Elevated size and body condition and altered feeding ecology of the grouper Cephalopholis argus in non-native habitats

Abstract

In 1956, the shallow-water grouper Cephalopholis argus was introduced from Moorea (French Polynesia), where grouper diversity (14 species) is high, to the Main Hawaiian Islands (MHI), where only 2 rare native deep-water groupers occur. In this non-native environment, the species has flourished and has become the dominant apex predator on many reefs. In the present study, a comparison of non-native populations of C. argus in the MHI with native populations in Moorea showed that mean total length (32.0 vs. 26.9 cm), mass (722 vs. 326 g), growth, and body condition were each significantly elevated in the MHI. In addition, while an ontogenetic shift towards larger prey occurred in both locations, it was faster and more consistent in Moorea than in the MHI. As a result, while small C. argus of comparable size in the 2 locations consumed similar-sized prey, large C. argus in Moorea consumed significantly longer and deeper-bodied prey than their counterparts in the MHI. This pattern was unrelated to the size distributions of available prey and may thus reflect stronger intra-and interspecific competition for small prey in Moorea. Although ecological release in a broader sense (i.e. a combination of predator release, parasite release, and competitive release) may play a role, the most direct explanation for the observed differences between C. argus in native habitats in Moorea (with many competing grouper species) and non-native habitats in the MHI (few competitors) would be competitive release (here used in the sense of benefits resulting from the reduction of interspecific competition). KEY WORDS: Competitive release · Ecological release · Interspecific competition · Niche shift · Invasive species · Peacock hind · Main Hawaiian Islands · Moorea (French Polynesia)Resale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 439: 203-212, 2011 204 Due to their geographic and hydrographic isolation, the Main Hawaiian Islands (MHI hereafter) have a unique assemblage of coral reef and shore fish species, with one of the highest rates of endemism (~25%) in the world (Randall 2007). Compared to most tropical Pacific locations, several fish families are underrepresented or completely absent from the shallow inshore reefs of the MHI. Among these is the family Serranidae, specifically the subfamily Epinephelinae, or groupers (Randall 1987). In 1956, the grouper species peacock hind, Cephalopholis argus, was introduced into this environment from Moorea, French Polynesia (where it is known as 'roi') (see Fig. 1) in an attempt to create a grouper fishery (Oda & Parrish 1981, Randall 1987. Initially introduced to the islands of Oahu and Hawaii, it has since spread to all of the MHI, and has become the domi nant apex predator on many reefs ). Concern about potential negative effects of this -in evolutionary terms -new predation source on native Hawaiian reef fish assemblages, which have evolved without shallow water groupers, have resulted in recent investigations of the feeding ecolo...

Biodiversity effects of the predation gauntlet

“…There were, however, two notable predator species that disproportionately affected rare prey species and significantly lowered rarefied diversity: the dottyback Pseudochromis fuscus (Almany et al 2007) and peacock grouper Cephalopholis argus . From a conservation perspective, this disproportionate effect on rare species is particularly concerning in the case of the peacock grouper, because this non-native mesopredator, introduced to Hawaii in the mid-1950s, now constitutes more than 80% of the large piscivore biomass in some locations (Meyer and Dierking 2011). The unique effects of these two species suggest we need to further study the foraging behavior of mesopredators and in particular their functional responses (sensu Stier et al 2013a;Stier and White 2014), because predators with a preference for rare species and a Type I or II functional response can destabilize prey population dynamics and catalyze reductions in reef biodiversity (White et al 2010).…”

“…Abundance of coral-reef mesopredators (e.g., small-bodied groupers and snappers) has also increased through the introduction of non-native predators. In some cases, these introduced predators have become extremely successful, for example, the intentionally introduced peacock grouper (Cephalopholis argus) in Hawaii (Meyer and Dierking 2011) and the accidentally introduced Pacific lionfishes (Pterois volitans and Pterois miles) in the Atlantic and Caribbean (Côté et al 2013) have each become numerically dominant mesopredators in their respective invaded communities. Because predation is known to be a key driver of ecosystem and evolutionary dynamics (Hixon 1991(Hixon , 2015, these fishing-and invasion-associated shifts in the abundance and biomass of predators are considered cause for concern among coral-reef managers and conservation practitioners.…”

Demographic patterns in the peacock grouper (Cephalopholis argus), an introduced Hawaiian reef fish

“…This behavior requires suitable habitat as the availability of prey resources have been shown to increase with both habitat composition and complexity (Ruttenberg et al 2005, Shibuno et al 2008. Therefore, it is not surprising that C. argus is typically found in coral rich habitats and feeds primarily on small, reef-associated fishes (Meyer & Dierking 2011). By extension it is expected that fishes will be more robust, grow to larger sizes, and live to greater ages when there are more resources and/or preferable habitats.…”

“…In Hawaii, the diet of C. argus is composed of fishes across a wide range of taxa, including acanthurids, holocentrids, and chaetodontids among many others (Dierking et al 2009). A study found that length, weight, and body condition were significantly greater for C. argus in Hawaii than in a native South Pacific population, indicating competitive release (Meyer & Dierking 2011).…”

Working with, not against, coral-reef fisheries

“…This has certainly been in part because the WHFC has set aside about 35% of the coast as reserves, but it is possibly also because larger individuals are left for population replenishment. In addition, the introduced predator Cephalopholis argus cannot efficiently prey on larger individuals (Meyer and Dierking 2011). Slot-limit fishing and predation may both be occurring and contributing to a sustainable fishery.…”