The importance of oceanic atoll lagoons for coral reef predators

Predators on coral reefs play an important ecological role structuring reef fish communities and are important fishery targets. It is thought that reef predator assemblages increase in density and diversity from inner lagoonal to outer edge reefs. Oceanic atolls may differ though, as nutrients are available throughout. Reef predator populations are declining, but there is little known about how their distributions may vary across oceanic atolls. Using a combination of underwater visual census and baited remote underwater video, this study aimed to compare reef predator populations between inner and outer reefs of North Malé Atoll (Maldives) and determine which reef metrics may drive any differences in assemblage structure. We found that predator assemblages were significantly different between inner and outer atoll. Body sizes of several predator families were consistently larger in the outer atoll, however, abundance, biomass and species richness were similar between outer edge reefs and inner lagoonal reefs suggesting atoll lagoons may be undervalued habitats. Depth and complexity were consistently important predictors of the predator assemblage. Inner atoll lagoonal habitat is equally as important for reef predator assemblages as outer reef slopes, although the dominant species differ. This study provides important information on reef predator populations in the Maldives, where detailed assessments of the reef predator assemblage are lacking but the reef fishery is thriving and annual catch will continue to increase.

Diverse and durophagous: Early Carboniferous chondrichthyans from the Scottish Borders

ABSTRACTChondrichthyan teeth from a new locality in the Scottish Borders supply additional evidence of Early Carboniferous chondrichthyans in the UK. The interbedded dolostones and siltstones of the Ballagan Formation exposed along Whitrope Burn are interpreted as representing a restricted lagoonal environment that received significant amounts of land-derived sediment. This site is palynologically dated to the latest Tournaisian–early Viséan. The diverse dental fauna documented here is dominated by large crushing holocephalan toothplates, with very few, small non-crushing chondrichthyan teeth. Two new taxa are named and described. Our samples are consistent with worldwide evidence that chondrichthyan crushing faunas are common following the Hangenberg extinction event. The lagoonal habitat represented by Whitrope Burn may represent a temporary refugium that was host to a near-relict fauna dominated by large holocephalan chondrichthyans with crushing dentitions. Many of these had already become scarce in other localities by the Viséan and become extinct later in the Carboniferous. This fauna provides evidence of early endemism or niche separation within European chondrichthyan faunas at this time. This evidence points to a complex picture in which the diversity of durophagous chondrichthyans is controlled by narrow spatial shifts in niche availability over time.

Annelid fauna of a Mediterranean lagoon (Gialova Lagoon, south-west Greece): community structure in a severely fluctuating environment

The annelid community of a shallow Mediterranean lagoon (Gialova Lagoon, Ionian Sea) was studied on a seasonal basis. Out of the 39 species identified eight are reported for the first time from the central Mediterranean. The dominant species were the polychaetes Capitella capitata, Neodexiospira pseudocorrugata, Malacoceros fuliginosus, Perinereis cultrifera, Hediste diversicolor, Heteromastus filiformis and the oligochaete Limnodriloides maslinicensis. Uni- and multivariate methods were employed to study the community structure. The coenocline observed is strongly related to the degree of isolation; its main features (i.e. number of species, density, geometric abundance and size-classes) in space and time are presented and discussed in detail. The distribution pattern of the annelid community has been found to be governed by a different set of environmental factors in each season. Although this narrow lagoonal habitat suffers severe dystrophic episodes it manages to recover, demonstrating a seasonal community pattern.