Ontogeny of microhabitat use and two-step recruitment in a specialist reef fish, the Browncheek Blenny (Chaenopsidae)

Abstract

Ecological specialization is common on coral reefs and almost certainly contributes to the high diversity of fishes and invertebrates associated with reefs. Here, the recruitment pathway of an endemic Gulf of California fish, the Browncheek Blenny, Acanthemblemaria crockeri (Teleostei: Chaenopsidae), which specializes as an adult on vacant invertebrate tests or tubes, is reported. Like most reef fishes, Browncheek Blennies have a planktonic larval stage that leaves the reef and later settles on suitable habitat as a fully developed juvenile. These blennies follow a clear, ''two-step'' recruitment pathway, however, and do not reside in invertebrate tests until reaching an adult body size. Individual juveniles and adults were observed for 3 min intervals in order to develop average time budgets for this species. Members of both sexes and all post-settlement life-history stages were included in the analysis. The difference in habitat use by post-settlement juveniles and adults is striking; the average juvenile spends none of its time inside a test, and the average large adult spends all of its time inside a test. Using data on intermediate-sized individuals, the behavioral change associated with invading a test was determined to be size-cued, and it occurs between 20 and 30 mm standard length. Changes in feeding and predator avoidance behaviors are also associated with the ontogenetic shift from life in the open to life in a shelter. Addition of artificial shelters demonstrated the essential role of access to this specialized resource in the population regulation of adults but not juveniles of these blennies.

Shelters and Their Use by Fishes on Fringing Coral Reefs

“…Using observations plus experimental removal of shelters and increases in fish density, Robertson and Sheldon [22] did not find evidence for limitations in the availability of nocturnal shelters in the diurnal bluehead wrasse Thalassoma bifasciatum . On the other hand, studies of shelter addition [26] , [55] , density-dependent mortality in relation to shelter density [17] , [56] , and small, experimental artificial reefs [7] , [11] – [14] have provided evidence that population density does increase with greater shelter availability in coral reef fishes. Thus, our study adds support for the hypothesis that shelters are sometimes limiting by applying it to the assemblage of shelter-using fishes and to spatial variation in fish density within larger, natural reefs.…”

“…Among the studies that did measure and count shelters on reefs, very few presented the data and instead provided only correlations, qualitative indices or integrated measures from ordination analyses [2] , [10] , [18] – [21] , preventing comparisons among studies. To the best of our knowledge, no studies have examined variables that influence shelter availability other than coral cover and most studies of shelter use by coral reef fishes have focused on one or a few related species (e.g., [17] , [22] – [26] ). No study has attempted to identify the whole assemblage of shelter-using fishes or to document the variables that influence which of the available shelters are used.…”

Evolution of a Neotropical marine fish lineage (Subfamily Chaenopsinae, Suborder Blennioidei) based on phylogenetic analysis of combined molecular and morphological data

“…Chaenopsins are significant models for the study of ecology and evolution, in part because they are site attached, often abundant (Thomson and Gilligan, 2002) and readily observed. As a consequence, the ecology, habitat use and mating behavior of several species are relatively well known (e.g., Clarke, 1999;Hastings, 1986Hastings, , 1988aHastings, ,b, 1992aHastings, , 2001aHastings, , 2002Hastings and Galland, 2010;Lindquist, 1980Lindquist, , 1985. Tube blennies occupy shelters in a variety of ecological settings that include rocky reefs, coral reefs, and along the margins of these reefs where sand and shell rubble are common (see Table 1).…”

Extreme habitat specialisation and population structure of two gorgonian-associated pygmy seahorses

“…Ecological specialisation is common on coral reefs and is among the facets that enhance the biological diversity in this ecosystem , Wilson et al 2008, Hastings & Galland 2010. Habitat specialisation involving a patchy resource can determine population dynamics and social group size; however, the importance of such associations and the role they play in animal abundances and distributions are as yet unclear (Munday et al 1997, Munday 2002, Schiemer et al 2009.…”

“…A spectrum of habitat specialisation is found in coral reef species ranging from generalists, loosely associated with the physical structure of the reef, to extreme specialists found in an obligate association with a single species , Jones et al 2004). The populations of habitat specialists tend to be smaller than those of generalists and take longer to recover following perturbation, as a result of invasion by generalists and an inability of specialists to respond plastically to change (Vázquez & Simberloff 2002, Hastings & Galland 2010. The populations of some habitat specialists are closely linked with those of their preferred hosts, whilst others appear more loosely regulated by host abundance (Mitchell & Dill 2005).…”