The evolution of fishes and corals on reefs: form, function and interdependence

Abstract

Coral reefs are renowned for their spectacular biodiversity and the close links between fishes and corals. Despite extensive fossil records and common biogeographic histories, the evolution of these two key groups has rarely been considered together. We therefore examine recent advances in molecular phylogenetics and palaeoecology, and place the evolution of fishes and corals in a functional context. In critically reviewing the available fossil and phylogenetic evidence, we reveal a marked congruence in the evolution of the two groups. Despite one group consisting of swimming vertebrates and the other colonial symbiotic invertebrates, fishes and corals have remarkably similar evolutionary histories. In the Paleocene and Eocene [66-34 million years ago (Ma)] most modern fish and coral families were present, and both were represented by a wide range of functional morphotypes. However, there is little evidence of diversification at this time. By contrast, in the Oligocene and Miocene (34-5.3 Ma), both groups exhibited rapid lineage diversification. There is also evidence of increasing reef area, occupation of new habitats, increasing coral cover, and potentially, increasing fish abundance. Functionally, the Oligocene-Miocene is marked by the appearance of new fish and coral taxa associated with high-turnover fast-growth ecosystems and the colonization of reef flats. It is in this period that the functional characteristics of modern coral reefs were established. Most species, however, only arose in the last 5.3 million years (Myr; Plio-Pleistocene), with the average age of fish species being 5.3 Myr, and corals just 1.9 Myr. While these species are genetically distinct, phenotypic differences are often limited to variation in colour or minor morphological features. This suggests that the rapid increase in biodiversity during the last 5.3 Myr was not matched by changes in ecosystem function. For reef fishes, colour appears to be central to recent diversification. However, the presence of pigment patterns in the Eocene suggests that colour may not have driven recent diversification. Furthermore, the lack of functional changes in fishes or corals over the last 5 Myr raises questions over the role and importance of biodiversity in shaping the future of coral reefs.

Body size and mortality rates in coral reef fishes: a three-phase relationship

“…Remarkably, these small fishes are the most abundant size class on coral reefs [27]. Reef fishes have a mean length of just 45 mm and approximately half of all reef fishes may remain under this size threshold for their entire lives [27,38]. Growth appears to be critical for fishes in this mortality regime.…”

“…The average length of all reef fishes is just 45 mm [38]. These small fishes have relatively high mortality rates, and short lifespans [18,39].…”

“…Surprisingly, half of all reef fish individuals remain in this vulnerable phase two throughout their entire lives. This factor probably underlies the high productivity of cryptobenthic fish communities, driving the fast growth rates that fuel ecosystem processes [38]. By shaping population sizes and energetic and trophic connectivity in coral reef fishes, the relationship between body size and mortality rate appears to be a key factor in our understanding of the ecology of coral reef fishes.…”

Ontogenetic and phylogenetic simplification during white stripe evolution in clownfishes

“…Among vertebrates, coral reef fishes provide classical examples of complex color patterns exhibiting a huge variety, and therefore, they offer a unique opportunity to better understand, in an integrated manner, the origin of those traits [7]. Most of coral reef fish species display spots, stripes, repeated lines, eyespots, grids, etc.…”

The evolution of jaw protrusion mechanics has been tightly coupled to bentho-pelagic divergence in damselfishes (Pomacentridae)

“…The Pomacentridae are a successful lineage of nearshore reef fishes (399 extant species; Eschmeyer and Fricke, 2016) that are one of the dominant vertebrate groups on coral reefs (Bellwood and Hughes, 2001;Allen, 1991;Bellwood et al, 2016). These fishes are highly amenable to this type of study because the evolution of their cranial morphology has tracked repeated transitions between benthic and pelagic feeding niches Frédérich et al, 2013;Olivier et al, 2016).…”