Why the damselfishChromis chromisis a key species in theMediterranean rocky littoral – a quantitative perspective

Abstract

The damselfish Chromis chromis is typically the most abundant fish species in the rocky littoral environment of the Mediterranean Sea, where it feeds in huge shoals on incoming zooplankton and rests near the seabed each night. Research has shown that large populations of C. chromis play a fundamental role by transferring carbon, nitrogen and phosphorus directly from the pelagic system to the littoral in the form of solid and liquid wastes and therefore that this species acts as a vital conduit for nutrients. In addition, C. chromis represents a major prey item for predatory fish and seabirds, it has been shown to exert significant predation pressure on coastal zooplankton populations, but it is also a major consumer of fish eggs and hence may have a strong influence on the dynamics of other fish species. In this review paper the contention is that C. chromis represents a key species in the Mediterranean Sea rocky littoral. This view is supported by quantitative evidence that has been amassed over a number of years, but is collated here for the first time. Chromis chromis is of only minor importance to commercial fisheries (it is usually discarded), but trends in population abundance of this species can be indicative of levels of fishing pressure on other commercial species. It has been demonstrated that where predator numbers are able to recover from intensive fishing (e.g.in marine protected areas; MPAs), this is often mirrored by lower densities of C. chromis. Several papers have championed C. chromis as a possible indicator species for human disturbance. As well as being directly and indirectly affected by fishing, the species is also sensitive to a number of other anthropogenic pressures, most notably poor water quality and noise pollution.

Behavioural traits and feeding ecology of Mediterranean lionfish and native species naiveté to lionfish predation

“…Such patterns of predation mirror those found for Atlantic lionfish (Green & Côté 2014, Chappell & Smith 2016). For example, in the current study, the heavily predated species T. pavo and the other Labridae juveniles fit the description of a small and shallow body shape combined with demersal behaviour, while the most heavily predated on species C. chromis are small sized and gather over the rocky substratum to feed on meroplankton at dusk, to shelter during the night and to breed (Harmelin 1987, Aguzzi et al 2013, Pinnegar 2018). In comparison, despite juveniles of S. rivulatus and S. cretense being the second and third most abundant species at the broad-scale level, with intermediate fine-scale abundance, both were not an important prey species for Mediterranean lionfish.…”

“…As both C. chromis and T. pavo play fundamental roles in the Mediterranean ecosystem (Guidetti & Dulčić 2007, Milazzo et al 2011, Galasso et al 2015, Pinnegar 2018), selective predation and localised reduction in populations may have substantial flow-on effects on the wider marine community. For example, C. chromis populations channel carbon, phosphorus and nitrogen from the pelagic-zooplankton system to the rocky littoral environment in the form of liquid and solid waste (Bracciali et al 2012, Pinnegar 2018), subsidising nutrients in one of the most oligotrophic seas in the world (Krom et al 2014).…”

“…Furthermore, C. chromis is the most abundant prey species of meso-predator fish and seabirds, and a major consumer of zooplankton and fish eggs itself (Pinnegar 2018), meaning that reductions in the abundance of C. chromis may have a strong negative impact on the coastal food web. In parallel, T. pavo feeds on small molluscs, crustaceans, annelids and echinoderms (Guidetti 2004, Galasso et al 2015, Sinopoli et al 2017), with its population abundance having been linked to top-down regulation of sea urchin populations (Guidetti & Dulčić 2007, Galasso et al 2015).…”

Understanding fish populations

“…Finally, the theme of Celebrating 50 years of the FSBI is exemplified in a global context by a review by Lyndon (2018) of the impact of the FSBI Small Research Grants Scheme which has now been running for 25 years and has distributed over £560 000 to researchers around the world, and in more specific terms by an impressive argument presented by Pinnegar (2018)…”

“…Finally, the theme of Celebrating 50 years of the FSBI is exemplified in a global context by a review by Lyndon () of the impact of the FSBI Small Research Grants Scheme which has now been running for 25 years and has distributed over £560 000 to researchers around the world, and in more specific terms by an impressive argument presented by Pinnegar () for why the Mediterranean damselfish Chromis chromis (L. 1758) is a key species in the Mediterranean rocky intertidal. This final paper is particularly fitting and satisfying because as was explained in more detail during its presentation at the symposium, this extensive chain of research was primarily initiated by the award in 1996 of a PhD Studentship to its author who has subsequently served on FSBI Council, including as Honorary Secretary, and is currently a co‐convenor of FSBI's next symposium in 2018.…”