Piscivore assemblages and predation pressure affect relative safety of some back-reef habitats for juvenile fish in a Caribbean bay

Abstract

An important process thought to drive habitat selection during (post-)settlement of coral reef fish is predation. It is assumed that in back-reef habitats such as seagrass beds and mangroves predation is lower than on coral reefs. However, recent studies have suggested that significant piscivore assemblages are present in back-reef habitats. The assumption of reduced predation pressure in back-reef habitats can therefore be debated. We compared piscivore assemblages along the coast of a Caribbean island using underwater visual census surveys in a spatial gradient of coral reefs, seagrass beds and mangroves. We also performed predation experiments in combination with video observations in these habitats using tethered recently settled Haemulon flavolineatum. High piscivore densities and reduced survival showed the presence of significant piscivore assemblages in both reef and back-reef habitats. Both reef-associated piscivores and piscivores that use back-reef habitats as a juvenile habitat contributed to the piscivore assemblage in the investigated gradient. Habitat type had a significant effect on the composition of the piscivore assemblage, density, and prey survival. Piscivore density was highest on the reef, mangroves and notches, all of which are habitats with a high structural complexity. On the contrary, seagrass beds showed lowest piscivore density. Tethering experiments showed lowest survival on the reef but also reduced survival on backreef habitats located close to the coral reef. Seagrass beds and mangroves located farther away from the reef into the bay showed highest survival. The present study shows that the concept of reduced predation in back-reef habitats used by juvenile fish does not apply to all habitats, since these habitats can harbour significant piscivore assemblages. However, depending on the spatial setting in the seascape (distance to the reef and presence of other habitat types), some Caribbean seagrass beds show low densities of piscivores and increased survival when compared to other habitats.

Growth potential and predation risk drive ontogenetic shifts among nursery habitats in a coral reef fish

“…Dorenbosch et al (2009) showed a similar degree of predation risk of early juveniles in bay habitats along a spatial gradient from the mouth of the bay. Therefore, predation risk is unlikely to act as the sole mechanism driving ontogenetic habitat shifts within the bay at this life stage.…”

“…Natural predators of H. flavolineatum can be diverse, but typically include large juvenile and adult predator fish species. At Curaçao, these include Ocyurus chrysurus and Lutjanus apodus in bay environments, while Aulostomus maculates is a common predator on the reef (Dorenbosch et al 2009). The risk of predation is highest during the nocturnal and dusk periods compared to diurnal periods (Danilowicz & Sale 1999).…”

“…to assess the effect of habitat and fish size on predation risk, not to measure absolute rates of predation. Although tethering experiments can produce biases that can confound results (Peterson & Black 1994), it is a widely used method to measure relative predation risk on a diverse suite of fish and invertebrate prey species (Shulman 1985, Acosta & Butler 1999, Dahlgren & Eggleston 2000, Baker & Sheaves 2007, Dorenbosch et al 2009). As the same tethering method was used across all habitats for the different fish size classes, possible tethering artifacts among treatments were expected to be relatively consistent (e.g.…”

“…In this study, we test the hypothesis that pervasive shifts among nursery habitats are driven by factors such as resource acquisition -which is integrated and expressed through habitat-based differences in growth rate, maturation rate, and condition. We further hypothesize that due to a lower predation risk in nurseries than adult habitats (Dorenbosch et al 2009, Grol et al 2011, factors other than predation risk (e.g. food availability) play a larger role in explaining ontogenetic shifts between nursery habitats.…”

Anthropogenic Disturbances in Estuarine Ecosystems: The Effects of Altered Freshwater Inflow, Introduction of Invasive Species, and Habitat Alteration in the Loxahatchee River, FL

“…Although no significant predation of lionfish has been documented in the Atlantic, the large predators (e.g., serranids) that may occasionally consume lionfish (Maljković et al 2008) are typically rare in estuarine systems compared to coral reefs (Dorenbosch et al 2009). The most abundant estuarine predators (e.g., juvenile lutjanids and carangids)…”