Macroscopic characteristics facilitate identification of common Antarctic glass sponges (Porifera, Hexactinellida, Rossellidae)

Glass sponges (Porifera, Hexactinellida) are conspicuous habitat-forming members of many Antarctic shelf communities. Despite their ecological importance, in-situ species identification remains problematic as it is traditionally based on micro- scopic analysis of spicules. External morphological features, in contrast, have largely been disregarded, so that different species have been mislabeled or lumped together when their identification was based on image material. In this paper, we provide a straight-forward guideline for in-situ identification of the most common rossellid sponges of the Antarctic shelf based on macroscopic characteristics. To determine diagnostic macroscopic characteristics of Anoxycalyx (Scolymastra) joubini and eight Rossella species, we combined examination of trawl-collected specimens, previous species descriptions and in-situ image material from the eastern Weddell Sea. Our study revealed that the smooth-walled species A. joubini, R. nuda and R. vanhoeffeni, previously often mixed up, can be distinguished by the form of their basal spicule tuft, their surface structure and their overall body form. The previously synonymized species R. racovitzae and R. podagrosa can be distinguished by their markedly different habitus. Based on our results, the so-called ‘R. racovitzae budding type’ in fact refers to R. podagrosa which occurs regularly in the eastern Weddell Sea. The species R. villosa, R. levis, R. fibulata and R. antarctica can be distinguished by the appearance of their conules, protruding spicules and overall body form. We conclude that macroscopic characteristics are helpful means for identification of Antarctic rossellid sponge species. This approach enables species-specific quantitative studies of Antarctic glass sponge grounds based on increasingly used non-invasive imaging technology

Calcification, photosynthesis and nutritional status of the hermatypic coral Porites lutea: contrasting case studies from Indonesia and Thailand

In situ incubation experiments, complemented by tissue analyses, were conducted with the coral Porites lutea at four sites featuring contrasting environmental conditions: two shallow (3m) reefs in Spermonde Archi-pelago (Indonesia) subjected to coastal pollution (Lae Lae, LL) and oligotrophic waters (Bonebatang, BBA), respectively; a deep (20m, KR-D) and a shallow (7m, KR-S) reef at off-shore Ko Racha (KR) in the Andaman Sea (Thailand) subjected to pulsed upwelling. Mean tem-perature varied only little (29-30°C). While most tis-sue parameters responded to light and nutrient changes as ex-pected, metabolic rates revealed surprising patterns: 3-fold elevated calcification occurred at KR-S compared to all other sites despite reduced gross photosynthesis. Fur-ther-more, equal photosynthesis occurred in 7 and 20m depth at KR, despite a 5-fold reduction in light intensity, which could not be solely ascribed to photo-acclimation processes, such as increased cell-specific chlorophyll a in 20m depth. These findings support the notion of a highly flexible species and indicate that this might partly be ascribed to a strong variation in the internal turnover of oxygen and nutrients between coral host and zooxanthellae, meaning a strong variation in the rates of energy ac-quisition. Those differences are particularly difficult to determine in situ, but require greater attention in the future in order to enhance our understanding of metabolic pro-cesses and acclimatization abilities

Neustonic copepods (Labidocera spp.) discovered living residentially in coral reefs

Pontellid copepods are archetypical representatives of the neuston — the highly specialized community living in the top 5–10 cm of the ocean surface. Their deep blue pigmentation and large eyes are unique adaptations to surface irradiation and carnivory, but poor prerequisites for survival in the transparent waters beneath the sea surface. Here, we report the discovery of three reef-associated representatives of this group — Labidocera bataviae A. Scott, 1909; L. pavo Giesbrecht, 1889; and Labidocera sp. — living residential in coral reefs. We (1) document the presence of Labidocera spp. for two separate coral reefs on two expeditions to Papua New Guinea, (2) describe their migration behavior and substrate preference, and (3) quantify the effects of benthic reef community composition on their abundance. All life stages of Labidocera spp. were 43 to 94 times more abundant at the reef sites compared to offshore sites. Although pontellids are generally considered non-migrators, Labidocera spp. showed discernible diel vertical migrations: living in reef substrates during the day, emerging into the water column at night (sometimes more than once), and returning to the substrate at dawn. Labidocera spp. showed a pronounced substrate preference for coral rubble, microalgae, and turf, over branching coral, massive boulder coral, and sand

Colonization by benthic algae on submarine in the southeastern area of the Gulf of Trieste

Scopo dello studio è stato quello di analizzare i processi di colonizzazione macroalgale su differenti tipi di substrati artificiali, in due aree del Golfo di Trieste (area nord-occidentale, area sud-orientale). Le due aree sono ecologicamente differenti, in termini di idrodinamismo, batimetria, esposizione a moto ondoso, sedimentazione, torpidità e struttura geologica del fondale. Tali fattori influenzano in maniera differente il processo di colonizzazione algale. Le fasi delle colonizzazioni macroalgali sono state seguite mediante immersioni subacquee dopo 2,6,12 e 24 mesi e i campioni sono stati prelevati tramite grattaggi del substrato. Per l’analisi dei campionamenti è stata utilizzata una scala arbitraria, già utilizzata in precedenti studi (Munda, 1978, 1979, 1991a, 2005). Dall’analisi dei campioni sono state osservate variazioni nel popolamento di alcune specie appartenenti ai gruppi Cystoseira e Sargassum come anche nelle associazioni di Fucales, quasi scomparse dal Golfo. In altri casi invece variazioni spazio-temporali (stagionalità) nella colonizzazione, sono state relazionate con la profondità del fondale, la tipologia dei substrati utilizzati e le diverse strategie di colonizzazione in particolare per quanto riguarda diatomee e macroalghe

Large-amplitude internal waves sustain coral health during thermal stress

Ocean warming is a major threat for coral reefs causing widespread coral bleaching and mortality. Potential refugia are thus crucial for coral survival. Exposure to large-amplitude internal waves (LAIW) mitigated heat stress and ensured coral survival and recovery during and after an extreme heat anomaly. The physiological status of two common corals, Porites lutea and Pocillopora meandrina, was monitored in host and symbiont traits, in response to LAIW-exposure throughout the unprecedented 2010 heat anomaly in the Andaman Sea. LAIW-exposed corals of both species survived and recovered, while LAIW-sheltered corals suffered partial and total mortality in P. lutea and P. meandrina, respectively. LAIW are ubiquitous in the tropics and potentially generate coral refuge areas. As thermal stress to corals is expected to increase in a warming ocean, the mechanisms linking coral bleaching to ocean dynamics will be crucial to predict coral survival on a warming plane

Ciliary flows in corals ventilate target areas of high photosynthetic oxygen production

Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O2) may lead to excess O2 in the diffusive boundary layer (DBL) above the coral surface. When flow is low, cilia-induced mixing of the coral DBL is vital to remove excess O2 and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O2-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O2 in the coral DBL in relation to the distribution of Symbiodiniaceae Chla in the tissue of the reef building coral, Porites lutea. Curiously, we found an inverse relation between O2 in the DBL and Chla in the underlying tissue, with patches of high O2 in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O2 concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O2 is related to ciliary-induced flows, causing a lateral redistribution of O2 in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O2 transport allocates parts of the O2 surplus to areas containing less chla, which minimizes oxidative stress. Cilary flows thus confer a spatially complex mass transfer in the coral DBL, which may play an important role in mitigating oxidative stress and bleaching in corals

A trophic link between the cold-water coral Desmophyllum dianthus and filter-feeding bivalves?

Cold-water corals play an important role as ecosystem engineers by providing the three-dimensional structural basis and habitat for a rich associated fauna. In southern Chile, the cold-water scleractinian Desmophyllum dianthus populates the steep walls of Comau Fjord. Where its principal energy source, the zooplankton, is less abundant in winter. This coral specie is often associated with filter-feeders, but the nature and possible trophic significance of this relationship remains enigmatic. Dense belts of the mussel Aulacomya atra and the brachiopod Magellania venosa thrive in the productive waters above and between D. dianthus, and both, visual observation and diver-operated push net samples revealed a rain of biodeposits (faeces and pseudofaeces) from these filter-feeders to the corals. This study aims to determine if the conversion by filter-feeders of microscopic plankton inaccessible to corals to macroscopic strings of faeces and pseudofaeces accessible to the corals’ tentacles may represent a new and so far overlooked trophic link channeling surface production to the corals. Preliminary in vitro experiments show that D. dianthus ingests biodeposits of the mussel Mytilus edulis, but only after the consumption of juvenile krill (Euphausia pacifica). This indicates that biodeposits of active filter feeders may play a role as a food supplement for corals. Follow-up experiments with biodeposits produced under natural conditions by the native filter-feeder community are expected to compound the evidence

Early life history of the cold-water coral Caryophyllia huinayensis from the Chilean Fjord Region

Cold-water corals (CWC) build complex, three-dimensional habitats for diverse communities of associated species. In spite of their importance, very little is known on their reproductive biology. In the Patagonian fjords of Chile, three caryophylliid CWC abound: Desmophyllum dianthus Es-per 1794 along with the recently described Caryophyllia huinayensis Cairns et al. 2005 and Tethocyathus endesa Cairns et al. 2005. This study reports first in situ and in vitro observations of the early life history of the latter two species along with in vitro growth data of juvenile C. huina-yensis. Both are brooding species with translucent tissues, which allowed us to detect and monitor larval development in the gastrovascular system of living specimens. In situ observations from summer 2017 showed between 15 and 25 milky white reproductive stages in the tentacle portion of the gastrovascular cavity of one adult specimen. Up to five younger, round stages were ob-served in groups in the tips of the tentacles. Small planulae of 1.13-1.28 mm length were observed in the tips of the tentacles or organized radially around the mouth. Observations from C. huina-yensis maintained (> 1 yr) in an aquarium system showed that the 620 µm large orange planulae may swim with a velocity of 230 µm s-1 and thus may move from the tentacle tip to the mouth within less than a minute and thereafter reappear in the same or another tentacle in the similar time. After release larvae were found to be negatively buoyant, crawl along the substrate and settle between four and 16 days. Recently settled juveniles increased their basal disc diameter with a rate of 10 µm d-1. After 30 months of maintenance in the aquarium system (Temperature: 12.5 °C, Salinity 32, pH 8, argonite >1, feed with Artemia salina nauplii twice a week) recruits may gain 4.22 (+/-) 0.03 mm yr-1 in diameter and reach the mean size observed for adults in the field after three years. Research on the early life history of CWC is important to understand larval dispersal and connectivity of populations threatened by a changing climate and increasing eutrophication by expanding salmon farming operations