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Home , Gulf of Honduras, Mangrove, Swamp

VOL. 30. NO.4 198B

Mangrove Communities by Klaus Riitzler, and Candy Feller Swamp

by Klaus Rulzler, and Candy Feller

"The gave off clicking sounds, and the odor was disgusting. We feillhat we were watching something horrible. No one likes the . w That is how John Steinbeck and Ed Ricketts depicted

The OOslrychielum communily. based on ,In inrerlid,ll ~ssociillion ofred . are localed al mid-lide ,md upper- levels. while the m;mgrove Iree crab and periwinkle stay above the Willer line. (Il1us/ralion by Candy feller)

16 Communities

the mangroves in 1941 in the ofCortez. Many Mangrove are used fOf water-resistant people agree with them. So why have two dozen timber, charcoal, dyes, and medicines. They resist scientists from the Smithsonian Institution, primarily coastal during stOfms and possibly promote from the National Museum of Natural History, and land-building processes by trapping and twice as many colleagues from American and producing . The protective subtidal syslem European universities and museums devoted a of the red mangrove serves as nursery ground for decade of exploration 10 one square kilometer of many commercially valuable of , -black mud, ... Oies and insects in great numbers , lobsle~, crabs, mussels, and oysters. An .. "' impenetrable ... mangrove roots ...; and assorted fauna of birds, reptiles, and mammals is also -, .. stalking. quiet murder"? at home in the mangrove and tidal channels. The study slarted in the early 19805, and Human disturbances have made a heavy focuses on an intertidal mangrove island known as impact on many mangroves near populated areas as Twin Cays, just inside the Tobacco section of a result of dredging and filling. overculting. insect the barrier reef of . a tiny Central American control. and garbage and sewage dumping. The nation on the (see article page 76). intertidal environment of mangroves is endangered The principal purpose of Ihis research is to by pollutants in the water, air, and soil. Accidental oil documenllhe biology, geology, ecological balance. spills appear to be particularly damaging. Oil and tars economic importance, and aesthetic value of a not only smother algae and invertebrates, but also prominent coastal ecosystem using the example of a disrupt the oxygen supply to the root system of the diverse and undisturbed swamp community. mangrove trees by coating the respiratory pores of the intertidal prop and air roots. Properties of Mangrove Mangrove swamp communities dominate the A Mangrove Laboratory in Belize world's tropical and subtropical , paralleling Belize (fOfmerly British ), boasts the longest the geographical distribuHon of coral reefs. barrier reef of the Northem Hemisphere, extending Mangroves on the Atlantic side of the American 220 kilometers from the Mexican border in the north coasts occur between and almost to the to the in the south. Behind this moulh of the Rio de Ia Plata (). and barrier lies an enormous system averaging 25 throughout the . like reefs, mangrove kilometers between the mainland and open . swamps are environments formed by organisms, but Mangroves border most of the coastline, extend unlike mosl coral communities, they thrive in the upstream from countless river mouths, and fringe or and endure a wide range of . cover most lagoon cays. '"Mangrove- refers 10 an assemblage of One of these is Twin Cays (Figure 1I-an from five families with common ecological, island divided into two by an S-shaped channel. morphological, and physiological characteristics that Twin Cays has become our study site and allow them 10 live in tidal swamps. Worldwide, at experimental field laboratory. Although we usually least 34 species in nine genera are considered to be spend the nights and conduct laboratory bench work true mangroves. P. B. Tomlinson's recent book, on nearby Carrie Bow Cay-site of the National Botany of Mangroves, defines this group of planls by Museum's field station for the last 15 five features: 1) they are ecologically restricted to years-most days and many nights are spent in the tidal swamps, 2) the major element of the mangrove channels, , , mud "a,s, and community frequently forms pure stands, 3) the even the trees. A self-.:ontained weather Slation plants are mOfphologically adapted with aerial roots established on one of the mud flats transmits data on and viviparity (producing new plants instead of wind, sun, rain, temperatures, and to a portable ), 4) they are physiologically adapted fOf salt computer on Carrie Bow Cay. exclusion Of salt excretion, and 5) they are The bibliographies on mangroves show that taxonomically isolated from terrestrial relatives, at during the last 200 years more than 6,000 papers least at the generic level. '"Mangrove swamp- Of have been published describing biological and '"mangal- refers to communities characterized by geological details from almost as many different mangrove plants. swamps over the world. Our ongoing study aims to

17 fobocco Ilonge

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a1... G,....,.j 5ot.>th """'* Cui 00 f"lCQI'" &ow .".,. lagoon C) 11 Coy PolCh Retl, g ./PD ';",,"0 CO".. Bow C", G)C",lew ..~ C...~C'" FiSure ,. ManstOVe ecosystem study area. Twin Cays. Belize. , The Nation

analyze as many components as possible of a single What they found below the mangroves was a mangrove swamp and, ultimately, assembk them to carbonate substrate consisting of a dense a mosaic reflecting structure as well as function of formed mostly by finger corals (Porites) with this unique ecosystem. abundant mollusk fragments. indicating an environment of deposition similar to today's calm­ Geologic~l History of Twin C~ys waler patch reefs. The sequence of peat, algal­ A popular theory holds that mangroves are builders produced sand, and mangrove oysters in the of land because they trap and hold fine . sediment cores indicales that this mangrove was Early on in our study we discovered thaI this is not apparently established on a topographic high formed necessarily true. We tried to reclaim nearby Curlew by a fossil patch reef, and kept pace with the rising Cay, which had been lost to a hurricane (it is now sea level. However, there is also evidence thatlhe known as Curlew ), by planting an assortmenl of island repeatedly changed its size and shifted young red mangroves, but were unsuccessful. So the position, generally building with lagoon sediments question arose, if islands are not buill by mangroves, on the windward coosts, while eroding at the how do they get started? leeward edge, which is characterized by shallow­ To learn more about the Holocene (recent water bottoms formed by stranded peat deposits. time-back to 18,000 years before present) The mangrove community itself can be stratigraphy under the present island, Ian G. thought of as being composed of three componenls: Macintyre of the Smithsonian Department of the above-water -.· the intertidal swamp. and Paleobiology, along with Robin G. Lighty and Anne Raymond 01 A&M University, drove pipes 8 meters into the sediment down to the Pleistocene • Ahhough lhe HoIcxenecan dale boKlc as much illS 18,000 level (marks the beginning of the Holocene), and yea~.thefe are only 7.000 yea~ of sedimenl accumulation retrieved sediment cores that date back 7.000 years: in lhis particular arN, as sea level did no! flood lhe Belize They also collected rock cores below this level. Iagooo unlillhe upper Holocene.

18 Figure 2. Channel (ringed by red mangro\lE'. and other sessile organisms are auached to prop roolS and 10 lhe underwashed peal bank 10 the righl; lurtle grass and algae cover lhe mud bollom. A black mangrove wilh short intertidal air roolS prolruding from the bottom is seen on Ihe lefl. (After RUIZ!er, 1969. Proceedings of a Coastal lagoon Symposium, City; redrawn by Molly Ryan)

High Tid,

';.'.

'.'.

the underw-ater system (Figure 2). In our open lagoon, resulting in an almost lO·fold net descriptions, we will start from the bottom and work production. "Po Red mangrove stilt roots line all channels, creeks, and ponds and, below tide level, support Environments Below the Tides spectacularly colored clusters of algae, sponges, The boUom of the mangrove from the intertidal to tunicates (sea squirts), anemones, and many 3 meters, the greatest depth of the main channel, is associates. They also provide hiding places for many composed of what most people would call muck. To mobile animals, such as crabs, lobsters, sea urchins, us, it displays many varieties, such as carbonate silt, and fishes. mud, and sand with varying amounts of mucus, Algae without the ability to root in mud organic detritus (products of and animal bottoms abound on the stilt roots. Mark littler. from decay), peat, and silicious skeletons derived from the Smithsonian Department of Botany, and co­ diatom algae and sponges. Many fine-grained workers Diane littler and Philipp Taylor found that, limestone sediments are produced by physical and curiously, fleshy algae seem to prefer roots that had biological erosion on the nearby reef and carried penetrated the water surface, but had not yet into the mangrove by water currents. Sands, on the reached the boltom of the channel or . other hand, are primarily produced within the Calcifying aigae (such as the sand-producing community by digestion or decay of calcareous Halimeda), on the other hand, are common on the green algae (Halimeda). submerged parts of anchored roots and along the The most abundant and ecologically channel banks. Experiments demonstrated that the important plant on the submerged mangrove hanging roots offer palatable plants protection from bottoms is the turtle grass (Thalassic1l. It stabilizes the benthic (bottom-living) herbivores such as sea muddy bottom, offers substrate (or egg cases and urchins and many fishes, whereas Halimeda has its many small sessile organisms, and provides food and own skeletal protection. shelter to animal groups ranging from microbes to Certain algae and many sessile invertebrates 2·meter . Jorg A. Ott, a ecologist on the subtidal mangrove roots are protected from from the University of Vienna, determined that turtle predators by toxic substances stored in their tissues grass in the Twin Cay mangrove is more dense, and and produced by their own metabolism. Sponges are grows 3 times faster, than Thalassia in the nearby particularly well-known for their antibiotic and

19 feeding-deterrent properties. The sponges, in tum, estimated 100 million individuals congregated during are used by many smaller organisms, such as the day in a band of swarms along a l,()()().meter anemones, polychaete worms, shrimps, crabs. stretch of channel bank. amphipod crustaceans, gastropod mollusks, and brittle stars as an effective physical and chemical The Intertidal Mangrove Swamp shelter. Collaborating with our Smithsonian Although the tidal range in the Caribbean is small, in colleagues, Krislian Fauchald, Gordon Hendler (now shallow coast.ll areas it can strongly influence current at the los Angeles County Museum), and Brian flow and distribution of organisms. At Twin Cays, the Kensley, we extracted up to 40 species and 400 mean tidal range is only 15 centimeters, yet a specimens of endozoans (species living within combination of astronomical, geomorphologic, and anOlher) larger lnan 2.5 millimeters from, as an meteorologic factors can cause a range of more than example, a l-liler fire (Tedania), a species a half meter. tnat causes burning. itching. aocl even severe Red mangrove () prop roots, black dermatitis in humans. mangrove () pneumatophores,. peat banks, Sponges are among the most common, and mud flats are the typical substrates of the massive. and colorful invertebrates in the submerged intertidal zone supporting distinctive communities. mangrove. To settle and metamorphose. their larvae (Chthama/us), boring isopods need solid substrate with low exposure to (Limnoria), oysters (Crasses/rea), and ·mangrove sedimentation, although we observed grown oysters· (lsegnomon, not a true ) are the best specimens surviving for months buried in light mud knowr indicators of intertidal hard substrates, while after they had fallen from their place of original fiddler crabs (Vcal are typical for the mud flats. attachment. Only two kinds of firm substrate are Green algal mats (Caulerpa, Halimeda) are found available to such settlers, red mangrove stilt roots, exposed on peat-mud banks during low tide. The and vertical or overhanging banks composed of a felt most abundant and characteristic intertidal of peat and mangrove rootlets and flushed by tidal mangrove community, however, is called the currents. bostrychietum, named after the principal In both locations, the competition for space is components of an association of red algae fierce, not only among sponges, but also between (Boslrychia, with Calanella and Calog/ossa). sponges and other sessile organisms, such as algae, The bostrychietum (see page 16) has a hydroids (the polyp-generation of many medusae), remarkable water-holding capacity, which allows the corals, anemones, bryozoans (moss animals), and plants and their associated animals to survive tunicates (sea squirts). With our colleagues Dale extended dry periods. We measured water loss rates Calder, Royal Ont.lria Museum, Ivan Goodbody, in two of the substrate spectes and found evidence University of the West Indies, and Jan Kohlmeyer, of two different methods of water retention. University of , we are analyzing the Bostrychja is a delicate, tufted plant that holds water sequence of settlement of species at different primarily interstitially (between the branches). seasons, following their growth and methods and Catene//a is more fleshy and less elaborately hierarchies of competition. branched, and holds water intracellularly (within the We have found that within days new cells), in its tissues. substrates (wood, plastics) are colonized by loren Coen, Dauphin Island Sea Lab, ubiquitous bacteria, fungi, and lower algae. Next to examined the animal associates of the arrive are coralline algal crusts, sponges, hydroids, bostrychietum, particularly in respect to grazing. He scyphozoan polyps (the polyp stage of the upside­ found that amphipods (Parhyale) become down ), anemones, serpulid and concentrated in the algal mats in high numbers sabellid worms, bryozoans, and ascidians (the Ialter during receding tides, and that their grazing on two are colonial, encrusting organisms). After 3 to 6 Bostrychia can match or exceed the algal growth. months, substrates are fully covered by a spedrum The mangrove crab, AralUs, and other crabs of organisms. This spedrum varies greatly, and from the low-tide level were also found with large depends on the season in which the experiment was quantities of Bosfrychia in their guls. started, the habitat position of the substrate, and the Desiccation and related problems of environmental endurance of the selliers. increased temperature and in organisms Not all subtidal mangrove life is restricted to subjected 10 exposure at low tide became the bottoms and roots. Fishes of all size and age particularly apparent during an extreme low tide in classes hide or feed in the around the June 1983. A 2().centimeter zone below mean low­ red mangrove roots and along the banks. Many of tide level became exposed during noon hours under these depend on , such as copepods and a clear sky. other small crustaceans (-like animals), for Large communities of low intertidal (rarely food. Members of both groups form characteristic exposed) and subtidal (never exposed) organisms, swarms during the day. Smithsonian's Frank Ferrari teamed up with Julie Ambler, Texas A&M University, Ann Bucklin, University of , and Richard • A feature of many mangroves is that some part of the root Modlin, University of Alabama, to study the system is exposed to the atmosphere. In an oxygen-poor systematics, ecology, and genetics of the swarms and substrate, o)(ygen is absorbed directly (rom the atmosphere. found population densities much greater than In the black mangrove, lkese aerial roots, termed eXpeded. They counted more than 2,000 copepods pneumalophor"es. occur as direct upward extensions of the per cubic meter of water in a small bay at night, and subteffilnean root syslem.

20 such as occupants of seagrass meadows (including Numerous stumps throughout the mud flats are the turtle grass itself), and mangrove mud banks and evidence that the trees that once grew there fell stilt roots, were killed during the long exposure fo victim to some environmental stress. The red desiccation. Estimates indicate that more species of mangrove trees growing around the margins of the algae and invertebrates, and much more living mud flats and in the ponds are severely stunted and matter (), were destroyed during those days widely spaced. Over the years, these natural bonsai of June than during two hurricanes combined (Fifi, have been distorted and pruned by their 1974; Greta, 1978). environment intO fantastic forms, seldom more than Collaborating eco-physiologist Joan Ferraris, 1.5 meters tall. Mt. Desert Island Biological Laboratory, is examining The above-water fauna on the cays is a number of organisms (sponges, sipunculan worms, considered by most investigators to be introduced shrimps, crabs) that are exposed to strong salinity­ from the Belizean mainland. Even on the largest temperature stress in their . mangrove islands, most of the oland· is intertidal; Results so far show a fine correlation between therefore, the only environments available to experimental tolerances in the animals and range of terrestrial animals are arboreal. The fauna is limited variability of stress factors in their natural habitat. In to birds, lizards, snakes, snails, and arthropods, such the case of sponges, regulatory mechanisms as land crabs, spiders, and insects. These animals controlling water-ion balances are still unknown, but probably reached the cays from the mainland by in the absence of organs, they must take place inside flying, or rafting on or in pieces of wood and other individual cells. floating debris. Unfortunately, the intertidal swamp is not .A few land bird species have established only an exciting biological study zone, but also a permanent breeding populations on the mangrove gallery of pollutants. Even in this remote location islands. Warblers, , hummingbirds, , every imaginable piece of floating debris discarded grackles, and white-crowned pigeons are among the by man can be found, washed in by currents among permanent residents. Several of the islands also the mangrove roots and deposited by the receding provide nesting sites for ospreys. These birds tides. frequently build their nests atop tall snags of black mangrove. Mangrove forest Above the Tide At Twin Cays, the green-back heron is the Unlike the adjacent marine systems, the above-water most commonly observed wading bird. It breeds on flora and fauna of the mangrove-covered islands the island, and builds its twig nest in the red appear less complex and diverse. From the water, an mangrove fringe along the channels. II is frequently unbroken, monotonous barrier of red mangrove seen diving for small in the shallow, interior trees confronts, and frequently intimidates, the ponds. The most conspicuous birds of the area are casual explorer. the and frigatebird, which fly The species composition of the above-water overhead or perch in mangrove trees. plant community around Twin Cays is relatively Insects are, by far, the most diverse and simple. Three halophytic· tree species, known abundant group of above-water animals inhabiting collectively as mangroves, dominate the natural the Belizean mangrove cays. , in 28 or so on most of the islands: Red mangrove species, are clearly the most abundant. , (Rhizophora), black mangrove (Avicennia), and white because of their huge nests and extensive covered mangrove (Laguncu/ar;a). On cays with slightly higher walkways, are the most conspicuous. Some major ground, additional woody and herbaceous (soft­ groups of insects, such as bees, are poorly stemmed) halophytes are associated with the represented in mangrove (auna. As is other tropical mangrove, such as buttonwood (), ecosystems, a large percentage of the insect species saltwort (Batis), and sea purslane (Sesuvium). that we have found associated with mangroves are In general, mangrove have well­ undescribed. defined horizontal zonation. On these mangrove islands, the seaward and channel margins typically Conclusions are fringed by dense, 4- to 1D-meter-tall stands of The red mangrove fringe, the specialized vegetation, red mangrove. Behind this fringe, the red mangrove the physical environment, and the associated fauna is usually more open and shorter, with black and and flora form a complex and diverse island white mangroves intermixed. The zonation is easily community above water as well as below. We have recognized: dull gray-green spires of black learned that mangroves produce fine sediments and mangrove, and flattened, yellow-green crowns of organic detritus. and stabilize them by modifying the white mangrove stand slightly above and behind the wave and current regime of the open lagoon. The dark green dome of the fringing red mangrove. inventory of species has yet to be completed, but The interiors of some of the larger islands off already we have shown that most phyla are Belize, like Twin Cays, have several extensive, represented by species of which 10 to 25 percent, unvegetated mud flats and shallow ponds. and in some cryptic (having a hidden or concealed lifestyle) microscopic-sized groups, up to 60 percent, are undescribed. The mangrove swamp is rich in •A plant growing in salty soil or sail waler, lermed a recycled and high in production rates, but halophyte, has unique physiological characteristics that its occupants are severely stressed by factors such as enable ilto oblain , excrete salt, and reduce fresh water loss.

21 A Gallery

M80Slon Bay, N Twin Cays. In Slinging sea anemone lhe foregroond are prop (Bunodeopsis) on lurtle fOOU of red mangn:wes 8~n.~obyG.Mme~ tRhilophora). (f>tx"fl.o by K. RiJuSer)

Black mangrove (Avkennia) pneomarophores. (Photo by M. Parrish)

Sponges, ascidi;lns, and anemone on a submerged roor. Clapper . (fhala by S. Canupp) (Photo by K. RutzlerJ of Mangrove Life

Seahorse (Hippocampus). Young upside-down (PhOlo by G. Mil/ed iellyfish (Cassiopea) on mud boflom. (PhOlO by K. ROlzler)

Mangrove oyslers (Isogoomon). (Pholo by K. RisrzlerJ

St,lftish (Oreasler). (PIJo(o by K. RilulerJ Drih goods deposited by 1M fidei under black mangrooves. (Pho(o by M. Parrish' continued from p.osr 21 Adtnowledgment The study described in this article is supported by grants salinity and temperature fluctuations, desiccation from the hxon (orpmaHon, the Smithsonian SCholarly potential, abundance of fine sediments, and shortage Studies Program, and the Smithsonian Women's of firm substrates. Space, from the sea bottom to the Commillee. tree tops, is distinctly partitioned by the animals that SeIKt~ R~fetenCft exploit this specialized plant community. These lugo, A. E.• and S. C. Sr>edaker. 1974. Tke e<:oIogy of m,mgroves. intertidal islands, because of their isolation from the AIInw! R~ 01 Ecology and Systematics 5: 39-64. Belizean mainland, provide us with ideal locations to Mal;nae, W. 1%8. A general account oflhe fauna and flora of study pure mangrove communities in the Caribbean. ""'ngrove swamps and forests in the Indo-West·PaciflC Regioo. AdvancE'l in 6: 73-270. Odum, W. E.. C. C. Mcivor. and T. J. Smith. ilL 1981. The EcoIotNoi Klaus ROIlier is Curalor of Lower Invertebrales and Program rhe Mangroves 01 SO

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