David A. Flemer

Long-term biological data sets: Their role in research, monitoring, and management of estuarine and coastal marine systems

Long-term records of biological data are extremely valuable for documenting ecosystem changes, for differentiating natural changes from those caused by humans, and for generating and analyzing testable hypotheses. Long-term sampling, however, is generally discouraged by a variety of institutional disincentives, so that today such records are uncommon. We discuss approaches for overcoming these disincentives through improved research planning and design, including clearera priori definition of management and regulatory actions and information needs, more rigorous adherence to hypothesis formulation and testing, and proper spatial and temporal scaling in sampling. We distinguish between prospective study design, in which the foregoing elements are essential for coast-effectiveness, and retrospective analysis, which relies on reconstruction of long-term records from existing data sets. We demonstrate the great value of retrospective analysis of encountered data, and argue for renewed attention to archival of data sets with documented data quality, interacalibration and documentation of methodologies, and long-term storage of samples for future analysis. Such practices are essential to ensure the quality of long-term records that are reconstructed for retrospective examination of new hypotheses in the future.

Linkage between microzooplankton grazing and phytoplankton growth in a Gulf of Mexico estuary

Microzooplankton dilution grazing experiments were conducted with water collected from Pensacola Bay, Florida (USA) on 12 dates at 2 sites. Statistically significant grazing rates were observed in 22 of 24 experiments. Grazing rates in Upper Bay and Lower Bay were similar averaging 0.54 and 0.51 d−1, respectively. Phytoplankton growth rates were also similar at the two sites, averaging 1.02 and 1.00 d−1 at Upper Bay and Lower Bay, respectively. Phytoplankton growth rates usually exceeded grazing rates by about a factor of two, though microzooplankton grazing represented a significant mortality for phytoplankton. The literature suggests a linkage between phytoplankton growth and microzooplankton grazing that spans a wide variety of aquatic environments. While individual growth and grazing rates were variable, growth frequently exceeded grazing by about two-fold. This implies that the role of microzooplankton is similar across a wide variety of aquatic systems.

Nutrient Enrichment of Chesapeake Bay and Its Impact on the Habitat of Striped Bass: A Speculative Hypothesis

Abstract Stocks of striped bass Morone saxatilis have declined in the Chesapeake Bay system over the last decade. We present evidence for the working hypothesis that the decline has resulted, in part, from loss of deep-water habitat for adults, caused by limiting concentrations of dissolved oxygen that are related, in turn, to nutrient enrichment and greater planktonic production. A related hypothesis is that changes in the near-shore habitat for juvenile striped bass, involving severe declines in submerged aquatic vegetation due to nutrient-driven planktonic shading, also have contributed to the decline of striped bass. Nutrients (nitrogen and phosphorus) and chlorophyll a, an indicator of phytoplankton biomass, have increased in many areas of the bay and tributaries over the past 20 to 30 years. These trends are qualitatively correlated with greater deoxygenation of the deep channel in the mid and upper bay. During the late 1970s, summer oxygen concentrations as low as 2 ml/liter approached to within 7–...

The relative influence of hypoxia, anoxia, andassociated environmental factors as determinants ofmacrobenthic community structure in aNorthern Gulf of Mexico estuary

Seasonal patterns (i.e., December 1986, and April and October 1987) in benthic macroinfaunal abundance,distribution, and taxa composition at 19 sites in Perdido Bay, AL/FL, are evaluated to assess the relative importance of environmental factors as determinants of community structure. A total of 46 taxa from five phyla were collected with diver-held bottom corers. Polychaetes were numerically dominant followed by crustaceans. Seventeen taxa co-occurred in samples during all three study periods. Maximum animal densities and taxa richness showed no statistically significant bay-wide seasonal pattern,however, a bay-wide trend was detected where these response parameters tended to be greater in April than December or October. Deeper upper bay stations were depauperate during December and October. Low dissolved oxygen (DO) largely explained the depauperate pattern. Mean taxa richness per core(10 cm dia.) ranged from 0.0 to 5.0, 1.2 to 4.6, and0.0 to 4.4 in December, April and October,respectively. Mean densities ranged from zero to 368,0 to 960, and 0 to 430 individuals per 0.1 m2 in December, April, and October, respectively. Results of a three-season statistical regression model indicated that DO deficiency was a primary determinant of taxa richness (partial R2: 0.27) but was less important in explaining animal densities (partialR2: 0.16). For December, when additional environmental variables were measured, DO was supplanted by weight loss on ignition (R2: 0.24)and the sediment C:N ratio (R2: 0.44) as highest explanatory factors for taxa richness and density,respectively. Application of a benthic index of environmental condition indicated wide-spread ecological stress on the benthic macroinfaunal assemblages.

Recolonization of estuarine sediments by macroinvertebrates: Does microcosm size matter?

Microcosms containing defaunated, fine estuarine sediments were field deployed to assess the effects of microcosm size on the rate of benthic macroinvertebrate recolonization and resulting community structure. Four sizes of microcosms (square acrylic plastic boxes: 7 cm side−1, 12 cm side−1, 20 cm side−1, and 32 cm side−1, all 6-cm deep) were deployed in upper Perdido Bay, Florida, and colonized for 6 wk. Absolute mean total number of organisms (TNO) differed (α=0.05) among all sizes, while normalized mean TNO (adjusted to 12 cm side−1 area) did not. Mean total number of taxa (TNT) was different among sizes: 7 cm side−1, 12 cm side−1, and 20 cm side−1, but not between sizes 20 cm side−1 and 32 cm side−1. Seven dominant taxa occurred in all size microcosms. Scaling of physical design features (size of microcosm) affected numbers of taxa in recolonization of fine-grained sediments in our study area, but effects on abundance and dominance were minimal.

Macrobenthic community colonization and community development in dredged material disposal habitats off coastal Louisiana

We examined marine benthic macroinvertebrate colonization and community structure at multiple spatial scales (study areas, reference and disposal sites, and depth zones within sites) within a 3-day period at three relatively widely separated (ca 60 km) dredged material disposal areas (Mermentau and Atchafalaya Rivers and Freshwater Bayou) in coastal Louisiana. Study areas had different histories of dredged material disposal, but all three are subject to frequent natural habitat disturbances (e.g. freshets). Nine phyla and 51 taxa were represented among the three study areas at reference (R) and disposal (D) sites (Freshwater Bayou: 21(R), 18 (D); Mermentau River: 14 (R), 17 (D) and Atchafalaya River: 38 (R), 40 (D)). Only 15 taxa were common to all three study areas. At the Freshwater Bayou, average taxa richness and abundance responded to water depth, not sites. These response variables averaged higher mean values at the Mermentau River disposal than at the reference site. No consistent pattern in the average of these response variables was detected between sites at the Atchafalaya River. Multidimensional scaling ordination and non-parametric multivariate inferential analysis provided a distinctly different picture of community structure within study areas compared to parametric analyses. A relatively moderate to strong separation in community structure between sites was detected depending on study area. Non-parametric multivariate inferential analysis detected significant differences in internal community structure at the scale of stations and sites within study areas. The weight of evidence suggests that frequent natural disturbances explain differences in macrobenthic animal community structure more than effects of dredged material disposal.

Seasonal growth stimulation of sub-temperate estuarine phytoplankton to nitrogen and phosphorus: An outdoor microcosm experiment

A study of nutrient limitation of phytoplankton biomass production with emphasis on nitrate-nitrogen (NO3−) and ortho-phosphate-phosphorus (PO43−) was conducted in Perdido Bay, Alabama-Florida. The experimental design employed 18-1 outdoor microcosms operated in a static renewal mode. Phytoplankton growth responses (i.e., growth stimulation) measured as chlorophyll a (chl a) fell into three principal categories: primary P stimulation occurred mostly during the cooler months at the upper bay (tidal brackish) and mid bay (lower mesohaline) stations; a total of 12 out of 36 experiments; primary N stimulation occurred mostly during the warmer months primarily at the mid-bay station and infrequently at the upper and lower bay stations (upper mesohaline); a total of 7 out of 36 experiments; and N+P costimulation occurred primarily during the warmer months in the upper bay and mid bay and during both warmer and cooler months of the lower bay; a total of 17 out of 36 experiments. Primary P stimulation was generally associated with high ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) (ratio range: 18 to 288). Conversely, primary N stimulation was associated with decreasing DIN:DIP ratios (range 8–46). Redfield ratios of particulate organic N (PON) to particulate organic P (POP) often indicated N limitation (i.e., values often less than 10). PON:chl a ratios often indicated N sufficiency, but three occasions were noted where PON:POP and PON:chl a ratios were not congruent. It is difficult to reconcile the inorganic and organic N and P ratios with the relatively low DIP and DIN concentrations. The phytoplankton assemblage appeared not to be strongly nutrient-limited but, given a nutrient increase, responded differentially to N and P, both seasonally and along the longitudinal salinity gradient. Grazing pressure in concert with nutrient limitation was advanced as an hypothesis to explain N+P co-limitation.

Laboratory effects of microcosm size and the pesticide chlorpyrifos on benthic macroinvertebrate colonization of soft estuarine sediments

Abstract A 42-d flow-through experiment was conducted to evaluate the effects of the organo-phosphate pesticide, chlorpyrifos, and microcosm size (small: 144 cm 2 ; large: 400 cm 2 ) on benthic estuarine macroinvertebrate colonization. Nested central and perimeter (outside margin) cores were used to assess animal distribution within microcosms. Fine-grained, organically-rich (approximately 4.0% organic carbon and 20% dry wt) sediments were nominally fortified with chlorpyrifos controls, low (1.0) and high treatments (10.0 μg −1 wet sediment). Large microcosms contained a significantly (p Neanthes succinea , the amphipod, Corophium acherusicum , and the barnacle, Balanus sp., was significantly greater in small microcosms but density of Ensis minor was significantly greater in large microcosms. In small and large microcosms, respectively, densities averaged significantly greater numbers in perimeter cores (e.g. 203.1 and 75.1) vs central cores (71.9 and 45.4). Average density decreased significantly with increasing chlorpyrifos concentration from controls (326.8), to low (123.8) and high (78.8) treatments. The density decrease was significantly related only to C. acherusicum whose densities decreased from controls (285.8) to low (88.5) and high (43.9) dosed microcosms. Application of an equilibrium partitioning model indicated that density of C. acherusicum was sensitive to an estimated interstitial water concentration of approximately 0.48 μg liter −1 . Non-metric multidimensional scaling ordination analyses provided important insights into response patterns not available through ANOVA procedures. A permutation procedure (ANOSIM) detected a significant size effect ( p p p p C. ascherusicum , as in the ANOVA analyses, dominated contributions to community average percent dissimilarity in most combinations of microcosm size and chlorpyrifos treatment effects (range: 8.4–21.9%). Community structure differed significantly in several combinations of microcosm size, core position and chlorpyrifos treatment. Results confirm earlier work that intrinsic design factors influence benthic macroinvertebrate community structure and determine taxa available to pesticide exposure in microcosms.

Recolonization of estuarine organisms: effects of microcosm size and pesticides

Two six-week laboratory experiments were conducted to evaluate effects of pesticides and microcosm size on benthic estuarine macroinvertebrate recolonization. Sediments fortified with the pesticides (fenvalerate: controls, 5 (low) and 50 µg g−1 wet sediment (high); endosulfan: controls, 1 (low) and 10 µg g−1 wet sediment (high)) were fine-grained, organically rich (approximately 3.5% organic carbon and 22% dry weight) material. Relative dominance of the four most abundant taxa in both experiments was consistent among treatments with few exceptions. The amphipod,Corophium acherusicum, dominated abundance in both experiments.In the fenvalerate experiment, large trays (400 cm2) contained significantly (p<0.05) more total number of taxa (TNT) than small microcosms (144 cm2) but tray size was not significantly related to total number of organisms (TNO). When size was adjusted to a common unit area, small trays contained significantly more TNO than large containers. Adjusted abundance of small trays was 2.5 times that of large containers; a ratio close to that of microcosm sizes (i.e., 2.8). This result suggests that larval supply may have been inadequate to ‘aturate’ the available sediment in large containers. Fenvalerate significantly reduced abundance in the high treatment compared to both controls and low treatment but low treatment was not significantly different from controls. The amphipod,Corophium acherusicum, accounted for most of the decrease in abundance in response to fenvalerate. The holothruroid,Leptosynpta sp. and the polychaete,Mediomastus ambiseta, increased in abundance significantly with increased concentration of fenvalerate.Combined effects of actual microcosm size and concentration of endosulfan were not significant for TNO or TNT. As in the fenvalerate experiment, adjusted abundance of small microcosms was 2.6 times that of large trays which approximated the ratio of unit area between microcosm sizes. Abundance of a few taxa responded significantly to adjusted and unadjusted unit area. Abundance of the tunicate,Molgula manhattensis, increased significantly with increased concentration of endosulfan. Abundance was affected by sample location (e.g., interiorvs exterior cores) within microcosms. Abundance adjusted to unit area resulted in significantly greater TNO in externalvs internal cores. This has importance for sequential sub-sampling of microcosms to determine temporal dynamics.Statistically significant effects were measured in benthic community structure associated with microcosm size; however, the magnitude was relatively small. There appears to be no major biological reason to select one microcosm size over the other for screening for contaminant effects. Where feasible, the small trays provide savings in sample preparation and analysis, allow more replicates where laboratory space is limiting and generate less chemical waste. These benefits may be off-set by less ‘artifacts’ associated with edge effects of larger microcosms and the need for a larger mass of sediment to accommodate additional analytical requirements (e.g., thin vertical surficial samples to refine contaminant exposure at the sediment/water interface).

Effects of sediment type on macrobenthic infaunal colonization of laboratory microcosms

We tested the effects of four different sediment types collected from northern Gulf of Mexico estuarine systems on macroinfaunal colonization and community development in our laboratory flow-through microcosm system. Four sediments, types included , a beach sand, two fine-grained muds, but from different locations, and a 50:50 mixture of one of the mud sediments and beach sand. Our hypothesis was that the pattern of colonization would differ among sediment types based on empirical field data and theory but the differences would be expressed most strongly at sediment type extremes (e.g., mud versus sand). A total of 49 taxa colonized the four sediments. Unidentified Actiniaria (sea anemones) numerically dominated densities among all four sediments with densities ranging between 46.5 to 60.5 per microcosm (20 cm side−1). Average taxa richness per microcosm (N: 10 replicates per sediment treatment) ranged from 10.4 in one of the mud treatments to 14.9 taxa in the sand. These were the only significant differences among sediment types (P≤0.05) in taxa richness and we detected no significant effects of sediment type on animal densities. Differences in community metrics, although statistically significant, were generally of a relatively small magnitude. Five of 10 microcosms per treatment were randomly selected to test for effects of sediment depth (e.g., top, mid, and bottom). In vertically sectioned microcosms, average taxa richness in sand treatments was significantly greater than those of the other three sediments. A non-parametric multivariate analysis (Primer) revealed that community structure in the vertically sectioned microcosms differed significantly between sand and one of the mud treatments. Mean taxa richness of top sections differed significantly from mid and bottom sections. We detected significantly higher animal densities and taxa richness (p≤0.05) in vertically sectioned versus non-sectioned microcosms. However, these differences were unexplained based on experimental protocols.