Functional Roles and Ecological Importance of Small Cetaceans in Aquatic Ecosystems

Abstract

Small cetaceans (dolphins, porpoises, and small toothed whales) occur from the poles to the tropics, and from freshwater habitats to the open ocean. Most ecological research has focused on the influence of abiotic factors on the abundance, distribution, and behavior of these species. The ecological impacts of small cetaceans on communities and ecosystems remain poorly quantified. Their movement patterns, often high local and regional abundances across a range of ecosystems, and high metabolic rates suggest that small cetaceans could have large effects on ecosystem structure, dynamics, and function through a variety of mechanisms. These include top-down (e.g., direct predation and risk effects) and bottom-up effects (e.g., translocation of nutrients within and across ecosystems), but also behavior-mediated processes where these predators can facilitate access to resources to other predators or modify the physical properties of habitat (e.g., bioturbation). Most small cetaceans can be consumed by other marine predators, particularly killer whales (Orcinus orca) and large sharks. Although consumption rates of small cetaceans can be high, there is a paucity of information on their effects on population sizes or behaviors of their prey. Mass-balance ecosystem models suggest that small cetaceans may impact the populations of short-lived prey species (particularly fish and cephalopods), but other factors (e.g., eutrophication and fisheries) also affect ecosystem functioning and population trends. Delphinids can also mediate the translocation and recycling of limiting nutrients between spatially distinct ecosystems on a diel basis. Despite intriguing possibilities, large gaps remain in our understanding of the roles and importance of small cetaceans in aquatic ecosystems, both marine and freshwater.

Seasonal distribution of an opportunistic apex predator (Tursiops truncatus) in marine coastal habitats of the Western Mediterranean Sea

“…Multiple roles are recognized for apex predators in the marine environment, fulfilling key ecological, economic, and cultural functions (Hammerschlag et al, 2019). Apex predators are indeed affected by bottom−up processes and can influence food webs via consumptive effects on prey (top−down effects) (Heithaus et al, 2008;Steneck, 2012;Kiszka et al, 2022). Hence, assessing their distribution is pivotal to understanding community interactions and defining management goals to be implemented (Hammerschlag et al, 2019).…”

“…Considering their widespread distribution and prominent presence in the coastal marine ecosystems, common bottlenose dolphins could have a significant role in the structure and function of these ecosystems (Diaz Lopez, 2019). However, significant gaps impede our capability to fully determine several critical attributes of the function of these predators, particularly their fine-scale distribution and movements, feeding rates, and prey selection (Kiszka et al, 2022).…”

Isotopic niche overlap between sympatric Australian snubfin and humpback dolphins

“…Thus, anthropogenic activities impacting prey abundance and diversity (e.g., overfishing, pollution) can potentially affect the future coexistence of snubfin and humpback dolphins. As dolphins may play important roles in maintaining the structure and function of marine communities and ecosystems (Kiszka et al, 2022 ), cumulative anthropogenic pressures on their prey need to be considered when planning future multi‐species conservation.…”

Application of a multi-species bio-economic modelling approach to explore fishing traits within eligible cetacean conservation areas in the Northern Ionian Sea (Central Mediterranean Sea)

“…This observation, like that observed at the global scale by Sumaila et al (2007), should be considered within an overall costs and benefits assessment addressed to planning effective spatial measures to conserve the cetaceans and biodiversity. Indeed, in a scenario of low losses for the fishing industry, other incomes could be acquired by other ecosystem services, such as those performed by small cetaceans (Kiszka et al, 2022), compensating and improving the ecological conditions and the sustainability of the socio-economic systems linked to the marine resources (Hammershalg et al, 2019).…”