Surface and submarine pollination in the seagrass Zostera marina L.

Abstract

COX, P. A., LAUSHMAN, R. H. & RUCKLESHAUS, M. H., 1992. Surface and submarine pollination in the seagrass Zostera marina L. Hydrophilous plants can be divided into three ecological categories depending upon whether their pollen is transported above, on, or under the water surface. A mixed mode of submarine and surface hydrophilous pollination occurs in the seagrass Zostera marina L. In the surface mode of pollination, pollen rafts or ‘search vehicles’ which superficially resemble snowflakes, form at low tide and are transported on the surface of the sea by winds and water currents. Some of the search vehicles collide with the floating female stigmas, effecting pollination. In the submarine mode of pollination, small pollen masses resembling whisk brooms travel beneath the surface of the water. Although we failed to observe a submarine pollination event, SEM analysis of stigmas from subtidal populations confirms that submarine pollination does occur in Z. marina. However, observations of stigmas positioned at and below the surface of the water show surface pollination to be highly efficient. Electrophoretic evaluation of both subtidal and intertidal populations indicates significant genetic variation between populations. Given the high flux rates of surface‐borne pollen and pollen viability in excess of 5 h, it is likely that surface‐borne pollen is a major source of gene flow in Zostera marina populations.

Relationships between bed age, bed size, and genetic structure in Chesapeake Bay (Virginia, USA) eelgrass (Zostera marina L.)

“…This is consistent with evidence that inbreeding occurs in situ with some regularity in eelgrass (Ruckelshaus 1996) and that Chesapeake eelgrass self-fertilizes with no apparent loss of fertilization success or seed set (Rhode and Duffy 2004); inbreeding without loss of reproductive effectiveness might be expected in a population that inbred over enough generations to purge its deleterious alleles. Inbreeding in these beds might be further reinforced by pollendispersal distances of less than 15 m (deCock 1980;Cox et al 1992;Ruckelshaus 1994Ruckelshaus , 1996, a range not broad enough to cover the unvegetated waters between beds (Williams andOrth 1998, Reusch et al 1999b). This inbreeding, combined with extensive vegetative reproduction, could also help to explain the lack of relationship between geographic and genetic distance, even among beds less than 5 km apart.…”

Reduced Genetic Diversity in Eelgrass Transplantations Affects both Population Growth and Individual Fitness

“…Neither does theory predict a natural increase in genetic diversity in small founder populations over time (Lacy 1987), although over the short term additive genetic variance can be increased (Cheverud et al 1999). A postestablishment increase in genetic variation within a single eelgrass transplantation will occur very slowly, if at all, based on the limited dispersal of seeds (Orth et al 1994, Ruckelshaus 1996 and limited dispersal and viability of pollen (Cox et al 1992, Ruckelshaus 1996.…”

Is asexual reproduction more important at geographical limits? A genetic study of the seagrass Zostera marina in the Ria Formosa, Portugal

“…The numerous spathes (inflorescences) along the flowering shoots each contain 1 row of alternating male and female flowers; however, their flowering is asynchronous (de Cock 1980), which is likely to reduce selfing. Pollination is subaqueous, with the filiform pollen released underwater and carried to stigmata through water movement (de Cock 1980, Cox et al 1992. Z. marina is widely distributed in shallow coastal waters of the northern temperate zone (den Hartog 1970, Phillips & Meñez 1988.…”