The PALMETTO, Winter 1994, Page 3 Johnson's : the Rodney Dangerfield of (gets no respect/ survives harsh conditions/ little or no known sex)

by Michael Durako and Fritz Wettstein

Come along as we reveal mysteries of the seagrasses and unravel the intrigue of , Johnson's seagrass.

Johnson's seagrass, Haloplzila john• root stem). Either a pair, or a star• sOl/ii, is a small, rare seagrass that is General Characteristics of the shaped cluster, of leaves are attached known to occur only in lagoons along Ha loplli la Seagrasses to the rhizome at each node (growing the southeast coast of Florida. The Presently, there are twelve recog• point; see Figure 1). Also, most Halo- National Marine Fisheries Service nized seagrass species in the Haloplzila plzila sea grasses are tiny (less than 4 (NMFS) recently proposed that John• (closely related marine inches tall), shallow-rooted, and much son's seagrass be listed as a threat• that are not really grasses). Halophila less bulky than seagrasses such as ened species under the En-dangered seagrasses grow in warm-temperate Thalassia testudinurJl (turtle grass) or Species Act. The NMFS also proposed and tropical seas, bays, and lagoons SyringodiurJl filiforme (manatee grass). that lagoon areas near five southeast worldwide, and are one of five Flor• Their small stature has led mailY to Florida inlets be designated as critical ida seagrass genera. The species Halo• believe that they are not important to habitat for it. The designation of criti• phila decipieJls, or paddle grass, grows the marine ecosystems. This is not cal habitat areas will focus manage• in the warm waters of the Atlantic, true. Because scientific studies have ment efforts on protecting sites that Indian, and Pacific oceans - making historically concentra ted on larger are deemed critical to the survival of it the only world-ranging member of seagrasses and their sea meadow this species. These proposals have the genus. In addition to being found communities, mysteries of the Halo• raised concerns over potential future over a wide area, Halophila seagrasses plzila genus have only recently begun conflicts between the actions needed cover the greatest range of water to be unveiled. to ensure this seagrass's protection depths in which seagrasses are found. Studies of Halophila seagrasses and activities associated with inlet Long documented as growing with have revealed important contribu• maintenance and port development. other seagrasses in shallow estuaries tions to marine ecosystems. Although Based on what is known about the and on intertidal shoals exposed at Haloplzila seagrasses are small, their abundance and distribution of John• low tides, Haloplzila seagrasses have growth rates, use as food by grazing son's seagrass, the situation is analo• recently been found growing on the marine animals, and rate of decompo• gous to having a small number of ocean floor in waters greater than 100 sition are comparatively high. Rapidly oilly female pandas left on earth. If feet deep. growing leaves, rhizomes, and roots Johnson's seagrass were an animal, it Halophila seagrasses have several are quickly cycled through an ecosys• would unquestionably be considered physical traits that differ from other tem as food and nutrients. From endangered. seagrasses. They are best distin• watching feeding behavior and exam• In addition to its rarity, the sur• guished by a unique connection of ining stomach contents of marine vival of the is threatened by an the leaves to the rhizome (the lateral animals, scientists know that green ironic twist of fate. This species is most abundant in the hazardous envi• ronments of developed ocean inlets. Because the seagrass has no known seed production, storms or channel dredging can eliminate significant populations. Protection by the Endan• gered Species Act will help ensure that more can be learned about this mysterious seagrass, and that human impacts, such as channel dredging and reduced water quality, do not threa ten it. What follows is a general descrip• tion of the genus Haloplzila and some of the unique characteristics of Halo• phila jol1l1soJlii, Johnson's seagrass. Figure 1. Paddle grass, (from Phillips and Mensez, 1988). Page 4, The PALMETTO, Winter 1994 sea turtles, West Indian manatees, Comparison of Johnson's seagrass and paddle grass. and feed on these sea• female flowers occur sinceon the same leavesgrowsleafminute,sunlightmonoeciousplant)toleratessalinityPaddlewideveinspantropicalmoreinandprickleandawatersGrassmakenarrowerroundedfloweringtemperatureat hairsdepths60-degreewith(H.rangerangeondecipiens)withdiminished(bothoverleafanglessawtoothof100malesurfaceseawaterand grasses.onlyplantsseawater)and(differentfemalein Sincedeepermaleandflowerstheychannelstemperaturesandhavefemalearebeentheplants)foundonly onsea• edgesJohnson's seagrass (H. johnsonii) no hairs on leaf surface leavesnarrowgrassgrowsleaflikelinearveinsH.homeincapableova/is,shallowwithmakerangeprobablysmooth45-degreeofwatersin formingsoutheasternedgesdioeciousin anglesintenseextensivefloweringFloridasunlight tolerates broad ranges of salinity (brackish to seagrass meadows in deep waters, Halophila seagrasses are important contributors to marine ecosystems. Within the genus, methods of producing new plants vary. Some have male and female flowers on different plants (called dioecious plants, meaning "two houses"); some have male and female flowers on the same plant (called monoecious, mean• ing "one house"). Both types are capa• ble of producing numerous seeds. One species, Halophila johnson ii, or Jo11nson's seagrass, appears to be sterile or capable only of producing unpollinated seeds, which may be• come clones identical to the female parent. High seed production and lateral growth rates enable most Halo• nists, N. J. Eiseman and C. McMillan, tion, scientists have found that John• phila seagrasses to quickly cover and had enough information to describe son's seagrass produces isozymes stabilize bottom sediments. Scientists Johnson's Seagrass as a new species. (proteins directly encoded from ge• have never observed new Halophila Due to its small size (less than an netic material) that are far different plants to grow from root or stem inch tall), limited range, and similar• from those produced by paddle grass fragments of another plant. This vege• ity to another small seagrass, early and more closely related to those of tative reproduction is common in seagrass experts either overlooked the H. ovalis. other seagrasses. tiny seagrass or lumped it in with Pertinent Facts about Halophila another small Haloplzila. When first jolmsonii, (Johnson's seagrass) seen in the Indian River lagoon, sci• entists thought it was a local form of Johnson's seagrass (see Figure 2) is the wide-ranging paddle grass, H. 1. the least known, and arguably the decipiens. Later, botanists studying rarest, seagrass in the world. At this Johnson's seagrass found it to be most point, scientists do not know how it closely related to a Pacific Halophila, H. ovalis, in both physical characteris• tics and genetics. Now it is known that Johnson's seagrass is one of o seven Florida seagrass species, and the only seagrass restricted to Flor• ~ Jupi~et Inlet ida's southeastern coast. Table 1 gives a comparison of Johnson's seagrass and paddle grass characteristics. ~ Scientists have shown that the physical traits of Johnson's seagrass \. 'if~~-O"c,yoe O.y .•--0l.~' _ represen t true genetic differences. Leaf shapes and sizes in some plants, Figure 3. Map of distribution of Johnson's such as the sassafras tree, can vary seagrass (from Kenworthy, 1992). greatly according to environmental The home range and habitat of conditions (low light = larger, mitten• Johnson's seagrass contribute greatly shaped leaves; intense light and dry to both its mystery and rarity. Be• conditions = smaller leaves with sim• cause seagrass seeds are usually dis• Figure 2. Johnson's seagrass, H. johnson;; pler shapes), making it appear as if persed by currents, most seagrasses (from Phillips and Menez, 1988), there could be two genetically differ• can range far and wide. Johnson's reproduces, since they have found ent plants. Growing plants with the seagrass, however, is restricted to only female plants. This mystery • different growth forms under the Florida's coastal lagoons from Sebas• coupled with the fact that Johnson's same conditions often reveals that tian Inlet in south Brevard County to seagrass grows primarily near inlets these differences are due to environ• Miami's Biscayne Bay (see Figure 3). where strong currents, moving sand, mental conditions and that the plants Within this narrow range it is the and human activities appear hostile to are one and the same. Grown under least abundant seagrass, with the a tiny marine plant - does not paint controlled conditions, the small, strap• largest, densest patches growing near a rosy picture for the future of John• shaped, smooth leaves of Johnson's Sebastian Inlet. Abundance decreases son's seagrass. seagrass remain true to form, and with distance from inlets and can As recently as 1980, a pair of bota- distinctive from paddle grass. In addi- vary dramatically by season and year. The PALMETTO, Winter 1994, Page 5 Compounded with its restricted for changing conditions. Understand• grasses with greater energy reserves, range, a preference for growing on ing the mysterious life history of such as turtle grass (Thalassia testu• sandy shoals near inlets gives John• Johnson's seagrass may reveal dinum), may better withstand burial son's seagrass the most limited distri• whether it was once more widely by new sediments or long turbulent bution of any known seagrass. Scien• distributed when the east coast Flor• periods when photosynthesis is re• tists believe this could be related to ida lagoons were pristine and clear, duced. Because it is at a disadvantage either the plant's limited reproductive or whether it is uniquely adapted to growing in seagrass meadows, John• strategy or loss of clear water habitat. inlet habitats. Not able to compete son's seagrass seems capable of grow• The limited niche may be related to with taller, longer-lived turtle or man• ing only where it has a slight edge• the small plant's struggle to compete atee grasses, or with faster-growing in inlets and channels. In such unsta• with larger seagrasses and algae for paddle grass, Johnson's seagrass may ble habitat conditions, the survival of space in the marine environment. have found a niche in the ever-chang• this small, fragile seagrass seems Johnson's seagrass grows where it ing habitat opportunities of inlet precarious. does not have to compete with other shoals and channels. References vegetation. It occurs primarily on As with its restricted range, the Dawes, C.J., C.S. Lobban, DA Tomasko. sandy intertidal shoals that are often habitat requirements of Johnson's 1989. A comparison of the physiological ecology of the seagrasses Halophila decip• exposed at low tide. This suggests seagrass may be related to little• iens Ostenfeld and H. johnsonii Eiseman that Johnson's seagrass possesses a understood reproductive strategies. from Florida. Aquatic Botany 33:149-154. tolerance for conditions that few sea• The wide tolerance to changing envi• Eiseman, N.J. 1980. An Illustrated Guide to the ronmental conditions and possible Sea Grasses of the Indian River Region of grasses can withstand: drying out at Florida, Technical Report No. 31. Harbor low tide, intense sunlight, and dra• sterility provide evidence that the Branch Foundation, Inc. matic temperature changes. It can plant may be the result of a genetic Eiseman, N.J. and C. McMillan. 1980. A new cross between two other species. The species of seagrass, Halophila johnsonii, also gain a toehold in deeper sandy from the Atlantic coast of Florida. Aquatic areas where the speed of the current lack of known seed production means is fast enough to otherwise erode that the plant can only survive by Kenworthy,Botany 9:15-19.J. W. 1992. The Distribution, Abun• sand on the bottom. Salinity tolerance continuously branching out to cover dance and Ecology of Halophila johnsonii (Eiseman) in the Lower Indian River, Florida. ranges from full seawater strength to lagoon bottonls. Thus, if a storm or National Marine Fisheries Service for the mixed salt! fresh water characteristic other catastrophic event damages Office of Protected Resources. seagrass beds, Johnson's seagrass may McMillan, C. and S.C. Williams. 1980. System• of estuaries. Its presence in inlets and atic implications of isozymes in Halophila on shoals - where sunlight is abun• not recover. Paddle grass, with its dant and tides bring clear seawater heavy seed production and faster Phillips,section R.C.,Halophila.and E.G.AquaticMenez.Botany1988.9:21-31.Sea• grasses. Smithsonian Contributions to the into the lagoon - shows either an . growth rate, can quickly re-colonize Marine Sciences; No. 34. Smithsonian Insti• affinity for clean water or a tolerance open lagoon bottoms. Large sea- tution Press, Washington D.C. Natives are our only business

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