The Epibiotic and Endolithic Species Associated with the Gastropod Shells inhabited by the Hermit Crabs Paguristes Oculatus and Pagurus Cuanensis

Abstract. Over 120 species, including epizoites, endolithic organisms, and an epiflora are associated with the gastropod shells inhabited by the hermit crabs Paguristes oculatus and Pagurus cuanensis in the North Adriatic Sea (Gulf of Trieste). The symbiotic organisms include members of three trophic levels - primary producers (rhodophytes), primary consumers (active and passive filter feeders), and secondary consumers (carnivorous species). Many of the invertebrates show a preferred distribution on the shells. The shells are a mobile substratum for a specific community. They are a sediment- and predator-free surface, and for their size are extremely stable substrates in terms of both time and orientation.
The hermit crab microbiocoenosis is a dynamic phenomenon that can be studied as a functional unit. The symbionts are responsible for two simultaneous processes - a constructive and a destructive process on the shells. Shell deterioration is due primarily to biological processes, not to mechanical destruction. The more frequently occurring species were classified according to their role in reinforcing or weakening shell structure. These developments are related to hermit crab activity. Epizoites grow through several shell changes by hermit crabs, and a number of forms are capable of surviving the final deposition of the shells.     

Mass Mortality in the Gulf of Trieste: The Course of Community Destruction

Abstract. Over a period of two weeks in September, 1983 a high biomass macroepifauna community characteristic of a greater part of the Gulf of Trieste suffered mass mortality. The affected area is estimated to cover several hundred km2. Within 2–3 days all sponges and the brittle star Ophiothrix quinquemaculata, which together make up over 60 % of the community biomass, were dead. Benthic fish, mostly gobiids, were already affected on the first day and littered the bottom in great numbers. Concurrently the complete spectrum of macroinfauna species including (in order of emergence) holothurians, burrowing shrimp, echinoids, polychaetes, sipunculids and bivalves appeared on the sediment surface. Within one week sea stars and all remaining ophiurids had died. At this time hermit crabs were found lying dead next to their shells. Several anemones survived into the last week, although many showed signs of severe stress and lay on the surface with exposed pedal discs. Oxygen deficiency is the apparent immediate cause of this phenomenon and several possible factors leading to anoxic conditions in the Gulf are discussed. This ecological catastrophy provides evidence that the affected community, considered to have achieved relative stability by developing a strategy effectively dampening the effect of physical oscillations, has a distinct tolerance limit to stress. The Gulf of Trieste, among the most productive areas in the Mediterranean Sea, must be considered as sensitive; September is a particularly critical month.     

Contamination patterns and molluscan and polychaete assemblages in two Persian (Arabian) Gulf oilfields

This study examined two shallow‐water, offshore oil facilities and their surroundings in the Umm Al Dalkh and Zakum oilfields [United Arab Emirates, Persian (Arabian) Gulf]. The focus was on sediment contamination levels and the detection of disturbance based on two representative invertebrate components of the benthos: molluscs and polychaetes. We tested the hypothesis that significant disturbance to the community has occurred, by examining whether distance from the platform or variation in contaminants explains among‐site variation in the composition of benthic communities. Moreover, we also tested the hypothesis that organic enrichment because of oil input has modified the feeding guild structure by examining whether the relative abundances of filter‐feeders, deposit‐feeders and omnivores are correlated with distance from the platform or with contamination by hydrocarbons. The contamination levels and their spatial distribution in the sediments differed significantly between the two fields, as did their mollusc and polychaete communities. The within‐field variability, however, was much lower: no clear structuring of contamination values and species composition and abundance was detectable in relation to distance from the oil platform. Contamination levels were low, often below detection levels or international guideline values. Variation in contaminant concentrations did not explain variation in taxonomic composition and abundance. The relative abundance of the above‐mentioned feeding guilds did not correlate with either distance from the platform or with contaminant concentrations. These patterns may reflect the long time that has elapsed since drilling (15–20 years), which appears to have allowed contaminants to disperse and degrade and assemblages to recover from the impact, if indeed such a disturbance ever occurred. In contrast to low values of barium and total petroleum hydrocarbons, associated with well drilling, some metals were at their highest concentrations beneath the central platforms. This suggests that production‐related activities (including platform cleaning and maintenance) are currently a more relevant contamination source.     

Research on intact marine ecosystems: a lost era

It is proposed that a new, fifth era should be added to the four historical phases of marine research identified by Rupert Riedl, specifically an era devoted to studying and ameliorating disturbed marine ecosystems. In an age of global environmental deterioration, many marine ecosystems and organisms are high on the list of threatened entities. This poor status prompts research that would otherwise have been unnecessary and hinders research that would normally have been conducted. I argue that research into intact marine ecosystems is becoming increasingly difficult, and that most of our future insights into marine habitats will stem from knowledge gained by examining various disfunctions of those systems rather than their functions. The new era will therefore differ from past research in its underlying aim, the range of topics studied, the selection and funding of those topics, the validity of its conclusions, and in its urgency. Sea turtles and cetaceans are cited as case studies at the organismic level, shallow-water benthic communities, including coral reefs, at the ecosystem level.