Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterflyfish species.

Avoiding costly fights can help conserve energy needed to survive rapid environmental change. Competitor recognition processes help resolve contests without escalating to attack, yet we have limited understanding of how they are affected by resource depletion and potential effects on species coexistence. Using a mass coral mortality event as a natural experiment and 3770 field observations of butterflyfish encounters, we test how rapid resource depletion could disrupt recognition processes in butterflyfishes. Following resource loss, heterospecifics approached each other more closely before initiating aggression, fewer contests were resolved by signalling, and the energy invested in attacks was greater. By contrast, behaviour towards conspecifics did not change. As predicted by theory, conspecifics approached one another more closely and were more consistent in attack intensity yet, contrary to expectations, resolution of contests via signalling was more common among heterospecifics. Phylogenetic relatedness or body size did not predict these outcomes. Our results suggest that competitor recognition processes for heterospecifics became less accurate after mass coral mortality, which we hypothesize is due to altered resource overlaps following dietary shifts. Our work implies that competitor recognition is common among heterospecifics, and disruption of this system could lead to suboptimal decision-making, exacerbating sublethal impacts of food scarcity.

Evaluating the effectiveness of teeth and dorsal fin spines for non-lethal age estimation of a tropical reef fish, coral trout Plectropomus leopardus.

This study investigated whether teeth and dorsal fin spines could be used as non-lethal methods of age estimation for a vulnerable and highly valued tropical fisheries species, coral trout Plectropomus leopardus. Age estimation of individuals from 2 to 9 years old revealed that dorsal spines represent an accurate ageing method (90% agreement with otoliths) that was more precise [average per cent error (APE) = 4·1, coefficient of variation (c.v.) = 5·8%] than otoliths (APE = 6·2, c.v. = 8·7%). Of the three methods for age estimation (otoliths, dorsal spines and teeth), spines were the most time and cost efficient. An aquarium-based study also found that removing a dorsal spine or tooth did not affect survivorship or growth of P. leopardus. No annuli were visible in teeth despite taking transverse and longitudinal sections throughout the tooth and trialling several different laboratory methods. Although teeth may not be suitable for estimating age of P. leopardus, dorsal spines appear to be an acceptably accurate, precise and efficient method for non-lethal ageing of individuals from 2 to 9 years old in this tropical species.

Historic hybridization and introgression between two iconic Australian anemonefish and contemporary patterns of population connectivity.

Endemic species on islands are considered at risk of extinction for several reasons, including limited dispersal abilities, small population sizes, and low genetic diversity. We used mitochondrial DNA (D-Loop) and 17 microsatellite loci to explore the evolutionary relationship between an endemic anemonefish, Amphiprion mccullochi (restricted to isolated locations in subtropical eastern Australia) and its more widespread sister species, A. akindynos. A mitochondrial DNA (mtDNA) phylogram showed reciprocal monophyly was lacking for the two species, with two supported groups, each containing representatives of both species, but no shared haplotypes and up to 12 species, but not location-specific management units (MUs). Population genetic analyses suggested evolutionary connectivity among samples of each species (mtDNA), while ecological connectivity was only evident among populations of the endemic, A. mccullochi. This suggests higher dispersal between endemic anemonefish populations at both evolutionary and ecological timeframes, despite separation by hundreds of kilometers. The complex mtDNA structure results from historical hybridization and introgression in the evolutionary past of these species, validated by msat analyses (NEWHYBRIDS, STRUCTURE, and DAPC). Both species had high genetic diversities (mtDNA h > 0.90, π = 4.0%; msat genetic diversity, gd > 0.670). While high gd and connectivity reduce extinction risk, identifying and protecting populations implicated in generating reticulate structure among these species should be a conservation priority.

Increased seawater temperature and decreased dissolved oxygen triggers fish kill at the Cocos (Keeling) Islands, Indian Ocean.

At the Cocos (Keeling) Islands in the north-eastern Indian Ocean >592 fishes from at least 11 species died in a series of events in December 2007, January and February 2008 and April 2009. The dead fishes were from a wide range of taxonomic families, indicating that conditions exceeded the tolerances of a broad array of species. The 2007-2008 die-off events occurred on the warmest and calmest days of a significantly warmer and calmer summer. Fishes died in the southern inshore areas of the coral atoll lagoon at survey sites where seawater temperature was highest (33-35° C) and dissolved oxygen was lowest (1·4-1·8 mg l⁻¹). The water temperature at these fish-kill survey sites (33-35° C) was significantly warmer than previous years (1997 to 2005, mean ±s.e. = 28·7 ± 0·1° C). Fishes probably died because they were unable to obtain the additional oxygen required for metabolism at higher temperatures. Repeated die-off events over the last 130 years indicate that some fishes have not yet adapted to rises in seawater temperature. This study provides empirical evidence to support suggestions that differences in physiological tolerances to increasing sea temperatures may be important in determining the structure of future coral-reef fish communities with respect to climate change.