Mark W. LaSalle

A comparison of the diets of Gulf killifish,Fundulus grandis Baird and Girard, entering and leaving a Mississippi brackish marsh

We examined the diets of Gulf killifish,Fundulus grandis Baird and Girard, collected monthly from March through July 1988 with unbaited minnow traps during two sampling periods: (1) on flood tides before they reached the marsh surface, and (2) on ebb tides as they left the marsh. Thirty-five prey taxa, plant parts, and detritus were identified from the stomach contents of 110 Gulf killifish (mean SL = 55 mm, range = 30−82 mm). Fiddler crabs,Uca longisignalis Salmon and Atsaides; amphipods, mostlyCorophium louisianum Shoemaker; tanaidaceans,Hargeria rapax (Harger); and hydrobiids,Littoridinops palustris Thompson, were their most important prey. Killifish diets differed both quantitatively and qualitatively relative to the habitat in which they were feeding. Fiddler crabs and polychaetes were consumed more frequently and in greater numbers in the intertidal zone, whereas more amphipods were eaten by killifish feeding in subtidal and low intertidal areas. Gulf killifish consumed a greater volume of food when they had access to the marsh surface than when they were confined to subtidal areas.

Evaluation of the flora and fauna of aSpartina alterniflora marsh established on dredged material in Winyah Bay, South Carolina

Approximately 35 hectares ofSpartina alterniflora marsh has, over a 14-year period, developed naturally on unconfined dredged material placed within the intertidal zone of Winyah Bay, South Carolina. The above-and below-ground vegetative structure, benthic macrofauna, and resident fish and shellfish assemblages of two varying-aged zones (4 and 8 years) of this marsh were evaluated and compared in September 1988. Vegetative structure (stem height, density, percent cover, and biomass) in both zones was within the range reported for natural sites, with a trend toward greater below-ground development with age. The macrofaunal assemblages of both zones were similar in both species composition and numbers of species (17–21 species), with oligochaetes and polychaetes dominating both assemblages. Overall density of macrofauna in the 8-year-old zone (19,943 individuals per m2) was significantly greater than that in the 4-year-old zone (4,628 individuals per m2). Differences between zones (particularly the presence of large-bodied molluscs in the older site) seemed to reflect age. The fish and shellfish assemblage collected from the younger site was dominated byFundulus heteroclitus andPalaemonetes pugio. Gut contents ofF. heteroclitus included a variety of marsh-surface prey, similar to that reported elsewhere. Overall, both zones seemed to represent well established, viable, low intertidal marsh habitat.

Seasonal abundance of aquatic diptera in two oligohaline tidal marshes in Mississippi

Nineteen species of Diptera (16 in each zone) from seven families were found in monthly collections (June 1979 through May 1980) in two Mississippi marsh plant zones dominated byJuncus roemerianus Scheele andSpartina cynosuroides (L.) Roth, respectively. TheJuncus zone was dominated by a species ofPalpomyia-Bezzia complex, two species ofBezzia (Ceratopogonidae),Paratendipes sp.,Limnophyes sp. (Chironomidae) andThinophilus frontalis (Dolichopodidae).Palpomyia-Bezzia sp.,Culicoides hollensis, Ormosia sp. (Tipulidae) andPelastoneurus abbreviatus (Dolichopodidae) dominated theSpartina zone. Total inset density and species richness were lowest in June and July in both zones, corresponding to a pulse of adult emergence. Overall, total density was significantly higher in theSpartina zone with mean values of 165 and 245 insects m−2 for the {Juncus} and {Spartina} zones, respectively. In addition to total density, differences in abundance were apparent for a number of species between marsh zones. Patterns could be attributed to species-specific habitat preference., predation by aquatic predators, and/or by interactions of the infauna themselves.

Comparing benthic macrofaunal assemblages of creekbank beds of the spikerushEleocharis parvula (R&S) link and adjacent unvegetated areas in a Mississippi brackish marsh

The benthic macrofaunal assemblages inhabiting creekbank beds of the dwarf spikerushEleocharis parvula and adjacent unvegetated areas were compared in a brackish marsh in Mississippi to determine the importance of diminutive plants as invertebrate habitat. Benthic samples were collected over a 12-month period.Eleocharis beds contained 3.6 times higher densities of organisms than adjacent unvegetated areas. Fifteen of 35 taxa collected in beds accounted for 94.7% of the total assemblage (13,266 organisms per m2). Fifteen of 37 taxa collected in bare areas represented 92.4% of the total assemblage (3,625 organisms per m2). Dominant species in beds were the oligochacteMonopylephorus parvus, the crustaceansHargeria rapax andCorophium louisianum, and the insectHydrellia americana (a leaf miner ofEleocharis). Dominant species in bare areas were the polychaetesStreblospio benedicti andHobsonia florida and the crustaceanH. rapax. Overall, the greatest proportion of organisms (60–100%) were distributed within the upper 2 cm of substrate in both areas. Although several factors may explain observed differences in diversity and abundance between beds and bare areas, organisms inEleocharis beds probably benefit most from the relative stability provided by the physical structure of beds. Plants provide attachment sites for tube-building species and may limit predation and disturbance from large aquatic organisms.

Seasonal abundance and diversity of spiders in two intertidal marsh plant communities

The spiders of two Mississippi marsh communities were studied from January 1982 through March 1983. Monthly collections were made in two adjacent marsh plant zones dominated bySpartina cynosuroides (L.) Roth andJuncus roemerianus Scheele respectively. A total of 38 species of spiders (36 inSpartina, 33 inJuncus) representing 13 families were collected. The dominant species in theSpartina zone includedPirata mayaca Gertsch,Lycosa watsoni Gertsch (Lycosidae),Clubiona saltitans Emerton,Scotinella formica (Banks) (Clubionidae),Floricormus sp. (Linyphiidae),Dictyna sylvania Chamberlin & Ivie (Dictynidae),Paramaevia hobbsae (Barnes) (Salticidae), andAgelenopsis barrowsi Gertsch (Agelenidae). The dominant species in theJuncus zone includedLycosa watsoni, Pirata mayaca, Clubiona saltitans andSarinda hentzi (Banks) (Salticidae). Density, biomass, species richness and equitability peaked in May in theJuncus zone and in June in theSpartina zone. Peak levels of density and biomass corresponded to the reproductive activity of the common species, while diversity patterns were attributable to the reproductive activity of the less common species. Mean values of density and biomass over the study period were 84.8 spiders per m2 and 155.6 mg per m2 in theSpartina zone and 39.4 spiders per m2 and 133.0 mg per m2 inJuncus zone. The Juncus zone was flooded more frequently, contained less litter, and supported lower overall density and diversity of spiders.

Energy Lost to the Exuviae During Molting of Lycosa Watsoni Gertsch (Araneae: Lycosidae)

The loss of carbon compounds during molting for Lycosa watsoni was determined as percentage of total weight and total calories lost. The mass of exuviae from 20 spiders, from 1.3 to 4.7 mm carapace width ranged from 0.18 to 5.40 mg dry weight and from 4.4 to 10.6% of the total weight of spiders. The mass of exuviae as a % of body weight increased in the amount of material lost during successive molts and was linearly related to carapace width (y = 3.17 + 1.3x) and body weight (y = 5.51 + 0.06x). The caloric content of exuviae was 8.7 @+ 1.86 cal./mg dry weight and could amount to between 1.57 and 46.98 cal per molt over the range of spider sizes studied. Similar trends were observed from comparable data reported for the lycosid spider, Pardosa lugubris.