TANE 20 1974

KAWERUA CRABS

by B.W. Hayward*

Sixteen brachyuran crabs and three anomuran crabs are listed from Kawerua as a locality record for students wishing to study individual species. Their overall morphology and distribution is illustrated in Figure 1. This note may be used as an introduction for intertidal ecology studies at Kawerua. All but three of the species listed were collected and identified in November 1973. This list contains all the common crabs and some of the rarer species. It cannot, however, be claimed to be an exhaustive list of the crab fauna.

ANNOTATED SPECIES LIST TRIBE BRACHYURA

Family Majidae Notomithrax minor (masking crab) Found washed up behind reefs. Lives amongst algae at low tide and below. Notomithrax ursus (masking crab) Occasionally found in low-tidal pools amongst the algae. Family Hymenosomatidae Halicarcinus innominatus (pill-box crab) Very common part of interstitial fauna of mussel and algal holdfasts. Hymenicus pubescens (hairy pill-box crab) Found in sandy silt beneath lower eulittoral rocks. Elamena producta (paua crab) Found under low tidal rocks or amongst algae, and frequently commensal with the paua. Haliotis iris, where it lives under the edge of the shell or between the foot and the mantle.

Family Xanthidae Heterozius rotundifrons (big-hand crab) Frequently found under mid to lower eulittoral rocks. Ozius truncatus (black-finger crab) Commonly found beneath mid to lower eulittoral rocks.

Family Pinnotheridae Pinnotheres novaezelandiae (pea crab) Lives within the mantle cavity of mussels.

•Geology Department, University of Auckland.

159 Family Grapsidae Leptograpsus variegatus (large purple shore crab) Very common on solid rocky shores where they scuttle into crevices for protection at all levels of the eulittoral. They also commonly occur on boulder shores - notable are the darker hued juveniles that rapidly scuttle away when boulders of the mid to upper eulittoral are shifted (Fig. 1). (Here as noted by Dell (1968) these young L. variegatus appear to have filled the niche usually occupied by Hemigrapsus edwardsi further south). Planes cyaneus (oceanic crab) Several specimens of this dull blue crab were found washed up alive on the ocean beach south of Kawerua together with abundant individuals of Velella velella (by-the-wind sailor), Physalia physalis (Portugese man-O'-war) and Janthina janthina (violet snail), in May 1973. Pachygrapsus marinus (oceanic crab) This species, and Planes cyaneus, live attached to pieces of floating driftwood or debris, and can be found washed up at times, particularly on pieces of driftwood covered in the goose barnacle Lepas anatifera. P. cyaneus has a smooth carapace, whereas P. marinus has faint low transverse ridges across the back. Hemigrapsus crenulatus Commonly found beneath mid to upper eulittoral rocks on sandy silt of the lower Waimamaku Estuary. Helice crassa (mud crab) Live in burrows in the silty mud sides of the middle to upper Waimamaku Estuary. Cyclograpsus lavauxi (high-tidal crab) Commonly found beneath rocks of the eulittoral fringe (normally too dry for other crabs) and also beneath rocks at high tide level in the lower Waimamaku Estuary. Plagusia chabrus (red rock crab) Sometimes seen beneath boulders or in crevices at low tide level and in the sublittoral fringe. (Formerly Plagusia capensis. Family Portunidae Ovalipes punctatus (swimming crab) Found wholly or partially buried in sand submerged by shallow water at low tide. An active swimmer.

TRIBE ANOMURA Family Porcellanidae Petrolisthes elongatus (blue-green half crab) This is the most abundant crab found, lives beneath rocks of the mid to lower eulittoral. Petrocheles spinosus (small mauve-pink half crab) Frequently found amongst holdfasts of low tidal algae, mussels and beneath low tidal rocks.

Family Paguridae Pagurus novaezelandiae (common hermit-crab) Extremely common in intertidal pools, living in a wide variety of gastropod shells.

The distribution of crabs on the east coast of New Zealand is well known, but records from the west coast are still very sparse and insufficient for any conclusions to be made about their distribution. It is interesting to note that Hemiplax hirtipes (low tidal mudflat crab) has not been found at

160 Kawerua. On the east coast it is absent north of the Bay of Islands. Similarly Hemigrapsus edwardsi is not found on the east coast north of the Bay of Islands and has not been recorded from Kawerua, though found at Opononi by Dell.1 Heterozius rotundifrons and Hemigrapsus crenulatus are not found in any abundance north of the Bay of Islands on the east coast and occur at Kawerua on the west coast.

ACKNOWLEDGEMENT

The author would like to thank Dr. R.V. Grace for critically reading the manuscript and for the records of Elamena producta and Pachygrapsus marinus which he found at Kawerua in July 1971.

REFERENCE

Dell, R.K. 1968 Composition and distribution of the New Zealand Brachyuran fauna. T.R.S.N.Z. 10(25): 225-40.

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