STUDIES ON THE NATURAL HISTORY OF THE CARIBBEAN REGION: Vol. 71, 1992 Endolithicalgaein livingstony corals: algal con- centrations under influenceof depth-dependent lightconditionsandcoral tissue fluorescence in Agaricia agaricites (L.) and Meandrinameandrites (L.) (Scleractinia, Anthozoa) by Laurent Delvoye Abstract Endolithic in corals: concentrations under in- DELVOYE, L., 1992. algae living stony Algal fluence of depth-dependent light conditions and coral tissue fluorescence in Agaricia agaricites (L) and Meandrina meandrites (L.) (Sclereactinia, Anthozoa). Studies Nat. Hist. Carib- bean Region 71, Amsterdam 1992: 24-41. The relation between Scleractinians and their endolithic algae was studied in the depth of 10 35 in Endolithic concentrations found in the skeleton range to m Curaçao. algal are of corals in dead in coral rubble. The in- under the living tissue stony and never parts or fluences of depth-dependentlight conditions and coral tissue fluorescence on endolithic of both algal concentrations were studied in a non-fluorescent and a fluorescent form Agaricia agaricites and Meandrina meandrites. Spectroscopy shows that this fluorescence has a photosynthetic potential for both their zooxanthellae and their endolithic algae. The hypothesis that the width of the algal con- centrations and their depth below the tissue are correlated with depth on the reef could not be confirmed, with one exception. This only can be explained by the redistribution of zooxanthellae in the coral tissue with increasing depth, making it more transparent. No evidence was found that fluorescence is indeed enhancing the photosynthesis in the endolithic algae of both corals. Ground section histology shows that endolithic algae are in contactwith soft coral tissue and are associated with fungi. Key words: Endolithic algae, stony corals, fluorescence, spectroscopy, algal pigments. • c/oFound. Sci. Res.Car. Region, PlantageMiddenlaan 45, 1018 DC Amsterdam, The Netherlands. ENDOLITHIC ALGAE IN LIVING STONY CORALS 25 INTRODUCTION It has been known that endolithic of the Ostreobium long green algae genus in the skeletons of reef corals And in are present living (DUERDEN 1902). more recent times, also bacteria (DISALVO 1969) and fungi (KENDRICK et al. 1982; BAK & LAANE 1987) have been found. It is clear that endolithic algae and fungi play a role in the erosion of marine carbonate substrates (GOLUBIC 1969; KOHLMEYER 1969). Micro- borings by such organisms in carbonate deposits occur early in the geologi- cal time scale (KOBLUK & RISK 1974). Therefore it is generally assumed that microboring organisms in living corals do indeed contribute to the destruction of reefs, but in fact little is known about their ecology ortheir relationships to living corals (HUTCHINGS of 1986). However, on basis this geologically old relationship, one may as- sume that endolithic micro organisms and their coral hosts have become In coral Meandrina the mutually adapted. some species (Agaricia sp., meandrites) green algal band is found deeper in the skeleton than in other species living S. This in about the same depth range (Sideastrea siderea, radians, Porites sp.). observation suggests that this adaption has species-dependent aspects. Recent histological work has revealed contacts between endolithic algae, fungi and the living coral tissue (PETERS 1984&pers.comm., E. H. GLADFEL- TER pers. comm.) and associations between endolithic algae and fungi (this the ideathat there is established paper), lending support to an relationship between boring micro-organisms and living corals. One ofthe most important abiotic factors in the ecology ofendolithicalgae will be of the availibility photosynthetically active light. Depending on spec- tral composition and penetration in the coral skeleton, the intensity of this 6 light may vary between 10" % and 2.0% of the incident flux (HALLDAL 1968). In the decreases with the the seawater, light intensity depth. At same time, out. longer wavelengths are progessively filtered Between 15 and 20 m there is a transition zone, as most red and yellow light is absorbed QERLOV 1968; DUSTAN 1979). conditions have effect the behaviourof Depth-dependent light may an on endolithic algal concentrationsin living corals. An other effect onendolithic algae is to be expected from the fluorescence ofliving corals, as compared reef. to non-fluorescent corals of the same depth on the This fluorescence 26 LAURENT DELVOYE is caused by substances in the living coral tissue, which are excited by blue and ultraviolet in This of the solar rays sunlight. part spectrum penetrates deep in clear oceanic waters (JERLOV 1968; SCHLICHTER et al., 1987). In this paper the results ofa study on endolithicalgae inliving coralsonareefalong the S.W. coast of Curasao (Netherlands Antilles) are presented, focussing on the following questions: - Does the ofconcentrationsofendolithic in coral skeletons presence algae depend on the presence or absence of living coral tissue? - there between Is a relationship the width ofthe green algal band in the skeletons ofliving corals and their depth on the reef? - Is there a relationship between the distance of the green band from the light receiving surface of the coral and the water depth? - Is fluorescence light from coral hosts active in the photosynthesis oftheir endolithic algae? MATERIALS AND METHODS The carried in first obtain of the study was out two steps: a survey to a general picture distribution of endolithic algae and the occurrence of fluorescence in living corals. Sec- a closer examination of selected the with to the ond, species during survey regard ques- tions stated above. The of the fluorescence of corals studied with for composition light was spectroscopy its photosynthetic potential. In order to reduce local variations and to minimize seasonal for the detailed the second have been collected effects, samples investigation during step, of reef at the same stretch and within a three month's interval of time. Coral colonies or fragments of colonies were collected by means of SCUBA-diving between Buoy 1 and 1 near Piscadera Bay (DELVOYE 1989)on the SW-coast ofCurasao(June - Augustus 1988). Samples of non-fluorescent A. agaricites were collected from about 10, 20 and 30 m, of 35 fluorescent A. agaricites between 17 and m. Both the fluorescent and non-fluorescent forms ofMeandrina meandrites were collected from depthsof about 10, 20 and 30 m. Samples carried the in In the labora- were to laboratory separate plastic bags containing seawater. tory, the samples were labeled and kept in small aerated aquariums. The forfluorescence dark samples were tested in the laboratory at night or in the during daytime, using a Philips 8 W 08 UV-A 'black light' lamp. This type of lamp emits a con- tinuum around 350 which several emission lines nm on mercury are superimposed. of fluorescence, Photographs and spectrograms ifoccurring, were taken when possible. For spectroscopy, a prism spectrograph with a resolution of 5 nm in blue light was em- A SLR-camera, with F/3.5 135 recorded the ployed. equipped a mm objective, spec- Kodak TMax-400 film times from trograms on (Fig. 1). Exposure ranged one to ten minutes. Spectrograms were measured with a calibrated eyepiece micrometer in a stereo binocular microscope. The mercury emission lines at 404.66 and 435.83 nm ofthe 'black light' lampand the Fraunhofer absorption lines B, C, D, E, bl, F, G, H and K in the solar with the spectrum, photographed same set-up, were chosen as references (NORTON 1959). Subsequently, the samples were slabbed on a rock saw, taking care to saw throughthe ENDOLITHIC ALGAE IN LIVING STONY CORALS 27 FIGURE 1. Spectrograph set-up. 1. ‘Blacklight’ lamp under cardboard hood (black inside). 2. Coral sample in small aquarium, with black cardboard on bottom. 3. Front surface aluminized reflects fluorescence into: F/2 — SRL covered mirror, light 4. 50 mm objective with UV-haze filter,acting as a collector and projecting light source on: 5. Adjustable slit in collimating unit. 6. Unit containing three identical 45°-prisms. 7. SRL-camera with modified viewfinder for maximum transmission and eye relief, equipped with a F/3.5 — 135 mm objective. 8. Coarse wavelength scale, for use with bright spectra. point of attachment of the colony and perpendicular to the coral surface. Then the distance from the of the 'hills' the coral surface the bottom of the (taken top on to algal and the width ofthe in the skeleton measured with concentration) green layer were a pair of with of 0.5 This done for several within 2/3 calipers, an accuracy mm. was positions ofthe distance from the centre to the rim of each colony. For each colony, the mean value of calculated. The variation these values from a sequence was around mean ranges 0.5 to 1 mm. For section ground histology according to DONATH (1987) selected sample slabs were fixed in a mixture of36% formalin and seawater (1 + 9, by volume) and stored in sealed Slabs from material to five fixed in the also plastic bags. up years old, same mannerwere used. Sections perpendicular to the coral surface were sawn, ground and polished in a thickness from 10 40 micrometer and stained with iron range to Weigert's hematoxylin- erythrosin-orange-G (DELVOYE 1989; modified), toluidin blue or Heidenhain's Azan (DONATH 1987). In these sections the coral skeletons with endolithic organisms and soft tissue can be studied under the compound microscope, using a magnification of 100- 200x. 28 LAURENT DELVOYE TABLE I PRELIMINARY RESULTS OF A SURVEY ON THE PRESENCE OR ABSENCE