Marine Ecology

Ecology of Some Benthic Cnidarians Inhabiting Marine Environment in Egypt.

 

Dr. Fayez A. M. Shoukr

 

Professor of marine Invertebrates, Zoology Department, Faculty of Science,

Tanta University, Tanta 31527,Egypt.

 

Shoukr, F. A. 2004. Ecology of some benthic cnidarians inhabiting marine environment in Egypt. Electronic internet document available at http://www.marine.tanta.8m.net/ Published by the author, web page established December, 2004.

Key words: Cnidaria, Sea Anemones, Habitats, Ecological associations ,Symbioses,

Commensalism.

ABSTRACT: Cnidarians are worldwide in distribution and common in the Egyptian fauna in the Red Sea, Suez Canal and Mediterranean Sea as well as in some Lakes such as Lake Manzalah and Lake Qarun. They occupy different ecological habitats among benthos of the coral reefs, marine fouling and intertidal zone of rocky, sandy and muddy shores. Swimming behavior of some benthic cnidarians e.g. sea anemones is characteristic for some species e.g. Boloceroides hermaphroditica from Suez Canal and Telmatactis forskaii from Lake-Manzalah. This swimming habit of benthic cnidarians performs to escape from predation & disturbance or as avoidance reaction from an ecological stress as the strong illumination. The anemones swim by means of the tentacles and body column or floating using a gas bubble held within folds of the pedal disk as in the swimming anemone of Lake Manzalah.

The cnidarian benthic anemones are ecologically important animals for their beneficial relationships with other marine organisms like dinoflagellate protists (zooxanthellae), clownfishes, hermit crabs as well as harmful relationships with parasitic arthropods, nudibranchs and sea stars. Symbiotic dinoflagellates affect the ecology of their anemone host e.g. Anemonia sulcata. They contribute to their nutrition and oxygen supply, thus, the anemones flourish and attain full expansion in sun light with high activity. The endosymbiont of the anemone Anemonia sulcata is recognized as Symbiodinium microadriaticum using the transmission and scanning electron microscopy. This represents a first record for the Egyptian fauna.

The anemonefish commensal with the host anemone Entacmaea quadricolor and live happily among their stinging tentacles seeking for protection from predators. The anemone fish is an active hunter for its anemone host with small sharing of food. Furthermore, the ecological triangle of the symbiotic relationship between some sea anemones, hermit crabs and gastropod shells has yielded valuable information on their role and importance in the ecosystem. The anemone protects the hermit crab from the attacks of molluscan cephalopod predators. For the anemones, the nutritional gains obtained from movement with the anomurans are thought to be significant.

INTRODUCTION

The ecological associations between benthic sea anemones and different organisms have been extensively studied in different countries of the world. These associations may be beneficial and include the mutualism (symbiosis) with dinoflagellate protists as well as the commensalism with clownfishes, hermit crabs and shrimps. The harmful associations include the parasitism by some arthropods e.g. copepods, pycnogonids (sea spiders) and barnacles as well as the predation from their enemies such as molluscan undibranchs, sea stars and fishes. Comprehensive reports on the ecological relationships of sea anemones have been published by various authors such as Gohar, 1948; Davenport and Norris, 1958; Ross, 1960; Vader, 1970; Ghobashy et al., 1979; Palincsar et al., 1988; Mebs, 1994; Fautin et al., 1995; Costanzo et al., 1996; Shoukr, 1997 and Engebretson & Muller-Parker, 1999.

The recent interesting association is the cropping of sea anemone tentacles by a symbiotic barnacle (Yusa & Yamato, 1999). Other ecological studies focussed on the effects of ultraviolet (UV) radiation, social organization and aggression, in sea anemones e.g. Anthopleura elegantissima (Brandt) (Ayre and Grosbery, 1995, 1996 and Westholt et al., 1999). Furthermore, the association between sea anemones and other macrobenthos were studied seasonally by diving and indicated the abundance of some amphipod crustaceans, pycnogonids, nematodes and cirratulid polychaetes (Excoffon et al., 1999).

The primary objectives are to identify: 1-the habitats and ecological distribution of sea anemones especially in the Egyptian fauna. 2- the swimming behavior of some benthic anemones and their ecological significance. 3- the ecological significance of beneficial symbiotic associations between benthic sea anemones and other organisms through mutualism (symbiosis) with dinoflagellate protists and commensalism with clownfishes and hermit crabs. 4-the ecological significance of harmful associations to benthic sea anemones through parasitism by the arthropods and predation by the nudibranchs and starfishes.

Ecology of Benthic Cnidarians (Sea Anemones)

1. Habitats and ecological distribution:

Benthic sea anemones are world wide in distribution and usually inhabit the marine environment. They occur almost from pole to pole, reaching their elaborate development in the warmer seas. None of the sea anemones are found in fresh water habitats. However, few species are able to colonize brackish areas. The sea anemone Nematostella vectensis Stephenson is widely distributed in estuaries, bays and marshes in North America (Hand and Uhlinger, 1994). Also, the sea anemone Actinia bermudensis McMurrich occurs in both marine and estuarine habitats from Florida, USA (Monteiro et al., 1998). Some anemones are particularly interesting, since they apparently wandered from continent to continent on ships bottom. e.g. the fouling anemones.

Several sea anemones such as Actinia equina L. and Anemonia sulcata (Pennant) form a group of some ecological significance, since they are peculiarly characteristic of the intertidal zone and occur in great numbers in rocky shores of many parts of the world (Larkman & Carter, 1980). Other anemones such as Phelliactis hertwigi and P.robusta are reported in the deep-sea floor in the northeast Atlantic ocean and extended deeper to about 2173 m (Van – Praet et al., 1990).

There is an interesting correlation between some anemones (e.g. Anemonia sulcata) and their symbiotic algae (dinoflagellate protists). The symbionts release oxygen, during the process of photosynthesis in sunlight. Consequently, the anemones flourish best in well lighted habitats, and prefer these, both in aquarium and in the wild (Ghobashy et al., 1979). Other studies on habitats of sea anemones reported that some species tend to cover themselves with broken molluscan shells or corals, sand grains, gravel and any available foreign matter. The latter attached to the column of anemones by means of adhesive verrucae. The anemone species which have this habit are Bunodactis rubripunctata (Grube) and Antheopsis crispus (Ehrenberg) (Shoukr, 1984).

Some sea anemones e.g. Anemonia sulcata and Anthopleura elegantissima characterized by the presence of marginal spherules (acrorhagi) on the upper column. The acrorhagus has specific types of large nematocysts used for aggression. In these anemones, fighting ability appears to be an important determinant of the outcomes of interclonal competition for space (Ayre and Grosberg, 1996).

It is worthy to mention that anemones are widely distributed throughout the Egyptian marine water in Suez Canal, Red sea and Mediterranean sea (Carlgren, 1927 & 1949 and Schmidt, 1972). It seems clear that sea anemones prefer certain type of habitats and substrates in different locations in Egypt .

The anemones Entacmaea quadricolor (Rueppell & Leuckart), Antheopsis crispus (Ehrenberg) and Anthopleura stellula (Ehrenberg), are most obvious in the coral reefs of the Red sea at Al-Ghardaqa. These anemones are common inhabitants of the fringing and barrier coral reefs as well as the intertidal zone. They are extremely abundant along the reef-flat among a wide variety of benthic invertebrates including fleshy soft corals e.g. Sarcophyton, Dendronephthya, Heteroxenia and Xenia; echinoderms as the long spined sea-urchin Diadema setosum and the large tough black sea cucumber Holothuria marmorata as well as the hermatypic corals Acropora, Coeloria and Favia. Branched colonies of the living elk-horn coral Acropora frequently harbor large individuals of the sea anemone Entacmaea quadricolor. Other anemones are firmly attached within coral crevices on sand reefs. The common sea anemones Entacmaea quadricolor show the occurrence of two forms differing in habitats. The first form is large, reaches to 120 mm at base diameter, solitary, hole dwelling and often deeper water living as that obtained from the barrier coral reefs of Shab Abou Sadaf. The second form is smaller, about 25mm in base diameter, clustering in small clumps at shallow water zones as found on stones of the fringing coral reefs and intertidal region at the vicinity of the Marine Biological Station at Al-Ghardaqa, Red sea. Moreover, the anemone Entacmaea quadricolor shows strong contraction on touching without stings from their tentacles. The latter change its shape from digitiform to bulbous form and this may be governed by sunlight or presence of anemonefish (Gohar, 1934,1948; Fishelson, 1965 and Dunn, 1981).

The anemone Aiptasia diaphana (Rapp) is widely spread among marine fouling in Suez canal . This species forms considerable portion of fouling community on wrack and stationary vessels of some localities in the Suez canal e.g. Port-Said and Lake Timsah. These anemones usually seek calm clean water and dim shelters among fouling community (Shoukr et al., 2000). Furthermore, The anemones Anemonia sulcata, Bunodactis rubripunctata and B. verrucosa inhabit the intertidal region of rocky shores at Alexandria (Shoukr, 1978). Among these anemones, Anemonia sulcate can evoke painful stings to humans due to the presence of venomous nematocysts (Shoukr, 1996).

2. Swimming behavior and ecological significance:

The Swimming anemone Telmatactis forskalii (Ehrenberg) displayed both sessile and mobile positions over sand-muddy substrates among sea algae in Lake-Manzalah, Egypt. The behavior of this anemone is interesting. The individuals change their life style from a benthic form to a swimming (floating) form . They often move from the bottom by releasing their pedal disk from the substratum. They float using a gas bubble held within folds of the pedal disk and other anemones swim by means of the tentacles and body column. After moving actively they attach their basal disc to floating seaweed, which have green or brown colors, in the surface water. Other swimming anemones are known to exhibit the same behavior such as Boloceroides hermaphroditica Carlgren, Stomphia coccinea Muller and Bunodeopsis medusoides (Robson, 1963; Josephson and March, 1966 and Elliott et al., 1989). Swimming of anemones may be served as a mean of escape from predators or from an ecological stress as strong illumination.

3. Beneficial ecological relationships:

3.1.Mutualism (symbiosis):

Many members of the phylum Cnidaria, such as sea anemones, harbor interacellular photosynthetic dinoflagellate protists (zooxanthellae) in a mutually beneficial symbiotic association. Many anemone hosts are obligatory symbiotic with zooxanthellae. The latter are located in vacuoles within the host endoderm cells. Symbiotic dinoflagellates exhibit a high rate of photosynthesis (Weis, 1991). Recently, it is reported that the sea anemone Anthopleura elegantissima contains both dinoflagellate zooxanthellae and green algae known as zoochlorellae. This anemone occurs in the Northern Puget sound region, Washington (Engebretson and Muller – Parker, 1999).

It is obvious that symbiotic dinoflagellates of sea anemones usually belong to genus Symbiodinium (Muller – Parker et al., 1996 and Smith & Muscatine, 1999). A new genus namely Gymnodinium is firstly recognized as dinoflagellate symbiont in a cnidarian jellyfish which is different from Symbiodinium of sea anemones (Trench and Thinh, 1995).

The ecological significance of cnidarian - zooxanthellar symbiosis (mutulasim) has been recognized for over 70 years. Symbiotic dinoflagellates require three factors for their growth: external food supply; a minimum period of time following feeding (11 – 36 h), presumably for digestion, and a period of light following feeding (Fitt, 2000). Thus, zooxanthellae are found in very high concentration in some sea anemones.

The symbioses between sea anemones and dinoflagellates have been viewed as association involving various hosts of anemones and symbionts . Among zooxanthellate anemones, the intertidal actinian Anemonia sulcata is common along the east and west coasts of Alexandria on the Mediterranean Sea. This anemone extends its green and brown snaky tentacles fully in sunlight as well as in artificial light. It seems that the symbiotic zooxanthellae are important for the activity and flourishing of the anemone host.

The sea anemone A. sulcata, collected from the Egyptian marine water, is never found without its algal partner Symbiodinium microadriaticum which may suggest that the symbiosis here is obligatory and not facultative. The partnership involves transfer to the anemone host of energy, organic carbon, oxygen and probably organic nitrogen and even phosphorus and sulfur compounds in product release by the symbionts. The symbiont may gains carbon dioxide, inorganic nitrogen, phosphate and sulfur compounds, shelter and sometimes vitamins from the host (Smith, 1981). Zooxanthellae excrete glycerol, glucose and up to 80% of the carbon fixed by zooxanthellae may be release as maltose with smaller amounts of alanine and glycollic acid. The algal photosynthetic product, glycerol, is easily transported outside zooxanthellae to the benefit of the host (Muscatine, 1967).

3.2. Commensalism:

Anemonefishes are found in obligate symbiosis (Table 4) and specialized for living with particular species of host sea anemones (Fautin and Allen, 1992; Fautin et al., 1995 and Elliott et al., 1999). The earlier works of Gohar (1934 and 1948) and Shoukr (1990) were mainly devoted to the ecology and behavioral characteristics of anemones and fish association from the Red Sea.

In 1948, Gohar described the mutual benefit between fish and anemones. He mentioned that the anemone Actinia quadricolor and Discosoma giganteum are usually found in nature with their commensal fish Amphiprion bicinctus and Tetradrachmum trimaculatus. The association between the fish and anemones appears intimate and it seems that each of them lives much more happily in presence of the other (Fig.4a).

In 1990, observations of Shoukr through snorkeling, in Al-Ghardaqa coral reefs as in Shab Abou – Sadaf and in vicinity of Hur palace village, showed that the large anemones of Entacmaea quadricolor and Antheopsis crispus accompanied some brightly colored fish, namely Amphiprion bicinctus. The latter fish live amongst the stinging tentacles without ill effects. During feeding by the author, the fish appears as an active hunter for its anemone partner with a small share of food. The symbiotic association between anemones and clownfishes is well known in the Red sea and studied by other authors e. g. Fishelson, 1965; Schlichter, 1968; Mariscal, 1970 and Dunn, 1981.

Symbiotic relationship between Sea anemones and hermit crab (Table 5) with gastropod shell has yielded valuable information on their role and importance in their ecosystem, which usually known as ecological triangle . The hermit crab Pagurus pollicaris Say is more frequently associated with a protective anemone, Calliactis tricolor (Lesueur), in areas with high predation pressure than in areas with low predation pressure (Bach and Herrnkind, 1980). Moreover, the anemone Calliactis parasitica (Couch) appears to be an active member of the symbiosis with hermit crab, as it can move from shell to shell on its own. The hermit crab gains protection from predatores. For the anemone, the nutritional gains obtained from movement with hermit crab are thought to be significant (Christidis et al., 1997).

4. Harmful ecological relationships:

4.1. Parasitism:

Sea anemones are parasitized to some extent by specific organisms, but probably not greatly to their detriment. Parasitic arthropods (Table 6) are reported to feed on their host anemones. These arthropods include crustacean copepods, pycnogonids (sea spiders) and pedunculate barnacles (Vader, 1970; Briggs, 1976; Mercier and Hamel, 1994; Costanzo et al., 1996 and Yusa & Yamato, 1999).

Several studies have revealed that the sea anemones Anemonia sulcata are parasitized by the crustacean copepod Paranthessius anemoniae Claus . Moreover, the pycnogonids have deleterious effects on sea anemones e.g. Bartholomea annulata .

A very interesting association in recent years, is observed in Japan, in which the pedunculate barnacles Koleolepas avis feed actively on the tentacles of the sea anemone Calliactis japonica and live on the pedal disc of the anemone . The behavior of this association is recorded with a time – lapse video recorder (Yusa and Yamato, 1999).

4.2. Predation:

A number of sea anemone enemies have been cited, among them various molluscan nudibranchs and echinoderm starfishes. Certain nudibranchs are well known as devourers of anemones. Predation behavior of the molluscan nudibranch Spurilla neapolitana on the sea anemone Anemonia sargassensis from Florida involves four distinct phases: approach, initial contact and withdrawal, re-approach, and feeding (Conklin and Mariscal, 1977).

Moreover, the two asteroids Dermasterias imbricata and Hippasteria spinosa are known to feed on the anemones Stomphia coccinea and S. didemon (Siebert) from Washington (Elliott et al., 1989). Surprisingly that the predator sea stars may become a prey for the anemones such as the predation of a sea anemone of the genus Tealia on the starfish Asterina miniata (Nybakken, 1997).

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Correspondence To :

 

 

 

 

Dr. Fayez A. M. Shoukr, Professor of Marine Invertebrates, Zoology Department, Faculty of Science, Tanta University, Tanta 31527,Egypt.

E-mail :fayez_shoukr@hotmail.com

Web site :http://www.fayezshoukr.5u.com/

How To Cite This Site :

Shoukr, F. A. 2004. Ecology of some benthic cnidarians inhabiting marine environment in Egypt. Electronic internet document available at http://www.marine.tanta.8m.net/ Published by the author, web page established December, 2004.

 

العلاقات البيئية لبعض اللاسعات القاعية التي تقطن البيئة البحرية في مصر.

د. فايز عبد المقصود شكر

قسم علم الحيوان ، كلية العلوم ، جامعة طنطا ، مصر

 

تعتبر اللاسعات القاعية مثل شقائق النعمان البحرية من الأحياء اللافقارية عالمية الانتشار في بحار ومحيطات العالم وهي شائعة في الفونه المصرية بالبحر الأحمر وقناة السويس والبحر المتوسط وبعض البحيرات مثل بحيرة المنزلة وبحيرة قارون وبجيرة التمساح. وتشغل هذه الأحياء البحرية الجالسة بيئات متنوعة بين أحياء القاع المنتشرة في الشعاب المرجانية ومجتمع الحشف البحري ومنطقة المد والجزر علي الشواطئ الصخرية. وقد تم تسجيل سلوك العوم لبعض الأنواع من اللاسعات القاعية المنتشرة لأول مره في مصر ببحيرة المنزلة . ويعتبر سلوك العوم وسيلة للهرب من الأعداء وكتفاعل لتجنب بعض الضغوط البيئية مثل شدة درجة الأضاءه والحرارة. ويتم العوم بواسطة اللوامس والجذع أو الطفو عن طريق استخدام فقاعة هوائية داخل ثنيات القرص القاعدي للحيوان.

اللاسعات القاعية مثل شقائق النعمان البحرية ذات أهمية بيئية نظراً لعلاقاتها التكافلية الهامة المفيدة والضارة مع غيرها من الكائنات البحرية الأخرى وكذلك الإنسان. تشتمل العلاقات البيئية المفيدة لشقائق النعمان البحرية علي علاقة التكافل والتعايش. ويتم التكافل بين شقائق النعمان البحرية والطلائعيات ثنائية الاسواط (الزوزانثيللي) حيث تمد هذه الكائنات الدقيقة شقائق النعمان البحرية بواسطة الغذاء (الكربوهيدرات) والأكسجين الذي يتم تكوينه أثناء عملية البناء الضوئي ولذا فإن شقائق النعمان البحرية تزدهر وتنتعش وتصل إلي أقصى درجة من التمدد في وجود ضوء الشمس اللازم لإتمام هذه العملية.أما هذه الكائنات الدقيقة فستفيد من الحماية داخل أنسجة شقائق النعمان البحرية في بيئة عالية الإضاءة كما أن نواتج الإخراج من شقائق النعمان البحرية مثل ثاني أكسيد الكربون تستخدم في عملية البناء الضوئي لها.وقد تم تعريف أحد الأنواع الشائعة من هذه الزوزانثيللي المتكافلة مع شقائق النعمان البحرية بواسطة المجهر الإلكتروني لأول مره في مصر.

يتم التعايش بين شقائق النعمان البحرية والأسماك المهرجة التي تعيش بسعادة بالغة بين اللوامس اللاسعة باحثة عن المأوي والحماية من الأعداء. وتعتبر هذه الأسماك صياد ماهر يعمل علي تغذية شقائق البحر كما أنها تشاركه في الغذاء. وكذلك يتم التعايش بين شقائق البحر والسرطان الناسك الذي يسكن داخل صدفة بعض الرخويات من بطنيات القدم. وتقوم شقائق النعمان البحرية بحماية السرطان الناسك من هجوم أعداءه من الرخويات رأسية القدم. أما الفائدة التي تعود علي شقائق النعمان البحرية فتتمثل في حرية الحركة مع السرطان الناسك واكتشاف أماكن غذائية جديدة. تشتمل العلاقات البيئية الضارة لشقائق النعمان البحرية علي علاقة التطفل والافتراس. ويتم التطفل علي شقائق النعمان البحرية بواسطة بعض المفصليات مثل القشريات وعناكب البحر والاطومات التي تقوم بالتغذية علي اللوامس. ويتم الافتراس علي شقائق النعمان البحرية من بعض الأعداء مثل الرخويات عارية الخياشيم ونجوم البحر والأسماك.