Here I review some recent research papers that caught my eye and got me thinking, or suggested some practical actions we could take for ponds. Results from PONDERFUL are also now beginning to make valuable additions to our understanding of ponds so keep an eye out for the project’s scientific publications.
Ponds and other small freshwaters
Andy Green and colleagues working on seed dispersal by water birds have developed a truly impressive understanding of the substantial role that birds play in moving both wetland and terrestrial plant propagules around the landscape. A recent addition to this work charts the history of our understanding of seed dispersal by water birds, including an interesting analysis of what we still believe (incorrectly) about seed dispersal as a result of rather uncritically repeating some of Charles Darwin’s original ideas. Of course, Darwin got the most important thing right – that water birds transport plant propagules – but for several other of his hunches, still repeated in the scientific literature, we now know better. So, Darwin thought that seeds eaten by water birds were destroyed by digestion, that dry-fruited seeds are mainly dispersed on fur or feathers (i.e. on the outside of animals) and waterbirds only disperse aquatic plants, all things we now know not to be true. I’m sure Darwin would have been the first to appreciate that science ever grows and would love the fact that his observations, as has so often been the case, opened up a whole new branch of Conservation Biology.
As well as observations on seed dispersal, Green and colleagues have continued to make valuable observations on the ponds of the Doñana National Park, including both the basic ecology of the ponds and the need for their protection. In the paper ‘Hydroperiod length, not pond age, determines zooplankton taxonomic and functional diversity in temporary ponds, they evaluate the influence of different environmental factors on zooplankton community structure in 96 ‘new’ (created in 2005) Mediterranean Temporary Ponds. They suggest that, overall, future restorations of Mediterranean Temporary Ponds should aim to increase pond heterogeneity in order to maintain zooplankton diversity, and also to benefit other aquatic taxa. Additionally, to maintain and restore adequate hydroperiods in the face of climate change, water supplies to ponds should be guaranteed by restoring their catchment areas and preventing groundwater overexploitation, a particular problem in the Doñana National Park that is likely to be significant elsewhere. The experimental temporary ponds dug in the park in 2005 were only 30 cm or 60 cm deep when created and the authors suggest that greater depth would help increase the length of time for which they hold water, helping to counteract the effects of climate change.
Given the condition of the Doñana National Park, a recent publication from the same team provides an important lesson on the importance of talking to the locals when diagnosing environmental problems. In this high-profile location they emphasise the importance of local technical knowledge of the effects on ponds and other wetlands of groundwater abstraction for fruit farming, and the need to build that knowledge into the identification of solutions.
We have often in PONDERFUL remarked that ponds occur from high mountains to low-lying coasts, where the land meets the sea. But the distribution and ecology of mountain ponds is not well-known so a recent study mapping high-altitude Italian ponds provides useful practical information on the location of these important waterbodies. ‘High-altitude’ was defined as land above 300 m and ponds were identified using satellite images of Copernicus Sentinel-1 and Copernicus Sentinel-2, which provided data on area, perimeter and altitude of the ponds. A total of 2156 ponds were found with 62% in the Alps and 38% in the Apennines. The authors not that the list is not complete as a result of the difficulties of seeing ponds under trees.
Most readers of this newsletter will have a clear idea that adding non-native Goldfish (Carassius auratus) to ponds is not likely to be good for pond biodiversity, but perhaps not know so much about the detailed effects. So it is useful to have a detailed study of the effect of adding Goldfish to ponds and the impact this has on pond biodiversity. In the study of Benjamin Lejeune and colleagues, introduced Goldfish replaced Palmate Newts (Lissotriton helveticus) as the top predator. Global trophic diversity of consumer communities was reduced by a factor of three in Goldfish compared with newt ponds. Proxies of food chain length, basal resource diversity use and trophic redundancy were also all reduced by a factor of two. Consistent with theories of Food Chain Length, newt ponds displayed higher abundance and diversity of predatory macroinvertebrates, with ‘predator’ and ‘macroinvertebrate’ being the dominant modalities of the ‘feeding’ and ‘food type’ traits in these communities, respectively. By contrast, Goldfish ponds were almost completely devoid of predatory invertebrates, with trait modalities related to low trophic levels (i.e., ‘detritus’ food type, ‘deposit feeder’ and ‘filter feeder’ feeding types), indicative of a truncated food web, or trophic downgrading. Rightly the authors conclude that in such small size ecosystems, the consequences of alien omnivore introductions such as Goldfish can be particularly dramatic, requiring greater recognition and warranting conservation actions.
In South Africa, Charl Deacon and colleagues provide valuable evidence of the role of the whole networks of ponds and other small freshwater habitats for biodiversity. They considered the contribution of 10 freshwater biotypes in KwaZulu-Natal Province, South Africa in maintaining dragonfly communities. The waterbody types were open natural ponds, forested natural ponds, open marshes, vegetated marshes, forested marshes, open wallows, forested wallows, open streams, forested streams and the habitats associated with one large lake. They conclude that it is the variety of habitats that is important for maintaining dragonfly functional diversity, both in protected areas and in the conservation corridors among forestry plantations. They note that traditional freshwater conservation efforts have placed strong emphasis on large waterbodies such as lakes but conclude that, in the study area, a wide variety of lentic and lotic biotope types, both small and large, and in both in protected areas and ‘conservation corridors’ in modified landscapes, must remain intact to maintain the full diversity of dragonfly species in the region. In other words, dragonfly conservation in this area requires a full waterscape approach.
Other interesting papers
The use of inappropriate analytical methods may be leading to overestimation of global freshwater invertebrate recovery according to a recent (October 2024) report by Laurence Gaume and Marion Desquilbet. Many people reading this newsletter will be aware of the on-going debate on whether freshwater invertebrate communities are becoming richer or declining in diversity and this paper adds some detailed notes of caution about methodological approaches to the analysis of long-term trends in large datasets. With reference particularly to a prominent paper in the journal Science, which reported declines in terrestrial, but increases in freshwater, insect abundances, the authors document numerous methodological problems with this analysis. Specifically, they found more ‘problem types’ per dataset in the freshwater realm than in the terrestrial realm. Overall, they conclude that, in its current state, the database neither enables the study of temporal trends of insects worldwide nor their drivers.
Practical actions
A recent update on the need to bend the curve on the loss of global freshwater biodiversity, by David Dudgeon and David Strayer, makes gloomy reading. The authors comment on the likelihood of reducing the seemingly inexorable decline of freshwater biodiversity, particularly through the adoption of the recommendations of the Emergency Recovery Plan (ERP) for freshwater. They conclude that, although ‘hopefulness is a defining feature of the ERP’, ‘we may be unable to bend the curve as much as is needed. Further commenting that ‘implementation of established methods for protecting freshwater biodiversity may not…[be]…enough to prevent continued ecosystem degradation and species loss’, suggests that something urgently needs to change.
Practically, a major new publication by IUCN on ‘Designing and managing protected and conserved areas to support inland water ecosystems and biodiversity’ will be of interest to everyone protecting freshwater biodiversity. Although the guide is a bit light on ponds, the approaches and methods recommended provide a useful international checklist – and now of course with the PONDERFUL Technical Handbook much of the pond detail is readily available.
More optimistically, a study on the value of small water bodies in Mediterranean agricultural landscapes for farmland birds provides quantitative data on the value of these habitats for conservation-priority and threatened species. Considering cattle ponds, drinking troughs and artificial pools, the authors document the role of these habitats in providing water, food, refuge and nest material resource, finding that different trophic groups of birds used small water bodies in different ways. Overall, the ponds and pools were used by 80 species from 34 avian families including nine species listed as conservation-priority in the EU Birds Directive and 12 species threatened at national or regional scale. The authors conclude that agri-environment schemes should (1) ensure the protection and sustainable management of the existing traditional small water bodies, (2) foster the creation of near-natural small water bodies (e.g., ponds with smooth shoreline and muddy bottom to provide birds with safe access for bathing and abundant emerging insects or nest-building material, respectively) in those regions where natural ponds are vanishing, and (3) promote the diversity of microhabitats at SWB scale (e.g., adjacent trees and scrubs, small ground-level puddles and non-vegetated open shoreline zones). These management measures would also benefit other threatened animal groups which are frequently associated to SWB, such as bats and amphibians. All of these recommendations would be valuable suggestions for the new Nature Restoration Plans that EU states have to make for agricultural areas for the new Nature Restoration Law.
Professor Jeremy Biggs, Freshwater Habitats Trust