APES Ch 6 Coral Reefs PDF

W h y Should We Care ab out Coral Reefs? carbonate. Stud jes by t h e Global Cora| photosynthesis. Also, the water I" which Reef Monitoring N e t w...

W h y Should We Care ab out Coral Reefs? carbonate. Stud jes by t h e Global Cora| photosynthesis. Also, the water I" which Reef Monitoring N e t w o r k and other s¢j. C o r a l r e e f s form in clear, warm shallow reefs live must have a tempera- entific groups estimate that since the coastal waters in tropical areas. These ture of 18-30°C (64-86°F) and cannotb e 1950s, some 4 5 % - 5 3 % of the world?s stunningly beautiful natural wonders (see too acidic. This explains w h y am a j o r shallow coral reefs have been destroyeg chapter-opening photo) are among the long-term threat to coral reefs is climate or degraded. A n o t h e r 2 5 % - 3 3 % could world?s oldest, most diverse, and most change, which could raise thew a t e r be lost within 20 to 40 years. These productive ecosystems. temperature above tolerable limits 1n centers ofbiodiversity are by far the Coral reefs are formed by massive most reef areas. The closely related prob- m o s t threatened marine ecosystems. colonies of tiny animals called polyps (close lem of ocean acidification could make it In this chapter, w e explore the nature relatives of jellyfish). They slowly build reefs harder f o r polyps to build reefs and by secreting a protective crust of limestone o af quatic ecosystems, and w e begin to could even dissolve some of their calcium (calcium carbonate) around their soft bod- examine the effects of human activities carbonate formations. on the:se vital forms of natural capital. @ ies. When the polyps die, their empty One result of stresses such as pollu- crusts remain behind as part of a platform tion and rising ocean water temperatures for more reef growth. The resulting elabo- is coral bleaching (Figure 6.1), which can rate network of crevices, ledges, and holes cause the colorful algae, uponw h i c h serves as calcium carbonate ?condomini- oral reefs provide many ecological and corals depend for food, to die off. With- ums? f o r a variety of marine animals. economic services. H o w w o u l d the loss of out food, the coral polyps die, leaving C o r a l reefs are t h e result o f a m u t u a l l y coral reefs affect humans? behind a white skeleton of calcium beneficial relationship between polyps a n d t i n y s i n g l e - c e l l e d a l g a e called z o o x a n - t h e l l a e ( " z o h - Z A N - t h e l - e e " ) t h a t live i n t h e tissues o f t h e polyps. The algae pro- vide t h e polyps w i t h food and oxygen t h r o u g h p h o t o s y n t h e s i s , a n d help t h e corals p r o d u c e c a l c i u m c a r b o n a t e. A l g a e also g i v e t h e reefs their s t u n n i n g color- a t i o n. The polyps, in t u r n , p r o v i d e t h e algae w i t h a well-protected h o m e and s o m e o f their n u t r i e n t s. A l t h o u g h shallow and deep-water c o r a l reefs o c c u p y o n l y a b o u t 0. 2 % o f t h e ocean floor, they provide i m p o r t a n t e c o s y s t e m a n d e c o n o m i c services. They a c t as n a t u r a l barriers t h a t h e l p to protect 1 5 % o f t h e world?s coastlines f r o m f l o o d - i n g a n d e r o s i o n caused b y b a t t e r i n g w a v e s a n d s t o r m s. They also p r o v i d e habitats, food, and spawning g r o u n d s for o n e - q u a r t e r t o one-third o f the organisms t h a t live in t h e o c e a n , a n d t h e y p r o d u c e a b o u t o n e - t e n t h o f t h e g l o b a l fish catch. T h r o u g h t o u r i s m a n d fishing, they p r o v i d e g o o d s a n d services w o r t h a b o u t $ 4 0 b i l l i o n a year. Coral reefs are v u l n e r a b l e to d a m a g e b e c a u s e they g r o w slowly a n d are dis- r u p t e d easily. R u n o f f o f soil a n d o t h e r m a t e r i a l s f r o m t h e land can c l o u d t h e w a t e r and block the sunlight that the FIGURE 6.1 This bleached coral has lost most of its algae because of changes in the algae in s h a l l o w reefs n e e d f o r environment such as warming of the waters and deposition of sediments. CHAPTER 6 AQUATIC BIODIVERSITY  6.1 WHAT IS THE GENERAL NATURE of d r i f t i n g organisms called phytoplankton, w h i c h includes OF AQUATIC SYSTEMS? m a n y types of algae. These t i n y a q u a t i c plants a n d even smaller u l t r a p l a n k t o n ? t h e second g r o u p of p l a n k t o n ? a r e the producers t h a t m a k e up the base of most aquatic food CONCEPT 6. 1 A Saltwater and freshwater aquatic life zones chains a n d webs (see Figure 3.11, p. 7 3 ). T h r o u g h p h o t o - cover almost three-fourths of the earth?s surface, with oceans synthesis, t h e y produce about half of the earth?s o x y g e n , dominating the planet. o n w h i c h w e depend for survival. CONCEPT 6. 1 B The key factors determining biodiversity in The t h i r d g r o u p is made up of d r i f t i n g animals called aquatic systems are temperature, dissolved oxygen content, zooplankton, w h i c h feed o n p h y t o p l a n k t o n a n d o n o t h e r availability of food, and access to light and nutrients necessary z o o p l a n k t o n (see Figure 3.11, p. 73). The m e m b e r s o f this for photosynthesis. group range in size f r o m single-celled p r o t o z o a to large invertebrates such as j e l l y f i s h (Figure 6.2). A second m a j o r type o f aquatic organism is n e k t o n , Most o f t h e Earth Is Covered strongly s w i m m i n g consumers such as fish, turtles, a n d with Water whales. The t h i r d type, b e n t h o s , consists of b o t t o m - Saltwater covers about 7 1 % of the earth?s surface, and dwellers such as oysters and sea stars (Figure 6.3), w h i c h a n c h o r themselves to o c e a n - b o t t o m structures; clams a n d freshwater occupies r o u g h l y a n o t h e r 2%, A l t h o u g h the w o r m s , w h i c h b u r r o w i n t o the sand o r m u d ; a n d lobsters global ocean is a single and c o n t i n u o u s body of water, geographers divide it i n t o five large a r e a s ? t h e Atlantic, and crabs, w h i c h w a l k about on t h e sea floor. A f o u r t h m a j o r type is d e c o m p o s e r s ( m o s t l y bacteria), w h i c h Pacific, Indian, Arctic, and S o u t h e r n Oceans?separated by the continents. The largest ocean is the Pacific, w h i c h con- break d o w n organic c o m p o u n d s i n the dead bodies a n d tains more t h a n half of the earth?s w a t e r a n d covers one- third of the earth?s surface. Together, the oceans hold almost 9 8 % o f t h e earth?s w a t e r (Concept 6.1A). Each of us is connected to, a n d u t t e r l y dependent on, the earth?s global ocean t h r o u g h the w a t e r cycle (see Figure 3.14, p. 77). The aquatic equivalents of biomes are called a q u a t i c life z o n e s ? s a l t w a t e r a n d f r e s h w a t e r p o r t i o n s o f the bio- sphere that can s u p p o r t life. The d i s t r i b u t i o n of m a n y aquatic organisms is d e t e r m i n e d largely by the water?s s a l i n i t y ? t h e a m o u n t s o f various salts such as sodium chloride (NaCl) dissolved i n a given v o l u m e of water. A q u a t i c life zones a r e classified i n t o t w o m a j o r types: s a l t w a t e r or m a r i n e l i f e z o n e s (oceans and t h e i r bays, estuaries, coastal w e t l a n d s , s h o r e l i n e s , c o r a l reefs, a n d m a n - grove forests) and f r e s h w a t e r l i f e z o n e s (lakes, r i v e r s , Streams, and inland wetlands). Some systems such as estuaries are a m i x o f s a l t w a t e r a n d f r e s h w a t e r , b u t s c i e n t i s t s classify t h e m as m a r i n e s y s t e m s f o r p u r p o s e s o f d i s c u s s i o n. A q u a t i c Species D r i f t , Swim, C r a w l , a n d C l i n g Saltwater and freshwater life zones contain several major types of organisms. One type consists of p l a n k t o n , w h i c h FIGURE 6. 2 Jellyfish are drifting zooplankton that use their can be divided i n t o three groups. The first g r o u p consists long tentacles with stinging cells to stun o r kill theirprey. 155  «2 WHY ARE MARINE AQUATIC SYSTEMS IMPORTANT? CONCEPT 6.2 Saltwater ecosystems provide major ecosys. tem and economic services and are irreplaceable reservoirs of biodiversity. a e Oceans Provide V i t a l Ecosystem and Economic Services Oceans provide e n o r m o u s l y valuable ecosystem and ecg. n o m i c services (Figure 6.4) t h a t help keep us and other species alive and support o u r economies. T h e y Produce more than half of the o x y g e n w e breathe and, as a vita] part of the w a t e r cycle, p r o v i d e most of the rain that sustains o u r water supply. F I G U R E 6. 3 Starfish on a coral eef. The starfish i called a sea star because it is not a fish. ish is also As land dwellers, we have a distorted a n d limited view o f t h e o c e a n s t h a t c o v e r m o s t o f t h e earth?s s u r f a c e , We k n o w m o r e about the surface o f the m o o n t h a n we k n o w a b o u t t h e earth?s o c e a n s. A c c o r d i n g t o a q u a t i c scientists, wastes of aquatic organisms into nutrients that aquatic the scientific i n v e s t i g a t i o n o f p o o r l y understood martine p r i m a r y p r o d u c e r s c a n use. a n d f r e s h w a t e r a q u a t i c s y s t e m s c o u l d y i e l d i m m e n s e eco. K e y f a c t o r s d e t e r m i n i n g t h e types a n d n u m b e r s o f or- logical and e c o n o m i c benefits. g a n i s m s f o u n d i n d i f f e r e n t a r e a s o f t h e o c e a n a r e tempera- ture, dissolved oxygen content, availability o f food, and a v a i l a b i l i t y o f l i g h t a n d n u t r i e n t s r e q u i r e d f o r photosynthesis, s u c h a s c a r b o n (as d i s s o l v e d C O , gas), n i t r o g e n (as NO3>), a n d p h o s p h o r u s ( m o s t l y as P O , * ) ( C o n c e p t 6. 1 8 ). Natural C a p i t a l I n d e e p a q u a t i c systems, photosynthesis is largely con- f i n e d t o t h e u p p e r l a y e r ? t h e euphotic or photic z o n e ? M a r i n e Ecosystems t h r o u g h w h i c h s u n l i g h t can penetrate. The depth of the Ecosystem Economic e u p h o t i c z o n e i n oceans a n d deep lakes is reduced w h e n Services Services t h e w a t e r is c l o u d e d b y excessive g r o w t h of algae. This is c a l l e d a n algal bloom a n d i t results f r o m n u t r i e n t overloads. Oxygen Food supplied through This c l o u d i n e s s is called t u r b i d i t y. It is also caused by soil photosynthesis Energy from waves a n d o t h e r s e d i m e n t s b e i n g carried by w i n d , rain and melt- i n g s n o w f r o m c l e a r e d land into a d j o i n i n g bodies of water. Water purification and tides T h i s is o n e of t h e p r o b l e m s plaguing shallow coral reefs Climate moderation Pharmaceuticals (Core Case S t u d y ). In s h a l l o w s y s t e m s s u c h as s m a l l o p e n s t r e a m s , l a k e co.2 absorption Harbors and edges, a n d ocean shorelines, a m p l e supplies of nutrients Nutrient cycling transportation routes f o r p r i m a r y p r o d u c e r s a r e u s u a l l y a v a i l a b l e , w h i c h t e n d s to m a k e t h e s e a r e a s h i g h i n b i o d i v e r s i t y. B y c o n t r a s t , in most Reduced storm Recreation and damage (mangroves, tourism areas o f t h e o p e n ocean, nitrates, phosphates, iron, and barrier islands, o t h e r n u t r i e n t s are o f t e n i n s h o r t supply, a n d this l i m i t s coastal wetlands) Employment net primary productivity ( N P P ) (see F i g u r e 3. 1 3 , p. 7 5 ) Biodiversity: species a n d t h e d i v e r s i t y o f species. and habitats Minerals C H E C K P O I N T F O R U N D E R S T A N D I N G 6.1 FIGURE 6. 4 Marine systems provide a number of impor- tantecosystem and economic services ( C o n c e p t 6.2). 14. Identify several abiotic (nonliving) factors that determine the C r i t i c a l t h i n k i n g : Which t w o ecosystem services and type of organisms that can live in marine and freshwater l i f e. which t w o economic services do you t h i n k are the most important? Why? zones. Top: Willyam Bradberry/Shutterstock.com. Bottom: James A. Hartis/Shutterstock.com. 4 5 6 @ CHAPTER 6 AQUATIC BIODIVERSITY  CONSIDER T H I S... oo gently sloping, s h a l l o w edge o f the continental shelf ( t h e LEARNING F R O M N A T U R E OS 1 submerged p a r t o f t h e c o n t i n e n t s ). It makes u p less t h a n ' Engineers are learning how whales use sound waves to com- 10% of the world?s ocean area, b u t it c o n t a i n s 9 0 % of all | municate over long distances underwater to improve our under- | m a r i n e species and most large c o m m e r c i a l fisheries. This water communication technologies. zone?s aquatic systems i n c l u d e estuaries, coastal marshes, aa B T a ad m a n g r o v e forests, a n d coral reefs. Estuaries a n d Coastal W e t l a n d s M a r i n e aquatic systems are e n o r m o u s reservoirs of biodiversity. M a r i n e life is f o u n d i n three m a j o r life zones: Are Highly Productive the coastal zone, t h e pelagic zone (open sea), a n d t h e A n e s t u a r y is an aquatic zone w h e r e a r i v e r meets the sea ocean b o t t o m ( F i g u r e 6.5), (Figure 6.6). It is a p a r t i a l l y enclosed b o d y o f w a t e r w h e r e T h e c o a s t a l z o n e is t h e w a r m , n u t r i e n t - r i c h , s h a l l o w seawater mixes w i t h t h e river?s freshwater, as w e l l as w i t h water that extends f r o m the h i g h - t i d e m a r k on land to the n u t r i e n t s a n d p o l l u t a n t s i n r u n o f f f r o m the land. ? Coastal Zone Pelagic Zone (Open Sea) ? ? ? _ _ _ e Depth in Sea level ~ S meters ~~ 0 sEstuarine ~ so 8 € ?Zone a 2 100 8 a Continental sheif 200 ? 500 | = S 1,000 2 1,500 ? Water temperature drops rapidly between the 2,000 euphotic zone and the. abyssal zone in an area called the thermocline. 3,000 » ov & a 4,000 9 5,000 10,000 9 5 10 15 20 2 30 Water temperature (°C) FIGURE 6.5. Major life zones and vertical zones (not drawn to scale) in an ocean. Actual depths of zones may vary. Available light determines the euphotic, bathyal, and abyssal zones. Tempera- ture zones also vary with depth, shown here by the red line. C r i t i c a l t h i n k i n g : How is an ocean Similar to a rain forest? (Hint: See Figure 5.20, p. 139.) 157  oa FIGURE 6.7 C o a s t a l m a r s h in t h e s t a t e o f S o u t h C a r o l i n g , Rocky a n d Sandy Shores Host Different < 2 2 Types o f Organisms F I G U R E 6. 6 Satellite photo of an estuary. A sediment plume The gravitational p u l l of the m o o n and sun causes tides, (cloudiness caused by runoff) forms at the mouth of Madagas- o r periodic flows of w a t e r o n t o a n d off the shore, to rise car's Betsiboka River as it flows through the estuary and into and fall about every 6 hours i n m o s t coastal areas. The the M o z a m b i q u e Channel. area of shoreline between l o w and high tides is called the i n t e r t i d a l z o n e. Organisms living i n this zone must be able to avoid being swept a w a y or crushed by waves. They Estuaries are associated w i t h coastal w e t l a n d s ? need to survive w h e n i m m e r s e d d u r i n g high tides and left coastal l a n d areas covered w i t h w a t e r all or part of the year. These w e t l a n d s i n c l u d e coastal marshes, o r salt marshes ( F i g u r e 6. 7 ) a n d mangrove forests (Figure 6.8). T h e y are s o m e o f t h e earth?s m o s t p r o d u c t i v e ecosystems (see F i g u r e 3.13, p. 7 5 ) because of h i g h n u t r i e n t inputs from r i v e r s a n d f r o m a d j o i n i n g l a n d , rapid c i r c u l a t i o n of n u t r i - ents b y t i d a l flows, a n d a m p l e s u n l i g h t penetrating the s h a l l o w w a t e r s. M a n g r o v e forests a r o u n d the w o r l d host 6 9 d i f f e r e n t species o f trees a n d shrubs t h a t can g r o w in s a l t y w a t e r. T h e y p r o v i d e habitat, food, a n d nursery sites f o r a v a r i e t y o f fishes, shellfish, crabs, snakes, and o t h e r a q u a t i c species. Seagrass beds ( F i g u r e 6.9), a n o t h e r c o m p o n e n t of ma- r i n e b i o d i v e r s i t y , o c c u r i n s h a l l o w coastal waters and h o s t as m a n y as 6 0 species o f grasses and o t h e r plants. T h e s e h i g h l y p r o d u c t i v e a n d p h y s i c a l l y c o m p l e x systems s u p p o r t a v a r i e t y of m a r i n e species. L i k e o t h e r coastal s y s t e m s , seagrass beds o w e t h e i r h i g h NPP to a m p l e sup- § p l i e s o f s u n l i g h t a n d p l a n t n u t r i e n t s that f l o w f r o m the land. é nAND t z e FA These coastal a q u a t i c systems p r o v i d e i m p o r t a n t ecosys- gf | I t e m a n d e c o n o m i c services. T h e y help to m a i n t a i n w a t e r g ma X NYS ? q u a l i t y i n tropical coastal zones by f i l t e r i n g toxic pollutants, ERM A pas Xt e YD excess p l a n t n u t r i e n t s , and sediments, and by absorbing o t h e r p o l l u t a n t s. T h e y p r o v i d e food, habitats, and nursery 3 Migs el oe sites f o r a v a r i e t y o f a q u a t i c a n d terrestrial species. T h e y also FIGURE 6. 8 Mangrove forest on the coast of Thailand. r e d u c e s t o r m d a m a g e a n d coastal erosion by absorbing Mangroves have roots that curve up from the mud and w a v e s a n d storing excess w a t e r produced by storms and w a t e r fo obtain oxygen from the air, working somewhat like a snorkel. tsunamis. 1 5 8 @ C H A P T E6R A Q U A T I C BIODIVERSITY  The Importance of Wetlands H o w d o scientists characterize a wetland? Suspended solids absorb heat f r o m the sun, P o s s i b l e R e s p o n s e : One type o f m a r i n e W e t l a n d s can be coastal o r inland, fresh- a n d daily tides vary t h e a m o u n t of salt w a t e r ecosystem is an estuary. A n estuary is a water, or marine. They are d e f i n e d as areas t h a t mixes w i t h t h e freshwater runoff. coastal w e t l a n d w i t h a varying i n f l u x of that are s a t u r a t e d w i t h w a t e r all o r part of Both f r e s h w a t e r and marine ecosystems fresh water, causing t h e t e m p e r a t u r e a n d the year, have standing s h a l l o w w a t e r w i t h provide m a n y valuable ecosystem services salinity to change daily. Because estuaries emergent vegetation, and contain commu- a n d e c o n o m i c benefits (Figures 6.4 a n d are highly productive ecosystems, t h e y nities o f p l a n t s a n d animals t h a t have 6.13). However, humans have greatly i m - serve as nurseries f o r fish a n d shellfish. adapted t o continuously w e t conditions. pacted both freshwater and marine w e t - They also serve to buffer storms, absorbing They are h i g h l y p r o d u c t i v e ecosystems. lands (Figure 6.12). t h e i m p a c t of w i n d and waves. The loss or Freshwater w e t l a n d s include swamps, d e g r a d a t i o n of estuaries can reduce t h e marshes, bogs, fens a n d prairie potholes. FRQ A p p l i c a t i o n a m o u n t o f fish and shellfish harvested b y M a r i n e w e t l a n d s include estuaries, m a n - Q u e s t i o n : W e t l a n d s have historically been c o m m e r c i a l fishermen resulting in loss of grove s w a m p s , a n d coastal marshes. O r g a n - altered by humans for a variety of reasons. revenue. It could also increase t h e eco- isms t h a t live in estuaries m u s t be adapted I d e n t i f y and d e s c r i b e ONE type of marine n o m i c cost of storm surges as m o r e p r o p - to w i d e l y f l u c t u a t i n g t e m p e r a t u r e and salin- erty is destroyed d u e to t h e lacko f w e t l a n d. I d e n t i f y TWO ecosystem services ity. Seasonal t e m p e r a t u r e s vary, and s n o w provided b y t h a t w e t l a n d and e x p l a i n t h e b u f f e r i n g by t h e estuary melt and rain carry soil a n d organic material e c o n o m i c i m p a c t of t h e loss of those eco- f r o m land t h a t mixes w i t h t h e salt water. system services. CONSIDER T H I S... ' LEARNING F R O M NATURE | The blue mussel produces a nontoxic, biodegradable glue to | cling to underwater rocks in oceans. Scientists have mimicked » this process to produce nontoxic glues that can be used under , and above water. ~~ o r g a n i s m s h i d e i n p r o t e c t i v e s h e l l s , d i g in, o r h o l d o n t i g h t to something. On some coasts, steep rocky shores are pounded by waves (Figure 6.10, top). The n u m e r o u s pools and other habitats in these intertidal zones contain a great variety of species. Each occupies a different niche to deal w i t h daily and seasonal changes in e n v i r o n m e n t a l conditions such as temperature, water flows, and salinity. Other coasts have gently sloping barrier beaches, o r sandy shores, that support other types of marine organisms (Figure 6.10, b o t t o m ). Most of t h e m keep hidden from FIGURE 6. 9 Seagrass beds, such as this one near the coast view and survive by b u r r o w i n g , digging, and t u n n e l i n g i n of San Clemente Island, California, support a variety of marine the-sand. These beaches a n d their adjoining coastal wet- species. lands are also home to a variety of shorebirds that have evolved in specialized niches to feed on crustaceans, insects, and other organisms (see Figure 4.9, p. 99). high a n d d r y (and m u c h h o t t e r ) at l o w tides. T h e y must M a n y of these same species also l i v e o n barrier also survive c h a n g i n g levels of salinity w h e n heavy rains i s l a n d s ? l o w , n a r r o w , sandy islands t h a t f o r m offshore, dilute saltwater. To deal w i t h such stresses, most intertidal 159  Shore crab Rocky Shore Beach Hermit crab Sea star Sea lettuce e e e r r ae ? - i e ? 4 B a r r i e r Beach Peanut w o r m Sandpyp e t s oh ETT White sand macoma Sand dollar Moan snail F I G U R E 6. 1 0 Living between the tides: Some organisms with specialized niches are found in various zones on rocky shore beaches (top) and barrier or sandy beaches (bottom). Organisms are not drawn t o scale. 1 6 0 @ CHAPTER 6 AQUATIC BIODIVERSITY  par a l l e l to c o a s t l i n e s. U n d i s t u r b e d b a r r i e r b e a c h e s g e n e r - ally have o n e o r m o r e r o w s of s a n d d u n e s i n w h i c h the Ocean acidification and other forms of degradation could sand is h e l d i n place by the r o o t s o f grasses a n d o t h e r have devastating effects on the biodiversity and food webs of plants. These d u n e s are t h e first l i n e o f d e f e n s e a g a i n s t t h e coral reefs. This will i n t u r n degrade the ecosystem services that reefs provide. It w i l l also have a severe impact on the r a v a g e s o f t h e sea. R e a l e s t a t e d e v e l o p e r s frequently re- approximately 500 m i l l i o n people w h o depend o n coral move the p r o t e c t i v e d u n e s o r cover t h e m w i t h b u i l d i n g s reefs for food or f o r income f r o m fishing a n d tourism. a n d roads. L a r g e s t o r m s can t h e n f l o o d a n d e v e n sweep a w a y seaside c o n s t r u c t i o n a n d s e v e r e l y e r o d e t h e s a n d y beaches. The O p e n Sea a n d t h e Ocean F l o o r Host a V a r i e t y o f Species The sharp increase i n w a t e r depth at the edge o f t h e c o n - tinental shelf separates the coastal zone f r o m the vast Revisiting Coral R e e f s ? A m a z i n g v o l u m e of the ocean called the p e l a g i c z o n e , or o p e n Centers o f Biodiversity sea. This aquatic life zone is divided i n t o three vertical zones (Figure 6.5), o r layers, p r i m a r i l y based o n the degree of Coral reefs (see Core Case S t u d y a n d c h a p t e r - o p e n i n g p e n e t r a t i o n of sunlight. Temperatures also change w i t h photo) are some o f t h e world?s oldest and m o s t diverse and depth (Figure 6.5, red line) a n d scientists use t h e m to productive ecosystems. T h e y are t h e m a r i n e equivalents of define zones of varying species d i v e r s i t y i n these layers. tropical r a i n forests, w i t h c o m p l e x interactions a m o n g The euphotic zone is the b r i g h t l y lit u p p e r zone, w h e r e their diverse p o p u l a t i o n s o f species. drifting p h y t o p l a n k t o n c a r r y o u t about 4 0 % of the world?s W o r l d w i d e , coral reefs a r e b e i n g d a m a g e d and p h o t o s y n t h e t i c activity. Large, f a s t - s w i m m i n g p r e d a t o r y destroyed at a n a l a r m i n g r a t e b y a v a r i e t y of h u m a n fishes such as swordfish, sharks, and b l u e f i n t u n a p o p u l a t e activities. T h e n e w e s t g r o w i n g t h r e a t is o c e a n a c i d i f i c a - the e u p h o t i c zone. t i o n ? t h e r i s i n g levels of a c i d i t y i n o c e a n waters. This is N u t r i e n t levels are l o w and levels of dissolved o x y g e n occurring because t h e oceans absorb a b o u t 2 5 % of t h e are high i n the e u p h o t i c zone. The exception to this is those CO; e m i t t e d i n t o t h e a t m o s p h e r e by h u m a n activities, areas called upwelling zones. A n u p w e l l i n g , o r u p w a r d especially t h e b u r n i n g o f fossil fuels. The CO); reacts w i t h m o v e m e n t o f ocean water, brings cool a n d n u t r i e n t - r i c h ocean w a t e r t o f o r m a w e a k a c i d ( c a r b o n i c acid, H,CO3). w a t e r f r o m the b o t t o m o f the ocean to the w a r m e r surface. This r e a c t i o n decreases t h e levels o f c a r b o n a t e ions There i t supports large p o p u l a t i o n s of p h y t o p l a n k t o n , zoo- (CO;*-) n e c e s s a r y f o r t h e f o r m a t i o n o f c o r a l reefs a n d t h e p l a n k t o n , fish, and fish-eating seabirds. Strong u p w e l l i n g s shells a n d s k e l e t o n s o f m a n y m a r i n e organisms. This occur along the steep w e s t e r n coasts o f some c o n t i n e n t s makes i t h a r d e r f o r t h e s e species t o t h r i v e a n d repro- w h e n w i n d s b l o w i n g along the coasts push surface w a t e r duce. A t s o m e p o i n t , t h i s r i s i n g a c i d i t y c o u l d s l o w l y a w a y f r o m the land. This draws w a t e r u p f r o m the ocean dissolve corals a n d t h e shells a n d s k e l e t o n s of some b o t t o m (Figure 6.11 a n d Figure 5.3, p. 122). Figure 5.7 marine species. (p. 125) shows t h e oceans? m a j o r u p w e l l i n g zones. FIGURE 6. 1 1 A shore upwell- ing occurs w h e n deep, cool, nutrient-rich waters are drawn up to replace surface water moved away from a steep coast by wind flowing along the coast toward the equator.  We Are Still Learning about the Ocean's Bio diversity than had previously been thought. Scientists have long assumed that open- other microbes. It was the most thorough Ocean-water microbes play an important ocean waters contained few microbial life of such censuses ever conducted. role in the absorption of carbon by the Using a supercomputer, they counted forms. But recent research haschallenged ocean, as well as in the ocean food web, that assumption and greatly increased our genetic coding for 6 million new pro- Venter has led more expeditions to con. knowledge of the ocean's genetic diversity. teins?double the number that had previ- tinue the sampling in other areas. A team of scientists led by J. Craig ously been known, They also reported Venter took 2 years to conduct a census that they were discovering new genes {an estimated count based on sampling) and proteins at the same rate at the end of ocean microbes. They sailed around of their voyage as they had at the start of the world, stopping every 320 kilometers it, This indicated that there is still much w h y was t h e rate o f discovery of new (200 miles) to pump seawater through more of this biodiversity to discover. extremely fine filters, from which they This means that the ocean contains a genes and proteins i m p o r t a n t to Venter and his colleagues? Explain. gathered data on bacteria, viruses, and much higher diversity of microbial life The second m a j o r o p e n sea zone is t h e bathyal zone, the 6.3 HOW HAVE H U M A N d i m l y lit m i d d l e zone t h a t receives little sunlight and t h e r e f o r e does n o t c o n t a i n p h o t o s y n t h e s i z i n g producers. ACTIVITIES AFFECTED Z o o p l a n k t o n a n d s m a l l e r fishes, m a n y of w h i c h migrate to MARINE ECOSYSTEMS? feed o n the surface at n i g h t , are f o u n d i n these waters. The deepest o p e n sea zone, called the abyssal zone, is CONCEPT 6. 3 Human activities threaten aquatic biodiversity d a r k a n d cold. T h e r e is n o s u n l i g h t to support photosyn- and disrupt ecosystem and economic services provided by thesis, a n d this w a t e r has little dissolved oxygen. Never- marine ecosystems. theless, t h e deep ocean f l o o r is t e e m i n g w i t h life because it contains e n o u g h n u t r i e n t s to support a large n u m b e r of species. M o s t of t h i s zone?s organisms get t h e i r f o o d from showers of dead and decaying o r g a n i s m s ? c a l l e d marine Human Activities Are D i s r u p t i n g s n o w ? d r i f t i n g d o w n f r o m the u p p e r zones. Some abyssal- a n d D e g r a d i n g M a r i n e Ecosystems zone organisms, i n c l u d i n g m a n y types of w o r m s , are Certain h u m a n activities are d i s r u p t i n g a n d degrading deposit feeders, w h i c h take m u d into t h e i r guts a n d extract m a n y of the ecosystem a n d e c o n o m i c services provided by n u t r i e n t s f r o m it. Others such as oysters, clams, and marine aquatic systems, especially coastal marshes, shore- sponges are f i l t e r feeders, w h i c h pass w a t e r t h r o u g h o r over lines, m a n g r o v e forests, a n d coral reefs (see Core Case t h e i r bodies a n d extract n u t r i e n t s f r o m it. Study) (Concept 6.3). N e t p r i m a r y p r o d u c t i v i t y (NPP) is quite l o w in the open A c c o r d i n g to t h e W o r l d W i l d l i f e F u n d { W W F ) , more sea, except i n u p w e l l i n g areas. However, because the open t h a n 3 5 % of t h e world?s o r i g i n a l m a n g r o v e forest area sea covers so m u c h of the earth?s surface, it makes the larg- had been lost to a g r i c u l t u r a l a n d u r b a n e x p a n s i o n , mari- est c o n t r i b u t i o n to the earth?s overall NPP. In fact, scientists nas, roadways, a n d o t h e r f o r m s o f coastal development. h a v e l e a r n e d t h a t the o p e n sea contains m o r e biodiversity A c c o r d i n g t o the I n t e r n a t i o n a l U n i o n f o r t h e Conserva- t h a n t h e y t h o u g h t a f e w years ago (Science Focus 6.1). t i o n of N a t u r e ( U C N ) , m o r e t h a n o n e o f e v e r y six spe- C H E C K P O I N T FOR U N D E R S T A N D I N G 6.2 ; c i e s o f m a n g r o v e are i n d a n g e r of e x t i n c t i o n. I n addition, il since 1980 a b o u t 2 9 % o f t h e world?s seagrass beds have 1. Explain w h y m o s t aquatic life is found in coastal areas, Why been lost to p o l l u t i o n a n d o t h e r d i s t u r b a n c e s. I n a 4-year is m o s t commercial fishing done in t h e continental shelf 4 study, an i n t e r n a t i o n a l t e a m o f scientists f o u n d t h a t hu- region rather than o u t in t h e open ocean? We m a n activities h a v e h e a v i l y a f f e c t e d 4 1 % of t h e world?s :. Describe h o w intertidal organisms adapt to the stressful Ocean area. c o n d i t i o n s of t h e intertidal zone. H a r m f uul i h u m a n a c t i v i t i e s i n c r e a s e w i t h t h e number of peopl €. Explain t h e i m p o r t a n c e ofu p w e l l i n g s. l i v i n g o n o r near Coasts. C u r r e n t l y a b o u t 45% of t h e world?s p o p u l a t i o n a n d m o r e t h a n h a l f of the 162 CHAPTER 6 AQUATIC BIODIVERSITY  F I G U R E 6. 1 2 Human activities have major Natural Capital Degradation: «=. harmful impacts on all marine ecosystems (left) and particularly on coral reefs (right) M a j o r H u m a n I m p a c t s o n M a r i n e Ecosystems a n d Coral Reefs ( C o n c e p t 6.3). C r i t i c a l t h i n k i n g : Which t w o of the threats to marine ecosystems do you M a r i n e Ecosystems t h i n k are the most serious? Why? Which t w o o f the threats to coral reefs do you t h i n k are t h e most serious? Why? Top left: Jorg Hackemann/Shutterstock.com. Top right: Rich Carey/Shutterstock.com. Bottom left: Piotr Marcinski/Shutterstock.com. Bottom right: Rostislav Ageew/ Shutterstock.com. s h e l l f i s h t h a t f o r m t h e i r shells f r o m cal- cium carbonate. O t h e r m a j o r threats t o m a r i n e systems from human activities include the following: * Coastal d e v e l o p m e n t , w h i c h destroys o r degrades coastal! habitats ¢ R u n o f f of p o l l u t a n t s such as fertilizers, pesticides, a n d l i v e s t o c k wastes a n d MN O G e e p o l l u t i o n f r o m cruise ships a n d o i l He t a n k e r spills ¢ O v e r f i s h i n g a n d d e p l e t i o n of Half of coastal wetlands lost to Ocean warming c o m m e r c i a l fish species p o p u l a t i o n s agriculture and urban development ¢ D e s t r u c t i o n o f ocean b o t t o m habitats Rising ocean acidity Over one-fifth of mangrove forests by f i s h i n g t r a w l e r s d r a g g i n g w e i g h t e d lost to agriculture, aquaculture, and Rising sea levels development nets Soil erosion ¢ I n v a s i v e species t h a t deplete Beaches eroding d u e to development and rising sea levels p o p u l a t i o n s o f native species Algae growth from fertilizer runoff F i g u r e 6. 1 2 s h o w s s o m e o f t h e effects of Ocean-bottom habitats degraded by Bleaching dredging and t r a w l e r fishing these h u m a n impacts o n m a r i n e systems i n Increased UV exposure general ( l e f t ) a n d o n coral reefs i n p a r t i c u - At least 2 0 % of coral reefs severely Damage f r o m anchors and from lar ( r i g h t ). Scientists are w o r k i n g to l e a r n damaged and 2 5 - 3 3 % more threatened fishing and diving more about the little-understood marine ecosystems, o u r effects o n t h e m , a n d the ways i n w h i c h w e can seek to p r e s e r v e t h e m ( I n d i v i d u a l s M a t t e r 6.1). p o p u l a t i o n l i v e a l o n g o r n e a r coasts, a n d these p e r c e n t - CONSIDER T H I S... ages a r e r i s i n g. T H I N K I N G A B O U T Coral Reef Destruction The biggest t h r e a t to m a r i n e systems, a c c o r d i n g to How might the loss of most of the world?s remaining tropical m a n y m a r i n e scientists, is c l i m a t e change ( w h i c h w e ex- coral reefs (see Core Case S t u d y ) affect your life and the lives p l o r e f u l l y i n C h a p t e r 2 0 ). Because land-based glaciers i n of any children or grandchildren you might have? What are t w o Greenland a n d o t h e r parts o f the w o r l d are s l o w l y m e l t i n g , things you could do to help reduce this loss? and w a r m e r o c e a n waters e x p a n d sea levels are rising. T h e ? ~ rise i n sea levels projected f o r this c e n t u r y w o u l d d e s t r o y m a n y s h a l l o w coral reefs a n d f l o o d coastal marshes a n d C H E C K P O I N T FOR U N D E R S T A N D I N G 6. 3 o t h e r coastal ecosystems, as w e l l as m a n y coastal cities. A second t h r e a t , w h i c h s o m e s c i e n t i s t s v i e w as m o r e i 1. Identify the greatest threats to marine ecosystems. serious t h a n the threat of c l i m a t e change, is o c e a n ?2. Explain why ocean acidification is a serious threat to coral a c i d i f i c a t i o n. It is e s p e c i a l l y t h r e a t e n i n g to c o r a l reefs reefs, phytoplankton, and shellfish. (see C o r e Case S t u d y ) a n d t o p h y t o p l a n k t o n a n d m a n y re  Enric Sala: Working to Protect Ocean Ecosystems Marine biologist Enric Sala has made a career of working to protect undisturbed marine ecosys- tems. He travels to remote areas with the goal of learning what marine ecosystems were like be- fore human activities disrupted them. In 2008, he launched National Geographic's Pristine Seas project to find, survey, and help protect the last wild places in the ocean. Pristine Seas aims for an ocean where representative examples of all major ecosystems are protected, so that they can be healthier, more productive, and more resilient to the impacts of ocean warming and acidification. After exploring the Southern Line islands undisturbed coral reef system in the South Pacific, Sala reported that ?all the scientific data confirm that humans are the most important factor in determining the health of coral reefs.? He says that reefs are killed by ?a combination of the local impact of human activities such as fishing and pollution with the global impact of human-induced climate change.? Sala suggests that in order for coral reefs and other systems to survive and function, we need tected ocean habitat, free of human to "take out less and t h r o w in less.? One way to accomplish this is to establish large areas of pro Pristine Seas has helped to create activities of any kind. Sala was instrumental in establishing such marine protected areas. To date, than six times the area of nine of the largest marine reserves on the planet, covering an area of over 3 million square k m ? m o r e Spain. Over the next f e w years, Salas team will target 12 more locations, aiming to inspire the protection of a total of 20 of the wildest places in the ocean. For his outstanding scientific work, Sala has been named a National Geographic Explorer. 6.4 W H Y ARE FRESHWATER e r y ECOSYSTEMS IMPORTANT? Freshwater Systems CONCEPT 6.4 Freshwater ecosystems provide major ecosys- Ecosystem = = = g y Economic tem and economic services and are irreplaceable reservoirs of Services a. 4 Services biodiversity. : a Climate moderation & 4. Food W a t e r Stands in S o m e Freshwater Nutrient c i n g agen S y s t e m s a n d F l o w s in O t h e r s P E M ! Drinking water Precipitation that does not sink into the ground or Waste treatment. evaporate becomes : : s u r.f a c e w a t e r ? f r e s h w a t e r that + Irrigation water flows or is stored in bodies of water on the earth?s sur- Flood contro! face. Freshwater aquatic life zones include standing (lentic) bodies of freshwater such as lakes, ponds, ' and inland * Groundwater J Q 3 wetlands, and flowing (lotic) systems such as streams and recharge La Hydroelectricty rivers. Surface water that flows into such bodies of water is Habitats for m ? : called r u n o f f. A w a t e r s h e d , o r drainage basin, is the species any : Transporation l a n d area t h a t delivers r u n o f f , s e d i m e n t , and dissolved substances to a stream, lake, o r w e t l a n d. A l t h o u g h fresh- Genetic resources w a t e r systems c o v e r less t h a: n 2. 2 % of t h e earth?s surface, and biodiversity. Re t h e y p r o v i d e a n u m b e r o f i m p o r t a n t ecosystem a n d eco- ecreation n o m i c services (Figure 6.13). scientific L a k e s are large natural bodies of standing freshwater information d Empl : ?Se. ~ Employmen f o r m e d w h e n p r e c i p i t a t i o n , r u n o f f , streams, rivers, a n d g r o u n d w a t e r seepage f i l l depressions i n the earth?s surface. FIGURE 6. 1 3 Freshwater Systems provide many important Causes of such depressions i n c l u d e glaciation, displace- , y - B e e t a a ecosystem and economic services (Concept6.4). Critical ment of the earth?s crust, and volcanic activity. A lake?s t h i n k i n g : Which two ecosystem services which tw and watershed supplies it w i t h water from rainfall, melting economic services do you think are the mosti m p Ne Why? snow, and streams. Top: Gala AndnushkaiShuterstock com, -keuShitenickcom 1 6 4 @ C H A P T E 6R AQUATIC BIODIVERSITY  Freshwater lakes vary i n size, depth, and n u t r i e n t con- zone is nourished m a i n l y by dead m a t t e r t h a t falls f r o m tent. Deep lakes n o r m a l l y consist of f o u r distinct life zones the littoral and l i m n e t i c zones a n d by s e d i m e n t w a s h i n g that are defined by t h e i r depth and distance from shore into the lake. (Figure 6.14). The top layer, called the /ittoral zone, is near the shore and consists of the shallow sunlit waters to the depth S o m e Lakes H a v e M o r e N u t r i e n t s at which rooted plants stop growing. It has a high level of biodiversity because of a m p l e sunlight and inputs of n u t r i - than Others ents from the surrounding land. Species living i n the littoral Ecologists classify lakes according to t h e i r n u t r i e n t c o n t e n t zone include m a n y rooted plants; animals such as turtles, and p r i m a r y productivity. Lakes that have a s m a l l s u p p l y frogs, and crayfish; a n d fish such as bass, perch, and carp. of p l a n t n u t r i e n t s are called o l i g o t r o p h i c l a k e s. This type The next layer is the limnetic zone, the open, sunlit surface of lake (Figure 6.15) is often deep a n d can h a v e steep layer away from the shore that extends to the depth pene- banks. Glaciers and m o u n t a i n streams s u p p l y w a t e r to trated by sunlight. This is the main photosynthetic zone of m a n y of these lakes, w h i c h u s u a l l y h a v e crystal-clear w a - the lake, the layer that produces the food and oxygen that ter a n d small p o p u l a t i o n s of p h y t o p l a n k t o n and fish spe- support most of t h e lake?s consumers. Its most a b u n d a n t cies, such as s m a l l m o u t h bass and trout. The steep sides of organisms are p h y t o p l a n k t o n and zooplankton. Some large o l i g o t r o p h i c ponds a n d lakes d o n o t a l l o w e n o u g h area f o r species of fish spend most of their time i n this zone, w i t h emergent and submergent plants to root, a n d a c c u m u l a t e d occasional visits to the littoral zone to feed and reproduce. nutrients i n t h e benthic zone are o u t of reach of t h e f e w The profundal zone is the v o l u m e of deeper w a t e r l y i n g plants that m a y inhabit the l i t t o r a l zone. Because o f t h e i r between t h e l i m n e t i c zone and the lake b o t t o m. It is too l o w levels of nutrients, these lakes h a v e a l o w net p r i m a r y dark for photosynthesis. W i t h o u t s u n l i g h t a n d plants, o x y - p r o d u c t i v i t y (NPP). gen levels are o f t e n low. Fishes adapted to the lake?s cooler Over time, sediments, organic material, a n d i n o r g a n i c and darker water, such as perch, are found i n this zone. n u t r i e n t s wash i n t o most o l i g o t r o p h i c lakes, a n d plants The b o t t o m of the lake is called the benthic zone, inhab- g r o w and decompose to f o r m b o t t o m sediments. A lake ited mostly by decomposers, d e t r i t u s feeders, and some w i t h a large s u p p l y of n u t r i e n t s is called a eutrophic lake bottom-feeding species of fish such as catfish. The benthic (Figure 6.16). Such lakes t y p i c a l l y a r e s h a l l o w a n d have Northern 2 y BF? yy? ) OUR CS Ploodworms/ ? k eos FIGURE 6. 1 4 A typical deep temperate-zone lake has distinct zones of life. C r i t i c a l t h i n k i n g : How are deep lakes similar to tropical rain forests? (Hint: See Figure 5.20, p. 139.) 165  ? e Measuring Productivity in an Aquatic Ecosystem Primary productivity measures the rate at which sunlight is stored by plants in the formo fo r ganic molecules, or, in other words, the at various depths within a water col- rate of carbon fixation. By measuring the amount of oxygen (a byproduct ofphotosynthesis) umn, a depth profile can be constructed showing the relationship between turbidity (cloudiness) and productivity. From these data, researchers can compare the relative productivity of different bodies of water. FRQ A p p l i c a t i o n Productivity is expressed as mg C/mi/day. Therefore, if oxygen production is measured in mL O,fiter/nour, these values must be con. verted. For every milliliter of O, produced, 0.536 mg of carbon is fixed. Using these conversion units, productivity can be calculated at various depths in a pond: 1 ml 02 = 0.536 mg C 1m? = 1000 liters A w a t e r s a m p l e is t a k e n at t h e s u r f a c e o f a p o n d. The a m o u n t o f o x y g e n p r o d u c e d is m e a s u r e d a t 0. 1 4 mL O , / l i t e r / n o u r. D e t e r m i n e P r i m a r y p r o d u c t i v i t y b y c o n v e r t i n g t h i s m e a s u r e m e n t t o m g C/m?/day. First, convert the mL of 0 , t o mg C: 0.14 mL O,fliter/nour x e r e s€ = 0. 0 7 5 mg CAliter/hour ? (mLs o f O2 cancel) mi Q2 N e x t , c o n v e r t liters t o c u b i c meters: 4000 L 0.075 mg CAliter/hour x = = 75.04 mg C/m*/hour (liters cancel) m Since there are 24 hours in a day: 75.04 mg C / m / h o u r X 24 hours = 1800.96 mg C/m3/day ?2 P a s as ecs FIGURE 6.15 Trillium Lake i n t h e state o f O r e g o n w i t h a v i e w o f M o u n t H o o d. 166 CHAPTER 6 AQUATIC BIODIVERSITY  Nicholas Rjabow/Dreamstme.com FIGURE 6. 1 6 This eutrophic lake has received large flows of plant nutrients. As a result, its surface is covered w i t h mats of algae. excessive n u t r i e n t s into lakes (See Critical Concepts i n murky brown or green water. Here, there is ample area Sustainability). where plants can root and water is not very deep, allowing light to penetrate and drive photosynthesis. As organic Matter falls into these ponds and vegetation dies back, bot- Freshwater Streams and Rivers Carry tom sediments accumulate, slowly building up over time Large Volumes of Water and providing nutrients for plant growth. Because of their I n drainage basins, w a t e r accumulates i n small streams high levels of nutrients, eutrophic lakes have a high NPP. t h a t j o i n to f o r m rivers. Collectively, streams and rivers Most lakes are classified as m e s o t r o p h i c and fall some- c a r r y h u g e a m o u n t s of w a t e r f r o m highlands to lakes a n d where between the t w o extremes of nutrient enrichment. oceans. T h e y d r a i n an estimated 7 5 % of the earth?s l a n d Human inputs of nutrients through the atmosphere surface. M a n y streams begin i n m o u n t a i n o u s o r h i l l y and from urban and agricultural areas within a lake's areas, w h i c h collect a n d release w a t e r falling to t h e earth?s Watershed can accelerate the eutrophication of the lake. surface as precipitation. The d o w n w a r d f l o w of surface This process, called c u l t u r a l e u t r o p h i c a t i o n , often puts 167 Cultural Eutrophication Eutrophication is defined as the physical, chemical, and biological changes that take place after a freshwater system such as a lake, slow-moving stream, or estuary receives an influx of nutrients from the surrounding watershed. Nutrients like nitrate and phos- phate are limiting factors for plants, and when they are introduced to a body of water, they are assimilated quickly, causing algal blooms. When human actions are the cause of eutrophication, it is called cultural eutrophi- cation. Sources of nutrients include fertiliz- ers from farms or lawns, phosphates in detergents, feedlot runoff, treated and un- treated municipal sewage, runoff from streets, mining and construction, and nitro- gen oxides from air pollution. F I G U R E 6. A. This flowchart shows the sequence of events in Cultural eutrophication is a sequence cultural eutrophication. of events that results in a shift of living high levels of oxygen to survive. Explain penetrating, causing aquatic plants to die. organisms in a body of water (Figure 6.A). the relationship between the influx of nutri- Aerobic decomposers break d o w n the dead FRQ A p p l i c a t i o n ents and the death of the trout. vegetation, causing a drop in oxygen levels. Q u e s t i o n : After a rainstorm on a small Increased turbidity (suspended solids) can farm, c o w manure is washed into a slow- Possible Response: Cow manure contains also increase water temperature, leading to moving stream adjacent to the c o w pasture. nitrates, a limiting factor for plants. When a loss of oxygen. Death o f intolerant organ- A drop in dissolved oxygen results, leading nitrates enter a waterway, an algal bloom isms such as trout results w h e n oxygen lev- to the death o f many trout, fish that require occurs. This blocks sunlight from els are too low t o support them. w a t e r a n d g r o u n d w a t e r f r o m m o u n t a i n highlands to the f l o w i n g h e a d w a t e r streams. M o s t o f t h e p l a n t s i n this sea t y p i c a l l y takes place i n three aquatic life zones charac- zone are algae a n d mosses a t t a c h e d to rocks a n d other terized by d i f f e r e n t e n v i r o n m e n t a l conditions: the source surfaces u n d e r w a t e r.. zone, t h e transition zone, a n d the floodplain zone (Figure 6.17). I n the transition zone ( F i g u r e 6. 1 7 , c e n t e r ) , headwater Rivers a n d streams can d i f f e r f r o m this generalized m o d e l. streams merge to f o r m wider, deeper, a n d w a r m e r streams I n the n a r r o w source zone (Figure 6.17, left), h e a d w a t e r that f l o w d o w n gentler slopes w i t h f e w e r obstacles. They streams are u s u a l l y shallow, cold, clear, and swiftly f l o w i n g can be m o r e t u r b i d ( c o n t a i n i n g suspended sediments) and ( F i g u r e 6.17, inset p h o t o ). As this w a t e r tumbles o v e r rocks, s l o w e r f l o w i n g t h a n h e a d w a t e r streams, a n d t h e y tend to waterfalls, a n d rapids, it dissolves large amounts of oxygen have less dissolved o x y g e n. The w a r m e r w a t e r and other f r o m t h e air. M o s t o f these streams are n o t very productive conditions i n this zone support m o r e p r o d u c e r s , as w e l l as because o f a Jack of n u t r i e n t s and p r i m a r y producers. Their c o o l - w a t e r and w a r m - w a t e r fish species (such as black n u t r i e n t s c o m e p r i m a r i l y f r o m organic matter, m o s t l y bass) w i t h s l i g h t l y l o w e r o x y g e n r e q u i r e m e n t s. leaves, branches, and the bodies of living and dead insects As streams f l o w d o w n h i l l , t h e y shape t h e land that fall i n t o the stream f r o m nearby land. t h r o u g h w h i c h t h e y pass. O v e r m i l l i o n s of years, the The s o u r c e z o n e is p o p u l a t e d by c o l d - w a t e r fish spe- f r i c t i o n of m o v i n g w a t e r has l e v e l e d m o u n t a i n s and cut cies t h a t n e e d lots of dissolved o x y g e n. Fishes i n t h i s d e e p c a n y o n s. Sand, gravel, a n d soil c a r r i e d by streams h a b i t a t , such as t r o u t a n d m i n n o w s , t e n d to h a v e a n d rivers have been d e p o s i t e d as s e d i m e n t i n l o w - l y i n g s t r e a m l i n e d a n d m u s c u l a r bodies t h a t a l l o w t h e m to a r e a s. In these floodplain zones ( F i g u r e 6.17), streams join s w i m i n the r a p i d , s t r o n g c u r r e n t s. O t h e r animals such i n t o w i d e r a n d deeper rivers t h a t f l o w across broad, flat as r i f f l e beetles h a v e c o m p a c t , hard, o r f l a t t e n e d bodies valleys, W a t e r in this zone u s u a l l y has h i g h e r tempera- t h a t a l l o w t h e m to l i v e a m o n g o r u n d e r stones i n fast- tures a n d less dissolved o x y g e n t h a n w a t e r i n the t w o 168 CHAPTER 6 AQUATIC BIODIVERSITY  Lake Glacier Headwaters Tributary Flood plain Oxbow lake Salt marsh Deposited sediment Source Z o n e Transition Zone Water Sediment F I G U R E 6. 1 7 T h e r e a r e t h r e e z o n e s in t h e d o w n h i l l f l o w of w a t e r : t h e s o u r c e z o n e , w h i c h c o n - tains h e a d w a t e r s t r e a m s f o u n d in h i g h l a n d s a n d m o u n t a i n s (see inset p h o t o ) ; t h e transition z o n e , w h i c h c o n t a i n s w i d e r , l o w e r - e l e v a t i o n streams; a n d t h e f l o o d p l a i n zone, w h i c h c o n t a i n s rivers t h a t e m p t y i n t o l a r g e r rivers o r i n t o t h e o c e a n. C r i t i c a l t h i n k i n g : H o w m i g h t t h e b u i l d i n g o f m a n y dams and reservoirs alonga river's path to the ocean affect its sediment input into the ocean and change the river's delta? higher zones. T h e s l o w - m o v i n g rivers s o m e t i m e s sup- _ CONSIDERT H I S... - p o r t large p o p u l a t i o n s o f p r o d u c e r s such as algae and C O N N E C T I O N S Stream Water Quality and Watershed Land cyanobacteria, as w e l l as r o o t e d a q u a t i c plants a l o n g the Streams receive most of their nutrients f r o m bordering land shores. ecosystems. Such nutrients c o m e f r o m falling leaves, a n i m a l fe- ces, insects, a n d o t h e r forms o f biomass washed into streams Because o f increased e r o s i o n a n d r u n o f f o v e r a larger