HOBSON: FEEDING RELATIONSHIPS OF FISHES 



Predators Specialized to Seek Prey 

 in Reef Crevices 



Here I am concerned primarily with muraenid 

 eels, order Anguilliformes, and the brotulids, 

 order Gadiformes. Members of both groups, but 

 the eels in particular, have elongated bodies 

 suited to maneuvering through the crevices that 

 honeycomb coral reefs. Their similar mor- 

 phologies led early Hawaiians to group eels and 

 brotulids together by the generic term puhi. There 

 are a number of other secretive forms on Kona 

 reefs — small inconspicuous fishes like the 

 pseudochromid Pseudogramma polyaccanthus, 

 which were occasionally visible at night during 

 this study — but because I have little knowledge of 

 their habits they are not considered here. 



The muraenid eels are products of an evolution 

 that has diverged widely from the main teleostean 

 line: today they possess many specialized features 

 that equip them for hunting in reef crevices. The 

 primary specializations, for example their excep- 

 tionally solid skulls, are adaptive for wedging 

 through small openings, and they can back out of 

 any hole they enter (Gosline, 1959, 1971 ). Many of 

 the morays, and at least some of the brotulids, for 

 example Brotula multibarbata in Kona, are noc- 

 turnal; however, other morays are diurnal. Obvi- 

 ously hunting conditions in reef crevices differ 

 between day and night. 



Reef crevices are havens for numerous crea- 

 tures. Many diurnal forms rest there at night, 

 some of them virtually asleep, and many noctur- 

 nal forms shelter themselves there in daylight 

 (Hobson, 1968a, 1972). Moreover, most reef ani- 

 mals find refuge in these crevices when they are 

 injured or distressed; obviously, sheltering in reef 

 crevices is adaptive for prey threatened by the 

 many predators on the surface of the reef But it is 

 equally obvious from their long successful history 

 on tropical reefs that eels have acquired adaptive 

 means to exploit such prey. 



Predators with Sensory Specializations 

 That Detect Concealed Prey 



In this category I am concerned with the mul- 

 lids, order Perciformes, which are prominent on 

 Kona reefs. Their distinctive sensory chin barbels 

 permit them to locate prey that go undetected by 

 other fishes. And, like the muraenid eels, above, 

 their numbers include both diurnal and nocturnal 

 forms, as well as species that hunt effectively dur- 



ing both day and night. This fact, and the great 

 diversity in their prey, shows that mullids, with 

 their distinctive modes of feeding, have available 

 to them a broad range of predatory activity denied 

 most other fishes. 



Although seeking refuge under rocks, algae, or 

 sand is adaptive for many small animals ap- 

 proached by a predator, this tactic probably plays 

 to the advantage of some mullids. For example, 

 the diurnal Parupeneus chryserydros preys 

 mostly on small diurnal fishes that typically take 

 cover when threatened. This mullid may use its 

 exceptionally long barbels not only to locate such 

 animals, but also to drive them into the open. 



Many small organisms that seek cover when 

 threatened rest in the same refuges when they are 

 inactive, and at such times may be prey for other 

 mullids, notably P. bifasciatus. This species seems 

 to feed with equal effectiveness day and night, 

 although its food habits differ between these two 

 periods. In this respect, a comparison with the 

 serranid Epinephelus labriformis in the Gulf of 

 California is insightful. As noted above, E. lab- 

 riformis also feeds regularly day and night, taking 

 mostly crustaceans after dark and small fishes in 

 daylight; thus, its food habits agree with the 

 generalization that crustaceans are most vulner- 

 able at night, and fishes most vulnerable in day- 

 light. Parupeneus bifasciatus seems to be a suc- 

 cessful exception to this generalization, because it 

 takes fishes more often at night than during the 

 day and crustaceans more during the day than at 

 night. Apparently, P. bifasciatus is specialized to 

 capture prey that rest under cover, safe from pred- 

 ators with generalized feeding equipment. 



Thus, at least some mullids find prey among 

 animals that have sheltered themselves in the 

 reef, just as do some of the muraenid eels, so that, 

 like the eels, they have gained advantage from 

 what generally are successful defensive behaviors 

 in their prey. But whereas the eels probe deep into 

 reef interstices, the mullids confine their activity 

 to the superficial covering on the reef. 



Predators Specialized to Take Prey Among 

 the Plankton During the Day 



There are clear distinctions between diurnal 

 and nocturnal planktivorous fishes on coral reefs, 

 with the diurnal species inactive at night and the 

 nocturnal species inactive during the day (Hob- 

 son, 1965, 1968a, 1972; Starck and Davis, 1966). 

 Emery (1968) showed that the composition of 



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