ASPECTS OF FEEDING BEHAVIOUR OF
WEST INDIAN REEF CORALS
William Stephen Price
Thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science,
March 1973.
® William Stephen Price 1973 ABSTRACT
The feeding behaviour of 35 species of West Indian hermatypic corals was observed underwater, on the reefs off Bellairs Institute,
Barbados, West Indies. Observations were supplemented by laboratory study. Food varied from large zooplankton to fine suspended particulate material, which was secured and ingested by tentacular activity and mucus secretions. Long 'sweeper tentacles', up to 80 mm in length, were observed in the polyps of several species. Ciliary currents did not reverse in any of the species and did not aid directly in feeding. Extracoelenteric activity of mesenterial filaments is not considered normal behaviour.
William Stephen Price Marine Sciences Centre McGill University Résumé
Le comportement nutritif de 35 espèces de coraux hermatypiques des Antille fut observé sous l'eau, sur les récifs au large de l'Institut
Bellairs, à la Barbade, aux Petites Antilles. Les observations furent complétées par des études en laboratoire. La nourriture est saisie et absorbée grâce à l'activité des tentacules et à sécrétions mugueuses.
Sa grosseur varie entre le zooplancton de grande taille et la matiére particulaire en suspension. Chez quelques espèces, de longues
"tentacules balayeuses" atteignant jusqu'à 80 mIn de longueur furent observées dans les polypes. Les courants ciliares n'ont pas été inversés chez aucune des espèces et n'ont pas aidé directement à la nutrition. L'activité extracoelentérique des filaments mésentériques n'est pas considérée comme un comportement normal.
Stephen William Price Marine Sciences Centre NcGill University i
TABLE OF CONTENTS
Introduction Page l
Materia1s and Methods 10
Resu1ts 13
Group l 15
Group II 53
Group III 76
Group IV 103
Discussion 110
Sunnnary 117
Literature Cited 120 ii
ACKNOWLEDGEMENTS
l would like to express my appreciation to those people who have made this project possible: Dr. John Wells, Cornell University, Ithaca,
New York, who identified several coral specimens; Mt. Bruce Ott and
Mt. Alex Urban who took part in many hours of diving with me; and
Dr. John Lewis, to whom l wish to express special thanks, as my supervisor who supplied both academic and financial assistance, and suggested the project. Hi
LIST OF TABLES
Table 1. Systematic list of Barbados hermatypic coral species examined. Page 8
Table 2. Division of the 35 species of hermatypic corals into four feeding groups. 13 iv
LIST OF FIGURES
Figure 1. Map of Barbados showing location of reefs and study sites. Page vii
2. Porites porites - fully expanded 19 3. P. porites - ciliary currents 20 4. P. porites - tentacular feeding 20 5. 1. astreoides - fully expanded 22 6. P. astreoides - mucus sheath 22 7. Madracis mirabilis - fully expanded 27 8. M. mirabilis - ciliary currents 28 9. M. mirabilis - tentacular feeding 28 10. M. mirabilis - 'sweeper tentacle' 29 11. M. mirabilis - ingestion of organic particles 29 12. Eusmilia fastigiata - fully expanded 31 13. E. fastigiata - branching tentacles 32 14. E. fastigiata - ciliary currents 32 15. Montastrea cavernosa - fully expanded 35 16. M. cavernosa - 'sweeper tentacles' 36 17. M. cavernosa - tentacular feeding 36 18. M. cavernosa - mucus strand feeding 37 19. M. cavernosa - feeding with polyps contracted 37 20. Mussa angulosa - fully expanded 39 21. M. angulosa - ciliary currents 40 22. M. angulosa - tentacular feeding 40 23. Isophyllia multiflora - fully expanded 42 24. I. multiflora - tentacular feeding 42 25. I. multiflora - ingestion of organic particles 43 26. Dichocoenia stokesi - fully expanded 45
27. ~. stokesi - partially expanded [,.5 28. Favia fragum - fully expanded 48 29. K. fragum - partially expanded 49 30. F. fragum - ciliary currents 50 31. F. fragum - ejection of mucus bolus 50 v
Figure 32. Stephanocoenia michelini - fully expanded Page 52 33. Colpophyllia sp. - fully expanded 59 34. Colpophyllia sp. - ciliary currents on periphery of colony 60 35. Colpophyllia sp. - ciliary currents 60 36. Colpophyllia sp. - excretion of fecal bolus 61 37. Colpophyllia sp. - mucus strand feeding 61
38. Colpr~hyllia sp. - 'zipper action' of tentacles 62 39. Colpophyllia sp. - 'zipper action', sequence of movements 63 40. Colpophyllia sp. - capture of small zooplankton 64 41. Colpophyllia sp. - baffle or 'snow fence' effect 64 42. Diploria clivosa - fully expanded 66 43. D. strigosa - fully expanded 68 44. D. labyrinthiformis - fully expanded 70 45. D. labyrinthiformis - 'zipper action' 71 46. MYcetophyllia lamarckiana - expanded soft tissue 73 47. M. lamarckiana - solitary tentacle structure 74 48. M. lamarckiana - tentacular feeding 74 49. M. lamarckiana - juvenile form 75 50. Siderastrea siderea - tentacular arrangement 79 51. S. siderea - collection detritus 80 52. S. siderea - mucus strand feeding 80 53. S. siderea - tentacu1ar feeding 81
54. ~. siderea - excretion of fecal pellet 81 55. S. radians - ciliary currents and tentacular arrangement 83 56. S. radians - ingestion of organic particles 83 57. Agaricia agaricites - fully expanded 85 58. A. agaricites - 'sweeper tentacles' 86 59. A. agaricites - mucus strand feeding 86 60. A. lamarcki - fully expanded soft tissue 88 61. Helioseris cuculata - portion of colony 90
62. ~ cuculata - ciliary currents 91 vi
Figure 63. wycetophy11ia danaana - expanded co1ony with mucus strings Page 93
64. ~etophy11ia sp. - fu11y expanded 93 65. M. ferox - fu11y expanded 95 66. Montastrea annu1aris - fu11y expanded 98 67. M. annu1aris - po1yps in different postures 98 68. Acropora pa1mata - expanded apical polyps 100 69. A. pa1mata - expanded po1yps showing tentacu1ar arrangement 100 70. A. cervicornis - fu11y expanded 102 71. Dendrogyra cy1indrus - fu11y expanded 105 72. Meandrina lliE:!mdrites, f. meandrites, f. danae - fu11y expanded 108 73. M. meandrites - partia11y expanded 108 74. M. meandrites , f. danae - expanded soft tissue 109 75. M. meandrites - mucus string feeding 109 vii
N
Bellairs Site 1. ---~,~. Site 2.---f Bath -----Site 3,
Bridgetown
5 miles
Figure 1. Map of Barbados showing location of reefs and
study sites .
... Active1y growing reef. 1
INTRODUC TION
Unti1 recent1y reef cora1s were regarded as being primari1y carnivores feeding on zoop1ankton (Yonge, 1940). However, single ce11ed a1gae, the zooxanthe11ae present in the endoderm of a11 reef building cora1s (Yonge, 1963), are a1so being considered as an important source of nutrition (Franzisket, 1969; Johannes, Co1es and
Kuenze1, 1970). It is genera11y assumed that the zooxanthe11ae and the coral form a symbiotic re1ationship. The princip1e photosynthetic product re1eased by the symbiotic a1gae after isolation from hosts is a soluble carbohydrate. "It is 1ike1y that glycero1 is the carbohydrate form trans10cated in associations invo1ving zooxanthe11ae, since the rate of 1iberation of glycero1 'in vitro' is stimu1ated by the presence of some compone~~ of the host tissue and in the intact associations, such as cora1s, the animal tissues are rich in 1abe11ed glycero1 derivatives, such as
lipid • • ." (Smith et al., 1969, page 27).
In genera1, the detai1s and the biochemica1 significance of the coe1enterate-zooxanthe11ae association is uncertain. There have been, however, assumptions concerning the genera1 metabo1ic characteristics.
Geddes (1882) suggested that the uptake of carbon dioxide and the production of oxygen during the photosynthesis wou1d faci1itate the anima1's respiration and gas exchange. The assimilation by the a1gae of inorganic waste products of the host was postu1ated by Yonge and Nicho11s (1931).
The 1ink has a1so been considered to encompass the incorp9ration of
photosynthetic materia1 into the organic matrix of the animal (Muscatine and 2
Rand, 1958). The presence of zooxanthellae in the corals has been demonstrated to increase the rate of calcification (Goreau, 1959; Goreau and Goreau, 1959). Yonge (1963) postulated that the algae remove excretory waste such as ammonia and phosphates. It was concluded by Smith
~ al. (1965, page 33) that "thesE: interactions . . undoubtedly take place to some extent in some associations but as yet there is little direct evidence that any of them are essential to the host."
Recent speculations about other possible food sources for corals concerns suspended organic matter, organic aggregates, and dissolved substances circulating in the boundary water of the reef (Goreau et al.,
1971). Marshall (1965) found that there was much fine organic material in the water not collected by fine plankton nets. Large amounts of suspended calcareous material are formed by coral-browsing acanthurid and scarid fish
(Bardach, 1961). Surge currents and wave turbulence also stir up the leptopel from the bottom sediment, making it available to the benthonic fauna. Baylor and Sutcliffe (1963) have shown that colloidal and dissolved organic mattet' may aggregate into large particles on the surface of bubbles stirred up by the surge. They have suggested that this is a possible source of nutrition for intertidal filter feeders and copepods. Several small organic molecules of biological significance, such as glucose and amine acids, have also been found to be removed from dilute solutions by the coral
Fungia scutaria (Stephens, 1962).
Bacteria function primarily as nutrient regeneration agents in the sea, because they possess the ability to convert dissolved organic matter into cell substances and to chemo-synthesize protoplasm below the photo synthetic zone. Zobell and Feltham,(1937-38) proposed that if bacteria 3
were sufficiently abundant in the sea water, they may serve as food for
several types of suspension feeding invertebrates. Bacteria, however, are too small to be filtered individually, but the periphytic or epiphytic nature of most marine bacteria results in their attachment to
particulate ~~~anic matter, plankton and other solid surfaces (Zobell,
1936) • DiSalvo (1971) examined selected coral species (Fungia scutaria and Pocillopora damicornis) for their methods of ingesting particles and the nature of the bacteria living on the particle surfaces. A mixture of radioactive bacteria (labelled with 358) and "plankton particles"
(his quotes) was fed to the corals. Fractionation data 24 hours later indicated that the coral tissue had hydrolyzed and assimilated the bacteria.
Duerden (1902, 1906) and Vaughan (1913) gave preliminary accounts of their observations on the feeding behaviour of several species of
Atlantic reef corals. Carpenter (1910) reported on the feeding reactions of the rose coral polyps belonging to the genus Isophyllia. The first early review of the subject was given by Boschma (1925). However, it was not until the report of the Great Barrier Reef Expedition in 1928-29 that the subject was explored in any great detail. Of the series of papers on the physiology of corals, Yonge (1930) devoted the first to feeding mechanisms and examined forty genera. It was from this work that Yonge helped to create the classical concept that reef corals are superbly efficient and voracious carnivores, feeding not only on zooplankton but also on any kind of particulate animal food. For all genera, evidence was given that these corals capture and digest zooplankton and that vegetable matter was invariably refused. The ectoderm of all corals was 4
found to be thickly ciliated and Yonge suggested that they function primarily in the removal of silt and waste material from the polyps and general surface of the colony.
In a few species the ciliary currents were considered to assist in the transportation of food to the mouth. However, in these cases water movements aided the removal of material from the surface. In the Agarididae and in those species where the tentacles are reduced or lost, ciliary currents were considered to be " ••. exclusively concerned with the transport or presentation of food to the mouth, • • • . Where the tentacles are very small the reversaI of ciliary currents may follow stimulation by food. The currents have thus a double function.
ReversaI was observed only on the meandrines and in the Fungiidae and only in genera or species with small tentacles, the relation between the two being clear." (Yonge, 1930, page 55).
Vaughan (1913, 1919) had indicated that animal matter caused a reversaI of ciliary as the food is carried in mucus strings to the mouth. Yonge (1935a), however, concluded from his observations of
Meandrina aereolata that this reversaI was only apparent (his emphasis) and was abnormal, and undoubtedly due to excessive mucus production and formation of mucus strings. He did not consider it a normal feeding behaviour.
The role of mucus secretion in corals has been suggested as being important " in the protection of the polypal surface from foreign objects and in the keeping it clean, and also in entanglement and ingestion of prey and food substances." (Duerden, 1906, page 614).
If the polyps of a coral are only capable of lindted expansion, 5
or if the food is too large to be swallowed, mesenterial filaments are believed to be freely extruded in certain genera. In these cases, digestion and absorption take place extra-coelenterically. Mucus assists ciliary action when prey are paralyzed in regions of the ectoderm other than the tentacles. Duerden (1902), Matthai (1918), and Goreau (1956) have stated that most species are capable of extra coelenteric digestion of food matter by means of mesenterial filaments extruded through temporary openings at any place on the colony surface.
More recently, Lang (1971) stated that these extended filaments were used against other corals as aggressive and digestive organs.
Yonge (1930, page 54) indicated that corals possess a "capturing surface" which is far greater in proportion to the bulk of the tissues than any other group of animaIs and " • • • that when an animal possesses an organ or set of organs which perform certain functions with perfect efficiency, it can be taken as axiomatic that such organs are used."
The food this 'capturing surface' is believed to collect is " ••• aH available animal material, alive, moribund or disintegrated, froID the most minute to the size of medium crustaceans and small fishes." (Yonge,
1968, page 341.)
However, zooplankton densities are low in tropical waters, and it has been suggested that the supply of zooplankton is insufficient for the energy demands of the coral (Bochma, 1925; Gardiner, 1931; Johannes et al., 1970). Consequently it is considered possible that this 'capturing surface' may not restrict itself to the trapping of zooplankton. Goreau et al. (1970, pages 253, 256) have since proposed that "in stony corals, the absorption of dissolved organic matter takes place mainly in the 6
epidermis of the co1umn wall, tentac1es, oral disc and stomodaeum, i.e.,
the entire surface in direct contact with the externa1 medium." They
added that "in spite of their phy1etic disparity, the epiderma1 cells
of sc1eractinian cora1s and the absorptive epithe1ium of mamma1ian
kidney and duodenum are remarkably simi1ar in genera1 features of their histochemistry and functions, In view of these considerations,
it is not unlike1y that these epithelia a1so perform simi1ar functions."
This study is an attempt to broaden the scope of our present
know1edge of coral feeding behaviour patterns and mechanisms under
natura1 and laboratory conditions. It also re-eva1uates the
effectiveness of the 'specialized carnivore' in its natural env ir onment ,
and affords an opportunity ta ascertain if there are other aspects of
coral feeding behaviour not recorded. Apparently feeding mechanisms of
the Atlantic species have not been extensive1y surveyed, as investigations
to date have focused on Pacific corals (Abe, 1938; Carlgren, 1905;
Coles, 1969; Duerden, 1906; Marisca1 and Lenhoff, 1968; Stephens,
1962; Yonge, 1930, 1935a, 1935b).
Yonge's (1930, 1935a, 1935b) early work on feeding mechanisms
provided the guideline for this study. In his work he inc1uded a description of the soft tissue structure, the ciliary currents, and the method of seizure of particu1ate food. For this investigation tentacu1ar
feeding, ci1iary currents, mucus secretions, and mesenterial fil~~nt activity have a1l been considered as separate mechanisms.
Most of the reef cora1s examined in this study were found on reefs
opposite the Bel1airs Research Institute in Barbados, West Indies (Figure
1). A description of the reefs has been pub1ished by Lewis (1960). The 7
mean month1y sa1inities of the waters of the west coast of Barbados
o 0 vary between 32 /00 and 36 /00 and the surface water temperature varies between 26° and 29°C (Lewis et al., 1968). 8
TABLE 1
Systematic list of Barbados herrnatypic coral species examined.
The nomenclature is based on the work of Vaughan and Wells (1943).
Family ASTROCOENIIDAE Stephanocoenia michelini Milne-Edwards and Haime
Farnily ACROPORIDAE Acropora cervicornis (Lamarck) Acropora palmata (Lamarck)
POCILLOPORIDAE Madracis mirabilis (Duchassaing and Michelotti)l 11adracis decactis (Lyman)
SIDERASTREIDAE Siderastrea radians (Pallas) Siderastrea siderea (Ellis and Solander)
Family AGARIC l IDAE Agaricia agaricites (Pallas) forma agaricites forma danae forma purpurea Agaricia lamarcki Milne-Edwards"and Haime Helioseris cuculata (Elli~ and Solander)
Family PORITIDAE Porites astrèoides Lamarck Porites divaricata Lesueur Porites furcata La~rck Porites porites (Pallas)
Farnily FAVIIDAE Favia fragum (Esper) Diploria clivosa (Ellis and Solander) Diploria strigosa (Dana) Dip16ria labyrinthiformis (Linnaeus) Colpophyllia amaranthus (Muller) Colpophyllia natans (Muller) Mancina areolata (Linnaeus) forma mayori Montastrea annularis (Ellis and Solander) Montastrea cavernosa (Linnaeus) 9
Fami1y MEANDRINIDAE Meandrina meandrites (Linnaeus) Dichocoenia stokesi Milne-Edwards and Haime Dichocoenia ste1laris Mi1ne-Edwards and Haime Dendrogyra cylindrus Ehrenberg
Fami 1y MUSSIDAE Mussa angu10sa (Pallas) Isophy1lia sinuosa (Ellis and Solander) Isophy11ia multif10ra Verri11 MYcetophy1lia sp. MYcetophy11ia danaana Mi1ne-Edwards and Haime MYcetophy1lia ferox (n. sp.)2 MYcetophy1lia lamarckiana Mi1ne-Edw~Lds and Haime
Fami1y CARYPHYLLIDAE Eusmi1ia fastigiata (Pallas)
1Reported as Madracis asperula (Vaughan and Wells 1943) and has subsequently been identified as M. mirabilis (Goreau and Wells 1967).
2Id ent1·f· 1cat10n . 0 f speC1es . by J ••W We 11s. 10
MATERIAL AND METHODS
Experiments were begun in September 1970 and continued unti1
May 1971. Most of the species studied were found on two outer-reefs,
1ying 1 to 1.3 km from the shore and at a depth of 20 to 30 m. The
greater diversity of cora1s and common occurrence of most species made
these outer-reefs (Site No. 2) a preferable location for study.
Because the inner-reefs are exposed to more surge action and turbidity,
observation of the cora1s there was more difficu1t.
However, a few species cou1d on1y be found on the inner-reefs~
~ite No. 1). Porites furcata (Lamarck) and g. divaricata Lesueur were
transported from Bath (Site No. 3) to the 1aboratory at the Institute,
and Acropora pa1mata (Lamarck) was co11ected from Maycocks Bay (Site
No. 4).
Investigations were carried out at a11 times of the day. It was
necessary to mark the study area during the day by interconnecting the
colonies of coral with a guide 1ine, in order to locate them more
readi1y at night. A large orange buoy identified the site from the
surface.
SCUBA diving gear was used as it enabled the investigator to
stay under water for.a 1engthy and unhurried observation period.
Observations were aided by the use of a hand magnifying glass and notes
were recorded with a 1ead penci1 on a roughened p1exig1ass plate. Clo3e-
up photographs supplemented the observations. The camera used was a
Nikonos II, with a 28 mm f/3.5 underwater Nikor lens, coupled with one
or two close-up rings. A smal1 rod was attached to the front of the
lens to measure focal distances. 11
For photographic lighting, a synchronized Braun electronic flash
unit housed in an underwater case was found to be more convenient than
flash bulbs. The high speed of the electronic flash also minimized
unwanted illumination from suspended particles. The use of flood lights
was ruled out because an extended period of light affects the activities
of most corals.
For non-photographic observations a hand lantern and a helmet
light attached to a diving hood were carried by the investigator. It was necessary to wear extra wei~l,ts or tie oneself down in order to
remain as stationary as possible. A wet suit jacket was required for
protection against the stings of sea urchins, abrasions from the coral
and cold.
The four main activities of the corals examined were carnivorous
feeding, mucus secretion, ciliary currents, .and excretion of fecal matter.
Species which were normally expanded only in the dark were observed with
a red filter over the light source. Species normally expanded during
the day were examined in natural light.
Feeding patterns could not be adequately examined by watching
zooplankton entrapped and ingested under natural conditions. Most of
the feeding takes place in the dark hours and artificial light was
required. Also, in order to observe the feeding activities in the
period before the soft tissue contracted due to the light, the
concentration of zooplankton was increased artificially. If a coral
species was not too sensitive to light, the concentration could be
increased by shining the helmet light in the immediate area to be
investigated. Highly sensitive corals were fed by supplying the polyps 12
with laboratory-reared brine shrimp, Artemia salina Linnaeus. The brine shrimp were concentrated in a rearing dish by a localized light source and sucked into 25 ml plastic syringes with hose extensions (20 cm). The brine shrimp could then be released in higher concentrations close to the polyps to observe feeding. This app.aratus could also be attached to the bracket of the Nikonos camera so that the brine shrimp were conveniently released near the focal field while photographs were taken. Feeding patterns were more carefully observed under a dissecting microscope in the labora tory. As in the field, brine shrimp were supplied to the coral by means of plastic syringes.
Ciliary currents and the trapping of sediment and detritus by mucus secretions were examined in two ways. Sediments were scooped up by hand and diffused over the colony, and carmine or powdered fish was released from syringes.
The laboratory observations were carried out with a stereoscopic dissecting microscope. Colonies were detached below the living tissue from the substrate with the use of a hammer and chisel. The specimens of who le, live branched corals were impossible to transport and fragments had to be snipped off with wire cutters. The samples were brought to the laboratory in plastic pails, then placed individually in finger bowls in a running sea water table, (27 to 31°C). 13
RESULTS
It was found that, of the 35 species of Atlantic corals
examined, the similarity in the feeding patterns was not so much
related to taxonouw, but to the skeletal and soft tissue morphology.
This it was more convenient to group the corals into four categories
shown in Table 2.
TABLE 2
Division of the 35 species of hermatypic corals into four feeding groups.
1. Corals with long active tentacles and distinct individual polyps. When fully expanded the tentacles and usually the polyp stalk are raised weIl above the coenosarc.
Porites porites Porites astreoides Porites furcata Porites divaricata Madracis mirabilis Madracis decactis Eusmilia fastigiata Montastrea cavernosa Mussa angulosa Isophyllia multiflora Dichocoenia stokesi Dichocoenia stellaris Favia fragum Stephanocoenia michelini
II. Brain corals; those corals forming continuous thecal ridges and valleys.
Colpophyllia natans Colpophyllia amaranthus Manicina areolata Isophyllia sinuosa Diploria clivosa Diploria strigosa Diploria labyrinthiformis MYcetophyllia lamarckiana • 14
III. Cora1s with short, comparative1y inactive tentac1es. Expansion of the po1yp body is s1ight.
Siderastrea siderea Siderastrea radians Agaricia agaricites Agaricia lamarcki Helioseris cuculata MYcetophyllia danaana MYcetophyllia sp. Mycetophyllia ferox Montastrea annularis Acropora palmata Acropora cervicornis
IV. Corals having a dense tentacu1ar surface.
Dendrogyra cylindrus Meandrina meandrites 15
GROUP l
This category includes those corals which employed both active tentacles (approximately 2 to 8 mm in length) and batteries of nematocysts for feeding on zooplankton. The majority of the corals in this Group, such as Porites porites, extended the polyp stalk weIl above the coenosarc. On the other hand, Favia fragum, Dichocoenia stokesi and D. stellaris had active tentacles but a recessed polyp structure.
In general the members of this Group remained expanded both day and night. Eusmilia fastigiata and Mussa angulosa usually expanded only at night, but were commonly distributed in the deeper waters of the outer-reef. It was noted, however, that when these colonies were found in the inner- or mid-reef zones, they were generally located in a shaded area. In these locations they were often found partially expanded during the day. Assuming that these corals rely heavily on zooplankton as a food source, it would seem that their location and expanded posture was associated with the available zooplankton. Emery
(1968, pages 301-302) made the observations "that plankton is abundant in small caves and crevices in the reef and that the plankters school in the larger caves and near coral heads." It is likely that the expansion of the soft tissue was induced by the lower light intensity, as weIl as by the presence of zooplankton.
Porites porites was found distributed over a wide range on the reef from depths of 1 to 25 m. Although isolated colonies were found in various stages of expansion during the day, it was more usual for 16
them to be fully expanded both day and night (Figure 2).
Ciliary currents
The observation of ciliary currents on the polyps proved
practically impossible in the field. Particulate material landing on
the polyps appeared to be moved by the combined effect of the surge
currents and the sway of the polyps themselves. particles settling on
the oral disc became entrapped in the circle of tentacles and were
subsequently less susceptible to the surge currents. The length and
flexibility of the polyps caused them to bend with the surge, and when
the oral disc reached a near vertical position the particles were easily
displaced.
Laboratory observations, however, indicated regular ciliary
current patterns (Figure 3). The currents travelled from the periphery
of the mouth to the base of the tentacles, or between them and down the
polyp stalk. These downwardly directed currents on the polyp columns
converged between the adjacent polyps to form an upwelling. Such
upwellings returned particles to the level of the polyp tentacles, where
they were easily carried away by currents. Ciliary currents also
travelled around the base of each polyp stalk. The conical peris tome
had orally-directed ciliary currents and these appeared to increase in
strength when the peristome was raised. The inclination of the cone
caused particles to fall back and revolve in the area between the peristome
and the oral disco The speed of the ciliary currents increased with the
addition of weak concentrations (10 ppt) of mixed amino solutions or meat
juices, and with offensive substances such as Evan's blue or sulphuric 17
acid. Ciliary currents were generated at aIl stages of expansion of
the polyps. Under no conditions were ciliary currents observed to
reverse direction.
Tentacular feeding
On the reef, P. porites was observed to feed with its tentacles
both during the day and night. This method of feeding was more closely
observed by providing brine shrimp to the specimens in the laboratory.
Initially the prey contacted the tentacles and was stung and held fast by
the nematocyst discharge on the tentacle tip. Nematocyst batteries were
observed further down the tentacles, but a brine shrimp contacting these
areas as weIl as the area around the oral disc or stalk, apparently
suffered no ill effects. Immediately after a shrimp was secured, the
tentacle violently contracted and bent toward the mouth. As the polyp
stalk shortened by about one third of its length the remaining tentacles
contracted and folded over. The polyp continued to contract slowly into
the thecal cup until the folded tentacles were flush with the coenosarc
(Figure 4). Often when one polyp caught a shrimp, the entire branch became highly activated; tentacles twitched, and complete feeding contractions occurred in polyps located randomly across the entire branch.
It was noted that during this procedure, ciliary currents did not reverse on any polyps.
Capture by two polyps took place when a shrimp became entrapped between the stalks of adjacent polyps. The tentacles extended horizontal1y and the stalks contracted, thus trapping and paralyzing the prey below.
Eventually, and for no apparent reason, one polyp would release the prey 18
while the other polyp would proceed to ingest it.
Mucus strands and nets
Laboratory observations indicated that a great quantity of mucus could be released from the entire surface of the polyp, often forming an extensive net over the colonies. When particulate material settled on a colony, it became entrapped and was drawn into the mouth with the net or individual strand of mucus. Material not digested was usually expelled from the mouth shortly thereafter in the form of a bolus.
In the field, zooplankton were seen struggling in mucus strings before they were ingested by a polYPe Observations of this feeding method in the laboratory indicated that, if the string was attached to a tentacle, the pull on the string by the shrimp appeared to initiate feeding contractions of the polyp, resulting in the ingestion of the prey.
Extracoelenteric feeding and digestion
It aFpears that R. porites is capable of digesting large fragments of organic material. A piece of shrimp was allowed to settle on a colony; as it touched the surface, the polyps directly under the fragment contracted into their corallites and those in the vicinity bent toward it.
After a period of about 10 minutes, the morsel of shrimp was gently raised from the surface by a probe. The mouths of the polyps directly below the shrimp were opened to such a degree thatthe tentacles and the oral disc were not visible. The meat was entangled with mucus and mesenterial filaments and was presumably in the process of being digested
(Matthai, 1918; Goreau, 1956; Yonge, 1930). Figure 2. Parites parites - tip af calany with palyps fully expanded. 19
Figure 2. 19
Figure 2. Figure 3. Porites porites - ciliary currents and upwelling between adjacent polyp stalks. Note revolving currents caused by conical peris tome.
Figure 4. Porites porites - sequence of tentacular feeding movements: A-A. salina contacting nematocyst knob on the tentacular tip. B - Contraction of tentacle toward mou th. C - Ingestion of zooplankton as the polyp has contracted into the thecal Cup.
Figu]~e key: c, colunn1; cs, coenosarc; d, oral disc; ez, edge-zone; m, mouth; nk, nematocyst knob; p, peris tome; t, tentacle; z, zooplankton;
--+ direction of ciliary currents; -- ~ path of moving body. 20
c __ l
--'
Figure 3.
nk---.... ,/ ..J.
-c
A B c Figure 4 21
Porites astreoides was distributed over the reef from depths of
1 to 30 m. The polyp structure resembled that of P. porites except for the shorter stalk (Figure 5). Feeding behaviour was similar to
that found in R. porites. On. the reef, colonies were observed with
thick particle laden mucus sheaths covering the living tissue (Figure 6).
These coverings generally appeared under adverse weather conditions, and were eventually removed by surge currents. The sheaths were also observed in laboratory specimens that had been kept for a period of several days. Under the sheath the circles of tentacle tips were clearly visible. Lewis (in press) has suggested that these sheaths protect the soft tissue under unfavourable conditions and possibly against the predaceous polychaete worm Hermodi~e carunculata. Figure 5. Porites astreoides - portion of fully expanded
colony. Note short polyp stalks.
Figure 6. Porites astreoides - mucus sheath (MS) covering
part of the colony,with particulate material
adhering to it. Note tear in sheath (lower
left corner) as a result of surge currents. 22
Figure 5.
Figure 6. 22
Figure 5.
Figure 6. 23
Pori tes furcata was found only on the east coast of Barbados from depths of 1 to 4 m. Ciliary currents were similar to, but somewhat swifter than those of E. porites. Feeding patterns were essentially the same as those found in P. porites.
Porites divaricata was not found on the Bellairs' reef, specimens from the south and east coasts were examined in the laboratory. Feeding patterns were similar to those of P. porites. .24
Madracis mirabilis was observed on the mid-reef zone between depths of 3 to 15 m. Colonies formed slender irregular branches and occurred in isolated clumps or as large beds. The polyps were found expanded both day and night (Figure 7). Each polyp usually had 20 tentacles in an alternating pattern of a long tentacle followed by three short ones.
Ciliary currents were similar to those of ~. porites, except that the currents of the polyp stalk were orally directed. These combined with the inter-polyp currents to give trace particles a clockwise spiralling motion as they were transported up the stalk
(Figure 8). Occasional observations indicated definite ciliary currents from the base of the tentacles toward the mouth.
Basically the tentacular feeding sequence was the same as in
1. porites. A slight difference noticed was that the tentacle tips remained exposed in the final feeding posture, except for the one holding the prey (Figure 9). In M. mirabilis the release of the prey from a tentacle could be more readily observed than in Porites spp.
As the mouth opened, the mesenterial filaments extruded into the stomodaeum and attached themselves to the prey. The prey was then released from the tentacle as the mouth closed, and the filaments were drawn in with the prey. When a small piece of dried fish food was allowed to settle on the oral disc, the mouth opened toward the food and swallowed it. When several pieces were dropped on the oral disc, the entire peris tome became funnel-shaped as it sank. The particles were then drawn into the mouth on mucus strings (Figure Il). 25
Extended tentac1es, subsequent1y referred to as 'sweeper
tentac1es', up to 7 mm in length, were often observed in~. mirabilis
(Figure 10). The bodies of these tentac1es were extreme1y thin and
transparent, except for the nematocyst club on the tip. The tentac1es were continuous1y swung in wide arcs by the surge currents. This
1ength variation, as we11 as the area swept by these tentac1es
appeared to increase the feeding effectiveness of the coral. However, when they captured~. sa1ina contraction of the tentac1es toward the
mouth was slow. In the 1aboratory~. sa1ina were caught in the mid-
region of the long sweeper tentac1e and, in thése instances, the mouth
moved and opened toward the base of the contracting tentacle.
Specimens kept in the laboratory for a period of about three
days increased the visible activity of their mesenterial filaments.
On one occasion a filament was extruded from the mouth with a dark piéce
of materia1, which it then re1eased. The filament subsequent1y with-
drew into the coe1enteron and the mouth closed. Following these
observations, two pieces of powdered fish food were p1aced on the oral
disc. The mouth opened and a filament extruded, discarding another
bolus of waste materia1. The filament then swung over an.d appeared
to draw up the pieces of fish food in a loop. After securing the
partic1es of food, the filament withdrew into the coelenteron.
The addition of a few drops of glycene (10 ppt) into a finger
bow1 with the coral caused mesenterial filaments to extend into the
tentacular cavities. Whell brine shrimp were re1eased and caught by
these po1yps, the filaments withdrew from the cavities. On another
occasion mesenteria1 filaments were extruded through the tantac1e tips 26
when no solutions had been added to the water in the finger bowls. It is be1ieved that the extrusion of filaments is unnatural and occurs on1y under stress conditions. Lewis (1971) has stated that this phenomenon was common1y found in 1aboratory-kept specimens of Agaricia agaricites, Porites porites and Favia fragum.and he considered them unhea1thy. Figure 7. Madracis mirabilis - three branches of M. mirabilis with the polyps fully expanded. Note the alternate
tentacula~~arrangement clearly shawn in the polyp 1. , .. ~ marked 'X'. 27 27
- Figure 8. Madracis miraoilis - ciliary currents.
Figure 9. Madracis mirabilis - sequence of polyp postures during tentacular feeding. D: Note posture of indicated tentacle as compared to posture of indicated tentacle in Figure 4-C.
Figure key: c, column; cs, coenosarc; d, oral disc; m, mouth; nk, nematocyst knob; p, peris tome;
t, tentacle; z, zooplankton; ~ direction
of ciliary currents; -- ~ path of moving body. 28
t
Figure 8.
c- o A B c Figure 9. Figure 10. Madracis mirabilis - extension of 'sweeper tentac1e' (see a1so Figure 16).
Figure 11. Madracis mirabilis - ingestion of organic partic1es (fish food). A: partic1es sett1ing on oral dise. B: sinking of oral dise into funne1-shape as the food partic1es are drawn into the mouth.
Figure key: e, co1umn; d, oral disc; f, food mass; m, mouth; nk, nematocyst knob; sw, 'sweeper tentac1e'; t, tentae1e; - --+ path of moving body. 29
sV-: //
Figure 10.
c-
A B
Figure II. 30
Madracis decactis occurred between depths of 10 and 30 m.
The corals were encrusting or formed thick, short-branched colonies.
The polyps were similar to those of N. mirabilis but with a reduced (2 rom) sta1k and somewhat longer tentacles. Feeding activity appeared identical to ~. mirabilis except that the ci1iary currents were stronger between the po1yps.
Eusmilia fastigiata. Colonies of li. fastigiata were found scattered over the reef between depths of 1 and 30 m. The tentac1es were general1y found expanded only at night (Figure 12). During the day partially expanded colonies were often found in shaded crevices and under coral overhangs. The tentacles were long (1 to 2 cm) and translucent, except for the white nematocyst batteries and knobs.
Bi- and trifurcate tentac1es were noted (Figure 13). .li. fastigiata appeared to re1y to a great extent on its tentacles for the capture of food. Tentacu1ar feeding on zoop1ankton was observed both in the laboratory and the field and was excèptiona11y quick and effective.
Ciliary currents trave1led between the sc1erosepta1 fo1ds, away from the mouth and were met by currents moving over the edge-zone toward the tentacles (Figure 14). Figure 12. Eusmilia fastigiata - oral view of fully expanded polyps at night. The nematocyst (N) batteries are clearly visible as white spots on the translucent tentacles. 31
Figure 12. 31
Figure 12. Figure 13. Eusmi1ia fastigiata - three types of branching tentacles observed.
Figure 14. Eusmilia fastigiata.- pattern of ciliary currents.
Figure key: cl, cora1lite; ez, edge-zone; d, oral disc; nk, nematocyst knob; m, mouth; st, sub-tentacle; t, tentac1e.
\ 32
nk -nk \ ....nk
-nk
Figure 13.
nk~- --:t
1 ez 1
1 ------ 1 t i J!~cl cl ---'1'
1
1 Figure 14.
1 ! 1 i \ 1 33
Montastrea cavernosa was found commonly on the reef in depths from 2 to 40 m. The colonies formed massive boulders up to 1.5 m in diameter. The colour of this species varied from dark brown to a red-, greenish- or grey-brown.
AlI M. cavernosa were found fully expanded during the hours of darkness (Figure 15). During the day, individual colonies were found in a partially or fully expanded condition. Often only those polyps on the sides of the colony would be expanded, while the top-most polyps remained closed. The occasional colony was found with expanded polyps scattered over the entire surface.
The polyps had three cycles of tentacles, as shawn in Figure 15.
During the night, tentacles of the middle cycle were observed to extend to lengths ranging from 30 to 80 mm (Figure 16). These were similar to the '~~eeper tentacles' noted in M. mirabilis. Onlyone to three
'sweeper tentacles' were observed per polyp. The polyps with these tentacles were most numerous along the periphery of the colony, where surge currents appeared strongest. The tentacles continuously swung in large arcs and when capturing visible zooplankton were only c~pable of slow contraction.
Ciliary currents were identical to those of 1. porites.
Tentacular feeding was very effective since the surface of the colony had a very dense coverage of long, well-armed tentacles. Prey was very quickly seized and transferred to the mouth.(Figure 17).
In the field, mesenterial filaments were often observed coiled midway up the tentacular cavities. Yonge (1930) reported that filaments protruding through the column wall were common and apparently 34
a natural occurrence. This was not observed in the field or
laboratory.
Strands of mucus which captured food were observed during
the day and night (Figure 18). These strands with the attached
particles were observed being drawn back into the mouth.
Observations in the field indicated that particulate material was collected and ingested during the day when the polyps were fully contracted. Material settling on the colony simply fell into the open mouths (Figure 19), due to the funnel shape of the polyp cup. Figure 15. Montastrea cavernosa - fully expanded polyps showing dense covering of colony surface. Note arrangement of the three cycles of tentacles. :\
35
Figure 15.
l 1 ,1 1 \ 1 35
Fig'Jr
Figure 17. Montastrea cavernosa - tentacu1ar feeding on the reef. The tentac1e which has secured and is coi1ed around the prey (P), is in the process of depositing it into the mouth. 36
Figure 16.
Figure 17. 36
Figure 16.
Figure 17. Figure 18. Montastrea cavernosa - mucus strands with attached particu1ate materia1 (P). The strands have been out1ined and can be c1ear1y seen extruding from the po1yp mouths (M).
Figure 19. Montastrea cavernosa - contracted soft tissue as seen during the day. Particu1ate materia1 which has sett1ed on sorne of the po1yp cups, is simp1y being funne11ed into the open mouths (indicated by M).
\. 37
Figure 18. 37
Figure 18.
Figure 19. 38
Mussa angu10sa was found within the mid- and outer-reef at depths of 10 to 30 m. The co1our of the soft tissue varied from green to red to blue-gray. The soft tissue remained contracted during the day. The expanded tentac1es formed three cycles on the outer edge of the po1yp cup (Figure 20).
Ci1iary currents are shown in Figurè 21 and were found to be comparative1y weak. Mucus strings and nets were common1y observed in the 1aboratory. In the field the constant surge currents appeared to reduce them to one or two heavier mucus strands, which swept around the po1yp cup co11ecting detritus as they trave11ed. These strands were eventua11y ingested. Large anne1ids (2 cm) were seized by severa1 tentac1es, as opposite tentacu1ar ridges converged to the centre of the po1yp cup. They then fo1ded over in a zipper-1ike fashion, sea1ing the prey beneath. However, sma11 prey was usua11y captured by a single tentac1e. The mouth was e1evated and the musculature of the oral disc contracted toward the feeding tentac1e (Figure 22). (
Figure 20. Mussa angulosa - ful1y expanded polyp at night. 39
Figure 20. 39
Figure 20. Figure 21. Mussa angulosa - arrangement of tentacles on the rim of the polyp cup and the direction of the ciliary currents are shawn.
Figure 22. Mussa angulosa - tentacular feeding.
A: capture of~. sa1ina by a tentacle. B: contraction of the tentacle and section of oral disc, as the prey is deposited into the open mou th.
Figure key: cl, corallite; d, disc; ez, edge-zone; m, mouth; nk, nematocyst knob; p, peris tome; t, tentac1e; tc, tentacle contracted;
z, zooplankton; ~ direction of ciliary
current; --~ path of moving body. 40
Figure 2 \.
t---'
A B Figure 22. 41
Isophyllia multiflora was distributed sparsely over the reef between depths of 10 and 25 m. The colonies were generally dome- shaped and less than 10 cm in diameter. The colour of the soft tissue was a dark br own , speckled with small white spots.
The coral was extremely sensitive to light and was found expanded only during the dark hours. Polyps had two cycles of tentacles. Those of the outer cycle were slender and extended approximately horizontally, while the inner, larger tentacles extended almost vertically (Figure 23).
Ciliary currents were similar to those of Mussa angulosa (see page 40) and in general did not appear strong. Mucus strand feeding was observed in the field and laboratory. Tentacular feeding
(Figures 23 and 24) was often accompanied by a general swelling of the soft tissue. Large prey was effectively caught by the co-ordinated response of aIl the tentacles. Particulate food dropped on an expanded polyp evoked similar responses, as reported by Carpenter (1910). The edge-zone of the polyp swelled, so that the thecal walls became vertical and the food particle dropped on to the oral dise. The swelling continued until the polyp cup had sealed over (Figure 25).
A few particles remaining on the exposed edge were drawn into the mouth by mucus strands. Figure 23. Isophyllia multiflora - fully expanded polyps. Note plastic spout in extreme lower left corner, through which!. salina will be released.
Figure 24. Isophyllia multiflora - feeding contraction of polyps immediately after capture of !. salina. 42
Figure 23.
Figure 2.4. 4·2
Figure 23.
Figure 24. Figure 25. Isophyllia multiflora - feeding reaction of a contracted polyp to a drop of suspended fish food. A: fish food settling on oral dise. B: sinking of the oral dise and infolding of the edge-zone, trapping the food beneath.
Figure key: d, orâl dise; ez, edge-zone; f, food mass; m, mouth; nk, nematocyst knob; se, selerosepta; te, tentaele contraeted. 43
A
eZ Il._---
~ p,./?'>o sc ~ , m/.... ",#> B l'
Figure 25 44'
Isolated Dichocoenia stokesi colonies were found in the mid- and outer-reef zones at depths of 10 to 25 m. The colonies were dome-shaped with a yellow- to green-brown hue.
The polyps were usually fully expanded only at night (Figure 26).
During the day the tentacles were often partially expanded (Figure 27).
Polyps had two cycles of tentacles approximately 3.0 mm in length and heavily armed with nematocyst batteries.
Tentacular feeding, similar to other members in the group was observed both in the field and in the laboratory. Ciliary currents travelled out of the polyp cup and betweenthe tentacles, where they were met by oppositely-directed currents moving over the interpolyp coenosarc. The peristome had orally-directed currents. Mucus strands were observed collecting and ingesting particulate matter during the day.
One specimen of Dichocoenia stellaris was found on the outer reef at a depth of 30 m. Feeding was similar to that of~. stokesi. Figure 26. Dichocoenia stokesi - photograph taken at night when the polyps were fully expanded. The tentacles are well armed with comparatively large nematocyst batteries.
Figure 27. Dichocoenia stokesi - partial expansion of the soft tissues during the day.
\ 45
1
~1
1
Figu r
Figure 2.7. 45
Figure 26.
.... Figure 27 . 46
Favia fragum was found in the shallow water of the inner- and mid-reef zones. At night the soft tissue was fully expanded (Figure
28) and during the day, partially expanded (Figure 29).
Ciliary currents generally followed a typical pattern, shown in
Figure 30. On a few occasions, a narrow current flowing into a polyp cup was observed, while currents in the remaining areas of the cup travelled in the normal direction. It was not possible to state that the current was the result of a localized ciliary reversaI or even direct ciliary activity.
An extensive mucus net was often formed over laboratory specimens.
The principal points of attachment of the net were the tentacles and the mouths. Particulate material landing on the mesh became embedded in the mucus, which was subsequently drawn into the mouth.
~ Tentacular feeding was similar to that of other members of Group
1. During one set of observations the tentacles of a polyp were extended in a horizontal position over the polyp cup. Below the tentacles, three pieces of detritus, strung together with mucus, were observed slowly rotating in the cup. A few carmine particles were allowed to settle on the polyp and they too became incorporated in the mucus. Shortly there- after, the musculature of the thecal wall and a section of the oral disc contracted, resulting in the tentacles sliding down the thecal wall and the mouth moving beneath the bolus.
Mesenterial filaments were occasionally observed extruding from the mouths of laboratory specimens. These filaments were active in the transport of solid excrement from the coelenteron, through the mouth to the exterior (Figure 31). Filaments were often seen close to the inner 47
surface of the tissue during experiments where glycogen, A. salina, or carmine had been added to the water. Figure 28. Favia fragum - fully expanded soft tissue as seen during the night. Particulate material (P) has been secured by the tentacles and is being transferred to the mouth. 48
Figure 28 . 48
28. Figure 29. Favia fragum - partial1y expanded soft tissue as seen during the day. 49
Figu re 29. 1="'.Ijure 29 Figure 30. Favia fragum - direction of ciliary currents and representation of the expanded soft tissue.
Figure 31.· Favia fragum - ejection of mucus bolus of carmine particles. Mesenterial filament extruding from the mouth releasing the· bolus.
Figure key: ctv, central thecal valley; d, oral disc; mf, mesenterial filament; ms, mucus strand; m, mucus; n, nematocyst batteries; p, peris tome; sc, sclerosepta; t, tentacle;
tp, trace particle; ~ ciliary currents. 50
ctv
r __ 1
Figure 30.
Figure 31. 51
Stephanocoenia michelini was found in the shallow waters in the tnner- and mid-reef zones. Colonies were dome-shaped or incrusting and were not larger than about 20 cm.
The soft tissue of ~. michelini was brownish in colour and the polyps were expanded both day and night (Figure 32). The peristome was usually raised and encircled by a ring of Il to 12 tentacles, 2 to
3 mm in length, bearing large nematocyst knobs on the tips. A second cycle of shorter tentacles lay distal to the first. The shorter tentacles alternated with the larger and arched away from the mouth.
Because the two cycles of tentacles were situated close to the mouth, they formed a dense covering over the entire surface of the colony.
The pattern of ciliary currents and the mucus forming activity was similar to that of Favia fragum. Tentacular feeding was similar to Dichocoenia stokesi and long 'sweeper tentacles' were present
(Figure 32). Figure 32. Stephanocoenia michelini - colony with soft tissue fullyexpanded. Note the 'sweeper tentacles' in the lower right corner of the photograph (ST). 52
Figure 32. 52
Figure 32. 53
GROUP II
These corals, commonly referred to as 'brain corals', are characterized by their continuous thecal ridges and valleys. Mouths and tentacular structures did not function as individual polyp units, but acted in a collective manner. The tentacles, well armed with nematocyst batteries, formed double ridges along the edges of the thecal platforms and were extremely effective in securing zooplankton. The typical feeding pattern was the 'zipper action', in which opposing tentacular ridges folded over, trapping the prey beneath them.
Juvenile colonies of this J,~:r.:()\lP had feeding patterns similar to those in Group l, as they formed individual cups and did not have the ridge structure.
These corals were most abundant in the mid- and outer-reef zones. They expanded at night, although those colonies in the areas of overhangs or caves were often partially expanded during the day.
Diploria clivosa did not fit particularly well into this Group.. It was fully expanded during the day as well as at night and was only found in the very shallow waters of the inner reef. The soft tissue was characterized by the unusual polypous surface.
Brain corals have a surface morphology which aids in the formation of boli of mucus and particulate material. The vertical tentacular ridges acted as a baffle, or 'snow-fence', system creating eddies and causing particulate material to settle in the oral valleys.
The particles were swept back and forth by the oscillating surge currents, forming large mucus and detrital aggregates, which were often trapped and 54
ingested. At the end of the valleys the overlying tentacles acted as a sieve mechanism, catching particulate matter including zooplankton. 55
Colpophyllia natans, Colpophyllia amaranthus, Manicina areolata forma mayori and Isophyllia sinuosa - These four species are described together as their feeding patterns were essentially the same. They were found in the same depth range of 2 to 25 m over the mid-reef zones.
During the daylight hours the soft tissue was contracted and the mouth either open or tightly closed. As the light intensity dropped in the evening, the soft tissue expanded to form a broad, fIat platform above each thecal ridge, the sides of which dropped vertically to the long, meandering oral valleys (Figure 33). The platform has a central thecal valley and was fringed on each side with a double row of alternating tentacles, with an angle of about 60° between each row.
Ciliary currents
On the reef, the movement of particulate material over the surface of the colony was due to the combined effect of continuaI surge currents and the relief of the coral surface. During periods of little surge action particulate material was observed in two areas: on the corallum border particles travelled toward the periphery
(Figure 34), along the scleroseptal ridges; and, on the thecal platform particles moved down between the tentacles. Ciliary current patterns examined in the laboratory are diagrammed in F.igure 35. Currents travelled toward the mouth over the peristome. In the area around the peris tome currents travelled in the opposite direction, moving out along the septal ridges and between the tentacles, where they were met by opposing currents from the thecal platform.
Yonge (1930, page 53) reported that "in Madreporaria reversaI 56
of ci1iary current on1y occurs in the genera or species with tentac1es too sma11 to range over the surface of the disc or adjacent coenosarc or to convey food to the mouth. Thus in the meandrines reversa1 was found in
Meru1ina and Triacophy11ia ••. , and a1so by Vaughan (1913, 1919) in the Meandra [= Manicina] areo1ata." In this study no evidence of reversa1 was found in M. areo1ata and during the dark hours tentac1es covered the co10ny surface profuse1y. The long tentac1es were capable of transporting materia1 from anywhere on the coenosarc to the mouth.
Mucus strands and nets
The secretion of large quantities of mucus was common in
1aboratory specimens. During examination of ci1iary currents, added partic1es of carmine travelling up the theca1 wa11s became entang1ed in the mucus strings and were then drawn into the mouths. There appeared to be one string between adjacent tentac1es. Short mucus strands aided in the trapping of zoop1ankton and the prey, in its strugg1es to get free, usua11y contacted the nematocyst batteries of a tentac1e and was ingested. If the strand was attached to a tentac1e, the tug of the prey on the tentac1e often initiated a feeding response in which the mucus strand was transferred to the mouth. The mucus strand with the entang1ed prey was then drawn into the coe1enteron.
Mucus nets effective1y co11ected particu1ate materia1 landing on the coral surface. After a period of time the net with the attached materia1 was drawn into the mouth and, a few minutes 1ater, the undigested materia1, such as carmine, was ejected from the mouth in a tight bolus (Figure 36). 57
In the field the numerous mucus strands observed in the
laboratory were not seen. Aga in, it appeared as though they became unified into thick (0.5 to 1.0 mm) single strands or cords, translucent
in colour and about 10 mm in length (Figure 37). These strands were often seen extruded from the mouths of corals and, as surge currents caused them to be swept in circ les, they gathered any free particles in their paths. After an indefinite period the strands with the attached particles wou Id be ingested. Often the strands would reappear shortly thereafter with the particles removed and, on one occasion, a strand completed this cycle three times in five minutes.
T~ntacular feeding
Tentacular feeding took place only at night. Zooplankton upon contacting the tentacles were stunned and held by the discharge from the nematocyst batteries. The tentacle securing the zooplankton contracted immediately and was pulled down the thecal wall, toward the oral valley, followed by the adjacent tentacles. This action was duplicated by the opposing tentacles on the collateral thecal ridge.
The tentacles interlocked with a 'zipper action', enclosing the prey
(Figures 38 and 39). Contraction of the oral valley musculature often resulted in the shifting of the peris tome midway up the thecal wall to receive the prey (Figure 40).
In the field, it was noted that the erect tentacles acted as a baffle, causing suspended material and zooplankton to fall into the oral valleys (Figure 41). The particles of zooplankton were then moved back and forth in the valleys by the oscillations of the surge. Because of 58
the irregularities in the oral valleys, water currents had to pass through the overlying mesh of tentacles which filtered out the suspended material, including zooplankton.
On one occasion in the field, tight clumps of filaments were observed extruded from several mouths of one colony. In the laboratory, when filaments were extruded from the mouths they secured any particulate material contacting them.
In the early hours of the morning, large boli of excrement were often found protruding from opened mouths of these corals. These boli were found to be composed of zooplankton exoskeletons, sand, silt, and other unidentified particulate matter embedded in a thick mucus mat. Figure 33. Colpophyllia sp. - fully expanded soft tissue. Tentacular ridges (TR) with alternate tentacular rows are clearly visible and several mouths (M) can be seen in the oral valleys. 59
Figure 33. 59
Figure 33. Figure 34. Colpophyllia sp. - patterns of ciliary currents on the periphery of the colony as noted during periods of little surge activity.
Figure 35. Colpophyllia sp. - expanded soft tissue structure and ciliary currents.
Figure key: ctv, central thecal valley; ID, IDouth; nk, nematocyst knob; p, peris tome; sc, sclerosepta; t, tentacle; th, theca; ciliary currents. 60
Figure 34.
Figure 35. Figure 36. Colpophyllia sp. - excretion of fecal bolus (F)
from an open mouth during the morning hou~s.
Figure 37. Colpophyllia sp. - collection of particulate material by a mucus strand (MS). These strands were most commonly found in a curve of the thecal ridge as in this case. 61
Figure '36.
Figure 37. 61
Figure '36.
Figure 37. Figure 38. Colpophyllia sp. - the 'zipper actiod (ZA) of tentacular ridges as they start to fold over, sealing the prey beneath.
\ t 62
Figure 38. 62
Figure 38. Figure 39. 'Zipper action' typical of Group II.
A: prey contacts tentacle which then starts to fold over. B: tentacle ridge is starting to shift down the thecal wall, followed by the opposite ridge. C: the tentacles of the opposing ridges have interlocked as they move toward the oral valley. D: the mouth has opened to receive the prey as the tentacles complete their movement.
Figure key: ctv, central thecal valley; m, mouth; nk, nematocyst knob; p, peris tome; t, tentacle; tr, tentacular ridge;
z, zooplankton; -- -t movement of body. 63
z 1 nk
A
B
,~ .. - c
o
. Figure 39. Figure 40. Colpophyllia sp. - capture of small zooplankton by individual tentacles. The mouth shifts up the opposite thecal wall to receive the prey.
Figure 41. Copophyllia sp. - baffle or 'snow-fence' effect: eddy currents caused by the tentacles as the currents pass over the colony surface cause the suspended particles to fall into the oral valleys.
Figure key: ctv, central thecal valley; f, food mass; t, tentacle; th, theca; tr, tentacular ridge;
z, zooplankton; ~ water currents. ti4
Figure 40.
ctv ------/
Figure 41. 65
Diploria clivosa was found encrusting the rocky substrate of the inner-reef zone, where field observations proved very difficult. The soft tissue was expanded during the day and night. As the thecal ridges were narrow and had the lowest relief of this Group, the surface of the expanded soft tissue appeared somewhat undifferentiated as to thecal ridges and valleys (Figure 42). The tentacles were short (2 to
4 mm), stout, and equipped with nematocyst batteries that formed semi circular bands and terminated at the tip of the tentacle with large knobs. The tentacles originated from a tentacular ridge that varied in position on the thecal wall. The most conspicuous characteristic of the soft tissue was the polypous coenosarc surface.
Ciliary currents were similar to those of Colpophyllia natans and laboratory work indicated that mucus production and strand formation were more profuse than in other members of this group. The
'zipper action' of the tentacles was not uniform or very effective.
The polypous surface of the coenosarc did not increase the carnivorous feeding ability, for although brine shrimp contacted this area, they were not secured. Figure 42. Diplora clivosa - fully expanded soft tissue. Note the undifferentiated appearance of the oral valleys and thecal ridges. The band like nematocyst batteries (NB) and polypous coenosarc are clearly visible. 66
Figure 42. 66
Fig v re 42.. 67
Diploria strigosa was distributed over the inner- and outer reef zones between depths of 2 and 40 m. The soft tissue was observed to expand between dusk and dawn (Figure 43), although during the day the soft tissue over the oral valleys was occasionally raised.
Ciliary currents and tentacular feeding patterns were similar to those of Colpophyllia natans.
During the feeding of a suspension of ground fish food to a colony in the laboratory, a regular pattern of parallel white filamentous bandswereobserved below the soft tissue, between the indentations of the septa. This phenomenon was very similar to that observed in Favia fragum and Helioseris cuculata.
Solid waste material, composed chiefly of sand, silt, and zooplankton exoskeletons, was most actively excreted in the morning.
During excretion the mouths opened wide, and the filaments actively attached to the bolus released it as soon as they reached the
stomodeaum. Figure 43. Diploria strigosa - fully expanded soft tissue as seen during the night. Several mouths (M) are visible in the oral valleys. Note the mesenterial filaments (F) extending into the tentacular cavities. 68
Fig ure 43. 68
Figure 43. 69
Diploria labyrinthiformis was found in the same areas as
~ strigosa. Th~ soft tissue was completely expanded during the night (Figure 44) anq during the day, the tentacles were sometimes expanded to approximately one-third of their greatest length. The tentacles were armed with short, horizontal, banded batteries of nematocysts.
Ciliary currents and mucus production were similar to those of Colpophyllia natans and tentacular feeding using the 'zipper action' was very effective (F~gure 45}. Figure 44. Diploria labyrinthiformis - fully expanded soft tissue as observed during the night. Tentacular ridges (TR) and the central thecal valleys (CTV) are weil defined in this species. 70
Figure 44. 70
Figure 44. Figure 45. Diploria labyrinthiformis -'zipper action' (ZA) demonstrated during the capture of several
released~. salina. 71
Figure 45. 71
Figure 45. 72
Mycetophy11ia 1amarckiana was found in iso1ated colonies at depths of 10 to 35 m. The soft tissue was comp1ete1y expanded on1y at night (Figure 46) and, un1ike other species in this Group, the po1yps had conica1 peris tomes raised about 2 to 3 mm. Occasiona11y bi- or trifurcate tentac1es were observed on the theca1 ridges and large,
solitary tentac1es with sub-tentac1es branching from them, were often located on the wide oral valley f100rs (Figure 47).
Ci1iary currents were weak, but were simi1ar to those in the
Dip1oria. Mucus feeding was common in the field and appeared to be an important mechanism. Tentacular feeding was of a typical pattern except for a pronounced doub1ing over of the tentac1e tips when seizing prey. The peristome increased in length and moved across the wide oral valley toward the food as the musculature of the oral region contracted (Figure 48). Mesenterial filaments were frequent1y observed in the tentacu1ar cavities. Juvenile colonies demonstrated feeding patterns very similar to those of the cora1s in Group l
(Figure 49). Figure 46. Mycetophyllia lamarckiana - portion of tentacular ridge showing fully.expanded soft tissue structure. Note upward bend of the tentacles along the thecal ridges. The central thecal valley is clear in this photograph.(CTV). 73
Figu re 461 73
Figu re 46, Figure 47. MYcetophyllia lamarckiana - expanded soft tissue structures. Note the raised peris tomes and solitary tentacle with sub-tentacles in centre or oral valley.
Figure 48. Mycetophyllia lamarckiana - tentacular feeding. The sequence of movements (A to D) of the tentacles and the peris tome is illustrated.
Figure key: ctv, central thecal valley; m, mouth; nk, nematocyst knob; p, peris tome; st, sub-tentacle; tc, tentacle contracted; tr, tentacular ridge; z, zooplankton;
-- ~ movement of body. 74
ctv ctv \ f
Figure 47.
A B
ctv 1
c
Figure 48. Figure 49. Juvenile forro of Mycetophyllia lamarckiana. Tentacular feeding of particulate leptopel (P). The feeding pattern is siroilar to that of Group 1. 75
Figure 49. 75 76
GROUP III
Corais of this Group did not appear to rely to a great extent on their tentacles as a means of capturing visible zooplankton, because the tentacles were generally short. The trapping of particulate material was brought about by means of mucus secretions and aided by either the concavity of the individuai polyp cups, as in the Siderastrea, or by the Iow relief of the coral surface as in Agaricia Iamarcki.
Expansion of the soft tissue was generally limited to the appearance of the short tentacles during the night. Siderastrea radians and~. siderea, however, were found expanded during the day as weIl. 77
Siderastrea siderea occurred from the inner- to the mid-reef
zones,between depths of land 25 m. Colonies were generally
hemispherical in form and ranged from a few centimeters to over a meter
in diameter. The soft tissue was usually completely expanded both day
and night, although there were periods during the day when the tentacles were only partially expanded. There were three cycles of tentacles, as
illustrated in Figure 50. The tentacles of the inner two cycles were
bifurcate. This arrangement covered the entire soft tissue with a
uniform distribution of tentacles. The mouth was usually elevated by
the conical peris tome to the same height as the tentacles and, unlike
other species, appeared to be surrounded by a white border of nematocyst
batteries.
Ciliary currents
In the laboratory, ~. siderea gave off great quantities of mucus,
and consequently ciliary currents were difficult to trace. In order to
remove the excess mucus, strong water currents were generated in the
finger bowls. Strong ciliary currents travelled up the cup walls and
around the tentacles untii they reached the edge of the polyp (Figure 50),
where they were met by opposing currents from adjacent polyps. Currents
over the peris tome were directed orally and because of the raised mouth,
particles were sent upwards out of the cup.
The presence of copious amounts of mucus secretions in the
laboratory and on the reef, suggests that the role of mucus is important.
Almost every polyp in the field contained a loose aggregate of particulate
material embedded in mucus (Figure 51). Some of the aggregates were 78
blown off by surge currents (as was also seen by Johannes, 1967)~ and others were drawn into the mouths. Extremely large, thick strands and cords with attached detritus were also found (Figure 52).
Tentacular feeding
Zooplankton capture was basically similar in pattern to that of other corals such as MYcetophyllia lamarckiana. The distance from
the mouth to the short tentacles was relatively long and transfer of
the prey to the mouth was achieved by the mouth and tentacles moving toward each other (Figure 53), as in M. lamarckiana. Solid wastes were found to be held together with mucus and were excreted as a dense pellet (Figure 54). Figure 50. Siderastrea siderea - ciliary currents found in the polyp cup. The tentacular arrangement is indicated as (1) for the inner cycle, (M) for the middle cycle, and (0) for the outer cycle. For explanation see text. The tentacles are about 1 mm in length. 79
Figure 50. Figure 51. Siderastrea siderea - aggregates of particulate material and mucus. These boli and mucus strands were found in almost every polYPe
Figure 52. Siderastrea siderea - collection of particulate material on a thick mucus strand. 80
Figure 51.
Figure 52. 80
Figure 51.
"'"
" •~ ~. ,
,", _...1.<. - Fi 9 ure 52. Figure 53. Siderastrea siderea - capture and ingestion
of ~. salina.
A: ~. salina contacting tentacle of rniddle cycle. B: Tentacle contraeting as the peristome leans toward the tentacle. C: Mouth opens as the brine shrimp is deposited by the tentacle. Contraction of the musculature has drawn the tentacles and mouth together.
Figure 54. Siderastrea siderea - excretion of fecal pellet from polyp during the morning.
Figure key: ez, edge-zone; m, mouth; n, nematocyst batteries; p, peris tome; te, tentacle eontraeted; z, zooplankton; movement of body. 81
'0 A
Figure 53 .
.figure 54. 81
'0 A
Figure 53 .
.figure 54. 82
Siderastrea radians occurred in the shallow water of the inner
reef. As a very few specimens were found on the leeward side of the
island, those studied were collected from Bath (Figure 1). The
colonies were small hemispherical or encrusting forros, usually not more
than 5 cm in diameter.
Specimens expanded their soft tissue during the day and night.
The tentacles appeared very dark and the outer cycle reached weil above
the skeleton, giving the colony a similar appearance ta Dichocoenia
stokesi. As in~. siderea there were three cycles of tentacles, but
the inner and outer cycles were bifurcate, while the middle cycle was
regular (Figure 55).
Ciliary currents (Figure 55) and mucus feeding activity appeared
identical ta those of ~. siderea. Tentacular feeding was also similar,
but ~. radians trapped and ingested its prey more quickly.
Organic matter (fish food) settling on the surface of the polyps
èvoked a response much the same as that observed in Madracis mirabilis.
After the particles had been on the oral disc for a short period, the
latter collapsed and the mouth opened ta form a funnel-shaped cup.
This resulted in tœdownward movement of the particles through the mOt~th
and into the coelenteron (Figure 56). Figure 55. Siderastrea radians - ciliary currents and tentacular arrangement. The tentacular arrangement is indicated as (I) for inner cycle, (M) for middle cycle, and (0) for outer cycle.
Figure 56. Siderastrea radians - reaction of the polyp to a drop of suspended fish food. A: particles landing on the surface. B: sinking of the oral disc and opening of the mouth. As the particles fell into the mouth it appeared as if they had also become entangled with mucus.
Figure key: ez, edge-zone; m, mouth; ms, mucus strands; nk, nematocyst knob; t, tentacle; ----+ ciliary
currents; - -~ movement of body. 83
Figure 55.
ez 1
A
ez
B
Figure 56. 84
Agaricia agaricites; f. agaricites; f. danae; and f. purpurea.
Colonies of !. agaricites were found in the shallow waters of the inner
reef and to depths of 40 m on the outer-reefs. The three forms are described together as they had similar feeding behaviour patterns. At night the soft tissue was limited to the appearance of short tentacles
(Figure 57). During one period of observations in the field, however, a colony was found to have several polyps situated on the periphery of
the colony with 'sweeper tentacles', 4 to 6 mm in length (Figure 58).
Ciliary currents reserohled those of Siderastrea siderea. As added carmine particles travelled up the thecal walls, they became entangled in mucus, this was either drawn into the coelenteron or removed by water currents.
The concavity of the individual polyp cups appeared to play an important role in the trapping of particulate material. As the particles passed over the colony surface they often settled in the depression of the cups. Once in the cups, the mucus secretion from the coral seemed to hold and aggregate the particles as mucus boli, many of which were ingested. Thick mucus cords (Figure 59) were observed to be effective in the capture of suspended particles and A. salina, both in the field and in the laboratory.
Tentacular feeding on naturally available zooplankton was not observed, but capture of released!. salina was essentially the same as in~. siderea. The 'sweeper tentacles', however, were found to be extremely effective in the securing of brine shrimp, although contraction of these tentacles was slow.
Protrusion of mesenterial filaments into the tentacular cavities is shown in Figure 58. Figure 57. Agaricia agaricites - colony surface, showing the numerous polyp depressions in which particulate matter is collected and retained. The short tentacles are shawn bordering the mouths. 85
Figure 57. 85
Figure 57. Figure 58. Agaricia agaricites - crevice between~. agaricites and Diploria strigosa showing 'sweeper tentacles'. A mesenterial filament can be seen extending into the tentacular cavity.(marked MF).
Figure 59. Agaricia agaricites - mucus strand feeding. Particulate material collected by this thick strand is visible. 86
Figure 58.
Figure 59. 86
~_r_."
F-igure 58.
Figure 59. 87
Agaricia 1amarcki formed thin 1aminar colonies and was common1y found on the outer-reef face between 20 and 40 m.
Short tentac1es (usua11y 12 per po1yp) of a whitish appearance, arranged in a tight cycle were expanded during the night (Figure 60).
Ci1iary currents, mucus secretion and the formation of mucus bo1i were much the same as those of ~. agaricites. A1though the tentac1es were sma11 they were seen to capture zoop1ankton. Figure 60. Agaricia lamarcki - soft tissue structures. Note short tentacles and confluent septal ridges. A large bolus of mucus and particulate material has been formed and is about to be removed by surge currents. 88
Figure 60. 88
Figure 60. 89
He1ioseris cucu1ata occurred in colonies scattered over the mid- and outer-reefs. Many of the individua1 po1yp cups were concave in shape, having high cora11ite wa11s and a1most horizontal axes
(Figure 61). In the field, short tentac1es were seen extended around the mouth during the night. Laboratory specimens, hawever, did not ex tend these tentac1es and it is fe1t that this was re1ated to the disturbance during collection.
Laboratory examination shawed that the ci1iary currents radiated from the mouth a10ng the confluent septa1 ridges. The po1yp cups in the central area of the co1ony possessed a1most vertical cora11ite wa11s.
As the currents trave11ed up these ridges, the transported materia1 was presumab1y removed by surge currents. One side of the cup formed a very 1aw but vertical wall and the cora11ite wallon the other side of the cup was horizontal, often extending to the periphery of the co1ony.
Added carmine partic1es were found to trave1 out of a cup to the edge of the cora11ite, where they wou1d drop into the next cup, 1anding on the exterior edge of the mouth and continue from there to be swept to the periphery (Figure 62).
Mucus secretion activity was simi1ar to that of Agaricia agaricites. The securing and ingesting of!. sa1ina by tentac1es was demonstrated in the field, but cou1d not be shawn in the 1aboratory since the tentac1es did not expand.
The appearance of the fi1amentous structures 1ying within the coe1enteron was often noted in the 1aboratory. The structures formed a circu1ar pattern around the mouth. Figure 61. Helioseris cuculata - large portion of colony with soft tissue contracted. The lack of definite boundaries for each coral lite and the confluent septa are apparent. 90
Figure 61. 90
Figvre 61. Figure 62. Helioseris cuculata - ciliary currents travelling over the confluent septa toward the periphery of the colony. Mucus strands are shown entrapping the carmine particles which are then drawn back into the mouth.
Figure key: m, mou th; ms, mucus strand; pr, periphery; th, theca; tp, trace particle; ciliary current. j 91 j j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
Figure 62. j j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j
j 92
Mycetophyllia danaana (Figure 63) and Mycetophyllia sp. (Figure
64) occurred in the mid- and outer-reef zones. They resembled each other closely except for subtle differences in colouration and M. danaana did not have the continuity of the thecal ridges that the other species possessed.
Soft tissue expanded during the dark hours. However, sections of the tentacular ridges generally remained contracted, and unlike other corals of Group III, they had expanded thecal platfor~ with convex surfaces.
Ciliary currents followed patterns like those of M. lamarckiana.
Collection and ingestion of particulate material by mucus strings
(F~gure 63), or by the formation of loose mucus aggregates in the oral valleys (Figure 64), was observed on the reef. Tentacles were observed to capture &. salina if these were released in large quantities, but only on a few occasions were naturally occurring zooplankton trapped. Figure 63. Mycetophyllia danaana - mucus strings (MS) over colony with attached particulate material.
Figure 64. Mycetophyllia sp. - bolus of mucus (B) and particùlate material is shawn in the oral valley (lower left corner). Mouths (M) and tentacles (T) are indicated.
\ 93
Figure 63,
Fig u re 64. 93
Figure 63,
.... -\.. :'~~
~:- ,
Fig ure 64. 94
The few colonies of MYcetophyllia ferox that were found on the reef were distributed between depths of 10 to 30 m. The colonies were generally of a delicate, frond-like shape, stalked, and sometimes reached 20 cm in diameter. The colour of the coral was grayish-red or green.
At night there was a slight expansion of the soft tissue and delicate short tentacles appeared along the thecal ridges. The oral valleys were broad and covered with small nodules about 1 mm in height and diameter (Figure 65). Ciliary currents followed patterns similar to those of other MYcetophyllia, except over the valley floors where the nodules created irregular patterns. Mucus strands were abundant and trapped both brine shrimp and particulate material. !. salina released near the surface of a colony was not trapped by the coral.
Because of these observations and the shortness and sparsity of tentacles, it is suspected that tentacular feeding is of little importance. Figure 65. MWcetophyllia ferox - colony fully expanded at night. Note incomplete expansion of the tentacular ridges (TR), and polypous coenosarc (C). Moutœare indicated (M). 95
Figure 65. 95
Figure 65. 96
Montastrea annularis was found in abundance from the shallm~s
of the mid-reef to depths of 40 m on the outer-reef. The colonies were genera1ly bou1der-shaped when they were found on the reef floor
and tended toward shingle-shaped forms on the sides of buttresses and reef slopes (Lewis, 1960).
Complete expansion of the soft tissue was generally observed
during the night (Figure 66) and occasionally a colony or portion of
a colony was found with expanded polyps during the day. Often the
polyps on the top-most surface remained closed, while those on the
sides were in varying degrees of expansion (Figure 67).
The morpho1ogy of the soft tissue structure was much different
from that of other corals examined. The tentacles were short and
slender, with white nematocyst knobs, and just reached or were bent
slightly over the rim of the thecal cup. The soft tissue wall of the
thecal cup extended vertically to form a turret-shaped structure for
each polYPe The mouth was elevated on a conical peristome to a level
slightly lower than the rim of the polyp cup.
Ciliary currents generally appeared weak unless stimulated by
organic or offensive substances. A drop of suspended fish food not
only caused strong currents to sweep up the outside of the polyp, but
also resulted in the expansion of the thecal walls. Currents were
found to travel from the base of the inner side of the thecal wall
toward the centre of the oral dise. The trace particles then became
embedded in mucus strings and were drawn into the mouth.
Mucus boli were observed in many of the polyp cups in the field.
These boli were effectively held within the polyp cups de~pite heavy 97
surge action. The reasons for this would appear to be the turret
shape of the cup and the mucus strands helping to anchor the particles
to the surface.
During many hours of observation in the field no zooplankton were observed to be caught by the polyps. When a sufficient
concentration of ~. salina was released in the immediate vicinity of
a polyp, an occasional shrimp was caught when it contacted a tentacle
tip. Once secured by the tentacle, the portion of the wall
circumjacent to it immediately folded over and was followed by the
remainder of the wall. This action completely sealed off any possible
escape of the prey. Figure 66. Montastrea annularis - fully expanded. ~e extended tentacular ridges form the turret shaped polyp structures, with the tentacle tips (T) barely discernable over the rim.
Figure 67. Montastrea annularis - colony with polyps in various postures of partial (P) and complete (C) expansion. 98
Figure 66.
Figure 67. 98
Fig ure
Figure 6'1 • 99
Acropora palmata was found as isolated colonies on the leeward reefs of Barbados. As the individual corallites were very fragile, great care was taken in transporting specimens to the laboratory.
Polyps were expanded during the day and night, although not all
the polyps of a colony were expanded to the same extent. Generally,
the slightly larger ones along the apical margin were expanded to the greatest degree (Figure 68). Water currents helped induce the polyps
to expand, although they made close observation more difficult. Each cylindrical corallite was crowned with a ring of about twelve translucent stubby tentacles, all of approximately the same length, but having no noticeable nematocyst batteries (Figure 69).
A. palmata usually grew in regions of shallow water and relatively heavy surf. Ciliary currents, traced in the laboratory, moved away from the mouth and also distally from the base of the cylindrical corallites.
In the field, mucus strings with attached particles were
extended from the polyps and in the laboratory, powdered fish food caught on similar strings were drawn into the mouths.
Tentacular capture of zooplankton was not observed in the
field during many hours of observation. In the laboratory, brine
shrimp were released so as to contact a partially expanded polyp; on contact a tentacle would contract but did not hold the shrimp. Figure 68. Acropora palmata - apical margin of colony showing larger, fully expanded polyps.
Figure 69. Acropora palmata - section of colony with fully expanded polyps, showing the short, stubby tentacles and their arrangement. Nematocyst batteries are not noticeable. 100
Figure 68.
Fig u re 69. 100
Figure 68.
Figure 69 101
Acropora cervicornis genera11y occurred between depths of 1 and 25 m over the reefs. The tentacu1ar arrangement, noticeab1y different from that of~. pa1mata,had six extended tentac1es a1ternating with six rudimentary ones, with one tentac1e longer than the others
(Figure 70). Tentacu1ar nematocyst batteries were sma11 but c1ear1y visible and, in the field, ~. sa1ina was successfu11y secured by the po1yp tentac1es. The apical po1yp was most efficient in capturing prey.
Mucus strings with attached particu1ate matter were observed extending from po1yps in the field. During the day several colonies were seen extruding large (up to 7.5 mm diameter) fecal pellets from the apical polyps. Figure 70. Acropora cervicornis - expanded soft tissue showing the different tentacular arrangement of the large apical polyp as compared to the smaller polyps (a weIl defined polyp is indicated X). Nematocyst batteries are barely visible. 102
Figure 70. 102
Figure 70. 103
GROUP IV
The corals of this Group relied almost exclusively on tentacles for the capture of food, although sometimes mucus strands and nets were employed. The expanded soft tissue consisted of long, well-armed tentacles which completely covered the surface.
This Group is comprised of Dendrogyra cylindrus and Meandrina meandrites f. meandrites and f. danae.
Dendrogyra cylindrus was found only in a few isolated colonies in the mid-reef zone, between depths of 5 and 20 m. Mature colonies were found to reach heights'oi 1 to 1.5 m.
The soft tissue was expanded both day and night (Figure 71), but on occasion during the day, periods of only partial expansion were observed. The tentacles were about 1 cm in length and so numerous that other features of the soft tissue were obscured from view.
Laboratory specimens were subjected to a good deal of shock during the process of fracturing them from a colony and consequently only a few completely recovered in the laboratory.
The pillar form of the colonies facilitated removal of waste material by a combination of gravitational force and surge currents.
Examination of the ciliary currents in the laboratory indicated that these currents travelled out of the oral valleys, between the tentacles, to the edge of the thecal ridges.
The tentacles were long (6 to 12 mm) and densely covered with small nematocyst batteries (Figure 71). They were rapid at securing and transferring aIl sizes of zooplankton (up to 2 cm) to the mouths.
Mucus strands were occasionally observed in the field. Small 104
quantities of particu1ate materia1 adhered to them and they were a1so capable of securing zoop1ankton. Occasiona11y these mucus strands with their attached food were transferred to the mouths by the tentac1es.
However, heavi1y 1aden strands were often swept away by surge currents. Figure 71. Dendrosyra cylindrus - this photograph shows a portion of the dense tentacular surface. The long tentacles with their numerous small nematocyst batteries can be seen clearly. One mouth (M) is visible, otherwise there appears to be little order, to the expanded soft tissue. 105
Figure 7\. 105
Figure 7\. 106
Bothfurms of Meandrina meandrites, f. meandrites and f. danae, were common1y found on the inner- and outer-reefs. The colonies were
f1at or dome-shaped, reaching sizes of about 40 cm. The f. meandrites was distinguished by its translucent ye110w hue, whi1e f. danae
appeared as a darker brown (Figure 72).
The tentacles were expanded only during the night and reached
a length of approximately 10 mm. Duting the day, the tentacles were
c1ear1y visible (Figure 73), but were on1y 2 to 4 mm in 1ength. The
mouths of f. meandrites were slit or oval-shaped and did not usua1ly
exceed 6 mm in 1ength. The tentacles were somewhat thinner and
shorter in f. danae and the nematocyst batteries appeared as circular
dots. The mouths of f. danae were usual1y long, slit-1ike structures,
reaching 2 to 3 cm in length (Figure 74) and the nematocyst batteries has more irregular shapes. This form was 1ess sensitive to light than
f. meandrites.
Ci1iary currents and mucus secretions
Ci1iary currents traced in the laboratory gave a pattern resembling
that of Co1pophy1lia nat&ns. Currents travelled up the conical peristome
toward the mouth. From the base of the oral valley, currents moved up between the septa1 fà1ds and tentacles, where they were met by opposing currents from the central theca1 valley. The particles used to trace
the currents inevitably became entang1ed in mucus strings, which were
subsequently drawn into the mouths.
In the field, during the day, boli of mucus and particulate materia1 were often observed in the oral va1leys. Mucus strands laden with particu1ate materia1, attached to tentac1es or extruding from mouths, were seen both during the day and at night (Figure 75). 107
Tentacular feeding
Tentacular feeding was voracious and quick in both of these forms. The pattern was typical of corals in Group l or II, with the exception that the tentacle coiled around the prey before depositing it into the mouth. Small zooplankton were seized and ingested by individual tentacles, while large zooplankton were captured by several tentacles. Figure 72. Meandrina meandrites f. meandrites and f. danae - both colonies are fully expanded, with f. meandrites on the right and f. danae on the left.
Figure 73. Meandrina meandrites - partial expansion of the soft tissue during the day. The thecal ridges (TR) and mouths (M) are indicated. 108
Fig ure 72.
Figure 73. 108
Figure
Figure 73 Figure 74. Meandrina meandrites f. danae - showing expanded soft tissue, long sulcate mouths CM) and numerous nematocyst batteries (N).
Figure 75. Meandrina meandrites - collection of particulate material on a mucus strand during the day. 109
Figure 74.
'':'(.
,l' A, .•.. ,,:,. .... =:a '~,~j .", '"......
Fig ure 75. 109
t~J~ .-. c;;1 ". '. " .
Figure 110
DISCUSSION
The West Indian corals, studied on the Bellairs reefs of Barbados, secured roacroscopic food by tentacular activity and by mucus secretion.
The roaterial ingested by the corals varied from large zooplankton to fine suspended particulate material.
The diurnal change in the 'capturing surfaces' of roany species appears to be related to the occurrence of plankton. At night, plankton are more abundant near the bot tom than higher up in the water column
(Emery, 1968). It is during this night period that the corals with the longest and most numerous tentac1es expand their 'capturing surfaces', presuroably in response to the avai1able prey. The contracted posture during the day, however, was found to assist the effective collection of particulate and detrital materia1 in many species.
Corals possessing a dense coverage of individual po1yps with short tentac1es, such as Porites spp., Madracis spp., Siderastrea spp., Acropora spp., Dip10ra clivosa and Stephanocoenia miche1ini, were expanded both day and night. Generally those species with the longest and most active tentacles expanded their soft tissue only at night. Examples are the
'brain corals' of Group II, Eusmilia fastigiata, Dichocoenia stokesi,
Mussa angulosa and Meandrina meandrites. In these species, partial expansion was observed during the day in colonies located in caves, in crevices, or under coral overhangs. A sampling of p1ankton swarms found in these areas during the day by Emery (1968), gave a tentative estiroate of abundance of 100,000 copepods 1m3 of water. It is probable that not only the lower light intensity, but also the organic substances 111
given off by the zoop1ankton, induce cora1s living in these areas to extend their tentac1es. Laboratory evidence supported this hypothesis.
Introduction of !. sa1ina into finger bow1s containing specimens resu1ted in a noticeab1e expansion of the soft tissue of species in
Groups l, II, and IV.
Dendrogya cy1indrus a1so had long active tentac1es, but remained expanded during the day and night. However, un1ike other massive cora1s, this species formed thick, vertical (up to 1.5 m) pi11ars.
Species such as Siderastrea siderea, ~. radians, Agaricia agaricites, He1ioseris cucu1ata and Montastrea annu1aris, with short tentac1es and recessed po1yps (except for the turret-shaped ones of
~. annu1aris) appeared to re1y on this pitted topography of the co1ony surface, mucus feeding mechanisms, and possib1y ci1iary activity for the collection of their food. Particu1ate materia1, either sett1ing on the colonies or suspended in the water, was the most common substance trapped and ingested by the cora1s. Mucus strands successfu11y entang1ed
!. sa1ina re1eased in high concentrations near the surface of these colonies. However, natura11y avai1ab1e zoop1ankton was rare1y seen trapped and ingested by this means.
The Acroporidae are considered "the most protean and probab1y the most high1y deve10ped (at 1east, the most successfu1) genus of cora1s with over 125 living species representing 25% of the total species of living reef corals." (Vaughan and Wells, 1943, page 107). They a1so have the highest growth rate recorded from the Atlantic region (Lewis ~ al., 1968).
Colonies of both Acropora cervicornis and !. pa1mata were observed in
Aruba and MuStique growing from the reef oT. shore bottom in such dense 112
stands that they were impenetrab1e to a swimmer.
Thus it is paradoxica1 that the tentac1e and mucus feeding mechanisms were fOllnd to be so ineffectual. It is apparent that the nutritiona1 sources availab1e to this genus must be carefu11y examined.
Bay10r and Sutc1iffe (1963, page 371) have proposed " •.. that large communities of intertida1 fi1ter feeders may be supported part1y by an abundance of particu1ate materia1 produced by the foaming action of waves breaking on rocks and beaches." As both species were often seen growing close to the shore or water surface, this nutritiona1 source cou1d weIl be of importance ta them and may a1so he1p to exp1ain the
1ack of tentacu1ar [~eding.
In genera1 the tentac1es were not 1imited to the trapping of zoop1ankton. Nematocyst discharges effectively secured sand, silt, organic, and even meta11ic particles, and the tentacles deposited aIl materia1s so secured in the polyp mouths.
Extremely long tentac1es, the 'sweeper tentac1es', were observed in Madracis mirabilis, Montastrea cavernosa, Agaricia agaricites, and
Stephanocoenia michelini. These tentac1es were from polyps genera1ly
10cated on the periphery of the colony. Often the edge of the co10ny formed a crevice or narrow channel with another colony. Since surge currents passing between the colonies were swift, the greater 1ength of tentacles and greater volume of water screened by them, presumab1y increased the trapping potential of the polyps. In the 1aboratory, an induced water current that approximated the rate of the surge currents, not only caused a genera1 expansion of the soft tissue but a marked increase in the length of the tentac1es. 113
Mucus strings a~d nets were often observed spanning large areas
of a co1ony surface in the field. The more common1y occurring, thicker
and shorter strands extruded from the mouths, were drawn in with their
attached materia1 after a variable period of a few minutes to a few hours. A1though the figures inc1uded show on1y those strands that adhered to the co1ony surface, strands were often very long and were
swept about by the surge; they were thus very effective traps for
particu1ate materia1 and zoop1ankton.
In the 1aboratory, nets of mucus 1ying over specimens were often observed. Particu1ate materia1 landing on the surface became entang1ed
in these nets, which were subsequent1y drawn into the mouths. Even
after the surface had been c1eared, new strands immediate1y appeared between each sc1erosepta1 fo1d. Carmine partic1es 1anding on the oral disc trave11ed on1y a short distance before becoming entang1ed in these new1y forming strands. In a11 cases, the strands were subsequent1y
drawn into the mouths. It is be1ieved that this phenomenon accounts
for many of the reports of apparent ci1iary reversa1s. In the field, mucus nets usual1y turned into thick strands, which swept a wide area of the co1ony.
Ci1iary currents examined in the 1aboratory showed a consistent
and definite pattern in a11 species. As the currents did not 1ead direct1y into the mouths, it is doubtfu1 that they are a direct feeding mechanism. Partic1es 1anding on the surface of a co1ony resu1ted in an increase in the rate of ci1iary currents as we11 as an increase in mucus production.
Using a simi1ar technique in the field, ci1iary currents cou1d 114
not be traced. Surge currents and gravity removed the particles as soon as they touched the surface. Large grains of sand or silt not blown off by the currents did appear to be slowly removed from the surface by ciliary action.
Observations suggest, therefore, that a primary function of the cilia is to prevent materia1 from becoming embedded in the soft tissue.
Once 1ifted off the surface of the coral, the partic1es slide free1y and either become trapped in mucus or are removed by gravity and surge currents.
Yonge (1930, page 55) writes that in certain of the Agaricidae, where the tentacles are reduced or lost, ciliary currents are considered to be " ••.. exclusive1y concerned with the transport or presentation of food to the mouth . • Il However, the observations in this study indicate that ciliary currents did not transport materia1 to the mouth.
Yonge (1930, page 52) also conc1uded that "cora1s with sma11 po1yps, such as . . . Porites, have upward1y directed ciliary currents on the co1umn and outer sides of the tentac1es, so that food captured by the nematocysts on the surface of the coenosarc between the po1yps is conveyed in this manner to the mouth." Contrary to these observations,
Porites porites, 1. astreoides, 1. furcata and 1. divaricata were found to have downward1y directed currents on the co1umn. A1so no food was seen captured on the surface of the coenosarc between the po1yps and when!. sa1ina contacted this area, they appeared to suffer no il1 effects.
Laboratory examination of specimens kept for a long period of time, or exposed to different experimenta1 conditions, frequent1y showed unexpected and abnormal behaviour. It was on1y after considerable 115
experience in collection and selection of specimens that consistent patterns of behaviour could be observed. These specimens did not exhibit any of the bizarre behaviour seen in preliminary work or noted in some of the older literature. Field observations strongly indicated that many of these behavioural patterns seen in the laboratory were not only unimportant, but probably did not occur in nature.
An example is the commonly held view that most species shoot out mesenterial filaments through the ectoderm as a norrnal occurrence.
Several hundred observations of this phenomenon were made by the investigator while assisting in a pollution study (Lewis, 1971) and this behaviour was considered a syndrome of an unhealthy specimen, or of one having been exposed to stress conditions. Extracoelenteric feeding by mesenterial filaments was not observed in the field during the 150 or more hours of close observation.
The protrusion of filaments into the tentacular cavities occurred both in thefield and in the laboratory. This event was frequently observed in the 'sweeper tentacles'.
A general swelling of the soft tissue was observed after~. salina or weak concentrations of amino acids were added to finger bowls in which the specimens were examined. Swelling occurred when speéimens were contracted or expanded, and was observed in Madracis spp., Siderastrea spp., Agaricia spp., Colpophyllia natans, Mycetophyllia lamarckiana, and
Meandrina meandrites.
Excretion of solid waste was most frequent in the morning.
Fecal material examined contained sand, silt, exoskeletons of zooplankton, and other unidentified material. Usually the feces formed compact 116
pellets or 100se aggregates held together by mucus. 117
SUMMARY
1. The tentacles and their batteries of nematocysts were important devices in the capture and ingestion of zooplankton. The tentacles trapped particulate material with equal facility.
2. The 'capturing surface' of reef corals retained not only zooplankton, but also sand, silt, leptopel, and a variety of other particulate material suspended in the water.
3. The 'zipper action' of the tentacles of the 'brain corals' is described, and was observed to be extremely effective in the capture of a wide size range of zooplankton.
4. 'SWeeper tentacles' were observed in Madracis mirabilis,
Montastrea cavernosa, Stephanocoenia stokesi, and Agaricia agaricites.
In both~. agaricites and~. cavernosa these tentacles were found almost exclusively on those polyps located at the periphery of the colonies.
The lengths of the tentacles found in~. cavernosa were from 30 to 80 mm; those of ~. agaricites were from 3 to 12 mm.
5. Bi- and trifurcate tentacles are reported in Eusmilia fastigiata,
MYcetophvllia lamarckiana, Siderastrea radians, and~. siderea.
Isolated branching tentacles were observed in the middle of oral valleys or discs of MYcetophyllia lamarckiana and Mussa angulosa.
6. Corals expanded during both the day and night were found to have short tentacles (2 to 4 mm). These corals include Madracis spp.,
Parites spp., Acropora spp., Stephanocoenia michelini, and Diploria clivosa, aIl being most common in the shallow waters of the inner- and mid-reef 118
zones. A conspicuous exception was Dendrogyra cylindrus, which had
long tentac1es (approximately 10 mm) and was generally found in the
deeper waters of the mid-reef zone.
7. Ciliary currents were generated by the po1yps at all stages of
expansion and under no conditions were th~y observed to reverse
direction.
8. The speed of the ciliary currents increased with the presence
of weak concentrations (10 ppt) of amino acid solutions or offensive
substances, such as Evan's blue or sulphuric acid.
9. Ciliary currents did not appear to be instrumental in the
transport of macroscopic food particles from the polyp surfaces to the
mouth. In al1 species, the currents were found to carry particles
off the oral di sc toward the edge zone or areas of the polyp structure
exposed to surge currents. In so doing they effectively cleansed the
surface.
10. The most common forms of mucus secretions found in the field were nets, strings extending for long distances over the colony surface,
and thicker strands extending from the mouths of the polyps. After a
variable period these strings and strands were drawn into the mouths.
These forms were efficient in the capture of particu1ate materia1 and
zoop1ankton. Thick blankets of mucus were seen covering colonies of
Pori tes astreoides in the field.
11. The extrusion of mesenterial filaments through the body wall was
not seen in the field during the 150 or more hours of observation. This
is not considered a natura1 feeding activity. 119
12. Mesenterial filaments extruding into the tentacular cavities is reported in Madracis mirabilis, Montastrea cavernosa, Diploria strigosa, Eusmilia fastigiata, and Agaricia agaricites.
13. Solid waste was excreted most frequently in the morning and was found to contain sand, silt, exoskeletons of zooplankton, and other unidentified material. 120
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