Crustaceans and Marine Heterobranchia: A New Symbiotic Relationship in the Mediterranean Sea

The “solar-powered” Elysia timida (Risso, 1818) is an endemic Mediterranean sacoglossan living in rocky substrates at shallow water. During a scuba dive, one E. timida was photographed and collected. The observation revealed the presence of a small crustacean of the Pinnotheridae family. It was not possible to assign the crustacean to a genus, but it shares typical ecological and external morphological features with other Pinnotherinae species. This is the first report of a pea crab hosted by a non-shelled Heterobranchia and the first case of a symbiotic association between crustaceans and marine Heterobranchia reported in the Mediterranean Sea.

Studies on Animals Closely Associated with Some New Zealand Marine Shellfish

<p>Between March 1973 and September 1974, 858 Perna canaliculus (Gmelin), 150 Mytilus edulis aoteanus Powell, 237 Crassostrea qlomerata (Gould) and 153 Ostrea lutaria Hutton, were surveyed for parasites. From these four commercially important shellfish species, a total of two sporozoans, three species of trematode sporocyst, and a copepod were found. A second copepod and pea-crabs were found associated with certain of the shellfish, but the nature of this association is uncertain. During the examination of each shellfish the ratio of the meat volume to internal shell volume was measured. This provided a condition factor for the shellfish, and gave an indication of the effect of the parasite on the meat weight of the bivalve. Perna canaliculus was collected from Ahipara, Wellington Harbour, and the Marlborough Sounds. Spores of a gregarine, Nematopsis sp., were abundant in the Ahipara mussels, common in Wellington and rare in the Sounds. The fellodistomid trematode sporocyst known as Cercaria haswelli Dollfus was found in mussels from all three locations. Laboratory infection experiments established that the cercaria from this sporocyst develops into the trematode Terqestia aqnostomi (manter). Gravid specimens of this trematode were obtained for the first time, from the mullet Aldrichetta forsteri Cuvier & Valanciennes. Two specimens of the bucephalid sporocyst described by Haswell (1903) were recovered and re-described. The copepods pseudomyicola spinosus Raffaele & Monticelli and Lichomolgus.n sp. were associated with the mussels, but their status is uncertain. The post-planktonic stages of the pea-crab Pinnotheres novaezelandiae Filhol are described for the first time, and the seasonal abundance, effect of depth on abundance, and the effect of the crab on the host's condition are described. Differences between the zoea of apparently identical female crabs from different host species are noted and the significance of these is discussed. Because of the difference between the zoea of crabs from P. canaliculus and Atrina zelandica Gray, only the crabs from the former host are refered to as P. novaezelandiae. The pea-crabs found in A. zelandica, C. glomerata, and M. edulis aoteanus, have not been assigned to a species. Mytilus edulis aoteanus is host to Tergestia aqnostomi sporocysts, Pseudomyicola spinosus, and Pinnotheres sp. Crassostrea glomerata was collected from the Bay of Islands. Only one parasite, the copepod Pseudomyicola spinosus, was found in this host. A pea-crab Pinnotheres sp. is occasionally found associated with the oyster. A disease of this oyster, a symptom of which is the formation of necrotic pustules in the adductor mussel, could not be traced to any parasite. This disease is discussed in an appendix. Ostra lutaria was obtained from Wellington Harbour, the Marlborough Sounds, and Foveaux Strait. Sporozoan cysts were found to occur in 10% of the oysters from Foveaux Strait, but were not observed to adversly affect the oyster. The sporocysts of the trematode Bucephalus longicornutus (Manter) occur in the areas sampled. Pseudomyicola spinosus lnfests the oyster in Wellington and in the Sounds, but not in Foveaux Strait. It was concluded that there were no serious pathogens likely to infect the shellfish farms growing these species, and that there was little farmers could do at present to reduce the effect on the host of the symbionts already present in the shellfish beds. A checklist and bibliography of all the parasites infecting New Zealand marine molluscs is included is an appendix.</p>

Studies on Animals Closely Associated with Some New Zealand Marine Shellfish

<p>Between March 1973 and September 1974, 858 Perna canaliculus (Gmelin), 150 Mytilus edulis aoteanus Powell, 237 Crassostrea qlomerata (Gould) and 153 Ostrea lutaria Hutton, were surveyed for parasites. From these four commercially important shellfish species, a total of two sporozoans, three species of trematode sporocyst, and a copepod were found. A second copepod and pea-crabs were found associated with certain of the shellfish, but the nature of this association is uncertain. During the examination of each shellfish the ratio of the meat volume to internal shell volume was measured. This provided a condition factor for the shellfish, and gave an indication of the effect of the parasite on the meat weight of the bivalve. Perna canaliculus was collected from Ahipara, Wellington Harbour, and the Marlborough Sounds. Spores of a gregarine, Nematopsis sp., were abundant in the Ahipara mussels, common in Wellington and rare in the Sounds. The fellodistomid trematode sporocyst known as Cercaria haswelli Dollfus was found in mussels from all three locations. Laboratory infection experiments established that the cercaria from this sporocyst develops into the trematode Terqestia aqnostomi (manter). Gravid specimens of this trematode were obtained for the first time, from the mullet Aldrichetta forsteri Cuvier & Valanciennes. Two specimens of the bucephalid sporocyst described by Haswell (1903) were recovered and re-described. The copepods pseudomyicola spinosus Raffaele & Monticelli and Lichomolgus.n sp. were associated with the mussels, but their status is uncertain. The post-planktonic stages of the pea-crab Pinnotheres novaezelandiae Filhol are described for the first time, and the seasonal abundance, effect of depth on abundance, and the effect of the crab on the host's condition are described. Differences between the zoea of apparently identical female crabs from different host species are noted and the significance of these is discussed. Because of the difference between the zoea of crabs from P. canaliculus and Atrina zelandica Gray, only the crabs from the former host are refered to as P. novaezelandiae. The pea-crabs found in A. zelandica, C. glomerata, and M. edulis aoteanus, have not been assigned to a species. Mytilus edulis aoteanus is host to Tergestia aqnostomi sporocysts, Pseudomyicola spinosus, and Pinnotheres sp. Crassostrea glomerata was collected from the Bay of Islands. Only one parasite, the copepod Pseudomyicola spinosus, was found in this host. A pea-crab Pinnotheres sp. is occasionally found associated with the oyster. A disease of this oyster, a symptom of which is the formation of necrotic pustules in the adductor mussel, could not be traced to any parasite. This disease is discussed in an appendix. Ostra lutaria was obtained from Wellington Harbour, the Marlborough Sounds, and Foveaux Strait. Sporozoan cysts were found to occur in 10% of the oysters from Foveaux Strait, but were not observed to adversly affect the oyster. The sporocysts of the trematode Bucephalus longicornutus (Manter) occur in the areas sampled. Pseudomyicola spinosus lnfests the oyster in Wellington and in the Sounds, but not in Foveaux Strait. It was concluded that there were no serious pathogens likely to infect the shellfish farms growing these species, and that there was little farmers could do at present to reduce the effect on the host of the symbionts already present in the shellfish beds. A checklist and bibliography of all the parasites infecting New Zealand marine molluscs is included is an appendix.</p>

Population Biology of Mussels (Aulacomya Maoriana, Mytilus Galloprovincialis and Perna Canaliculus) From Rocky Intertidal Shores in Wellington Harbour, New Zealand

<p>This study examines the population ecology and dynamics of three co-existing mussel species (Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus) in Wellington Harbour, New Zealand. The present study investigates the role of multiple environmental factors and their multiple effects on the intertidal mussel population. Wellington Harbour is a complex system, supporting speciose intertidal invertebrate communities. CTD data loggers recording seawater temperature, turbidity, chlorophyll a concentration and salinity at Evans Bay, Seatoun, Matiu-Somes Island and Petone provided the environmental data. The data suggest the existence of distinct zones within Wellington Harbour, with different hydrological regimes present at each zone. Consistently high salinity (35.08 + 2.9 PSU) and chlorophyll a concentration (9.42 + 4.33 μg l-1) were found at Evans Bay, while these parameters displayed a degree of temporal variation and were significantly lower at Seatoun (31.5 + 4.17 PSU and 2.15 + 2.1 μg l-1) and Matiu-Somes Island (33.26 + 0.99 PSU and 1.23 + 1.79 μg l-1). At Petone, a site located near the Hutt river mouth, salinities were reduced (31.59 + 3.21 PSU) while chlorophyll a levels were similar to those at Matiu-Somes Island (1.64 + 1.08 μg l-1). Mean turbidity values were similar at Seatoun and Evans Bay (11.51 + 18.53 FTU and 11.89 + 5.52 FTU, respectively), with mean turbidity slightly reduced at Petone (8.20 + 11.16 FTU) and elevated at Matiu-Somes Island (15.35 + 11.12 FTU). Further, CTD data revealed similar seawater temperature at all sites, with mean values oscillating around 13 - 15ºC. The ecology of larval stages was expressed in this study by quantifying the rates at which mussel larvae settled on the experimental substrate. A year-round spawning, as well as temporal and spatial variability in mussel recruitment at four experimental sites was revealed. Evans Bay was the site with consistently higher recruitment rates but not the mean recruit numbers (721 + 879 larvae), while the highest number of recruits (9851 larvae) was recorded at Petone (1041 + 2112 larvae). Recruitment rates were lower at Seatoun (729 + 536 larvae) and Matiu-Somes Island (410 + 636 larvae). However, only at Seatoun was this variability clearly linked to the environmental conditions of water turbidity, chlorophyll a concentration, and salinity. The post-larval ecology part of this study concentrates on the condition index and gonad mass, and the degree of infestation with a parasitic pea crab Pinnotheres novaezelandiae studied at four sites. Spatial and temporal variation in condition index and gonad mass was revealed in all three species investigated, with both condition index and gonad mass of adult mussels being highest at Matiu-Somes Island (14.59 + 4.41 and 0.21 + 0.16 g), followed by Kau Point (13.47 + 6.99 and 0.17 + 0.10 g), Seatoun (13.32 + 7.79 and 0.11 + 0.10 g) and Evans Bay (11.99 + 2.78 and 0.14 + 0.14 g). Condition index was significantly correlated with gonad mass, and was highest in Aulacomya maoriana (15.85 + 9.38), followed by Perna canaliculus (12.52 + 4.39) and Mytilus galloprovincialis (11.66 + 5.91). The condition was generally reduced in mussels infested with the pea crab Pinnotheres novaezelandiae, although the overall infestation rate was low (3.28%). In order to describe the pattern of mussel community development, patches of bare rock were experimentally created in the mid-intertidal zone. Subsequently, predatorexclusion cages were set up in those areas and monitored regularly. The abundance of main groups of intertidal taxa settling on the cleared substrate was expressed in terms of percent cover, and was highest at Evans Bay (59.57 + 80.27%), lowest at Kau Point (13.96 + 26.18%) and intermediate at Seatoun (22.56 + 41.64%). However, the bottomup factors were visibly linked to the community development at Seatoun. The full cage experimental treatment provided the maximum protection from predation and desiccation, therefore the community recovery was most pronounced under this treatment. Mytilus galloprovincialis was revealed as the most competitive mussel species, in some cases able to colonise the entire available substrate and exclude other two mussel species. Further, seasonality of mussel response to wave action and desiccation was investigated. Mussel species-specific strength of attachment to the rocky substrate was expressed in kg (effectively the force) required for the mussel to be removed from the rocky substrate at shores facing south and north in Wellington Harbour. The strength of attachment was highest in Perna canaliculus (5.81 kg + 2.27), followed by Aulacomya maoriana (3.63 kg + 1.63) and Mytilus galloprovincialis (3.44 kg + 1.70). Mussel strength of attachment was generally higher at south-facing sites, due to stronger waves generated by southerly winds. In a separate experiment, in which mussels were exposed to air at six different shore levels within the intertidal zone, desiccation tolerance was highest in Mytilus galloprovincialis on the south-facing sites (LD50=0.62m and 0.87 for north- and south-facing sites, respectively), followed by Aulacomya maoriana (LD50=0.65 and 0.75m for north- and south-facing sites, respectively) and Perna canaliculus (LD50=0.20 and 0.35m for north- and south-facing sites, respectively). LD50 desiccation exposure values were lower in all three species found on the north-facing shores, indicating that mussels on those shores are less tolerant to desiccation-induced stress and therefore died more rapidly.</p>

Population Biology of Mussels (Aulacomya Maoriana, Mytilus Galloprovincialis and Perna Canaliculus) From Rocky Intertidal Shores in Wellington Harbour, New Zealand

<p>This study examines the population ecology and dynamics of three co-existing mussel species (Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus) in Wellington Harbour, New Zealand. The present study investigates the role of multiple environmental factors and their multiple effects on the intertidal mussel population. Wellington Harbour is a complex system, supporting speciose intertidal invertebrate communities. CTD data loggers recording seawater temperature, turbidity, chlorophyll a concentration and salinity at Evans Bay, Seatoun, Matiu-Somes Island and Petone provided the environmental data. The data suggest the existence of distinct zones within Wellington Harbour, with different hydrological regimes present at each zone. Consistently high salinity (35.08 + 2.9 PSU) and chlorophyll a concentration (9.42 + 4.33 μg l-1) were found at Evans Bay, while these parameters displayed a degree of temporal variation and were significantly lower at Seatoun (31.5 + 4.17 PSU and 2.15 + 2.1 μg l-1) and Matiu-Somes Island (33.26 + 0.99 PSU and 1.23 + 1.79 μg l-1). At Petone, a site located near the Hutt river mouth, salinities were reduced (31.59 + 3.21 PSU) while chlorophyll a levels were similar to those at Matiu-Somes Island (1.64 + 1.08 μg l-1). Mean turbidity values were similar at Seatoun and Evans Bay (11.51 + 18.53 FTU and 11.89 + 5.52 FTU, respectively), with mean turbidity slightly reduced at Petone (8.20 + 11.16 FTU) and elevated at Matiu-Somes Island (15.35 + 11.12 FTU). Further, CTD data revealed similar seawater temperature at all sites, with mean values oscillating around 13 - 15ºC. The ecology of larval stages was expressed in this study by quantifying the rates at which mussel larvae settled on the experimental substrate. A year-round spawning, as well as temporal and spatial variability in mussel recruitment at four experimental sites was revealed. Evans Bay was the site with consistently higher recruitment rates but not the mean recruit numbers (721 + 879 larvae), while the highest number of recruits (9851 larvae) was recorded at Petone (1041 + 2112 larvae). Recruitment rates were lower at Seatoun (729 + 536 larvae) and Matiu-Somes Island (410 + 636 larvae). However, only at Seatoun was this variability clearly linked to the environmental conditions of water turbidity, chlorophyll a concentration, and salinity. The post-larval ecology part of this study concentrates on the condition index and gonad mass, and the degree of infestation with a parasitic pea crab Pinnotheres novaezelandiae studied at four sites. Spatial and temporal variation in condition index and gonad mass was revealed in all three species investigated, with both condition index and gonad mass of adult mussels being highest at Matiu-Somes Island (14.59 + 4.41 and 0.21 + 0.16 g), followed by Kau Point (13.47 + 6.99 and 0.17 + 0.10 g), Seatoun (13.32 + 7.79 and 0.11 + 0.10 g) and Evans Bay (11.99 + 2.78 and 0.14 + 0.14 g). Condition index was significantly correlated with gonad mass, and was highest in Aulacomya maoriana (15.85 + 9.38), followed by Perna canaliculus (12.52 + 4.39) and Mytilus galloprovincialis (11.66 + 5.91). The condition was generally reduced in mussels infested with the pea crab Pinnotheres novaezelandiae, although the overall infestation rate was low (3.28%). In order to describe the pattern of mussel community development, patches of bare rock were experimentally created in the mid-intertidal zone. Subsequently, predatorexclusion cages were set up in those areas and monitored regularly. The abundance of main groups of intertidal taxa settling on the cleared substrate was expressed in terms of percent cover, and was highest at Evans Bay (59.57 + 80.27%), lowest at Kau Point (13.96 + 26.18%) and intermediate at Seatoun (22.56 + 41.64%). However, the bottomup factors were visibly linked to the community development at Seatoun. The full cage experimental treatment provided the maximum protection from predation and desiccation, therefore the community recovery was most pronounced under this treatment. Mytilus galloprovincialis was revealed as the most competitive mussel species, in some cases able to colonise the entire available substrate and exclude other two mussel species. Further, seasonality of mussel response to wave action and desiccation was investigated. Mussel species-specific strength of attachment to the rocky substrate was expressed in kg (effectively the force) required for the mussel to be removed from the rocky substrate at shores facing south and north in Wellington Harbour. The strength of attachment was highest in Perna canaliculus (5.81 kg + 2.27), followed by Aulacomya maoriana (3.63 kg + 1.63) and Mytilus galloprovincialis (3.44 kg + 1.70). Mussel strength of attachment was generally higher at south-facing sites, due to stronger waves generated by southerly winds. In a separate experiment, in which mussels were exposed to air at six different shore levels within the intertidal zone, desiccation tolerance was highest in Mytilus galloprovincialis on the south-facing sites (LD50=0.62m and 0.87 for north- and south-facing sites, respectively), followed by Aulacomya maoriana (LD50=0.65 and 0.75m for north- and south-facing sites, respectively) and Perna canaliculus (LD50=0.20 and 0.35m for north- and south-facing sites, respectively). LD50 desiccation exposure values were lower in all three species found on the north-facing shores, indicating that mussels on those shores are less tolerant to desiccation-induced stress and therefore died more rapidly.</p>

Spatial Dynamics of Two Host-Parasite Relationships on Intertidal Oyster Reefs

Intertidal reefs comprised of the eastern oyster (Crassostrea virginica) have long experienced habitat loss, altering habitat patch characteristics of size and distance from edge to interior, potentially influencing spatial dynamics of host-parasite relationships. Using two parasitic relationships, one between eastern oyster host and parasitic oyster pea crab (Zaops ostreum) and the other between a xanthid crab (Eurypanopeus depressus) and a parasitic rhizocephalan barnacle (Loxothylacus panopaei), we examined how host-parasite population characteristics varied on intertidal reefs by season, reef size, and distance from edge to interior. Pea crab prevalence was more related to habitat characteristics rather than host density, as pea crab prevalence was the highest on large reefs and along edges, areas of comparatively lower oyster densities. Reef size did not influence densities of parasitized or non-parasitized xanthid crabs, but densities varied from edge to interior. Non-parasitized xanthids had significantly lower densities along the reef edge compared to more interior reef locations, while parasitized xanthid crabs had no significant edge to interior pattern. Organismal size had a varied relationship based upon habitat characteristics, as pea crab carapace width (CW) varied interactively with season and reef size, whereas CW of parasitized/non-parasitized xanthid crabs varied significantly between edge and interior locations. These results demonstrated that influential habitat characteristics, such as patch size and edge versus interior, are both highly species and host-parasite specific. Therefore, continued habitat alteration and fragmentation of critical marine habitats may further impact spatial dynamics of host-parasite relationships.

Isotopic niche provides an insight into the ecology of a symbiont during its geographic expansion

The study of the recent colonization of a symbiont and its interaction with host communities in new locations is an opportunity to understand how they interact. The use of isotopic ratios in trophic ecology can provide measurements of a species’ isotopic niche, as well as knowledge about how the isotopic niches between symbiont and host species overlap. Stable isotope measurements were used to assess the sources of carbon assimilated by the host species (the bivalves Mytilus galloprovincialis and Scrobicularia plana) and their associated symbiont pea crab Afropinnotheres monodi, which occurs within these bivalves’ mantle cavities. The mixing model estimates suggest that all of them assimilate carbon from similar sources, particularly from pseudofaeces and particulate organic matter in this symbiotic system based on filter feeding. The symbiotic species occupy comparable trophic levels and its association seems to be commensal or parasitic depending on the duration of such association. The pea crab A. monodi reflects a sex-specific diet, where males are more generalist than the soft females because the latter’s habitat is restricted to the host bivalve. The high isotopic overlap between soft females and M. galloprovincialis may reflect a good commensal relationship with the host.

A Review of the Ecomorphology of Pinnotherine Pea Crabs (Brachyura: Pinnotheridae), with an Updated List of Symbiont-Host Associations

Almost all pea crab species in the subfamily Pinnotherinae (Decapoda: Brachyura: Pinnotheridae) are considered obligatory endo- or ectosymbionts, living in a mutualistic or parasitic relationship with a wide variety of invertebrate hosts, including bivalves, gastropods, echinoids, holothurians, and ascidians. While the subfamily is regarded as one of the most morphologically adapted groups of symbiotic crabs, the functionality of these adaptations in relation to their lifestyles has not been reviewed before. Available information on the ecomorphological adaptations of various pinnotherine crab species and their functionality was compiled in order to clarify their ecological diversity. These include the size, shape, and ornamentations of the carapace, the frontal appendages and mouthparts, the cheliped morphology, the ambulatory legs, and the reproductive anatomy and larval characters. The phylogenetic relevance of the adaptations is also reviewed and suggestions for future studies are made. Based on an updated list of all known pinnotherine symbiont–host associations and the available phylogenetic reconstructions, it is concluded that, due to convergent evolution, unrelated species with a similar host interaction might display the same morphological adaptations.