Presence Of Submerged Vegetation Research Articles

Exploration of spatial and temporal patterns of fish diversity and composition in a tropical estuarine system of Mexico

There are many studies of fish assemblages intemperate systems, but little informationexists about tropical estuarine systems,particularly in the Western Atlantic Regionincluding Mexico. We investigated the fishcommunity structure in the Pueblo Viejo lagoon,Veracruz. Biological samples were collectedmonthly for one year at six sites: three withdense stands of Ruppia maritima and threesites without submerged vegetation. For eachsample, temperature, salinity, dissolvedoxygen, turbidity and depth were analyzed. Theunbiased Simpson diversity index, CanonicalCorrespondence Analysis (CCA) and DiscriminantAnalysis (DA) were used to analyze the fishcommunity. Environmental abiotic variablestended to show significant temporal, but notspatial differences. Fish diversity showedonly a weak significant correlation with watertemperature, and relatively strong diversitypeaks, from June to August and April, wererelated to production peaks in the system. Thetwo first axes of CCA accounted for 65% of thespecies-environment biplot variance, whichsuggested that monthly changes of salinity,turbidity and precipitation, and presence orabsence of submerged vegetation, were the mostimportant environmental variables indetermining the observed variability in fishcommunity composition. Further, fish diversitywas significantly different between habitatswith and those without the presence ofsubmerged vegetation (P < 0.02). A DA showedsignificant differences (P < 0.03) in fishcommunity composition between both kinds ofhabitats, with Lagodon rhomboides,Mugil curema and Menidia beryllina(substantially more abundant in habitat withsubmerged vegetation) as the most importantspecies in the discrimination of spatial fishcomposition. Considering both habitatscombined, fewer differences were observed infish diversity and community compositionbetween rainy and dry seasons. Fish communitycomposition showed greater similarity betweenseasons than between habitats, despite the factthat environmental abiotic variables showed aninverse pattern, suggesting that site factors,such as the presence of submerged vegetation,play a more important role in the maintenanceof fish community patterns than those relatedto temporal influence.

Macroinvertebrate communities in relation to submerged vegetation in two Chara-dominated lakes

Relationships between macroinvertebrates and the presence ofsubmerged vegetation were studied in two shallow eutrophiclakes inThe Netherlands, Lake Veluwemeer and Lake Wolderwijd. A shiftfromturbid water with sparse macrophyte cover (Potamogetonperfoliatus, Potamogeton pectinatus) towards clearwaterwith a dense cover of submerged vegetation (Chara spp.)hasbeen observed in the lakes over the past 10 years. RelativelylargeChara meadows (300–500 ha) have recently developed inbothlakes. The composition of macroinvertebrate fauna wasdetermined atsites varying in cover and dominant vegetation type bysamplingsediment and water during 1992 and 1994. Macrophyte biomass,sampling year and vegetation type were the major determinantsofmacroinvertebrate community composition. Valvatapiscinalis,Bithynia tentaculata, Gammarus tigrinus and Chironomussp.characterized the sites with high charophyte biomass, whereasPotamopyrgus antipodarum, Cladotanytarsus sp., Stictochironomus sp. dominated the samples with lowcharophytebiomass. Chara vegetation was different from Potamogeton sp. by showing lower densities of the midgelarvaeEinfeldia dissidens and Cricotopus gr. sylvestris.Seasonal variations in densities of the dominant molluscspecies(V. piscinalis, P. antipodarum) were closelyrelated tothe development of Chara biomass as well as toperiphytoncover on charophytes. Thus, changes of the light climate inbothlakes, which have led to an increase in colonization bysubmergedvegetation (particular Chara meadows), indirectly had alargeimpact on macroinvertebrate communities.