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Home , Caribbean Sea, Ecological extinction, Loggerhead sea turtle, Ocean, Sea turtle, Turtle

PHOTO TIM CALVER

WHY HEALTHY NEED : THE IMPORTANCE OF SEA TURTLES TO

Wilson, E.G., Miller, K.L., Allison, D. and Magliocca, M.

oceana.org/seaturtles TURTLES | Protecing h T e e W the a t u u o w ’s o h s r d l w Oceans a l u o o s l n k c A d k i l k i l f o e e O t o t a e c o t a h h t a n o a n k n ’ k l w s h T o w a K e r n e r k m e g d e e r t S t o o j B a s i a s n r e v d n a d e s F l u o a r o f n u t d t n e h e l t r t a r e i n o .s r i v e f r o s e w t i e h f o r i h t o p p u s s PHO r o p e r TO t r .t M I C HA E L S TUB L E FIEL D TABLE OF CONTENTS WHY HEALTHY OCEANS NEED SEA TURTLES

3 Executive Summary 4 U.S. Sea Turtles 5 Importance of Sea Turtles to Healthy Oceans 6 Maintaining Importance of Green Sea Turtles on Beds Impact of Hawksbill Sea Turtles on Reefs Benefit of Sea Turtles to 9 Maintaining a Balanced Sea Turtles and Sea Turtles Provide Food for 11 Nutrient Cycling Loggerheads Benefit Ocean Floor Ecosystems Sea Turtles Improve Nesting 12 Providing Habitat 14 The Risk of Ecological 15 Conclusions

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OCEAN TURTLES | Protecing the World ’s Oceans PH OT O TIM CALVE R EXECUTIVE SUMMARY Sea turtles have played vital roles in maintaining the health of the world’s oceans for more than 100 million . These roles range from maintaining productive ecosystems to transporting essential nutrients from the oceans to beaches and coastal dunes.

Major changes have occurred in the oceans because sea turtles have been virtually eliminated from many areas of the globe. Commercial , loss of nesting habitat and change are among the human-caused threats pushing sea turtles towards extinction. As sea populations decline, so does their ability to fulfill vital functions in ocean ecosystems.

Our oceans are unhealthy and under significant threat from , and . It is for us to protect sea turtles and rebuild their populations to healthy levels as a vital step in ensuring healthy and resilient oceans for the future.

PHOTO TIM CALVER

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P TURTLES an o. l l HO s e i c e er PHOT O ( i d co D END e r E T ( en O esp ite C a ER back some A E S Br d n e r a SMIT o m t eed ing | ED/THREA TEN o ANGE Protecin g Sea S f s a w t t TEPH HSO a e s a s y l e h c tions pop ul a ted ass oci a Col o c Se e r a NIA RED e t s i l T e l t r u t N ny/A urt a N at t M. the T b m i MUS d Tu ll S le ) s CHEL o s a World’s and T R U the r s EUM m i w s rt r p ED i c e a c r les onti are ot B a d n oli ve at ec as Oceans ,) nu e n i g n ti K on r h t e id ley e SE L e r t ’p m s e o m d ’d l r o w dec li Logge easu res, r o ( i p e L Hawk s d i r n e t a e r h t ne. y e l s c o d EN c o T PH no ( y l e h e L :s n a e HRE DAN OT bill sea s y l e h c o d i p d e O s ATE d MI GERE l o Se d n u P k c a b t a l f turt CH HO e c a v i Se NE E a TO r e le LL D a Tur D sp eci es GARY E h t a S Turtles ). e k e CH ( tle y Ever a N E ii p m YOS A d n R t s a E d e r e g n a h R o t ,) as s r pe a e l e d re ci t co e r p k c a b r e h es ver p S ex s Olive Kemp’s Me E )s u s ed c e cep t NDA xi s e i c e , o ( n m r e D g B f o or c A n e e r Ridley r ug h GER e e E t th di ng Ridley N ( c o e ) A S E to DANGE ( a i n o l e h C tb ack fla D/THREATE Co l e h be P lo HO Sea s y e r o m ny/A removd T O Sea ae c a i r o c RE ll K E in hab it o PH D sa d y m Turtles DA n a h t t he r OT O R Turtl NED a G from r O 3 e ,) s N as R ,) 0 PS E es IMPORTANCE OF SEA TURTLES TO HEALTHY OCEANS

Humans have caused populations to decline significantly all over the world. 1 Initially, direct fishing for sea turtles was the main reason for population declines. Today, other threats, including injury or death in commercial , habitat degradation and climate change the list. 2 The resulting population Sea turtles — even at diminished declines have reduced the ’ ability to fulfill their roles in maintaining healthy marine ecosystems. 3 population levels — play an important role in ocean ecosystems. Because large sea turtle population declines occurred centuries ago, we lack a proper perspective or a reliable baseline against which to compare their current state. 4 Due to the lack of historic information, some of the past ecological functions of sea turtles during periods of great have certainly been forgotten. 5

Although we cannot now fully understand the roles sea turtles played centuries ago, it is important that we discover as much as possible. Better understanding of these roles will allow us to determine what structure and functions were lost in the ocean ecosystems , the environmental effects of remaining populations, and management and conservation measures required for sea turtles to reach historic levels—and the improvements in ecos ystem health that could result from restored sea turtle populations. 6

What we do know is that sea turtles—even at diminished population levels—play an important role in ocean ecosystems by maintaining healthy seagrass beds and coral reefs, providing habitat for other marine , helping to balance marine food webs and facilitating

nutrient cycling from to . PHOTO TIM CALVER

oceana.org/seaturtles 5 S E L T R U T

MAINTAINING HABITAT

Impact of Green Sea Turtles on Seagrass Beds

Green sea turtles, one of tShteafteuws: laErgnedspaecniegs eofrheerdbivores that eat seagrass, help to maintain healthy seagrass beds. When green sea turtles graze, they increase the and nutrient content of seagrass blades. 7,8 Without constant grazing, seagrass beds become overgrown and obstruct currents, the bottom, begin to decompose and provide suitable habitat for the growth of slime molds. 9,10 Older portions of seagrass beds tend to be overgrown with , , and fungi. 11

Sea turtles forage on seagrass just a few centimeters from the bottom of the blades, allowing older, upper portions of the blades to float away. 12,13 As the turtles crop and re-crop the same plot, seagrass blades are removed from the area rather than accumulating on the bottom. This results in a 15-fold decrease in the supply of nitrogen to seagrass roots, which impacts species, nutrient cycling, densities and predator-prey relations. 14 As seen in the , the decline of green sea turtles can result in a loss of productivity in the food web – including commercially exploited reef fish – decreasing the amount of protein-rich food available for people. 15

Florida and the Gulf of are two excellent examples of the importance of green sea turtles on the health of seagrass beds. The die-off of seagrass in these areas during the 1980s has been directly linked to the ecological extinction of greens. 16

PHOTO TIM CALVER

When green sea turtles graze, they increase the productivity and nutrient content of seagrass blades.

6 OCEANA | Protecting the World’s Oceans Hawksbills allow other species, such as coral, to colonize and grow by removing from reefs.

PHOTO GARY YOSS

Impact of Hawksbill Sea Turtles on Coral Reefs

Equipped with -like mouths, hawksbill sea turtles forage on a variety of marine sponges. By doing this, PHOTO JUAN CARLOS CALVIN they change the species composition and distribution of sponges in coral reef ecosystems. 17 Sponges compete aggressively for with reef-building . By removing sponges from reefs, hawksbills allow other species, such as coral, to colonize and grow. 18,19 Without hawksbills, sponges are likely to dominate reef communities, further limiting the growth of corals and modifying the very structure of coral reef ecosystems. 20

The physical and chemical defenses of sponges the y expose food to marine species typically unable prevent most fish and marine from eating to penetrate the ’s exterior, making sponges more them. 21 As hawksbills rip sponges apart during feeding, vulnerable to predators. 22,23 Through their selective forag - ing behavior, hawksbills impact the overall diversity of reef communities. 24

PHOTO CARLOS SUAREZ

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Sea Turtles and Jellyfish

Leatherbacks, the largest of the sea turtles, travel the farthest of any sea turtle species and have wide ranging effects on the ocean . Surprisingly, leatherbacks get their and nutritional needs from a small, gelatinous source—jellyfish. 30 Growing up to 9 feet in length and migrating across entire oceans, leatherbacks rely on large concentrations of jellyfish to satisfy their appetites. 31 They have been known to consume up to 440 pounds of jellyfish – nearly the weight of an adult African lion– each day .32,33 PHOTO MABEL NAVA

As significant consumers of jellyfish globally, leatherbacks play a pivotal ecological role as a top Declining leave jellyfish with less jellyfish predator. 34 Declines in leatherback turtle for food, resulting in proliferation of jellyfish populations along with declines in other key predators, around the world. 37 The increase in jellyfish is already such as some commercially valuable fish species, proving detrimental to the recovery of fish stocks could have repercussions for jellyfish population since jellyfish prey on fish and larvae. 38,39 control. 35 Fewer fish result in more jellyfish, which means even fewer fish in the future. Because leatherbacks This is of particular concern since, as a result of consume large amounts of jellyfish, declines in leatherbacks could further shift species overfishing of many finfish populations, jellyfish are from fish to jellyfish. gradually replacing once-abundant fish species. 36 Other sea turtle species, including loggerhead and green sea turtles, also consume jellyfish.

Leatherbacks get their energy and nutritional needs from jellyfish.

PHOTO PBS.ORG

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Loggerheads Benefit Ocean Floor Ecosystems

Loggerheads are equipped with powerful jaws to feed floor in search of food, loggerheads create trails in the on hard-shelled prey, such as . This allows . 57 This behavior is important for them to reduce the shells of their prey into fragments both loggerheads and the habitat. 58 The loggerheads that are either discarded on site or further away in the trails affect the compaction, aeration and nutrient form of feces. 54 By breaking up the shells while foraging, distribution of the sediment, 59 as well as the species loggerheads increase the rate at which the shells diversity and dynamics of the benthic ecosystem. 60 disintegrate 55 and increase the rate of nutrient When foraging, loggerheads naturally alter the ocean recycling in benthic or ocean bottom ecosystems. bottom and benefit the underwater .

Loggerheads also find prey by clearing away sand to expose their next meal. 56 As they glide along the sea

Sea Turtles Improve Nesting Beaches

Female migrations from foraging grounds to nesting to absorb the nutrients. 66 In addition, nesting and beaches are ecologically significant journeys. 61 When the emergence of hatchlings bring and females lay their eggs on sandy shorelines, they introduce to the surface. 67 These processes help nutrients and energy from distant and dispersed foraging disperse nutrients to small organisms in beach sand. 68 grounds into relatively small and nutrient-poor Consequently, the presence of turtle eggs drives beaches. 62,63 One of the longest and most impressive communit y dynamics on nesting beaches. 69 examples of this transfer of nutrients is by leatherbacks, which feed on jellyfish near the circle and nest on tropical beaches. 64,65

Sea turtle eggs have four possible fates, each with its own energy path: 1) the eggs hatch and most of the nutrients return to the sea as hatchlings, leaving some nutrients on the beach in the form of eggshells and embryonic fluid; 2) the eggs fail to hatch, allowing nutrients to enter the detrital ; 3) the eggs are consumed by PHOTO CORY WILSON predators; or 4) the eggs are penetrated by roots, enabling

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The loggerhead’s transatlantic migration to the Mediterranean is believed to play a key role in expanding the ’s range and genetic diversity. 82 Species Sea turtles offer an oasis to fish and associated with a host, such as sea turtles, are important to generating and maintaining diversity throughout the in the open ocean. world’s oceans. 83 Continued loss of loggerheads and other sea turtle species means a decrease in available substrate for the growth and livelihood of such marine diversity. 84 not extremely water-resistant. 87 By perching on sea turtles, seabirds that would otherwise be vulnerable to In the open ocean, miles from , sea turtles offer an attack, find refuge from . 88 Small baitfish also use oasis to fish and seabirds. Similar to floating debris, sea sea turtles for protection, by forming tight schools beneath turtles can be used as a place to rest, a foraging ground the turtle’s body. 89 These schools of fish then provide a and even a safe haven from potential predators. Of all food source for resting seabirds. 90 Some seabirds the sea turtle species, olive ridleys are most frequently occasionally feed on inhabiting the sea turtle’s associated with seabirds, particularly in the Eastern shell. 91 By offering a location to roost, feast and hide, sea Tropical Pacific. 85 As they surface to bask in the sun, olive turtles represent an important for and fish ridleys expose the center of their shell and create a at sea. 92 platform for seabirds to . 86 Some seabirds take advantage of this opportunity to roost if their feathers are

oceana.org/seaturtles 13 S E

L PHOTO TIM CALVER T R U T

THE RISK OF ECOLOGICAL EXTINCTION

Sea turtles clearly play important roles in marine ecosystems. Each sea turtle species uniquely affects the diversity, habitat and functionality of its environment. Whether by grazing on seagrass, controlling sponge distribution, feasting on jellyfish, transporting nutrients or supporting other , sea turtles play vital roles in maintaining the health of the oceans.

Unfortunately, over the past few centuries, sea turtle populations have experienced significant declines. Before a species goes physically extinct, it can become ecologically extinct. Ecological extinction, which occurs when the number of individuals in a species becomes so small that it is unable to perform its ecological role, happened to green sea turtles in the Caribbean. At the time of Columbus’ voyages to the Caribbean, sea turtles were so abundant that vessels that had lost their way could follow the noise of sea turtles swimming along their migration route and find their way to the . 93 Current estimates of turtle populations at that time range from 33 million to 660 million. 94 Greens in the Caribbean consumed such large amounts of seagrass, sponges and jellyfish that their virtual ecological extinction resulted in major changes in the structure and function of the . 95

Sea turtle populations around the world have dwindled in recent centuries and in many places, continue to decline. For some populations, there is risk not only of ecological extinction, but of physical extinction as well. In the words of Aldo Leopold, one of the most influential conservation thinkers of the 20th century, “To keep every cog and wheel is the first precaution of intelligent tinkering.” 96 Applying this principle to the oceans, quite simply, we need to keep all of the species. managers are moving towards an “ecosystem approach” to managing the oceans. The first step in taking an ecosystem approach is to ensure the survival of the key components of the ecosystems, which unequivocally must include sea turtles. The next step is to ensure their populations actually recover. Increased populations o f sea turtles are a key step in restoring the balance among ocean species, an essential step toward restoring healthy ocean ecosystems.

Some populations of sea turtles risk not only ecological extinction, but physical extinction.

14 OCEANA | Protecting the World’s Oceans CONCLUSIONS

As sea turtle populations decline, so does their ability to perform vital roles in maintaining the health of the world’s oceans. Death and injury in commercial fisheries, loss of important habitat, pollution and climate change are among the many human-caused threats pushing sea turtles towards extinction. More proactive conservation measures are needed to protect sea turtles and rebuild their populations to healthy levels so they can fulfill the full extent of their historic roles in ocean ecosystems. At historic levels, sea turtles will help restore the health of our oceans and make them more resilient to future threats.

The following actions must be taken to protect and restore sea turtle populations: • Reduce sea turtle interactions and mortalities in commercial fisheries • Protect key habitat areas on land and in the water • Pass comprehensive legislation that establishes a system to protect and restore sea turtle populations

PHOTO JACOB TUTTLE

oceana.org/seaturtles 15 16 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 E R 8 7 6 5 4 3 2 1 0 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 Ser. Ser.III, ecosystems: Thayer, Bjorndal, Bjorndal, Bjorndal, Bjorndal, Bjorndal, Bjorndal, R Gul ko, Losey, Purcell, Gibbons, Duron-Dufrenne, Houghton, Houg hton, Bou chard , Jac kson. Mc Clen achan , Th ayer, Th ayer, Bj orndal , Jac kson, Jac kson, Zi eman, The En vironmen t overfis hin g envi ronment. Houg hton, Bou chard , Bou chard , Bou chard , Hann an, Gul ko, Sazima, tion.va obser Schofield, mu n i d u t r e t su d i p s i h y Biolog Series Losey , Sch ofield , Losey , Sch ofield , Purcell, Lynam, Lynam, Meyl an, Meyl an, Leon, Leon, Leon, Meyl an, Meyl an, Lynam, Leon, Bjorndal, y Biolog 350: 304: Y.M ., Y.M ., Y.M . Y.M ., G.S, D.A D.A 24 5: OCEAN G.S, G.S, R E F G.W., G.W. G.W., J.E., . C.P., C.P., 16(13): C.P., J.C ., I., J.E. L.B., A. A. A. A. M.J. K.A K.A, K.A, K.A, K.A, K.A, K.A

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