Reproduction in False Bay


Caught in the Act!  This pair of mating amphipods was found in the Ulva area.  The larger male often clasps the smaller female for days at a time, hoping to mate with her when she molts.
The organisms found in False Bay have diverse reproductive habits. However, there are a few unifying factors. All must deal with the once or twice-daily draining of the bay and the associated flow of very large amounts of water in and out. Eggs or larvae spawned freely into the water at high tide will be swept out of the bay and away from the parental habitat as the tide ebbs. However, eggs and larvae left attached to the bottom or brooded by parents are faced with the high temperatures and other associated hazards of low tide.

The majority of the fauna observed in False Bay consist of polychaete worms, bivalves, snails, and crustaceans. Reproductive strategies can be divided into two categories: those species in which development takes place away from False Bay in the plankton (free-spawning and epitoky), and those in which development occurs benthically in the bay (oviposition and brooding). This page will focus on a sampling of species exhibiting these habits.

The majority of the fauna observed in False Bay spend part or all of the larval stage in the plankton. The sand dollar Dendraster excentricus spawns both eggs and sperm (separate individuals) in late spring/summer. Although cues for spawning are unknown, it has been suggested that following low tide, spawning is induced by the influx of cold water on the incoming tide (Strathmann 1987). This strategy would ensure that Dendraster embryos are carried safely out into the plankton on the next ebb tide and also that embryos are not exposed to the harsh, hot conditions of low tide at False Bay.  Sand dollar larvae spend a variable period of time in the plankton, and often prefer to settle near pre-existing populations of adults (Strathmann 1987).


Epitoky is an unusual mode of reproduction unique to polychaetes in which the worm undergoes a partial or entire transition into a pelagic, sexually reproductive morph known as an epitoke. Polychaete epitokes can often be seen swarming around submerged lights during summer nights in the San Juan Islands. In many cases, epitoky involves loss or degeneration of digestive structures and enhancement of swimming, sensory, and gonadal structures (Strathmann 1987). In the case of False Bay, worms such as nereids and glycerids that engage in epitoky leave the sandflats and enter the plankton in order to reproduce. Populations are replenished when larvae come in on the incoming tide and settle out of the plankton to take up the benthic lifestyles of adult polychaetes.
Benthic Oviposition

Many snails and some worms of False Bay lay their eggs in gelatinous masses anchored to sand, algae, or bits of debris.  Bubble snails such as Melanochlamys and Haminoea develop in embryo masses to at least the veliger stage, at which time they become planktonic for a period before settlement.  Embryo masses are exposed to extreme temperature fluctuations and other hazards of low tide, as well as predation at both high and low tide.
Haminoea adult
Haminoea egg mass


Many False Bay animals, particularly arthropods, exhibit brooding behavior. Upogebia pugettensis, the mud shrimp, carries eggs cemented to its abdominal appendages throughout the winter.  Larvae are released in spring and spend 2 or 3 weeks, as a stage called a zoea, in the plankton before returning to the mud flats on nocturnal spring flood tides (Dumbauld et al 1996). Brooded embryos and larvae are protected from predation and from the worst extremes of tidal fluctuations. However, brooding incurs a significantly higher cost of reproduction to the female parent than reproductive strategies in which parental responsibility ends with egg release.

Brooding female Upogebia, ventral view.  The eggs are cemented to the abdominal 
appendages, called pleopods, to the left.
Summary of Reproductive Strategies of False Bay Animals
Taxon Reproductive Mode Taxon Reproductive Mode
Annelida: Polychaeta Mollusca: Bivalvia
Maldanidae brood to 7-setiger or later Macoma inquinata Free-spawn
Terebellidae unknown Macoma nasuta Free-spawn
Arenicolidae brood or free-spawn Clinocardium nuttalii Free-spawn
Glyceridae epitokous Orbitella rugifera Brood to veliger
Lumbrineridae benthic oviposition Tresus capax Free-spawn
Nereidae epitokous Transennella tantilla brood to juvenile
Onuphidae brood to 6-setiger stage
Orbiniidae benthic oviposition? Mollusca: Gastropoda
Phyllodocidae epitokous Lacuna variegata benthic oviposition
Chaetopteridae free-spawn Haminoea vescicula benthic oviposition
Nephytidae free-spawn Melanochlamys diomedia benthic oviposition
Hesionidae free-spawn?
Echinodermata Grandifoxus grandus Copulatory; brooding
Leptosynapta internal brooding Other amphipods  Copulatory; brooding
Dendraster excentricus free spawn Upogebia Copulatory; brooding
Neotrypea Copulatory;? 
Nemertea Pinnixa tubicola Copulatory;? 
Paranemertes peregrina free-spawn Pagurus spp. Copulatory; brooding
Amphiparous free-spawn Leptochelia (Tanaid) Copulatory; brooding
Tubulanus free-spawn