MAMMALS IN INTERTIDAL AND MARITIME ECOSYSTEMS: INTERACTIONS, IMPACTS AND IMPLICATIONS

Abstract

Although much information exists on the role of non-human mammals (both terrestrial and marine) on seashores and in maritime terrestrial environments, it is widely scattered in the literature. This review represents the first attempt to draw this disjointed information together. The reasons for past neglect are several: in some habitats, e.g. temperate rocky shores, such interactions are genuinely of relatively minor significance and have typically been ignored; the focus of marine mammal research on land has generally been ethological, not synecological; and the activity of small mammals, being predominantly nocturnal, passes largely unnoticed by (mostly) diurnal ecologists. Oceanic and inshore island populations are most at risk from introduced mammals. Cats, dogs, rats and mink are important predators of seabirds. Grazers such as goats and sheep cause coastal habitat degradation. Eradication of goats is especially important on islands and in faunas with high proportions of endemic species. Attention is focused below on mammalian involvement in ecological processes in a range of ecosystems: viz. salt marshes and shore meadows, sand dunes and machair, intertidal sand flats, shingle beaches, rocky shores, caves, cliffs, lava tubes, mangroves, seagrass and kelp beds and ice-edge habitats. Ecological observations on Marsupialia, Insectivora, Chiroptera, Lagomorpha, Rodentia, Cetacea, Carnivora, Sirenia, Perissodactyla, Artiodactyla and Primates are presented. Contemporary issues involving coastal mammals (particularly livestock husbandry) are collated, namely marine pollution by nutrient outwash (eutrophication), microbiological water quality, radioactivity and the impact of climate change and sea-level rise (particularly on ice-edge and saltmarsh habitats). Any exploitation of shores by terrestrial mammals has to be intermittent and cyclical on a tidal basis. Evictions of terrestrial mammals from feeding or nesting sites in coastal ecotone habitats may follow tidal or storm events, and can be locally catastrophic (generating carcasses for scavengers). Expanding mammalian populations on islands run the risk of exhausting food resources and starving, especially in winter. Certain marine mammals, however, like manatees, dugongs and bottle-nosed dolphins, may exploit the intertidal zone during its periodic immersion at high tide. The role of mammals, particularly grazing livestock, is much greater in saltmarsh and sand-dune ecosystems (including machair habitats) than in the intertidal zone. Occasional strandings of cetaceans or deaths of seals, particularly neonates, provide intermittent bounties of energy for opportunistic scavengers like foxes, hyenas, jackals or bears (even humans in isolated situations), depending on location. Other coastal energy bounties come in the form of turtle and iguana nests raided for eggs by foxes, raccoons and mongooses. Bearded pigs may also intercept hatchlings on their way to the sea. Fringing densely wooded hinterlands, shorelines and beaches form unobstructed highways for larger animals and may, historically, have played an important role in facilitating their post-glacial dispersal. The importance of productive shorelines for foraging by grazing, predatory and scavenging mammals will be magnified along bleak hinterlands, for example, desert coasts.