Lamun atau sea grasses adalah satu-satunya kelompok tumbuh-tumbuhan berbunga yang terdapat di lngkungan laut dan hidup di perairan pantai yang dangkal. Seperti halnya rumput di darat, mereka mempunyai tunas berdaun yang tegak dan tangkai-tangkai yang merayap yang efektif untuk berkembang biak. Lamun berbunga, berbuah, dan menghasilkan biji. Mereka juga mempunyai akar dan sistem internal untuk mengangkut gas dan zat-zat hara. Terdapat 4 hal ciri-ciri lamun:
- Toleransi terhadap kadar garam lingkungan.
- Tumbuh pada perairan yang selamanya terendam.
- Mampu bertahan dan mengakar pada lahan dari hempasan ombak dan arus.
- Menghasilkan polinasi hydrophilous ( benang sari yang tahan terhadap kondisi perairan)
- (Hadi Endrawati, 2000)
Lamun (seagrass) adalah tumbuhan berbunga (angiospermae) yang berbiji satu (monokotil) dan mempunyai akar rimpang, daun, bunga dan buah. Jadi sangat berbeda dengan rumput laut (algae) (Wood et al. 1969; Thomlinson 1974; Askab 1999). Lamun dapat ditemukan di seluruh dunia kecuali di daerah kutub. Lebih dari 52 jenis lamun yang telah ditemukan. Di Indonesia hanya terdapat 7 genus dan sekitar 15 jenis yang termasuk ke dalam 2 famili yaitu : Hydrocharitacea ( 9 marga, 35 jenis ) dan Potamogetonaceae (3 marga, 15 jenis). Jenis yang membentuk komunitas padang lamun tunggal, antara lain : Thalassia hemprichii, Enhalus acoroides, Halophila ovalis, Cymodoceae serulata, dan Thallasiadendron ciliatum Dari beberpa jenis lamun, Thalasiadendron ciliatum mempunyai sebaran yang terbatas, sedangkan Halophila spinulosa tercatat di daerah Riau, Anyer, Baluran, Irian Jaya, Belitung (Nyabaken, 1992)
Secara ekologi, kebun lamun mempunyai beberapa fungsi penting di daerah pesisir. Lamun merupakan sumber utama produktivitas primer di perairan dangkal di seluruh dunia dan merupakan sumber makanan penting bagi banyak organisme (dalam bentuk detritus). Selanjutnya mereka berfungsi menstabilkan dasar-dasar lunak dimana kebanyakan spesies tumbuh, terutama dengan sisten akr yang padat dan saling menyilang. Penstabilan dasar olah akar ini sangat kuat dan mampu bertahan dalam topan badai sekalipun. Sebaliknya, sistem ini dapat melindungi banyak organisme. Jadi terdapat banyak hewan umum yang dijumpai di kebun lamun, tetapi tidak berhubungan dengan tingkatan makanan secara langsung. Kebun lamun berperan juga sebagi tempat pembesaran bagi banyak spesies yang menghabiskan waktu dewasanya dilingkungan lain. (Nyabaken, JW. 1992)
Menurut den Hartog (1977), rumput laut / lamun diseluruh dunia hanya mencakup sekitar 50 spesies. Ini adalah yang terkecil dibanding dengan kepentingan ekologinya. Kebanyakan spesies lamun mempunyai morfologi luar yang secara kasar hampir serupa. Mereka mempunyai daun-daun yang panjang, tipis, dan mirip pita yang mempunyai saluran-saluran air, serta bentuk pertumbuhannya monopodial. Tumbuhan ini tumbuh dari rizoma yang merambat. Jika dibandingkan dengan tumbuhan perairan tawar, jumlah spesies lamun lebih sedikit dan ragam morfologinya juga lebih sedikit. (Nyabaken, JW. 1992)
Ekosistem lamun merupakan salah satu ekosistem bahari yang produktif. ekosistem lamun perairan dangkal mempunyai fungsi antara lain:
a. Menstabilkan dan menahan sedimen–sedimen yang dibawa melalui.
b. Daun-daun memperlambat dan mengurangi arus dan gelombang serta mengembangkan sedimentasi.
c. Memberikan perlindungan terhadap hewan–hewan muda dan dewasa yang berkunjung ke padang lamun.
d. Daun–daun sangat membantu organisme-organisme epifit.
e. Mempunyai produktifitas dan pertumbuhan yang tinggi.
f. Menfiksasi karbon yang sebagian besar masuk ke dalam sistem daur rantai makanan ( Philip and Menez, 1988 )
Selanjutnya dikatakan Philips & Menez (1988), lamun juga sebagai komoditi yang sudah banyak dimanfaatkan oleh masyarakat baik secara tradisional maupuin secara modern. Secara tradisional lamun telah dimanfaatkan untuk :
1. Digunakan untuk kompos dan pupuk
2. Cerutu dan mainan anak-anak
3. Dianyam menjadi keranjang
4. Tumpukan untuk pematang
5. Mengisi kasur
6. Ada yang dimakan
7. Dibuat jaring ikan
Pada zaman modern ini, lamun telah dimanfaatkan untuk:
1. Penyaring limbah
2. Stabilizator pantai
3. Bahan untuk pabrik kertas
6. Sumber bahan kimia
Padang lamun merupakan habitat bagi beberapa organisme laut. Hewan yang hidup pada padang lamun ada berbagai penghuni tetap ada pula yang bersifat sebagai pengunjung. Hewan yang datang sebagai pengunjung biasanya untuk memijah ataumengasuh anaknya seperti ikan. Selain itu, ada pula hewan yang datang mencari makan seperti sapi laut (dugong-dugong) dan penyu (turtle) yang makan lamun Syriungodium isoetifolium dan Thalassia hemprichii (Nontji, 1987).
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( see drawing to the right). 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.
Where are seagrasses found?
Worldwide, there are about 12 major divisions, consisting of approximately 57 species of seagrass. They are mainly found in bays, estuaries and coastal waters from the mid-intertidal (shallow) region down to depths of 50 or 60 metres. Most species are found in shallow inshore areas.
Seagrasses inhabit all types of ground (substrates), from mud to rock. The most extensive seagrass beds occur on soft substrates like sand and mud. Seagrasses cover areas in coastal waters from tropical (hot) to temperate (cool) regions. The number of species is greater in the tropics than in the temperate zones. Only two species, Halophila ovalis and Syringodium isoetifolium , occur in both regions.
Over 30 species can be found within Australian waters. The most diverse seagrass communities are in the waters of north-eastern Queensland and are an important part of the flora in the Great Barrier Reef region.
How are seagrasses important to the marine ecosystem?
Seagrass communities are one of the most productive and dynamic ecosystems. They provide habitats and nursery grounds for many marine animals, and act as substrate stabilisers.
In northern Australia, seagrass meadows are important as they provide sheltered refuges and feeding areas for prawns and juvenile fish. In some coastal areas, entire fisheries may depend on the productivity of these seagrass beds.
The rhizomes and roots of the grasses bind sediments on the bottom, where nutrients are recycled by microorganisms back into the marine ecosystem. The leaves of the grasses slow water flow, allowing suspended material to settle on the bottom. This increases the amount of light reaching the seagrass bed and creates a calm habitat for many species.
Seagrass meadows are a major food source for a number of grazing animals in the Great Barrier Reef region. The dugong ( Dugongdugon ) and the green turtle ( Cheloniamydas ) mainly feed on seagrass. An adult green turtle eats about two kilograms of seagrass a day while an adult dugong eats about 28 kilograms a day.
What threatens seagrass?
A number of problems face the long-term survival and health of seagrass populations in our coastal zone.
Human pollution has contributed most to seagrass declines around the world. The greatest pollution threat to seagrass populations is from high levels of plant nutrients. High nutrient levels, often due to agricultural and urban run off, cause algae blooms that shade the seagrass. Reduction in light decreases seagrass growth and can kill whole populations.
Suspended sediments also reduce light. This sediment can come from land development run off and through drains. Boating activity may also stir up sediment, reducing light levels.
Other threats to seagrass include damage to the leaves, stems and roots by boat propellers, trawlers’ nets, and dredging.
Loss of seagrass habitats will mean losses in marine ecosystem productivity as well as extinction of species that depend on seagrass for survival.
Pernah mendengar ikan sidat? Makhluk laut yang berasal dari lautan dalam ini merupakan ikan yang memiliki tubuh menyerupai ular. Belut? Berbeda. Ini ikan sidat.
Di Jepang, ikan sidat cukup terkenal. Dagingnya dianggap lezat dan memiliki kandungan vitamin yang sangat tinggi. Sehingga, banyak restoran-restoran Jepang yang menjadikan sidat sebagai menu andalan, seperti Kabyaki dan Unadon.
Sementara di Indonesia, ikan sidat masih terdengar asing di telinga. Apalagi manfaat-manfaatnya. Bentuknya yang bulat dan memanjang seperti belut atau ular membuatnya tidak terlalu menarik bagi masyarakat Indonesia. Itu yang menyebabkan tingkat konsumsi sidat terbilang rendah.
Menurut Rohkmin Dahuri, Kketua umum Masyarakat Akuakultur Indonesia, selain dagingnya yang lezat, sidat juga memiliki harga yang fantastis di pasar luar negeri.
“Untuk sidat yang masih benih (Glass eel) harganya US$7, atau setara Rp70.000 per ekor. Sedangkan per kilogramnya yang terdiri dari 5.000 benih bisa mencapai Rp350 juta,” kata Rokmin, di acara Diskusi Peran Riset, Teknologi Budaya, dan Pemasaran Ikan Sidat di Kantor BPPT, Jakarta, Kamis 20 Juni 2013.
Di pasar luar negeri, harga ikan sidat dewasa mencapai Rp70 juta per kilogram, sementara di pasar Indonesia harganya Rp1,2 juta per kilogram.
“Harga yang luar biasa mahal itu yang membuat ikan sidat lebih banyak diekspor, baik dalam bentuk benih atau yang sudah dewasa,” kata Rokhmin.
Menurut Mantan Menteri Kelautan dan Perikanan itu, kegiatan ekspor dapat membahayakan, karena nilai tambahnya tidak ada di Indonesia. Kalau negara ini mau menjadi besar, seharusnya dapat melihat ikan sidat sebagai peluang.
“Saya lebih menginginkan ikan sidat menjadi komoditas unggulan. Kenapa? Karena kebutuhan ikan sidat di pasar di Indonesia cukup tinggi, terutama untuk restoran-restoran Jepang,” kata Rokhmin.
Saat ini, pembibitan ikan sidat masih sangat sulit dilakukan. Banyak peneliti Jepang yang sudah menelitinya, namun tidak berhasil.
Menurut Iwan Eka Setiawan, Peneliti Biologi Kelautan BPPT, pembibitan ikan sidat sebenarnya bisa dilakukan, tapi pertumbuhannya sangat lama. Berbeda dengan pertumbuhan ikan sidat di alam bebas.
“Saat ini, untuk mendapatkan bibit ikan sidat masih dengan cara menangkapnya di lautan. Tak hanya itu, proses pembesaran dari bibit menjadi ikan dewasa juga masih cukup sulit,” kata Iwan. (umi)
Oleh : Muhammad Chandrataruna, Tommy Adi Wibowo
Some chuckle at the name given to the lemon shark until they see one. This shark is yellow in color which is where the name derives from. They mainly stay close to the surface of the water. They also prefer water that is moderate or warm compared to the colder waters.
Lemon sharks are mainly found along the Southeastern coast in the United States. The Gulf of Mexico is also a prime location for them. They have been known to migrate to places including West Africa. You will notice them more in the summer months when they tend to migrate.
Interesting Facts about Lemon Sharks
Most people are very curious about lemon sharks due to their color. They are basically loners but they sometimes form small groups. They have been known to attack people from time to time. It is believed this is done out of fear and not aggression. There have only been 22 reported lemon shark attacks on humans with each person surviving.
The have a magnetic sensor in their nose that allows them to attract prey and to find others to mate with. They depend on this sense of smell because they have very poor eyesight. Without that sensor they would have a very hard time surviving.
The Food Source for Lemon Sharks
Lemon sharks feed on various types of fish that are found in the waters. Mainly they stick to small prey that aren’t able to put up much of a fight. When meat can’t be readily found the lemon shark will even end up feeding on mollusks and crustaceans. They don’t require a large volume of food due to their small size so they can go quite a while without feeding.
The Anatomy of a Lemon Shark
The lemon shark has one of the most peculiar colors of all the species. With a yellow color and white on the belly it is distinctive and won’t be mixed up with other species of sharks. They are a small species of sharks with the largest ones no more than 10 feet.
Like most sharks it has very sharp teeth but you will notice they are shaped differently. They are curved rather than straight up and down. This is to allow them to easily catch fish that are slippery and could otherwise get away.
Reproduction for a Lemon Shark
The mating of lemon sharks has been closely observed. The males and females will travel very long distances in order to find someone to mate with. Even if there are others in the area they tend to mate with those from a distance. Researchers aren’t sure what this means but they believe it has to do with not breeding with closely related males and females.
The lemon shark gives live birth to its young in the water. They may have a litter with four to about fourteen pups at a time. The females will migrate to very shallow waters before the birth occurs. This way the pups will have a good chance of surviving. The mother will leave them as soon as they are born to care for themselves.
What does the Future hold for the Lemon Shark?
Conservation status: Near Threatened
The lemon shark seems to do quite well on its own so there aren’t any concerns about its future. There has been a drop in numbers over recent years though and it is believed to be due to the use of the waters they once lived in for other purposes.
Some people believe they are in danger due to the number of them in captivity. However, researchers have found that the lemon shark does well in captivity so they are able to observe their behaviors and abilities. It has allowed them to learn a great deal about sharks in general.
Facts about Basking Sharks
This particular shark is found in locations throughout the world. They prefer to live in warmer water temperatures though. They can be found close to land so people do see them on a regular basis in Hawaii and other areas. Where you will see them depends on the time of the year. They migrate both for reproduction and to be able to take advantage of the warmer climates at various times of the year.
Facts about Basking Sharks
The basking shark gets its name due to being slow moving and enjoying time basking in the sun. It is strange to researchers to see such a large shark so close to the surface though. The basking shark is the second largest shark found in the world. They do move to deeper water in the winter months though.
Sometimes the basking shark is seen jumping out of the water. It is an amazing sight to see due to the sheer size of them. Researchers believe this is done in an effort to remove as many parasites from the body as possible.
It has an extremely large liver, bigger than most species of sharks. The liver is believed to be ¼ of the overall body weight. This liver not only stores oil to help reduce the need to feed but it allows the basking shark to have plenty of energy all the time.
They are one of the few species of sharks that form groups as most sharks are loners. The group may only have a few members or it can have up to 100. The larger sized groups are very rarely found though.
Food Basking Sharks Eat
In addition to basking in the sun, this shark also tends to feed close to the surface as well. They are referred to as a filter feeder which means they move along the water with their mouth open. Their body filters out the water and they are able to consume what they find in it. A great deal of cleaning up the waters is taken care of by the basking shark in this manner. Various types of debris are completely eliminated from it when they are present.
Anatomy of Basking Sharks
Basking sharks are very big indeed. They can end up being up to 5.2 tonnes and 30 feet long. Even so, the design of their body allows them to easily get around in the water. They are very similar in style to the great white so many people panic when they see them. There are some significant differences though to tell them apart.
First, the basking shark has an extremely wide jaw. They also have large gill slits found at the back of their head. They also have small eyes while they great white has huge eyes. The basking shark also has as distinct nose that has a hook to it.
The skin of a basking shark is covered in placoid scales. You may notice pits and what resembles scars in it as well.
Reproduction of Basking Sharks
Researchers have concluded that only the right ovary of the female basking sharks allow for reproduction. This is a characteristic that hasn’t been discovered in any other species of shark. The females seek out shallow water in a warm area in order to give birth. They may migrate in order to achieve this.
What is the Future going to be like for the Basking Shark?
Conservation status: Vulnerable
The future is quite grim at the point for the basking shark. It is on the brink of extinction at this time. They have been hunted fiercely to keep up with the demand out there in the market for various products. They also have been known to be eaten by the aggressive tiger shark. As a result the basking shark is protected from hunting in certain locations.
Facts about Megamouth Sharks
The megamouth shark is one you won’t readily see when you are in the water. It is rarely seen and it has only been in the past 30 years that it has even been recognized as a species of shark. The first one was spotted around Hawaii. They have also been spotted around Japan in recent years. Other sightings have taken place in the Pacific, Atlantic, and Indian oceans though so they are out there.
Since they are so rarely seen it isn’t uncommon for thrill seekers to do their best to find them. They know pictures of them as well as videos will be worth a great deal of money to researchers. There isn’t any information relating to how they interact with humans though so you need to be careful.
Facts about the Megamouth Shark
The megamouth shark is considered to be one of the most rare forms of sharks out there. They aren’t often seen by people and that can lead one to wonder if they have decent numbers or not. Only 54 of them have been seen and documented with only 3 of them captured on film.
They weren’t discovered until 1975 when a navy ship accidentally found one caught up in their anchor. Yet it wasn’t until 1983 that it was proven to actually exist. In fact, since the early sighting it was rumored to be just a hoax by the military in an effort to gain attention.
Meals for a Megamouth Shark
This is one of the three types of sharks that are filter feeders. They have uniquely designed jaws and gills for it. The water and anything in it is taken into the mouth. Then it is filtered out by grates around the gills. They water is pushed back out with the various debris found in it consumed.
Filter feeders help to keep the water clean for all aquatic life. There also never seems to be a lack of food available for such sharks. They really enjoy it though when they are able to get some jellyfish or plankton in there too. In fact they will likely surf areas known for such creatures first so they can get the food source they really want before they take what they can get.
Anatomy of Megamouth Sharks
One of the most distinct features of the megamouth shark is the head. It is many times larger than other species. It doesn’t seem to be in proportion to the rest of the body either. It also has lips that are different from anything you have seen before. They help with the process of filter feeding.
There isn’t very many pictures of the megamouth shark though so being able to readily identify other characteristics of it are very difficult. They do have a small dorsal fin and a slightly tipped tail though to help with balance as they move in the water. They are believed to be brownish in color. Based on what has been seen though they are believed to be from 13 to 16 feet in length. They are also believed to get up to 2,700 pounds.
Reproduction of Megamouth Sharks
There isn’t very much information known about the reproduction of the megamouth shark. What is known is that the females carry eggs inside of them with the pups until they are ready to hatch. The estimated number of pups per litter isn’t known.
The Future of Megamouth Sharks
Conservation status: Data deficient
The future of the megamouth shark remains mystifying. Since we don’t really know how many of them exist it is extremely difficult to calculate how many of them there are. Scientists believe they have healthy numbers though and that they are quite versatile so they can easily survive. More research has to be done but finding these sharks can prove to be difficult.