Resource use by Enneapterygius Rufopileus and Other Rockpool Fishes

Low-intertidal fish communities, including Enneapterygius rufopileus (Tripterygiidae), were studied in rockpools in Sydney, Australia to consider the role of physical factors and food availability in their distribution and abundance. The rockpool fish community in Sydney was speciose (23 species), of which 35% of individuals were E. rufopileus. Fish abundance and 13 physical and biological parameters were measured in twenty-two rockpools spread among 4 sites. Abundance of E. rufopileus was best predicted by the number of rock overhangs, algal cover (Zonaria sp. and Hormosira banksii), and the encrusting ascidian cunjevoi (Pyura sp.). Experimental increase or decrease in available shelter (mainly boulders and macroalgae) in rockpools did not significantly affect the abundance of fishes, however some pools consistently supported more fishes in total, despite repeated defaunation, indicating that underlying deterministic processes may have a significant effect on rockpool fish communities. The diet of Enneapterygius rufopileus included unidentified crustacean remains, harpacticoid copepods, and gastropods. Gastropod abundance was greater in the diets of larger fish, which also consumed more food overall. Total weight of food was not dependent on E. rufopileus density in pools or the densities of all fish species in pools. Therefore, the study does not support the hypothesis that resources were limiting for this fish species in rockpools.     

Aspects of the Cryobiology of the Intertidal Harpacticoid CopepodTigriopus brevicornis(O. F. Müller)

Cold-resistance studies of marine invertebrates have concentrated on intertidal sedentary organisms, which are often subjected to subzero air temperatures in winter. Mobile rock pool inhabitants have been rarely studied because such habitats are thought to buffer environmental variation. However, it is not uncommon for small upper-shore rock pools ( approximately 2 by 1 cm) to become completely frozen. Such supralittoral habitats are subject to extreme physicochemical fluctuations especially in salinity (0 to 300 per thousand) and temperature (-1 to +32degreesC) due to evaporation and dilution. The dominant invertebrate in such habitats is the harpacticoid copepod Tigriopus brevicornis. Aspects of the cryobiology of T. brevicornis were investigated using differential scanning calorimetry (DSC). Thermograms obtained from DSC allowed determinations of freeze-onset (supercooling point, SCP), melt-onset, and melt-peak (melting point, MP) temperatures, together with estimation of the proportion of water freezing in the samples. The effects of acclimation salinity, temperature, starvation, and reproductive state on these cryobiological parameters were investigated. Acclimation to increasing salinity depressed the SCP, with the highest salinity (70 per thousand) producing the lowest SCP, melt-onset, and MP temperatures at -27.5, -15.2, and -9.5degreesC respectively. The highest acclimation temperature (20degreesC) produced the lowest SCP (-23.4degreesC). Starvation significantly increased the SCP, melt-onset, and MP temperatures in comparison to fed individuals acclimated to the same salinity. The presence of eggs or ovaries in individual copepods elevated the SCP compared to nongravid females and males. LT50 studies showed that acclimation to high salinity improved the ability of T. brevicornis to survive in frozen seawater. Seventy parts per thousand acclimated individuals had an LT50 of 64.9 h compared with just 1.4 h for 5 per thousand acclimated individuals in frozen seawater at -5degreesC. The study shows that the cold-resistance capabilities of T. brevicornis can be affected by several different factors, and the link between the osmoconforming nature of this species and its cold resistance is discussed. Copyright 1997 Academic Press. Copyright 1997Academic Press     

A new species of Micragasma J. Sahlberg, 1900 (Coleoptera: Hydraenidae) from Crete

We describe a new species of Micragasma J. Sahlberg, 1900 (Coleoptera, Hydraenidae), which is here treated as a subgenus of Ochthebius Leach, 1815 Leach, W.E. (1815), ‘Entomology’, in The Edinburgh Encyclopaedia (Vol. 9), ed. D. Brewster, Balfour: Edinburgh, pp. 57–172. [Google Scholar]. The new species, O. (Micragasma) minoicus sp. n., was found at the margins of a coastal rockpool in the island of Crete. The species differs from the other two known species of Micragasma in both external and genital characters, but shares with them the presence of small setiferous tubercles on the surface of the head, pronotum and elytra, and a strong medial gibbosity on the head. In some characters, such as the structure and shape of the aedeagus, O. (M.) minoicus sp. n. is similar to other species of the genus Ochthebius, in particular of the subgenus Cobalius Rey, 1886 Rey, C. (1886), ‘Histoire naturelle des coléoptères de France (suite)’, Annales de la Société Linnéenne de Lyon, 32, 1–187, pl. 1–2.[Crossref] , [Google Scholar], typical of coastal rockpools.

http://zoobank.org/urn:lsid:zoobank.org:act:BCEAE1EE-7C5E-4017-A753-559738221502     

Aspects of the Cryobiology of the Intertidal Harpacticoid CopepodTigriopus brevicornis(O. F. Müller)

Cold-resistance studies of marine invertebrates have concentrated on intertidal sedentary organisms, which are often subjected to subzero air temperatures in winter. Mobile rock pool inhabitants have been rarely studied because such habitats are thought to buffer environmental variation. However, it is not uncommon for small upper-shore rock pools (2 by 1 cm) to become completely frozen. Such supralittoral habitats are subject to extreme physicochemical fluctuations especially in salinity (0 to 300‰) and temperature (−1 to +32°C) due to evaporation and dilution. The dominant invertebrate in such habitats is the harpacticoid copepodTigriopus brevicornis.Aspects of the cryobiology ofT. brevicorniswere investigated using differential scanning calorimetry (DSC). Thermograms obtained from DSC allowed determinations of freeze-onset (supercooling point, SCP), melt-onset, and melt-peak (melting point, MP) temperatures, together with estimation of the proportion of water freezing in the samples. The effects of acclimation salinity, temperature, starvation, and reproductive state on these cryobiological parameters were investigated. Acclimation to increasing salinity depressed the SCP, with the highest salinity (70‰) producing the lowest SCP, melt-onset, and MP temperatures at −27.5, −15.2, and −9.5°C respectively. The highest acclimation temperature (20°C) produced the lowest SCP (−23.4°C). Starvation significantly increased the SCP, melt-onset, and MP temperatures in comparison to fed individuals acclimated to the same salinity. The presence of eggs or ovaries in individual copepods elevated the SCP compared to nongravid females and males. LT₅₀studies showed that acclimation to high salinity improved the ability ofT. brevicornisto survive in frozen seawater. Seventy parts per thousand acclimated individuals had an LT₅₀of 64.9 h compared with just 1.4 h for 5‰ acclimated individuals in frozen seawater at −5°C. The study shows that the cold-resistance capabilities ofT. brevicorniscan be affected by several different factors, and the link between the osmoconforming nature of this species and its cold resistance is discussed.     

Interspecific competition in metapopulations

The assumptions and predictions of metapopulation models for competing species are discussed in relation to empirical studies of colonization and extinction in metapopulations. In three species of Daphnia in rockpools, interspecific competition increased local extinction rates, while no effects on colonization rates were detected. Distributional patterns were consistent with several predictions of the competition model; for example, the number of species on an island increased with the number of pools and the proportion of pools occupied by each species decreased with increasing species number. It is concluded that interspecific competition is important for the distributional dynamics of Daphnia species in rockpools, but the question whether the coexistence of these species depends on metapopulation dynamics is still unresolved. Other studies on the effects of interspecific competition on colonization and extinction rates are discussed.     

The effect of environmental variation on the reproductive development time and output of the high-shore rockpool copepod Tigriopus brevicornis

The extreme environmental changes observed in high-shore rockpools occupied by Tigriopus brevicornis, provide a significant physiological challenge that may have implications for the energetics and hence the life history characteristics of this species. The present study was designed to assess the effect of this environmental variation on the reproductive development time and output of T. brevicornis in terms of duration of the various stages in ovary and egg sac development and maturation as well as naupliar development time to the first copepodite stage and total numbers of copepodites produced.There was a significant difference in reproductive development time and output in the three test salinities with only successful development to copepodite I stage seen in normal seawater (35 psu). There was also a successful release of nauplii seen at the low salinity (5 psu), but no subsequent survival to the copepodite I stage, whilst there was not even a development of egg sacs in the high salinity test medium (70 psu). There was also a significant difference in reproductive development times in the three test temperatures with fastest ovary development in the high temperature (23 °C) and slowest development time in the lowest temperature (5 °C). However, it should be noted that the highest number of nauplii produced was actually in the mid temperature (12 °C), not the high temperature. Exposure to hypoxic and anoxic conditions had a significantly detrimental effect on reproductive development with slower development time through the reproductive stages and no individuals surviving to copepodite stage I from the hypoxic and anoxic test conditions, but good development from the normoxic conditions.The present study indicates that animals living in high-shore rockpools may incur a considerable energetic cost, due to the environmental changes that are characteristic of this habitat and the importance of resource allocation in these different physiological conditions is paramount to the species' survival.