seareport2

Seagrass Beds and Fauna of St Kilda Harbour

Continued

Report to Earthcare on Marine Flora and Fauna of St Kilda Breakwater

Guy Werner

Introduction

This is the third investigation of the St Kilda Breakwater for Earthcare by the author. It focuses on identifying the macro-organisms at different seagrass bed sites within the breakwater. Further aims were to identify eels seen in the area and compare the springtime biota with the autumn biota (see Werner & McArthur 2000).

Method

Fieldwork was conducted on 22/10/00. Two opera-house traps baited with bluebait were deployed at 1105 and 1110 hours in the vicinity of the launching slipway out from the Royal Melbourne Yacht Squadron in an effort to catch eels. The traps were retrieved at 1510 hours.

Dives were conducted at the same sites and in the same order as for the autumn study (Werner & McArthur 2000; see appendix also). All sites are shown on the previously faxed chart of the area.

Dives were limited to approximately thirty minutes each. Note was taken of all attached macro-algae and larger animal species (>~2cm). Where on-the-spot identification was not possible, underwater photographs were taken or the specimen was collected. Three surface sediment samples were also collected from site three for chemical analysis (Results not covered by this report). Samples were collected by hand (covered by dive glove) into new, seawater-rinsed polythene bags.

An extra (snorkel) dive was made along the slipway to look for eels.

Sabella spallanzanii - European Fan Worm

Results

Of note was the presence of three Bottle-nosed Dolphins, Tursiops truncatus, within the breakwater late in the morning.

The seagrass at all sites was Heterozostera tasmanica. Density was considered to be sparse (almost none), dense, and dense with extensive bare sand patches at dive sites 1, 2, 3, respectively.

Species observed at each dive site are given in the following table. Site two had considerably more species than sites one and three. Site two also has more hard surfaces in the form of refuse from the nearby pier than the relatively featureless sites one and three. Some species were present at all three sites. These included Caulerpa simpliciuscula, Caulerpa scalpelliformis, Colpomenia peregrina, Ulva lactuca, Jeannerettia sp., Gracilaria secundata, Pyura stolonifera, Asterias amurensis, Mytilus edulis, Sabella spallanzanii and the Diopatra sp..

Compared with the previous survey, new species were observed at each site and some species were not observed. New species at site one that were not observed in autumn included Caulerpa longifolia, Ulva lactuca, Caulocystis cephalornithos, Colpomenia peregrina, Jeannerettia, Styela clava, Halicarcinus ovatus, the medium-sized crab, Palaemon serenus, Asterias amurensis and the jellyfish. Species that were not recorded on this survey but were recorded in autumn at site one included Dictyota dichotoma, Wrangelia, Acanthopagrus butcheri, Arenigobius bifrenatus, the pipefish, Platycephalus speculator, Ostrea angasi and Anthopleura aureoradiata.

The majority of species at site two were not recorded in autumn. These included Caulerpa brownii, Caulerpa simpliciuscula, Ulva lactuca, Colpomenia peregrina, Dictyopteris muelleri, Sargassum paradoxum, Champia, Grateloupia filicina, Nemastoma, Diodon nicthemerus, Platycephalus speculator, the styelid ascidian, Patiriella calcar, Mytilus edulis, Diopatra, the jellyfish, Epiactis australiensis and the sponge. Species that were not recorded on this survey but were recorded in autumn at site two included Chaetomorpha, Laurencia filiformis, Acanthopagrus butcheri, the leatherjacket, Philyra laevis and the onuphid polychaete.

New species at site three that were not observed in autumn included Ulva lactuca, Gracilaria secundata, Wrangelia, Trygonorrhina guanerius, Coscinasterias muricata, Cirriformia filigera, Epiactis australiensis and E. thomnsoni. Species that were not recorded on this survey but were recorded in autumn at site three included Caulerpa brownii, Champia, Trygonoptera testacea, Neodax balteatus, Anapella cycladea and Nassarius pyrrhus.

The opera house traps caught no eels. The first trap contained nothing and the other one, which was in shallower water, contained a few gastropods.

Furthermore, no eels were seen on the snorkel dive around the slipway. Despite the poor visibility plenty of Black Bream and some Spiny Globefish were seen.

Macro-organisms at St Kilda Breakwater

		Organisms Observed
DIVE SITE	DEPTH (m)	Scientific Name	Common Name
1	3.5	Chlorophyceae
		Caulerpa brownii Caulerpa longifolia Caulerpa scalpelliformis Caulerpa simpliciuscula Ulva lactuca	Sea Lettuce
		Phaeoophyceae
		Caulocystis cephalornithos
		Colpomenia peregrina
		Rhodophyceae Jeannerettia sp.? Gracilaria secundata
		Phylum Chordata Teleosts Neoodax balteatus	Little Rock Whiting
		Pyura stolonifera Styela clava	Cunjevoi Leathery Sea Squirt
		Crustacea
		Halicarcinus ovatus Medium large crab (too fast to be identified) Palaemon serenus	Serene's Shrimp
		Echinodermata
		Asterias amurensis	Northern Pacific Seastar

		Mollusca
		Mytilus edulis planulatus	Blue Mussel
		Polychaeta
		Sabella spallanzanii	European Fan Worm
		Diopatra sp.
		Cnidaria Unidentified medium-sized red jellyfish
		ORGANISMS OBSERVED
Dive Site	DEPTH (m)	Scientific Name	Common Name
2	2.8	Chlorophyceae
		Caulerpa brownii
		Codium fragile tomentosoides
		Caulerpa longifolia Caulerpa scalpelliformis Caulerpa simpliciuscula Ulva lactuca	Sea Lettuce
		Phaeophyceae
		Colpomenia peregrina
		Dictyopteris muelleri
		Sargassum paradoxum
		Rhodophyceae
		Champia sp.
		Gracilaria secundata Grateloupia filicina Jeannerettia sp.?
		Laurencia sp. Nemastoma sp.?
		Phylum Chordata
		Teleosts Diodon nicthemerus Neoodax balteatus Platycephalus speculator	Globe Fish Little Rock Whiting Yank Flathead
		Pyura stolonifera
		Colonial ascidian (Family Styelidae)
		Echinodermata
		Asterias amurensis
		Patiriella calcar
		Mollusca
		Mytilus edulis planulatus
		Ostrea angasi
		Polychaeta Diopatra sp
		Sabella spallanzanii
		Cnidaria Red Jellyfish Epiactis australiensis
		Porifera Family Tedaniidae?
		Patiriella calcar - Common seastar
	DEPTH	ORGANISMS OBSERVED
DIVE SITE	(m)	SCIENTIFIC NAME	COMMON NAME
3	2.6	Chlorophyceae Caulerpa scalpelliformis Caulerpa simpliciuscula Ulva lactuca	Sea Lettuce
		Phaeophyceae Colpomenia peregrina
		Rhodophyceae Gracilaria secundata Jeannerettia sp. Wrangelia sp.
		Phylum Chordata Chondrichthyes Trygonorrhina guanerius	Southern Fiddler Ray
		Teleostoi Platycephalus speculator	Yank Flathead
		Pyura stolonifera
		Echinodermata Asterias amurensis Coscinasterias muricata (formerly C. calamaria)	Pacific Seastar
		Mollusca Mytilus edulis planulatus	Blue Mussel
		Polychaeta Sabella spallanzanii Cirriformia filigera? Diopatra sp.	European Fan Worm Cirratulid worm Onuphid worm
		Cnidaria Epiactis australiensis Epiactis thomsoni

Discussion

The presence of dolphins is perhaps a testament to the abundance of prey items within the breakwater area.

The seagrass cover at the dive sites appeared similar to cover during the autumn survey. Possibly cover at site one had declined. However, this is difficult to ascertain due to the qualitative method used and the difficulty of diving exactly the same spot.

The higher diversity of organisms at site two compared to sites one and three is probably due to a more varied habitat. While all sites were subtidal and depth did not vary greatly, sites one and three were flat and fairly featureless except for the seagrass beds and drift algae. Site two contained some man-made refuse that formed mini reefs among the seagrass etc. It was also the site closest to the pier. It appeared that these extra microhabitats offered a topographically diverse seascape as well as different surfaces for sessile organisms to grow on.

The presence or absence of species from the collections over time or space must be viewed critically. There are a variety of reasons a species may or may not be recorded other than the obvious one (that it was or was not present at the time of collection). Rare species have a greater probability of being missed by a survey. Small (e.g. Halicarcinus ovatus) or cryptic (e.g. Platycephalus, Palaemon, pipefish) species, likewise, are less likely to be seen. Shy and mobile species (i.e. crabs, fish, sharks and rays) are also likely to evade detection. Nocturnal species that hide during the day are also unlikely to be recorded during a diurnal survey such as this.

Ulva lactuca - Sea Lettuce

Having said that, it appears that certain species are widespread within the breakwater (species noted at all three sites). Two of the Caulerpa species are included in this list. Their ability, unusual for macro-algae, to grow on soft sediments is probably the key to their success. Ulva lactuca is an opportunistic, cosmopolitan species (an introduction?) which grows strongly under enhanced nutrient levels. Colpomenia peregrina is able to grow epiphytically on seagrass and this accounts for its widespread distribution within the breakwater. Pyura stolonifera is a common organism of shallow sediments around Port Phillip Bay so it is no surprise to record it here. Asterias and Sabella are well known invaders of Port Phillip. The density of Asterias within the breakwater appears to have greatly increased since the autumn survey. No Asterias were found at site one in autumn, for example. This should be of concern regarding biological diversity within the breakwater. Asterias is a voracious predator with broad tastes in prey. Mytilus edulis is a common organism of Port Phillip Bay (The Centre for Research on Introduced Marine Pests believes it to be an early introduction to PPB). The beds of it were dense enough once upon a time to support a dredge industry within the bay.

Seasonal or longer-term community changes may best be detected using the macro-algae and sessile or easily seen invertebrates. Differences in species observed between this survey and the last one may indicate which species are seasonal inhabitants. Dictyota dichotoma, Anthopleura aureoradiata, Chaetomorpha and Laurencia filiformis were recorded within the breakwater in autumn but not spring. Ulva lactuca, Caulocystis cephalornithos, Styela clava, the red jellyfish, Coscinasterias muricata, the cirratulid worm, the two Epiactis species, Dictyopteris muelleri, Sargassum paradoxum, Grateloupia filicina, the styelid ascidian, Patiriella calcar and the sponge were recorded within the breakwater in spring but not autumn. Some other species that have been recorded from the breakwater are known to be seasonal annual species. The sporophyte of the Japanese Kelp, Undaria pinnatifida, grows from approximately the start of winter to the end of spring. The exotic subspecies Codium fragile tomentosoides grows throughout the warmer months. Codium fragile found in winter is likely to be the native subspecies, not the exotic one.

Unfortunately, despite not having observed any eels, we cannot say for certain whether they frequent the breakwater or not. The author has seen several eels on one dive around the mouth of St Kilda Marina. Considering the proximity of the marina to the breakwater (approx. 1 km) we feel it is possible the same eel species inhabits the breakwater, at least seasonally.

Appendix

Dive site one was near the perimeter of the study area, outward from the marina pier and on a bearing of 65 (=245-180) degrees magnetic from the end of the breakwater. Dive site two was on a seagrass bed near and approximately north of the kiosk. Dive site three was on a seagrass bed closer to shore.

More detailed identification of red algae gave the following results:

Site One: Griffithsia teges, Gracilaria chilensis ( not. G secundata), Dictyopteris muelleri

Site Two: Laurencia arbuscula, Pterosiphonia pennata ( female) with epiphytic Acrosorium venulosum, Rhodoglossum gigartinoides (female), Lomentaria australis (female).

Site Three: Brougniartella australis (not wrangelia as thought). Medothamnion prosentum.

Epiphytes found on seagrass around site 3

Red algal epiphyte Poysiphonia infestans Harvey

Green algal epiphyte Enteromorpha prolifera

Diatoms
Melosira sp.

Cocconeis sp.

Climacosphaemia sp.

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