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Home , Habitat

. . CHAPTER 16

Habitat- Biotic Interactions

Charles A. Simmstad, Stephm B. Brandt. Alice Chalmers. Richard Dame. Linda A. Deegan. Robert Hodson. and Edward D. Houde ~ .

Abstract

Conventional concepts of estuarine and near-shore coastal are gen- erally inadequate descriptions of processes and that respond to habitat variability and change or integrate far larger and more complex "habitat landscapes." In particular, the role of structure within and among , networks through which organisms and critical processes that influence secondary production operate. and the role of estUarine circula- tion "control point" featUres in shaping -web structure and variability are poorly known. In response to these gaps, the Habitat-Biotic Interac- tions Working Group established as their goal to identify approaches needed to synthesiu a mechanistic understanding of how habitat structure influences rr estuarine secondaryproduction and food webs. We recommend eight major steps to enhance synthesis of natural and anthropogenic changes in estUar- ine production related to habitat-biotic interactions:.(l) develop an estUar- ine habitat classification scheme that relates habitat srructure to estuarine production and food-web processes; (2) examine existing long-term data sets to identifY the scope and frequency of variability in habitat structUre; (3) implement comparative stUdies of habitat ; (4) develop and link habitat and landscape models that captUre the dynamics of biota and process interactions over large estuarine scales; (5) develop indicators of habitat integrity, dynamics. and variability; (6) link site-spe~ific field experiments -and modeling approaches to scale processes and process understanding across and landscapes; (7) apply advanced mea- surement technologies to give details of distriburions and abundances of secondary consumers not now achievable; and (8) link habitat structUre to assessment and prediction of managemenr scenarios. Addressing ecosystem change in response to habitat structUre, as well as the impacts of coastal zone management impacts upon ecosystems. will require innovalive 418 p"" IV. Con"ols of £,tu",;nt /I"b;,,,,, Chop.CI 16. lIobim-Bio.ic In,o,o"ions 419

syntheses a( much more expanded dme and space scales (han heretofore considered. of the anthropogenic components of change is essential to both managing our exploitation of coastal resources and minimizing the impacts on these resources of our occupation of the coastal margin. However, variabiliry and Introduction change in biotic interactions associated with natural variation in habitat stnlC- ture can be difficult to separate from anthropogenic degradation or shifts in '10 a large degree. the and structure of estUarine and coastal habitats habitats. Habitat structure natUrally varies and changes over a hierarchy of control ecosystem productiviry and communiry structure. Resources such as spatial and temporal scales among different or within anyone estu- nUtrients and that limit can be extensively inRu- ary. Different types of estUaries reRect dramatically different occurrences and enced by inpurs from and (chapter 4. Fisher et al.; chapter II, distribUtions of habitats because of geologic origins and hisrories and contem- Boynton and Kemp; chapter 2, Howarth et al.; and chapter 3. Vorosmarty porary climatic settings that embrace thousands of square kilometers and and Peterson) or, to a lesser extent, the shelf and open . On the other years. Within short time and space scaJes (for example, annual-decadal, hand, many of the processes within estuaries and coastal zones that affect meters). variability and change in habitat can also introduce variability in the nutrient cycling and the conversion of the responding primary production quantity and quality of at all trophic levels. I.rwhat are perceived into secondary producer are likely related more to habitat strucrure. as the most stable of habitats, such as salt . habitat structure changes Thus, the source and amount of organic matter at the base of estuatine food over diflerent space and time scales, some of which are relatively predictable webs are determined by diverse allochthonous and aUtochthonous processes, (for example, seasonal al1d successional changes in biota) and others highly and prone (0 considerable spatial and temporal variability. bUt habitat struc- stochastic (f()rexample, events). While scientists have long recog- ture inRuences the pathways and efficiencies of transfer ro - nized that variability and change in habitat structure is reRected in variable isms at higher levels in the . This dichoromy may explain some of levels of production by estUarine biota, understanding of the underlying the noise and uncertainity inherent in estimating high-trophic-Ievel produc- processes is meager. As a result, the diagnostic and. prderably, predictive capa- tion based only on nutrient budgets and stoichiometry. bility that is necessary to separate natural dynamics in estuarine habitat change Overall, the scientific view of habitats has until recently been relatively and production from changes imposed by anthropogenic effects is insufficient restricted and narrow in terms of taxonomic groupings. ecosystems, and scales for coastal management decisions. As has been implied already in chapter 12 (McCoy and Bell 199 I). Although we have nor conducted a comprehensive (Kremer et al.), ecologically complete syntheses require both mechanistic and review of the literature similar to that of McCoy and Bell, our familiarity with predictive understanding of the underlying processes that control the compo- the contemporary literature suggests this myopic view is particularly true for sition and production of higher trophic levels. Management of influ- estuarine and coastal ewsystems. For example, the areal extent of specific estu- ences on important ecosystem processes will not improve until interactions arine and coastal habitats such as marshes and submerged aquatic between estuarine habitats and dependent biotic resources. such as fish. shell- has long been used as an index of fish and production, especially when fish. and wildlife, are understood and at least somewhat predictable at larger addressing rearing (nursery) habitats of economically important fish and shell- spatial and temporal scales. fish. bur examination of interactions of these biota among habitats over time is The Habitat-Biotic Interactions Working Group's objecrive was to ilSsm infrequent and ecosystem-scale analyses are rare. Although within-habitat link- how more synthetic approachesshould be brought to on fundamental ques- ages to production of higher trophic levelsare gradually emerging (such as, fish tiom about the role of habitat strttcture and variability in estuarine ecosystem growth and survival relative to salt- structure), estimates of processes processes.While there is a breadth of valid questions that readily emerge across the esruarine landscape, or comparisons among esruaries with different around this issue (table 16-I), the Working Group focused on processes thaI habitat structUres, are wanting. Yet the strength of interactions between biota affected biotic production, and specifically higher production. and their habitat. whether physical (larval transport. aggregation offood parti- which to a large degree defines our socioeconomic and cultural dependence on cles) or ecological (feeding efficiency. refugia from predators), may be the ulti- estuarine ecosystems. We immediately concluded that the ecosystem context mate determinant of productive capacity and composition of consumers at the of these questions precluded the traditional single-. single-habitat apex of estuarine and coastal food webs. approach to understanding the role of habitat structure. Understanding the Understanding change in the structure of habitat. its inRuence on funda- association between estuarine biota and habitats demands history. physio- 1111:IIIalecmystcm processes. responses of habitat-associated biota. and effects logical. and ecological knowledge of esruarine colllmunities as they inrerarr 431 Po,' H'. CO,II,O" of E,III."in, 1I00i,all Ch.p.« 16. ...hi Bioli. Im.r'Clions HO

TABLE 16-1 The Concept of Habitat and Habitat Structure Predominance of pelagic vs. benthic food webs? What eSlUarinecharacteristicsdetermineswhich predominales? Safriel and Ben-Eliahu (1991) provide a comprehensive definition of habi- WIII:nvariable.what comrols swilchingbetweenpalhways? tat that is particularly appropriate to estuarine and coastal ecosystems: "the What is Ihe role ofbeOlhic-pdagic couplings? environment of a confined to a portion of the landscape," including three components: (I) physicochemical fearures such as salinity Is biotic diversity related to estuarine productivity? and ; (2) resources such as food and space; and (3) interacting Do species inlroductions change food webs? Does food web efficiency change with ? organisms other than those functioning as resources, such as predators, competitors, and mutualists. While the concept of habirat is commonly Are there estuarine indicators of estuarine productivity and food web structure recognized, definitions of habitat structure are more numerous and diverse and efficiency? Whal iOirahabital slruCiural auriblUes (e.g.. edge:) inRuence secondary produc,ion? depending on different taxa and scale viewpoints but may be defined as What landscale-scale fealUres (e.g.. habitat linkages. configurations. location) affect sec- the arrangement of objects or features in the environment (McCoy and ondary production? Bell 1991). J

Ilow prevalent and variable are regional, extraestuarine influences on estuar- ine food web structure and production? Habitat Landscapes What is the importance and variability of higher trophic level (top-down) con- In conventional usage. habitat has been defined by the occupation of a par- trols on different descriptors of estuarine biotic communities? Composiuon? ticular , that is, the locality, site, and particular type of local envi- Food web slruclUrc:? ronment in which an organism is found. However, a broader ecosystem Food web efficiency? perspective would suggest that habitat embraces any part of the environment ProduClivilY? on which consumer organisms, directly or indirectly, depend during the estU- DireCi vs. indirect effects? arine portion of their life histories. Motile consumers (nekton) integrate dif- How have anthropogenic changes in disturbance regimes changed biotic inter- ferent habitats in moving among spawning grounds, nursery areas, refugia actions, community structu~e, ~d production ~rnamics? from , feeding zones, and migration routes (Ayvazian et at. 1992). This use of "habitat landscapes" involves multiple scales of space (meters to hundreds of meters) and time (hours to seasons), as aptly illustrated (figure across the mosaic of habitats that comprise estuarine landscapes. New per- 16-1) for tidal marsh nekton by Kneib (1997). Over a hierarchy of spatial spectives and analY9<=altOols are required to gain such an understanding. scales within and among habitats, the movement of nekton across the land- Consequently, the Working Group formulated the question, What are the scape is theorized to account for a "trophic relay" of intertidal primary pro- effects of habitat structure and change on interactions at ecosystem space-time duction that changes over the habitat range and life stage of the nektOn (for scales?Implicit in this question are the concepts of (1) Strength, (2) variability, example, juvenile and adult resident, transient predatOry) and habitat (figure and (3) time/space scales of interactions berween either individual habitats or 16-2, Kneib 1997). At the extremes of the scale, many species and overall estUarine habitat structure and estUarine production. particularly tOp-level account for major fluxes of organic matter In the Working Group deliberations and the summary below, our goal was and nutrients into or out of the estuarine ecosystem as larvae, juveniles, and (0 identifY approachesneeded to synthesizea mechanistic understanding of how adults, with accompanying variability due to both biotic dynamics (for exam- habitllt structure influences estuarine secondaryproduction and food webs. This ple, , behavior) and physical dynamics (such as flow goal complements the goal of the Linking Biogeochemical Processes to and coastal currents; Deegan 1993). Estuarine Food Webs Working Group (Kremer et al., chapter 12) byexamin- It may be a useful convention to visualize habitats asdiscrete segments of the ing the relative importance of non-biogeochemical controls on the transfer of environment that fit together to make a place for communities of organisms to organic matter to higher trophic levels. In this respect, the overall "carry- persist. These pans include the physical environment (such as substrate pro- home" messageof this volume should ultimately involve integration of recom- vided by plants, sediments, and even organisms, such as ), and the mendations by both of these working groups. 43~ Pari/V. Cont,ols of Ellu.,,;nt /lab;'a" Coha.,..r 16. Ihbiu.-Bio.ic 1",

Intertidal Migrations (hours or days) intertidal H intertidal or subtidal H intertidal

Gauntlet Species Ontogenetic Migrations .,hMic.." (d.rtc'a_II 'a marrllJ.. (weeks) ...... JU'I8nll... I pea..'d pr.WDI) " JUY8IIII.. .. ,",Mic..,. (indirtc' a_II) .. .lIull.I . 11.1.chlp.la, '1IIfI1i11U) intertidal subtidal " " or- FIG U R E 16 -2 Trophic relay of intertidal marsh production involving different shallow subtidal - open estuary life stages of resident and transient nekwn across habitat landscapes (from Kncib 1997. used with permission); gauntlet species are nekton. particularly forage fishes. j, whose juveniles encounter a gauntlet of predators during their large-scale migrations from the spawning ground to the estuary and back.

Seasonal Migrations (months) SCALE - Size01 organism or groups 01 organisms responding to slruclure -Spatial and temporal variation in compIexily and helerogeneily allributes -Stabilily, resistance, and resilience pen estuary - coastal ocean - Disturbance regimes (Irequencies and inlensi«esl

COASTAL HETEROGENEITY~ ':.a COMPLEXITY OCEAN - Divelsily 01dine/enl habilat elements - Densily 01individual habilal elemenls - Conneclivily. nelworks. corridors, and barriers . Habilat palch size, shape, and Iragmenlalion FIG URE 16-1 Nekwn movement among estUarine tidal-marsh habitats demon- - Aggregation and grain ------strating range of shorr-term (behavioral movement between interridal and subtidal) to longer-term (ontogentic [life-history] and growth-related) space and time scales (from FIGURE 16-3 Components of habitat structUre. Modified from McCoy and Bell Kncib 1997. used with permission). 1991. 434 1'"" IV. ConlTO{,oj1:."Jlu"r;"tl/"b;I"" ChaplCf 16. Habiu,.Bio,ic 1'lIo"clion. 435 bivalves such as oysters and that form reefs, and tubes, burrows. and of nutrients and dissolved and particulate materials; Dame et al. 1992) and castings of soft-substratum macrofauna such as and bivalves provide corridors of access for nekton along the marsh edge and (Sebens 1991). seeking refuge within marsh vegetation (Rozas and Odum 1987; Rozas et al. . The relationship betWeen an organism and its habitat is also highly depen- 1988; Minello et al. 1994; Kneib 1997). The continuum of habitats and dent on the organism's . size. and trophic status. The habitat of a linking corridors become particu.larly important to anadromous and catadro- protozoan, which might entirely encompass the sphere of an estuarine aggre- mous nektOn species, such as salmon, which must traverse the eruire estuar- gate <50 ~Imin diameter. is vastly different from striped bass habitat, which ine gradient at several stages in their life history (Simenstad and Cordell, in includes several different locations within estuaries as well as near-coastal revision). Therefore. habitat structure at the ecosystem scale encompasses the waters outside the estuary. From an ecological perspective. however, there can configuration, and arrangement and connectivity, of habitat eIemcnts that be strong linkages betWeen the protOzoan and striped bass because the striped rypify most estuaries (figure 16-4). bass may depend on a food-web pathway initiated by the protozoan. Unique water-column features of estuarine hydrodynamics also contribute In defining habitat, the primary descriptors have been physical location. to habitat structure. In addition to tidal fronts, where concentration of plank- , and biological features because these provide a convenient tOn and Other food particles provide a distinct furagin~ interface for fishand organizational typology. Tlms, a habitat is most directly described by its posi- , circulation "control points" along the estuarine gradient can be sites tion along a saliniry gradient, tidal Aooding regime (or tidal elevation as a of intcnse geochemical and biological activiry (color plate 12). Comrol points indicator) substrate rype, (wave. current) exposure, and dominant bio- may be described as circulation discontinuities that are caused by focusing of logical components, as demonstrated by the U.S. Fish and Wildlife Service's advective and diffusive processes. These locally intensify chemical and biolog- National Inventory (NWIi Cowardin et al. 1979). However, the bio- ical interactions either directly because of circulation (lor instance, upwelling) logical components often become the primary descriptOrs, such as marshes. or indirectly because of organisms' volitional responses to the feature (such as tidal forested swamps, reefs, beds, eelgrass , mangroves. fish ailll bird foraging). One of the bener examples of such control points is and intertidal and subtidal mudAats or sandAats. Less obvious. but equally important. examples are structural features inherent in different rypes of estu- arine circulation. such as tidal fronts separating different water masses or plumes of low-saliniry water produced by large rivers (color plate II). . Physicochemical characteristics that determine physiological and behav- ioral responses of estuarine biota also delimit organisms' habitats. Environ- mental propeni~such as tcmperature. salinity, and dissolved oxygen greatly influence the scope of use of habitats, especially where extrcme variation occurs, as in most interridal habitats. Evolutionary and real-time responses limit organisms' , foraging, and gencral movement. This is illus- trated in the estimatc of growth potclllial of miped bass in Chesapeake Bay, as estimatcd by bioencrgetic models using temperature, prey density, and prcy size distributions (Brandt and Kirsch 1993i see also figure 15-5 in this volume).

Connectivity and Conh'o/ Points Landscape features that link habitats influence the flux of dissolved and sus- pended constituents and the management of organisms. Networks and corri- dors, such as dendritic tidal rivulet and channel systems. play particularly FIGURE 16-4 Complex estuarine continuum of forested warershed, freshwater important roles because they link a geohydrologic continuum of habitats tidal marsh, sail marsh, creeks and pannes, Plum Island Sound (Massachusetts), bar- wirh varving !!cochernical flll1criolls(for example, constitute sinks or sources rier beach, maririme fores!, and rhe Arlanric Ocean. ,; 'I 436 PIt"~/I'. C""".b .f Ell"",;", lI"b;,,,,, Chap'" 16. lIabiu..Biolic InI

estUarinetUrbidiry maxima (ETM), where residual circularion and other mentally over a variery of time and space scalesare lesswell known and quite effects produce a region of intense trapping and aggregation of inorganic and often are indistinguishable from changes due to natUral sources. Furthermore, particles, zooplankton, and larval fish, and high bacterial acriviry there have been very few comparisons of habitat change across diverse estu- (Uncles and Stephens 1993; Baross et at. 1994; Bernat et al. 1994; Jay 1994; arine ecosystems that lead toward a general understanding of the conse- Simenstad et al. 1994a, 1994b; Morgan et al. 1997; Crump and Baross 1996). quences to estUarine food webs. ETM havebeen shown to account for a disproportionallyhigh contribution to the food web in the Columbia River estuary (Simenstad et al. 1990), and to be associated with recruitment processes of anadromous fish and blue crab ACllte Habitat Cha1lge growth in Chesapeake Bay(Boynton et at. 1997). Because of the intense con- Acute habitat change tends to result from direct impacts, usually intense nat- centration of material and activiry at control points, they likely form an ural disturbances (for example, hurricanes, freshwater Aooding) or activities important lateral extension of shoreline habitats, such that consumers in by (such as dredging or filling). These can cover extensive areas, as in peripheral shallow and benefit from the proximiry (0 ETM through hurricane effects(Chabreckand Palmisano 1973), but often do not result in increased food resources. I a permanent change in estuarine processes. The persistence of natural estuar- ine processesfacilitatesnatural recoveryof the pre-disturbancehabitat struc- I I tUre. However,both continual removalof estuarine habitat and alteration of I I i. Habitat Variability,Natural and Anthropogenic Change natural physical-and geomorphic processes results in a comparatively perma- nent shift in production. Maryland and Connecticut have lost 74% of their Habitat variabiliry is a consequence of changes in geomorphology (water, I estuarine wetlands, California, 91% (Dahl and Johnson 1991). Dredging, circulation, basin morphology), watershed, and water quality (Iightanenuarion, diking,and fillingof emergentwetlandsalone is principallyresponsiblefor a chemistry), and biological characteristics (rhe structUral etTectsof organisms loss of greater than 94% of 's historic marsh habitat II such as submerged aquatic vegetation, oysters, and the like) inAuencing (Nichols et al. 1986), and an average of 42.5% of these important, highly r estuarine and near-coastal environments. A knowledge of these three factors and I productive habitats have been removed from PacificNorthwest estuaries, their inAuence on food-web pathways is required to assesslevels,efficiency,and with many havinglostover60% (Bortlesonet al. 1980;Boule 1981; Bouleet variabiliry in estuarine productiviry. Estuaries vary in their fundamental charac- al. 1983; Bouleand Bierly1987). Dredging of canalsand navigation chan- teristics that relate forcing (for example, tidal, river flow, wind) (0 physical nels alone hascauseda direct lossof ~ 16% (12,000 ha) of Louisiana'scoastal processes (circulation and sediment transport; seeJay et aI., chapter 7). Some of marshes (Turner and Cahoon 1988; Boesch et al. 1994). The most recent the variablesffnmestuaryto estuarythat can affectfood websandproductiviry analysis of Statm and Trends of Wetlands in the Contermillom United SI,lteS arewaterinputs, tidalinAuences,waterand particleresidencetimes,stratifica- (Dahl and Johnson 1991; Dahl and AJlord 1997) suggests that these dramat- tion characteristics,and basin morphologies.For example,the Columbia and ic rates of intertidal habitat loss are declining, but betWeen 1985 and 1995 an Chesapeake estUaries,while sharing some common estuarine features, are alarming 3,760 ha of total estuarine wetl~nd habitat, and 734 ha of estUarine !I notable for their distinct differences in habitat structure, which result in subtidal habitat, disappeared. contrasting levelsand qualiry of productiviry. Chesapeake Bay hassuffered significant habitat losses and modifications Numerous documented and anecdotal observations of changes in estuarine that impact fisheries productivity and have diminished qualiry of bay habitats productiviry are associated with changes in habitat. However, while we have for overall biological productiviry.Early declines in anadromous fish (shads, considerable knowledge of productiviry and food-web processes in some estu- river herrings, striped bass) were a consequence of blockages and on arine systems,we lacksynthetic abiliry (0 extend that knowledgeto other es- spawning tributaries (Hildebrand and Schroeder 1928), but later declines tUarieswith similar or different habitats. Many obvious effects of major .~ that became precipitous in the 1970s probably were attributable to multiple habitat changes introduced by humans, such as , wetland loss, causes,includingfishing,habitatloss,and declinesin habitat qualiry.For damming of rivers, increased nutrient loading, and introductions of exotic example, 2.5% of the wetlands in the bay watershed were lost during the species, are known for many estUaries.Comparably dramatic natural changes, period 1982to 1989 (Tiner 1994).Although not easily assignable to any spe- such asfrom hurricanes(Ruzeckiet al. 1976),havealsobeendescribed.More cific cause, declines in fisheries productiviry followed Hurricane Agnes in ~lIhr1r indirrrt rffrrt~ ofhahitat change that may occur progressively or incre- J972 and wert'concurrent with increasednurrient loadings,lossesof I'd" IV, Control. 0/ E",,,,,ilJrlIabi/dU Chap'.. 16. Ihbila,-Hiolic I..'c.."iollo 439 438 meadows, and concomi(ant effects on habitat quality. American shad, once and growth of small fish (Deegan and Buchsbaum in press). These changes occur long before the SAYhabitat disappears. the object of the most valuable fishery in the bay, dwindled to levels that More subtle differences in the character or quality of a habitat may also be required a moratOrium on fishing (Anonymous 1989). Striped bass stocks reAected in varying production. The growth of juvenile fish, for example, is recovered under greatly reduced fishing mortality, demonstrating that habitat deterioration alone was not the cause of the species' collapse (Richkus et al. demonstrably different in different estuarine habitats (see Sogard 1992, 1994; Sogard and Able 1992). Recruitment growth and survival that varies as a func- 1992). Oysters have declined to disastrously low levels in the bay. While the tion of river Aow may relate to control-point dynamics and position, or rela- causes are debatable, heavy fishing, destruction of habitat by the fishing tionship to other habirars (such as nurseries; Stevens 1977). process, siltation of oyster beds, and the prevalence of disease in the stressed, remnant stOck (Rothschild et al. 1994) indicated that was one significant contributor to the disastrous decline. The role of seagreasses in Examples of Documented Habitat Changes fisheries productivity has not been clarified for Chesapeake Bay, bUt recent and Estua,.ine Responses signs of modest recoveries in bay (Anonymous 1995) are viewed Examples of some of the better-documented changes in esiuarine function with optimism by ecologists and fishery managers concerned about the bay's associated with habitat alteration include (1) impacts of major water witll- fisheries resources. drawals from river Aow into San Francisco Bay, the Gulf of Mexico, and the Sea of Azov; (2) construction and operation of the High Aswan ; Subtle Habitat Change (3) eutrophication of Chesapeake Bay; (4) extensive colonization of exotic species in San rrancisco Bay; and (5) a complex combination of natural and Subtle, long-term habitat changes can involve more chronic or indirect mecha- anthropogenic changes in the delta. nisms, including (I) degradation of water quality from eUtrophication (for River inflow to estuaries Auctuates naturally and both and flood example, increased areas and persistence ofhypoxia/anoxia); (2) loss/reduction extremes alter habitat-associated production and food-web relationships. For of sediment sources (such as shifting from accretion to erosion regimes in example, drought effects on fish production, caused primarily by changing marshes); (3) shifts in estuarine circulation (for example, salinity distribution) due to riverdiversion and regulation; (4) coastal ;and/orsea-Ievel rise; optimum habitat Utilization, has been documented to alter secondary produc- tivity and trophic structure (Austin and Bonzek 1996; Livingston et al. 1997). (5) disturbance or removal of keystOnespecies or other compo- However, anthropogenic diversion and regulation of river flow can impose far- nents by fisheries or other mechanisms (such as disease), and (6) introductions reaching impacts, over diverse time scales, to fundamental habitat-structuring and expansions of exotic species.Compared to acute habitat changes, these more ,J' subtle, chronic changes typically produce nonlinear and often highly complex processes in estuaries that, unlike natural Auctuations, may be di~ficult to reverse (Simenstad et al. 1992). Alterations of the natural hydroperioJ can responses by estUarin~biota that are often difficult to distinguish from natural affect estuarine circulation on different time and magnitude scales, ranging fluctuations. ' These more subtle anthropogenic influences can significantly alter the from short-term (diel, peak power-generation cycles) to longer-term (seasonal or interannual) changes. As a result, longitudinal and vertical estuarine habitat processes that control higher trophic level production independent of obvious Structure is altered by changes in mixing and salinity regimes, and the position structural changes such as measurable loss of habitat. A well-documented and dynamics of control-point features altered. 'Iruncated Aooding can reduce example of this is the effect of eutrophication on fish production in submerged sediment and nutrient inpUts to estuarine wetlands. Reduction in flooding aquatic vegetation (SAY) habitats (Deegan and Buchsbaum in press). reduces disrurbance frequency and intensity in modifYing estuarine geomor- Eutrophication increases algal growth (plankron, , and macroalgae) phology, allowing wetlands and other intertidal habitats to evolve toward preferenrially over vascular plants. This change in affects higher successional stages. Loss of riparian habitat Aooding may also reduce food acquisition 'and survivorship of juvenile fish that use the SAYhabitat asa the Auxof organic matter Aux to the estuary. critical nursery area. Food webs are altered as the community Even partial loss of freshwater flow imposes stresses on natural estuarine responds to changing plant assemblages, in part as invertebrate susceptibility habitat funcrions. Lossesof 40-60% of the freshwater flow (and higher diver- (() predation by small fishes declines as increased algal cover provides more sions during high flow periods), and 60-75% of rhe sediment input, into north refuge. The declines in vascular planr density, biomass, height, and health San Francisco Bay have impacted the production of estuarine biota, parricu- increase the susceptibility of small fish (0 predation, The integrated result of crion and archirecture is a decline in the .I""I',fh~J~I<,il'.1,,,hir:lI," .n , ...nrimarv"v"'n' nro',n,fh("'ntHlllnnl nt ~1I1)m('rp('(1:1ClIJaflCvegc:tau larly ~b~~~~.~S..s£!~\~I.~~.~1.\~.i.~I ~I~~.~xi.{iEa! .~W;~pJ.HliHe}11.1i~~m,t(?IW) 9Wl ('Sill;! ri lit' Ch'''ler 1(.. 'hhilal.Diolic Inloucliooo 44.\ 442 Pa,t /I'. CotJIrnt. of E,t"a,;//, lIab;tatJ

Action Items and Recommendations 4. develop and link habitat and habitat landscape models; 5. develop indicators of ecosystem habitat integrity. dynamics, and variabilityj Need for Ecosystem Approach 6. link site-specific field experiments and modeling approaches to scale A~ong the nine issuesthat the National Research Council (1994) identified as processes across ecosystems and landscapes; posing significant threats to the integrity of coastal ecosystems, five (eurrophi- cation. habitat modification, hydrologic and hydrodynamic disruption, intro- 7. apply advanced measurement technologies to give details of distributions duction of nonindigenous species, global change and variability) and abundances of secondary consumers not now achievable; and directly involve the issue of habitat changes on esruarine secondary produc- B. link habitat structure to assessment and prediction of resource manage- tion. Recent emphasis placed on "" under reaurhorization ment scenarios. of the Magnuson-Stevens Fisheries Act further illustrates acknowledgment of a direct link hetween fisheries production and the integrity of aquatic habitats. The focus of these initiatives is (Q develop and synthesize information on However, esruarine science has rarely deah in a diagnostic or predictive man- estuarine habitat-biotic interactions that can be empll?}'ed(Qcompare habitat ner with assessingchange, either within-habitat variability over a landscape, or differcnces and production processes in divergei1(estUarine ecosystems. much less, the consequences to sustainable resources. Continued investment in habitat-specific applications of models, comparisons, and experiments will J. Developan estuarinehabitat classificationschemethat rei/lieshabitat structure not alone provide the scientific and management communiry with the infor- to estuarine prodtlttion and food-web processes. Any synthetic approach (0 mation needed (Qscale the effects of habitat change on production to the level assessing habitat-biotic interactions requires an esruarine classification of esruarine ecosystems. This "ecosystem approach" requires understanding of scheme that incorporates physical. geomorphic. and geochemical attribUtes the fundamental linkages among ecosystem components, biological responses of habitats that have ecological significance (Jay et al.. chapter 7). Systematic to physical and geochemical processes. rates and variability of these underlying habitat classification is particularly important for ecosystem comparisons. processes. and the effect of disturbance and other modes of ecosystem change. With lite exception of rhe recent of the hydrogeomorphic (HGM) But even more holistic approaches are required. especially those that approach system (Brinson 1993), estuarine habitat classification has not progressed habitats as landscapes and enable the discrimination of natUral from anthro- significantly since development of the estuarine system structure under rhe pogenic change. Inquiry intO the importance of estuarine habitat strucrure (Q Cowaradin et al. (1979) Narional Wetland Inven(Qry system. While HGM production processes requires a highly integrated understanding of funda- incorporares more geomorphic attribures, it does not classifYvariabiliry in mental physical, chemical, and biological processes derived from the iteration within- or among-habitat structure. between data and Ffnthesis (figure 4-2, Fisher et al.. chapter 4). An ecosystem- or habitat landscape-based classification scheme should uri- lize diagnostics of both within-habirat and interhabitat processes, such rhar we Recommendations can progress beyond the persistent assumption that biotic production is lin- early related (Qhabitat area. Little attention has been paid (Q landscape char- The Working Group recommends eight major initiatives that would advance acterisrics, such as position along the estuarine gradient, connecrions berween syntheses of natural and anthropogenic changes in habitat-biotic interactions similar habirats. and habitat patch size and shape. Furrhermore. such an estu- on estUarine production: arine habirat classification scheme needs to be placed in a hierarchical comexr I. develop an estUarine habitat classification scheme that relates habitat within a higher-order classification of the type of estuary and watershed (Jay er structure (0 estUarine production and food-web processes; aI., chaprer 7).

2. examine existing long-term data sets to better define variability in sec- 2. Examine existing long-term data sets. Within-estuary fish and macro- ondary productivity as a function of change in habitat structure and inverrebrate catches need to be examined and compared in order to under- II1tegntyj stand the variability in secondary production across different rypes of estuaries with different habitat composition and extent. Most of rhe "con- 3. implement comparative stUdies of habitat function and change among and within estuaries; trols" on various esruarine processes are actually rhe producrs of interactive 444 Par/IV C.""nl,.f E,,,...rinrn,bila" Chap'« 16. 'labital.Biol;c In.craclion. 445 10,000 processes. For example, high river discharge has a different effect in estUaries with vast expanses of as compared to estuaries with large, shallow, 1,000 NO REGULATION unvegetated areas. We need to develop broad-scale relationships between iIII mu!tiple and interconnected habitat configurations and measure secondary W .CBP production over sufficient periods to capture the effects of interannual vari- 100 i= . AS ability. w Similarly, covariability relationships betWeen growth and survival of con- 0 HB Z 10 sumer life-history stages and their residence in control-point and other habitat .RA. · . . ES. . .. features should be explored relative to the temporal and spatial dynamics of O. B'.CBO RE(3UL.ATION ...J these features. For instance, the position and intensity of tidal fronts and estU- 0 · SSF arine turbidity maxima vary in part as a function of river-Aow forcing. The recruitment and year-class strength of fish and macroinvertebrates that are 0.1 0.1 specifically associated with these habitat features, or occupy adjacent habitats, 10 100. I,OIJJ 10,000 100,000 could relate directly or with some predictable lags to variation in intra- and RESIDENCE TIME (days) interannual river flow. FIGURE 16-5 ~elationship between bivalveclearancetime and residence time, 3. Implement comparativestudies. Cross-system comparisons of estuaries with and potential for suspension feeding (0 dominate trophic structure, in a number of es- different habitat structUre, which may be related to inherent differences in tuaries (from Dame 1996, used with permission from CRC Press); AS = Asko, Baltic land-margin characteristics (see first recommendation, Jay et aI., chapter 7) as Sea; BB = Bayof Brest; CBO = Chesapeake Bay,past; COP = Chesapeake Bay.present; DB = Delaware Bay; ES = Eastern Scheldtj NB = Narragansett Bayj NI = North Inletj well as anthropogenic changes, provide one of the most powerful mechanisms MO = Marennes-Oleron Bay; RA = Ria de Arosa; SSF = South San Francisco Bay; to explain differences or changes in estuarine production processes. In partic- SY = Syltj WW = Western Wadden Sea. ular, variability in fish and shellfish production (for instance, commercial catches) that is evident in comparisons of nutrient loading (Nixon et al. 1986; tWo-and three-dimensional hydrodynamic models and other large ecosystem Boynton et al. 1995) may be elucidated further by relating both the quantity models to explicitly iricorporate relevant space and time scales. Although still and quality of habitats that are known or suspected to affect the survival and complex and requiring extensive code and input data, such ecosystem models production of fisheries species. Other system contrasts that would be relevant can be designed to address fundamental questions aboUt long-term, subtle to habitat-biotic interactions include freshwater inAow regimes; quantity and and nonlinear responses of estuarine biota to habitat change. Examples of quality of organic matter Auxes;estuarine circulation features (such as estuar- symhesis approaches that are amenable to spatially explicit ecosystem models ine tUrbidity maxima); and invasions and changes in prominence of exotic include (I) examining scenarios or comparing differences in estuarine species. One example of an insightful comparison is the inherent difference in structure at the estuary or watershed scale; (2) testing hypotheses concerning processes dominating estuarine food webs, or in phase shifts among dramati- whole-ecosystem processes such as benthic-pelagic couplings; (3) modeling cally different processes, relative to the role of physical and geomorphic char- natural experiments such as the impact of different nUtrient-loading regimes acteristics of different estuaries. Dame (1996) illustrated this relationship betWeen estimated estuarine residence time and bivalve clearance rates that on bottom-up (verses top-down) effects; (4) evaluating the significance of taxonomic or functional group changes by testing the sensitivity of model discriminates where suspension feeding does or does not regulate system predictions to different species, size, or functional groups; and (5) predicting trophic structUre (figure 16-5). habitat and associated biotic responses to changes in circulation (such as

.~~ !>, residence time and stratification/mixing) due to river inAow manipulation. 4. Develop and link habitat and habitat landscape models. Recent technical and conceptual developments in spatially explicit modeling (see Demers 5. Develop indicators of ecosystemhabitat integrity, dynamics. and variability. et aI., chapter 15) provide the means to relate habitat structure to estuarine Despite the plethora of paradigms about the importance of estuarine habitats processes. It is now feasible to incorporate habitat-specific submodels into to secondary production, particularly fisheries and aquaculture resources, 448 Pari IV. Cont,ols of £"U4';//' lIabitatl Chap,e, 16. Uabila,-Biolic In,eracrions 449

esruarine habitats and the resulting ecosystem responses. The lIse of Boule. M. E., T. Miller. and N. Olmstead. 1983. Inventory of wetlalld resoureesalld "ecological performance indices" such as posed by Done and Reichelt (1998), evaluation of wetland management in western Washingtoll.Olympia, WA: Wash- relating the temporal and spatial scale and imensity of fishery disrurbance (0 ingwn Depanmem of . habitat distributions and successional stages, presems one sllch approach (0 Boule. M. E.. and K. F. Bierly. 1987. History of esmarine wetland developmenr and alteration: What have we wrought? Northwest Ellviron. J. 3: 43-61. . -evaluatingthe alternativesbetWeendegraded and desirableecosystemstates. Boymon. W. R., J. H. Garber, R. Summers. and W. M. Kemp. 1995. Inpms. trans- formations. and nansport of nitrogen and phosphorus in Chesapeake Bay and selected tribmaries. Estuaries 18: 285-314. References Boymon. W. R.. W. Boicoun, S. Brandt. L. Harding. E. Houde, D. V. Holliday. M. Aleem, A. A. 1972. Effect of river and flow management on . Marine Biol- Jech. W. M. Kemp, C Lascara. S. D. Leach, A. P.Madden. M. Roman, L. San- ogy 15: 200-208. ford, and E. M. Smith. 1997. Imeractions berween physics and biology in the Alpine, A. E., and J. E. Cloem. 1992. Trophic interactions and direct physical effects esmarine turbidity maximum (ETM) of Chesapeake Bay, USA. /111.Council conrrol phytoplankwn biomass and production in an estuary. l.imnology and Explor. Sea. ICES CM 1997/S:11. ..l Oceanogmphy 37: 946-55. Boynron. W. R.. and W. M. Kemp. "Influence of River Flow and Nutriem Loads on Anonymous. 1989. ChesapeakeBay alosid management plall. Annapolis. MD: Chesa- Selected Ecosystem Processes: A Symhesis of Chesapeake Bay Data." Chap. II., peake Bay Program. this volume. Anonymous. 1995. Trendsin the distribution, abundance. and habitat quality ofsub- Brandt. S. B.. and J. Kirsch. 1993. 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