Structural variability and its relation to edaphic attributes of mangroves in the south‐west coast of India

We estimated the tree structural variables (density, frequency and basal area) of true mangroves and soil variables like particle size distribution, carbon, available nitrogen and phosphorus, sulphur, nutrient cations (K, Na, Ca, Mg) of Cochin mangroves and examined the relationship between vegetation and environment. The study sites were classified as seaward fringe, riverine and interior. Of the thirteen true mangrove species present, Avicennia officinalis, Sonneratia caseolaris and Excoecaria agallocha showed higher Importance Value Index. The mean stem density varied from 80 to 25,000 no./ha and basal area from 0.1 to 39.68 m²/ha. Seaward mangroves showed maximum stand basal area and biomass production while riverine exhibited maximum density. Maturity Index value of Cochin mangroves revealed a very low degree of structural maturity. Interior mangroves were characterized by silty soil with higher nutrient concentrations. Principal component analysis of soil data revealed that the major factors influencing mangrove vegetation were soil texture, nutrients, salinity and oxidation–reduction potential. The stem density and basal area of different species correlated highly with soil nutrients and texture (p < .001) while salinity showed negative correlations with vegetation characteristics. The data generated in the study would be fundamental in site‐specific management and conservation efforts of these degrading mangroves.     

Mesozooplankton community structure in a degrading mangrove ecosystem of the Cochin coast,India

The diversity, abundance and community structure of mesozooplankton from the hydrographically differing mangrove habitats in Cochin, Kerala (India), were investigated. Eleven zooplankton groups were identified, with calanoid copepods (62%) comprising the predominant population, followed by crustacean nauplii (22%) and mysids (12%). Nitrogen limiting (N: P ratio 5.13 ± 7.03) with a mixo‐mesohaline salinity (8.96 ± 3 psu) and relatively low temperatures (30.28 ± 0.9 °C) was a characteristic feature of the study zones. Non‐metric multidimensional scaling based on Bray–Curtis similarity (PRIMER) analysis revealed there was little variation in the mesozooplankton structure among sampling sites (stress 0.05; ANOSIM test Global R:0.325). BEST analysis indicated that temperature and salinity exhibited the best correlation (ρ = 0.701) with fauna. The results of this study indicated a severe reduction in zooplankton abundance, biomass and diversity. It is clear that the zooplankton communities are depleting, along with the mangrove vegetation, because of the shallowness and unsuitable environmental conditions of the water bodies attributable to anthropogenic stresses.