View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquila Digital Community Gulf of Mexico Science Volume 14 Article 3 Number 2 Number 2 1996 Feeding Guilds Among Artificial-Reef Fishes in the Northern Gulf of Mexico Brian D. Nelson University of West Florida Stephen A. Bortone University of West Florida DOI: 10.18785/goms.1402.03 Follow this and additional works at: https://aquila.usm.edu/goms Recommended Citation Nelson, B. D. and S. A. Bortone. 1996. Feeding Guilds Among Artificial-Reef Fishes in the Northern Gulf of Mexico. Gulf of Mexico Science 14 (2). Retrieved from https://aquila.usm.edu/goms/vol14/iss2/3 This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf of Mexico Science by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Nelson and Bortone: Feeding Guilds Among Artificial-Reef Fishes in the Northern Gulf Gulf of Mexico Scimce, 1996(2), pp. 66-80 Feeding Guilds Among Artificial-Reef Fishes in the Northern Gulf of Mexico BRIAN D. NELSON AND STEPHEN A. BORTONE To examine the diets of 25 demersal artificial-reef-associated fish species, 540 fishes were collected with spears and hand-nets off Panama City, Florida, in the summer of 1993. Fishes were preserved whole in the field. Stomach contents were later analyzed by frequency of occurrence, numerical abundance, and percent volume. These measures were combined into an Index of Relative Importance (IRI). The data set was then analyzed with cluster and detrended correspondence (DCA) analyses. Forage items of the reef fishes were dominated by fishes, xanthid crabs, unidentified items, squids, polychaetes, and penaeid shrimps. The DCA and cluster analysis revealed that these 25 artificial reef fishes could be organized into seven feeding guilds: lower structure pickers, ambush predators, lower struc­ ture crustacean predators, upper structure pickers, upper structure predators, water column pickers, and reef-associated open-water feeders. All of the demersal gamefish in this study were in the same feeding guild (i.e., reef-associated open­ water feeders). Species in this feeding guild were associated with artificial reefs diurnally and foraged away from reefs nocturnally. Our data indicate that many important artificial-reef-associated fishes in the northern Gulf of Mexico obtain most of their energy foraging away from the artificial reef structure. rtificial reefs attract and retain fish assem­ Researchers studying both coral and artifi­ A blages soon after deployment (Gascon cial reef ecology have called for further ex­ and Miller, 1980; Brock and Norris, 1987; amination of the trophic dynamics of reef fish Bohnsack, 1991). Moreover, they have tremen­ assemblages (Bohnsack and Sutherland, 1985; dous potential in the management of habitat­ Bohnsack, 1989;Jones et al., 1991). Research­ limited species (Polovina, 1991). However, the ers in other fields have found that studying trophic habits and competitive interactions of functional groups of organisms can provide in­ artificial-reef fish assemblages have not been sights to food web dynamics. Utilization of the studied extensively. Most studies thus far have guild concept has been a useful approach un­ characteristically focused on only a few species der these circumstances. Austen et al. (1994) (Bohnsack, 1991). Bailey-Brock (1989:580) de­ reviewed the importance of the guild concept scribed several possible feeding schemes for in fisheries management and indicated that if Hawaiian reef fish on an artificial reef; these statistically delineated guilds based on key re­ include feeding, " ... on the developing ben­ sources (described as a "super species") were thos, foraging over acljacent natural reefs, uti­ used, then guild management could be effec­ lizing both feeding grounds, and some may use tive in managing fisheries stocks. the reef solely for cover and forage some dis­ Root (1967) provided ecologists with a con­ tance from the reef." Information on coral ceptual tool to examine how groups of organ­ reef fishes indicates the importance of the soft­ isms interact. He introduced the term "guild" bottom communities surrounding reefs as a to ecology and defined the term as a group of source of prey organisms Qones et al., 1991). organisms that use the same resource in a sim­ Bohnsack (1989) reported that fishes associat­ ilar manner. This term is not limited by taxo­ ed with artificial reefs feed both on organisms nomic boundaries (Root, 1986). If, for exam­ associated with the reef structure and on the ple, avo organisms being studied use the same surrounding benthic communities. Although food resources in a similar manner, they are studies of artificial-reef fish foraging have been considered members of the same feeding guild conducted (Davis et al., 1982; Hueckel and (Gerking, 1994). For the present investigation, Stayton, 1982; Steimle and Ogren, 1982; a feeding guild will be considered as a portion Hueckel and Buckley, 1987; Ambrose and An­ of the reef fish assemblage that uses similar derson, 1990), the results provide no clear par­ prey items without regard to feeding morphol­ adigm. It is still unknown where most of the ogy. While guilds can be based on several fac­ prey organisms for reef-associated predatory tors or combinations of factors (diet, mor­ fishes originate. phology, behavior, etc.) we have chosen to ex- © 1996 by the Marine Environmental Sciences Consortium of Alabama Published by The Aquila Digital Community, 1996 1 Gulf of Mexico Science, Vol. 14 [1996], No. 2, Art. 3 NELSON AND BORTONE-FEEDING GUILDS AMONG ARTIFICIAL-REEF FISHES 67 amine diet directly because literature reports likely to bias the stomach contents by regurgi­ are contradictory on the usefulness of mea­ tation or feeding during collection (Randall, sures such as feeding morphology in determin­ 1967; Bowen, 1983; Helfman, 1983). ing guild membership (e.g., Weins, 1977; Vitt Once captured, fish were placed into mesh and De Carache, 1995), especially in fishes bags and retained by the divers for the dura­ (Zaret and Rand, 1971). tion of the dive (typically not more than 20 The present study was designed to examine min). All fishes were chilled in an ice brine for the prey taxa of 25 of the most common de­ 15-20 min to anesthetize them before fixation mersal artificial-reef assemblage fishes in the and to reduce the possibility of regurgitation. northern Gulf of Mexico, compare the relative Fishes were subsequently fixed in 10% Forma­ importance of various prey taxa in the diets of lin-seawater. Before immersion in the Forma­ these reef fishes, determine the guild mem­ lin-seawater solution, however, larger fishes bership of these fishes, and comment on the had their body cavities slit open to facilitate partitioning of resources among them. The re­ fixation and minimize digestion. After fixation sults of this study provide information on the for 7 d, samples were rinsed in tap water for diets of the most common artificial-reef assem­ 15 min to remove excess Formalin, and stored blage fishes, preliminary data that will lead to in 40% isopropyl alcohol. an enhanced understanding of where artificial­ In the laboratory, fishes were measured to reef assemblage fishes feed (which will, in turn, the nearest 1.0 mm (fork length, FL) and contribute information on the optimal spacing weighed (whole body, wet weight) to the near­ of artificial reefs), and a guild structure that est 0.1 g. The gape (maximum distance be­ can then be examined more directly by fish tween the jaws when forced open) of each fish ecologists studying competition and resource was measured with calipers to the nearest 0.1 partitioning. mm. The stomachs were then removed. For fishes without a distinct stomach (e.g., Halicho­ METHODS eres bivittatus) the first quarter of the gut was considered the stomach (Hueckel and Stayton, Fishes were collected from artificial reefs 1982). On removal, a stomach fullness index composed of bridge rubble off Panama City, (SFI) was determined for each stomach (0-5 Florida (Fig. 1). The reefs were 2-5 km from highest subjective score). The stomachs were shore and in shallow water ( <22 m). Each reef stored in 40% isopropyl alcohol until identifi­ site selected for this study had an established cation and analysis could be completed. Stom­ benthic community including hydroids, bar­ achs without contents (SFI = 0) were noted nacles, and algae. Individuals of 25 resident de­ but not retained. mersal fish species were collected that repre­ The stomach contents for each fish species sented common artificial-reef assemblage fish­ were removed and sorted into various taxa. es in the northern Gulf of Mexico (Bortone et Prey groups were then identified to the lowest al., in prep.). However, the inclusion of a given practical taxon. Voucher specimens for each fish species in this study was not necessarily prey taxon were retained for identification. due to its actual numerical abundance, but to Bowen (1983) stated that in most studies of the divers' ability to collect representatives of predator-prey interactions, order or family is a that species. low enough taxon for prey identification and All fish collections were made by divers using little information is gained by identifying to SCUBA. Collections generally occurred in the the species level. For each taxon, the number morning hours (0700-1200 CDT) to take ad­ of food items was recorded. If the items were vantage of the nocturnal and crepuscular feed­ not whole, particular parts were counted to ing habits predicted for diurnal reef inhabi­ roughly estimate the number of organisms tants (Hobson, 1973). Because most fishes (e.g., eye stalks, claws, or opercula). If the item were being collected in the morning hours, di­ was not recognizable as an individual but could gestion of stomach contents was expected to be identified as belonging to a particular taxon be minimal.