Litter dynamics in riverine mangrove forests in the Guayas River estuary, Ecuador

Abstract

The hypothesis that rates of litter turnover in mangroves are controlled by local geophysical processes such as tides has been studied at sites with mostly small tides (<1 m) and minor crab consumption of leaf litter. Our study describes litter dynamics of three riverine mangrove sites (M1, M2, M3), inhabited by the mangrove crab Ucides occidentalis, located in a macrotidal (>3 m) river-dominated tropical estuary in Ecuador (2.5°S latitude). There were statistical effects of site and depth on soil salinities, but all mean salinities were <17 g kg. Daily rates of leaf litter fall were higher in the rainy compared to the dry season, although no seasonal effects were observed for other components of litter fall. Annual total litter fall rates were significantly different among sites at 10.64, 6.47, and 7.87 Mg ha year for M1, M2, and M3, respectively. There were significant site (M3 > M2 > M1) and season (rainy > dry) effects on leaf degradation, and both effects were related to differences in the initial nitrogen content of senescent leaves. Mean leaf litter standing crop among the sites ranged from 1.53 to 9.18 g m, but amounts were strongly seasonal with peak values during September in both years of our study (no significant year effect) at all three sites. Leaf turnover rates based on leaf fall estimates and litter standing crop were 10- to 20-fold higher than estimated from rates of leaf degradation, indicating the significant effect of leaf transport by tides and crabs. Field experiments demonstrated that the mangrove crab can remove daily additions of leaf material within 1 h at all three sites, except during August-October, when the crab is inactive on the forest floor. Even though there is seasonally elevated leaf accumulation on the forest floor during this time, leaf turnover rates are much higher than expected based on leaf degradation, demonstrating the importance of tidal export. This is the first description of how crabs influence litter dynamics in the New World tropics, and results are similar to higher rates of crab transport of leaf litter in the Old World tropics. Even in riverine mangroves with high geophysical energies, patterns of litter dynamics can be influenced by ecological processes such as crab transport.

Litter degradation and CN dynamics in reforested mangrove plantations at Gazi Bay, Kenya

“…Water soaking causes leaching of labile materials and promotes microbial activity both of which Table 4 The density of sediment infauna (macrobenthos) in the S. alba and R. mucronata treatments (Extracted from Bosire et al, 2004) increase decomposition rates (Tam et al, 1990;Ashton et al, 1999). Other than specific mangrove stand physical characteristics, differences in litter quality have also been found to be critical in influencing decay rates (Robertson, 1988;Steinke et al, 1990;Twilley et al, 1997). High tannin content is known to be aversive to detritivores and thus inhibit microbial activity (Steinke et al, 1990;Ashton et al, 1999), while nutritious leaf material with low C:N ratios have higher decay rates (Wieder and Lang, 1982).…”

“…Most studies on mangrove litter degradation and concomitant nutrient dynamics have hitherto concentrated on differences among: tidal elevations (Twilley et al, 1986(Twilley et al, , 1997Mfilinge et al, 2002), species and seasons (Tam et al, 1990;Twilley et al, 1997;Woitchik et al, 1997;Mfilinge et al, 2002) and litter components (Steinke et al, 1983;Van der Valk and Attiwill, 1984;McKee and Faulkner, 2000). Specific stand management regimes, i.e., regulated exploitation versus excessive extractive pressure which leads to deforestation, and subsequent reforestation in areas where natural regeneration is impeded, do influence nutrient recycling (Ashton et al, 1999), Reforestation has been found to alter site physico-chemical conditions (McKee and Faulkner, 2000;Bosire et al, 2003) and is thus assumed to ultimately restore the functional importance of nutrient fluxes through it among other ecosystem functions.…”

Changes in Organic, Inorganic contents, Carbon Nitrogen ratio in decomposingAvicennia marinaand Rhizophora mucronataleaves on tidal mudflats in Hajambro creek, Indus delta, Pakistan

“…Since leaves of both species were exposed to the same environmental conditions, so the differences in the decompo sition rates are probably due to the differences in the leaf morphology, texture and chemical Volume 4 | Number 1 | January | 2014 39 39 composition. Differences in leaf quantity are known to affect decomposition rates [5,21,36]. Different decay constant had been recorded for different mangroves species in different geographical location and in different regions (Table II), probably due to the differences in the nitrogen and tannin contents [6,13,35,37].…”

“…The fallen mangrove litter on the forest floor is decomposed by the bacterial action and other organisms, as well as acted upon by physical, chemical and biological processes [1][2][3][4][5][6], and generate a continuous source of nutrients in mangrove ecosystem [7][8][9][10]. These nutrients ions (most importantly the ammonium, nitrate, nitrites) are finally available for primary production and this in turn supports a wide variety of consumers [5][6][11][12]. The process of decomposition of mangrove leaves can be divided in three phases [3].…”

Effect of Anthropogenic Activities on Mangrove Crab Diversity in Cameroon Atlantic Coast

“…The consequences of deforestation on mangrove fauna have not yet been documented in West Africa. The significant role of crabs as a engineer species starts to be recognized, but their ecological answers with respect to human pressures are poorly known compared to other aspects of their life such as diversity, distribution, sex ratio, ecological roles, feeding ecology, plant periodical migrations, physiological adaptations, domestic wastewater effects,… [22,23,24,25,26,27,28,29,30]. So, the aim of this study is to determine the impact of human pressures on mangrove crab biodiversity in Cameroon.…”