Feeding Biology of Holothurians (Phylum:Echinodermata)

RESEARCH ARTICLE ISSN:2319-6955

FEEDING BIOLOGY OF HOLOTHURIANS (PHYLUM:ECHINODERMATA)

FROM THIRUMULLAVARAM ROCKY SHORE, SOUTH KERALA

DEEPA R. PILLAIAND PONNU L.

Department of Zoology, M.S.M. College, Kayamkulam, Kerala.

Correspondence to:

Abstract: Holothurians commonly called sea cucumbers are marine invertebrates, habitually found in the benthic areas and deep seas across the world. The present study aimed at thespecies level identification and feeding biology of sea cucumbers from the intertidal rocky shore of Thirumullavaram, south Kerala. The period of study was from February to June 2014. Identification is based on the microscopic examination of calcareous depositions-spicules. Two species identified in the present study are Holothuria cinerascens and Holothuria pardalis. Holothurians feed either by ingesting material on the surface of the substrate or by swallowing nutrient laiden sediments. The sediment ingested by the two deposit feeding holothurians comprise mainly inorganic compounds likesand, shell remains, coral debris and organic detritus like algae and other microbes.

Key words: Holothuria cinerascens, Holothuria pardalis, Thirumullavaram, sea cucumber, gut content analysis

INDRODUCTION

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RESEARCH ARTICLE ISSN:2319-6955

Holothurians or sea cucumbers are abundant and diverse group of echinoderms found in the nearly every marine environment, inhabiting tropical eulittoral coral reefs and adjacent sandy areas around the world (Pawson, 2007). They are soft bodied, sedentary animals usually avoiding areas exposed to high wave action and are found on all types of substrateslike algal beds, muddy sand and rocky intertidal shores. Their flexible body wall contains circular and longitudinal muscles and a skeleton made up of isolated calcite particles called spicules. These spicules represent a vestige of the normal endoskeleton and have paramount importance in the species level identification (Hyman, 1955).

Sea cucumbers are chiefly deposit feeders, feeding on tiny particles like algae, minute aquatic animals or waste materials. Deposit feeders are among the most important consumers of detritus on the ocean floor and play an important role in the removal, recycling and repackaging of organic matter(Jumars and Self, 1986). Holothurians are the convenient taxa to investigate ingestion and digestion in deposit feeders as they exhibit a wide range of deposit feeding strategies (Roberts, 2000). They are crucial to the marine food web as they clean the ocean floor from organic debris and filter it to create oxygen in the water and provide nutrients to the ocean floor(Hammond, 1979) and thus through their feeding activity they play important role as benthic nutrient recyclers (Uthicke, 2001).

Holothurians feed by either ingesting material on the surface of the substrate or by swallowing nutrient- laiden sediments. The sediment ingested by deposit feeding holothurians comprise mainly inorganic compounds like coral debris, shell remains; organic detritus such as seagrass, algae; microorganisms such as bacteria, protozoansand fecal pellets of other animals(Massin, 1982).There exist difference in feeding pattern between sea cucumbers and the difference in food selection criteria can lead to the segregation between different species living in same habitat (Massin and Doumen, 1986).

One of the simplest approaches to investigate holothurian feeding activity is to estimate their bulk diet, through the examination of the gut contents. Using light microscopy, the size and type of ingested particles can be ascertained for a variety of holothurian species (Hauksson, 1979;Levin, 1999). The sizes of particles and the way in which the animal feeds will have a significant effect on gut residence time. For shallow water tropical species it was found that the gut residence times can range from 3 to 18 hours(Roberts, 2000).

Holothurians take fine particles of sand and mud in to their mouth by means of tentacles and transfer them to the gut. Gut of sea cucumber includes the oesophagus, the mid gut and the hind gut.The selection of a particle for ingestion is determined by the adhesive forces and shape of the tentacle which takes particles in to the mouth (Massin, 1982). Large variations in tentacle morphology exist within holothurians and the type of tentacle influences the mode of feeding in each species of holothurians. Peltate tentacles facilitates ‘sweep strategy’ feeding whereas a ‘rake feeder’ is more likely to use branched digitate tentacles (Roberts and Moore, 1997).

The present study focused on the identification and feeding biologyof two species of sea cucumbers collected from Thirumullavaram rocky shore, Kerala.

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RESEARCH ARTICLE ISSN:2319-6955

MATERIALS AND METHODS

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Inorder to study feeding biology, two species of sea cucumbers were collected from Thirumullavaram rocky shore (08o 53’ N; 76o 32’ E) near Kollam. Collections were taken from February to June 2014. A total of 4 specimens belonging to two species were collected from the selected sites.

a)Collection and identification of sea cucumbers

Sea cucumbers were collected by hand picking during low tide with the help of local fishermen. They were transported to the laboratory in well oxygenated polytene bags and maintained at room temperature (280C-300C) in glass tanks containing sea water. For studying feeding behaviour, specimens were narcotized in menthol for eviscerating the gut. Morphometrical analysis was done and the length of the guts was measured. Photos were taken using digital camera. The dead specimens were preserved in 70% ethanol.

Identification was based on microscopic examination of the spicules by placing a small piece of skin on a slide and adding a few drops of NaOH or KOH. The slide was then dried and observed under binocular microscope at 45x magnification.Drawings were made using camera lucida. Identification was done based on the ‘Monograph of shallow water Indo west pacific echinoderms’(Clark and Rowe, 1971).

b)Gut content analysis

For gut content analysis, gut were taken from the two species separately and opened with a sterilized spatula. The gut contents were transferred to different petridishes. Each sediment sample was transferred in a vial and stored in 70% ethyl alcohol for preservation. Gut contents were dried and segregated into different size grades by passing through standard sieves of 125, 500, 700µ sizes. Each fraction was weighed and expressed as percent of total gut content weight.

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RESULT

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Collections were taken from Thirumullavaram from February to March 2014. Because of high tide and rough sea, sea cucumbers were not available in all months. Holothuria cinerascens were collected on the months of March and April. Holothuria pardalis was collected on the months of February and April. Using light microscopy, gut of each species were examined for the dominant particle type and size wise categorization was done with suitable sieves.

A) Identification

1. Holothuria cinerascens (Brant) (Class: Holothuroidea; Order: Aspidochirotida; Family: Holothuriidae) (Figure 1)

Dark brown coloured specimen. Length ranged from16 to 21cm and weight ranged from 14 to 16.8gm. Tentacle peltate type and 19 in number arranged in two rows. Its spiculeconsisted of finely spinose rods, and tables with a reduced disc.Calcareous ring well developed with 5 large radials and 5 short interradials.

1. Holothuria pardalis(Selenka, 1867) (Class: Holothuroidea; Order: Aspidochirotida; Family: Holothuriidae) (Figure 2)

Colour of the specimen chocolate brown with 8 to 10 dark spots arranged in two rows along the dorsal side. Length ranged from 9 to13cm and weight of the specimen ranged from 13.2 to 14g. Tentacle peltate and 20 in number. Body cylindrical and tapering at its ends. Spicules include clumsy tables with a low to moderate spire with a spiny disc and irregular shaped buttons with varying number of perforations.Calcareous ring consists of 5 large radials and 5 short interradials. Radials almost double the size of interradials.

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Figure 1: Holothuria cinerascens

Figure 2: Holothuria pardalis

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b)Gut content analysis (Table 1)

1.Holothuria cinerascens (Brant) (Figure 3 & 4): The gut length of H.cinerascens ranged from 19 to 25cm. The gut contentswere weighed, sieved and observed. The gut contents include sand, mud and shell debris. H. cinerascenshadtaken particles mostly of the size ranging between 125- 250µm. The average weight of gut contents indicated that the dominant particle type were sand (49%), followed by mud(31.5%), and shell debris(19%).

2.Holothuria pardalis(Selenka, 1867) (Figure 5 & 6): The length of the gut of H. pardalis ranged from 19 to 21cm. The gut content include mud, sand, shell debris and algal content. The average weight of gut contents showed that dominant gut particles were mud (38%),followed by sand (31%), shell debris(21%) and algal content (10%).Here the particles size ranged between 125- 500µm.

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RESEARCH ARTICLE ISSN:2319-6955

Table1 showing gut content analysis of the two Holothurians

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Figure 3 showing eviscerated gut of H.cinerascens

Figure 4 showing gut ofH.cinerascens

Figure 5 showing gut contents of H.cinerascens

Figure 6 showing gut of H. pardalis

Figure 7 showing gut contents of H.pardalis

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DISCUSSION

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Sea cucumbers by their deposit, detritus feeding behavior play very significant role in ecological sustainability. The study of the gut contents provide information on the feeding specifics of benthic animals; and has long since been accepted methodology (Theel, 1882).

In the present study two species of sea cucumbers were collected and identified as Holothuria cinerascens and H. pardalis and their gut content were analyzed. In the case of H. cinerascens, the major gut content was sand, followed by mud and shell debris. In the species H. pardalis, the dominant gut contentwas mud followed by sand, shell debris, and algae. Holothurians extract only organic matter out of the sand or mud taken together (Costelloe, 1984) and similar results were obtained for H. scabra (Basker, 1994).

Feeding behaviour depends on various physical and physiological factors. Holothurians remained active feeders during spawning seasons. The variability in the age, size, length of the animal and gut may influence food intake. In this study feeding activity of holothurians showed slight monthly variations. H. cinerascens was sluggish and showed little movement in its natural habitat whereasH. pardalis was found to be some more active and seemed to scratch algae from rocks. Thus their deposit feeding behavior promotes nutrient recycling and mixing of oxygen in the marine environment.

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ACKNOWLEDGEMENT

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The authors thank the Principal, M.S.M.College, Kayamkulam, Kerala, India for encouragement and providing facilities for the study. The authors are grateful to the University Grants Commission (UGC), India for funding the project (MRP(S)-1396/11-12/KLKE011/ UGC-SWRO).

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