Fishes on coral reefs: changing roles over the past 240 million years

Abstract

Key morphological traits reveal changes in functional morphospace occupation of reef fish assemblages over time. We used measurements of key functional attributes (i.e., lower jaw length and orbit diameter) of 208 fossil fish species from five geological periods to create bivariate plots of functional morphological traits through time. These plots were used to examine possible function and ecological characteristics of fossil reef fish assemblages throughout the Mesozoic and Cenozoic. A previously unknown trend of increasing orbit diameter over time became apparent. The Teleostei are the principal drivers of this change. The Eocene appears to mark a dramatic increase in two previously rare feeding modes in fishes: nocturnal feeding and high-precision benthic feeding. Interestingly, members of the Pycnodontiformes had relatively large eyes since the Triassic and appear to be the ecological precursors of their later teleost counterparts and may have been among the earliest nocturnal feeding fishes. Our results highlight potential changes in the roles of fishes on coral reefs through time.

Evolution of long-toothed fishes and the changing nature of fish–benthos interactions on coral reefs

“…These were compared with representatives from 45 extant genera from the Great Barrier Reef (GBR). The fossil assemblages all had coral-bearing hard grounds in the vicinity and, with excellent preservation, provide an indication of the functional capabilities of fishes in the vicinity of coral reefs through time 14,19,25 .…”

“…It is interesting that specialized detritivory arose so late in reef fish history, as most reef fish families, and associated feeding modes, were well established in the early Cenozoic 19,41,46 . The Cenozoic thus seems to have had two waves of trophic innovation, with an early Palaeocene-Eocene phase in which major reef fish groups and basic feeding modes were established, and a later OligoceneMiocene phase where more specialized feeding modes arose.…”

“…These items are characterized by high rates of consumption, rapid digestion and the potential to support a dynamic high-productivity low standing-stock system 9 , the essence of a modern coral reef ecosystem. 19 . These were compared with representatives from 45 extant genera from the Great Barrier Reef (GBR).…”

“…These changes in the benthos mirror shifts in grazing invertebrate groups in the Mesozoic and the rise of grazing fishes in the Cenozoic 13,14 . These latter changes in fishes represent part of a broader reassembly of fish morphotypes through time 18,19 .…”

“…In many cases, changes in fish morphology and the appearance of new higher taxonomic groups mark major shifts in the nature of fish-benthos interactions 14,19,20 . However, on modern reefs, and in aquatic systems in general, herbivory and other biotic interactions are characterized by considerable complexity 16,21 .…”