United States Environmental Protection Agency Environmental Research Laboratory Narragansett Rl 02882 Research and Development EPA-600/S3-83-082 June 1984 4>EPA Project Summary Effects of Thermal Additions on the Dynamics of Fouling Communities at Beaufort, North Carolina W. W. Kirby-Smith The effects of long-term, low-level thermal additions on recruitment and structure of the marine epibenthic community were investigated in a laboratory system maintained at 0°C (an unheated control), 2°. 4°C, or 6°C above the ambient temperature. Com- munities developed on ceramic tile plates over a three-year period were sampled nondestructively at monthly intervals for percent cover by individual species. Recruitment also was assessed monthly. The experimental system modified the laboratory communities compared to those on field plates, enhancing the recruitment of some species and decreasing or eliminating others. The laboratory communities were composed of epifaunal species common in North Carolina. Thermal addition had a pronounced effect upon recruitment of certain species and on species number and diversity on the permanent community plates, but had little effect on the community type. The laboratory com- munities were dominated by the oyster Crassostrea virginica and the polychaete Spirorbis borealis. Temperature eleva- tions of 2°C produced measurable effects on recruitment and percent cover by individual species; these effects were more apparent at the 4°C and 6°C elevations. Community com- plexity was markedly reduced by elevations of 6°C in midsummer when the 36°C temperature apparently ex- ceeded thermal limits of many species. Caution is urged in applying these findings to the field or using them for regulatory decision making; i.e., this experimental system is limited in simulating the natural environment. Additionally, it is possible that certain temperature responses observed may be unique to this particular fouling community. This Project Summary was developed by EPA's Environmental Research Laboratory. Narragansett. Rl. to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The purpose of this investigation was to determine the consequences of long- term, low-level elevations intemperature on larval recruitment and to observe community development and structure of the marine epifaunal (fouling) community at Beaufort, North Carolina. The project represents one approach to the study of sublethal consequences of thermal additions by estuarine and coastal power plants. The literature concerning effects of temperature on marine communities has been developed primarily from investiga- tions of unnatural thermal discharges from steam electric stations. Field studies ------- have been very useful in understanding the effects of thermal additions in a general sense; however, it is often difficult from field studies alone to quantify the biological consequences of specific levels of thermal elevation, particularly those of a sublethal nature. In addition, a good record of the tempera- tures actually experienced in the field is rarely available. Quantitative information on thermal effects is important for power plant siting and design and for environmental regula- tory uses. Controlled laboratory studies resulted in more precise examination of the relationships between elevated temperature and biological effects. Most of the studies tested single species. The applicability of the results to the field often has been constrained by such limitations as the short duration of the study, the use of unusually high tempera- tures, an inability to test for full life cycle effects, or difficulties in predicting the community level consequences of such tests. A long-term laboratory study with a natural assemblage such as the fouling community is an approach that should overcome many of these limitations. Wolfson (1974) conducted a laboratory study of the effects of temperature on a fouling community at Scripps Institution of Oceanography. Unfiltered coastal seawater was pumped through four aquaria in an open-flow system. Two aquaria were unheated controls; thethird was maintained continuously at 3°C above ambient temperature, and the fourth was cycled with six-hour intervals at 3°C above ambient followed by six- hour intervals at ambient. Asbestos plates were suspended in the tanks in March to encourage development of the fouling community which was observed for one year. The response of individual species to elevated temperature varied from positive to negative effects on recruitment and growth, depending upon which species was considered. In the summer, when water temperatures were highest, survival was reduced in a number of species. Species exposed to the cycling thermal regime were much less affected than those exposed to constantly elevated temperature. Com- munity species diversity was similar in all treatments in the spring. During the summer, there was a decrease in diversity of both elevated temperature tanks. In the fall, the diversity of the communities exposed to the cycling temperatures was similar to those in the ambient temperature treatment, but diversity in the constantly heated treat- ment remained depressed. The results of 2 the experiments by Wolfson agreed with this study's observation at field sites experiencing thermal addition. However, Wolfson's experiments were of short duration relative to the time required for complete fouling community development; nor did they address community changes caused by the experimental system perse in the absence of thermal additions. Moreover, seawater temperatures in southern California cycle over a range of approximately 12°C (12°C-24°C), while temperatures of the bay and estuarine waters along the mid-Atlantic cycle over a range of 25°C (5°C-30°C). Methodology Two aspects of community dynamics, recruitment of species and development of the community, were followed over a three-year period under field conditions and in an open-flow laboratory seawater system with continuous temperature elevations of 0°C (no heat added), 2°C, 4°C or 6°C above the ambient seawater temperature. The community was defined as those species which were recruited and grew on the underside of continuously submerged, unglazed ceramic tile plates (232 cm2). Field plates were located 0.3 m below mean low water near the seawater intake at the Duke University Marine Laboratory, Beaufort, North Carolina; laboratory plates were submerged in tanks supplied with constantly flowing, temperature controlled, seawater. Com- munities developed from planktonic larvae which settled on these plates. For each month of the study, changes in community structure on permanent community plates were followed by nondestructive point sampling to deter- mine the percent cover of individual species; at one-month intervals, recruit- ment was determined by enumerating all identifiable individuals on larval recruit- ment plates which had been submerged throughout the preceding one month. Experiments were conducted over the period of November 1976 to November 1979. Conclusions Long-term, low-level thermal additions produced dramatic effects on some aspects of recruitment and structure of the fouling community; but on other parameters the additions produced few effects. Within the laboratory system, increasing temperatures resulted in a complex of effects on the recruitment and percent cover of individual species. The direction and magnitude of the effects on recruitment of species were not often the same as those observed for percent cover. A 2°C increase in temper- ature resulted in significant differences in recruitment of individual species in an average of 40.7 percent of the cases where significant recruitment occurred in one or the other of the treatments being compared. This effect increased to 53.5 percent at the 4°C differential and 62 percent at the 6°C differential. The significant differences in recruitment were either positive or negative, often depending upon the species, the treat- ment, and the time of year. For example, the number of individuals recruited increased in each elevated temperature treatment for Bugula neritina and Spirorbis borealis and decreased for Schizoporella errata and Balanus spp. (+2, +4°C only). From the community standpoint, increas- ing temperature did result in a decrease in the average number of species recruited in the summer and in an increase in winter. However, no temper- ture effect on the community structure of recruits was evident when evaluated by cluster analysis of the average number of individuals recruited by each species for each treatment for the 29 sequential time periods. On the permanent community plates, the average number of species and diversity decreased with increasing temperature; this effect was particularly evident when comparing 6°C with 0°C plates in midsummer. Cluster analysis of the percent cover data for permanent plate communities did not show a temperature effect on community struc- ture. This result is due mainly to the dominance of Crassostrea virginica and Spirorbis borealis on the community plates in most temperature treatments. Cluster analysis is not a good technique for distinguishing treatment effects in communities with only two dominants, since the species clusters are most affected by the presence or absence of the dominant species and their relative (not absolute) abundance. A comparison of field results with results obtained in the laboratory in the 0°C treatment (tanks with no thermal addition) indicated that the laboratory system itself had a large effect upon recruitment of most species and the development of the communities. Re- cruitment of species on field plates and laboratory 0°C treatment plates was significantly different in 76 percent of the 270 cases analyzed. The pattern of these differences was complex and varied through time; there were positive, negative, and neutral effects on the number of individuals recruited. Specie^ composition of the community as deter-^ ------- mined by cluster analysis of percent cover data also differed, with only one species (the oyster, Crassostrea virginica) being a significant member of both field and laboratory 0°C communities. The per- centage of unoccupied space was siginfi- cantly greater on laboratory 0°C plates than on field plates. However, the number of species per plate and the diversity, based on percent cover data, were similar for field and laboratory 0°C plates. Although the community com- position differed, all species in both communities were common members of the epibenthic community in North Carolina. Some of the differences between the laboratory and field communities may have resulted from ingestion of larvae by suspension feeders in the tank commu- nities, as there was a large decrease in suspended material in laboratory tanks relative to that in the field. Analysis of flow rates, chlorophyll a values, and rates of suspension feeding by communities suggested that the system was probably food stressed during the warmer months of the year in all temperature treatments and throughout the year at the 6°C differential. The laboratory system also incompletely simulated the field in other ways, including the absence of strong currents, rapid turnover of water, and pelagic predators, plus the potential for loss of some larval recruits and food due to damage by pumping or ingestion by any fouling organisms in the seawater lines and tanks. In this study, a chronic 2°C elevation in temperature had measurable effects on some parameters of community develop- ment (e.g. suppressed or enhanced recruitment for some species and, in the permanent plate communities, a slight reduction in species number during June). Increases of 4°C and 6°C caused similar, but more pronounced effects. At 4°C, species number on the community plates was reduced during all seasons. At 6°C, species number and diversity were reduced markedly, particularly in the summer and autumn months after ambient temperatures were the highest. However, these findings should be applied with caution to field or regulatory questions concerning the consequences of thermal additions, recognizing the limitations of the experiment systems. Recruitment of larvae and their subse- quent growth and survival were probably influenced by the experimental system, in some ways positively and in others negatively. The limited food supply in the system doubtless compromised growth and possibly survival of the oysters, one of the two community dominants. Yet given careful interpretation, these results do illustrate some of the ways in which long-term, low-level thermal addition may alter population and community structure of a warm temperate zone biota. Recommendations This study highlights two issues which should be considered when assessing the consequences of thermal addition for estuarine and coastal communities. First, conspicuous effects are most likely to occur during the season when water temperatures are naturally at their maximum. To predict allowable thermal additions during this period, an estimate of the long-term, incipient upper thermal limit should be experimentally determined for the communities of concern. If community studies are not practical, studies should be conducted for the community dominants. Secondly, during seasons that the community upper thermal limit would not be exceeded, subtle changes may nonetheless occur. Very low-level thermal additions (e.g. 2°C) may have little effect other than increasing the duration and the intensity of community spawning and recruitment. Higher levels of chronic additions (e.g. 4° or 6°C) may alter community structure, as evidenced here by reductions in species number and community diversity. The long-term implications of such changes for community integrity or for the protection of populations of particular concern will require further investigation of the communities or species in question. Marine epibenthic communities hold potential as a research tool to investigate the long-term effects of sublethal envi- ronmental stress, including anthropogenic perturbations of a conservative or non- conservative nature. These communities develop readily on clean surfaces, they integrate natural changes in environ- mental conditions, and their species composition may be ascertained easily in a nondestructive fashion. Interaction among species is simple; it is predomi- nantly competition for primary space. However, there are some problems which must be resolved when employing the fouling community in experimental studies. The problem of providing adequate food may be addressed by increasing the water exchange rates, assuring that seawater delivery lines are free of fouling organisms, and minimizing the biomass in each experimental tank. Maintenance of a strong current within the tanks may also be considered, as this will enhance the development of additional species typical of this community. Other conditions normally experienced by this assemblage are difficult to simulate in the laboratory, such as the presence of predators. In order to address community questions, it may be necessary for the study to be conducted for more than a year, since the epibenthic community which is initially established may have only one dominant, with a monoculture resulting. Given additional time, the assemblage usually moves towards increased diversity. Experimental studies on communities should employ multiple parameters to describe community structure and deve- lopment. In this research, one parameter of community structure was percent cover. No treatment effects were evident for this parameter by cluster analysis. However, cluster analysis is considered to be a relatively insensitive technique for a community having only two dominants. In contrast, other community parameters, such as diversity using percent cover data and percent unoccupied space, did show significant influence of thermal additions. In addition, it is important to recognize that an environmental stress (either natural or anthropogenic) may have a negative influence on one species or characteristic of a community, a positive effect on another, and no effect on a third. Reference Cited Wolson, A.A. 1974. Some effects of increased temperatures on the settlement and development of a marine community in the laboratory. University of California Institute of Marine Resources UC-IMR Reference No. 74-13. 159 p. ------- W. W. Kirby-Smith is with Duke University Marine Laboratory, Beaufort, NC 28516. D. C. Miller is the EPA Project Officer (see below). The complete report, entitled "Effects of Thermal Additions on the Dynamics of Fouling Communities at Beaufort, North Carolina," {Order No. PB 83-260 489; Cost: $26.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Research Laboratory U.S. ^Environmental Protection Agency South Ferry Road Narragansett, Rl 02881 •{t U.S GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7724 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 Pb 0000329 U S tNVIR PROTECTION AkJ£i\iCY REGION 5 LIBRARY ISO S DEARBORN STKfcET CH1CAG.U IL 60604 ------- |