The roles of food supply and shelter in the relationship between fishes, in particular Cnidoglanis macrocephalus (Valenciennes), and detached macrophytes in the surf zone of sandy beaches

J. Exp. Mar. Biol. Ecol., 1989, Vol. 128, pp. 165-176

165

Elsevier

JEMBE 01256

The roles of food supply and shelter in the relationship between fishes, in particular Cnidoglanis macrocephalus (Valenciennes), and detached macrophytes in the surf zone of sandy beaches R. C. J. Lenanton md N. Caputi Western Australian Marine Research Laboratories, North Beach, Western Australia, Australia

(Received 4 October 19X8;revision received 15 March 1989; accepted 17 March 1989) Abstract: Reguiar night-time sampIing was conducted over a I-yr period in the surf zones of two adjacent sandy beaches, Iocated in the Marmion region near Perth, Western Australia. The catches of most of the 37 fish species were dominated by juveniles. An earlier series of daytime and night-time nettings at the same sandy beach sites established that the abundance of these surf-zone fishes was positively correlated with the volume of drift macrophytes. This relationship reflected the provision by the drift weed of a rich invertebrate, primarily amphipod, food supply and a refuge from diurnal predation by the cormorant Phalacrocorax variw (Gmelin). The present study demonstrated a significant positive relationship between the total number of fishes and the volume of drift macrophytes. This relationship was based on sampling performed throughout the year; demonstrating a very persistent association between those two variables. Seasonahty also contributed to the observed variation in the number of fish caught. However, the most impo~~t result of the present study demonstrated that at night, when the risk of predation and thus tbe need to seek shelter was low, the abundance of one oftbe dominant nocturnal and commercially important fish, 0 + -yr-old Cnidogkmismacrocephephnlus (VaIenciennes), cat&t per netting was also siguiticantiy positively correlated both with the vofume of drift macrophytes and with the volume of fine red algae and dead seagrass components of the drift macrophytes. However, these two components of the drift have previously been shown to provide an essenti~ habitat and food supply for amphipods, p~rnar~y~~~o~he~~escompressa Dana which is the major food item for ~~jdog~an~ ma~roce~hai~. These results provide conclusive evidence that the &m-time drift weed-juvenile C. macro~ep~al~ association is related pimply to the food requiremeuts of this fish. There appears to have been no other instances reported of an important commercial species being so dependent on a particular assembiage of drift macrophyte species for its survivai. Key words: C#idog~a~~ macrocephalus; Detached macrophyte; Fish assemblage; Food; Shelter; Surf zone

Fishes found in the surf zones of sandy beaches in various parts of the world are mostly planktivores and are usualIy represented primarily by juvenile stages (Modde & Ross, 1981; Las&k, 1983, 1986; McDermott, 1983; Senta & Kinoshita, 1985; Ross et al., 1987). However, in surf zones with increased habitat complexity, such as drift Correspondence address: R. C. J. Lenanton, Western Australian Marine Research ~borato~es, 20, North Beach, Western Australia 6020, Australia. ~~22-~9~i~S9~S~3.~~0 1989 Ebevier Science Pub&hers B.V. (Biomedical Division)

PO Box

166

R.C.J. LENANTON

AND N. CAPUTI

macrophytes, natural reef, or man-made structures, such as jetties, increased fish richness and diversity is related to the increased availability of benthic, rather than planktonic food, and shelter (Edwards, 1973a,b; Wheeler, 1980; Peters & Nelson, 1987). Indeed, previous work on surf-zone fishes undert~en at two sites in the Marmion region, Western Australia (Robertson & Lenanton, 1984), showed that the abundance of these fishes was positively correlated with the volume of drift macrophytes. It was argued that this relationship reflected the provision by the drift weed of a rich invertebrate food supply, and a refuge from diurnal predation by the cormorant Phalacrocorax varius. At that time, however, the extent of the independent contributions of both food supply and shelter to this relationship was unclear. The amphipods, primarily Allochestes compressa, associated with drift macrophytes are the major food items for the fishes associated with those macrophytes (Lenanton et al., 1982; Robertson & Lenanton, 1984). While A. compressa relies on the finely branched red algae for shelter, it feeds on a variety of other macrophytes, mainly the alga Ecklonia radiata and dead seagrass that contribute to the drift (Robertson & Lucas, 1983). Thus, the relationship between fishes and drift macrophytes, and the abundance of fishes that depend on the amphipods for food, could be influenced by the species composition of the macrophytes. Visual observations by the authors showed that P. varius feed during the day in the M~mion region; as it does elsewhere (Stonehouse, 1967; Schreiber & Clapp, 1987). There was, therefore, no threat of predation by P. v~r~~~at night. Nevertheless, the results of the 1981-83 pro~~me (Robe~son & Lenanton, 1984) revealed that even at night the abundance of surf-zone fishes was still positively correlated with the volume of drift macrophytes. Thus, sampling at night could clarify the extent of the independent contributions of both food supply and shelter to the fish-drift macrophyte relationship. To achieve this first objective, it would be necessary to show that during the night-time, when the risk of predation was low, the abundance of a dominant nocturnal fish, i.e., 0 + -yr-old cobbler Cnidoglanis macrocephalus, that fed almost exclusively on the amphipods associated with weed was correlated with the volume of fine red algae and either Ecklonia radiata or dead seagrass. Choosing a single fish species which was dependent on drift macrophytes would also improve the chances of clarifying the fish-drift weed relationship. Secondly, it must be recognised that the results of the 1981-83 programme were based on data collected on only two sampling occasions (i.e., June and October). In the present study, data collected at night at regular monthly intervals throughout the year from the same sites sampled in the previous study were used to test the strength of the relationship between fish abundance and drift macrophytes. Thirdly, the role of temporal and spatial effects in the ash-deft macroph~e relationship was further investigated using data obtained from regular year-round sampling.

RELATIONSHIP

BETWEEN M~mom

SAMPLING

AND

PROCESSING

THE

FISHES

AND DETACHED

AND

MACROPHYTES

167

MATERIALS

CATCH

All sampling of fishes was within the surf zone of Mullaloo and Sorrento beaches near Perth, Western Australia (3 lo 51’ S : 115 “45’ E) (for further details of the sites, see Robertson & Lenanton, 1984). The two beaches are 1 km apart. The surf zone at Mulialoo nearly always harbours large qmantities of detached macroph~es while the surf zone at Sorrento is mostly free of large a~~umula~ons of drift macrophytes. From May 1984 to April 1985, a beach seine was used to take a total of 42 night-time samples (1900-2200) of the fishes and drift macrophytes from the surf zone. The net was 41 m long, with the wings and pocket having a stretched mesh size of 25 and 10 mm, respectively. It sampled a maximum depth of 1S m and an area of z 260 m2. The seine net used in this study was larger than the one employed in the 198 l-83 study (Robertson & Lenanton 1984). Also, the net was set rapidly from a dinghy speciticahy designed for surf-zone netting rather than being walked into the surf zone, Thus, the chances of catching any larger piscivorous predators that may have been feeding around the surf-zone weed accumulations were maximised. At least two replicate samples were taken from the Mullaloo and Sorrento sampling sites on the same night each month. On three occasions, however, October 1984 (Sorrento and Mullaloo) and December 1984 (Mullaloo), deteriorating netting conditions prevented a second sample being taken. The individ~~s of each fish species from all nettings were counted and measured (total length to the nearest mil~imetre~. All of the most abundant species from each netting were grouped into 0 + and > 0 + year classes, on the basis of monthly length-frequency distributions produced over the duration of the sampling programme and the results of previous studies on these species (Lenanton, 1982; Lenanton et al., 1982; Robertson & Lenanton, 1984; Nel et al., 1985). The total volume of detached macrophytes in each netting was recorded to the nearest litre, using a 25-l plastic bucket as a measuring device. Ma~rophytes were always softly tamped down as they were loaded into the pfastic bucket. AI1 the macrophytes or, in the case of large volumes, a subsample of ma&rophytes (50-100 1) from at least one netting from each site and each month was retained for component species anaIysis. Subsamples were usually taken randomly from the volume of macrophytes lying in the beached seine net assuming that component species were uniformly or randomly mixed throughout the total sample. In the laboratory, the macrophytes were sorted into the following genus groups: (1) fine red algae (~~~~~~, ~~~~~~I~~~~, ~~~ycf~~j~~,(2) other red algae (Lawemia, other ~~~~~e~~~~~~~ (3) S~~~~~~~~ (4) live and (5) dead seagrass (Hererozostera, ~~lphiba~~~,~ala~hi~a~Pcwidonia), (6) Eckfmia radiata, (7) green algae (Ulva, Caulerpa, GvdWt, Chae~o~~~h~) and (8) other algae (brown algae and coralline algae). Excess water was shaken from each component before it was weighed to the nearest gramme. Assuming that the density of each species group was similar, the percentage that each component group contributed to the sample weight was used to

168

R.C.J.

LENANTON

AND N. CAPUTI

convert the total sample volume into its respective component volumes. The volume of each species group of drift weed collected * netting- ’ was determined on 34 of the 42 netting occasions. Samples of drift weed collected during the remaining eight nettings were inadequate for estimating the volumes of genus groups. STATISTICAL

ANALYSIS

Stepwise multiple regression analyses (Sokal & Rohlf, 1981) were used to assess the effects of netting location (Sorrento and Mullaloo), total volume of drift weed and the volume of component groups of drift weed on both the numbers of all fish, and the numbers of 0 + CnidogEanismacrocephalus. Logarithmic transformations of the dependent variables (total number of fish and number of 0 + C. macrocephalus) were necessary so that some assumptions required for statistical inference from the regression analyses, i.e., the distribution of deviations around the mean regression line are normal and homoscedastic, were satisfied. To determine whether there was a regular seasonal cycle of fish abundance, the following four harmonic functions of time were included as additional independent variables, sin(o), cos(D), sin(2D) and cos(2D), where D = 2 K R/365 and R = the relative day of the year, i.e., Day 1 is 1 January, Day 365 is 3 1 December.

RESULTS FISH-COMMUNITY

COMPOSITION

A total of 37 species from 27 families was recorded in the 42 nettings, with eight species contributing 95 % of the total number of fishes captured (Table I). Five species, SEago bassensis, ~nidoglan~ ma~rocepha~us, Torquigener pleurogramma, Pelsartia humeralis and Crapatelus arenarius, were captured in > 50% of all nettings and three, Trachurus novaezelandiae, Aldrichetta forsteri and Atherinomorous ogilbyi, were taken in

> 30% of all nettings. Five of the eight dominant species were represented only by the 0 + age class. Juveniles contributed up to 95 y0 of the catches of the other three species, Torquigener pleurogramma, Crapatelus arena&s and Trachurus novaezelandiae. Eight individuals representing three piscivorous species, five of Pomatomus saltator, two of ~latycephalus speculator and one of ~phyraena novaehozlandiae,were recorded during the study. They were all small 0 + individu~s and, therefore, posed an insignificant threat as predators to juvenile fishes in the surf zone. DRIFT

MACROPHYTES

During most months sampled, in particular May and August 1984 and March 1985, more drift macrophytes . netting- ’ were sampled from Mullaloo than from Sorrento. The most obvious exception was during October when severe storms resulted in large volumes of drift weed being sampled from the surf zone of both beaches (Fig. I).

RELATIONSHIP

BETWEEN FISHES AND DETACHED

MACROPHYTES

R. C. J. LENANTON AND N. CAPUTI

170

*---*Mullal -Sorrento

500 $L E g

400

-

fi 300 a

-

F 5

6i 2 f_ 200 u-

-

f5 8

100 -

2 3 0 > O-

1984

1985

Fig. I. Volume (1) of drift weed taken in each of 40 nettings conducted on Sorrento (n = 18) and Mullaloo (n = 22) beaches between May 1984 and April 1985. Shading highlights range of data from Mullaloo,

TOTAL NUMBER OF FISH

Relatively low numbers of fishes (;\: = 27, range = 5-105 * netting- ‘) were consistently caught at Sorrento during the sampling period. Higher numbers (X = 130, range 2-606 - netting- ‘) were frequent at Mullaloo, the highest catches being taken during October and February 1985 (Fig. 2). The major effect of location was also shown by multiple regression analysis (Table II) while season and volume of dead seagrass were less important (Table II). There were, however, substantially greater volumes of drift macrophytes recorded from Mullaloo (Fig. 1). By excluding netting location from the analysis, the total volume of weed became the most significant variable. Seasonality and volume of Surgassum were less important variables in the multiple regression (Table II). NUMBER OF 0 + C. ~~CR~CEP~A~U~

Consistently more C. macrocephaius associated with drifting macrophytes were caught at Mullaioo than Sorrento Beach (Fig. 3). The highest catches of C. macrocephalus were taken during most of the months when the greatest volumes of detached weed were present in the catches (i.e., August and October 1984, and February and March 1985). Multiple regression analysis confirmed this trend by showing that the

variables

’ ’

Log (no. of Cm + 1)

Log (no. of Cm + I)

Number of 0 + c‘. mcc~mcepholus

Log no. of fish. netting

Log no. of fish. netting

Total number of fish

Dependent

Stepwise multiple regression

II

excluded

Beach

1.323***

(beach)

Netting location

0.555*+

0.45 1, 0.483*

0.562’

0.4g5*

cos (20)

Seasonality

Sin (D)

-.

0.70s*

.-~~

Sargassum

0.250***

0.127*

0 268***

algae

-

Fine red

Dead

of the drift

seagrass

Components

excluded

0.136*** Total weed

0.081***

Total weed

.-

0.235

0.3x9

2.895 2.976

Constant

0.85

0.72

0.76 0.73

Multiple correlation

of total number of fish and number of 0 + Cnidoglunis macrocephalus (Cm) caught in surf zone of two Western beaches between May 1984 and April 1985, *P < 0.05, **P -=z 0.01, ***P< 0.001.

TABLE

sandy

***

***

+** ***

of regression

Overall significance

Australian

172

R. C. J. LENANTON -----• w

l

600

AND N. CAPUTI

Mullalao Sorrento

iz E

!’

300-

%I cc ii! iFI 200u. & cc ;

loo-

3 z

O-

-/ M

J

J

A

S

0

D

J

F

M

A

1985

7984

Fig. 2. Number of fish taken in each of 42 nettings conducted on Sorrento (n = 20) and Mullaloo (n = 22) beaches between May 1984 and April 1985. Shading highlights range of data from Mullaloo.

33 1984

M

J

J

A

s

0

D

*---* w

Mullaloo Sorrento

J

F

M

A

1985

Fig. 3. Number of 0 t CnidogIanis macrocephalus taken in each of 42 nettings conducted (n = 20) and Mullaloo (n = 22) beaches between May 1984 and April 1985. Shading highlights from Mullaloo.

on Sorrento range of data

RELATIONSHIP

BETWEEN FISHES

AND DETACHED

MACROPWYTES

173

number of 0 + C. ~acrocep~a~~s was positively correlated with the total volume of drift weed (Table II). To determine which of the component species groups affected the variation in the 0 + C. ~~~~~&~~~~~~caught during the study, total volume ofdrift weed was excluded from the analysis. The v&me of fine red algae and the volume of dead seagrass became the most s~~~~ant variables, with seasonality also e~pl~ning a less significant mount of the variance {Table If).

The composition of the numerically dominant fish fauna in the current study was remarkably similar to that of the previous study (Robertson & Lenanton, 1984) (Table 1). This was true, even though the current study was based entirely on night-time sampling whereas the previous study was based primarily on daytime nettings (47 vs. 16). T~~~~u~~~~v~eze~~~jae was observed to be active at night, moving from beyond the surfzone to the outer surf zone to feed during the early evening. This behaviour together with the more efficient use of a larger net in the night-time study, which on occasions fished just beyond the surf zone, probably accounted for the relatively large numbers of this species (H = 174) taken in the current study, compared to its previous absence. Nearly al1 cf. ~~vae~e~~~~j~~ (170) were taken in nettings at ~~11~00 s~gges~ngthat this species feeds at night along the edge of the surf-zone drift-weed accumulations in much the same manner as that reported for ~ld~ic~ett~forsteti during the daytime (Robertson k L~n~ton~ 1984). Although a related species T~~c~~~s t~ac~~~~ (L.) is abund~t in open sandy South African surf zones, this species fed extensively on ~l~nktoni~ or~~isms as did other n~eri~~ly do~nant fish species caught in that env~onment (Lasiak, 19%) The weed-associated ~#~~~~ s~~~as~~a~~was most abund~t in the daytime nettings in the previous study. The capture of only one individual of this species in the current study may reflect a movement away from the surf-zone drift macrophyte habitat at night. Annual variation in re~r~tment of young 1%,~e~~~~~~~~may have also comributed to its low abundance during this study. FACTORS

C~NTKIBUTIN~

TO TRENDS

IN FISH ABUNDANCE

Fish abundance and the volume of detached macrophytes were strongly correlated when based on sampling performed throughout the year rather than just for 2 months, demonstrating that this association is persistent. Since the data were collected at night when there was no risk of cormorant predation, and the risk of predation by large piscivores was demonstrably low, it is concluded that the fuod r~q~~rerne~t of these fish is the major factor responsible for the significant fish-drift weed association, The number of fishes in the surf zone varied seasonally> and the iehthyofauna was dominated by juveniles as is ChWiGteriStiGof other surf zones (M~dde & Ross, 1981;

R.C.J. LENANTON

174

AND N. CAPUTI

La&k, 1983,1986; Senta& Kinoshita, 1985; Peters&Nelson, 1987; Ross et al., 1987). Many of the commerci~~y and recreational impo~~tly species found in inshore marine habitats in Western Australia breed in the summer (Lenanton, 1982; Lenanton & Hodgkin, 1985). For example, C. macrocephalus spawns between October and December (Nel et al., 1985), with the young first appearing in the seine net samples taken in this study in January, at a total length of 40 mm. They then build up to maximum abundance in February and March before becoming much less abundant around September. The relative volume of detached plant material over a 46-km length of this coast was previously shown to be low during late summer and early autumn (Fig. 1; Lenanton et al., 1982). When considered over a restricted area, such as Mullaloo Beach, however, volumes of drift can be relatively high during this period. Juvenile C. mffcrocephu~~s clearly take advantage of this situation as well as the relatively high water temperatures (21.0-24.7 “C) that occur at this time (Hodgkin & Phillips, 1969). Associated with this phenomenon is a greater nearshore productivity (Johannes & Heart-r, 1985) in relatively calm seas which creates very favourable conditions for growth before the onset of the cooler winter and hence slower period of growth.

C. MACROCEPHALUS

AND

SPECIES

COMPOSITION

OF MACROPHYTE

DETRITUS

Robertson & Lenanton (1984) provided evidence that cormorants feeding in surf zones of temperate Western Australia are major predators of C. macrocephalus. During the day, when the risk of cormorant predation was high, C. macrocephalus was only caught in drift weed. The stomach contents of these 0 + -yr-old and older C. macrocephalus consisted mainly of amphipods which are typically associated with drift weed. At night, however, when there was no risk of cormorant predation, Robertson & Lenanton (1984) showed that small numbers of C. mucroceph#~~ were caught over the sand with infaunaI bivalves as the major component of their stomach contents. The large numbers of mostly 0 + -yr-old C. mucrocephafus caught in the drift weed at night had weed-associated amphipods as the major component of their stomach contents. During the night, therefore, the association of 0 + C. macrocephaZus with drift weed is primarily related to food supply rather than shelter whereas during the day the weed provides both shelter and a source of food. The phaeophyte Ecklonia radiata and dead seagrass are the two most important dietary items of the weed associated amphipod Allochestes compressa (Robertson & Lucas, 1983). Compared with seagrass, however, the macroalga Eckloniu radiata breaks down relatively quickly in the surf zone into small particles (= 3 cm) which are the preferred food of amphipods (Robertson & Lucas, 1983). It is likely, therefore, that the seine net would selectively retain the more persistent seagrass and lose much of the small E. radiate particles. This mesh selection would explain why dead seagrass, not E. radiata, was identified, together with tine red algae, as the two components of the drift

RELATIONSHIP

BETWEEN

FISHES

AND DETACHED

MACROPHYTES

175

related to high weed-associated amphipod abundance, and hence the abundance of 0 + C. macrocephalus. Whereas phytoplankton is the major input of primary production to the beach habitats occupied by fish communities studied elsewhere in the world (McLachlan et al. 1981; Senta & Kinoshita, 1985; Lasiak, 1983; Ross et al., 1987), drift macrophytes provide the major input to sandy beach habitats in temperate Western Australia (Robertson & Hansen, 1982; Hansen, 1984; Robertson & Lenanton, 1984). A number of species that occur in this region, including the commercially important and abundant C. macrocephalus, are very dependent on the drift weed for food and shelter. Fish have been shown to utilise macroinvertebrates which inhabit drift macrophytes found in other marine habitats in the world (Mitchell & Hunter, 1970; Stoner & Livingston, 1980; Kulczycki et al., 1981; Kingsford & Choat, 1985). Apparently, however, there have been no instances reported where a major commercial species such as C. macrocephalus (Lenanton & Potter, 1987) depends to such a degree on particular species of drift weed for its food and shelter.

ACKNOWLEDGEMENTS

M. Cliff and J. Shaw assisted with collection and analysis of samples and preparation of the figures for publication. I. C. Potter, N. Longeragan, and J. Shaw and a number of other colleagues commented on earlier drafts of the manuscript. REFERENCES Edwards, R. R. C., 1973a. Production ecology of two Caribbean marine ecosystems. I. Physical environment and fauna. Estuarine Coastal Mar. Sci., Vol. 1, pp. 303-316. Edwards, R. R. C., 1973b. Production ecology of two Caribbean marine ecosystems. II. Metabolism and energy flow. Estuarine Coastal Mar. Sci., Vol. 1, pp. 319-333. Hansen, J.A., 1984. Accumulations ofmacrophyte wrack along sandy beaches in Western Australia. Ph.D. thesis, Botany Department, University of Western Australia. Hodgkin, E. P. & B. F. Phillips, 1969. Sea temperatures on the coast of south-Western Australia. J. R. Sot. West. Amt., Vol. 52, pp. 59-62. Johannes, R. E. & C. J. Hearn, 1985. The effects of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off Perth, Western Australia. Estuarike Coastal ShelfSci., Vol. 21, pp. 789-800. Kingsford, M. J. & J. H. Choat, 1985. The fauna associated with drift algae captured with a plankton mesh purse seine net. Limnol. Oceanogr., Vol. 30, pp. 618-630. Kulczycki, G. R., R. W. Virnstein & W.F. Nelson, 1981. The relationship between fish abundance and algal biomass in a seagrass-drift algal community. Es&urine Coastal Shelf Sci., Vol. 12, pp. 341-347. Lasiak, T.A., 1983. The impact of surf-zone fish communities on fauna1 assemblages associated with sandy beaches. In, Sandy beaches as ecosystems, edited by A. McLachlan & T. Erasmus, Dr. W. Junk Publishers, The Hague, pp. 501-506. Lasiak, T. A., 1986. Juveniles, food and the surf-zone habitat; implications for teleost nursery areas. S. Afr. J. Zool., Vol. 21, pp. 51-56. Lenanton, R. C. J., 1982. Alternative non-estuarine nursery habitats for some commercially and recreationally important fish species of south-Western Australia. Amt. J. Mar. Freshwater Res., Vol. 33, pp. 881-900. Lenanton, R. C. J., A. I. Robertson & J. A. Hansen, 1982. Nearshore accumulations of detached macrophytes as nursery areas for fish. Mar. Ecol. Progr. Ser., Vol. 9, pp. 51-57.

176

R. C. J. LENANTON AND N. CAPUTI

Lenanton, R.C.J. & E.P. Hodgkin, 1985. Life history strategies of fish in some temperate Australian estuaries. In, F&h community ecology in estuan-es and coastat lagoon. Towards an ecosystem ~~e~u~ion, edited by A. Yanez-Arancibia, UNAM Press, Mexico, pp. 267-284. Lenanton, R. C. J. & I. C. Potter, 1987. Contribution of estuaries to commercial lisheries in temperate Western Australia and the concept of estuarine dependence. Estuaries, Vol. 10, pp. 28-35. McDermott, J. J., 1983. Food web in the surf zone on an exposed sandy beach along the mid-Atlantic coast ofthe United States. In, Sandy beaches as ecosystems, edited by A. McLachlan & T. Erasmus, Dr. W. Junk Publishers, The Hague, pp. 529-538. McLachlan, A., T. Erasmus, A. H. Dye, T. Wooldridge, G. van der Horst, G. Rossouw, T.A. Lasiak & L. McGynne, 1981. Sand beach energetics: an ecosystem approach towards a high energy interface. Es~~~ne Coasta! Shelf,%%, Vol. 13, pp. 1l-25. Mitchell, C.T. & J. R. Hunter, 1970. Fish associated with drifting kelp, ~uc~~c~~f~ pyr$n-o, off the coast of southern California and northern Baja California. CuZ$ Ftih Game, Vol. 56, pp. 288-297. Modde, T. & S.T. Ross, 1981. Seasonality of fishes occupying a surf-zone habitat in the northern Gulf of Mexico. Fish. Bull. NOAA, Vol. 78, pp. 91 l-922. Nel, S.A., I.C. Potter & N.R. Loneragan, 1985. The biology of the catfish Cnidoglanis macrocephalus (Plotosidae) in an Australian estuary. Estuarine Coastal Shelf Sci,, Vol. 21, pp. 895-909. Peters, D. V. & W. G. Nelson, 1987. The seasonality and spatial patterns of juvenile surf-zone fishes of the Florida east coast. Fla. Sci., Vol. 50, pp. 85-99. Robertson, A. I. & J. A. Hansen, 1982. Decomposing seaweed; a nuisance or a vital link in coastal food chains? &SiBO I)&. Fish. Rex Rep., No. 1980-1981, pp. 75-83. Robertson, A.I. & R.C. J. Lenanton, 1984. Fish community structure and food chain dynamics in the surf-zone of sandy beaches; the role of detached macrophyte detritus. J. Exp. Mar. Biol. Ecok, Vol. 84, pp. 205-283. Robertson, A.I. & J. S. Lucas, 1983. Food choice, feeding rates and turnover of macrophyte biomass by a surf-zone inhabiting amphipod. J. Exp. Mar. Biol. Ecol., Vol. 72, pp. 99-124. Ross, S.T., R.H. McMichael & D. L. Ruple, 1987. Seasonal and die1 variation in the standing crop of fishes and macroinvertebrates from a Gulf of Mexico surf zone. Estuarine Coustul Sherf Sci., Vol. 25, pp. 391-412. Schreiber, R. W. & R. B. Clapp, 1987. Pelec~iform feeding ecology. In, Seabirds,~eding ecologv and role in marine ecosystems, edited by J.P. Croxall, Cambridge University Press, London, pp. 173-188. Senta, T. & I. Kinoshita, 1985. Larval and juvenile fishes occurring in surf zones of western Japan. Trans. Am. Fish. Sot., Vol. 114, pp. 609-618. Sokal, R. R. & F. J. Rohlf, 1981. Biometry. W.H. Freeman & Co., San Francisco, second edition, 859 pp. Stonehouse, B., 1967. Feeding behaviour and diving rhythms of some New Zealand shags, Phalacrocoracidae. Ibis, Vol. 109, pp. 600-605. Stoner, A. W. & R. J. Livingston, 1980. Distributional ecology and food habits of the banded blenny Paruciinus fasciatus (Clinidae): a resident in a mobile habitat. Mar. B&Z., Vol. 56, pp. 234-246. Wheeler, A., 1980. Fish-algal relations in temperate waters. In, The shore environmeni. VoI. 2. Ecosystems, edited by J. H. Price et al., Academic Press, London, pp. 677-698.