Ecosystem Modeling in Cobscook Bay, Maine: A Boreal, Macrotidal Estuary 2004 Northeastern Naturalist 11( Special Issue 2):13–22 Notes on the Environmental Setting and Biodiversity of Cobscook Bay, Maine: A Boreal, Macrotidal Estuary PETER FOSTER LARSEN* Abstract - Cobscook Bay, a boreal, macrotidal estuary in the northeastern Gulf of Maine, is noted for its species richness. The Bay area is biogeographically complex due to present temperature regimes as well as historical, climatological, and physiographic changes since the last glaciation. Early investigators recognized the resulting zoological richness, and a significant portion of the collection and taxonomic description of North American marine fauna was centered in the northern Gulf of Maine. A compilation of the results of 19th- and 20th-century research leads to the conclusion that the Cobscook region contains the highest level of marine invertebrate biodiversity in eastern North America north of the tropics. In addition, Cobscook Bay is characterized by noteworthy biological attributes such as the intertidal occurrence of many normally subtidal species and the manifestation of giantism in several populations. These phenomena are summarized briefly as a prelude to a major ecosystem modeling effort. Introduction The utilization of marine resources in the Cobscook Bay region has a long history (Larsen 2004). The earliest scientific investigators quickly recognized the biological richness of the area and qualitatively documented its biodiversity, especially in terms of marine invertebrates. For the past century and a half, the high biodiversity observed in Cobscook Bay has been accepted as a given. Little effort has been expended on quantitative documentation of the biodiversity. Indeed, to date no quantitative studies of the benthic fauna of Cobscook Bay have been published. Likewise, there has been no comprehensive effort to explain why this level of biodiversity should exist in Cobscook Bay. Certainly, qualitative confirmations of diversity levels have been produced, and scattered, or anecdotal, partial explanations of the ecological forces at work have been forwarded. These are intriguing and certainly contribute to our understanding of Cobscook Bay ecology, but they are not integrated with the larger forces at work. The present interdisciplinary, multi-institutional effort to produce an energy systems model of the Cobscook Bay ecosystem addresses the question of why this mid-latitude bay should exhibit such high productivity and species richness. In light of this effort, it seems appropriate to *Bigelow Laboratory for Ocean Sciences, PO Box 475, West Boothbay Harbor, ME 04575; plarsen@bigelow.org. 14 Northeastern Naturalist Vol. 11, Special Issue 2 review, briefly, the most salient past research, observations, and ideas on Cobscook Bay and the eastern Gulf of Maine in order to provide some historical, environmental, and ecological context for the papers presented in this special issue of the Northeastern Naturalist. Brief Environmental History The Gulf of Maine/Bay of Fundy system is a semi-enclosed, continental, macrotidal sea (Fig. 1) strongly influenced by a climate with both continental and marine elements (Hertzman 1992). Its complex topography and hydrography, in combination with a recent and rapid geological evolution, have created a highly productive, ecologically Figure 1. The Gulf of Maine, a semi-enclosed, eastward facing continental sea. Box indicates the Quoddy region. (After Brooks et al. 1999). 2004 P.F. Larsen 15 diverse system. This situation is expressed most intensely in and around Cobscook Bay at the mouth of the Bay of Fundy. Over the last several thousand years, major changes have occurred in both sea level and tidal range. The region was overlain by glaciers perhaps as many as five times (Knott and Hoskins 1968). Much of the Gulf’s surficial geological character results from the last glaciation and the erosional processes and alterations of relative sea level that followed (see Kelley 1987, Shipp et al. 1991). Relative sea level changes since the last glaciation have been large and rapid (Belknap et al. 1987), which has had significant influence on the marine and terrestrial climates (Campbell 1986). The present distribution of shallow water invertebrates, as reflected by summer surface water temperatures, is described in Figure 2 (Bousfield Figure 3. The Gulf of Maine at about 11,000 years B.P. illustrating the restricted connection with the Atlantic Ocean (Courtesy of J. Shaw, Bedford Institute of Oceanography). Figure 2. The present-day Canadian Atlantic and northern New England coastal regions showing summer surface water temperatures. Blue = < 12 oC, Green = 12–15 oC, Yellow = 15–18 oC, and Red = > 18 oC. (After Bousfield and Thomas 1975). 16 Northeastern Naturalist Vol. 11, Special Issue 2 and Thomas 1975). The most noteworthy feature for our purposes is the summer, cold-water pocket at the mouth of the Bay of Fundy. The historical, climatological, and physiographic changes that occurred since the last glaciation and resulted in the present-day distribution of fauna are described by Bousfield and Thomas (1975) and Campbell (1986). Very briefly and simply, the biological system responded to the geological and oceanographic evolution as follows. Relative sea-level was significantly lower than at present as the ice began to retreat about 15,000 years B.P. Seawater would have been stratified at that time because of glacial melt and summer warming, resulting in a boreal, as opposed to subarctic, fauna in our region. Through the next several millennia, the emergent Georges and Browns Banks limited exchange of water, materials and energy between the Gulf and the open Atlantic Ocean (Fig. 3). By 11,000 years B.P., the Gulf is clearly a large lagoon (Fig. 3). Further warming and rising sea levels through 9500 years B.P. allowed the spread of warm water fauna into the region as suitable habitats opened up. As the climate continued to warm, the Gulf became more estuarine in nature (Campbell 1986). By 7000 years B.P., the climate was warmer than at present and sea level was rising rapidly, but the tidal range was still small allowing for surficial warm summer conditions and the spread of warm-water fauna throughout the area. Relative sea-level continued to rise as a consequence of crustal rebound until the cross-sectional area between the Atlantic Ocean and the Gulf of Maine was sufficient for the development of a tide within the Gulf (Grant 1970) at about 4000 years B.P. (Scott and Greenberg 1983). The tidal range continued to increase over time (Scott and Greenberg 1983), and thermal stratification of the water column was broken down, especially near the mouth of the Bay of Fundy (Yentsch and Garfield 1981). The result of the extreme tidal mixing is relatively cold water temperatures in summer and relatively mild water temperatures in winter that has allowed the reintroduction of subarctic species. Presently, 15–20% of the invertebrate species found at the mouth of the Bay of Fundy are considered sub-arctic in affinity (Bousfield and Thomas 1975). At present in the Cobscook region, cold water species find suitable water temperatures for reproduction in the winter and early spring, while warmer water species may reproduce in the summer. Continued rising sea level, with a concomitant increase in tidal range and tidal mixing (Greenberg 2001), is increasingly restricting the distribution and reproductive abilities of warm water species (see below). The Cobscook region may be experiencing more rapid coastal submergence and, hence, rising relative sea level than other parts of the Gulf of Maine (Anderson and Borns 1989). The eastern Gulf of Maine and Cobscook region is thus zoogeographically complex due to present temperature regimes as well as historical, climatological, and physiographic changes since the last glaciation. Present-day tidal mixing stabilizes the environment of the 2004 P.F. Larsen 17 Cobscook Bay region by greatly narrowing the annual variations in water temperature and salinity relative to other regions of the east coast of North America. The system is dynamic, and continuing physiographic evolution will have on-going influence on the nature of the biological system. Some Noteworthy Biological Attributes Perhaps the most noteworthy biological feature of the Cobscook region is the high level of biodiversity. This feature was noted and documented, especially concerning the invertebrates, very early as a result of the investigations of the US Fishery Commission. The noted naturalist, A.E. Verrill, a Maine native and the first Professor of Zoology at Yale University, wrote in 1871: “The number and variety of marine animals that can be collected at low water within a few minutes walk of Eastport is really surprising to persons accustomed to collecting on other parts of the coast. Even under and among the lofty wharves a very respectable collection may be made, including at least 200 species, and representing nearly all the classes.” Further early evidence comes from H.E. Webster and his colleagues who, in the 1870s and 1880s, dedicated their efforts to describing the annelid worms of the east coast of the United States. These worms usually dominate benthic communities in terms of numbers of species and individuals. The Eastport area proved to be the most diverse area even though less time was spent collecting here than in the other regions. In just six weeks, Webster and Benedict (1887) found more annelid families, genera, species, and species new to science than were found in Virginia, New Jersey, and the Woods Hole region (Table 1). More recently, compilations of invertebrate species lists by Larsen and Doggett (unpublished), Linkletter et al. (1977), MacKay (1978), Trott (2004), and others indicate that roughly 1500 benthic species may occur in Passamaquoddy and Cobscook Bays, an area of only about 350 km2. One note of special interest is the fact that more polychaete species have been found in Cobscook Bay than have been recorded for the entire coast of Maine (Trott and Larsen 2003). The biodiversity is not distributed evenly across this region, but is concentrated in Cobscook Bay and Table 1. The number of annelid families, genera, and species found along the US east coast. Numbers of genera and species new to science are in parentheses. Derived from Webster and Benedict (1887). Locale Families Genera Species Virginia 23 49 (4) 59 (22) New Jersey 23 50 (2) 57 (14) Cape Cod 25 70 (3) 90 (16) Eastport 29 89 (7) 111 (26) 18 Northeastern Naturalist Vol. 11, Special Issue 2 in the area of Head Harbor Passage between Deer and Campobello Islands (Fig. 4) (G. Pohle and A. MacKay, pers. comm.). It is through Head Harbor Passage that most of the tidal exchange between Cobscook Bay and the Bay of Fundy occurs (Brooks et al. 1999), and the areas share similar physical characteristics including strong tidal currents, extreme vertical mixing, and a high incidence of fog. The number of species found in this limited region is nearly twice the number of species found in all of Chesapeake Bay (M. Wass, pers. comm.). Indeed, one may be able to make the case that, in terms of benthic invertebrates, Cobscook Bay and Head Harbor Passage are the most species rich areas in the western North Atlantic north of the tropics. Other evidence adds insight about the species richness of the region. Bousfield (pers. comm., 9/28/79) believes that, within the Gulf of Maine region, about 100 macroinvertebrate species are regionally unique to the Head Harbour Passage Figure 4. Map of Cobscook Bay with principal place names indicated. 2004 P.F. Larsen 19 mouth of the Bay of Fundy and Cobscook Bay. These populations are disjunct from their main population centers to the north or south or are even amphi-Atlantic species with their North American population centers at the mouth of the Bay of Fundy, such as the amphipod Corophium volutator Pallas. This is, indeed, a high figure, but considering the high total number of species found, the fact that only 100 species are unique supports the conclusion that the species richness is high because so many widely distributed species populate the area, rather than because it is a pocket of endemism. Eastern Maine and the Cobscook region are also notable because normally subtidal species can be found living intertidally. This phenomenon was also noted very early (Fuller 1862a,b; Stimpson 1851). Bousfield and Laubitz (1972) mention 15 such species and data of Larsen and Doggett (unpublished) show that 98 species can be found in the intertidal east of Mt. Desert Island, ME, most notably in Cobscook Bay, that are only found subtidally elsewhere. The significance of some of these occurrences has been formalized as part of Maine’s Critical Areas Program (Reports available from the Maine State Planning Office, Augusta). Two theories to explain this phenomenon have been put forward. Both probably have validity. The first is that extreme spring low tides in this region of the world occur in the early morning and late afternoon. This is because the dominant astronomical tidal constituent is the phase of the moon (Trites and Garrett 1983) and has the result that the lowest intertidal levels are not exposed to the noonday sun. Secondly, the extreme tidal mixing characteristic of Cobscook Bay insures cool summer water temperatures. The contrasting summer air and water temperatures produces heavy fog that insulates the intertidal organisms from the desiccating effects of the summer sun. Eastport experiences fog on 40% of July days which is three times the level of Portland, ME, 300 km to the southwest. Naturally, the larger the air and water temperature differential, the greater the probability of fog developing and, hence, we can expect fog on the warmest days that would be most detrimental to the survival of intertidal organisms. Another noteworthy feature observed at the mouth of the Bay of Fundy and in Cobscook Bay is the manifestation of giantism, often called gigantism, in several invertebrate species, i.e. these species attain an unusually large size. Among these species are starfish, brittlestars, tunicates, and sea urchins (N. Meinkoth, Swarthmore College, pers. comm.). The best known example is the common periwinkle, Littorina littorea L., that is heavily harvested in Cobscook Bay because its unusually large size, 2–3 times normal, makes it more marketable. Hypotheses as to why certain populations of a species grow to abnormally large size include slower growth to maturity because of low temperatures, good feeding conditions, poor feeding conditions, latitudinal genetic differentiation, 20 Northeastern Naturalist Vol. 11, Special Issue 2 and parasitism. Whereas the latter can be discounted (C. Schaeffer, University of Connecticut, pers. comm.), the cause of the giantism in so many species in such a limited area has not been researched. It seems likely that populations living at the subnormal temperatures of Cobscook Bay require a longer than normal time to reach sexual maturity (Kinne 1970), while somatic growth continues in the food rich environment. The coexistence of these several phenomena, i.e., extremely high biodiversity, the southernmost availability of many boreal and subarctic species, intertidal accessibility to normally subtidal species, and the existence of especially large specimens has attracted many collectors to the area who seek an efficient, inexpensive way to supply museum and university collections. A full 44% of the Maine specimens in the Gray Museum of the Marine Biological Laboratory, Woods Hole, MA, were collected in Cobscook Bay (Larsen and Doggett, unpublished). These same phenomena, together with the fisheries resources and concentration of endangered marine mammals, were instrumental in the decision of the Carter administration to contest the licensing of the proposed oil terminal and refinery in Cobscook Bay in the late 1970s (T.K. Bick, Tighe Patton Armstrong Teasdale, Washington, DC, pers. comm.). Summary Present conditions in the eastern Gulf of Maine and the Cobscook region are a function of geological history and present-day hydrographic conditions. The extreme tidal mixing stabilizes the environment of Cobscook Bay by greatly narrowing the annual variations in water temperature and salinity relative to other regions of the east coast of North America. The timing of low tides and the high incidence of fog further ameliorates the normally harsh conditions found in the intertidal zone. The biological community has responded to the physical conditions with a convergence of high biodiversity and other unusual ecological conditions and phenomena that are not reproduced elsewhere. Acknowledgments The writing of even a short historical overview of this type makes one reflect on the influences that shaped the moment. It allows me to acknowledge my gratefulness to some of the people who over the years, knowingly and perhaps unknowingly, provided the knowledge, inspiration, and encouragement to pursue a comprehension of the zoogeography, ecological functioning, and historical ecology of the Gulf of Maine. With the perspective of time, I wish to thank John S. Rankin, Jr., Spencer Apollonio, Marvin Wass, Charlie Yentsch, Ed Bousfield, Howard Sanders, Wim Wolff, Jack Pearce, Stewart Fefer, Erik Rasmussen, Jørgen Hylleberg, Graham Daborn, Dave Greenberg, and several other US, Canadian, and European colleagues. A collective thanks is due to the enthusiastic participants in the New England Estuarine Research Society and the 2004 P.F. Larsen 21 Fundy Environmental Studies Committee. My co-authors in this special issue, and many individuals cited in the bibliographies, have been active collaborators for upwards of three decades. Finally, my colleagues and former colleagues at the Bigelow Laboratory for Ocean Sciences and the Maine Department of Marine Resources have provided a fertile atmosphere and tangible support for investigating all questions concerning the Gulf of Maine. Literature Cited Anderson, W.A., and H.W. Borns, Jr. 1989. Neotectonic activity in coastal Maine: United States of America. Pp. 195–212, In S. Gregersen and P.W. Basham (Eds.). Earthquakes at North-Atlantic Passive Margins: Neoteconics and Postglacial Rebound. Kluwer Academic Publishers, Dordrecht, The Netherlands. Belknap, D.F., B.G. Andersen, R.S. Anderson, W.A. Anderson, H.W. Borns, Jr., G.L. Jacobson, J.T. Kelley, R.C. Shipp, D.C. Smith, R. Stuckenrath, Jr., W.B. Thompson, and D.A. Tyler. 1987. Late Quaternary sea-level changes in Maine. Pp. 71–85, In D. Nummedal, O.H. Pilkey, and J.D. Howard (Eds.). Sea-Level Rise and Coastal Evolution. Society of Economic Paleontologists and Mineralogists, Tulsa, OK, Publication No. 41. Bousfield, E.L., and D.R. Laubitz. 1972. Station lists and new distributional records of littoral marine invertebrates of the Canadian Atlantic and New England regions. Biological Oceanography Publication No. 5, Canadian National Museum of Natural Sciences, Ottawa, ON, Canada. Bousfield, E.L., and M.L.H. Thomas. 1975. Postglacial changes in distribution of littoral marine invertebrates in the Canadian Atlantic region. Proceedings of the Nova Scotia Institute of Science. Supplement 3:47–60. Brooks, D.A., M.W. Baca, and Y.-T. Lo. 1999. Tidal circulation and residence time in a macrotidal estuary: Cobscook Bay, Maine. Estuarine, Coastal, and Shelf Science 49:647–665. Campbell, D.E. 1986. Process variability in the Gulf of Maine: A macroestuarine environment. Pp. 261–275, In D.A. Wolfe (Ed.). Estuarine Variability. Academic Press, Orlando, fl. 509 pp. Fuller, C.B. 1862a. Report on marine zoology [of Maine]. Pp. 129–133, In Second Annual Report upon the Natural History and Geology of the State of Maine, 1862. Stevans and Sayward, Augusta, ME. Fuller, C.B. 1862b. Note on the animals of Eastport Harbor. Proceedings of the Portland Society of Natural History 1:91. Grant, D.R. 1970. Recent coastal submergence of the Maritimes Provinces, Canada. Canadian Journal of Earth Sciences 7:676–689. Greenberg, D.A. 2001. Climate change, mean sea level, and tides in the Bay of Fundy. Pp. 1–16, In Increased flood risk in the Bay of Fundy in scenarios for climate change. CCAF Project S00-15-01. Bedford Institute of Oceanography, Dartmouth, NS, Canada. 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. 22 Northeastern Naturalist Vol. 11, Special Issue 2 Kelley, J.T. 1987. An inventory of coastal environments and classification of Maine’s glaciated shoreline. Pp. 151–176, In D.M. Fitzgerald and P.S. Rosen (Eds.). Glaciated Coasts. Academic Press, New York, NY. Kinne, O. 1970. Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters. Volume 1. Wiley-Interscience, New York, NY. 681 pp. Knott, S.T., and H. Hoskins. 1968. Evidence of Pleistocene events in the structure of the continental shelf off the northeastern United States. Marine Geology 6:5–43. Larsen, P.F. 2004. Introduction to ecosystem modeling in Cobscook Bay, Maine: A boreal, macrotidal estuary. Northeastern Naturalist 11(Special Issue 2):1–12. Linkletter, L.E., E.I. Lord, and M.J. Dadswell. 1977. A checklist and catalogue of marine fauna and flora of the lower Bay of Fundy of New Brunswick. Huntsman Marine Laboratory, St. Andrews, NB, Canada. 68 pp. MacKay, A.A. 1978. Bay of Fundy Resource Inventory. Final Report to the New Brunswick Department of Fisheries, Frederichton, NB, Canada. Six volumes. Scott, D.B., and D.A. Greenberg. 1983. Relative sea-level rise and tidal development in the Fundy tidal system. Canadian Journal of Earth Sciences. 20:1554–1564. Shipp, R.C., D.F. Belknap, and J.T. Kelley. 1991. Seismic-stratigraphic and geomorphic evidence for a post-glacial sea-level lowstand in the northern Gulf of Maine. Journal of Coastal Research 7:341–364. Stimpson, W. 1851. Observations of the fauna of the islands at the mouth of the Bay of Fundy. Proceedings of the Boston Society of Natural History 4:95–100. 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. Department of Fisheries and Oceans, Ottawa, ON, Canada. Canadian Special Publication in Fisheries and Aquatic Sciences 64. Trott, T.J. 2004. Cobscook Bay Inventory: A historical checklist of marine invertebrates spanning 162 years. Northeastern Naturalist 11(Special Issue 2):261–324. Trott, T.J., and P.F. Larsen. 2003. Cobscook Bay, Maine: The crown jewel of biodiversity in the Gulf of Maine. In Proceedings of the 32nd Annual Benthic Ecology Meeting, Groton, CT. Verrill, A.E. 1871. Marine Fauna of Eastport, ME. Essex Institute, Salem, MA. Bulletin 3:2–6. Webster, H.E., and J.E. Benedict. 1887. Annelida Chaetopoda from Eastport, Maine. Report of the US Fishery Commission (1885):707–755. Yentsch, C.S., and N. Garfield. 1981. Principal areas of vertical mixing in the waters of the Gulf of Maine, with reference to the productivity of the area. Pp. 303–312, In J.F.R. Gower (Ed.). Oceanography From Space. Plenum Press, New York, NY.