STONER: FEEDING ECOLOGY OF LAGODON RHOMBOIDES 



Table 7. — Trophic ontx)geny of pinfish collected at Crystal River 

 and Apalachee Bay, Fla. Crystal River data were taken from 

 Carr and Adams (1973). 



Feeding stage 



Size of fish 

 (mm SL) 



Crystal River 

 1 . Planktivore on copepods 



2 Carnivore on shrimp, myslds, and amphipods 



3 Herbivore on epiphytes 



4. Omnivore on epiphytes, shrimp, and fish 



5. Carnivore on shrimp and fish 



Apalachee Bay 



1 . Planktivore on copepods and Invertebrate eggs 



2. Carnivore on amphipods and harpacticoids 



3. Omnivore on amphipods. harpacticoids, shrimp, 



and epiphytes 



4. Omnivore on epiphytes, amphipods, polychaetes. 



and Isopods 



5. Herbivore on epiphytes and vascular plants 



food habits just as food abundance explained local 

 variations in food habits among stations in 

 Apalachee Bay. Carr and Adams described their 

 study site as dominated by Ruppia maritima and 

 Halodule wrightii. In Apalachee Bay, benthic veg- 

 etation was dominated by T. testudinum; there- 

 fore differences in food habits of pinfish between 

 the two areas, may be due to characteristics of the 

 habitat other than prey abundances. For example: 

 1) the wide blades of T. testudinum may provide 

 better refuge from predation for shrimp and other 

 crustaceans than that provided by narrow blades 

 ofi?. maritima and//, wrightii, and/or 2) the plant 

 material near Crystal River was, in some way, 

 unsuitable as food for large pinfish. Hansen ( 1969) 

 also reported that plant material was the domi- 

 nant food item of pinfish from dense Thalassia and 

 Ruppia beds in Pensacola Bay, Fla., suggesting 

 that some characteristic of Thalassia beds pro- 

 motes herbivory in pinfish. Similar to the present 

 study, Hansen found that seasonal variation in 

 plant consumption was related to seasonal avail- 

 ability of benthic macrophjdes. 



Trophic ontogeny in pinfish can be explained in 

 terms offish morphology. Width and height of the 

 mouth in the open position was linearally related 

 to standard length of pinfish and increased body 

 and mouth size permitted pinfish to capture a 

 broader range of prey sizes (Stoner 1979a). The 

 same characteristics undoubtedly explain in- 

 creases in numbers of prey types associated with 

 increasing body size in juvenile fish. Increasing 

 range of prey sizes and types with fish body and 

 mouth size has been reported by many authors 

 (e.g., Wong and Ward 1972; Ware 1972, 1973; Ross 

 1978). Transition to herbivory by pinfish, first as a 

 microepiphyte nibbler and later to a seagrass 

 grazer is associated with changes in dentition with 



growth. Very fine conical jaw teeth only are found 

 in fish at 15 mm SL, but conical teeth are replaced 

 by longer caninelike teeth in fish between 23 and 

 35 mm. Conical and canine teeth are well adapted 

 for capturing small animal prey, but chisel-shaped 

 incisors, which appear in fish >35 mm, provide 

 pinfish with the dentition required to graze plant 

 material. Because of its dentition, the pinfish is 

 probably an obligate carnivore until it reaches 

 about 35 mm SL (for further discussion and illus- 

 tration of ontogeny in pinfish dentition, see Cald- 

 well 1957). 



Given the morphological constraints of L. 

 rhomboides, its reproductive seasonality is par- 

 ticularly well adapted for exploitation of food re- 

 sources in seagrass meadows of Apalachee Bay. 

 Postlarval pinfish entered the seagrass beds in 

 midwinter at the time of peak abundance of cala- 

 noid copepods, appropriately small prey or- 

 ganisms. Winter spawning placed juvenile fish 

 (16-35 mm) on the seagrass beds in the spring 

 when the most valuable prey species, amphipods 

 and harpacticoid copepods, were beginning to re- 

 produce and reaching maximum abundance 

 (Stoner^; Thistle^). Optimal prey for larger pinfish 

 (36-80 mm) probably includes larger organisms 

 such as shrimp which had peak abundance in the 

 fall. Reproductive timing and growth placed large 

 pinfish on the grass beds in the fall. The life his- 

 tory strategy of L. rhomboides, therefore, appears 

 to be adapted to seasonal patterns of productivity 

 and abundance in prey and macrophyte species. 

 Although pinfish were among the fishes that were 

 shown to influence the abundance of zooplankton 

 in the Newport River estuary (Thayer et al. 1974), 

 it is unlikely that pinfish postlarvae affect the 

 abundance of calanoid copepods in Apalachee Bay 

 because of the low number of pinfish postlarvae in 

 the shallow bay (Brady 1980). However, pinfish 

 probably do regulate the abundance of certain 

 amphipod species in the bay (Stoner 1979a, b). 



Variation in food habits with space, both on 

 local and geographic scales, was a function of food 

 availability and habitat structure. Food habits of 

 fishes in Apalachee Bay were dramatically differ- 

 ent at stations separated by distances as little as 2 



^Stoner.A. W. 1980. Abundance, reproductive seasonality, 

 and habitat preferences of amphipod Crustacea in seagrass 

 meadows of Apalachee Bay, Florida. Manuscript in review. 



6D. Thistle, Assistant Professor, Department of Oceanog- 

 raphy, Florida State University, Tallahassee, FL 32306, pers. 

 commun. December 1978. 



347 



