John M. Teal

Transport of groundwater-borne nutrients from watersheds and their effects on coastal waters

Anthropogenic activities on coastal watersheds increase nutrient concentrations of groundwater. As groundwater travels downslope it transports these nutrients toward the adjoining coastal water. The resulting nutrient loading rates can be significant because nutrient concentrations in coastal groundwaters may be several orders of magnitude greater than those of receiving coastal waters. Groundwater-borne nutrients are most subject to active biogeochemical transformations as they course through the upper 1 m or so of bottom sediments. There conditions favor anaerobic processes such as denitrification, as well as other mechanisms that either sequester or release nutrients. The relative importance of advective vs. regenerative pathways of nutrient supply may result in widely different rates of release of nutrients from sediments. The relative activity of denitrifiers also may alter the ratio of N to P released to overlying waters, and hence affect which nutrient limits growth of producers. The consequences of nutrient (particularly nitrate) loading include somewhat elevated nutrient concentrations in the watercolumn, increased growth of macroalgae and phytoplankton, reduction of seagrass beds, and reductions of the associated fauna. The decline in animals occurs because of habitat changes and because of the increased frequency of anoxic events prompted by the characteristically high respiration rates found in enriched waters.

DISTRIBUTION OF FIDDLER CRABS IN GEORGIA SALT MARSHES

The study of the distribution of animals in nature is especially interesting when several species of one genus occupy the same general area. Along the east coast of the United States there are three species of fiddler crabs of the genus Uca which live in the salt marshes. All three are found in the marshes surrounding Sapelo Island, Georgia, and this paper deals with experiments concerning their distribution in these marshes. I deal with the problem of why the crabs live in certain habitats within their range and not in others, not what determines or has determined their geographical range. The three species of crabs are: Uca mtinax, the largest, generally associated with brackish water; CUca ptigilator, commonly known as the sand fiddler crab, and Uca. pitgnax, found generally throughout the salt marsh. Components of the environment which might be important in determining the distribution of these animals are substratum, food, salinity, exposure or tides, and other animals. The effects of these factors can be evaluated by answering the questions: W~hat is the substratum choice of the animals when other factors are constant? Does the presence of other species of fiddler crabs affect this choice? Can the three species survive in all types of salt marsh or are they restricted to certain types ? What are the salinity and temperature tolerances and salinity preferences of the species ? \Vlhat do the crabs feed on and how is this food distributed in the marsh? Adult animals were used in most of the experiments. It is true that choice of area for settling by the megalops larvae is important in the distribution of the adults; nevertheless, adult fiddler crabs can and do move considerable distances over the marsh and could easily move to an environment different from that chosen by the larvae.

Predation by the salt marsh killifish Fundulus heteroclitus (L.) in relation to prey size and habitat structure: Consequences for prey distribution and abundance

Laboratory feeding preference experiments show that the maximum size of prey eaten (the snail Melampus bidentatus (Say) and the amphipod Orchestia grillus (Bosc)) increases with increasing size of the predator, Fundulus heteroclitus (L.). Melampus > 7 mm in shell height escape predation by even the largest killifish. In the laboratory, consumption of prey is reduced in high marsh habitat relative to low marsh, particularly in the case of larger fish. Low marsh has few grass stems per unit area, while high marsh is considerably more complex, with dense small stems providing cover for prey and reducing successful fish hunting. The population of Melampus in low marsh within Great Sippewissett salt marsh consists mainly of large snails but this size is rare in high marsh. The size-distribution is inverse for Orchestia, with large amphipods more abundant in high marsh. The construction of fences excluding Fundulus from the marsh surface led to low marsh size-distributions of Melampus and Orchestia resembling those of high marsh, in agreement with the laboratory results. Killifish predation seems to be an important factor regulating the abundance and size-distribution of the two prey species in the two marsh habitats.

Interactions of Nutrients, Plant Growth and Herbivory in a Mangrove Ecosystem

The effect of nutrient enrichment of red mangroves (Rhizophora mangle) was studied by comparing two mangrove-covered islands in the Indian River at Ft. Pierce, Florida, USA, one (high nutrient) with and one (low nutrient) without a breeding colony of pelicans and egrets. Repeated measurements taken on > 100 tagged branches in each area revealed higher growth rates at the high nutrient site. Trees at the high nutrient site showed greater additions of (1) leaves; (2) reproductive parts; (3) new lateral branches; and (4) larger increments to existing stems. Growth in the fertilized stand also began earlier in the year and had a second maximum not shared by the low nutrient area. Both leaves and fruits at the high nutrient site were richer in nitrogen. More striking than the effects on plant growth, however, was the proportionately much greater stimulation of herbivory by insects in response to nutrient enrichment. Larvae of the five lepidopteran species that we observed feeding on buds or leaves were either more abundant or only present in the high nutrient area, as was the scolytid beetle that infested seedlings before they dropped from the parent tree. This difference in herbivory between sites disappeared when the birds seasonally migrated away from their nesting areas at the high nutrient site. This observation and the demonstration that the mangrove skipper Phocides pigmalion attains a higher growth efficiency on high nutrient leaves are both consistent with the hypothesis that increased nutritive value of vegetation (correlated with the increased concentration of nitrogen) is responsible for the 4x greater losses to herbivores in the high nutrient. Implications for environmen- tal management and in more complex communities are discussed.

Decomposition in salt marsh ecosystems: The phases and major factors affecting disappearance of above-ground organic matter

Decay of litter of salt marsh grasses occurs in three phases. First there is an early phase lasting less than a month, with fast rates of weight loss, during which 5 to 40% of the litter is lost, probably by leaching of soluble compounds. A second slower phase lasts up to a year. In this second phase, microbial degradation of organic matter and subsequent leaching of hydrolyzed substances remove an additional 40 to 70% of the original material. A third phase may last an additional year; in this phase decay is very slow because only relatively refractory materials remain. By this third stage as little as 10% of the original material may remain. Differences in the chemical makeup of litter are the major factors affecting the amount of decay during the leaching and decomposer phases. Such chemical differences may be due to differences in the chemistry of the plant species producing the litter or in nutrient supply. Spartina patens (Ait.) Muhl., for example, produces litter that decays more slowly than that of S. alterniflora Loisel. Increases in internal nitrogen content of litter increase loss of weight during the leaching and decomposer phases, while the external supply of nitrogen increases decay rates only during the decomposer phase. Temperature increases decay rates to some extent during the decomposer phase. The feeding activity of large detritus-feeding invertebrates produces a small but significant increase in decay rate during the decomposer phase. Decay rate in litterbags mimics decay of litter in the field, and makes possible estimates of litter turnover. The turnover of litter of S. alterniflora was 1.1–1.4 · yr−1. Litter of S. patens turns over more slowly, 2.1 · yr−1. Nutrient enrichment accelerates turnover of litter up to 24% compared to control litter. Since eutrophication of salt marshes both enriches litter and changes species of plants, it has broad consequences for ecological processes dependent on decomposition of organic matter.

The Nature of Growth Forms in the Salt Marsh Grass Spartina alterniflora

Increases in nutrient supply convert swards of the short form of Spartina alterniflora into plants tending to resemble the tall form, in biomass/m2 and in general morphology. Competition for light is probably responsible for the vertically elongate, widely dispersed growth habit of tall form. Provision of added nutrients led to larger δ13C values, probably by the incorporation of heavier carbon from the internal air spaces of S. alterniflora during high tide, when exchange of gases with the atmosphere is prevented. The amount of interstitial water replenished at each tide is greater in areas supporting tall-form vegetation than where short form grows. There are also greater densities of mussels near creek banks, and their feeding and defecation lead to larger accumulations of particulate matter and nutrients where tall form is found. The amount of nitrogen delivered by algal nitrogen fixation does not differ greatly under the two forms. Seedling establishment usually produces tall-form plants, and a higher percentage of tall-form plants than short form produce seed. However, since electrophoretic results show no genetic differences, the form of seedlings is probably principally the result of lack of competition for nutrients and is modified by other factors. The probable sequence of events is for seedlings to become established at the edge of the banks and to grow into tall plants. If sedimentation leads to elevated marsh surfaces, as it usually does, competition by the extant plants reproducing vegetatively eventually results in short plants. This succession may be reversed by an increase in nutrient supply. This pattern over time and space is probably found in a variety of other aquatic plants.

Oil spill studies: A review of ecological effects

We reviewed seven particularly well known and/or studied oil spills that have occurred since the National Academy of Sciences 1975 report, “Petroleum in the Marine Environment” or that occurred prior to that report but about which significant new information has since been acquired. The spills studied were from the bargeFlorida, and tankersArrow, Argo Merchant, Amoco Cadiz, andTsesis and blowouts from the Bravo and Ixtoc I platforms.These “best” studies yield only limited insight into effects because they lack controls and have a high degree of natural variability. TheTsesis, Florida, andAmoco Cadiz cases are exceptional since they occurred in areas of ongoing research programs and had nearby areas suitable for controls. Oil spills have produced measurable effects on ecosystems that have not been readily predictable from laboratory studies on isolated organisms. However, ecosystemlevel interactions are poorly understood even without the complications resulting from effects of pollution. These generalizations emerge: oil regularly reaches sediments after a spill; oil in anoxic sediments is persistent; oil regularly contaminates Zooplankton and benthic invertebrates; fish are also contaminated, but to a lesser extent; oil contamination decreases the abundance and diversity of benthic communities.

Regulation of body temperature by the bluefin tuna

Abstract Bluefin tuna (Thunnus thynnus Linnaeus) can control the temperature of their bodies (25–30°C) so that the warmest portion of the muscle mass varies only 5°C over a 10°C–30°C range of water temperature.

Mako and porbeagle: warm-bodied sharks.

Abstract 1. 1. Mako and porbeagle sharks are able to conserve metabolic heat and maintain their bodies 7–10°C above ambient temperatures. 2. 2. Highly developed countercurrent heat exchangers located in the vascular system of these fish form a thermal barrier which prevents heat from being carried off by the circulating blood and lost in the gills.

An Experimental Study of the Structure of Herbivorous Insect Communities in a Salt Marsh

Factors regulating the numbers and species of herbivorous insects in a salt marsh were experimentally investigated by chronic fertilization of plots. All biweekly nutrient enrichments (urea or three dosages of a mixed fertilizer) resulted in increased grass standing crop in low and high marsh habitats. Plant nitrogen content increased only in those plots receiving the two highest levels of mixed fertilizer. Grass responses were most rapid where the highest nutrient load was applied. In all plots, fertilization resulted in increased standing crop of low and high marsh insect herbi- vores. However, the greatest herbivore loads occurred where grass nitrogen content as well as stand- ing crop had increased. Life history data and laboratory experiments indicated that the herbivore increases were largely due to in situ changes in survivorship and fecundity in response to higher plant nitrogen content. The herbivore response to fertilization was rapid, tracking in a single summer the nutrient and biomass changes of the grasses. The rate of increase, however, differed among herbivore species, and was positively related to the annual number of generations. Nutrient additions did not alter the diversity of the high marsh herbivore community, but led to increased diversity in low marsh. This was achieved primarily through greater equitability of the species abundances. All of the herbivore species collected in the fertilized plots occurred in the undisturbed salt marsh. The low marsh herbivore community responded to fertilization mainly with greater numbers of mirids, cicadellids, and grasshoppers, although normally dominated by the del- phacid Prokelisia marginata. Potential increases in number of P. marginata in response to fertilization were apparently checked by the increased abundance of spiders. The delphacids were more suscep- tible to spider predation than other salt marsh herbivores, due to their small size and low position in the grass canopy. Plant nutritional quality is of major importance in governing the abundance of salt marsh herbivores, with life history characteristics and predation interacting to structure the com- munity.