Patterns of biogeographic and regional life-history trait variation in four large-bodied tropical wrasses

Ectotherms display substantial demographic variation across latitudinal gradients of temperature. Higher temperatures are often associated with smaller size, rapid initial growth rates, and early maturation, generally described as the Temperature-Size Rule (TSR). The longevity of most ectotherms also declines at warmer, lower latitudes. However, these patterns may be modified by increases in food resources that can flow on to continuous growth and large adult size. The present study estimates age-based demographic parameters of large-bodied tropical wrasses (Hemigymnus melapterus, H. fasciatus, Cheilinus fasciatus, and Oxycheilinus digramma) collected from Philippine fish markets (9-11 degrees N) and sampled from Palm (18.53-18.70 degrees S) and Whitsunday (20.05-20.21 degrees S) reefs on the Great Barrier Reef, Australia (GBR). Differences in longevity, initial growth rates, and the age at sexual maturation at a biogeographic scale, between the Philippines and GBR, conformed to predictions of the TSR. However, Philippine specimens exhibited greater relative body condition and sustained periods of growth beyond sexual maturity resulting in larger adult size than GBR samples. Size-structure data from Philippine marine reserves and fished sites indicated that these differences were not confounded by fishery-dependent sampling. Moreover, latitudinal length-weight relationships could not be explained by lower densities of the focal wrasses in the Philippines or by relative gonad size. Less pronounced patterns of demographic variation that differed across species were evident at a regional scale, among Palm and Whitsunday reefs. Patterns of demographic variation between the Philippines and GBR strongly suggest that differences in food resource levels will be important in explaining the observed geographic variation

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy-forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life-history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta-analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal-associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life-history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal-associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal-associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal-associated fish and fisheries