Robert J. Livingston

Ontogenetic patterns in diet and feeding morphology in sympatric sparid fishes from seagrass meadows

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FRESHWATER INPUT TO A GULF ESTUARY: LONG-TERM CONTROL OF TROPHIC ORGANIZATION

A long-term (9.5 yr) study addressed the relationship of the trophic orga- nization of a river-dominated Gulf of Mexico estuary with interannual trends of freshwater input and biological controlling features. Alluvial river flow characteristics were evaluated with respect to seasonal and interannual changes in physical, chemical, and biological trends in the receiving estuary. Infaunal and epifaunal macroinvertebrates and fishes taken over the period of sampling in the Apalachicola Bay system were transformed into their trophic equivalents. The long-term trophic organization of the bay was then related to observed changes in the physical and chemical conditions in the receiving estuary with particular attention to long-term response to a 2-yr drought. Within limited natural bounds of fresh- water flow from the Apalachicola River, there was little change in the trophic organization of the receiving estuary over prolonged periods. The physical instability of the estuary was actually a major component in the continuation of a biologically stable estuarine system. However, when a specific threshold of freshwater reduction was reached during a prolonged natural drought, we suggest that the clarification of the normally turbid and highly colored river-estuarine system led to rapid changes in the pattern of primary production, which, in turn, were associated with major changes in the trophic structure of the system. Increased light penetration due to the cessation of river flow was an important factor in the temporal response of bay productivity and herbivore/omnivore abundance. There was a dichotomous response of the estuarine trophic organization, with herbivores and omnivores responsive to river-dominated physicochemical factors whereas the carnivores responded to biological factors. Trophic response time could be measured in months to years from the point of the initiation of low-flow conditions. The reduction of nutrient loading during the drought period was postulated as a major cause of the loss of productivity of the river-dominated estuary during and after the drought period. Recovery of such productivity with resumption of increased river flows was likewise a long-term event. Based on the observed trends in the bay, postulated permanent reductions of freshwater flows due to anthropogenous ac- tivities could lead to major reductions of biological productivity in the Apalachicola Bay system. The long-term data indicated that, with reduction of freshwater flow below a level specific for the receiving system, the physically controlled, highly productive river-estu- arine system would become a species-rich, biologically controlled bay with substantially reduced productivity.

Diurnal and seasonal fluctuations of organisms in a north Florida estuary

Abstract Monthly samples of demersal fishes and invertebrates were taken in an unpolluted, river-dominated estuary in north Florida (Apalachicola Bay) for a 2-year period. Trawling methods were examined. Small (2-min) repetitive samples yielded substantially higher numbers of individuals and species than single (14-min) trawl-tows. Various methods of analysis were used to determine adequate sample size for comparative analysis of the results. Several species richness and diversity indices were compared. Regular diurnal (24-h) and seasonal variations of such parameters were related to complex interactions which included river flow, salinity variations and temperature changes. The various species diversity indices were highly correlated in spite of theoretical distinctions. There were varying relationships of such parameters with their richness and equitability components and these relationships were not always the same for fishes and invertebrates. There were basic differences in species composition and numbers of individuals of invertebrates taken throughout a 24-h period. For fishes, such variations were primarily quantitative with some short-term alteration of community structure. Seasonal peaks of numbers of individuals, numbers of species and species diversity usually occurred during summer and fall periods. Although there were some variations, a general pattern of an annual double peak of fish and invertebrate richness and diversity was noted. Nocturnal patterns were more clearly defined than diurnal ones. Relative dominance remained high, with a seasonal succession of dominant fish and invertebrate species. It was postulated that there was a constantly changing series of interactions of the various community components that precluded a single mechanism for the observed phenomena. Apalachicola Bay was seen as an unpolluted system that underwent considerable seasonal fluctuations of richness and diversity in response to extreme variations of natural (physical) functions. Such changes were stable over time, and this form of variation was seen as a considerable limitation to the general use of species diversity as an indicator of pollution and other man-induced activities in such estuarine systems.

BARNEGAT BAY–LITTLE EGG HARBOR ESTUARY: CASE STUDY OF A HIGHLY EUTROPHIC COASTAL BAY SYSTEM

The Barnegat Bay-Little Egg Harbor Estuary is classified here as a highly eutrophic estuary based on application of the National Oceanic and Atmospheric Administrations National Estuarine Eutrophication Assessment model. Because it is shallow, poorly flushed, and bordered by highly developed watershed areas, the estuary is particularly susceptible to the effects of nutrient loading. Most of this load (;50%) is from surface water inflow, but substantial fractions also originate from atmospheric deposition (;39%), and direct groundwater discharges (;11%). No point source inputs of nutrients exist in the Barnegat Bay watershed. Since 1980, all treated wastewater from the Ocean County Utilities Authoritys regional wastewater treatment system has been discharged 1.6 km offshore in the Atlantic Ocean. Eutrophy causes problems in this system, including excessive micro- and macroalgal growth, harmful algal blooms, altered benthic invertebrate communities, impacted harvestable fisheries, and loss of essential habitat (i.e., seagrass and shellfish beds). Similar problems are evident in other shallow lagoonal estuaries of the Mid-Atlantic and South Atlantic regions. To effectively address nutrient enrichment problems in the Barnegat Bay- Little Egg Harbor Estuary, it is important to determine the nutrient loading levels that produce observable impacts in the system. It is also vital to continually monitor and assess priority indicators of water quality change and estuarine health. In addition, the application of a new generation of innovative models using web-based tools (e.g., NLOAD) will enable researchers and decision-makers to more successfully manage nutrient loads from the watershed. Finally, the implementation of storm water retrofit projects should have beneficial effects on the system.

Factors controlling seagrass growth in a gulf coastal system: Water and sediment quality and light

Abstract A combined field descriptive/experimental and laboratory experimental study was carried out to determine the relationships of water quality, qualitative and quantitative light factors and sediment characteristics in the definition of the distribution of submerged aquatic vegetation (SAV) offshore of two streams, one polluted and one natural, that drain into the northeastern Gulf of Mexico. Release of pulp mill effluents into a small drainage system were associated with increased loading of dissolved organic carbon (DOC), water color and nutrients to offshore areas relative to an unpolluted reference system. This loading resulted in changes of water quality factors and light transmission characteristics in the receiving Gulf area. Sediments in affected offshore areas were characterized by increased silt/clay fractions and altered particle size relative to reference sites. Based on the field data, the best (statistically significant) predictors of SAV distribution were photic depths, qualitative aspects of wave length distributions, water quality factors (color, DOC and chlorophyll a ) and sediment characteristics. Photic depths were good predictors of SAV distribution, with depth as an important modifying factor. Mesocosm experiments showed that pulp mill effluent in direct contact with Thalassia testudinum and Syringodium filiforme had significant adverse impacts on growth at relatively low concentrations (1–2%) of effluent. Light mesocosm experiments indicated that light levels in inshore Fenholloway areas were associated with reduced growth of Halodule wrightii , S. filiforme and T. testudinum . Field transfer experiments showed that altered sediment and water quality in inshore polluted areas induced significant adverse effects on growth indices of all three species. By comparing the field and experimental results, a hierarchy of habitat requirements for the subject seagrass species was determined. Salinity, temperature and depth restraints are important habitat variables that control seagrass growth; when such variables are not limiting, light, sediment and nutrient characteristics become important in the determination of the distribution of seagrasses in coastal areas.

Field sampling in estuaries: The relationship of scale to variability

The spatial/temporal scaling problem (i.e., fitting a given research question to the dimensions of variability of the study area) is particularly pronounced in highly variable systems such as estuaries. Long-term, multidisciplinary studies in the Apalachicola Bay system were used to evaluate variation of different physical, chemical, and biological factors. Specific limitations of weekly, monthly, and quarterly sampling intervals were directly related to the efficiency of the sampling gear, the range of variation in the study parameters, and specific biological features (motility, recruitment, natural history) of infaunal macroinvertebrates and epibenthic organisms. There are families of spatial and temporal scaling phenomena that should be considered when establishing a given field sampling program. The dimensions of variation change along spatial/temporal gradients of salinity, habitat complexity, and productivity and among different levels of biological organization. The limits of variation define the needed sampling effort for a given level of estimation. Without an adequate evaluation of such variation, representative samples cannot be taken; the resulting inadequate sampling effort often precludes reliable comparisons and robust generalization. There is a continuum of scaling dimensions (and sampling problems) that ranges from small-scale experimental approaches to system-wide analyses. Misapplication of such scaling estimates has led to overgeneralization of experimental results. Currently, there is widespread misapplication of combinations of unrelated, limited sampling efforts to broad-scale resource problems. The loss of valuable estuarine resources is favored by the lack of adequate scientific databases that are consistent with the dimensions of the individual study areas. Unless experimental studies and field sampling programs are scaled to the dimensions of the research problem and the study area in question there will be a continued proliferation of trivial studies at one end of the continuum and the progressive deterioration of estuarine resources at the other.

Impact of kraft pulp-mill effluents on estuarine and coastal fishes in Apalachee Bay, Florida, USA

A 2-year field study was carried out to determine the impact of kraft pulp-mill effluents on the fish fauna of a shallow-bay system in north Florida (Apalachee Bay, USA). Offshore areas that received kraft-mill effluents (KME) displayed significant increases in color and turbidity and reductions in (benthic) dissolved oxygen compared to a nearby control area. Estuarine and marsh fish assemblages in areas of acute impact were severely reduced in terms of numbers of individuals (N) and species (S). Offshore areas exposed to varying (chronic) levels of KME were characterized by complex interactions that included seasonal variations of impact. A broad offshore area showed reductions in numbers of individuals and species taken per month. However, the cumulative (annual) number of species taken was the same for polluted and unpolluted (control) areas due to a recruitment of relatively rare species in the areas of impact. Such polluted areas showed decreased dominance as well as qualitative differences in species composition compared to control areas. Inshore bay stations that were most severely affected by KME were dominated by the bay anchovy, Anchoa mitchilli. While species richness and species diversity were lower at the highly stressed stations, in other outlying areas of moderate impact (reduced N and S) there were no reductions of such parameters compared to control areas. Thus, species diversity was not an indicator of pollution per se, and was useful only when taken in conjunction with various other parameters. Transition areas (between polluted and unpolluted portions of the bay) showed substantial (although periodic) increases in N, S, and species diversity. Equitability indices were unchanged in polluted portions of the bay. In general, the effects of KME on offshore fish assemblages appeared to be due to a complex combination of habitat alteration, reduced benthic productivity, and individual behavioral reactions. The alterations of fish assemblages were compared to other studies in this area on benthic macrophytes and invertebrates in an effort to assess the usefulness of various indices in studies on the long-term effects of pollution on estuarine and coastal systems. It was found that kraft pulp-mill effluents had a pronounced effect on the benthic standing crop of plants and animals, but that intensive sampling over prolonged periods of time was necessary for an adequate assessment of the problem. Overall, there were some significant changes in the biota such as reduced dominance and productivity in polluted areas that were similar for the various types of organisms sampled.

The relationship of physical factors and biological response in coastal seagrass meadows

Continuous, long-term studies of coastal grassbed assemblages in the N.E. Gulf of Mexico indicate complex relationships between physical controlling factors and biological response. Such seagrass systems are physically unstable over short periods. Seasonal ranges of temperature, salinity, and natural water quality conditions are considerable with periodic, recurrent “catastrophic” events such as floods and cold winters. These factors control the distribution and productivity of the seagrasses and algae which constitute the habitat and organic substrate for diverse assemblages of organisms. In addition, the benthic plants mediate predator-prey relationships and competitive interactions. Despite the physical instability, timed sequences of distinct ontogenetic feeding populations are generally stable from year to year as are other population and community characteristics. Thus, physical processes determine overall habitat conditions and productivity cycles whereas biological processes such as predation and competition define specific community relationships. However, seemingly minor changes in the physical environment due to anthropogenous activities can lead to major reorganization of the biological system; the observed biological stability of the seagrass beds can be ephemeral if important habitat features are altered in a way that exceeds the adaptive response of the system. Concepts are discussed which relate observed sequences of ontogenetic feeding units to food web patterns and geographic differences of population-niche relationships from one estuary to another.

PHYTOPLANKTON BLOOM EFFECTS ON A GULF ESTUARY: WATER QUALITY CHANGES AND BIOLOGICAL RESPONSE

A long-term (16-year) study addressed the relationship of the trophic organization of a river-dominated Gulf of Mexico estuary (Perdido River–Bay system) with interannual trends of freshwater input, nutrient loading, and biological controlling features. The purpose of this study was to determine the long-term consequences of anthropogenic nutrient loading on a river estuarine system with an emphasis on the origin and impacts of a series of plankton blooms that were directly linked with nutrient loading to the Perdido drainage system. A multidisciplinary database was used to determine responses of plankton assemblages and associated coastal food webs to natural and anthropogenic nutrient loading. Orthophosphate and ammonia loading from a pulp mill into Elevenmile Creek and the bay generated a series of plankton blooms dominated by diatoms, raphidophytes, dinoflagellates, and cyanobacteria. Blooms followed species-specific seasonal patterns. Interannual phytoplankton trends were associated with nutrient loading and rainfall cycles. Blue-green algae blooms (Merismopedia tenuissima) in the receiving Elevenmile Creek were enhanced by drought conditions. There were statistical associations of reduced biological activity with the Merismopedia blooms. In the bay, initial diatom blooms were replaced by raphidophytes and dinoflagellates in time. Bloom effects on phytoplankton assemblages included initial reductions of species richness/diversity and direct/indirect replacement processes. Long-term changes of plankton blooms indicated complex adaptive processes that led to nonlinear responses to nutrient loading and time-based alterations of interspecific relationships. Blooms and related changes in phytoplankton composition were accompanied by loss of fish and invertebrate populations and altered food web processes. Raphidophyte (Heterosigma akashiwo) and dinoflagellate (Prorocentrum cordatum) blooms in the bay were statistically associated with reduced invertebrate and fish populations and disruptions of bay food webs. Reduced nutrient loading by the pulp mill resulted in diminished bay plankton blooms and partial recovery of infaunal macroinvertebrates. However, nutrient loading from a second source in the upper bay during later years was associated with increased bloom activity. This was added to reduced benthic invertebrate and fish assemblages in deeper bay areas affected by hypoxia caused by salinity stratification. Lower Perdido Bay was adversely affected by nonpoint source runoff from agricultural and urban sources with diminished water quality and loss of sediment organisms. Cumulative impacts due to anthropogenic nutrient loading from multiple sources and associated plankton blooms, along with altered physicochemical conditions due to a dredged opening at the bay terminus, resulted in widespread reductions of secondary productivity in Perdido Bay. Long-term trends of bay productivity are the result of interactions of natural climatological cycles and anthropogenic activities.

Distributional ecology and food habits of the banded blennyParaclinus fasciatus (Clinidae): a resident in a mobile habitat

An ecological study of the banded blennyParaclinus fasciatus (Steindachner, 1876) showed that the fish is tolerant of physical/chemical conditions in the shallow subtidal area of Apalachee Bay, Florida (USA). Population density ofP. fasciatus was unrelated to physical/chemical characteristics and seagrass biomass at field stations. A strong correlation was found between numbers ofP. fasciatus captured and abundance of unattached red algae (drift algae) at the field sites, although seasonality in population density was related to summer spawning. Spawning began at approximately 28°C. The life span of the clinid is probably little longer than 1 yr. Long-term variation in population size was also demonstrated.P. fasciatus was found to be a highly specialized carnivore which consumes only a few species of amphipods and shrimps; however, major seasonal variation in diet occurred. Variations in food habits were related to known patterns of prey abundance in Apalachee Bay. The most important prey species taken byP. fasciatus, includingCymadusa compta andHippolyte zostericola, are associates of red algae masses, further substantiating the close functional relationship of the clinid with its algal habitat which moves about the bay. The driftalgae habitat is probably an important source of shelter, food, and dispersal for the banded blenny. The eurytolerance ofP. fasciatus makes it particularly well adapted for life in an unusual, mobile habitat.