Common Planktonic Organisms Of  Indian Coastal Waters

Since the marine zooplankton form the most important part of food of marine organisms and fish and the abundance of fishery in the locality depend largely on the availability of marine zooplanktons in coastal areas of the region, the common zooplanktonic organisms of Indian waters are given below.

Copepods which are very small crustaceans form the most important element in the zooplankton and consists of many hundred species. It forms a major group constituting nearly 50 per cent of the zooplankton in the sea. The more common planktonic copepods of Indian coastal waters are given below:

Sub order: Calanoida

1. Paired compound eyes never preset …………2

2. Second antennae and mouth parts

present, developmental stages usually free swimming; adults free swimming or ectoparasitic only …………3

3. Body not depressed land habits not

ectoparasitic except in very rare cases; metasomes ends behind the segment of the 4^th or 5^th pair of legs; sternal fork not present ………… 4

4. Urosome includes genital and abdominal segments

only;first antennae of the male, if geniculate, geniculate on one side only, commonly the right side ………… Calanoida

5. Body usually cylindrical, the metasome passing into the

urosome without abrupt change in width; basal segment of the fifth legs usually showing an inner expansion; males distinguished from the females in all cases by the geniculation of the first antennae; egg sacs usually unpaired, carried underneath …………Harpacticoida

6. Body usually depressed with the metasome much wider than the urosome; basal segment of the fifth legs without an inner expansion;geniculation of the first antennae of the male is usual but not invariable egg sacs paired, carried laterally or subdorsally ………… Cyclopoida

The members of the above three suborders are the more common species around Indian coastal waters. A few of them are mentioned below:

Sub order: Calanoida

Family – Calanidae

a) Calanus tenuicornis , b) Nanrocalanus minor,

c) Canthocalanus pauper, d) Undinula vulgaris,

e) Undinula darwini

Family---Eucalanidae

a) Rhincalanus cornutus b) Rhincalanus nasutus

c) Eucalanus elongatus d) Eucalanus craosus

Family -- Pseudocalanidae

a) Calocalanus pavo

Family --- Paracalanidae

a) Paracalanus parvus, b) Paracalanus aculeatus

c) Acrocalanus gibber, d) Acrocalanus gracilis

Family ---Euchaetidae

a) Euchaeta concinna, b) Euchaeta marina

Family ---Scolecithricidae

a) Scolecithrix danae

Family --- Centropagidae

a) Centropages orsinii, b) Centropages furcatus,

c) Isias tropica

Family ---Pseudodiaptomidae

a) Pseudodiaptomus aurivilli, b) P.serricandatus

c) P.annandalei

Family ---Temoridae

a) Temora turbinata, b) T.stylifera

c) T.discandata

Family ---Lucicutiidae

a) Lucicutia flavicornis

Family ---Arietellidae

a) Metacalanus aurivilli

Family ---Candaciidae

a) Candacia discandata, b) C.bradyi

c) C.pachydactyla

Family ---Potenllidae

a) Calanopia elliptica, b) C.aurivilli, c) C.minor,

d) Labidocera acuta, e) L.pinctata, f) L.minuta

g) Pontella secruifer, h) P.spinipes, i) Pohtellopsis

derdmani, j) Potellina plumata

Family ---Acartidae

a) Acartia spinciauda, b) Acartiella sewelli

Family ---Tortaniae

a) Tortanus barbatus, b) T.gracillis

Sub. Order : Harpacticoida

Family –Longipediidae

a) Longipedia weberi, b) L.coronata

Family—Ectinosmidae

a) Microsetella norvegica b) M.rosea

Family ---Macro—setellidae

a) Mafcrosetella gracilis b) M.oculata,

c) Miracia efferata

Family –Clytemnestridae

a) Clytemnestra scutellata, b) C.rostrata

Family –Tachididae

a) Enterpica acutiforons

Family—Metidae

a) Metis jonseeaumei

Sub. Order: Cyclopoida

Family –Oithonidae

a) Oithona spinirostris, b) O.plumifera

Family –Oucaeidae

a) Oncaea venusta b) O.conifera

Family –Corycaeidae

a) Corrycaeus speciosus b) Corycella gibbula

c) Copilia vitrea

Family –Sapphirindae

a) Sapphirina ovatolanceolata

Family –Bomolochidae

a) Bomolochus species

The planktonic form consists of three genera namely,(a) Sagitta, b) Petrosagitta and c) Krohnitta of which the first one is the commonest form around the coastal waters of India.

It is one of the three genera of the phylum chaetognatha, which are commonly known as "arrowworm" due to the characteristic shape of its body. It is a holoplanktonic animal. The body is divided into head, trunk and tail. They are hermaphrodite and feed on other zoo and phyto planktonic organisms. Some species of sagitta are considered as biological indicators of water movements.

Phylum-Annelida (Polychaets)

This is one of the few adult planktonic polychaets of the phylum Annelida. The body is flattened to help a pelagic planktonic life. The head is provided with a pair of long tentacles. The parapodia are well developed throughout the body. They form the food of plankton feeding fishes at times.

The marine crabs are divided into three main groups:

i. Auomura --- Without well developed claws

ii. Brachyura --- With well developed claws

iii. Porcellanid -- Between the above two groups.

All of them are demersal and benthic in habit in their adult stage. But in their larval stages they are planktonic in form and form the food of fishes. The larval forms are:

1. Zoea of crab

The zoea of crab is easily recognised by the two long cephalic spines. It has paired stalked eyes a large cephalothorax and a narrow abdomen. The abdominal appendages are not developed. The zoea after a series of moults develops into characteristic megalopa larvae of crabs.

2. Megalopa of crab

In this stage the long spines of the zoea disappears and the carapace, thoracic limbs and abdomen are more crab like (the abdomen remains extended unlike the adult). Megalopa sinks to the bottom and finally tucks in relatively a small abdomen under the cephalothorax to become a young crab which lives at the bottom of the sea.

The mud crabs of the Indo-Pacific region belong to more than one species of the genus Scylla, of which the species serrata constitute the important commercial and recreational fisheries.

In Andaman sea 53% of the mud crab stocks consisted of the size group varying from the 9-11 cm., 22% from 11-13 cm, 23% less than 9 cm, in length and 2% consisted of a size group larger than 13 cm. Proportion of male and female catches vary in different seasons, male crabs are harvested more in October to January, while females are abundant in February to April. Females attain sexual maturity with 11 cm. carapace width. Reproduction is continuous through out the year with highest gonadal growth in October-December; and the matured females migrate for spawning in October to February from estuaries with abundant growth of mangroves with the influence of freshwater entering the area during rains. Also matured female crabs in Andaman sea migrate to off-shore waters for spawing.

Mud crabs are nocturnal feeder for the natural food, chiefly being molluscs and crustaceans.

In captivity mud crabs become cannibalistic eating other crabs, specially newly moulted ones. Indirect cannibalism is observed from megalopa stage onward, causing serious problem in crab culture. The fecundity of the crab is 1-7 million eggs per spawning. The incubation period is 12 days at 27⁰ c and 32 ppt salinity. Metamorphosis into megalopa and crab stage take place in 30 to 37 days respectively after spawning. To reach adult stage, the crab would pass through 15 to 17 post-larval moults, which are divided into 4 phases—the larvae, the juveniles from 28 to 80 mm., the sub adult from 70 to 150 mm and adult with carapace length greater than 150 mm. Mud crab exhibited (I) a free ranging movement and an offshore migration by females. Crabs in narrow creeks show limited movement.

Mud crabs are abundantly found in coastal rivers, lagoons, around inshore islands and in brackish water and mangrove vegetation area. The species also occur in the mud-flats of the inter tidal zone, mostly in the littoral and part of supra littoral zone upto long range saline zone from the interior brackish water to the Oceanic waters. They prefer mangrove swamp as habitat and found to tolerate high salinity fluctuation, the most congenial range being 10-15 ppt. They prefer burrows in the mud to survive. 80% of the catches from burrows are males. The burrows have a depth of 1-2 m. from the surface, with an opening of 8-16 cm.

There are various types of gears used to catch the crabs. They are gill net, lift net, baby trawl, beach seine, fish pot, push net, cast net, fype net, traps and spear. The harvested crabs are sold within 2-3 days of capture. Sizes below 200 gm.males and 150 gm.females are rejected for export and are sold in the local market. Exports are made to Singapore, Hongkong and to other South East Asian Countries.

Mud flat and mangrove belt along Indonesian coast, covering 3 million ha.are utilised for crab farming

Crabs raised in 10-12 ppt salinity grow faster than in waters of 0-2 ppt, 20-22 ppt and 30-32 ppt saline waters. Mortality is highest in 0-2 ppt saline waters. The male crab grow faster (1.3 g/day) than female crabs (0.9 g/day) during culture. Mortality is highest in 0-2 ppt saline waters.

Highest return on investment, returns on equity and shortest pay back period are obtained from a stocking density of 5000/ha.

In India an average monthly growth of 9 mm/10g in laboratory tanks, 11 mm/19 g.in cages and 14 mm/29g. in ponds with 74% survival and laboratory tanks, 86% in cages and 28% in pond trials are obtained. The estimated production in 494 to 600 kg/ha in mono culture and 690 kg/ha in polyculture trials with fish. Trash fish and shrimp head are well accepted as feed by crabs with food conversion ratio (FCR) of 1:21:1 on dry weight basis and 6:03:1 on wet weight of trash fish and shrimp heads.

Morphometric measurements are used as an index for estimating yield of meat in mud crab. The edible portion of meat in mud crab is between 29-36% in respect of the crab body and 32-42% in respect of the claws and legs. The weight of shell is estimated of 22-24% of the body and 36-38% of claws and legs.

Crab meat has high protein content with high quality free amino-acids. In crabs carrying eggs, these values are less.

Mud crabs are very hardy and should survive without water for several days if kept moist. This adaptation has an advantage for its marketing in live condition even for export.

During winter the crabs migrate of offshore waters for breeding. Peak harvesting season is between mid to late monsoon (June-August). For capturing the crabs fishermen use indigenous crafts and gears. Night catch is always higher than the day catch; also new moon catch is better than full moon catch. The weight of same size crabs caught during new moon is relatively higher than that caught during full moon period.

The urochorda order having a single family, the appendicularidae, consists a group of planktonic forms suits as Olikoplura. They resemble larval tunicates. Olikopleura has a definite head, a long tail and a series of ganglia in the tail portion of urochorda. The animal is able to secrete a ‘house’ whose functions are filter feeding and locomotion. These house is frequently discarded and a new one secreted. It is hermaphrodite and forms a food item of many plankton feeding fish.

The most commonly encountered adult molluscan planktons are the Pteropods. In Pteropods the foot is produced into two large fins for locomotion. The shell is thin and delicate and sometimes absent. Pteropods often occurs in vast swarms to the point of discolouring many spermoides of ocean surfaces. Some of them are eaten by whales and fishes.

The lucifer is the only genus of the order Decapoda, that is highly modified for a planktonic life throughout the life. They are characterised by a long cephalothorax and a narrow abdomen. The eggs hatch out into the nauplius larvae, which develop into protozoa, zoea etc. before attending the adult characters. Lucifer is a very common elements in the marine plankton and is concerned by many fishes.

The medusae are the sexual forms in the life history of hydrozoean coelenterates. They have a characteristic umbrella, tentacles, and a mouth at the end of a manubrium. They are free swimming form and develops either to a male or female gonads.

These are polymorphic floating coelenterate. The colony consists of specialized individuals performing different functions. Thus they have swimming bells for locomotion.

As feelers gastrozoids for feeding and gonozoids for reproduction.

Larva of eels. Planktonic leaf like and glassy. When first discovered the leptocephalus was thought to be a new species of fish. They feed on plankton unlike adult eels, which are carnivorous in habit. The leptocephalus metamorphoses into elver which finally acquire the adult characters.

Salpids come under the sub phylum Urochoradata (Tunicata) of the phylum chordata, when the notochord is restricted to the tail region of the larvae and disappears in the adult due to retrogressive metamorphosis. Salpids are characterised by a barrel shaped body and circular muscle bands. There are two distinct forms, the sexual and asexual, the two alternating the life history. The sexual forms are hermaphrodites. Salpids form long chain of colonies. Some salpids are indicators of water movement. Pomfrets feed on salpids.

Ctenophora is a class of the phylum Coelentrata, holoplankton. Unlike other coelentrates, colony formation is unknown in ctenophores. A modified medusa with stinging cells modifies into lasso cells, by the help of which, they catch the pray. Provision of ctens with cilia in the form of comb help the animal to swim. They are hermaphrodites. Comb like structures arranged in eight meridional rows.

Stomatopods

It has two stages of life cycles (I) Ericthus larva, which are planktonic and (II) Alima larva, which are pelagic. Adults are pelagic and make an important part of nekton. Most common genus is Squilla, also known as, Mantes shrimp.

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