Marine conservation palaeobiology: What does the late Quaternary fossil record tell us about modern-day extinctions and biodiversity threats?

Abstract

Near-time conservation palaeobiology uses palaeontological, archaeological and other geohistorical records to study the late Quaternary transition of the biosphere from its pristine past to its present-day, human-altered state. Given the scarcity of data on recent extinctions in the oceans, geohistorical records are critical for documenting human-driven extinctions and extinction threats in the marine realm. The historical perspective can provide two key insights. First, geohistorical records archive the state of pre-industrial oceans at local, regional and global scales, thus enabling the detection of recent extinctions and extirpations as well as shifts in species distribution, abundance, body size and ecosystem function. Second, we can untangle the contributions of natural and anthropogenic processes by documenting centennial-to-millennial changes in the composition and diversity of marine ecosystems before and after the onset of major human impacts. This long-term perspective identifies recently emerging patterns and processes that are unprecedented, thus allowing us to better assess human threats to marine biodiversity. Although global-scale extinctions are not well documented for brackish and marine invertebrates, geohistorical studies point to numerous extirpations, declines in ecosystem functions, increases in range fragmentation and dwindling abundance of previously widespread species, indicating that marine ecosystems are accumulating a human-driven extinction debt.

Keywords: Quaternary; conservation palaeobiology; extinctions; extirpations; marine habitats.

Graphical abstract

Figure 1.

Comparison of four major invertebrate phyla (arthropods, cnidarians, echinoderms and molluscs) across marine, brackish, freshwater, and terrestrial systems as recorded in the IUCN Red List Database (IUCN, 2023a). (a) The total number of species reported in the database for each of the four systems (numbers indicate the total number of species). (b) The Red List status of invertebrate species grouped into four broad categories (‘Extinct’, ‘Endangered’, ‘Lower Risk’, and ‘Unknown’) tallied separately for each system. The broad categories were derived by pooling IUCN categories as follows: (1) “Unknown” – “Data Deficient”; (2) “Extinct” – “Extinct”, “Extinct in the Wild”; (3) “Endangered” – “Critically Endangered”, “Endangered”, “Vulnerable”; and (4) “Lower Risk” – “Near Threatened”, “Lower Risk/near threatened”, “Lower Risk/conservation dependent”, “Lower Risk/least concern”, “Least Concern”. See Supplementary Material for additional information.

Figure 2.

Conceptual illustration of how geohistorical data augment our understanding of global extinctions, extirpations, and ecological extinctions. In all examples, geohistorical knowledge indicates significant losses that would not be discoverable using modern scientific data alone. (a) Extinctions - an example of a clade for which the extinction rate is much higher once geohistorical data are considered (see text for a case example of the seabirds Puffinus). White bars indicate estimated stratigraphic ranges based on fossil occurrences (black circles), crosses indicate terminal extinction events; (b) Extirpations - an example of range contraction that becomes apparent only after geohistorical data are included (see text for case examples of seals and marine molluscs); (c) Ecological extinctions - examples of decimations (declines in population density) and functional shifts (e.g., shortened life spans, diminished body size) that become apparent once the fossil record is considered (see text for a case example of Crassostrea virginica in Chesapeake Bay, USA).

Figure 3.

(a) Proportions of taxa with none/low, intermediate, and high preservation potential grouped into marine, brackish, freshwater, and terrestrial systems with data restricted to four invertebrate phyla (arthropods, cnidarians, echinoderms, and molluscs). The bar width is scaled to the square root of the total numbers of species (the numbers reported on Figure 1a). (b–f) The barplots of all IUCN-assessed species (b, d, and f) compared to barplots of a subset of those species that belonged to orders categorised as ‘preservable’ (c, e, and g). (b-c) Marine systems. (d-e) Freshwater systems. (f-g) Terrestrial systems. Different colours represent different IUCN conservation status categories. Brackish systems were excluded because almost all brackish species assessed by IUCN are preservable so the two plots would be virtually identical. All data from the IUCN Red List Database were accessed on 2/20/2023 (IUCN, 2023a).