Keeping It Local: Dispersal Limitations of Coral Larvae to the High Latitude Coral Reefs of the Houtman Abrolhos Islands

Abstract

In 2011 the first recorded bleaching event for the high latitude Houtman Abrolhos Islands (HAI) coral communities was documented. This bleaching event highlighted the question of whether a supply of ‘heat tolerant’ coral recruits from the tropical north would be sufficient to provide a level of resistance for these reefs to future warming events. Using Lagrangian modelling we showed that due to its regional isolation, large-scale larval input from potential tropical northern source populations to the HAI is unlikely, despite the southward flowing Leeuwin current. Successful recruitment to artificial substrates was recorded following the bleaching event. However, this was negligible (0.4 ± 0.1 recruits per tile) compared to 2013 post impact recruitment (128.8 ± 15.8 recruits per tile). Our data therefore provides preliminary evidence suggesting that the connectivity of the HAI with coral communities in the north is limited, and population maintenance and recovery is likely driven primarily by self-recruitment. Given the low thermal tolerance of the HAI coral communities, the dominance of Acropora, and the apparent reliance on self-recruitment, an increased frequency of thermally anomalous conditions at the HAI (such as experienced in 2011) has the potential to reduce the long-term stability of the HAI coral populations and species that depend upon them.

Expansion of corals on temperate reefs: direct and indirect effects of marine heatwaves

“…Edmunds et al 2001), it is likely the long duration and high intensity of the 2011 heatwave would have had deleterious effects on reproduction and early life stages. Specifically, coral recruitment (likely due to reduced reproductive output) at the Houtman Abrolhos Islands (approximately 70 km northwest of the study region) in 2011 and 2012 was significantly reduced compared to subsequent cooler years, (Markey et al 2016). Further, adult coral colonies, which are generally more resilient to temperature stress than early life stages (larvae and microscopic recruits), experienced bleaching and reduced growth during the heatwave periods Thomson et al 2011;Abdo et al 2012;Moore et al 2012;Smale and Wernberg 2012;Foster et al 2014).…”

“…Long-distance dispersal from upstream sources would be required for an increase in warm-water species as the nearest coral reefs are ~70 km offshore at the Houtman Abrolhos Islands (28˚S). Under normal conditions, larval longevity could favour connectivity between the Houtman Abrolhos Islands and the mid-west as after ~100 d (the last stage of coral mortality) patterns show increasing mortality (Graham et al 2008;Markey et al 2016).…”

Restricted gene flow and local adaptation highlight the vulnerability of high‐latitude reefs to rapid environmental change

“…Little is known about coral larval recruitment in the islands, but coral communities have been previously thought to be reliant on the Leeuwin Current and larvae from the north to maintain healthy populations (Simpson, ; Babcock et al ., ). Similarity in community composition between the Houtman Abrolhos Islands and central range populations indicates an evolutionary connection, but recent analyses using Lagrangian particle tracking models suggest that the islands are largely self‐seeding and are not connected on ecological time scales (Markey et al ., ). Furthermore, high levels of genetic differentiation have been identified in populations of P. damicornis between Ningaloo Reef and the Houtman Abrolhos Islands based on allozyme analyses (Whitaker, ).…”

Understanding marine larval dispersal in a broadcast-spawning invertebrate: A dispersal modelling approach for optimising spat collection of the Fijian black-lip pearl oyster Pinctada margaritifera

“…each particle position was calculated using a bi-linear interpolation of the gridded surface currents, where only surface currents are taken into account and vertical movements neglected [14]. The particle age was retained and increased with simulation progression.…”

“…Biophysical models typically incorporate biological and physical information, and seek to identify dispersal pathways between larval source (spawning) and sink (recruitment) sites, along with transport corridors between them [7]. Models have also been used to support population genetic analyses to determine connectivity [6,12,13], evaluate biological factors affecting larval dispersal [7,10,14] and develop dispersal models for particular taxa [9,15,16]. For sedentary benthic taxa such as bivalve molluscs, stocks may occupy a discrete geographic region as large as an entire reef system, or as small as a single bivalve bed [5].…”