[Advances in Marine Biology] Advances in Marine Biology Volume 22 Volume 22 || Assessing the Effects of “Stress” on Reef Corals

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<ul><li><p>Assessing the Effects of Stress on Reef Corals </p><p>B. E. Brown and L. S. Howard </p><p>Department of Zoology, University of Newcastle upon Tyne Newcastle upon Tyne, England </p><p>I. Introduction . . . . . . . . . . . . . . . . . . . . 1 11. Natural Fluctuations and Man-made Influences . . . . . . . . . . 3 </p><p>A. Assessing changes on coral reefs . . . . . . . . . . . . 3 B. Interpreting temporal changes on coral reefs . . . . . . . . 5 C. 9 D. Predicting recovery of reefs . . . . . . . . . . . . . . 17 </p><p>111. Experimental Studies on Effects of Pollutants on Corals . . . . . . 20 A. Growth rate . . . . . . . . . . . . . . . . . . 20 B. Metabolism . . . . . . . . . . . . . . . . . . 27 C. Loss of zooxanthellae . . . . . . . . . . . . . . . . 29 D. Behavioural responses . . . . . . . . . . . . . . . . 35 E. Reproductive biology . . . . . . . . . . . . . . . . 46 F. Histopathology . . . . . . . . . . . . . . . . . . 48 G. Biochemical and cytochemical indexes . . . . . . . . . . 50 </p><p>IV. Discussion and Future Research Needs . . . . . . . . . . . . 51 References . . . . . . . . . . . . . . . . . . . . 55 </p><p>Effects and apparent lack of effects of pollution on coral reefs . . . . </p><p>1. Introduction </p><p>Some years ago Johannes (1975) published the first major literature re- view on the effects of marine pollutants on coral reefs. At that time he </p><p>1 </p><p>ADVANCES I N MARlNh BIOLOGY. VOL 22 Copyright (0 19x7. by Academic Press I n i (London) Ltd All rights of reproduction in any form reserved </p><p>ISBN 0-12-026122-7 </p></li><li><p>2 B . E. BROWN A N D L. S. HOWARD </p><p>highlighted the paucity of knowledge in many areas of the subjects. Al- though research efforts in the field have increased, particularly with re- spect to potential effects of pollution by oil (Loya and Rinkevich, 1980) and drilling muds (Dodge and Szmant-Froelich, 1984) there are still enor- mous gaps in our knowledge and serious contradictions in the existing literature. Much of this lack of information may be attributed to our limited understanding of the physiology of corals, although recent papers have contributed valuable data on growth (Highsmith, 1979), reproduction (Highsmith, 1982; Kojis and Quinn, 1981, 1982; van Moorsel, 1983), behavior patterns (Lasker, 1979), carbon turnover (Crossland ef ul., 1980b), calcification (Barnes and Crossland, 1978, 1982; Gladfelter 1982a), mucus production (Crossland et al., 1980a), and associated bacterial populations on living corals (Ducklow and Mitchell, 1979). </p><p>The aims of the present article are to consider long-term ecological studies in the light of known effects of disturbances on coral reefs and to ask whether the effects of disturbances can be distinguished from long- term fluctuations on the reef and also where other difficulties lie in assess- ment of pollution in the field. In addition, in an attempt to improve under- standing of the overall susceptibility of reef corals to marine pollution, an assessment is made of the responses of corals to stress and methods by which these responses have been monitored to date. </p><p>The definition of stress has been much discussed in the literature (Grime, 1979; Pickering, 1981; Stebbing, 1981; Rosen, 1982), particularly with reference to problems involved in identifying and quantifying such a condition. Working with plants, Grime (1979) defined stress as the exter- nal constraints limiting dry matter production by all or part of the vegeta- tion, while Rosen (l982), considering corals, described stressful condi- tions as those resulting in restricted growth and reproduction. Such specific definitions as these have not always been applied in many of the publications referred to in this article. For our purposes Rosens broader view of stress as a gradient between ideal conditions and the ultimate limits of survival will be adopted. As noted by Stebbing (1981), the term stress may be used as a cause or as an effect. In agreement with Stebbing and most other authors, we choose to view stress as an external force or stimulus. </p><p>The article is divided into three sections, the first section dealing with observations in the field, the second with laboratory assessment of pollu- tant effects, and the third section incorporating a general discussion of the validity of generalizations made to date on the overall vulnerability of coral reefs to man-made disturbance. </p></li><li><p>EFFECTS O F STRESS ON REEF CORALS 3 </p><p>II. Natural Fluctuations and Man-made Influences </p><p>A. Assessing Changes on Coral Reefs </p><p>Assessing change necessarily implies that reefs are monitored regularly by standard, repeatable methods. It is only in recent years, however, that quantitative methods have become routinely employed on permanent transects over time intervals. The first review of field methods applied on coral reefs was published by Stoddart in 1972. Subsequently other work- ers (Loya, 1972, 1978; Done, 1977; Bouchon, 1983; Dodge er al., 1982) have successfully tested various quantitative and semiquantitative meth- ods on the reef. Strictly quantitative techniques vary from plotless (Loya, 1978) to quadrat methods (Bak and Engel, 1979), and more recently work- ers have compared both approaches at the same sites in an attempt to gauge their relative efficiencies (Dodge et al., 1982; Bouchon, 1983). Al- though there appear to be no major differences in the results obtained by either methods, there are variations in the quantity and type of informa- tion generated and the time required for use; the line transect or inter- sected length method generally makes the most efficient use of the time spent underwater. </p><p>Measurements made on coral reefs using these techniques include coral cover, diversity, evenness (Loya, 1972, 1976a; Brown and Holley, 1982; Dodge et af . , 1982; Bouchon, 1983), colony number and colony size (Loya, 1972; Fishelson, 1977), and more recently spatial complexity (Rog- ers er af . , 1982, 1983) and spatial arrangement of both living and dead substratum components (Bak and Luckhurst, 1980). </p><p>Although monitoring of coral cover and diversity may yield fundamen- tal information about coral assemblages, few studies incorporate mea- surements of the cover and diversity of other components of the coral community, such as soft corals, zoanthids, algae, sponges, and ascidians. Recently, the importance of monitoring these groups has been highlighted by the publications of Benayahu and Loya (1977), Bak er af. (1981), and Tursch and Tursch (1982). Invasion and/or overgrowth of scleractinian corals by many species of soft corals (Nishihira, 1981; Tursch and Tursch, 1982) and ascidians (Bak er al., 1981; Sammarco er al., 1983; Syarani, 1983) has frequently been observed in both the Indo-Pacific and the Carib- bean provinces. </p><p>In studies where dominant components of the coral community have been considered (Rogers er af . , 1982), the effect of disturbance on coral reef diversity may be complex. Diversity of scleractinian corals as a result of hurricane damage in St. Croix was shown to decrease in shallow reef </p></li><li><p>4 B . E. BROWN A N D L. S. HOWARD </p><p>zones, whereas diversity of the community as a whole actually increased because of colonization of new substrata by a wide variety of reef organ- isms, e.g., algae, sponges, tunicates, bryozoa, and hydroids. Clearly quantitative measurements on coral reefs affected by disturbance should include some account of all major components of the reef community. </p><p>Such measurements are also improved by an appreciation of the struc- tural complexity of the coral reef environment. Rogers et al. (1982) used a modified transect method, with a linked chain following the contours of the reef, to obtain an index of reef topography or structural complexity. Done (1981) has applied the use of stereophotography to permanent tran- sects on the Great Barrier Reef. A stereo pair of photographs provides a great resolution of detail, a means of determining the three-dimensional coordinates of colonies and substratum, and a means of determining true dimensions and shapes of benthic organisms at any depth in the photo- graph. With automated stereoanalysis it should be possible to accurately map three-dimensional growth patterns of living corals and/or surface area of other substratum components. So complex are the interactions on coral reefs (Bak et al., 1982; Porter et al., 1982) that standard measure- ments of areal coverage, diversity, and abundance may not always be sensitive to changes in interactions which would be detected in a three- dimensional approach to community analysis. </p><p>Such an analysis should also consider the nonliving components of the substratum. Bak and Luckhurst (1980) have highlighted the importance of monitoring not only living cover but also nonliving substrata such as rock and sediments. Their study showed that alteration of spatial arrange- ment through dislodgement and collapse of substrata and changes in sedi- ment flow were of paramount importance in describing the community, particularly in shallow-water (10- and 20-m) quadrats. As the authors note, a continuous change in the cover of nonliving components must have serious implications for the settlement and survival of juvenile ben- thos. </p><p>One further factor should be considered when assessing changes on coral reefs, and that is the measurement of colony size. This parameter has been used by various workers (Loya, 1972, 1967a; Fishelson, 1977) involved in monitoring the effects of disturbance on coral reefs. It has recently been recognized (Hughes and Jackson, 1980) that partial colony mortality, colony fission, and colony fusion may affect any simple rela- tionship between the size and age of reef corals. Following known corals in photographs for successive years demonstrated that, in foliose Carib- bean corals, size and age are seldom related. Measurements such as those of Fishelson (1977) on age groups of faviids from polluted and nonpolluted sites, estimated from size dimensions, may require reinterpretation in the </p></li><li><p>EFFECTS OF STRESS ON REEF CORALS 5 </p><p>light of these more recent studies. Loya (1976a), however, recognizes the regenerative ability of corals when interpreting the effects of low tides at Eilat, and stresses that in the few cases where corals did not fully regener- ate the separate parts were considered as one individual.colony. His results suggested that whereas before the low tide coral colonies on the control reef fell into relatively large size categories, in 1973 after the catastrophic low tide, colonies fell into small size categories. Corals with marked regenerative ability included Cyphastrea microphthalma (La- marck), Pauona decussata (Dana), Millepora dichotoma (Forskal), and Porites lutea (Milne-Edwards and Haime). Generally the recovery of the control reef was mainly due to recolonization by coral planulae rather than regeneration of survivors. Nevertheless, regeneration of corals after partial mortality is an important process on all reefs, and it may be very difficult to decide if a small coral has recently settled or whether it is actually part of a much larger colony which has suffered partial colony mortality or colony fission. Such difficulties may be compounded in pol- luted areas, particularly those suffering from a high sediment load (per- sonal observation) (Fig. 1). Clearly this aspect requires further study on reefs affected by sedimentation where the growth form of massive species such as P. lutea and Goniastrea retiformis (Lamarck) appears nodular and where partial colony mortality is high. </p><p>Many long-term monitoring programmes incorporating techniques de- scribed earlier have now been initiated on coral reefs in both the Carib- bean and the Indo-Pacific, and much interesting information should grad- ually become available over the next decade-to quote Lewis (1976), considering long-term ecological surveillance on temperate rocky shores, to record change is no problem. There is much and it would be a remarkable investigation that showed none. The major need is to ensure that the change recorded is real and relevant. </p><p>B. Interpreting Temporal Changes on Coral Reex7 </p><p>Table I demonstrates major long-term changes observed as a result of mainly natural disturbances, while Table I1 records instances of man- made damage on coral reefs. It is clear from these tables that recent regular monitoring of fixed stations and transects in CuraGao (Bak and Luckhurst, 1980) and Eilat (Loya, 1976a) have produced interesting data on coral distributions and their spatial distributions with time. In addition, surveys before and after damaging natural events such as hurricanes (Stoddart, 1974; Shinn, 1976; Rogers et al., 1982), low temperatures (Shinn, 1976), and low tides (Loya, 1972) provide some insights into reef recovery and development. </p></li><li><p>TABLE I. LONG-TERM SURVEILLANCE OF NATURAL DISTURBANCES ON REEFS </p><p>Time Environmental Site span history Major changes observed Reference </p><p>British Honduras 1964- 1966 </p><p>Heron Island, Aus- 1963-1970 </p><p>Key Largo, Florida 1950-1965 tralia </p><p>Key Largo, Florida 1965-1967 </p><p>St. Croix, U.S. 1978-1979 Virgin Islands </p><p>Gulf of Eilat 1970 </p><p>Humcane damage </p><p>Hurricane damage </p><p>Hurricane damage </p><p>(1961) </p><p>(1966) </p><p>(1960) </p><p>Repeated hurricane damage (1965) </p><p>Humcane damage ( 1979) </p><p>Catastrophic low tide </p><p>Branching corals more susceptible than massive species </p><p>No marked change in coral abundance </p><p>Although colonies broken and much destruction within 1 year, difficult to recognize damage; by 1965 damage com- pletely healed </p><p>Damage not noticeable by 1967 </p><p>Effect of humcanes complex-may result in reduction in coral diversity but increase in community diversity due to provision of more light for slower growing corals and new substrate for algae and other invertebrates </p><p>Change in the community structure with rare species affected </p><p>Stoddart (1974) </p><p>Connell (1973) </p><p>Shinn (1976) </p><p>Shinn (1976) </p><p>Rogers er a / . (1982) </p><p>Loya (1972, 1976a) </p></li><li><p>Qatar, Persian Gulf </p><p>Dry Tortugas, Flor- </p><p>St. Croix, U.S. ida </p><p>Virgin Islands </p><p>Carysfort Reef, Key Largo, Florida </p><p>CuraGao </p><p>John Brewer Reef, </p><p>Discovery Bay, Australia </p><p>Jamaica </p><p>1965-1967 Low temperatures </p><p>1881-1976 Thermal shock </p><p>1976-1979 Bacterial infection (1976-1977) </p><p>March- No obvious natural November disturbances 1975 </p><p>1973-1978 No obvious natural disturbances </p><p>1976-1980 No obvious natural </p><p>1976-1980 Humcane Allen disturbances </p><p>(1979) </p><p>Regeneration of Acroporu sp. after chill; 2 years later colo- nies 2-20 cm high </p><p>Little change in area occupied by hermatypic corals; major changes were in coral species distributions </p><p>Death of Acropora palmara as result of white band dis- ease caused decrease in structural complexity of reef surface, decrease in living coral tissue and a reduction in CaC03 deposition on reef </p><p>suggested decline over 14-month study period Estimates of net recruitment and mortality of reef corals </p><p>Cover of living and nonliving components relatively constant throughout study; major differences lay in spatial arrange- ment of substrate components </p><p>Net increas...</p></li></ul>

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