Separate Feeding Between the Pelagic Stage of the Squat Lobster Munida gregaria and the Larger Sized Zooplankton Crustacean Groups in the Beagle Channel as Revealed by Stable Isotopes

In southern Patagonia, the Beagle Channel shows very low production during winter but simultaneously sustains very dense aggregations of the pelagic stage of squat lobster (Munida gregaria), a benthic decapod whose pelagic juveniles have the largest body size within the chitinous pelagic community. To assess the coexistence of the mesozooplankton community and the pelagic M. gregaria stage under the harsh feeding winter conditions, we conducted a research cruise at two locations connected to the Beagle Channel, Yendegaia Bay (land terminating-glacier) and Pia Fjord (marine-terminating glacier). Our results showed that the zooplankton communities were similar in these two fjords, that a single pelagic group dominated in terms of biomass (pelagic Munida gregaria), and that differences in vertical distribution existed between most of the principal crustacean zooplankton and pelagic M. gregaria. All groups showed consumption of terrestrially derived organic matter, as revealed by their δ13C values. However, the isotopic composition, trophic positions (TP), and isotopic niche areas of the groups separated pelagic M. gregaria, presenting some of the lowest δ15N and the highest δ13C values, and the narrowest isotopic niche width. Pelagic M. gregaria was dominated by a single body size class along the 0–100 m water column, with no diel changes in vertical distribution, remained mostly in the upper layers (0–50 m), and benefited from the slightly higher phytoplankton concentrations at shallower depths as revealed by their higher δ13C values and low trophic position. In contrast, the other groups, including zoea M. gregaria stages, developed changes in distribution between day and night or remained deeper in the water column. These groups showed higher δ15N values, higher TP, and lower δ13C values, most of which probably fed on a nanoheterotrophs and terrestrial particulate organic matter mixture at deeper layers. Thus, the different vertical distributions, different trophic level food sources, and slightly different organic carbon sources apparently reduced any potential competence for food resources and form part of the feeding strategy that may facilitate the coexistence of the different large pelagic crustaceans under harsh feeding winter conditions in this high latitude austral region.

Foraminifera-sponge interactions – commensalism to parasitism in the Norwegian-Greenland Sea

<p><span>This is the first study on the interactions between foraminifera and sponges. Although </span><span><em>Cibicides</em></span><span> and </span><span><em>Hyrrokin</em></span><span> are regarded as parasites on siliceous sponges, it is not yet clarified whether foraminifera specifically colonize sponges or are accidentally sucked in during the pelagic stage. To better elucidate these relationships, 12 sponges of different genera were examined and their foraminiferal communities analyzed. In 2018, the sponges for this study were collected with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponge parts were preserved in ethanol (96 %) and stained with Rose Bengal (2g l</span><sup><span>-1</span></sup><span>) to allow a differentiation between the living and dead foraminiferal fauna. </span></p><p><span>Each sponge sample contained several hundred live and dead foraminiferal individuals of up to 60 different species. Even on </span><span><em>Geodia baretti,</em></span><span> which is able to release barettin to avoid colonalisation of other organisms, few foraminiferal individuals were observed. On all sponges, the most abundant genus was </span><span><em>Cibicides, </em></span><span>with</span><span><em> Cibicides lobatulus</em></span><span> and</span><span><em> Cibicides refulgens </em></span><span>as the most common taxa. Other very common species were </span><span><em>Discorbinella bertheloti</em></span><span> or </span><span><em>Epistominella nipponica</em></span><span>. Also, </span><span><em>Hyrrokkin</em></span> <span><em>sarcophaga</em></span><span> was found on different sponges and following its lifestyle, penetrating the sponge surfaces. The fact that besides adult foraminifera splendid juvenile stages were found indicate that foraminifera reproduced while inside the sponges. This reproduction might be stimulated/triggered by enhanced food availability by the pumping sponge.</span></p><p><span>In summary, sponges are a special habitat for a high number of foraminiferal taxa. Their interaction ranges from parasitic lifestyle up to reproduction purposes. All these aspects highlight the importance of foraminifera-sponge interactions.</span></p>

Larval description and habitat utilization of an amphidromous goby, Redigobius bikolanus (Gobiidae)

Redigobius bikolanus(Gobiidae), which is distributed widely in the tropical regions of the West Pacific, is categorized as an amphidromous fish. Such fish reproduce in fresh water and newly hatched larvae immediately drift downstream to the estuary and sea where they spend a pelagic stage before returning upstream as juveniles. The morphology of larvalR. bikolanushas been reported mainly from Japan, whereas little is known about the early stages of this species on the Asian continent. To understand larval growth of this goby, monthly and bimonthly collections with ichthyoplankton nets were made in the Tien Yen estuary in northern Vietnam, from October 2014 to September 2015. A total of 282 larvae (preflexion to postflexion stages, 2.3-5.4 mm body length) ofR. bikolanuswere collected from the center of the current in May, but none were captured in the waters near the banks. The larvae were similar in general morphology to those of common gobies, but could be distinguished from other gobiid genera by two very large stellate melanophores on the ventral surface of the trunk and tail. Descriptions ofR. bikolanuslarvae based on a series of wild specimens are provided. The fishes occurred in low salinities (0.2-2.3 PSU) within 1 m from the surface layer. Together with the wide range of size and developmental stages, this suggests that larvae ofR. bikolanusutilize the center of the current of the Tien Yen estuary as their nursery area. This habitat has not been recorded in Japan.

The reproductive cycle and development of Crepipatella fecunda (Gastropoda: Calyptraeidae) from southern Chile

Crepipatella fecunda is a benthic, primarily suspension-feeding gastropod that occurs in great abundance along the Chilean coast. It is a protandrous species whose reproduction involves brooding of an encapsulated embryonic stage followed by the release of free-living planktotrophic larvae. Because its close sister species, C. dilatata, co-occurs with C. fecunda, understanding the details of reproduction in this species might shed light on differences in reproductive features that correlate with divergences in mode of development. In southern Chile, brooding occurs throughout the year except for May and June, and each female produces 3–7 broods. The smallest brooding female was 28·2 mm in shell length and the largest was 56·3 mm. All full-grown eggs from the ovary are deposited at one time in a single brood, and only smaller oocytes remain in the gonad after the female finishes ovopositing. Those females that host pinnotherid crabs do not deposit eggs. All the eggs develop into embryos whose intracapsular development is similar to Crepidula fornicata and Crepipatella lingulata. Planktotrophic larvae hatch at a mean shell length of 329·5 μm (SD=27·09) after 4–5 weeks. During the pelagic stage the shell and velum of the larvae grow, but little other morphological development is visible externally. The pelagic stage lasts for 15–16 days at 17°C, during which the larvae grow ∼20·7 μm d−1. Observations of cultured larvae and protoconchs of field-collected juveniles show that settlement occurs when the larvae reach a shell-length of 650 μm (SD=28·3 μm).