Storm versus calm: Variation in fauna associated with drifting macrophytes in sandy beach surf zones

New insights about nearshore dynamics came from studying the effects of regular storms in South Australia on drifting marine macrophytes, consequent wrack accumulation and associated fauna in beach surf zones across three different regions. This study examined whether the influence of storms may be more pronounced in sheltered coastal waters compared to more exposed coastlines where biota could have adaptations to persist in larger swell conditions. There were obvious regional differences for wrack species richness, abundances and assemblages that matched the attached floral subtidal landscape in each region. Consequently, invertebrates also differed amongst regions, which highlight the close affinity that some invertebrates have with drifting macrophytes. Fish were not so closely aligned to the regional patterns identified for wrack or invertebrates suggesting that many fish are using wrack accumulations as habitat but, being highly mobile, they may actively and constantly move into, out of and within these habitat features. Well-known beach-type models focused upon beach morphology may be more pertinent to the ecology of the surf zones offshore than previously thought, being the most consistent indicator of wrack accumulations and their fauna. This new evidence on the ecology of nearshore waters during storm versus calm weather in multiple regions and the subsequent influence on wrack-fauna associations in sandy-beach surf zones are important for future beach management, particularly when and where large wrack accumulations occur.