Introduction of the Indo-Pacific Pteriid Bivalve Electroma Sp. to the Tropical Western Atlantic

BULLETIN OF MARl E SCIENCE. 62( I): 269-274. 1998

NOTES

INTRODUCTION OF THE INDO-PACIFIC PTERIID BIVALVE ELECTROMA SP. TO THE TROPICAL WESTERN ATLANTIC

Francisco J. Borrero and Juan Manuel Diaz

The family Pteriidae (Bivalvia: Pterioida), which includes he group known as , pearl oysters," comprises three Recent genera, Pteria Scopoli 1777, Pinctada Roding, 1798, and Electro117a Stolickza 1871 (Hayes 1972; Vaught, 1989). This family i considered to be represented in American waters (in both the western Atlantic and the eastern Pacific) by nine recognized pecie belonging to the genera Pteria and Pinctada (Hayes, 1972) but no species of Electroma has yet been reported from either Recent Atlantic or eastern Pacific fauna. There is comparatively little information on recent invasions of marine organisms to the western Atlantic. Although a number of introductions may have oc- curred, they have not been rec gnized. At least four recent introductions of ben- t.hic marine organ.isms to the tropical western Atlantic have been interpreted as due to shipping activities specifically transport of ballast water: the algal com- mensal shrimp Hippolyte wstericola from other Atlantic locations (Wicksten, ] 989), the swimming crab Chalybdis helleri from the Indo-Pacific and I rael (Campos and Tiirkay, 1989), the green mussel Perna viridis from the Indo-Pacific to Trinidad and Tobago (Agard et aI., 1992) and possibly the Texas coa t (Hicks and Tunnell, 1993; Carlton, pers. comnl.), and tl1e blenniid fish Omobranchus pUl1ctatus from the Indo-Pacific to the northern coast of South Amelica (Springer and Gomon, 1975). The present report of the pteriid bivalve Electroma sp. i an addition to this growing list.

RESULTS AND DISCUSSION Abundant material of a small form of Pteriidae wa collected in 1983 in the Santa Marta area, Colombia, at depths ranging from 4 to 10 m, attached to hydroids (Cnidoscyphos sp.) and algae (Sargassul11 sp.). It was erroneou ly identified at that time as juvenile Pte ria colymbus (Roding) (Dfaz ]985). More recently, in course of a long term monitoring of settlement of bivalve spat on artificial collectors deployed monthly since 1994 in the same area (Uribe and Borrero, 1995; Uribe, 1996), the mo t abundant mollusc settling on the collectors in mo t month was found urprisingly to be the previously supposed P. colymbus. In April, the month of highe t abundance they literally covered the external urface of the collector bags, greatly impeding the collection of other pecies Uribe, 1996). A concurrent rudy on taxonomic composition and abundance of plankton.ic bivalve larvae in the same area indicated that in April 1994, larvae of this species com- prised up to 93% of the total bivalve larvae in quantitative plankton tows, reaching abundances of up to 5600 larvae m-3 (Zapata 1996). Since juvenile form of many other bivalve species, induding everal Pteriidae such as Pinctada imbricara (Roding) and true P. colymbus (Fig. ID E) have also been abundantly obtained from the collectors for almost 2 yrs, the taxonornic placement of that extremely abundant species had to be reconsidered. Specimens belonging to the species here reported have since been collected in large numbers at other localities in Colombia and Venezuela (Fig. 2).

269 270 BULLETIN OF MARIN SCIENCE. VOL 62. NO. I. 1998

Smm

Figure I. Specimens of £Iecrroma sp. (A-C) and young Prer;a co/ymhus (D,E) obtained from artificial spat" collectors near Sanla Marta, aribbean coast of C lombia (April 1994).

Laboratory growth observations and detailed morphomenic analysis with this species led us to conclude that it is a species of EleClroma Stouckza, 1871 sensu stricto (Hayes, 1972), a genus hitherto known exclusively from the Indo- West- Pacific. Despite recent exhau tive studies of the reef-associated molluscan fauna in the Santa Marta area and other locations of the Caribbean coast of Colombia (Dfaz and Gotting, 1986; Dfaz et a1. 1991; Ablanque and Borrero, 1995), no previous reports of Pteriid taxa different than PinClada and Pleria are available.

66 60"1

IS" N

' ~ ['A/UNBHAN EA <;; 0 0 D 12" D

Figure 2. Records (black dots) of Elecrroma sp. in the tropical western Atlantic and loc'1Jiries men- tioned in the text: (I) Santa Marw. attached to hydroids. algae, and spm collectors; (2) Golfo de Morrosquillo. on artificial spat collectors (March 1995, S. Hernandez, pers. comm.); (3) Dibulla, atrached 10 beach wrack composed mainly of algae of the genera S~//"ga.l".I"1I1J/ and ryp/onemia (Feb- ruary 1994. pers. obs.); (4), subtidal to -2 Ill. attached 1O several algal specie (February. 1994, pers. observ.); (5) Playa Tucacas. as gut content in marin catflshes (Ariidae) (August 1995. P. Penchaszadeh, pers. comm.): (6) Puerro BoIrvar. OTES 271

Like the majority of species placed in the genus Electroma, this species has a small and very fragile shell (maximum length 8 mm), the major axis of disc being oblique to the hinge line, a feature common to Pte ria, but unlike the latter, the hinge line is notably shorter than the height of the shell and the posterior margin i not sinuated. The shell is translucent amber with narrow dark brown zigzag lines. Specimens held in aquaria continued to live and exhibited good overall condition for at least 1 ma without discernible increase in size and then they died. This suggests that the size here reported is about the maximum size for the species, which also seems to have a comparatively short life span. Moreover, in ] 995, one of us (FJB) had an opportunity to examine an extensive collection of ElecTroma species at the Australian Museum, Sydney, from localities throughout the Indo-Pacific region. Several specimens in this collection beared resemblance to the pecie here reported. b th in general sheJJ hape and size, but not in color. The specific affiliation of the Electroma species found in Colom- bia and Venezuela remains thu to be e tabli hed. Apart from an exhaustive bib- liography of the species assigned to Electromo (Fischer-Piette, 1980), no com- prehensive taxonomic revision of thi genus has up to now been attempted, thus we abstain from de cribing thi form a a new pecies. Voucher specimens have been depo ited in the malacological collection at INVEMAR (Mol-l 099), and are available for examination. A econd striking issue about this species is its almost exclusive association with frondose algae rather than hydroids octocorals, or branching scleractinians, which constitute the main substrata for most Electroma pecies (Morton, 1983; Stanley, 1988· and references in these works). The report of Electromo from the southern CaJ;bbean constitutes the first men- tion of its presence in the Recenr fauna of the western Hemisphere. We conclude that the Electrollla species here reported is a known Indo-Pacific species, which has been introduced recently to the Caribbean through ne of the various mechanisms involved in non-purposeful man-mediated introduction of marine fauna (Carlton, 1987' Carlton and Geller, 1993), such as shipping (fouling and baJlast). Many, nonindigenous marine bivalves, both infaunal and epifaunal, have been introduced in the la t two decades to regions where they did not formerly exist. By 1990, the Pacific coast of NOlth America accommodated nearly 40 exotic species, the Atlantic coast 10, and the Gulf coast five or fewer (Carlton, 1992). The edible brown mussel. Pe/'l1(/ perna (Mytilidae), was later introduced to the Texas coast apparently from Venezuela Hicks and Tunnell, 1993), and a related Indo-Pacific species P. viridis, to the ea tern Caribbean. The coasts of both northern Colombia and western Ven zuela ho't important ports, regularly visited by commercial sh.ips from varied provenance including Asia and the western Pacific region. The introducti n f Electroma sp. to tllis area could have re ulted from releasing of ballast seawater by international vessels such a oil tankers in the Gulf of Venezuela and CUrac;:ao and ships visiting the coal harbor Puerto BoHvar (Fig. 2). Recent records of the Indo-Pacific winuning crab Charybdis helleri (Decapoda: Portunidae) from th northern coast of Colom- bia bave been interpreted as an introduction by means of the baUast water released in front of the entrance of Puerto BolIvar by ships from Israel (Campos and TUrkay, 1989). Besides the fact that nonindigenous species can rapidly pread and become pe t organisms, its introduction can have devastating impacts on native ecosystems (Carriker, 1992). The ecological role that Electroma sp. has taken in the southern Caribbean eem remarkably imilar to the spread and niche acquired by Mus- c~ilista senhousia (Mytilidae) introduced t Australia and New Zealand WiUan, 272 BULLETiN F MAIO E S lEN E. VOL. 62. NO. i. 1998

1987). Both species are small, opportunistic bivalves, with gregarious behavior, and have the ability to monopolize available substrata in the habitats they occupy. The presence of Electroma sp. in the southern Caribbean ba interesting implication in regard to practical aspects of aquaculture. It is so abundant tbat it constitutes a major problem for spat collection of commercialJy important bivalves in the region; in addition, the extremely beavy fouljng by this species can not be ignored for maintenance of culture structmes at some time f the year. Similar problems have been experienced with pear] oyster culture in the Red Sea and the Gulf of Mannar India, where heavy sets of small Pteriids referred to as ' avicu- llds" or 'Avicula p." (an earlier name for the group, and probably a species of ElectrO/na) rendered spat collection ineffecti ve for at least some periods (Cros - land, 1957; Alagarswami and Chellam, 1976). Analysis of natural mechanisms of ruspersal during geologic and Recent time, and of distribution' of shared molluscan species groups among the four tropical marine region, suggest that tbe Indo-West Pacific ha been chiefly a donor region of species, whereas the eastern Pacific has been a recipient region; the eastern and western Atlantic regions fall in the middle (Vermeij and Rosenberg, 1993). By contrast, a' result of human-mediated transocearuc biological invasions parts of the eastern Pacific (west coas of N rth America), the Hawaijan Islands and Australasia appear as major recipients for introduced species (Carlton, 1987). Thus, human-mediated dispersal of ma1"ine biota through intended introduction of aquaculture species and their epibiota, and through non-purposeful ballast water and fouling may be in partial or direct opposition to natural mechanisms of introduction of specie to new areas. As stressed by Carlton 1987), Willan (1987) and Carlton and Geller (1993), stiff regulations on relea e of ballast water are urgently needed to curtail the very serious effects of these biotic exchanges. Several observations suggest that Electrol11C1sp. may have an important impact on natural biotic assemblages at least locally in Caribbean locations: (l) It has been incorporated already as an important component in the diet of benthicftshes at Locations on the Venezuelan coast (Riera et al., ]995) and probably Colombia; (2) In the north rn portion of the Colombian Caribbean coast, it has virtually monopolized the subtidal algal substrata where it occurs which includes the most common species of algae; (3) Its temporal dominance in bentillc substrata and in the plankton community (larval stages) likely affects the availability of planktonic fo d to other suspension feeders. Due to the frequently very large population izes of small, opportumstic illtroduced pecic such as ElectromCi sp., the latter type of trophic impact has been id nrifted as of great impact in other habitats, particularly bodies of freshwater col nized by zebra mussels, Dreissena poly- morpho (Nalepa and Schloesser, ] 993) and clams, Corbicula jlwninea (Leff et a1., 1990) and potentially in Australian locations c Ionized by the marine mussel Musculista senhousia (Willan 1987). We do not know the geographic di tribution in the Indo-Pacific of the Electro- mo species here reported, so it i impossible to compare the breadth of habitats it occupies in its original di tributional range with those at locations in the we tern Atlantic. However, in the Caribbean it occur in regions ranging from rugh salinity (34.5-37%0) and relatively cool temperature (22-30°C) which are affected by easonal upwelling (northern half of the Colombian coast) to warmer (27-31 DC) estuarine conditions in the Golfo de Morrosguillo area (Bula-Meyer 1985; COR- PES, 1992). These areas includ a suite of substratum types from relatively ex- po ed rocky hores to mud/sand beaches. Thus, t.bjs species of Electroma exhibits generalized hab:itat requirements and capacity for adaptation to varied environ- mental condition .We can only speculate about the further fate of th:is Electroma. NOTES 273 species in the western Atlantic. Its presence in Colombian waters since at least 12 yrs suggests that the introduction has been successful, to the extent of becom- ing a dominant member of the shallow subtidal benthic macrofauna. On the other hand, both the rather wide current distribution range of the species in tbe southern Caribbean (inferred from the present records, Fig. 2) and its presumed life history strategy show, that it might be expan ive if ecological conditions support its occurrence and levels of competition and predation are low in comparison to its recruitment potential.

ACKNOWLEDGME TS

We are indebted to S. Hernandez. A. M. Uribe.

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DA TE ACCEPTED: lovember 20, 1996.

ADDRESSES: (F.J.B.) Univcrsidad de Los Andes. Depar/amelllo de ie/lc:ias Biol6gicos, A.A. 4976. SrllllllJe de BogNG. Colombia: (J.M. D.) 1I/.I'IillllO de 1I1"esligaciol/cs Marillas y Costenl.\' INVEMAR. A.A. 10/6. Sml/{1 Mana. Colombia.