ekosistem padang lamun

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EKOSISTEM PADANG LAMUN
Daerah perairan pantai adalah wilayah perairan yang berada antara
ujung paparan benua dengan kedalaman laut sekitar 200 m sampai pantai
yang didalamnya terdapat ekosistem mangrove, terumbu karang, estuari,
padang lamun, sumber hayati dan nonhayati, serta fasilitas-fasilitas seperti
pelabuhan dan pemukiman dan panorama pesisir.
Seagrass Ekosistem yang terabaikan
Sering dapat dilihat hamparan hijau pada dasar laut di pinggir
pantai yang menyerupai padang rumput hijau, yang tidak lain adalah
padang-lamun atau yang populer dikenal dengan seagrass. Seagrass
adalah tempat hidup bagi banyak organisme, seperti ikan, kepiting, udang,
lobster, seaurchin (bulu babi), dan lainnya. Sebagian besar organisma
pantai (ikan, udang, kepiting dll) mempunyai hubungan ekologis dengan
habitat lamun. Sebagai habitat yang ditumbuhi berbagai spesies lamun,
padang lamun memberikan tempat yang sangat strategis bagi perlindungan
ikan-ikan kecil dari "pengejaran" beberapa predator, juga tempat hidup dan
mencari makan bagi beberapa jenis udang dan kepiting.
ian.umces.edu/discforum/index.php?topic=108.0
Seagrass bukan "rumput laut"
Habitat Lamun atau yang lebih di kenal dengan kata seagrass
merupakan habitat pantai yang sangat unik. dengan di tumbuhi oleh lamun
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(golongan macrophyte) yang dapat beradaptasi dengan kondisi pantai yang
labil, tumbuhan lamun memebrikan amat sanagt banyak fungsi ekologis
bagi organisma yang berasosiasi dengannya. Banyak organisme yang
secara ecologis dan biologis sangat tergantung pada keberadaan
lamun. Banyak orang awam mengenal kata seagrass sebagai "rumput
laut" yang konotasinya ke arah seaweed. Namun jika dirunut lebih jauh
tentang kedua tumbuhan ini akan sangat jauh perbedaanya. Sebagai
tumbuhan sejati, seagrass merupakan tumbuhan yang mempunyai akar
(Ryzome dan serabut akar), batang, daun, bunga dan beberapa spesies
berbuah. Berbeda dengan seaweed yang merupakan alga besar (Macroalga) yang tidak mempunyai akar, batang dan daun sejati. Sebagai
tumbuhan tingkat tinggi, seagrass mempunyai sistem reproduksi dan
pertumbuhan yang khas.
research.myfwc.com/.../view_article.asp?id=20720
Seagrasses are submerged flowering plants found in shallow marine waters, such
as bays and lagoons and along the continental shelf in the Gulf of Mexico. A vital
part of the marine ecosystem due to their productivity level, seagrasses provide
food, habitat, and nursery areas for numerous vertebrate and invertebrate species.
The vast biodiversity and sensitivity to changes in water quality inherent in
seagrass communities makes seagrasses an important species to help determine
the overall health of coastal ecosystems. Seagrasses perform numerous functions:
 Stabilizing the sea bottom
 Providing food and habitat for other marine organisms
 Maintaining water quality
 Supporting local economies
Seperti layaknya padang rumput, seagrass dapat menyebar dengan
perpanjangan ryzome (batang akar). Penyebaran seagrass terlihat sedikit
unik dengan pola penyebaran yang sangat tergantung pada topografi dasar
pantai, kandungan nutrient dasar perairan (substrate) dan beberapa faktor
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fisik dan kimia lainnya. Kadang terlihat pola penyebaran yang tidak merata
dengan kepadatan yang relative rendah dan bahkan terdapat semacang
ruang-ruang kosong di tengah padang lamun yang tidak tertumbuhi oleh
lamun. Kadang-kadang terlihat pola penyebaran yang berkelompokkelompok, namun ada juga pola penyebaran yang merata tumbuh hampir
pada seluruh garis pantai landai dengan kepadatan yang sedang dan
bahkan tinggi.
Berbeda dengan seaweed, yang umunnya sangat memerlukan
benda keras di dasar perairan sebagai susbtrat untuk melekat. namun
memang ada juga banyak yang tumbuh dan menyebar secara alami
dengan substrat dasar yang lunak.
www.seagrasswatch.org/seagrass.html
A number of environmental parameters are critical to whether
seagrass will grow and persist. These include physical parameters that
regulate the physiological activity of seagrasses (temperature, salinity,
waves, currents, depth, substrate and day length), natural phenomena that
limit the photosynthetic activity of the plants (light, nutrients, epiphytes and
diseases), and anthropogenic inputs that inhibit access to available light for
growth (nutrient and sediment loading). Various combinations of these
parameters will permit, encourage or eliminate seagrass from a specific
location.
Seagrasses occupy a variety of coastal habitats. Seagrass
meadows typically occur in most shallow, sheltered soft-bottomed marine
coastlines and estuaries. These meadows may be monospecific or may
consist of multispecies communities, sometimes with up to 12 species
present within one location.
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The depth range of seagrass is usually controlled at its deepest
edge by the availability of light for photosynthesis. Exposure at low tide,
wave action and associated turbidity and low salinity from fresh water inflow
determine seagrass species survival at the shallow edge. Seagrasses
survive in the intertidal zone especially in sites sheltered from wave action
or where there is entrapment of water at low tide, (e.g., reef platforms and
tide pools), protecting the seagrasses from exposure (to heat, drying) at low
tide.
The habitat complexity within seagrass meadows enhances the
diversity and abundance of animals. Seagrasses on reef flats and near
estuaries are also nutrient sinks, buffering or filtering nutrient and chemical
inputs to the marine environment. They also stabilise coastal sediments.
They also provide food and shelter for many organisms, and are a
nursery ground for commercially important prawn and fish species. The
high primary production rates of seagrasses are closely linked to the high
production rates of associated fisheries. These plants support numerous
herbivore- and detritivore-based food chains, and are considered very
productive pastures of the sea. The associated economic values of
seagrass meadows are very large, although not always easy to quantify.
Seagrass/algae beds are rated the 3rd most valuable ecosystem
globally (on a per hectare basis), only preceded by estuaries and wetlands.
The average global value of seagrasses for their nutrient cycling services
and the raw product they provide has been estimated at 1994US$ 19,004
ha-1 yr-1 (Costanza et al. 1997). This value would be significantly greater if
the habitat/refugia and food production services of seagrasses were
included.
www.seagrasswatch.org/seagrass.html
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Identifikasi Seagrass
Seagrasses are aquatic flowering plants that form meadows in nearshore brackish or marine waters in temperate and tropical regions.
Australia has the highest diversity of seagrasses in the world , comprising
more than half of the world's species, and all but one genus. At the
broadest level, seagrasses are differentiated into temperate and tropical
species. Seagrass species can also differ in terms of the breadth of their
distributional ranges (broad vs restricted), their reproductive strategies (e.g.
rapid seeding, seed banks and vegetative reproduction), the degree of their
persistence (ephemeral vs persistent), physiology (e.g. growth dynamics,
nutrient cycling and response to disturbance) and in their ecological
interactions (e.g. influence of grazing, leaf canopy structure, detritus
production and epiphyte production). Assemblages of seagrass species
give rise to a series of dynamic and temporally and spatially variable
seagrass meadows. Changes in the species composition of seagrass
meadows may indicate slow but important changes in the environment, and
are a suggested indicator for State of the Environment .
www.ozcoasts.org.au/.../seagrass_species.jsp
Coastal seagrass habitats support high levels of primary productivity
and are the most biodiverse of all the seagrass habitats. The primary
controls on the species composition of these habitats are tidal range
(intertidal or subtidal), physical disturbance caused by storms and cyclone
related swell and waves, sediment movement, and the extent of grazing by
macroherbivores (e.g. turtles and dugongs). The seagrass communities of
reefs support a high level of biodiversity and are highly productive. The
species composition of these communities reflect low nutrient availability,
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unstable sediment and fluctuating water temperature and salinity. Deep
water seagrasses (15 - 58m) often form monospecific meadows. The
primary control on deep water seagrass meadows are low light levels (and
changes in spectral composition) caused by the refraction and absorption
of light in the water column and pulsed turbidity events.
Syringodium isoetifolium
Habitat
Tumbuhan laut sejati, tumbuh pada rataan terumbu
bersubtsrat pasir, tumbuh sampai kedalaman 3 m,
pada zona yang tidak terlalu lama terekspos udara
pada saat surut maksimal atau pada teluk yang
bersubstrat pasir terrigenous, tidak pernah
menyusun padang lamun monospesifik namun
tumbuh bersama-sama dengan jenis lamun yang
lain.
Karakteristik Morfologi Daun silindris dengan panjang mencapai 25 cm dan
lebar 2 mm.
Lokasi Tumbuh
Pantai Bama Taman Nasional Baluran Situbondo
Jawa Timur Indonesia
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Wide leaved species found in small numbers in the bay. A tropical species
found no further south. Grows in small areas of high productivity with a
number of other species creating a food source for dugongs.
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Posidonia oceanica
Posidonia form complete underwater ecosystems providing a crucial
sanctuary and feeding ground for sea turtles. They enable a unique habitat
to take form on the seafloor providing an array of nutrients and covering a
total surface area of roughly 20.000 square nautical miles. Posidonia
oceanica is a slow growing seagrass found at depths of 5 to 35 meters
along the Mediterranean coastline. It plays an important role in oxygenating
and clarifying coastal waters, provides a habitat for a rich diversity of plants
and animals, acts as a safe breeding-area for many species, and protects
beaches from erosion. These meadows also act as a "carbon sink"
absorbing carbon dioxide from the atmosphere. Due to the tough lignin that
covers its cells, it is only grazed by animals that have special microorganisms in their intestinal tract to help them digest it. One such animal is
the endangered green sea turtle, Chelonia mydas.
Posidonia thrive at depths of 3-5 metres all the way to 30-40 metres
in pristine conditions. They can be found on rocky as well as soft substrate,
in temperatures between 15 and 20 degrees Celsius, and at stable salinity
levels. Posidonia meadows are succeptible to even the slightest human
activity. Posidonia reproduce by vegetative reproduction (the breaking off of
fragments and replanting itself) , or through the dispersal of seeds. The
fruit of the plant is extremely light. This enables the fruit of the plant to
detatch itself and freely float to the surface where it will be taken away by
waves through the current. Eventually, the fruit will dissintegrate, allowing
the heavy seeds to sink to the seafloor and find a new home.
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Halophila spinulosa
Below depths of about 8 metres forms very dense stands of up to
800 shoots per square metre.
Fern like ; Leaves arranged in opposite pairs ; Erect shoot up to
15cm long ; Found at subtidal depths (>10m) .
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Halophila ovalis
Narrow leaved species. Can grow on the intertidal flats in sparse mixed
stands with Halodule uninervis and Halophila minor. These stands are the
preferred grazing area for dugongs. Grows rapidly.
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Oval shaped leaves in pairs
8 or more cross veins
No hairs on leaf surface
Preferred dugong food
Common early colonising species
Found from intertidal to subtidal depths
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Halophila minor
Narrow leaved species.
Mixed stands with H. ovalis and Halodule uninervis are preferred dugong
food source.
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Less than 8 pairs of cross veins
Small oval leaves occurring in pairs
Wedge-shaped leaf sheath
Found on shallow/intertidal sand flats
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Halophila decipiens
Has small translucent oval leaves.
Found in low densities in Shark Bay.
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Small oval leaf blade 1-2.5cm long
6-8 cross veins
Leaf hairs on both sides
Leaves usually longer than wider
Found at subtidal depths (>10m).
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Halodule uninervis
Apart from the 2 species above it is the only other species in the bay to
form monospecific stands eg at mouth of Wooramel delta, an important
summer feeding ground for dugongs. Rhizome of this species is rich in
starches. Can be found at high salinities of 62 parts per thousand but in
low numbers. Grows rapidly.
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Halodule pinifolia
Short leaved = (mean length range 49.70-57.43 mm, length range 40-80mm) .
Long leaved = (mean length range 83.91-102.52 mm, length range 60-166 mm).
Environment/Habitat : Inhabits the areas from the lower intertidal to the upper
subtidal zone with sandy and muddy bottoms in sheltered bays and coral reefs.
It has also been found in mangrove swamps. Commonly found in soft mud
together with Halophila ovalis and on compact mud together with Cymodocea
rotundata (den Hartog 1970).
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Halophila tricostata (HT)
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Erect shoots 8-18cm long
Leaves with 3 veins
2-3 leaves at each node
Leaves “whorl” around stem
Found at subtidal depths (>10m)
Endemic to Queensland, Australia
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Cymodocea serrulata
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Linear strap-like leaves, 5-9mm wide
Serrated leaf tip
Leaf sheath is broadly triangular with a narrow base
Leaf scars do not form a continuous ring around the stem
Found on shallow subtidal reef flats and sand banks
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Cymodocea rotundata
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Flat, strap-like leaves 2-4mm wide
Rounded, smooth leaf tip
Smooth rhizome
Scars from well developed leaf sheaths form a continuous ring around the
stem
Found on shallow reef flats .
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Thalassia hemprichii (TH)
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Short black bars of tannin cells in leaf blade
Thick rhizome with scars between shoots
Hooked/curved shaped leaves
Leaves 10-40cm long
Common on shallow reef flats.
Thalassodendron ciliatum (TC)
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Cluster of ribbon-like curved leaves at the end of an erect stem
Round, serrated leaf tip
Tough, woody rhizomes with scars from successive shoots
Very coiled, branched roots
Typically found in rocky areas with strong reef crests
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Thalassia testudinum
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Enhalus acoroides
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Very long ribbon-like leaves 30-150 cm long
Leaves with inrolled leaf margins
Thick rhizome with long black bristles and cord-like roots
Found on shallow/intertidal sand/mud banks (often adjacent to mangrove
forests)
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Zostera capricorni (ZC)
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Long strap-shaped leaves
5 longitudinal veins
Cross veins which form a mesh across leaf blade
Rounded leaf tip
Leaf grows straight from rhizome ie. no stem
Found on shallow and intertidal mud/sand flats
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Habitat Lamun atau yang lebih di kenal dengan kata seagrass
merupakan habitat pantai yang sangat unik, dengan di tumbuhi oleh lamun
(golongan macrophyte) yang dapat beradaptasi dengan kondisi pantai yang
labil, tumbuhan lamun memberikan amat sangat banyak fungsi ekologis
bagi organisma yang berasosiasi dengannya.
Seperti layaknya padang rumput, seagrass dapat menyebar dengan
perpanjangan ryzome (batang akar). Penyebaran seagrass terlihat sedikit
unik dengan pola penyebaran yang sangat tergantung pada topografi dasar
pantai, kandungan nutrient dasar perairan (substrate) dan beberapa faktor
fisik dan kimia lainnya. Kadang terlihat pola penyebaran yang tidak merata
dengan kepadatan yang relative rendah dan bahkan terdapat semacam
ruang-ruang kosong di tengah padang lamun yang tidak tertumbuhi oleh
lamun, kadang terlihat pola penyebaran yang berkelompokkelompok. Namun ada juga pola penyebaran yang merata tumbuh hampir
pada seluruh garis pantai landai dengan kepadatan yang sedang dan
bahkan tinggi. Berbeda dengan seaweed, yang umunnya sangat
memerlukan benda keras di dasar perairan sebagai susbtrat untuk melekat.
namun memang ada juga banyak yang tumbuh dan menyebar secara
alami dengan substrat dasar yang lunak.
Di pesisir pantai Indonesia ada tiga tipe ekosistem yang penting,
yakni terumbu karang, mangrove, dan padang lamun. Di antara ketiganya,
padang lamun paling sedikit dikenal. Kurangnya perhatian kepada padang
lamun, antara lain, disebabkan padang lamun sering disalahpahami
sebagai lingkungan yang tak ada gunanya, tak memberikan manfaat bagi
kehidupan manusia. Di kalangan akademisi pun masalah padang lamun
baru mulai banyak dibicarakan setelah tahun 2000.
Lamun
Lamun (seagrass) adalah tumbuhan berbunga yang telah
menyesuaikan diri hidup terbenam di dalam laut dangkal. Lamun berbeda
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dengan rumput laut (seaweed) yang dikenal juga sebagai makroalga.
Lamun berbunga (jantan dan betina) dan berbuah di dalam air. Produksi
serbuk sari dan penyerbukan sampai pembuahan semuanya terjadi dalam
medium air laut. Lamun mempunyai akar dan rimpang (rhizome) yang
mencengkeram dasar laut sehingga dapat membantu pertahanan pantai
dari gerusan ombak dan gelombang. Dari sekitar 60 jenis lamun yang
dikenal di dunia, Indonesia mempunyai sekitar 13 jenis.
kurrawa.gbrmpa.gov.au/.../1seagrasses.html
Suatu hamparan laut dangkal yang didominasi oleh tumbuhan
lamun dikenal sebagai padang lamun. Padang lamun dapat terdiri dari
vegetasi lamun jenis tunggal ataupun jenis campuran. Padang lamun
merupakan tempat berbagai jenis ikan berlindung, mencari makan, bertelur,
dan membesarkan anaknya. Ikan baronang, misalnya, adalah salah satu
jenis ikan yang hidup di padang lamun.
Amat banyak jenis biota laut lainnya hidup berasosiasi dengan
lamun, seperti teripang, bintang laut, bulu babi, kerang, udang, dan kepiting.
Duyung (Dugong dugon) adalah mamalia laut yang hidupnya amat
bergantung pada makanannya berupa lamun. Penyu hijau (Chelonia
mydas) juga dikenal sebagai pemakan lamun yang penting. Karena itu,
rusak atau hilangnya habitat padang lamun akan menimbulkan dampak
lingkungan yang luas.
Padang lamun sering dijumpai berdampingan atau tumpang tindih
dengan ekosistem mangrove dan terumbu karang. Bahkan, terdapat
interkoneksi antarketiganya. Karena fungsi lamun tak banyak dipahami,
banyak padang lamun yang rusak oleh berbagai aktivitas manusia. Luas
total padang lamun di Indonesia semula diperkirakan 30.000 kilometer
persegi, tetapi diperkirakan kini telah menyusut 30-40 persen.
Kerusakan ekosistem lamun, antara lain, karena reklamasi dan
pembangunan fisik di garis pantai, pencemaran, penangkapan ikan dengan
cara destruktif (bom, sianida, pukat dasar), dan tangkap lebih (over-fishing).
Pembangunan pelabuhan dan industri di Teluk Banten, misalnya, telah
melenyapkan ratusan hektar padang lamun. Tutupan lamun di Pulau Pari
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(DKI Jakarta) telah berkurang sekitar 25 persen dari tahun 1999 hingga
2004.
Mengingat ancaman terhadap padang lamun semakin meningkat,
akhir-akhir ini mulailah timbul perhatian untuk menyelamatkan padang
lamun. Undang-Undang Nomor 27 Tahun 2007 tentang Pengelolaan
Pesisir dan Pulau-pulau Kecil juga telah mengamanatkan perlunya
penyelamatan dan pengelolaan padang lamun sebagai bagian dari
pengelolaan terpadu ekosistem pesisir dan pulau-pulau kecil. Program
pengelolaan padang lamun berbasis masyarakat yang pertama di
Indonesia adalah Program Trismades (Trikora Seagrass Management
Demonstration Site) di pantai timur Pulau Bintan, Kepulauan Riau, yang
mendapat dukungan pendanaan dari Program Lingkungan Perserikatan
Bangsa-Bangsa (UNEP) dan baru dimulai tahun 2008.
”Blue Carbon”
Awal Oktober 2009, tiga badan PBB, yakni UNEP, FAO, dan
UNESCO, berkolaborasi meluncurkan laporan yang dikenal sebagai Blue
Carbon Report. Laporan ini menggarisbawahi peranan laut sebagai
pengikat karbon (blue carbon), sebagai tandingan terhadap peranan hutan
daratan (green carbon) yang selama ini sangat mendominasi wacana
dalam masalah pengikatan karbon dari atmosfer. Di seluruh laut terdapat
tumbuhan yang dapat menyerap karbon dari atmosfer lewat fotosintesis,
baik berupa plankton yang mikroskopis maupun yang berupa tumbuhan
yang hanya hidup di pantai seperti di hutan mangrove, padang lamun,
ataupun rawa payau (salt marsh). Meskipun tumbuhan pantai (mangrove,
padang lamun, dan rawa payau) luas totalnya kurang dari setengah persen
dari luas seluruh laut, ketiganya dapat mengunci lebih dari separuh karbon
laut ke sedimen dasar laut.
Keseluruhan tumbuhan mangrove, lamun, dan rawa payau dapat
mengikat 235-450 juta ton karbon per tahun, setara hampir setengah dari
emisi karbon lewat transportasi di seluruh dunia. Dengan demikian,
penyelamatan ekosistem padang lamun sangat penting, dan tidak kalah
strategis, dibandingkan dengan pengelolaan ekosistem terumbu karang
yang sudah mulai mendunia dengan Coral Triangle Initiative atau
ekosistem mangrove dengan Mangrove for the Future.
Ekosistem Lamun
Lamun (seagrass) merupakan satu-satunya tumbuhan berbunga
(Angiospermae) yang memiliki dan memiliki rhizoma, daun, dan akar sejati
yang hidup terendam di dalam laut beradaptasi secara penuh di perairan
yang salinitasnya cukup tinggi atau hidup terbenam di dalam air, beberapa
ahli juga mendefinisikan lamun (Seagrass) sebagai tumbuhan air berbunga,
hidup di dalam air laut, berpembuluh, berdaun, berimpang, berakar, serta
berbiak dengan biji dan tunas. Karena pola hidup lamun sering berupa
hamparan maka dikenal juga istilah padang lamun (Seagrass bed) yaitu
hamparan vegetasi lamun yang menutup suatu area pesisir/laut dangkal,
terbentuk dari satu jenis atau lebih dengan kerapatan padat atau jarang.
Lamun umumnya membentuk padang lamun yang luas di dasar laut yang
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masih dapat dijangkau oleh cahaya matahari yang memadai bagi pertumbuhannya. Lamun hidup di perairan yang dangkal dan jernih, dengan
sirkulasi air yang baik. Air yang bersirkulasi diperlukan untuk
menghantarkan zat-zat hara dan oksigen, serta mengangkut hasil
metabolisme lamun ke luar daerah padang lamun.
Hampir semua tipe substrat dapat ditumbuhi lamun, mulai dari
substrat berlumpur sampai berbatu. Namun padang lamun yang luas lebih
sering ditemukan di substrat lumpur-berpasir yang tebal antara hutan rawa
mangrove dan terumbu karang. Sedangkan sistem (organisasi) ekologi
padang lamun yang terdiri dari komponen biotik dan abiotik disebut
Ekosistem Lamun (Seagrass ecosystem).Habitat tempat hidup lamun
adalah perairan dangkal agak berpasir dan sering juga dijumpai di terumbu
karang.
Di seluruh dunia diperkirakan terdapat sebanyak 52 jenis lamun, di
mana di Indonesia ditemukan sekitar 15 jenis yang termasuk ke dalam 2
famili: (1) Hydrocharitaceae, dan (2) Potamogetonaceae. Jenis yang
membentuk komunitas padang lamun tunggal, antara lain: Thalassia
hemprichii, Enhalus acoroides, Halophila ovalis, Cymodocea serrulata, dan
Thallassodendron ciliatum. Padang lamun merupakan ekosistem yang
tinggi produktivitas organiknya, dengan keanekaragaman biota yang juga
cukup tinggi. Pada ekosistem ini hidup beraneka ragam biota laut (Gambar
17), seperti ikan, krustasea, moluska (Pinna sp., Lambis sp., Strombus sp.),
Ekinodermata (Holothuria sp., Synapta sp., Diadema sp., Archaster sp.,
Linckia sp.), dan cacing Polikaeta.
ian.umces.edu/.../displayimage-topn-0-790.html
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Lamun atau secara internasional dikenal sebagai seagrass
merupakan tumbuhan tingkat tinggi dan berbunga (Angiospermae) yang
sudah sepenuhnya menyesuaikan diri hidup terbenam di dalam
laut. Keberadaan bunga dan buah ini adalah faktor utama yang
membedakan lamun dengan jenis tumbuhan lainnya yang hidup terbenam
dalam laut lainnya, seperti rumput laut (seaweed). Hamparan lamun
sebagai ekosistem utama pada suatu kawasan pesisir disebut sebagai
padang lamun (seagrass bed). Pada ekosistem padang lamun berasosiasi
berbagai jenis biota laut yang bernilai penting dengan tingkat keragaman
yang sangat tinggi.
Padang lamun yang merupakan salah satu ekosistem di wilayah
pesisir memiliki keanekaragaman-hayati yang kaya dan merupakan
penyumbang nutrisi yang sangat potensial bagi perairan disekitarnya
mengingat produktivitasnya yang tinggi. Perannya sebagai pelindung
pantai, daerah asuhan bagi ikan, teripang, kuda laut dan udang, stabilisator
dan penangkap sedimen sangat penting bagi ekosistem lainnya seperti
ekosistem terumbu karang dan mangrove. Daun lamun yang lepas akan
mengendap di perairan sekitarnya dan dihanyutkan ke ekosistem atau
perairan lainnya. Daun lamun yang mengendap akan didekomposisi oleh
bakteri dan biota bentik pemakan serasah.
feww.wordpress.com/2009/06/
28
Padang lamun memiliki fungsi ekologis dan nilai ekonomis yang
sangat penting bagi manusia. Menurut Nybakken (1988), fungsi ekologis
padang lamun adalah: (1) sumber utama produktivitas primer, (2) sumber
makanan bagi organisme dalam bentuk detritus, (3) penstabil dasar
perairan dengan sistem perakarannya yang dapat menangkap sediment
(trapping sediment), (4) tempat berlindung bagi biota laut, (5) tempat
perkembangbiakan (spawning ground), pengasuhan (nursery ground),
serta sumber makanan (feeding ground) bagi biota-biota perairan laut, (6)
pelindung pantai dengan cara meredam arus, (7) penghasil oksigen dan
mereduksi CO2 di dasar perairan.
Nilai ekonomi dan ekologi padang lamun (manfaat ekonomi total),
terkait dengan biota yang hidupnya tergantung dengan ekosistem padang
lamun sebesar U$ 412.325 per ha per tahun atau 11,3 milyar rupiah per
hektar per tahun (Fortes, 1990). Terdapat hingga 360 spesies ikan (seperti
ikan baronang), 117 jenis makro-alga, 24 jenis moluska, 70 jenis krustasea,
dan 45 jenis ekinodermata (seperti teripang) yang hidupnya didukung oleh
ekosistem padang lamun di Indonesia. Disamping itu, padang lamun telah
dimanfaatkan secara langsung oleh manusia untuk memenuhi kebutuhan
hidupnya, seperti untuk makanan, pupuk, obat-obatan.
www.aims.gov.au/.../apnet-seagrasses01.html
They are called 'seagrass' because most have ribbon-like, grassy leaves,
but none is a true grass. There are many different kinds of seagrasses and
some do not look like grass at all. For example, they may have oval leaves.
Seagrasses have roots, stems and leaves. They also form tiny flowers,
fruits and seeds. Most seagrasses reproduce by pollination - the pollen is
transported to other plants by water.
The roots and horizontal stems (rhizomes), often buried in sand or mud,
anchor the grasses and absorb nutrients. Leaves, usually green, are
produced on vertical branches and also absorb nutrients. The stems and
leaves of seagrasses contain veins and air channels so they can carry fluid
and absorb gases. Seagrasses rely on light to convert carbon dioxide into
oxygen (photosynthesis). The oxygen is then available for use by other
living organisms.
29
SEAGRASSES AND NUTRIENTS:
Seagrasses: Why are they important?
Seagrass beds are of considerable ecological importance in coastal
and marine ecosystems where they play a significant role in the processes
and resources of nearshore coastal ecosystems. They are among the most
productive and dynamic elements of an aquatic ecosystem.
The growth and survival of seagrass communities is of major
importance to coastal waters as seagrasses are:
a. primary producers that contribute large quantities of fixed carbon
(the basis of all food chains) to coastal ecosystems;
b. important in stabilising bottom sediments because they slow
water movement which promotes sedimentation of particulate
matter;
c. part of the nutrient cycle in the aquatic system;
d. important in supplying shelter and refuge for adult and juvenile
animals and contributing large amounts of substrate for
encrusting animals and plants; and
e. essential food for dugongs (Dugong dugon) and green turtles
(Chelonia mydas).
Where do they grow in the Great Barrier Reef?
Seagrasses grow in shallow-water ecosystems, notably the inshore
lagoon of the Great Barrier Reef. The Great Barrier Reef lagoon is a largely
sheltered area and offers special protection to seagrass beds within the
reef itself and on the lee or landward side of reefs or embayments.
Surveys conducted of seagrasses between Cape York and Hervey
Bay show that they are most often found in areas that receive shelter from
the prevailing winds, such as in bays, behind northerly facing peninsulas,
behind islands, reefs and shoals, and on some reef platforms and fringing
reefs. The regional contribution of these seagrass beds to primary
production and as habitat for marine fauna is likely to be extremely
important.
The large majority of seagrasses found in the Great Barrier Reef
Region grow in the inshore lagoon in waters no deeper than 10 metres and
no greater than 10 kilometres from the coast (Lee Long et al. 1993; Larkum
et al. 1989). Large areas of deepwater seagrass (in waters of between 10
and 30 metres depth) have also recently been found in the Great Barrier
Reef. Seagrasses in close proximity to land are more likely to be affected
by material flowing from land and vulnerable to changes in coastal
processes. Recent studies of the factors contributing to seagrass decline
have shown that increased anthropogenic inputs to the coastal zone are
often linked to seagrass loss.
The species of seagrass found between Cape York and Hervey Bay
are common throughout northern Australia, including the Gulf of
Carpentaria and Torres Strait. Fourteen species have been recorded from
the seagrass habitats of north-eastern Australia (Larkum et al. 1989).
Tropical Australia supports well-developed seagrass communities and a
large proportion of all known seagrass species (> 22%). Tropical Australia
30
has a greater diversity of seagrass species than elsewhere in the tropical
Indo-West Pacific.
Seagrasses are an ecological group, not a taxonomic group, of
angiosperms (flowering plants), i.e. various seagrass families do not
necessary have to be closely related.
www.seagrasswatch.org/id_seagrass.html
Key environmental factors
The distribution and growth of seagrasses is regulated by a variety
of water quality factors such as temperature, salinity, nutrient availability,
substratum characteristics, turbidity and submarine irradiance. For example,
it is well known from overseas and temperate Australian studies that the
availability of nutrient resources affects the growth, distribution, morphology
and seasonal cycling of seagrass communities. In addition, seagrasses
depend on an adequate degree of water clarity to sustain productivity in
their submerged environment. Increased turbidity and sedimentation
reduce water clarity, which can affect the health and productivity of
seagrass communities.
Although natural events have been responsible for both large-scale
and local losses of seagrass habitat, recent evidence suggests that human
population expansion is now the most serious cause of seagrass habitat
loss. Increasing anthropogenic inputs to the coastal oceans are primarily
responsible for the enhanced nutrient input from the land and the worldwide
decline in sea grasses. Human activities that most affect seagrasses are
those that alter water quality or clarity. These activities can include nutrient
and sediment loading from agricultural run-off and sewage disposal,
31
dredging and filling, urban stormwater, upland development, and certain
fishing practices.
How do increased nutrients affect seagrass survival?
Nutrient loading is the primary factor responsible for both reduction
of water quality and stimulation of algal growth in coastal marine waters
(Short et al. 1996; Short and Wyllie-Echeverria 1996). Several studies
(Neverauskas 1987; Johansson and Lewis 1992; Phillips and Menez 1988;
Short et al. 1996) have related the decline of seagrass distribution to the
degree of nutrient loading within various catchments. Causes of seagrass
degradation include various forms of nutrient loading, including sewage
enrichment, enrichment of groundwater supplies and run-off from
agricultural lands. Loss of seagrasses in Cockburn Sound in Western
Australia is strongly correlated with the increase of discharge rich in plant
nutrients over a period of increasing industrial development.
Once impacted, seagrass colonisation and regrowth can be very
slow, or nonexistent, because of possible ongoing impacts and poor
dispersal capabilities of most seagrass species (Preen et al. 1995;
Dennison and Kirkman 1996). Loss of seagrasses can bring about a
change in the marine food chain with an accompanied shift in main primary
producers from benthic to planktonic and a reduction in leaf detritus
production. Continued seagrass loss can result in an ecosystem shift to a
lagoonal system dominated by high turbidity and algal growth or bare
sandy/silty substrate which may remain after the decline of the seagrass
beds. This change results in a considerable loss of diversity.
Seagrasses respond to changes at both a global and local scale but,
for the scope of this paper, only local or regional changes in the
environmental nutrient regime will be considered. At a regional scale,
increases in nutrient loading associated with eutrophication and changes in
light quality can adversely affect seagrass beds, resulting in either their
reduction or disappearance. Effects on seagrasses can be evident in four
different stages, these being structural impacts, diseases, reduced
photosynthesis (directly linked with reduced light) and ecosystem shifts.
Structural impacts
Under conditions of high nutrient loading, seagrasses take up
additional nutrients from the water. This can cause stress in the plant as
there is little intercellular tissue space available for nitrate accumulation. As
a consequence, high quantities of nitrate will be converted into ammonia,
either immediately, or following vascular storage (Brown 1993). Ammonia
production, in turn, requires the plant to divert substantial carbon resources
for immediate conversion into amino acids. After an extended period of
elevated nutrient uptake, the plant, even with abundant carbon available,
will not have the capacity to fix enough carbon to meet its total carbon
demand. Lack of carbon in the cellular tissue ultimately severely affects the
structural integrity of the seagrass, and results in the death of the plant.
Diseases
Physiological stresses imposed by nutrient supply imbalances may
also affect weakened plants by enhancing susceptibility to opportunistic
32
pathogens (i.e. wasting disease). This may be due to a decrease in the
production of anti-microbial compounds under conditions of enriched nitrate.
Reduced photosynthesis
A reduction in light reaching the seagrass can be brought about by
increased turbidity arising from living or non-living particulates in the water,
or increased shading by the deposition of silt on photosynthetic tissue
(Larkum et al. 1989). Elevated algal growth on the leaf surfaces or stems,
resulting from the uptake of additional nutrients by the epiphytic algae, can
also limit the amount of light reaching the underlying seagrasses. A
reduction in light reaching the seagrass chloroplast precludes effective
seagrass photosynthesis. Loss of structural integrity and increased
incidence of disease may be exacerbated by reduced photosynthesis.
Many documented cases of seagrass loss have followed
eutrophication of coastal embayments where enhanced nutrients have
resulted in a reduction in light penetration of the water column, or a
reduction in light reaching seagrass levels due to its interception by
epiphytic algae. In enhanced nutrient regimes of coastal areas, there is a
strong potential for interactions between water-column nitrate and
suspended sediment loading (or other sources of light reduction, such as
macroalgal overgrowth).
Ecosystem shifts
Nutrient enrichment can enhance the growth of macroscopic and
microscopic algae on seagrass leaf surfaces. Nutrients are required for
seagrass growth but the concentrations in tissues are lower than in
macroalgae. Due to differences in the carbon:nitrogen:phosphorus ratio,
macroalgae can dominate seagrasses under conditions of marked
eutrophication, both as epiphytes and as free-floating species which may
originate as attached epiphytes. Increased epiphytic growth results in
shading of seagrass leaves by up to 65%, which reduces the
photosynthetic rate and leaf densities.
Nutrient concentrations and seagrasses in Great Barrier Reef
waters
Eutrophication effects on seagrass beds are most severe in
sheltered habitats with reduced tidal flushing, where nutrient loadings are
both concentrated and frequent, and where temperatures fluctuate more
widely than in areas with greater water exchange. Shallow seagrass beds
found in the inshore Great Barrier Reef lagoon are exposed to potentially
higher nutrient inputs, infrequent flushing and temperature variability,
making them vulnerable to any changes in the nutrient and light regime.
In protected waters similar to those facing northward along the
Queensland coast, epiphytes and macroalgae respond so quickly to watercolumn enrichment that they can seasonally outgrow grazing pressure,
leading to severe light reduction and decline of the underlying seagrass.
Recent studies have shown that under conditions simulating poorly
flushed coastal habitats, even low levels of nitrate enrichment can promote
the decline of seagrasses. Growth and survival of seagrass species
33
significantly decreased at all enrichment levels, with the most rapid decline
occurring at the highest nitrate loading. Plant death was preceded by loss
of structural integrity in above-ground tissues.
Laboratory studies have found that the seagrass species Zostera
marina declined under low to moderate (3.5-7.0 mM) water-column nitrate
enrichment (Short et al. 1995; Burkholder et al. 1992). Long-term nitrate
additions cause severe seagrass decline, likely to be enhanced by
increasing temperatures and light reduction. Enriched levels of ammonia
(1.85-5.41 mM) and phosphate (0.22-0.50 mM) lead to a reduction in shoot
density and biomass of the seagrass population (Short et al. 1995).
Conversely, laboratory studies on Great Barrier Reef algae have
demonstrated increased algal growth associated with nutrient enrichment
(Schaeffelke and Klumpp 1997). Growth of epiphytic algae is also likely to
be promoted by excess water column nutrients. Small increases in water
column nutrient concentration can also result in increased growth of
seagrasses. This has occurred around Green Island following prolonged
discharge of untreated sewage.
On nearshore reefs, the water column nutrients are highly variable,
ranging from non-detectable to levels indicative of a eutrophication state
(Schaeffelke and Klumpp 1997; Bell 1992). Approximate ranges for (nonflood) inshore water quality concentrations have been measured between
non-detectable and 2 mM for dissolved inorganic nitrogen (predominantly
ammonia) and non-detectable and 0.2 mM for phosphate (Furnas et al.
1995; Furnas and Brodie 1997; Devlin et al. 1997; Schaeffelke and Klumpp
1997).
Nutrients and suspended particulate concentrations associated with
cyclones and floods are the highest that most Great Barrier Reef
communities are likely to be exposed to. Inshore seagrass communities are
episodically subjected to high dissolved nutrient and suspended loads more
typical of a eutrophic system. Water samples taken in flood plumes have
consistently recorded elevated ammonia (0.6-4.2 mM), nitrate-nitrite (0.2414.36 mM) and phosphate (0.13-1.98 mM) (Steven et al. 1997). In large
flood events, nutrient levels have remained high in the inshore lagoon for a
number of days to weeks.
34
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