Subtidal littering: Indirect effects on soft substratum macrofauna?

Changes in macrofauna community structure, abundance and species richness were examined both before and one year after the deployment of plastic and glass bottles at littered (litter density: 16 items / 100 m2) and non-littered (control) surfaces at three unimpacted coastal areas of the western Saronikos Gulf (Greece). In parallel, LOI% at the adjacent sediments and changes in the composition of feeding types of the megaepifauna that colonized the litter were examined across treatments. Significant changes in macrofauna community structure were demonstrated between before and after littering. At only one of the sites was there detected a significant difference in macrofauna community structure between control and littered plots after littering. This difference was linked with a significant increase in the abundance of opportunistic polychaete species and LOI% levels in the sediment surface due to the entrapment of macrophytal debris within the littered surface. The study did not show a consistent direct response of macroinfauna community to litter and the associated megafauna. Unlike the megafauna attracted by litter items, soft-substratum macrofauna is less responsive to the addition of novel hard substrates in adjacent sediments. Alternatively, it could be that the impact of littering with small items triggers a macrofauna response detectable in the long-run

Abundance of Octopus vulgaris on soft sediment

Until now the distribution and abundance of Octopus vulgaris had been investigated in the main fishing areas of the species only by fishing surveys. The catching efficiency of fishing gear is variable and depends on several aspects of the animal's behaviour and life history as well as on the type of the gear and the environmental characteristics of the area surveyed. A good alternative for studying the abundance of octopus is by visual census. The population density of O. vulgaris was measured by visual census with scuba diving. The survey was conducted in coastal areas of Greece and on soft sediment. O. vulgaris density ranged from 0 to 6.88 individuals/1000m2 and the mean density values of this study were much higher than those mentioned in other papers. Octopus density was significantly associated with season. Densities of octopuses lower than 500 g were higher in coarse sediments than in finer ones. The density of large octopuses (> 500 g) increased with depth. Octopuses larger than 200 g tended to dwell deeper during the period of intense thermocline than during the nothermocline period

Seasonal population dynamics of Octopus vulgaris in the eastern Mediterranean

The population density of Octopus vulgaris was measured by visual census with scuba diving in coastal areas in Greece (eastern Mediterranean). A time-variant, stage-classified, matrix population model was developed to interpret the seasonal variation of octopus stage densities and to estimate several life cycle parameters. An annual and a semi-annual periodic cycle were found in the stage densities. A main peak of benthic settlement was observed during summer and a secondary, irregular one during late autumn. Two spawning peaks were estimated, a main one during late winter-spring and a secondary one during late summer-early autumn. More than 50% of the just-settled individuals will eventually die after 3 months. Mortality rate declines, as individuals grow larger, reaches a minimum approximately 6 months after settlement, and then grows again probably because of terminal spawning. The life expectancy of recently settled individuals (<50 g) during their summer peak is approximately 5 months. The lifespan of the common octopus is estimated to be between 12 and 15 months. The octopuses' mean specific growth rates (±s.d.) in their natural environment were 1.61 ± 0.30 d -1 for 50-200 g individuals and 1.19 ± 0.31 d-1 for 200-500 g individuals. © 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved

Den ecology of Octopus vulgaris Cuvier, 1797, on soft sediment: Availability and types of shelter

To avoid predation, octopuses select and actively modify shelters (also called dens) in the substratum, where they remain most of the time, especially during daylight hours. The main questions that this study deals with are: Is den availability a significant constraint for the distribution of Octopus vulgaris on soft sediment? What kind of dens does O. vulgaris use on soft sediment and what factors affect the selection of one type instead of another? With population density measurements by SCUBA diving and enrichment experiments with artificial dens, we concluded that the availability of solid materials necessary for den construction is a limiting factor for the distribution of O. vulgaris on soft sediment. O. vulgaris used four different types of den on soft sediment: "well" (a vertical hole in the sediment), "rock/stone" (the octopus uses a rock or a large stone to dig a cavity under it), "shell" (an empty shell is used), "human origin" (a solid material of human origin is used). The relative proportion of the four types of den in the areas studied was: 38.7% "human origin", 29.7% "well", 21.5% "rock/stone", 2.9% "shell". Also, 7.3% of the octopuses were found outside their den. The main types of den were found in different relative proportions in relation to the depth, the distance from shore, the octopus size and the granulometry of the sediment

Effects of sublethal concentration of zinc on survival and fertility in four successive generations of Tisbe

In this study we determined the survival and fertility of successive generations of the harpacticoid copepod Tisbe holothuriae, after exposure to three sublethal concentrations of zinc (0.07; 0.01 and 0.007 ppm Zn). A direct relationship between mortality, exposure time and zinc concentration was observed. For the 0.07 ppm Zn concentration, equal to 1 10 of the 48 h LC50 population size is reduced to zero after the first generation whereas the population size of the fourth generation is not affected by a concentration of 0.007 ppm Zn. © 1988

Spatial and seasonal variations in size, body volume and body proportion (prosome:urosome ratio) of the copepod Acartia tonsa in a semi-closed ecosystem (Berre lagoon, western Mediterranean)

Variations in size (prosome), body volume and proportion (prosome:urosome ratio) of female Acartia tonsa copepods were studied during three different seasons (June, October and November) in a network of 13 stations distributed throughout the Berre Lagoon, near Marseille. Strong morphological differences were found between the populations collected through the different seasonal surveys, but also between the different stations or groups of stations. They were related to the variations of environmental parameters (temperature, salinity, chlorophyll, particulate seston) according to the season and to the location of the stations (submitted to the marine influence in the south and to the intake of fresh water in the north of the lagoon). Considering all seasonal data, the size and body volume were inversely related to temperature. Body volume also showed a negative correlation with chlorophyll and carbon and a positive one with the C:N ratio of particles. The body proportion was positively correlated with temperature, chlorophyll and carbon. For each seasonal survey, the relationship between morphological features and environmental factors did not reach the significant level except in October when body proportion and volume were positively correlated to chlorophyll. Nevertheless, for each season, significant spatial changes in size or body proportion appeared in parts of the population of Acartia tonsa, in relation with local specific conditions of environmental factors, especially chlorophyll. These biometric differences suggest that individuals must develop in situ for at least the final period of larval growth, despite the dispersion effect caused by hydrodynamic movements. This stability in horizontal distribution may result from the diurnal vertical migrations of copepods between the surface and the bottom, two layers displaying currents of opposite directions. These results justify the use of somatic features (size and body proportion) to discriminate sets of individuals belonging to the same population

Modelling the effect of temperature on hatching and settlement patterns of meroplanktonic organisms: The case of the octopus

The duration of embryonic development and the planktonic stage of meroplanktonic species is highly temperature dependent and thus the seasonal temperature oscillations of temperate regions greatly affect the patterns of hatching and benthic settlement. Based on data from the literature on embryonic development and planktonic duration of Octopus vulgaris (common octopus) in relation to temperature, and on observed temperature patterns, several models of hatching and settlement patterns were created. There was a good fit between observed settlement patterns and model predictions. Based on these models we concluded that in temperate regions: (1) when temperature is increasing (from early spring to mid summer) the hatching and settlement periods tend to shorten, while when the temperature is decreasing (during autumn) the hatching and settlement periods tend to lengthen; (2) hatching and settlement peaks are narrower and more intense than a spring spawning peak but wider and less intense than an autumn spawning peak; (3) at lower latitudes, hatching and settlement patterns tend to follow the spawning pattern more closely, (4) the periodic temperature pattern of temperate areas has the potential to cause a convergence of hatching during spring

The longevity of three generations of normal and pollution-impacted Acartia clausi (Copepoda) populations in the Saronicos Gulf (Greece)

The longevity of two populations of the planktonic copepod Acartia clausi in the Saronicos Gulf was estimated. One group lived in a heavily polluted area, the other group in a relatively clean area. Three annual generations were studied. A comparison was also made between fed and unfed animals. A temperature of 14°C appeared to be the most favourable for the survival of Acartia; however, the optimum survival temperature depended also upon the generation to which the Acartia belonged. The acclimatization temperature has a strong influence on survival. Acartia in its natural environment thrives best and has maximum longevity at colder temperatures. The pollution-adapted Acartia population survived longer under laboratory-controlled conditions than the population living in a non-polluted area. © 1981 Dr. W. Junk b.v. Publishers