Beach morphodynamics modulate the effects of multidirectional habitat loss on population density and size structure of the Atlantic ghost crab Ocypode quadrata

Sandy beaches are land-sea transitional habitats experiencing 'multidirectional' habitat loss due to coastal developments (e.g. armoring and/or conversion of natural vegetation into manmade structures) and beach erosion. This 'coastal squeeze' is a chronic and progressive process; however, its impacts on beach biodiversity across morphodynamic gradients are still to be unveiled. We hypothesized that the effects of multidirectional habitat loss would be more severe on dissipative than on reflective beaches, due to the higher elevation, amount of built up sediment, and width of the backshore compartment of the latter. We, thus, examined the effects of coastal developments and erosion on density and size structure of the Atlantic ghost crab, Ocypode quadrata, on beaches with different morphodynamics. Given that the living area of ghost crabs spans all cross-shore compartments and the whole dissipative-to-reflective morphodynamic gradient, they are appropriate organisms to access the synergic effects of coastal developments and beach erosion under different morphodynamic regimes. On dissipative beaches, density and mean crab size increased with moderate erosion, attributed to the effects of space loss, which might increase territorial competition, favoring the remaining larger individuals. However, mean size and density decreased with high erosion given the more intense reduction in the abundance of large-sized crabs living in up-shore habitats. Mean crab size also decreased in the presence of coastal development while crab density did not vary with loss of backshore habitats occupied by larger individuals. On reflective beaches, both density and crab size decreased with coastal development; the crab size decrease recorded under moderate erosion was more evident in the presence of coastal development. Under high erosion, mean crab sizes declined, reflecting those under low erosion conditions. Overall, populations on reflective beaches appeared more resilient to extreme erosion. Notwithstanding, coastal developments affected population structure across all beach types, and especially in areas subjected to high erosion, exhibiting a synergic effect. We predict that, in combination, these stressors may lead to functionally extinct populations where conditions necessary for individuals to reach sexual maturity (i.e. occurrence of only small-sized and immature individuals) are not met. Thus, the connectivity between water, beach compartments and dunes/coastal plain, on both local and regional scales, may be essential to maintain viable and connected populations of ghost crabs. Further, our results strongly suggest that both size and density (complemented with crab abundance) must be considered equally important and in combination in future efforts to assess anthropogenic stressors on ghost crab populations and when guiding conservation strategies and policies to prevent their local and regional extinctions.

Weather and butterfly responses: a framework for understanding population dynamics in terms of species' life-cycles and extreme climatic events

Understanding population responses to environmental conditions is key in the current context of climate change and the extreme climatic events that are threatening biodiversity in an unprecedented way. In this work, we provide a framework for understanding butterfly population responses to weather and extreme climatic seasons by taking into account topographic heterogeneity, species' life-cycles and density-dependent processes. We used a citizen-science database of Mediterranean butterflies that contains long-term population data (28 years) on 78 butterfly species from 146 sites in the Mediterranean mesic and alpine climate regions. Climatic data were obtained from 93 meteorological stations operating during this period near the butterfly sites. We studied how seasonal precipitation and temperature affect population growth while taking into account the effects of density dependence. Our results reveal (i) the beneficial effects of winter and spring precipitation for butterfly populations, which are most evident in the Mediterranean region and in univoltine species, and mainly affect the larval stage; (ii) a general negative effect of summer rain in the previous year, which affects the adult stage; and (iii) a consistent negative effect of mild autumns and winters on population growth. In addition, density dependence played a major role in the population dynamics of most species, except for those with long-term negative population trends. Our analyses also provide compelling evidence that both extreme population levels in previous years and extreme climatic seasons in the current year provoke population crashes and explosions, especially in the Mediterranean mesic region.

Secondary production of freshwater zooplankton communities exposed to a fungicide and to a petroleum distillate in outdoor pond mesocosms

Ecological risk assessment of chemicals in mesocosms requires measurement of a large number of parameters at the community level. Studies on invertebrate communities usually focus on taxonomic approaches, which only provide insights into taxonomic structure changes induced by chemicals. In the present study, abundance, biomass (B), theoretical production (P), and instantaneous P/B ratio were used as endpoints to assess the effects of the commercial form of the dithiocarbamate fungicide thiram (35 µg/L and 170 µg/L nominal concentrations) and of the hydrocarbon water accommodated fraction (HWAF) of a petroleum distillate (0.01 mg/L, 0.4 mg/L, 2 mg/L, and 20 mg/L loadings) on the zooplankton community in freshwater pond mesocosms. Endpoints were measured during a 4-wk treatment period (1 pulse/wk) followed by a 5-mo posttreatment period to evaluate zooplankton population recovery. The chlorophyll a concentration in water was significantly increased after treatment with HWAF, whereas it was not affected by thiram treatment. Zooplankton abundance-based analysis showed effects on a limited number of taxa, whereas other endpoints (mainly the P/B ratio) revealed that more taxa were impacted, with recovery depending on the chemical and concentration. Exposure to HWAF mainly had a negative impact on cladocerans, which resulted in top-down effects (between cladocerans and phytoplankton). Thiram negatively affected rotifers and copepods, suggesting more direct toxic effects. The results show that the use of secondary production as an endpoint provides a more comprehensive assessment of potential direct and indirect effects of chemicals on a community, and they also support evidence of alteration in functional processes.