ANALISIS STRUKTUR KOMUNITAS KEPITING DI KAWASAN MANGROVE STASIUN KELAUTAN UNIVERSITAS RIAU KELURAHAN PURNAMA KOTA DUMAI PROVINSI RIAU

This research was conducted in January 2019 in the mangrove area of Purnama Village, Dumai City, Riau Province. The purpose of this study was to determine the crab community structure which includes the type, abundance, crab distribution patterns, species diversity (H '), species uniformity (E), and species dominance (C) crabs. The method used in this study is a survey method. There are three observation stations with each of the three transects at each station, on each transect line there is a square plot with a size of 5x5 m2. Crab sampling is done quantitatively and qualitatively. Based on the results of the study it was found that the species of crabs identified at the area of the research were Sesarma reticulatum, S. guttatum, Uca dussumieri, U. rosea, U. vocans, Cardisoma carnifex, and Clistocoeloma merguinse. Furthermore, the abundance of crabs obtained is between 1560-2040 Ind / Ha with cluster distribution patterns. The average value of species diversity (H ') indicates moderate diversity, uniformity (E) indicates high species uniformity, and species dominance value (C) indicates no dominating species.This research was conducted in January 2019 in the mangrove area of Purnama Village, Dumai City, Riau Province. The purpose of this study was to determine the crab community structure which includes the type, abundance, crab distribution patterns, species diversity (H '), species uniformity (E), and species dominance (C) crabs. The method used in this study is a survey method. There are three observation stations with each of the three transects at each station, on each transect line there is a square plot with a size of 5x5 m2. Crab sampling is done quantitatively and qualitatively. Based on the results of the study it was found that the species of crabs identified at the area of the research were Sesarma reticulatum, S. guttatum, Uca dussumieri, U. rosea, U. vocans, Cardisoma carnifex, and Clistocoeloma merguinse. Furthermore, the abundance of crabs obtained is between 1560-2040 Ind / Ha with cluster distribution patterns. The average value of species diversity (H ') indicates moderate diversity, uniformity (E) indicates high species uniformity, and species dominance value (C) indicates no dominating species.

Survival and osmoregulation of the purple marsh crab (Sesarma reticulatum) at varying salinity and pH

Overfishing of top predators along the western Atlantic coastline has led to a trophic cascade in salt marshes, with increases in herbivorous purple marsh crab (Sesarma reticulatum (Say, 1817)) abundances in North American estuaries leading to overgrazing of cordgrass (Spartina alterniflora Loisel.) and shoreline erosion. To evaluate potential physiological limits on the range of S. reticulatum within an estuary, we evaluated survival and physiological tolerance of S. reticulatum from the Ashepoo–Combhee–Edisto (ACE) River Basin in South Carolina, USA, to combinations of salinity (5‰ and 30‰) and pH (pH 6.6, 7.6, and 8.6) challenges, representative of estuarine extremes. Survival, haemolymph ion concentrations, and gill Na+,K+-ATPase (NKA) and vacuolar-type H+-ATPase (VHA) activity were measured after a 48 h exposure to each experimental condition. Survival was nearly 100% and osmoregulatory control was maintained across estuarine salinity and pH ranges. Sesarma reticulatum appeared to be robust to all potential combinations of salinity and pH stressors examined in this study, and therefore are likely unrestricted in their fundamental niche based on these stressors throughout an estuary.

A Tripartite Interaction Between Spartina alterniflora, Fusarium palustre, and the Purple Marsh Crab (Sesarma reticulatum) Contributes to Sudden Vegetation Dieback of Salt Marshes in New England

Tripartite interactions are common and occur when one agent (an arthropod or pathogen) changes the host plant in a manner that alters the attack of the challenging agent. We examined herbivory from the purple marsh crab (Sesarma reticulatum) on Spartina alterniflora following exposure to drought or inoculation with Fusarium palustre in mecocosms in the greenhouse and in crab-infested creek banks along intertidal salt marshes. Initially, drought stress on S. alterniflora and disease from F. palustre were examined in the greenhouse. Then, a second challenger, the purple marsh crab, was introduced to determine how drought and disease from F. palustre affected the attraction and consumption of S. alterniflora. Plant height and shoot and root weights were reduced in plants subjected to severe drought treatment when compared with normally irrigated plants. When the drought treatment was combined with inoculation with F. palustre, plants were significantly more stunted and symptomatic, had less fresh weight, more diseased roots, and a greater number of Fusarium colonies growing from the roots (P < 0.001) than noninoculated plants. The effects were additive, and statistical interactions were not detected between drought and inoculation. Estimates of herbivory (number of grass blades cut or biomass consumption) by the purple marsh crab were significantly greater on drought-stressed, diseased plants than on healthy plants irrigated normally. Drought increased attraction to the purple marsh crab more than inoculation with F. palustre. However, when only mild drought conditions were imposed, plant consumption was greater on inoculated plants. Healthy, nonstressed transplants set into plots in crabinfested intertidal creek banks were grazed less each year than inoculated plants or plants that were exposed to drought. Several hypotheses relating to nutrition, chemotaxis, and visual attraction are presented to explain how stress from drought or disease might favor herbivory.