Ecosystem Modeling in Cobscook Bay, Maine: A Boreal, Macrotidal Estuary 2004 Northeastern Naturalist 11 (Special Issue 2):1–12 Introduction to Ecosystem Modeling in Cobscook Bay, Maine: A Boreal, Macrotidal Estuary PETER FOSTER LARSEN* Abstract - Cobscook Bay, at the mouth of the Bay of Fundy, exhibits extraordinary natural productivity and ecological richness that has been recognized for millennia. The co-existence of so many remarkable ecological attributes is of both practical and scientific interest and has intrigued researchers for over a century. Nevertheless, the question of why this high productivity and species richness should co-occur in this mid-latitude Bay has not been addressed on an ecosystem level. A grant from the Andrew W. Mellon Foundation through The Nature Conservancy allowed an interdisciplinary, multi-institutional team of marine scientists to investigate the physical, chemical, geological, and biological dynamics of the Bay in an integrated ecosystem context. This special issue of the Northeastern Naturalist presents the results of original field research on the physical forcing functions at work in the Bay and the contributions of the principal primary producers. This knowledge is combined with historical information into an energy systems model and emergy analysis that describes the flows of materials and energy through the system and allows comparisons with other estuarine systems. Introduction The extraordinary natural productivity and ecological richness of Cobscook Bay, ME, have been widely acknowledged by academics since the early days of North American marine science. In actuality, the concentration of exploitable marine resources in the Cobscook region was recognized several millennia earlier by Native Americans who established summer fishing villages here as early as 10,000 years B.P. (Rolde 2004). The Passamaquoddy Tribe continues to live on and fish these waters to the present day. Certainly, the rich fisheries played a role in the unfortunate decision of the French entrepreneur, Sieur de Mons, to initially locate his settlement on St. Croix Island in the adjacent St. Croix River in 1604. Since that time there have been several waves of exploitation of Cobscook Bay resources, with related scientific research, involving fisheries, lumber, tidal power potential, port development, and aquaculture. The confluence of these resource potentials, together with many notable biological *Bigelow Laboratory for Ocean Sciences, PO Box 475, West Boothbay Harbor, ME 04575; plarsen@bigelow.org. 2 Northeastern Naturalist Vol. 11, Special Issue 2 features, are remarkable on a world-wide scale. The co-existence of these many unusual characteristics must be the product of the functioning of the Cobscook Bay ecosystem. Still, four hundred years after the first European settlement, we can still ask the question “Why does the mid-latitude Cobscook Bay exhibit such a high productivity and species richness?” After all, one popular hypothesis that we learned in school is that species diversity declines from the tropics towards the poles (see for example Krebs 2001). This special volume describes the state of our knowledge of the structure and functioning of the Cobscook Bay marine/estuarine ecosystem. Its provenance was a long-standing general interest in this rich coastal embayment and the specific research interests of the issue authors and The Nature Conservancy. A common denominator was the desire to explain the co-occurrence of so many unique ecological features. The senior authors are cumulatively responsible for a large proportion of the research done in Cobscook Bay over the last three decades. Their research activities have been related to tidal power and oil refinery proposals, aquaculture, natural fin and shell fisheries, climate change, oceanography and hydrography, nutrient chemistry, biodiversity, and toxic contamination among other allied subjects. The opportunity to assemble this interdisciplinary, multi-institutional team of marine scientists resulted from a successful grant application to The Nature Conservancy’s Ecosystem Research Program which was supported by the Andrew W. Mellon Foundation. The project, entitled “Developing an Ecological Model of a Boreal Macrotidal Estuary: Cobscook Bay, Maine,” was instigated to investigate the ecosystem dynamics of Cobscook Bay, Maine. Cobscook Bay is a hydrographically and geologically complex estuary where very high levels of biodiversity and productivity co-exist (Brooks 2004, Kelley and Kelley 2004, Larsen 2004). Past and present human impacts are largely limited to activities related to living resource harvesting. Cobscook Bay is, therefore, probably in as close to a natural state as any large estuary on the east coast of the United States. This condition, combined with the well-defined physical features and forcing functions, makes Cobscook Bay the ideal focus for system ecosystem research directed at understanding our vital and valuable boreal estuaries and embayments. The overall goals of this research effort were: to identify the forcing functions that initially produced, and now maintain, this unusual co-occurrence of diversity and productivity; to quantify the pathways and rates of movement of energy and materials through the system; and to define the limits or carrying capacity of the various system components. The overarching 2004 P.F. Larsen 3 goal was to provide a sound and accessible information base to insure the continued integrity of the system. Emphasis in this two-year investigation was on primary productivity and factors regulating it. The Present Setting Cobscook Bay is located in the Quoddy region which is generally described as that region at the mouth of the Bay of Fundy between Cutler, ME, and Point Lepreau, NB, and from Grand Manan Island to the head of tide on the St. Croix River and other minor tributaries. Included are Cobscook and Passamaquoddy Bays, Campobello Island, the Deer Island archipelago, and many smaller islands. Some confusion between Cobscook and Passamaquoddy Bays exists in public perception; these are distinct although interconnected bays with similar climatic, geologic, and tidal settings. There are contrasts that must be recognized, however, so that generalities about one bay are not inappropriately applied to the other. Some of the relative differences are presented qualitatively in Table 1. Cobscook Bay is characterized by a narrow opening to the sea and a very convoluted shoreline (Fig. 1). High tide surface area is approximately 110 km2 with 325 linear kilometers of shoreline. The Bay has an average depth of about 10 m and at the deepest point is 45 m. Turbidity is low. Sunlight can reach the bottom everywhere in the Bay. Water temperatures are in the boreal range of about 0–12 oC (Forgeron 1959). Freshwater input from the modest, sparsely populated 1000 km2 watershed is small. Salinities are generally marine (> 30 ppt) throughout the Bay except at the heads of the very inner arms. Contaminant loads are low (Chase et al. 2001). The climate shows both continental and marine elements (Hertzman 1992). One of the outstanding features of Cobscook Bay is the large tidal range. The mean tide at Eastport is 5.7 meters. The geometry of the Bay enhances the tidal wave toward the inner Bay and causes a phase delay of over one hour. Extreme spring tides are 7.6 meters at Eastport. This large tidal range is the result of the near resonance of the semidiurnal Table 1. Qualitative comparisons of some relative differences between Cobscook and Passamaquoddy Bays. Cobscook Bay Passamaquoddy Bay Size Smaller Larger Average depth Shallow (10m) Deep (25m) Shoreline/area ratio Large Small Intertidal area/total area ratio Large Small Tidal prism Large Small 4 Northeastern Naturalist Vol. 11, Special Issue 2 tide of the North Atlantic Ocean with the Gulf of Maine/Bay of Fundy basin (Greenberg 1979). The dominant astronomical constituent controlling the tidal range in this region is the phase of the moon (Trites and Garrett 1983). This means that the most extreme low tides occur in the early morning and late afternoon. The interaction of the large tidal range with the structural geology of Cobscook Bay results in a very large intertidal zone. Indeed, approximately one-third of the area of Bay is exposed to the atmosphere at low tide and another significant portion remains covered by only very shallow water. In many places, the intertidal zone is a kilometer or more in width. More information on the Cobscook Bay and Quoddy region is contained in the recent bibliography of Larsen and Webb (1997). Figure 1. Map of Cobscook Bay, ME, with principal place names indicated. 2004 P.F. Larsen 5 Brief History Of Scientific Research Observations on the fauna and flora of the Quoddy region began very early. If we discount the general observations made by Champlain and his companions on St. Croix Island in 1604, the first scientific accounts are probably those of Mighels (1843) and Stimpson (1851a,b). These were quickly followed by the classic account of the invertebrates of the Quoddy region (Stimpson 1853). Less than two decades later, intensive and extensive government supported research began in response to a marked decline in fisheries landings in several regions of the US coast. The US Congress, in 1871, directed the President to appoint a Commissioner of Fish and Fisheries to investigate the causes of the decline. The Commissioner, S.F. Baird, who was to serve without salary, immediately set up headquarters in Woods Hole and assembled a team of leading US scientists. The importance of the fisheries in the Quoddy region, and the seriousness with which the sudden decline was perceived, is evidenced by the fact that in 1872, they chose Eastport as the headquarters from which to prosecute their second year of inquiries. This effort marks the first concerted US scientific investigation in the Cobscook area. It firmly established the species richness of the region and resulted in the description of many species new to science. Further detail is presented in Larsen (2004). Similar responses to the fishery crisis occurred in Passamaquoddy Bay across the international border and led to a heightened interest in the Quoddy region. This resulted in the establishment of the Biological Station at St. Andrews, NB, at the turn of the 20th century, first as a field station and then as a year-around laboratory. For over 100 years, St. Andrews, through the Biological Station and, since 1969, the Huntsman Marine Science Centre, has been the mecca for research on the Quoddy region. More information and references can be found in Thomas (1983). With no corresponding focus in the United States, research on the Quoddy region has been weighted towards Passamaquoddy Bay. Indeed, of the 629 references in the Quoddy bibliography by Larsen and Webb (1997), less than 100 relate specifically to Cobscook Bay. Although we are fully aware that ecosystem functions do not recognize national borders, we have emphasized US contributions in these pages in order to supplement existing material while reducing redundancy. The 1872 investigations determined that the damming of rivers and streams by the timber industry was the cause of the mid-19th century fisheries collapse in the Quoddy region. The dams blocked anadromous fish migration and spawning and removed the major food source of the cod populations. Clearly, ecosystem level re6 Northeastern Naturalist Vol. 11, Special Issue 2 sponses to human disturbance have a long history in Cobscook Bay. Analysis of subsequent research in Cobscook Bay reveals that a significant majority was stimulated by proposals for large scale engineering projects and their perceived threats to the valuable marine resources (Larsen and Webb 1997). Indeed, second only to documents on fisheries and invertebrates, many of which are related to impact analysis, applied documents related to proposed tidal power, oil facilities, and aquaculture are most numerous. Interest in harnessing the power of the large Fundy tides in the Quoddy region began early in the 20th century. Interest in tidal power has waxed and waned for nearly 100 years, as has related physical and biological research. The first papers appeared in the mid-1930s followed by a burst of research activity in the 1950s and early 1960s, when interest in the international Passamaquoddy tidal power project was renewed. It is interesting to note that construction on a single pool tidal power scheme in Cobscook Bay was actually begun in 1935. Before construction ceased, three causeways were built. Two of these produced a land bridge between the mainland and Moose Island (Eastport) and had the effect of closing two passages between Cobscook and Passamaquoddy Bays. From the late 1970s through the mid-1980s, two tidal power proposals stimulated the highest level of research ever to occur in the northern Gulf of Maine. The first was a small demonstration project by the Passamaquoddy Tribe. This was proposed for Bar Harbor in the northeast corner of Cobscook Bay (Fig. 1). Several questions regarding fisheries, shorebirds, eagles, marine mammals, and local impacts were raised and addressed. Ironically, Bar Harbor only obtained a suitable configuration for tidal power production because of the abortive construction of the Cobscook Bay tidal power project in 1935. The second salient proposal was for massive tidal barrages at the head of the Bay of Fundy. Because this project would have altered the tides throughout the Gulf of Maine, and thereby conceivably affected everything from climate to biodiversity, scientific thought and analysis was very much elevated to the systems level. Much of the research done at this time is especially relevant to our present efforts. A proposal for a deep-water oil port and refinery on Shackford Head in Cobscook Bay in the 1970s was also a major stimulus for activity. The controversy generated by the suggestion that the world’s largest oil tankers could safely navigate the narrow rocky, current-swept channels in the foggiest place on the East Coast led to a series of regulatory and judicial proceedings. Environmental issues included tanker safety, oil spill behavior, endangered species, fisheries, and the rich natural state of Cobscook Bay. Ultimately, it was the latter that was most influential 2004 P.F. Larsen 7 in convincing the Carter administration to intervene on the behalf of the environment (T.K. Bick, Tighe Patton Armstrong Teasdale, Washington, DC, pers. comm.). At each stage, proposal proponents, government regulators, and environmental groups presented new data, reanalyzed existing data, and brought in additional experts, with the result that a wealth of information was accumulated and became generally available. Ultimately, the refinery was not built. The latest large-scale development in the waters of Cobscook Bay is salmon aquaculture. The water temperature moderation and flushing provided by the large tides make Cobscook Bay an attractive site for pen-growing cold-water fish. Questions related to the disposition of excess feed and fish wastes have been addressed by research and monitoring from the 1990s to the present. Thus, to date, research in Cobscook Bay has been driven largely by development or proposals for large-scale projects. In each case, the underlying concern has been for the living marine resources. We have used the existing data extensively and couldn’t have achieved our goals without them. Specific references to past research are cited in our individual contributions, as appropriate, and are compiled in Larsen and Webb (1997). Conceptual Model Development An ecosystem is a semi-discrete unit of nature containing both abiotic and biotic components. For example, an aquarium is a simple ecosystem. It is confined by glass walls, contains abiotic components (gravel, water, and dissolved gases) and biotic components (plants, fish, and organic molecules). It is part of, and dependent upon, a larger system. In this case, light, heat, and food are imported from the larger system, are transformed by physical, chemical, and biological processes within the aquarium, and wastes are exported back to the larger system through cleaning. If imports and exports are balanced with internal processes, a healthy ecosystem is maintained. An ecosystem model attempts to describe and explain the functioning of an ecosystem, usually through the movement and transformation of energy or material in the system. An ecosystem can be presented as a simple pictorial of ecosystem components with arrows indicating directions of flows in a network fashion. More sophisticated models, as in the energy systems model presented here, use energy circuit language to link the structural and functional components, with lines representing equations describing the rates of flows between the components, and use symbols to represent the role of the components in controlling the flows (see Odum 1994 for detailed discussion). 8 Northeastern Naturalist Vol. 11, Special Issue 2 The construction of a meaningful ecosystem model begins with the collection and assimilation of all the information available on the system in question. The collection of data was initiated with funding from The Nature Conservatory for the production of an annotated bibliography of environmental research in the Quoddy region (Larsen and Webb 1997). Next, a multi-disciplinary scientific team was assembled that evaluated existing information in light of their own experience and intuition on the Cobscook Bay ecosystem. This stage was significantly enhanced through public workshops in the Cobscook region as well as by individual discussions with local residents and former Cobscook researchers. Finally, a conceptual model was constructed (Fig. 2). This model is an initial representation of the common components of the ecosystem and the processes at work. It is used to prioritize and plan the research program. The flow is from left to right. From the left enter watershed contributions and solar radiation. Nutrients pass through a storage component and flow to four identified classes of primary producers represented by bullet-shaped symbols. Energy and materials continue to flow through primary and secondary consumers represented by hexagons, and a detrital storage component. Interactions with the sea cross the right-hand boundary as two general processes: a tidally driven exchange of nutrients and passive biological components, and an active movement epitomized by migrations of fish and Figure 2. The initial conceptual model of the Cobscook Bay Estuarine Ecosystem expressed as an Energy Systems Language diagram (see Odum 1994). 2004 P.F. Larsen 9 birds. Each of these components and pathways is a generalization of much more complex interactions. The model was continuously updated as knowledge was upgraded and processes and interactions were quantified. Resource limitations prevented the team from evaluating each ecosystem component thoroughly. Good information existed, or could be reasonably inferred, on watershed contributions and solar radiation. Within the Bay, the best information was available on finfisheries, shellfisheries, and birds. It was, therefore, decided to emphasize the lower ecosystem elements that were understood least well. These included tidal exchange, principally of nutrients, and the primary producers grouped as phytoplankton, benthic microphytes, macroalgae, and eelgrass. These are the components that set the upper boundary of the ultimate productivity of the Bay. Issue Contents This special issue of the Northeastern Naturalist is organized as a series of papers roughly grouped along disciplinary lines. Each of these papers is self-contained in that each contains relevant background material and presents the results of specific scientific investigations. Individually, and as a group, they make significant contributions to the information needs of Cobscook Bay, the US side of the Quoddy region and an area not well documented or considered adequately by previous efforts (Thomas 1983). In total, however, the papers are much bigger than the sum of their parts. This is because each feeds into the energy systems model, and subsequent emergy analysis, to quantitatively address, for the first time, the question: “Why does the mid-latitude Cobscook Bay exhibit such a high productivity and species richness?” The majority of the papers in this volume involve research that was designed and funded to fill specific compartments of the systems model. These begin with Eastport native David Brooks’ hydrodynamic modeling of the tidal circulation within Cobscook Bay and water exchange with outside water bodies. Building on this effort, Chris and Jean Garside modeled the distribution of nutrients, principally nitrogen, within the Bay and calculated the relative importance of various nutrient sources to the Bay’s ecosystem. David Phinney, Charles Yentsch, and Douglas Phinney researched the productivity of single celled plants consisting of the free-floating phytoplankton and the microphytes that live attached to the bottom substrates. Part of their investigation involved the determination of seasonal patterns of production and the influence of light and nutrients on productivity. 10 Northeastern Naturalist Vol. 11, Special Issue 2 Robert Vadas, Brian Beal, and their colleagues comprehensively investigated the production of macrophytes, i.e. large plants, including rockweed, kelp, red and green algae, and eelgrass. Their results are presented as a series of four papers. The determination of habitat areas, needed to extrapolate the results of the productivity studies to the entire Bay, was accomplished by Peter Larsen and his colleagues by the use of satellite imagery. Several colleagues, supported by separate sources, contributed research results to the issue. These contributions fill important data gaps and help give a complete picture of the present knowledge of Cobscook Bay. Peter Larsen offers a brief historical review of the environmental setting and biodiversity of the Bay. Joseph and Alice Kelley provide the geological context of the Bay, both in terms of the underlying framework and the dynamics of the sediments that presently floor the Bay. John Sowles and Laurice Churchill present information on the important salmon aquaculture industry and consider its implications to the Bay’s nutrient budget. Results from the only known quantitative survey of the animals living in the bottom of the Bay are presented by Peter Larsen and Edward Gilfillan. Two papers by Thomas Trott also deal with the Bay’s fauna. The first is a comprehensive taxonomic list of all the invertebrates recorded in Cobscook Bay since the 19th century, and the second is a provocative consideration of recent possible faunal changes. The unifying feature of this issue is the construction of an improved energy systems model and emergy analysis of Cobscook Bay by Daniel Campbell. Dan assimilated all the information in the above papers, and in multitudinous other documents, to calculate the rates and pathways of energy and materials through the Cobscook Bay ecosystem. By converting all the properties of the ecosystem to common units, Dan is able to address the defining question of this issue. A final paper is provided that summarizes the major points of each contribution and their integration into the energy systems model and emergy analysis. Many of the more poorly understood elements of the ecosystem are identified, and some suggestions for future research priorities are suggested. Acknowledgments This work was conducted as part of a research program. “Developing an Ecological Model of a Boreal, Macrotidal Estuary: Cobscook Bay, Maine,” funded by a grant from the A.W. Mellon Foundation to The Nature Conservancy, with matching funds and services provided by Bigelow Laboratory for Ocean Sciences, University of Maine at Orono and Machias, Texas A&M University, US Fish and Wildlife Service Gulf of Maine Program, Suffolk 2004 P.F. Larsen 11 University (Friedman Field Station), Maine Department of Marine Resources, and The Nature Conservancy. Literature Cited Brooks, D.A. 2004. Modeling tidal circulation and exchange in Cobscook Bay, Maine. Northeastern Naturalist 11(Special Issue 2):23–50. Chase, M.E., S.H. Jones, P. Hennigar, J. Sowles, G.C.H. Harding, K. Freeman, P.G. Wells, C. Krahforst, K. Coombs, R. Crawford, J. Pederson, and D. Taylor. 2001. Gulfwatch: Monitoring spatial and temporal patterns of trace metals and organic contaminants in the Gulf of Maine (1991–1997) with the blue mussel, Mytilus edulis L. Marine Pollution Bulletin 42:491–505. Forgeron, F.D. 1959. Temperature and salinity in the Quoddy region. International Passamaquoddy Fisheries Board Report to International Joint Commission. Appendix 1: Oceanography; Studies in physical oceanography for the Passamaquoddy Power Project. International Joint Commission, Ottawa, ON, Canada, and Washington, DC. 56 pp. Greenberg, D.A. 1979. A numerical model investigation of tidal phenomena in the Bay of Fundy and Gulf of Maine. Marine Geodesy 2:161–187. Hertzman, O. 1992. Meteorology of the Gulf of Maine. Pp. 39–50, In J. Wiggin and C.N.K Mooers (Eds.). Proceedings of the Gulf of Maine Scientific Workshop. Urban Harbors Institute, Boston, MA. 394 pp. Kelley, J.T., and A.R. Kelley. 2004. Controls on surficial materials distribution in a rock-framed, glaciated, tidally dominated estuary: Cobscook Bay, Maine. Northeastern Naturalist 11(Special Issue 2):51–74. Krebs, C.J. 2001. Ecology. 5th Edition. Benjamin Cummings, San Francisco, CA. 695 pp. Larsen, P.F. 2004. Notes on the environmental setting and biodiversity of Cobscook Bay, Maine: A boreal, macrotidal estuary. Northeastern Naturalist 11(Special Issue 2):13–22. Larsen, P.F., and R.V. Webb. 1997. Cobscook Bay: An Environmental Bibliography. Bigelow Laboratory Technical Report No. 100. Published by the Maine Chapter of The Nature Conservancy, Brunswick, ME. 145 pp. Mighels, J.W. 1843. Catalogue of the marine, fluviatile, and terrestrial shells of the State of Maine and adjacent ocean. Boston Journal of Natural History 4:308–345. Odum, H.T. 1994. Ecological and General Systems: An Introduction to Systems Ecology. University Press of Colorado, Niwot, CO. 644 pp. Rolde, N. 2004. Unsettled Past, Unsettled Future: The Story of Maine Indians. Tilbury House Publishers, Gardiner, ME. 461 pp. Stimpson, W. 1851a. Revision of the Synonymy of the Testaceous Mollusks of New England. Phillips, Sampson, and Company, Boston, MA. 55 pp. Stimpson, W. 1851b. Observations on the fauna of the islands at the mouth of the Bay of Fundy, and on the extreme northeast corner of Maine. Proceedings of the Boston Society of Natural History 4:95–100. Stimpson, W. 1853. Synopsis of marine invertebrata of Grand Manan or the region about the mouth of the Bay of Fundy, New Brunswick. Smithsonian Contributions to Knowledge. 6:1–66. 12 Northeastern Naturalist Vol. 11, Special Issue 2 Thomas, M.L.H. 1983. Introduction. Pp. 1–4, In M.L.H. Thomas (Ed.). Marine and Coastal Systems of the Quoddy Region, New Brunswick. Canadian Special Publication in Fisheries and Aquatic Sciences 64. Department of Fisheries and Oceans, Ottawa, ON, Canada. Trites, R.W., and C.J.R. Garrett. 1983. Physical oceanography of the Quoddy region. Pp. 9–34, In M.L.H. Thomas (Ed.). Marine and Coastal Systems of the Quoddy Region, New Brunswick. Canadian Special Publication in Fisheries and Aquatic Sciences 64. Department of Fisheries and Oceans, Ottawa, ON, Canada.