THE DISTRIBUTION AND ECOLOGY OF THE BARNACLE BALANUS TRIGONUS1 WILLIAM E. WERNER, JR.~ Institute of Marine Science, University of Miami ABSTRACT New Ioca]ity records for Balanus trigon us on the F]orida and South American coasts are reported. Laboratory experiments indicate the species is relatively intolerant to both high and low temperatures, a fact which may restrict its geographic and littoral distribution. Specimens grown on panels reproduce throughout the year, with maximum settlement in spring and fa]1. Some individuals only 3 weeks old reproduce, and probably there are many broods in 1 year. There is evidence the species can be self-fer- tilizing. Growth studies show the fastest growing specimens are 10 weeks or less in age, or 9 mm or less in size, and tend to grow near the surface rather than at deeper positions. Temperature may affect growth, but there is no direct correlation of increasing sea temperatures and growth. INTRODUCTION Moore & McPherson (1963) reported the first record of the barnacle Balanus trigonus in the Miami area in March 1961, and suggested that the species is in the process of extending its range in this vicinity. The present study was made to determine the extent of its colonization along the Florida coast. Some aspects of its ecology possibly correlated with distribution, such as temperature tolerances, settlement preferences, and rate of growth were investigated. The study was completed during tenure of a postdoctoral fellowship occupied while on sabbatical leave from Blackburn College. The author is also indebted to H. B. Moore and C. E. Lane for advice in con- ducting the research, to D. J. Crisp for taxonomic help, to A. C. Fme and S. Miller for permission to use their dock and testing facilities and for settlement and temperature data, and to J. B. Lewis, J. Beers, I. Kris- tensen, I. Goodbody, D. Henry, R. Work, R. Manning, and B. Merrell for assistance in obtaining information on the distribution of the species. DISTRIBUTION Balanus trigonus has a wide distribution throughout the world, and has been reported from the Indian, Pacific, and Atlantic oceans. Although Darwin (1854) did not report it from the western Atlantic, subsequent studies have included it there. The earliest record of its occurrence in this part of the Atlantic was reported by Henry (1954). She stated (personal communication) that this record is from ALBATROSSSta. 2411, March 18, 1 Contribution No. 745 from The Institute of Marine Science, University of Miami. This study was supported by Grant No. HE-5489 from the Heart Institute of the National Institutes of Health. • Present address: Biology Department, Blackburn College, Carlinville, Illinois. 1967J Werner: Distribution and Ecology of Balanus trigonus 65 1885. The position of the station was 26°33'3"N, 83°15'30"W, or ap- proximately 55 miles west of the coast opposite Fort Myers, Florida, in the Gulf of Mexico. Pilsbry (1916) noted it from the Caribbean, based on a specimen taken from the outer hull of a Cape Cod whaling ship. He gave the range of the species in the western Atlantic as West Indies to southern Brazil. From collections made in 1936, Nilsson-Cantell (1939) recorded it just off the coast of South America from the Bay of Porlamar, Margarita Island; the Bay of Chacopata, near Coche Island; and Puerto Santo, east of Caru- pano, Venezuela. Kolosvary (1941) noted it from Venezuela. Cornwall (1958) reported it from Batia, Colombia. The Smithsonian records indi- cate this record is from Bahia Honda, Colombia, on the Caribbean (R. Manning, personal communication). Moore & McPherson (1963) were the first to record it on the mainland of the U. S. Ross et al. (1964) found it at Cape Lookout, North Carolina (34°37'N, 77°33'W) in 1963, and Wells et al. (1964) found it off Core Banks, North Carolina (34°42'N, 76°00'W) in 1961. I. M. Goodbody (personal communication) reports it as a part of the fauna of Jamaica. Other workers have failed to find the species in apparently suitable areas. Thus, recent studies of the fauna including barnacles of the U. S. coast of the Gulf of Mexico have failed to reveal its presence there. Brewer (1957) does not report it among the barnacles of Baffin and Alazan Bays, Texas. Whitten et al. (1950) did not find it near Galveston, Port Aransas, Free- port, or Brazos Santiago, Texas. Simmons (1957) did not find it in Upper Laguna Madre, Texas. Hulings (1961) did not find it near Panama City, Florida, nor did Tabb & Manning (1961) find it in their study of Florida Bay. Within the Caribbean, its known distribution is spotty. Collections from Bonaire, Curac;ao, and Aruba described by Nilsson-Cantell (1933) failed to include it from these islands, although it has been collected from other nearby islands. More recently, searches on St. Martin and Cura<;ao have also given negative results (I. Kristensen, personal communication). Lewis (1960) did not report it from Barbados, and has not found it there since (personal communication). Along the main coast of North America, earlier studies did not reveal this species. Stephenson & Stephenson (1950, 1952) did not find it in their studies of the intertidal zone of the Florida Keys, northern Florida, and the Carolinas, although Stephenson (1944) did find it in the intertidal zone of the African coast. Voss & Voss (1955) did not find it on Soldier Key, just below Miami, and Henry (1958) did not include the species in her report of the barnacles of Bermuda. J. Beers (personal communication) recently also has failed to find it on Bermuda. Failure to find the species in a given locality does not, of course, pre- 66 Bulletin of Marine Science [17(1 ) FIGURE I. Balanus trigon us, the scutum showing the longitudinal rows of pits. elude its presence in an area, especially since it is found living only below mean low tide mark. However, in areas where it is common, it can be readily found on shells and debris washed up on the beach. It is also easy to recognize. The aperture is roughly triagonal, and (most distinctive) on its scutum are a series of pits in parallel longitudinal rows (Fig. 1). Its walls bear prominent pink to purplish striations which are, however, some- what similar to those of Balanus calidus, B. amphitrite, and young B. tintinabulum (Fig. 2). Investigation of the Florida coast revealed its presence in the following locations (from north to south): Daytona Beach, Jupiter Inlet, Boca Raton, 1967] Werner: Distribution and Ecology of Balanus trigonus 67 FIGURE 2. Balanus trigon us, dorsal view showing the triangular opening and the prominent striations on the walls. Port Everglades, Miami Beach, Virginia Key, Key Biscayne, and Pigeon Key. In December, 1966, it was found at St. Petersburg Beach, Mullet Key, and Sanibel Island (Fig. 3). The R/V OREGON (Cruise No. 84, Feb. 18-27, 1963) collected B. trigonus from 16 stations off British Guiana, French Guiana, and the ex- treme northern tip of Brazil. TEMPERATURE TOLERANCES Temperature tolerance may be one of the factors involved in the dis- tribution of Balanus trigonus. Distribution records indicate that the spe- 68 Bulletin of Marine Science [17(1) lJaylona Beach (+) st. Petersburg Beach (-) FLOUIDA Jupiler Inlel (+) Hocoa Ilalon (+) I'orl Everglades (+) FIGURE 3. Sites surveyed for presence of Balanus trigonus; (+) indicates species was observed; (-) indicates species was not observed through 1965. See text for 1966 changes. 1967] Werner: Distribution and Ecology of Balanus trigol1us 69 TABLE 1 GEOGRAPHICDISTRIBUTIONOFBalanus trigon us Temperature (OC)' Sea surface Place Latitude Authority Feb. Aug. 200 m 400 m Northernmost Distribution Western Atlantic, Cape Lookout, N.C. 34°42' Ross et al., 21 27 10 10 1964 East Atlantic, Azores 38° Gruvel, 1920 16 22 14 12 Western Pacific, Misaki, Sagarni Sea, Japan 35° Nilsson- 14 25 15 10 Cantell, 1921 Eastern Pacific, Estero de la Luna Sonora, Mexico 27° Steinbeck & 18 20 9 8 Ricketts, 1941 Southernmost Distribution Western Atlantic, Southern Brazil 32° Pilsbry,1916 23 23 15 10 Eastern Atlantic, Cape Agulhas, Africa 25° Stephenson, 20 17 10 10 1944 Western Pacific, New Zealand 34°_46° Pilsbry, 1916 20 14 14 11 Eastern Pacific, Peru 5°_15° Darwin, 1854 19 16 12 9 1Thetemperaturesare frommapsin Sverdrup,Johnson& Fleming(1942). Accordingto a map by Wells in Hedgpeth(1957), the above distributionof B. trigon liS is within the 21 'C extended isotherm. des is confined to tropical and subtropical regions (Table 1). It has been reported from great depths (to 3000 m) but is not found living above mean low tide mark in the intertidal zone. This would indicate the possibility that the adult might tolerate low temperatures. Its absence from the intertidal zone suggests that at least some phase of the life history of the species cannot tolerate extremes of temperatures such as those found in the intertidal zone. It is the settling cyprid larva that would first be exposed to such intertidal variations, although the adult, ova, and early larval stages would also have to survive temperature fluctua- tions, since fertilized ova and nauplii are maintained in the adult mantle. Only the larval stages are planktonic and would not be exposed to inter- tidal temperature variations. In the Miami area, B. trigon us was found growing on red mangrove 70 Bulletin of Marine Science [17(1) (Rhizophora mangle) roots during the winter months. The aerial roots of the tree were in a pool of water about 1 m deep at low tide, when bottom was exposed only 1 or 2 m away from the trees. In the summer, the water over the surrounding tidal flats and around the mangroves became warm (temperatures as high as 37°C were recorded) and all the B.