Patterns of larval release by the Asian shore crab Hemigrapsus sanguineus : periodicity at diel and tidal frequencies

Journal of Shellfisheries Research, August, 2005 by Susan Park, Charles E. Epifanio, Raymond B. Iglay

ABSTRACT The Asian shore crab, Hemigrapsus sanguineus, is an invasive species along the Atlantic coast of North America. It has spread rapidly since its discovery in the USA in 1988 and has become the dominant crab species in rocky intertidal habitats at many locations in the Middle Atlantic Bight and in the southern Gulf of Maine. The reproductive biology of Hsanguineus has received only cursory study in native east-Asian waters. Available information consists mainly of descriptions of the larval stages and general characterizations of the natural history of the species. This study examined the periodicity of larval release in an invasive population of H. sanguineus near its original site of introduction at the mouth of Delaware Bay. We investigated larval release at diel and tidal frequencies. Analysis of laboratory data showed that larval release always occurs near the time of nocturnal high tide. Field sampling confirmed the presence of stage I zoeae in waters near adult habitat at the expected time of larval release. This pattern of release minimizes the impact of visual predators on newly hatched zoeae and takes advantage of circulation at tidal frequency to transport zoeae away from intertidal habitats where conditions may not be favorable for larval development. However, H. sanguineus is not unique among intertidal crabs in releasing larvae near the time of nocturnal high fide. This pattern has been reported for a large number of species with wide representation among families. Thus, the pattern of release observed in H. sanguineus does not provide any special competitive advantages over co-occurring native species, and the remarkable success of the species in North American habitats may be attributable to competitive interactions occurring after settlement and metamorphosis.

KEY WORDS: invasive species, Hemigrapsus, larval release, diel, tidal, Asian shore crab

INTRODUCTION

Reproductive activity of marine fish and invertebrates is often synchronized with seasonal cycles. Within these seasonal periods of reproduction, the actual release of larvae may occur in phase with lunar, semilunar, tidal, or diel cycles (e.g., Knowlton 1979, Rutberg 1987, Ims 1990). Many species of intertidal crab display a rhythm of larval release wherein hatching occurs during springtide periods near the time of nocturnal high tide (Forward 1987). This minimizes the impact of visual predators on newly hatched zoeae and takes advantage of tidal circulation to transport zoeae away from intertidal habitats where environmental conditions may not be conducive to larval development (Morgan & Christy 1996, Petrone et al. 2005).

The grapsid crab Hemigrapsus sanguineus is a recent invader of rocky intertidal habitat along the east coast of North America. H. sanguineus has spread rapidly since it was first discovered near the mouth of Delaware Bay in 1988, and the role of reproductive biology in promoting this spread is poorly known. The species currently ranges from Maine to North Carolina (ca. 36[degrees]44[degrees]N) in the United States and has been reported along the Atlantic and Mediterranean coasts of Europe (McDermott 1998a, Park et al. 2004, Breton et al. 2002, Schubart 2003). The reproductive biology of H. sanguineus has received only cursory study in native east-Asian waters. Available information consists mainly of descriptions of the larval stages and general characterizations of the natural history of the species (Kurata 1968, Gamo & Muraoka 1977, Hwang & Kim 1995). Earlier investigations of invasive populations have shown that H. sanguineus has an unusually long reproductive season (April to October) in North American habitats (McDermott 1998b, Epifanio et al. 1998). However, patterns of larval release within the reproductive season are not well known, and factors such as semilunar, diel and tidal rhythms of release could have important effects on the invasive potential of the species. An earlier study conducted with native Asian crabs indicated that H. sanguineus females release all of the larvae within a given brood as a single hatching event near the time of high tide and that larval release probably occurs throughout the spring/neap cycle (Saigusa & Kawagoye 1997). However, that investigation was conducted mainly in the laboratory, and results were complicated by the long periods of isolation from natural tidal and light conditions. Subsequent work with an invasive North American population investigated patterns of larval release on a semilunar scale and again found no clear evidence for spring/neap periodicity (Epifanio et al. 1998). In the current work, we present results of a study that used a combined field and laboratory approach to investigate tidal and diel patterns of larval release by H. sanguineus females in a North American habitat. The study addressed two research questions: (a) is there adiel cycle to larval release and (b) is tidal periodicity related to the putative diel cycle?

MATERIALS AND METHODS

General Aspect