Nutrient transfer from sea to land: the case of gulls and cormorants in the Gulf of Maine

Abstract

Summary1. The structure of communities is influenced by the transport of resources across ecosystem boundaries. Seabirds are capable of introducing large amounts of marinederived nutrients to land, thereby modifying resource availability to terrestrial species. 2. In this study we investigated the hypothesis that variation in nesting densities of great black-backed gulls Larus marinus and double-crested cormorants Phalacrocorax auritus would modify the effect of these species on soil nutrients and plant species composition on offshore islands in the Gulf of Maine, USA. 3. Our results showed a significant positive correlation between nest density and concentrations of ammonia and nitrate in soils, but no significant relationship between nest density and phosphate. Ammonia and phosphate concentrations were good predictors of plant species composition; there were more annual forbs than perennial grasses in the abandoned cormorant colony compared with the gull colonies. Extremely high concentrations of ammonia in the highest density colony (active cormorant) may have been the main factor inhibiting plant germination at this site. All of the plant species in gull and cormorant colonies showed enriched δ 15 N signatures, indicating substantial input of marine-derived nitrogen from seabirds. 4. Our study demonstrated that gulls and cormorants are effective vectors for the transport of marine nutrients to terrestrial ecosystems. However, transported nutrients occurred in particularly high concentrations in areas with nesting cormorants. Nesting densities and species-specific variation in resource transport should be considered when predicting the effects of seabirds and other biogenic vectors of allochthonous resources.

Guano deposition and nutrient enrichment in the vicinity of planktivorous and piscivorous seabird colonies in Spitsbergen

“…Furthermore, within the planktivore transect, soil dry mass was negatively correlated with guano deposition; hence, water content was higher, which would further encourage vegetation development. Similar findings have been reported in other studies in both polar regions (e.g., Tatur 1989; Odasz 1994; Leishman and Wild 2001), as well as at lower latitudes (e.g., Hawke and Powell 1995;Anderson and Polis 1999;García et al 2002;Ligeza and Smal 2003;Wait et al 2005;Ellis et al 2006). Our study provides evidence that planktivore and piscivore colonies affect surrounding tundra in subtly different ways, even though the absolute amount of guano deposited per unit time or area was similar.…”

“…Guano production and its composition are related to the diet, with different proportions of organic and non-organic fractions and particular mineral salts reported in analyses of the guano of plankton-, fish-, and bivalve-eating birds (Hutchison 1950;Galkina 1974;Bédard et al 1980). Guano deposition influences various physical and chemical soil parameters, such as concentration of ammonium, nitrate, phosphate, magnesium and potassium ions, as well as soil humidity, conductivity, and respiration rate (Gilham 1956;Ryan and Watkins 1989;Anderson and Polis 1999;García et al 2002;Wait et al 2005;Ellis et al 2006). Although guano itself is typically alkaline, the process of its decomposition in the soil often results in increased soil acidity being found near seabird colonies (Gilham 1956;García et al 2002;Ellis 2005;Wait et al 2005).…”

The complexity of ecological impacts induced by great cormorants

“…Deposition of uric acid and increased NH 4 concentration lead to soil acidification (Pearson & Steward, 1993), the conditions under which the uptake of cations is largely decreased (VanDijk et al, 1989). Seed germination is also usually affected under such conditions (Ishida, 1997;Ellis et al, 2006;_ Zółkoś & Meissner, 2008). Changes of soil and groundwater have a particular impact on herbs and shrubs with shallow root systems.…”

Influence of allochtonous nutrients delivered by colonial seabirds on soil collembolan communities on Spitsbergen

“…), which are present in soil in the vicinity of seabird colonies and even individual nest burrows compared to areas beyond their impact, enhance primary production (Smith 1976;Anderson and Polis 1999;García et al 2002;Stempniewicz et al 2006). Substantial guano deposition close to seabird colonies increases nutrient content in the soil (Ryan and Watkins 1989;Wainright et al 1998;Anderson and Polis 1999;Stempniewicz et al 2006) and plant biomass (Anderson and Polis 1999;Zmudczyńska et al 2008), as well as causing changes within plant communities (Vidal et al 2003;Ellis et al 2006;Zmudczyńska et al 2009). This feeds through the local food web, with more intensive use of such areas by invertebrate and vertebrate herbivores (Jakubas et al 2008), predators and scavengers (Croll et al 2005).…”