Survival of strandline spiders maintained on a diet of the kelp fly Thoracochaeta ancudensis (Sphaeroceridae)
Spiders commonly occur in marine strandlines, although with the exception of a few specialist species little is known of the behaviour and diet of spiders which occur in this habitat. In this study, 48 spiders were collected from strandlines at New Brighton beach, Canterbury, caged in plastic boxes and maintained under laboratory conditions. The spiders belonged to seven species: 15 Tenuiphantes tenuis, 10 Anoteropsis litoralis, 6 Anoteropsis hilaris, 7 Cryptachaea blattea, 4 Steatoda capensis, 4 Nyssus coloripes and 2 Ostearius melanopygius. The spiders were maintained for a maximum of 40 days on a diet of adult Thoracochaeta ancudensis, a species of sphaerocerid kelp fly, which is often highly abundant in strandlines in this region. Individuals of all spider species were observed attacking, capturing and feeding upon Thoracochaeta ancudensis, usually within 5 minutes of the fly being introduced. There were differences in patterns of survival among the spider species, although at least one individual of each species survived for the full duration of the 40 day trial. Anoteropsis hilaris, Cryptachaea blattea, Nyssus coloripes and Steotoda capensis exhibited high levels of survival, whereas Anoteropsis hilaris and Tenuiphantes tenuis did not perform well under these conditions. The results indicate that all the species of spider we examined will attack and feed on Thoracochaeta ancudensis, and we can speculate these behaviours may form a part of food webs in the strandline habitat under natural conditions. However, a diet consisting of just this prey species does not support long-term survival for all spider species we examined.