

 the fish fauna, surgeonfishes are the most important group 

 in converting primary productivity into animal tissue; they 

 convert large amounts of energy, whether or not they are 

 efficient. This impression has generally persisted among 

 reef ecologists. Hiatt and Strasburg also reported that all 

 parrotfishes they examined had scraped coral polyps and 

 that these animals may scrape smooth, algal-covered rocks 

 as well. This was disputed by some later studies, which 

 emphasized the grazing role of parrotfish rather than their 

 ingestion of coral polyps, although the latter activity is gen- 

 erally acknowledged to occur to a greater or lesser extent. 

 The Hiatt and Strasburg study has continued to be influen- 

 tial in shaping our thinking about reef ecosystems. 



Hobson and Chess (1978) studied trophic relationships 

 among fishes and plankton in the nearshore lagoon adja- 

 cent to windward islets. They found that feeding patterns 

 differed sharply between day and night and were strongly 

 influenced by current patterns. The adults of most diurnal 

 planktivorous fishes were numerous in certain places 

 where tidal currents were strong but much less numerous 

 where such currents were consistently weak. Strong- 

 current areas are rich and weak currents are poor in the 

 major zooplankton prey of the fishes (e.g., copepods, 

 larvaceans, and fish eggs). On the other hand, 

 zooplankton-poor waters close to island lees and interisland 

 lees are rich in reef debris; those fishes that could subsist 

 in those areas were abundant. Dascy/lus reticulatus was 

 numerous in such environments, though less so than where 

 currents were strong, and took algal fragments as an 

 important but secondary part of its diet. Other species that 

 fed largely on algal diets could be equally abundant in 

 strong- and weak-current areas or more numerous where 

 currents were weak. 



Major nocturnal planktivores, in contrast to the diurnal 

 feeders, were concentrated where the currents were weak 

 but were relatively sparse where the currents were strong. 

 These were found to be strictly carnivores that prey mostly 

 on large zooplankers (large calanoid copepods, mysids, iso- 

 pods, gammarid amphipods, postlarval carideans, and 

 brachyuran megalops) which were absent in the nearshore 

 water column by day. Such prey were reported to gener- 

 ally find conditions unfavorable where strong currents flow. 

 Most of these found shelter on or near specific nearshore 

 substrata during the day and entered the water column 

 only at night; others were found to be in deeper offshore 

 waters by day and moved inshore at night. 



Overall, the pattern was clear to Hobson end Chess; 

 most diurnal fish favored zooplankton rather than algal 

 fragments. This pattern was somewhat at variance with the 

 impressions that previous researchers had formed. The fish 

 morphology that permits faster swimming is more 

 developed in planktivores that swim farther from the reef; 

 Hobson and Chess interpreted this as an adaptation to 

 escape predators. 



