Michael Arvedlund

Abundance of giant sea anemones and patterns of association with anemonefish in the northern Red Sea

Patterns of distribution and abundance of giant sea anemones and anemonefish were compared among coral leefs along the coastline of Sinai in the northern Red Sea. The sea anemones varied widely in abundance between reef areas containing different habitat types. They were rare on steep reef slopes with abundant coral cover (=low-density anemone sites, 0.09 0.68 anemones per 1000 m 2 of reef area), but were common at a site containing patch reefs interspersed with sand (=high-density anemone site, 6.00-8.11 anemones per 1000 m 2 ). Distributions of the endemic two-band anemonefish (Amphiprion bicinctus) varied significantly between the two main host anemone species. At the high-density site, individuals of the sea anemone Heteractis crispa either did not contain anemonefish, or were occupied by single juvenile fish as shown in previous studies. At low-density sites H. crispa usually hosted clusters of juvenile anemone-fish. In contrast, individuals of the sea anemone Entacmaea quadricolor hosted either single adult fish (high-density site) or pairs of breeding adults (low-density sites), frequently in addition to some juvenile fish. Mechanisms that prevent anemonefish from reaching adult size and forming breeding pairs in H. crispa may include high fish mortality above a size threshold because this host cannot adequately protect them from predation when they become large, active emigration of fish to F. quadricolor as described in previous reports, and/or environmentally-controlled cessation of fish growth. We conclude that in the northern Red Sea, individuals of H. crispa potentially serve as nurseries for anemonefish.

The embryonic development of the olfactory system in Amphiprion melanopus (Perciformes: Pomacentridae) related to the host imprinting hypothesis

Development of the olfactory system in anemonefish embryos of the species Amphiprion melanopus was examined from day six post-fertilization, until hatching (day nine). An olfactory placode with receptor cells lining the epithelium and nerve axons from the placode into the olfactory bulb, was observed on newly hatched embryos. In addition, two different secondary bilateral receptor systems were found. These findings may firstly support the anemonefish host imprinting hypothesis, and secondly indicate that the ontogenetic timing of this imprinting mechanism occurs towards the end of the embryonic development.

First records of unusual marine fish distributions - can they predict climate changes?

Global climate change is impacting the ecology and biogeography of marine fish populations and will continue to do so in the future. Here, I review recent records of unusual marine fish distributions from different regions of the world, and discuss the relevance of such observations to climate changes. In conclusion, I suggest that first records of fish in unusual habitats may aid as an indicator of climate changes, provided each record is critically assessed and combined with recent records of fish population parameters, population dynamics, marine habitat assessments and abiotic data such as sea bottom, middle and surface temperatures.

Long-term observation in situ of the anemonefish Amphiprion clarkii (Bennett) in association with a soft coral

Coral Reefs (2005) 24: 698 DOI 10.1007/s00338-005-0007-3 Reef sites The anemonefishes are a well-known guild of 28 species (family: Pomacentridae) owing to their obligate symbiotic relations with ten species of giant tropical sea anemones (families: Actiniidae, Stichodactylidae and Thalassianthidae) throughout coral reefs in most of the tropical and suitable subtropical Indo-Pacific and the Red Sea (Fautin and Allen 1997). All species of anemonefishes exhibit species-specific patterns of association between host anemones in nature, from the extreme specialist living with one host sea anemone species (the spine-cheek anemonefish, Premnas biaculeatus) to the generalist living in all ten host anemones (Clark s anemonefish, Amphiprion clarkii) (Fautin and Allen 1997). In the Ryukyus Archipelago, southern Japan, at the southernmost local reef of Sesoko Island (Lat. 26.640¢N, Long. 127.867¢E) we observed, by the aid of snorkeling during 37 surveys in daytime hours (between 11:00 and 18:00), one adult anemonefish (SL=9 cm) of the species Amphiprion clarkii (sensu Fautin and Allen 1997) residing in the same soft coral (diameter=90 cm) of the genus Lobophytum sp. (sensu Fabricius and Alderslade 2001) at 1 m depth, over 20 months from May 2003 to December 2004 (Figs. 1, 2). The 1998 global coral bleaching event (Wilkinson 1998) had a serious impact on the local coral reefs of Sesoko Island (Loya et al. 2001). In addition, several host sea anemone species disappeared and the abundance of the surviving species declined seriously (Hattori 2002). At the time of writing (February 2005), the host anemones had not yet recovered (M. Arvedlund, personal observation). Observations in captivity of anemonefishes residing in unnatural sea anemones are common (Fautin and Allen 1997). Occasionally, it is also possible to observe anemonefishes in captivity accepting other invertebrate hosts than sea anemones, e.g. the anemonefishes Amphiprion ocellaris and A. melanopus may accept soft coral species (Sarcophyton spp.) and giant clams (Tridacna spp.; M. Arvedlund, personal observation). It may not be coincidental that it is the species A. clarkii which seems capable of longterm survival in nature in other hosts than sea anemones. This species often take shelter away from its host anemone when pursued (M. Arvedlund, personal observation), contrary to most other anemonefishes, which hide in the host. We speculate that the capability of A. clarkii associating with corals instead of host anemones for more than a year—possibly several years—may be crucial for the population dynamics of this species during severe community shifts. Finally we suggest that the host plasticity in A. clarkii may also at least partly explain why this species is the most widely distributed anemonefish (Fautin and Allen 1997).

Scanning electron microscopy of the peripheral olfactory organ in small and large juvenile Apogon cyanosoma (Apogonidae: Teleostei)

the olfactory organ in small and large juveniles of the tropical yellowstriped reef cardinalfish apogon cyanosoma , collected from the wild (total length [tl] range=17–32 mm, mean=25 mm) was examined by scanning electron microscopy. the olfactory organ consisted of two bilaterally radial rosettes in each fish. they were oval-shaped, located medioventrally, one in each of the olfactory chambers. in small juvenile a. cyanosoma the rosette comprised six lamellae, three on each side of a midline raphe while large juveniles had eight lamellae, four on each side. the lamellae had a continuous cover of cilia, except for the margins. in small juvenile a. cyanosoma (tl mean=24.3 mm) only microvilli were observed, whereas both microvilli and a few cilia, presumably from olfactory receptor neurons, were observed in large juvenile a. cyanosoma (tl mean=32 mm).

When cleanerfish become anemonefish

Here we report on a previously undocumented facultative symbiosis involving the wrasses Labroides dimidiatus and Thallasoma amblycephalum living in association with two species of sea anemones, on coral reefs in the north-western Pacific. By SCUBA diving we observed juvenile L. dimidiatus occurring in Entacmaea quadricolor (solitary type) cleaning the anemonefish Amphiprion frenatus and in Heteractis magnifica cleaning the anemonefish Dascyllus trimaculatus . Thallasoma amblycephalum co-existed in H. magnifica with the anemonefish D. trimaculatus , A. ocellaris and L. dimidiatus .

Calcium antagonists inhibit the discharge of cnidae in response to electrical stimulation in the giant tropical sea anemone Heteractis crispa Ehrenberger (Anthozoa)

The mechanisms involved in cnidocyst discharge among cnidarians are not well understood. In this study we examined the discharge mechanism in an anthozoan. We examined the effect of the Ca2+ antagonists (Mg2+, Co2+ and La3+), a Ca2+ agonist (Sr2+), and two cations (Ca2+ and K+) upon cnidocyst discharge, using electrical stimulation applied directly to sea anemone tentacles. In our experiment we used the sea anemone Heteractis crispa (Class: Anthozoa, Family: Stichodactylidae), a known host for anemonefishes, as a model organism. Our results show that the Ca2+ antagonists effectively inhibit, while all the other cations enhance the cnidocyst discharge of H. crispa. These results are comparable to those from a similar study on the hydrozoan, Hydra vulgaris, which also used the electrostimulation method. Our results demonstrate for the first time that the discharge mechanisms in Anthozoa and Hydrozoa are comparable, and support existing hypotheses concerning the importance of Ca2+ in cnidocyst discharge.