BULLETIN OF MARINE SCIENCE, 47(3): 598-612,1990 POPULATION STRUCTURE, DIETS AND BIOGEOGRAPHIC RELATIONSHIPS OF A ROCKY INTERTIDAL FISH ASSEMBLAGE IN CENTRAL CHILE: HIGH LEVELS OF HERBIVORY IN A TEMPERATE SYSTEM Carol A. Stepien ABSTRACT Intertidal fishes were sampled in August 1987 using Quinaldine or rotenone from rocky habitats near Viiia del Mar, Chile (33"OO'S),a region of biogeographic transition between northerly warm temperate and southerly cold temperate faunas. Fishes collected belonged to the following 9 families and 12 species, in decreasing order of abundance: Tripterygion cunninghami (Tripterygiidae), Myxodes viridis (Clinidae), Scartichthys viridis (B1enniidae), Graus nigra (Girellidae), Girella laevifrons (Girellidae), Auchenionchus microcirrhis (Labri- somidae), Aplodactylus puncta/us (Aplodactylidae), Sicyases sanguineus (Gobiesocidae), Hyp- soblennius sordidus (Blenniidae), Clupeafuegensis (Clupeidae), Auchenionchus variolosus (La- brisomidae), and Ophiogobiusjenynsi (Gobiidae). Seven species (and 52% of the total number of individuals sampled) were primarily warm temperate in distribution (M. viridis, S. viridis. G. laevifrons. A. punctatus, A. microcirrhis, H. sordidus, and S. sanguineus), the remainder were primarily cold temperate. Gut content analyses determined that four species (S. viridis, G. laevifrons, S. sanguineus, and A. punctatus) representing 20% of the total number of individuals and 51% of total biomass were primarily herbivorous. All of the primarily her- bivorous species had warm-temperate distributions. The present study suggests that intertidal fish herbivory is considerably more important in central Chile than in other known temperate systems. The central Chilean nearshore ichthyofauna has been little-studied. Several biogeographic studies have described a faunal break in the vicinity of the present study, north of Valparaiso (33°S), with warm-temperate Peruvian fauna to the north and cold temperate Chilean fauna to the south (Woodward, 1851-1856; Balech, 1954; Soot-Ryen, 1959; Mann, 1954). However, other studies have sug- gested a more southerly boundary separating these provinces at northern Chiloe Island (37°37'S) (Dall, 1909; Rathburn, 1910; Stuardo, 1964; Haig, 1955; Garth, 1957). Brattstrom and Johanssen (1983) describe a transitional area between 30° and 42°S, in which many species from both the warm temperate and cold tem- perate regions coexist. Although the nearshore fishes of this transitional region in central Chile have been described (Hildebrand, 1946; Fowler, 1951; Mann, 1954; Hubbs, 1952; de Buen, 1959; Stephens and Springer, 1973; Pequeno, 1982; Cas- tilla and Paine, 1987), no studies have investigated the comparative life histories, population structures, and general ecology of the intertidal ichthyofauna. Rocky intertidal zones of central Chile and the northeastern Pacific faunal transitional region of Pt. Conception, California (34.5°N, which roughly separates the southerly warm temperate Californian province from the northerly cold tem- perate Oregonian province; Hubbs, 1948; Hedgpeth, 1957; Valentine, 1961; New- man, 1979), share several ecological similarities. Common physical parameters 1 include latitude ; mean monthly and annual surface water temperatures (U.S. Coast and Geodetic Survey, 1952; Brattstrom and Johanssen, 1983; Scripps In- stitution of Oceanography data report, 1986); climate, including mean monthly and annual air temperatures, fog, and wind speed (Bryson and Hare, 1974; I Although the latitude of Monte mar, Chile (33OS)is actually equivalent to north of San Diego, California, its water and air temperatures are colder (Briggs, 1974). 598 STEPIEN: CENTRAL CHILEAN INTERTIDAL FISHES 599 Schwerdtfeger, 1976; Brattstrom and Johanssen, 1983); and mean semidiurnal mixed tide levels (N.O.A.A., 1987). Climatic differences include more rainfall during cold months in Chile (Bryson and Hare, 1974; Schwerdtfeger, 1976) and a lesser tidal range in central Chile (Brattstrom and Johanssen, 1983; N.O.A.A., 1987) which decreases extent of exposure at low tide. In addition, several Chilean intertidal fishes, including the blenny Hypsoblennius, the clinid kelpfish Myxodes, and the girellid Girella, have close relatives (belonging to the same tribe and/or genus) and apparent ecological equivalents in temperate northeastern Pacific tide- pools. The most abundant rocky intertidal fish species in both the temperate south- eastern and northeastern Pacific are relatively small, cryptic carnivores which eat small crustaceans. However, the Chilean intertidal fish fauna differs from other known temperate areas in having a higher proportion (number of species, number of individuals, and percent biomass) of herbivores, which are larger than most of the co-occurring carnivorous fishes. Although many studies have demonstrated that fish herbivory is important in structuring nearshore systems in the tropics (Gold schmid et al., 1980; Gibson, 1982; Choat, 1982; Hixon, 1986), there has been no such indication in temperate systems (Hixon, 1986). The objective of the present study was to provide a baseline survey of the relative abundances, morpho metrics, age structures, sex distributions, and diets of the common intertidal fishes in this faunal transitional region near Vifia del Mar, Chile. The central Chilean fish assemblage is compared with other temperate, as well as tropical, nearshore hard-substrate communities and possible ecological similarities are discussed. MATERIALS AND METHODS Fishes from the rocky intertidal zone were collected off the coast of Montemar, Chile, 10 Ian north of Viiia del Mar (33"8, 71°33'W) and 20 km north of Valparaiso. Fishes were collected with handnets and quinaldine sulfate anesthetic or rotenone, during five low spring tides in August 1987. Four to 10 collectors, including some with snorkel gear, took all fishes seen. The tidepools had a maximum depth of 1.5 m MLLW (mean lower low water). Sites had a variety of algal species and coverage. Samples from subtidal populations of some species were obtained from SCUBA collections (to 15 m) made off the coast of Quintero (25 km N of the sample site) and the Farallones Islands (45 km NW), which were compared with the intertidal data. Following collection, fishes were measured to the nearest mm for total (TL) and standard lengths (SL) and weighed to the nearest 0.5 g. Gut contents of several individuals (ranging in number from all specimens of a given species collected to 10 specimens of representative sizes per collection) of all but two (rare) species were examined as soon after collection as possible under a dissection microscope. Identifiable food items were classified (to order when possible) and relative percent volume of each food type was estimated. Representative samples (most individuals of all but two rare species) were sexed and their otoliths were removed for aging. Gonadal maturities were ranked on a scale of I to 5, I being immature and 5 being ripe (Stepien, 1986a). Individuals rated 3.5 and above were considered mature. Mean maturity ran kings per age class were estimated by dividing the sum of all maturities for all individuals in that age class by the number of individuals in it. Otoliths were stored dry for later reading. Otoliths were read independently by three investigators and final age determinations were based on agreement of at least two of the three estimates. Otoliths were submerged in water and examined against a black background with a dissecting microscope (25 to 50 x magnification). Ages were de- termined by counting annuli, using standard methods outlined by Fitch (1951), Jensen (1965), and Collins and Spratt (1969). The otolith of a large specimen of Girella laevifrons was sectioned and embedded before reading by J. Butler. For all but three (rare) species, regression analyses and F-tests were performed (Sokal and Rohlf, 1981) on relationships ofSL versus TL and weight versus TL. Logarithmic transformations were made where appropriate. For two of the most common species, Tripterygion cunninghami and Scartichthys viridis, regression analyses were also performed for age class versus TL. Histograms of length-frequency relationships for the five most common species were used to diagram population structures. 600 BULLETIN OF MARINE SCIENCE, VOL. 47, NO.3, 1990 Table 1. Intertidal fishes collected in central Chile in August 1987. Duration of intertidal residency (DIR): E = entire life, J =juvenile stage only, U = unknown (Mann, 1954). Food items: A = amphipods, B = barnacles, C = decapod crabs (primarily Petrolisthes spp., Pachycheles spp., and Cancer spp., G = green algae (Chlorophyta; primarily Viva), H = harpactacoid copepods, 1 = isopods, L = limpets, P = polychaetes, R = red algae (Rhodophyta), S = gastropod snails, U = unknown. Food item rankings: 1 = 70% or more of volume of gut contents, 2 = 40 to 70%, 3 = 10 to 40%, 4 = < 10% Family and species DIR Number Size range (TL, mm) Diet and rank A. Tripterygiidae I. Tripterygion cunninghami E 211 (22-95) C-I, A-3, P-4 H-4 B. Clinidae 2. Myxodes viridis E 195 (25-182) C-1, H-3, A-3 1-4, P-4 C. Blenniidae 3. Scartichthys viridis E 115 (49-312) R-I, G-2, B-4 4. Hypsoblennius sordidus E 4 (46-92) S-3, A-3, H-4 P-4 D. Kyphosidae 5. Graus nigra J 95 (50-211) C-1, A-4, S-4 6. Girella laevifrons J 9 (30-420) R-I, G-2, S-4 E. Labrisomidae 7. Auchenionchus microcirrhis E 5 (67-259) C-1, S-3, P-4 1-4 8. Auchenionchus variolosus E 2 (88-140) C-1, S-2 F. Ap10dactylidae 9. Aplodactylus punctatus J 5 (113-157) R-1, G-3 G. Gobiesocidae