Creating new littoral zones in a shallow lake to forward-restore an aquatic food web.

Current rates of habitat loss require science-based predictions on how to restore or newly create lost habitat types. In aquatic ecosystems, littoral zones are key habitats for food web functioning, but they are often replaced by unnatural steep shorelines for water safety. To reverse this trend, knowledge is needed on how to successfully (re)create littoral zones. We quantified the response of an aquatic food web to the large-scale creation of new heterogeneous littoral habitats in shallow lake Markermeer, the Netherlands. Lake Markermeer was formed by dike construction in a former estuary, which created a heavily modified homogeneous 70,000 ha turbid lake lacking littoral habitat. Fish and bird populations declined over the last decades, but classical restoration via return to former marine conditions would compromise water safety and the large spatial scale prohibited biodiversity offsets. Therefore, an innovative "forward-looking restoration" approach was adopted: a 1000 ha archipelago called "Marker Wadden" was constructed without using a historic reference situation to return to. This aimed bottom-up stimulation of the aquatic food web by adding missing gradual land-water transitions and sheltered waters to the lake. After four years, new sheltered shorelines had become vegetated if they were constructed from nutrient-rich sediments. Exposed and sandy shorelines remained free of vegetation. Zooplankton community diversity increased in sheltered waters due to bottom-up processes, which increased food availability for higher trophic levels, including young fish. The creation of sheltered waters increased macroinvertebrate densities threefold, with sediment type determining the community composition. The archipelago became new nursery habitat for 13 of the 24 fish species known to occur in the lake, with up to 10-fold higher abundances under sheltered conditions. We conclude that modifying abiotic conditions can stimulate multiple trophic levels in aquatic food webs simultaneously, even in heavily modified ecosystems. This provides proof-of-principle for the forward-looking restoration approach.

Body cooling and its energetic implications for feeding and diving of tufted ducks.

Wintering in a temperate climate with low water temperatures is energetically expensive for diving ducks. The energy costs associated with body cooling due to diving and ingesting large amounts of cold food were measured in tufted ducks (Aythya fuligula) feeding on zebra mussels (Dreissena polymorpha), using implanted heart rate and body temperature transmitters. The effects of diving depth and food ingestion were measured in two sets of experiments: we measured body cooling and energy costs of six tufted ducks diving to different depths in a 6-m-deep indoor tank; the costs for food ingestion and crushing mussel shells were assessed under seminatural winter conditions with the same ducks feeding on mussels in a 1.5-m-deep outdoor pond. Body temperature dropped during feeding bouts and increased gradually during intermittent resting periods. The temperature drop increased linearly with dive duration. The rate of body cooling increased with feeding depth, but it was lower again at depths below 4 m. Half of the increment in energy costs of diving can be attributed to thermoregulatory heat production, of which approximately 50% is generated after diving to warm up the body. The excess costs for ducks feeding on large-sized mussels could be entirely explained by the estimated energy cost necessary to compensate the heat loss following food ingestion, suggesting that the heat production from shell crushing substituted for thermoregulation. Recovery from heat loss is probably a major component of the activity budget of wintering diving ducks.