To redress the paucity of knowledge about the ecology of soft sediment intertidal pools, the physical characteristics of the pools, along with diet and tidal changes in the distribution of common nekton inhabiting these pools were studied. Studies conducted to determine the importance of these intertidal pools to the dominant species of nekton included temperature physiological tolerance studies, colonization and recolonisation studies, and movement pattern studies. Little is known about the ecology of soft sediment intertidal pools. These ephemeral structures are chiefly made by the feeding and burrowing behaviour of several species of sting rays (including Dasyatis kuhlii and Himantura uarnak) that inhabit the coastal waters of Moreton Bay, Queensland, Australia. A preliminary survey showed that common inhabitants of these pools include summer whiting, Sillago ciliata, the eastern king prawn, Penaeus plebejus,
and the spotted sand goby, Favonigobius lentiginosus .
In the process of studying these pools, a specific method of sampling (carbon dioxide bubbling) these areas was first developed and refined. During the CO2 study, it was found that between 120 and 150 sees gassing at 15 L/min was required for collection of the entire nekton community of each pool (avg size 12,708 cm3). Gassing in excess of 300 sees resulted in the mortality of all nekton. It was found that temperature did not alter during gassing but pH dropped considerably from 8.00 to 5.10. Recovery of the pool pH took approximately four hours.
Studies into the temporal persistence of these intertidal pools predicted that these pools usually last between one and three weeks if the weather conditions remained calm and if the sting rays did not feed over the same pools. It was also found that the pH and salinity remained relatively constant
throughout the year, while temperature was dependent on sampling times.
Seasonal abundance studies showed that S. ciliata decreased in abundance from May to August with higher numbers recorded from September to April, whereas P. plebejus and F. lentiginosus were abundant throughout the year. There was a significant seasonal variation in body size for both S. ciliata and P. plebejus, with an increase in length in a season. There was no significant seasonal variation in mean length of F. lentiginosus. Results also show that whereas only juvenile S. ciliata and P. plebejus were found in intertidal pools, juvenile, sub-adult and adult F. lentiginosus inhabited these pools.
The diets of two dominant fish of soft sediment intertidal pools in Moreton Bay (S. ciliata
and F. lentiginosus) were assessed at different tidal stages and for different areas of intertidal habitats to assess the extent of dietary overlap and whether these fish feed while occupying intertidal pools. Dietary overlap was low, with gobies consuming a greater range of prey items and including larger prey items such as polychaetes, amphipods and fish. Sillago ciliata consumed mainly meiobenthic and pelagic zooplankton. Both species fed when pools were immersed, but their Gut Fullness Index (GFI) values did not differ significantly between the four spatio-tidal zones; low water, high water, pool area at high tide and pools during low tide. The relatively and consistently lower GFI values suggest that F. lentiginosus may feed at night. The study indicates that intertidal pools are foraging habitats for S. ciliata and therefore constitute a nursery habitat for this species.
experiments on the nekton showed an ability to tolerate temperatures of up to 40°C when tested in the laboratory, and Qio values indicate that these intertidal nekton increased their metabolic rate with increased temperature but exhibited evidence of thermoregulation. Favonigobius lentiginosus regulated its metabolic rate until temperatures were greater than 28°C, after which there was a significant change in metabolic rate. Penaeus plebejus regulated its metabolic rate at a constant at both the lower (20°C and 24°C) and upper (32°C and 36°C) end of the temperature range tested. A site effect was found where animals collected from the One Mile Beach site had significantly lower metabolic rates than animals from Bramble Bay.
Colonisation experiments that were performed by constructing artificial intertidal pools indicated that pools were colonized during each tidal cycle and
that the artificial pools were recolonized by the same species and size range of species as those found originally inhabiting the pools prior to defaunation.
Soft sediment intertidal pools provide nursery habitats for the early life stages of S. ciliata and P. plebejus in Moreton Bay, and permanent habitats for F. lentiginosus. This habitat has rarely been examined, yet appears to support high densities of individuals throughout the year. Their recognition as nursery habitats is important as intertidal areas are most commonly influenced by pollution events (e.g. oil spills, storm water drainage). Their role should be recognised in management plans for marine conservation and the fisheries for P. plebejus and S. ciliata.