The spatial and temporal link between Common Terns Sterna hirundo and their prey fish in the Wadden Sea

Rezension zu: Dänhardt, Andreas 2011: The spatial and temporal link between Common Terns Sterna hirundo and their prey fish in the Wadden Sea. Vogelwarte 49: 25-27. Dissertation an der Carl-von Ossietsky Universität Oldenburg, Fakultät für Mathematik und Naturwissenschaften, betreut von Prof. Dr. Peter H. Becker

Depth-dependent nutritional condition of sprat Sprattus sprattus larvae in the central Bornholm Basin, Baltic Sea

Bimodal depth distribution patterns observed for sprat Sprattus sprattus larvae in previous field studies conducted in the deep basins of the Baltic Sea have led researchers to hypothesise that larval sprat condition was depth-dependent. We examined this hypothesis by measuring morphological, biochemical and otolith-based proxies for nutritional condition in sprat larvae collected in discrete 5 m depth intervals from the surface to the bottom in the central Bornholm Basin. Similar to earlier studies, larval sprat were most abundant in 2 depth strata (0 to 10 and 65 to 75 m). Their nutritional condition in surface and deep waters was not uniformly expressed by the different indices. For example, sprat larvae from 0 to 10 m could not be distinguished from conspecifics caught at 65 to 75 m by a long-latency condition proxy (otolith-based growth rates). Similarly, a medium-latency proxy (RNA:DNA) did not suggest differences in condition between the depths. However, short-latency proxies (protein:standard length and DNA:dry weight) supported the depth-dependent condition hypothesis. The lack of correspondence and pitfalls associated with the use and interpretation of multiple condition indices (e.g. the influences of temperature and body size) are discussed and recommendations to strengthen these various metrics are provided

Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia

Publication history: Accepted - 15 February 2018; Published - 16 May 2018.Aim: Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non-native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non-native holoplanktonic biological probe species on a continental scale. Location: Western Eurasia. Time period: 1980s–2016. Major taxa studied: ‘Comb jelly’ Mnemiopsis leidyi. Methods: Based on 12,400 geo-referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large-scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations. Results: Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non-native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year-round populations in highly interconnected regions can re-seed genotypes over large distances after local extinctions. Main conclusions: Although the release of ballast water from container ships may contribute to the dispersal of non-native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large-scale connectivity patterns and the potential source regions of non-native marine species.Danish Council for Independent Research; Grant/Award Number: DFF-1325-00102B; FP7 People: Marie-Curie Actions, Grant/Award Number: MOBILEX, DFF - 1325-00025; EU, BONUS, BMBF, Grant/ Award Number: 03F0682; Excellence Cluster “Future Ocean”, Grant/Award Number: CP153

Raw data age-specific chick survival and herring abundance

Raw data on age-specific survival (in days) of common tern chicks (hatched in a colony in Wilhelmshaven, Germany) in relation to year (1992-2015), brood size, hatching order and standardized North sea herring abundance

Data from: Age-specific offspring mortality economically tracks food abundance in a piscivorous seabird

Earlier offspring mortality prior to independence saves resources for kin, which should be more beneficial when food is short. Using 24 years of data on age-specific common tern (Sterna hirundo) chick mortality, best described by the Gompertz function, and estimates of energy consumption per age of mortality, we investigated how energy wasted on non-fledged chicks depends on brood size, hatching order and annual abundance of herring (Clupea harengus), the main food source. We found mortality directly after hatching (Gompertz baseline mortality) to be high and to increase with decreasing herring abundance. Mortality declined with age, at a rate relatively insensitive to herring abundance. The sensitivity of baseline mortality to herring abundance reduced energy wasted on non-fledged chicks when herring was short. Among chicks that did not fledge, last-hatched chicks were less costly than earlier hatched chicks, due to their earlier mortality. However, per hatchling produced, the least energy was wasted on chicks without siblings, due to their baseline mortality being most sensitive to herring abundance. We suggest that earlier mortality of offspring when food is short facilitates economic adjustment of post-hatching parental investment to food abundance, but that such economic brood reduction may be constrained by sibling competition

Data from: Age-specific offspring mortality economically tracks food abundance in a piscivorous seabird

Earlier offspring mortality before independence saves resources for kin, which should be more beneficial when food is short. Using 24 years of data on age-specific common tern (Sterna hirundo) chick mortality, best described by the Gompertz function, and estimates of energy consumption per age of mortality, we investigated how energy wasted on nonfledged chicks depends on brood size, hatching order, and annual abundance of herring (Clupea harengus), the main food source. The dataset contains raw data on age-specific survival (in days) of common tern chicks (hatched in a colony in Wilhelmshaven, Germany) in relation to year (1992-2015), brood size, hatching order and standardized North sea herring abundance

Cross-continental analysis of coastal biodiversity change

Whereas the anthropogenic impact on marine biodiversity is undebated, the quantification and prediction of this change are not trivial. Simple traditional measures of biodiversity (e.g. richness, diversity indices) do not capture the magnitude and direction of changes in species or functional composition. In this paper, we apply recently developed methods for measuring biodiversity turnover to time-series data of four broad taxonomic groups from two coastal regions: the southern North Sea (Germany) and the South African coast. Both areas share geomorphological features and ecosystem types, allowing for a critical assessment of the most informative metrics of biodiversity change across organism groups. We found little evidence for directional trends in univariate metrics of diversity for either the effective number of taxa or the amount of richness change. However, turnover in composition was high (on average nearly 30% of identities when addressing presence or absence of species) and even higher when taking the relative dominance of species into account. This turnover accumulated over time at similar rates across regions and organism groups. We conclude that biodiversity metrics responsive to turnover provide a more accurate reflection of community change relative to conventional metrics (absolute richness or relative abundance) and are spatially broadly applicable. This article is part of the theme issue ‘Integrative research perspectives on marine conservation’